Cover Page Statement - shares	9 Months Ended
	Dec. 31, 2016	Feb. 02, 2017
Document Information [Abstract]
Entity Registrant Name	LEGG MASON, INC.
Entity Central Index Key	0000704051
Document Type	10-Q
Document Period End Date	Dec. 31, 2016
Amendment Flag	false
Current Fiscal Year End Date	--03-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		97,446,938
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	Q3
Trading Symbol	LM
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes