Significant Accounting Policies	3 Months Ended
Jun. 30, 2016
Accounting Policies [Abstract]
Significant Accounting Policies	2. Significant Accounting Policies Consolidation In the normal course of its business, Legg Mason sponsors and manages various types of investment vehicles. For its services, Legg Mason is entitled to receive management fees and may be eligible, under certain circumstances, to receive additional subordinated management fees or other incentive fees. Legg Mason's exposure to risk in these entities is generally limited to any equity investment it has made or is required to make, and any earned but uncollected management fees. Legg Mason did not sell or transfer investment assets to any of these investment vehicles. In accordance with financial accounting standards, Legg Mason consolidates certain sponsored investment vehicles, some of which are designated and reported as consolidated investment vehicles (“CIVs”). The consolidation of sponsored investment vehicles, including those designated as CIVs, has no impact on Net Income Attributable to Legg Mason, Inc. and does not have a material impact on Legg Mason's consolidated operating results. The change in the value of all consolidated sponsored investment vehicles is recorded in Other Non-Operating Income (Expense) and reflected in Net income attributable to noncontrolling interests. Certain investment vehicles Legg Mason sponsors and is the manager of are considered to be variable interest entities ("VIEs") (as further described below) while others are considered to be voting rights entities (“VREs”) subject to traditional consolidation concepts based on ownership rights. Sponsored investment vehicles that are considered VREs are consolidated if Legg Mason has a controlling financial interest in the investment vehicle, absent substantive investor rights to replace the manager of the entity (kick-out rights). Legg Mason may also fund the initial cash investment in certain VRE investment vehicles to generate an investment performance track record in order to attract third-party investors in the product. Legg Mason's initial investment in a new product typically represents 100% of the ownership in that product. As further discussed below, these “seed capital investments” are consolidated as long as Legg Mason maintains a controlling financial interest in the product, but they are not designated as CIVs by Legg Mason unless the investment is longer-term. As of June 30, 2016, March 31, 2016, and June 30, 2015, no consolidated VREs were designated as CIVs. A VIE is an entity which does not have adequate equity to finance its activities without additional subordinated financial support; or the equity investors, as a group, do not have the normal characteristics of equity investors for a potential controlling financial interest. Legg Mason must consolidate any VIE for which it is deemed to be the primary beneficiary. Updated Consolidation Accounting Guidance Effective April 1, 2016, Legg Mason adopted updated consolidation accounting guidance on a modified retrospective basis. Under the updated guidance, if limited partners in a sponsored investment vehicle structured as a limited partnership or a similar entity do not have either substantive kick-out or substantive participation rights over the general partner, the entities are VIEs. As a sponsor and manager of an investment vehicle, Legg Mason may be deemed a decision maker under the accounting guidance. If the fees paid to a decision maker are market-based, such fees are not considered variable interests in a VIE. Additionally, if employee interests in a sponsored investment vehicle are not made to circumvent the consolidation guidance and are not financed by the sponsor, they are not included in the variable interests assessment, and are not included in the primary beneficiary determination. A decision maker is deemed to be a primary beneficiary of a VIE if it has the power to direct activities that most significantly impact the economic performance of the VIE and the obligation to absorb losses or receive benefits from variable interests that could be significant to the VIE. In determining whether it is the primary beneficiary of a VIE, Legg Mason considers both qualitative and quantitative factors such as the voting rights of the equity holders, guarantees, and implied relationships. If a fee paid to a decision maker is not market-based, it will be considered in the primary beneficiary determination. The adoption of this accounting guidance resulted in certain sponsored investment vehicles that are foreign mutual fund trusts that were previously accounted for as VREs to be evaluated as VIEs, and the consolidation of nine funds, which are also designated as CIVs. In addition, Legg Mason concluded it is the primary beneficiary of one sponsored investment fund VIE managed by EnTrust Capital ("EnTrust"), which is also consolidated and designated a CIV. The adoption also resulted in the deconsolidation of 13 employee-owned funds, as Legg Mason no longer has a variable interest in these funds. The impact to the Consolidated Balance Sheet as of June 30, 2016, is the addition of $38,676 of assets, $2,255 of liabilities, and $37,093 of redeemable noncontrolling interests from CIVs. Legg Mason also concluded it was the primary beneficiary of one sponsored investment fund VIE, which was consolidated (and designated as a CIV) as of June 30, 2016. This sponsored investment fund was also consolidated under prior accounting guidance, as further discussed below. Prior Consolidation Accounting Guidance Under prior accounting guidance, for most sponsored investment fund VIEs deemed to be investment companies, including money market funds, Legg Mason determined it was the primary beneficiary of a VIE if it absorbed a majority of the VIE's expected losses, or received a majority of the VIE's expected residual returns, if any. Legg Mason's determination of expected residual returns excluded gross fees paid to a decision maker if certain criteria relating to the fees were met. In determining whether it was the primary beneficiary of a VIE, Legg Mason considered both qualitative and quantitative factors such as the voting rights of the equity holders, economic participation of all parties, including how fees were earned and paid to Legg Mason; related party ownership, guarantees, and implied relationships. For other sponsored investment funds that do not meet the investment company criteria, Legg Mason determined it was the primary beneficiary of a VIE if it had both the power to direct the activities of the VIE that most significantly impact the entity's economic performance and the obligation to absorb losses, or the right to receive benefits, that could be significant to the VIE. Legg Mason concluded it was the primary beneficiary of one sponsored investment fund VIE, that was consolidated as of March 31, 2016, and June 30, 2015, despite significant third-party investments in this product. Also, as of March 31, 2016, and June 30, 2015, Legg Mason concluded it was the primary beneficiary of 14 and 18 employee-owned funds it sponsors, respectively, which were consolidated and designated as CIVs. As of June 30, 2015, Legg Mason had a variable interest in three collateralized loan obligations ("CLOs"). Legg Mason concluded it was not the primary beneficiary of these CLOs, which were not consolidated, as it held no equity interest in these investment vehicles and the level of fees they were expected to pay to Legg Mason was insignificant. See Notes 4 and 13 for additional information related to VIEs. Fair Value Measurements Legg Mason's financial instruments are measured and reported at fair value and are classified and disclosed in one of the following categories (the "fair value hierarchy"): Level 1 — Financial instruments for which prices are quoted in active markets, which, for Legg Mason, include investments in publicly traded mutual funds with quoted market prices and equities listed in active markets and certain derivative instruments. Level 2 — Financial instruments for which prices are quoted for similar assets and liabilities in active markets, prices are quoted for identical or similar assets in inactive markets, or prices are based on observable inputs, other than quoted prices, such as models or other valuation methodologies. Level 3 — Financial instruments for which values are based on unobservable inputs, including those for which there is little or no market activity. As a result of the acquisition of Clarion Partners in April 2016, Legg Mason holds investments in real estate fund partnerships, which are classified as Level 3. The fair values of investments in real estate funds are prepared giving consideration to the income, cost and sales comparison approaches of estimating property value. The income approach estimates an income stream for a property and discounts this income plus a reversion (presumed sale) into a present value at a risk adjusted rate. Yield rates and growth assumptions utilized in this approach are derived from market transactions as well as other financial and industry data. The discount rate and the exit capitalization rate are significant inputs to these valuations. These rates are based on the location, type and nature of each property, and current and anticipated market conditions. The cost approach estimates the replacement cost of the building less physical depreciation plus the land value. The sales comparison approach compares recent transactions to the appraised property. Adjustments are made for dissimilarities which typically provide a range of value. Many factors are also considered in the determination of fair value including, but not limited to, the operating cash flows and financial performance of the properties, property types and geographic locations, the physical condition of the asset, prevailing market capitalization rates, prevailing market discount rates, general economic conditions, economic conditions specific to the market in which the assets are located, and any specific rights or terms associated with the investment. Because of the inherent uncertainties of valuation, the values may materially differ from the values that would be determined by negotiations held between parties in a sale transaction. See Note 4 for additional information regarding fair value measurements. Contingent Consideration Liabilities In connection with business acquisitions, Legg Mason may be required to pay additional future consideration based on the achievement of certain designated financial metrics. Legg Mason estimates the fair value of these potential future obligations at the time a business combination is consummated and records a Contingent consideration liability in the Consolidated Balance Sheet. Legg Mason accretes contingent consideration liabilities to the expected payment amounts over the related earn-out terms until the obligations are ultimately paid, resulting in Interest expense in the Consolidated Statements of Income. If the expected payment amounts subsequently change, the contingent consideration liabilities are (reduced) or increased in the current period, resulting in a (gain) or loss, which is reflected within Other operating expense in the Consolidated Statements of Income. See Notes 3 and 9 for additional information regarding contingent consideration liabilities. Noncontrolling Interests Noncontrolling interests include affiliate minority interests, third-party investor equity in consolidated sponsored investment vehicles, and vested affiliate management equity plan interests. For CIVs and other consolidated sponsored investment vehicles with third-party investors, the related noncontrolling interests are classified as redeemable noncontrolling interests if investors in these funds may request withdrawals at any time. Also included in redeemable noncontrolling interests are vested affiliate management equity plan interests for which the holder may, at some point, request settlement of their interests. Redeemable noncontrolling interests are reported in the Consolidated Balance Sheets at their estimated settlement values. When settlement is not expected to occur until a future date, changes in the expected settlement value are recognized over the settlement period as an adjustment from retained earnings. Nonredeemable noncontrolling interests include vested affiliate management equity plan interests that do not permit the holder to request settlement of their interests. Nonredeemable noncontrolling interests are reported in the Consolidated Balance Sheets at their issuance value, together with undistributed net income allocated to noncontrolling interests. Legg Mason estimates the settlement value of noncontrolling interests as their fair value. For consolidated sponsored investment vehicles, where the investor may request withdrawal at any time, fair value is based on market quotes of the underlying securities held by the investment vehicles. For affiliate minority interests and management equity plan interests, fair value reflects the related total business enterprise value, after appropriate discounts for lack of marketability and control. There may also be features of these equity interests, such as dividend subordination, that are contemplated in their valuations. The fair value of option-like management equity plan interests also relies on Black-Scholes option pricing model calculations. Net income attributable to noncontrolling interests in the Consolidated Statements of Income includes the share of net income of the respective subsidiary allocated to the minority interest holders. See Note 11 for additional information regarding noncontrolling interests. Accumulated Other Comprehensive Loss, Net There were no significant amounts reclassified from Accumulated other comprehensive loss, net, to the Consolidated Statements of Income for the three months ended June 30, 2016 or 2015, except for $527 realized on the settlement of an interest rate swap for the three months ended June 30, 2016, as further described in Note 7. Income Tax Provision Noncontrolling interests in EnTrustPermal Group Holdings, LLC ("EnTrustPermal"), Clarion Partners, and Royce & Associates ("Royce") are structured as partnerships that pass related tax attributes to the related noncontrolling interest holders. As such, the consolidated financial statements do not generally include any tax provision/benefit associated with the net income allocated to these noncontrolling interests, which caused the effective tax rate to be reduced by 4.8 percentage points for the three months ended June 30, 2016. During the three months ended June 30, 2015, Legg Mason recognized an income tax benefit of $17,527 as a result of an increase in the value of deferred tax assets due to changes in the New York City tax code. This benefit reduced the effective income tax rate by 14.6 percentage points for the three months ended June 30, 2015. Recent Accounting Developments In February 2016, the Financial Accounting Standards Board ("FASB") updated the guidance on accounting for leases. The updated guidance requires that a lessee shall recognize the assets and liabilities that arise from lease transactions. A lessee will recognize a right-of-use asset to use the underlying asset and a liability representing the lease payments. The updated guidance also requires an evaluation at the inception of a contract, to determine whether the contract is or contains a lease. The guidance will be effective in fiscal 2020. Legg Mason is evaluating the impact of its adoption. In May 2014, the FASB updated the guidance on revenue recognition. The updated guidance improves comparability and removes inconsistencies in revenue recognition practices across entities, industries, jurisdictions, and capital markets. In March 2016, the FASB further updated the revenue guidance on determining whether to report revenue on a gross versus net basis. The updated guidance clarifies how entities evaluate principal versus agent aspects of the revenue recognition guidance issued in May 2014. The evaluation will require entities to identify all goods or services to be provided to the customer, and determine whether they obtain control of the good or service before it is transferred to the customer, where control would suggest a principal relationship, which would be accounted for on a gross basis. These updates are effective for Legg Mason in fiscal 2019. Legg Mason is evaluating the impact of its adoption.

