Name:	lm_ShareBasedCompensationArrangementByShareBasedPaymentAwardUnvestedOptionsVestedInPeriodWeightedAverageGrantDateFairValue
Namespace Prefix:	lm_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

This element represents the amount of unamortized compensation cost related to unvested options.

No definition available.

Name:	lm_UnamortizedCompensationCostOnUnvestedOptions
Namespace Prefix:	lm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Unvested options, forfeitures, weighted-average exercise price

No definition available.

Name:	lm_UnvestedOptionsForfeitedWeightedAverageExercisePrice
Namespace Prefix:	lm_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

Unvested options, forfeitures in period

No definition available.

Name:	lm_UnvestedOptionsForfeituresInPeriod
Namespace Prefix:	lm_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

Unvested options, granted

No definition available.

Name:	lm_UnvestedOptionsGranted
Namespace Prefix:	lm_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

Unvested options, granted, weighted-average price

No definition available.

Name:	lm_UnvestedOptionsGrantedWeightedAveragePrice
Namespace Prefix:	lm_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

Unvested Options, Number of Shares

No definition available.

Name:	lm_UnvestedOptionsNumberOfShares
Namespace Prefix:	lm_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

Unvested Options, options vested in period

No definition available.

Name:	lm_UnvestedOptionsOptionsVestedInPeriod
Namespace Prefix:	lm_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

Unvested options outstanding, weighted average exercise price

No definition available.

Name:	lm_UnvestedOptionsOutstandingWeightedAverageExercisePrice
Namespace Prefix:	lm_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Aggregate proceeds received by the entity during the annual period from exercises of stock or unit options and conversion of similar instruments granted under equity-based payment arrangements.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (j)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 123R

-Paragraph A240

-Subparagraph i

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Name:	us-gaap_EmployeeServiceShareBasedCompensationCashReceivedFromExerciseOfStockOptions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Disclosure of the aggregate tax benefit realized from the exercise of stock options and the conversion of similar instruments during the annual period.