This element represents the maximum number of shares of common stock that could be issued upon conversion of debt.

Name:	lm_ContingentConvertibleSeniorNotesNumberOfSharesMaximum
Namespace Prefix:	lm
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

This element represents the minimum number of shares of common stock that could be issued upon conversion of debt.

+ Details

Name:	lm_ContingentConvertibleSeniorNotesNumberOfSharesMinimum
Namespace Prefix:	lm
Data Type:	xbrli:sharesItemType
Balance Type:	na
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.

+ Details

Name:	lm_EarningsPerShareAdditionalDisclosuresLineItems
Namespace Prefix:	lm
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the number of equity units issued during the period.

+ Details

Name:	lm_NumberOfEquityUnitsIssued
Namespace Prefix:	lm
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

This element represents the number of equity units outstanding as of the balance sheet date.

+ Details

Name:	lm_NumberOfEquityUnitsOutstanding
Namespace Prefix:	lm
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) in the future that were not included in the computation of diluted EPS because to do so would increase EPS amounts or decrease loss per share amounts for the period presented.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 128
-Paragraph 13, 14

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 128
-Paragraph 171

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 128
-Paragraph 40
-Subparagraph c

+ Details

Name:	us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
Namespace Prefix:	us-gaap
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Interest rate stated in the contractual debt agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 22
-Article 5

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap
Data Type:	us-types:percentItemType
Balance Type:	na
Period Type:	instant

EARNINGS PER SHARE (Details 2) In Thousands, unless otherwise specified	12 Months Ended			1 Months Ended	12 Months Ended
	Mar. 31, 2011 Stock options	Mar. 31, 2010 Stock options	Mar. 31, 2009 Antidilutive shares due to net loss for the period	May 31, 2008 5.6% senior notes from Equity Units	Mar. 31, 2011 5.6% senior notes from Equity Units	Mar. 31, 2011 2.5% convertible senior notes
Additional earnings per share disclosures
Interest rate stated percentage of convertible senior notes (as a percent)						2.50%
Number of antidilutive shares excluded from EPS calculation	5,204	5,130	6,629
Number of Equity Units outstanding					2,061
Number of Equity Units issued				23,000
Minimum number of shares of common stock that could be issued, and are reserved for issuance (in shares)					1,525
Maximum number of shares of common stock that could be issued, and are reserved for issuance (in shares)					1,830	14,205