2. Significant Accounting Policies

Consolidation

In the normal course of its business, Legg Mason sponsors and manages various types of investment vehicles. For its services, Legg Mason is entitled to receive management fees and may be eligible, under certain circumstances, to receive additional subordinated management fees or other incentive fees. Legg Mason's exposure to risk in these entities is generally limited to any equity investment it has made or is required to make, and any earned but uncollected management fees. Legg Mason did not sell or transfer investment assets to any of these investment vehicles. In accordance with financial accounting standards, Legg Mason consolidates certain sponsored investment vehicles, some of which are designated and reported as consolidated investment vehicles (“CIVs”). The consolidation of sponsored investment vehicles, including those designated as CIVs, has no impact on Net Income Attributable to Legg Mason, Inc. and does not have a material impact on Legg Mason's consolidated operating results. The change in the value of all consolidated sponsored investment vehicles is recorded in Other Non-Operating Income (Expense) and reflected in Net income attributable to noncontrolling interests.

Certain investment vehicles Legg Mason sponsors and is the manager of are considered to be variable interest entities ("VIEs") (as further described below) while others are considered to be voting rights entities (“VREs”) subject to traditional consolidation concepts based on ownership rights. Sponsored investment vehicles that are considered VREs are consolidated if Legg Mason has a controlling financial interest in the investment vehicle, absent substantive investor rights to replace the manager of the entity (kick-out rights). Legg Mason may also fund the initial cash investment in certain VRE investment vehicles to generate an investment performance track record in order to attract third-party investors in the product. Legg Mason's initial investment in a new product typically represents 100% of the ownership in that product. As further discussed below, these “seed capital investments” are consolidated as long as Legg Mason maintains a controlling financial interest in the product, but they are not designated as CIVs by Legg Mason unless the investment is longer-term. As of June 30, 2016, March 31, 2016, and June 30, 2015, no consolidated VREs were designated as CIVs.

A VIE is an entity which does not have adequate equity to finance its activities without additional subordinated financial support; or the equity investors, as a group, do not have the normal characteristics of equity investors for a potential controlling financial interest. Legg Mason must consolidate any VIE for which it is deemed to be the primary beneficiary.

Updated Consolidation Accounting Guidance

Effective April 1, 2016, Legg Mason adopted updated consolidation accounting guidance on a modified retrospective basis. Under the updated guidance, if limited partners in a sponsored investment vehicle structured as a limited partnership or a similar entity do not have either substantive kick-out or substantive participation rights over the general partner, the entities are VIEs. As a sponsor and manager of an investment vehicle, Legg Mason may be deemed a decision maker under the accounting guidance. If the fees paid to a decision maker are market-based, such fees are not considered variable interests in a VIE. Additionally, if employee interests in a sponsored investment vehicle are not made to circumvent the consolidation guidance and are not financed by the sponsor, they are not included in the variable interests assessment, and are not included in the primary beneficiary determination.

A decision maker is deemed to be a primary beneficiary of a VIE if it has the power to direct activities that most significantly impact the economic performance of the VIE and the obligation to absorb losses or receive benefits from variable interests that could be significant to the VIE. In determining whether it is the primary beneficiary of a VIE, Legg Mason considers both qualitative and quantitative factors such as the voting rights of the equity holders, guarantees, and implied relationships. If a fee paid to a decision maker is not market-based, it will be considered in the primary beneficiary determination.

The adoption of this accounting guidance resulted in certain sponsored investment vehicles that are foreign mutual fund trusts that were previously accounted for as VREs to be evaluated as VIEs, and the consolidation of nine funds, which are also designated as CIVs. In addition, Legg Mason concluded it is the primary beneficiary of one sponsored investment fund VIE managed by EnTrust Capital ("EnTrust"), which is also consolidated and designated a CIV. The adoption also resulted in the deconsolidation of 13 employee-owned funds, as Legg Mason no longer has a variable interest in these funds. The impact to the Consolidated Balance Sheet as of June 30, 2016, is the addition of $38,676 of assets, $2,255 of liabilities, and $37,093 of redeemable noncontrolling interests from CIVs.

Legg Mason also concluded it was the primary beneficiary of one sponsored investment fund VIE, which was consolidated (and designated as a CIV) as of June 30, 2016. This sponsored investment fund was also consolidated under prior accounting guidance, as further discussed below.

Prior Consolidation Accounting Guidance

Under prior accounting guidance, for most sponsored investment fund VIEs deemed to be investment companies, including money market funds, Legg Mason determined it was the primary beneficiary of a VIE if it absorbed a majority of the VIE's expected losses, or received a majority of the VIE's expected residual returns, if any. Legg Mason's determination of expected residual returns excluded gross fees paid to a decision maker if certain criteria relating to the fees were met. In determining whether it was the primary beneficiary of a VIE, Legg Mason considered both qualitative and quantitative factors such as the voting rights of the equity holders, economic participation of all parties, including how fees were earned and paid to Legg Mason; related party ownership, guarantees, and implied relationships.

For other sponsored investment funds that do not meet the investment company criteria, Legg Mason determined it was the primary beneficiary of a VIE if it had both the power to direct the activities of the VIE that most significantly impact the entity's economic performance and the obligation to absorb losses, or the right to receive benefits, that could be significant to the VIE.

Legg Mason concluded it was the primary beneficiary of one sponsored investment fund VIE, that was consolidated as of March 31, 2016, and June 30, 2015, despite significant third-party investments in this product. Also, as of March 31, 2016, and June 30, 2015, Legg Mason concluded it was the primary beneficiary of 14 and 18 employee-owned funds it sponsors, respectively, which were consolidated and designated as CIVs.

As of June 30, 2015, Legg Mason had a variable interest in three collateralized loan obligations ("CLOs"). Legg Mason concluded it was not the primary beneficiary of these CLOs, which were not consolidated, as it held no equity interest in these investment vehicles and the level of fees they were expected to pay to Legg Mason was insignificant.

See Notes 4 and 13 for additional information related to VIEs.

Fair Value Measurements

Legg Mason's financial instruments are measured and reported at fair value and are classified and disclosed in one of the following categories (the "fair value hierarchy"):

Level 1 — Financial instruments for which prices are quoted in active markets, which, for Legg Mason, include investments in publicly traded mutual funds with quoted market prices and equities listed in active markets and certain derivative instruments.

Level 2 — Financial instruments for which prices are quoted for similar assets and liabilities in active markets, prices are quoted for identical or similar assets in inactive markets, or prices are based on observable inputs, other than quoted prices, such as models or other valuation methodologies.

Level 3 — Financial instruments for which values are based on unobservable inputs, including those for which there is little or no market activity.

As a result of the acquisition of Clarion Partners in April 2016, Legg Mason holds investments in real estate fund partnerships, which are classified as Level 3. The fair values of investments in real estate funds are prepared giving consideration to the income, cost and sales comparison approaches of estimating property value. The income approach estimates an income stream for a property and discounts this income plus a reversion (presumed sale) into a present value at a risk adjusted rate. Yield rates and growth assumptions utilized in this approach are derived from market transactions as well as other financial and industry data. The discount rate and the exit capitalization rate are significant inputs to these valuations. These rates are based on the location, type and nature of each property, and current and anticipated market conditions. The cost approach estimates the replacement cost of the building less physical depreciation plus the land value. The sales comparison approach compares recent transactions to the appraised property. Adjustments are made for dissimilarities which typically provide a range of value. Many factors are also considered in the determination of fair value including, but not limited to, the operating cash flows and financial performance of the properties, property types and geographic locations, the physical condition of the asset, prevailing market capitalization rates, prevailing market discount rates, general economic conditions, economic conditions specific to the market in which the assets are located, and any specific rights or terms associated with the investment. Because of the inherent uncertainties of valuation, the values may materially differ from the values that would be determined by negotiations held between parties in a sale transaction.

See Note 4 for additional information regarding fair value measurements.

Contingent Consideration Liabilities

In connection with business acquisitions, Legg Mason may be required to pay additional future consideration based on the achievement of certain designated financial metrics. Legg Mason estimates the fair value of these potential future obligations at the time a business combination is consummated and records a Contingent consideration liability in the Consolidated Balance Sheet.

Legg Mason accretes contingent consideration liabilities to the expected payment amounts over the related earn-out terms until the obligations are ultimately paid, resulting in Interest expense in the Consolidated Statements of Income. If the expected payment amounts subsequently change, the contingent consideration liabilities are (reduced) or increased in the current period, resulting in a (gain) or loss, which is reflected within Other operating expense in the Consolidated Statements of Income. See Notes 3 and 9 for additional information regarding contingent consideration liabilities.

Noncontrolling Interests

Noncontrolling interests include affiliate minority interests, third-party investor equity in consolidated sponsored investment vehicles, and vested affiliate management equity plan interests. For CIVs and other consolidated sponsored investment vehicles with third-party investors, the related noncontrolling interests are classified as redeemable noncontrolling interests if investors in these funds may request withdrawals at any time. Also included in redeemable noncontrolling interests are vested affiliate management equity plan interests for which the holder may, at some point, request settlement of their interests. Redeemable noncontrolling interests are reported in the Consolidated Balance Sheets at their estimated settlement values. When settlement is not expected to occur until a future date, changes in the expected settlement value are recognized over the settlement period as an adjustment from retained earnings. Nonredeemable noncontrolling interests include vested affiliate management equity plan interests that do not permit the holder to request settlement of their interests. Nonredeemable noncontrolling interests are reported in the Consolidated Balance Sheets at their issuance value, together with undistributed net income allocated to noncontrolling interests.

Legg Mason estimates the settlement value of noncontrolling interests as their fair value. For consolidated sponsored investment vehicles, where the investor may request withdrawal at any time, fair value is based on market quotes of the underlying securities held by the investment vehicles. For affiliate minority interests and management equity plan interests, fair value reflects the related total business enterprise value, after appropriate discounts for lack of marketability and control. There may also be features of these equity interests, such as dividend subordination, that are contemplated in their valuations. The fair value of option-like management equity plan interests also relies on Black-Scholes option pricing model calculations.

Net income attributable to noncontrolling interests in the Consolidated Statements of Income includes the share of net income of the respective subsidiary allocated to the minority interest holders.

See Note 11 for additional information regarding noncontrolling interests.

Accumulated Other Comprehensive Loss, Net

There were no significant amounts reclassified from Accumulated other comprehensive loss, net, to the Consolidated Statements of Income for the three months ended June 30, 2016 or 2015, except for $527 realized on the settlement of an interest rate swap for the three months ended June 30, 2016, as further described in Note 7.

Income Tax Provision

Noncontrolling interests in EnTrustPermal Group Holdings, LLC ("EnTrustPermal"), Clarion Partners, and Royce & Associates ("Royce") are structured as partnerships that pass related tax attributes to the related noncontrolling interest holders. As such, the consolidated financial statements do not generally include any tax provision/benefit associated with the net income allocated to these noncontrolling interests, which caused the effective tax rate to be reduced by 4.8 percentage points for the three months ended June 30, 2016.

During the three months ended June 30, 2015, Legg Mason recognized an income tax benefit of $17,527 as a result of an increase in the value of deferred tax assets due to changes in the New York City tax code. This benefit reduced the effective income tax rate by 14.6 percentage points for the three months ended June 30, 2015.

Recent Accounting Developments

In February 2016, the Financial Accounting Standards Board ("FASB") updated the guidance on accounting for leases. The updated guidance requires that a lessee shall recognize the assets and liabilities that arise from lease transactions. A lessee will recognize a right-of-use asset to use the underlying asset and a liability representing the lease payments. The updated guidance also requires an evaluation at the inception of a contract, to determine whether the contract is or contains a lease. The guidance will be effective in fiscal 2020. Legg Mason is evaluating the impact of its adoption.

In May 2014, the FASB updated the guidance on revenue recognition. The updated guidance improves comparability and removes inconsistencies in revenue recognition practices across entities, industries, jurisdictions, and capital markets. In March 2016, the FASB further updated the revenue guidance on determining whether to report revenue on a gross versus net basis. The updated guidance clarifies how entities evaluate principal versus agent aspects of the revenue recognition guidance issued in May 2014. The evaluation will require entities to identify all goods or services to be provided to the customer, and determine whether they obtain control of the good or service before it is transferred to the customer, where control would suggest a principal relationship, which would be accounted for on a gross basis. These updates are effective for Legg Mason in fiscal 2019. Legg Mason is evaluating the impact of its adoption.