Significant Accounting Policies MEP Details (Details)	12 Months Ended
Mar. 31, 2014
Accounting Policies [Abstract]
Profits interests equity plan participation percentage	15.00%
Annual Vesting Percentage	20.00%
Vesting period	5 years

Represents the percentage of participation in future growth in value of the affiliate available for participation by key employees under the terms of a profits interest management equity plan.

No definition available.

Name:	lm_ProfitsInterestsEquityPlanParticipationPercentage
Namespace Prefix:	lm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration