The period of time that the investment is subject to a lock-up, in years.

No definition available.

Name:	lm_InvestmentLockUpPeriod
Namespace Prefix:	lm_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

This element represents the percentage of the investment subject to monthly redemption.

+ References

No definition available.

+ Details

Name:	lm_PercentageOfMonthlyRedemption
Namespace Prefix:	lm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

This element represents the percentage of the investment subject to quarterly redemption.

+ References

No definition available.

+ Details

Name:	lm_PercentageOfQuarterlyRedemption
Namespace Prefix:	lm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

This element represents the percentage of the investment subject to lock-up or side pocket provisions.

+ References

No definition available.

+ Details

Name:	lm_PercentageSubjectToLockInPeriod
Namespace Prefix:	lm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

This element represents the percentage of the investment subject to daily redemption.

+ References

No definition available.

+ Details

Name:	lm_Percentagedailyredemption
Namespace Prefix:	lm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Fair value of investments in certain entities that calculate net asset value per share, including, but not limited to, by unit, membership interest, or other ownership interest. Investments include, but are not limited to, investments in certain hedge funds, venture capital funds, private equity funds, real estate partnerships or funds.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 6A
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=SL6742756-110258

+ Details

Name:	us-gaap_AlternativeInvestmentsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_FairValueInvestmentsEntitiesThatCalculateNetAssetValuePerShareLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=lm_ConsolidatedInvestmentVehiclesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_HedgeFundsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: