Accounts Receivable, Net, Current Investment advisory and related fees Accretion (Amortization) of Discounts and Premiums, Investments Accretion and amortization of securities discounts and premiums, net Accumulated Other Comprehensive Income (Loss), Net of Tax Accumulated other comprehensive income (loss), net Additional Paid in Capital Additional paid-in capital Unrealized Gain (Loss) on Investments Unrealized (gains) losses on investments Amortization of Deferred Sales Commissions Amortization of deferred sales commissions Amortization of Intangible Assets Amortization of intangible assets Asset Impairment Charges Impairment of goodwill and intangible assets CONSOLIDATED BALANCE SHEETS Cash and Cash Equivalents, at Carrying Value Cash and cash equivalents Cash and Cash Equivalents at Beginning of Period Cash and Cash Equivalents at End of Period Increase (Decrease) in Accounts Receivable Investment advisory and related fees receivable Increase (Decrease) in Deferred Compensation Deferred compensation Accrued compensation Increase (decrease) in income taxes payable Increase (Decrease) in Other Receivables Other receivables Proceeds from (Repayments of) Short-term Debt Net increase in short term borrowings Commitments and Contingencies Disclosure [Text Block] Commitments and Contingencies Common Stock Issued, Employee Stock Trust Employee stock trust Common Stock, Shares Authorized Common stock, authorized (in shares) Common Stock, Value, Issued Common stock, par value $.10; authorized 500,000,000 shares; issued 161,359,555 shares and 141,853,025 shares, respectively Compensation and Benefits Trust Deferred compensation employee stock trust Comprehensive Income, Net of Tax, Attributable to Parent Comprehensive Income (Loss) Attributable to Legg Mason, Inc. Liabilities, Current Total current liabilities Deferred Income Tax Expense (Benefit) Deferred income taxes Earnings Per Share, Diluted Diluted (in dollars per share) (Gain) loss on sale of discontinued operations, net of tax (Income) Loss from discontinued operations Effect of Exchange Rate on Cash and Cash Equivalents Effect of Exchange Rate Changes on Cash Share-based Compensation Stock-based compensation Impairment of intangible assets Income (Loss) from Continuing Operations Income (Loss) from Continuing Operations Increase (Decrease) in Other Operating Assets Other assets Increase (Decrease) in Restricted Cash Restricted cash, net (principally fund support collateral) Intangible Assets, Net (Excluding Goodwill) Intangible assets, net Interest Expense Interest expense Labor and Related Expense Compensation and benefits Compensation and benefits LIABILITIES AND STOCKHOLDERS' EQUITY Liabilities and Stockholders' Equity, Total Total Liabilities and Stockholders' Equity Total Liabilities Liabilities, Total Long-term Debt, Current Maturities Current portion of long-term debt Long-term Debt, Excluding Current Maturities Long-term debt Trading Securities, Current Investment securities Net Cash Provided by (Used in) Financing Activities Cash (Used For) Provided by Financing Activities Net Cash Provided by (Used in) Investing Activities Cash Used for Investing Activities Cash Flows from Operating Activities Net Cash Provided by Operating Activities Cash Provided by Operating Activities Proceeds from (Repayments of) Other Long-term Debt Third-party distribution financing, net Proceeds from (Payments for) Securities Purchased under Agreements to Resell Net increase in securities purchased under agreements to resell Net Income (Loss) Attributable to Parent Net Income (Loss) Attributable to Legg Mason, Inc. Net income (loss) attributable to Legg Mason, Inc. Net Income (loss) Cash and Cash Equivalents, Period Increase (Decrease) Net Increase in Cash and Cash Equivalents Communications and Information Technology Communications and technology Occupancy, Net Occupancy Nonoperating Income (Expense) Total other non-operating income (expense) Operating Income (Loss) Operating Income (Loss) Revenues Total operating revenues Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Interim Basis of Reporting Other Comprehensive Income, Available-for-sale Securities Adjustment, Net of Tax Net unrealized gains (losses) on investment securities Unrealized holding gains (losses) on investment securities, net of tax Unrealized gains (losses) on investment securities: Other Comprehensive Income, Foreign Currency Transaction and Translation Adjustment, Net of Tax Foreign currency translation adjustment Other Comprehensive Income (Loss), Net of Tax Total other comprehensive income (loss) Other Comprehensive Income, Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax Unrealized holding gains (losses), net of tax provision (benefit) of $(19), $54, $(17) and $30, respectively Unrealized holding gains (losses) on investment securities, net of tax Other Comprehensive Income, Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax Unrealized holding gains (losses) on investment securities, tax provision (benefit) Other Assets, Current Other Revenue, Other Financial Services Other Other Nonoperating Income (Expense) Other income (expense) Other Receivables Other Payments of Dividends Dividends paid Proceeds from Issuance of Common Stock Issuance of common stock Proceeds from Issuance of Long-term Debt Proceeds from issuance of long-term debt, net Proceeds from sales and maturities of investment securities Property, Plant and Equipment, Net Fixed assets, net Purchases of investment securities Payments to Acquire Property, Plant, and Equipment Payments for fixed assets Repayments of Long-term Debt Repayment of principal on long-term debt Restricted Cash and Cash Equivalents, Current Restricted cash Retained Earnings (Accumulated Deficit) Retained earnings Performance Fees Performance fees Proceeds from sales and maturities of investment securities Short-term Borrowings Short-term borrowings Significant Accounting Policies [Text Block] Significant Accounting Policies Goodwill and Intangible Assets Disclosure [Text Block] Intangible Assets and Goodwill Assets, Current Total current assets Weighted Average Number of Shares Outstanding, Diluted Diluted (in shares) Weighted Average Number of Shares Outstanding, Basic Basic (in shares) Property, Plant and Equipment Disclosure [Text Block] Fixed Assets Assets, Total Total Assets Investment Income, Interest Interest income Other Liabilities, Current Other Other Liabilities, Noncurrent Other Common Stock, Dividends, Per Share, Declared Dividends Declared per Share (in dollars per share) Deferred Tax Assets, Net, Noncurrent Deferred income taxes Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Stock-Based Compensation Deferred Tax Assets, Net, Current Deferred income taxes Deferred Tax Liabilities, Noncurrent Deferred income taxes ASSETS Fair Value Disclosures [Text Block] Fair Values of Assets and Liabilities Earnings Per Share, Basic Basic (in dollars per share) Excess Tax Benefit from Share-based Compensation, Financing Activities Excess tax benefit associated with stock-based compensation Common Stock, Shares, Issued Common stock, issued (in shares) Other Assets, Noncurrent Other Net Income (Loss) per Share Attributable to Legg Mason, Inc. Common Shareholders: Increase (Decrease) in Other Operating Liabilities Other liabilities Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Cumulative Effects of Changes in Accounting Principles, Noncontrolling Interest Income (Loss) before Income Tax Provision (Benefit) Common Stock, Par or Stated Value Per Share Common stock, par value per share (in dollars per share) Other Comprehensive Income, Reclassification Adjustment for Sale of Securities Included in Net Income, Net of Tax Reclassification adjustment for realized gains included in net income (loss) Income (Loss) from Operations before Income Tax Provision (Benefit) and Minority Interests Income Tax Expense (Benefit) Income tax provision (benefit) Other Expenses Other Long-term Debt [Text Block] Debt and Equity Units Goodwill Goodwill Operating Expenses Costs and Expenses Total operating expenses Document and Entity Information NOTES TO CONSOLIDATED FINANCIAL STATEMENTS Separate accounts Revenue recognized in the period for asset-based fees earned for providing investment advice, research and other services for customers relating to separately managed accounts. These fees are generally determined as a percentage of assets under management. Investment Advisory Fees: Separate Accounts Funds Revenue recognized in the period for asset-based fees earned for providing investment advice, research and other services for customers relating to management of mutual funds and closed-end funds. Investment Advisory Fees: Funds Distribution and service fees Fees earned from funds (including 12b-1 fees) to reimburse the distributor for the costs of marketing and selling fund shares and servicing proprietary funds. These fees are generally determined as a percentage of retail and institutional client assets. Reported amounts also include fees earned from providing client or shareholder servicing, record keeping, or administrative services to proprietary funds. Distribution and service fees The aggregate amount of expenditures for salaries, wages, profit sharing and incentive compensation, and other employee benefits, including include share-based compensation and pension & other postretirement benefit expense, but exlcuding transaction-based compensation. Compensation and Benefits, Non-transaction Related Compensation and benefits The aggregate amount of expenditures for compensation that is based on transactions. Transaction-related Compensation Transaction-related compensation Distribution and servicing Costs related to the marketing and selling of fund shares and servicing proprietary funds. Fees are generally determined as a percentage of client assets. Distribution and Servicing Income (Loss) from Operations before Minority Interests Sum of operating profit and nonoperating income (expense) after income taxes. Income From Continuing Operations before Minority Interests Income (Loss) from Discontinued Operations During Phase-out Period, Net of Tax, Per Basic Share The amount of income (loss) from discontinued operations during the phase-out period, net of related income taxes, per each share of common stock outstanding during the reporting period. Income (loss) from discontinued operations ( in dollars per share) Gain (Loss) on Disposal of Discontinued Operations, Net of Tax, Per Basic Share The gain (loss) from disposal of discontinued operations, net of related income taxes, per each share of common stock outstanding during the reporting period. Gain (loss) on disposal of discontinued operations (in dollars per share) Income (Loss) from Discontinued Operations During Phase-out period, Net of Tax, Per Diluted Share The amount of income (loss) from discontinued operations during the phase-out period, net of related income taxes, per each share of common stock and diluteive common stock equivalents outstanding during the reporting period. Income (loss) from discontinued operations (in dollars per share) Gain (Loss) on Disposal of Discontinued Operations, Net of Tax, Per Diluted Share The gain (loss) from disposal of discontinued operations, net of related income taxes, per each share of common stock and dilutive common stock equivalents outstanding during the reporting period. Gain (loss) on disposal of discontinued operations (in dollars per share) Depreciation and Amortization Excluding Amortization of Deferred Sales Commissions Depreciation and amortization The aggregate amount of depreciation expense and amortization expense. Depreciation expense is the noncash expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Amortization expense is the noncash expense charged against earnings in the current period that reflects the allocation of the cost of definite lived intangible assets and leasehold improvements over the shorter of their estimated remaining economic lives or the lease term. Excludes the amortization of deferred sales commissions. Value of Shares that are exchangable into Common Stock. STOCK EXCHANGEABLE INTO COMMON STOCK Common stock issued to a trust (for example, a 'rabbi trust') set up specifically to accumulate stock for the sole purpose of distribution to participating employees. This trust does not allow employees to immediately or after a holding period diversify into nonemployer securities. The deferred compensation plan for which this trust is set up must be settled by the delivery of a fixed number of shares of employer stock. EMPLOYEE STOCK TRUST Common stock issued to a deferred compensation employee stock trust, which is set up specifically to accumulate stock for the sole purpose of distribution to participating employees. This trust does not allow employees to immediately or after a holding period diversify into nonemployer securities. The deferred compensation plan for which this trust is set up must be settled by the delivery of a fixed number of shares of employer stock. DEFERRED COMPENSATION EMPLOYEE STOCK TRUST Acquisitions and Dispositions [Text Block] Description of a business acquisition or disposition (or series of individually immaterial business combinations or dispositions) planned, initiated, or completed during the period, including background, timing, and allocation of acquisition costs. Acquisitions and Dispositions Deferred Compensation Stock Trust [Text Block] The entire disclosure about the Deferred Compensation Stock Trust and related Employee Stock Trust.. Deferred Compensation Stock Trust Accumulated Other Comprehensive Income [Text Block] The entire disclosure of Accumulated Other Comprhensive Income. Accumulated Other Comprehensive Income Liquidity Fund Support The entire disclosure of Liquidity Fund Support, which includes the arrangements made to provide support to certain of the reporting entity's proprietary liquidity funds that hold securities issued by SIVs (Structured Investment Vehicles). Liquidity Fund Support [Text Block] Shares Issued During Period, Value, Deferred Compensation, Net Aggregate change in value for restricted stock transactions during the period. Deferred compensation, net Exchangeable Shares Converted into Common Stock, Value Aggregate change in value of stock during the period upon exchanging shares for common stock. Exchangeable shares Shares Issued to Employee Stock Trust Plans Aggregate change in value for stock issued during the period as a result of employee stock trust plans. Shares issued to plans Distributions and Forfeitures to Employee Stock Trust Plans Value of stock related to Employee Stock Trust Plans that was distributed and forfeited during the period. Distributions and forfeitures Exchangeable shares that can be converted into common stock. Shares exchangeable into common stock Shares Exchangeable Into Common Stock, Value The value of issued preferred stock that may be exchanged into common shares or other types of securities at the owner's option as long as it is in accordance with the issuer's terms. Classified within permanent stockholders' equity since nonredeemable. Convertible preferred stock, par value $10; authorized 4,000,000 shares; 0 and 0.36 shares outstanding, respectively Convertible preferred stock Convertible Preferred Stock, Value Cost of Convertible Note Hedge, Net Cost of Convertible Note Hedge, Net The costs related to a convertible note hedge. Cost of convertible note hedge, net Fund support Fund Support, Liabilities Aggregate carrying amount, measured as the fair value as of the balance sheet date, of liabilities for derivative instruments in connection with various money market credit support arrangements, including Letters Of Credit, Capital Support Agreements, and Total Return Swap. Fund Support, Income (Expense) Fund support Represents the aggregate amount of realized and unrealized gains and (losses) on fund support, including letters of credit, total return swaps, and capital support agreements, relating to certain proprietary liquidity funds. Amounts include the contractual obligations and benefits relating to the change in fair value of supported assets and related financing costs. Realized loss on sale of SIV securities Realized (Gain) Loss on Sale of Structured Investment Vehicle Securities The aggregate amount of expense (excess cost over sale proceeds and related costs) associated with the realized gain (loss) on the sales of SIV securities during the period. Unrealized (gains) losses on fund support Unrealized (Gains) Losses on Fund Support The aggregate decrease (increase) in the fair value of fund support, including letters of credit, total return swap, and capital support agreements, for certain proprietary liquidity funds during the period. Amounts also include related financing costs. Accounts payable and accrued expenses Increase (Decrease) in Accounts Payable and Accrued Expenses The net change during the reporting period in the obligation created by or pertaining to goods and services received from vendors; are incurred in connection with contractual obligations, or accumulate over time and for which invoices have not yet been received. This also includes payables for distribution and servicing costs related to the marketing and selling of fund shares. Distribution and servicing fees are generally determined as a percentage of client assets. Fund Support: Purchases of Structured Investment Vehicle Securities, Net of Distributions Purchases of SIV securities, net of distributions The cash outflow for the reporting period associated with purchasing securities issued by Structured Investment Vehicles (SIV's), including letters of credit, total return swaps, and capital support agreements. Amounts are net of any distribution received from SIV's. Proceeds from sale of SIV securities Fund Support: Proceeds from Sale of Structured Investment Vehicle Securities The cash inflow for the reporting period associated with sales of securities issued by Structured Investment Vehicles (SIVS's), including SIV's supported under letters of credit, total return swaps, and capital support agreements. Payments under liquidity fund support arrangements Payments under Liquidity Fund Support Arrangements The cash outflow for the reporting period associated with Liquidity Fund Support Arrangements. Increase (Decrease) in Accrued Compensation The net change during the reporting period in the total obligations incurred and payable for obligations related to services received from employees, such as accrued salaries and bonuses, payroll taxes and fringe benefits. Accrued compensation Fund Support: Entity Shares Exchangeable into Common Stock, Shares Outstanding Number of shares that are exchangable into Common Stock that are outstanding as of a certain date. Preferred Stock, Shares Authorized Preferred stock, authorized (in shares) Preferred Stock, Shares Outstanding Preferred stock, outstanding (in shares) Preferred Stock, Par or Stated Value Per Share Preferred stock, par value per share (in dollars per share) Preferred Stock, Value, Issued Preferred stock, par value $10; authorized 4,000,000 shares; no shares outstanding Earnings Per Share [Text Block] Earnings Per Share Net Income (Loss) Attributable to Noncontrolling Interest Less: Net income (loss) attributable to noncontrolling interests Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Deferred Compensation Liability, Classified, Noncurrent Deferred compensation Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Net Income (Loss) Net Income (Loss) Net income (loss) Income (Loss) from continuing operations Comprehensive Income, Net of Tax, Including Portion Attributable to Noncontrolling Interest Comprehensive Income (Loss) Comprehensive Income, Net of Tax, Attributable to Noncontrolling Interest Less: Comprehensive income (loss) attributable to noncontrolling interests Proceeds from (Payments for) Trading Securities Net sales (purchases) of trading investments Commitments and Contingencies Commitments and Contingencies CONSOLIDATED STATEMENTS OF CASH FLOWS Income Taxes Receivable, Current Refundable income taxes Proceeds from (Payments to) Noncontrolling Interests Net subscriptions received from/(redemptions/distributions paid to) noncontrolling interest holders Schedule of Subsequent Events [Text Block] Subsequent Event COMMON STOCK Dividends Dividends declared ADDITIONAL PAID-IN CAPITAL RETAINED EARNINGS ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS), NET Stock Issued During Period, Value, Share-based Compensation Stock options and other stock-based compensation Stock Issued During Period, Value, Conversion of Convertible Securities Preferred share conversions Adjustments, Noncash Items, to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities, Other Other Employee-related Liabilities, Current Accrued compensation Adjustments to Additional Paid in Capital, Equity Component of Convertible Debt Convertible debt CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY Non-cash items included in net income (loss): Noncontrolling Interests, Redeemable Redeemable Noncontrolling Interests The aggregate redemption value of noncontrolling equity interests with redemption features. Operating Revenues Imputed interest for 2.5% convertible senior notes Liabilities Current Liabilities Stockholders' Equity Current Assets Receivables: Other Non-Operating Income (Expense) CONSOLIDATED STATEMENTS OF OPERATIONS Decrease (increase) in assets excluding acquisitions: Increase (decrease) in liabilities excluding acquisitions: Cash Flows from Investing Activities Cash Flows from Financing Activities Increase (Decrease) in Stockholders' Equity Other comprehensive income gains (losses): Stockholders' Equity, Period Increase (Decrease) Stockholders' Equity Period Increase (Decrease) CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) Proceeds from (payments for): Statement [Table] Statement, Equity Components [Axis] Equity Component [Domain] Statement, Scenario [Axis] Scenario, Unspecified [Domain] Beginning balance, as adjusted Disposal Groups, Including Discontinued Operations, Disclosure [Text Block] Disposal Groups, Including Discontinued Operations Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Investments in Debt and Equity Securities and Certain Trading Assets Short-term Debt [Text Block] Short-term Debt Income Tax Disclosure [Text Block] Income Taxes Compensation Related Costs, General [Text Block] Compensation-related Costs, General Stockholders' Equity Note Disclosure [Text Block] Stockholders' Equity Segment Reporting Disclosure [Text Block] Segment Reporting Schedule of Variable Interest Entities [Text Block] Variable Interest Entities Derivative Instruments and Hedging Activities Disclosure [Text Block] Derivatives and Hedging Accounts Payable and Accrued Expenses Accounts payable and accrued expenses Carrying value as of the balance sheet date of obligations incurred and payable (excluding employee-related liabilities), pertaining to goods and services received from vendors; are incurred in connection with contractual obligations, or accumulate over time and for which invoices have not yet been received. This also includes payables for distribution and servicing costs related to the marketing and selling of fund shares. Distribution and servicing fees are generally determined as a percentage of client assets. Purchases of Investment Securities Purchases of investment securities The cash outflow from purchases of available-for-sale securities and held-to-maturity securities. Proceeds from Sales and Maturities of Investment Securities Proceeds from sales and maturities of investment securities The cash inflow associated with the aggregate amount received by the entity through sale or maturity of marketable securities (held-to-maturity, or available-for-sale) during the period. Other Comprehensive Income, Derivatives Qualifying as Hedges, Net of Tax Unrealized and realized gains on cash flow hedge, net of tax provision of $97 and $666, respectively Unrealized and realized gains on cash flow hedge, net of tax Beginning balance, as reported Increase (Decrease) in Income Taxes Receivable Refundable income taxes This amount represents the imputed interest, which is a non-cash expense, on contingent convertible debt required by FSP APB 14-1. Imputed Interest For Convertible Senior Notes Imputed interest for 2.5% convertible senior notes Weighted Average Number of Shares Outstanding: Deferred Compensation Employee Stock Trust, Stockholders Equity Impact Aggregate change in value for phantom 401k transactions during the period. Deferred compensation employee stock trust Proceeds from Sale of Assets The cash inflow associated with the amount received from the sale of assets or a portion of the company's business, for example a segment, division, branch or other business, during the period. Proceeds from sale of assets Other Payments to Acquire Businesses Payments for business acquisition-related costs Gains (Losses) on Extinguishment of Debt Loss on Equity Unit exchange Other Comprehensive Income, Derivatives Qualifying as Hedges, Tax Effect Unrealized and realized gains on cash flow hedge, tax provision Other Comprehensive Income, Available-for-sale Securities, Tax Other Comprehensive Income, Reclassification Adjustment for Sale of Securities Included in Net Income, Tax Cash outflows for inducements on Equity Units. Payment on Equity Unit exchange Payment on Equity Unit Exchange Recognition of conversion value of 2.5% senior notes, net of tax, pursuant to new accounting requirement Cumulative effect of initial adoption of FSP APB 14-1 on beginning additional paid-in capital and beginning retained earnings, net of tax. Recognition of Conversion Value of Senior Notes Net of Tax Pursuant to New Accounting Requirement Aggregate transaction amount during the period for exchange (issuance) of Equity Units. Equity Units exchanged (issued) Equity Units Exchanged Issued Statement [Line Items] Impairment of Investments Impairment adjustment for investment securities Contractual acquisition earn outs Payments for (Proceeds from) Previous Acquisition Other Asset Impairment Charges Lease impairment loss Stockholders' Equity, as Previously Reported Beginning balance, as reported Ending balance, as reported Total of Stockholders' Equity (deficit) items, net of receivables from officers, directors owners, and affiliates of the entity including portions attributable to the parent, as previously reported. Stockholders' Equity Attributable to Parent Total Stockholders' Equity Beginning balance Ending balance