Cover Page Statement - shares	6 Months Ended
	Sep. 30, 2017	Nov. 06, 2017
Document Information [Abstract]
Entity Registrant Name	LEGG MASON, INC.
Entity Central Index Key	0000704051
Document Type	10-Q
Document Period End Date	Sep. 30, 2017
Amendment Flag	false
Current Fiscal Year End Date	--03-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		91,937,502
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q2
Trading Symbol	LM
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes