Stock Repurchase Activity (Details) - USD ($) $ in Millions	12 Months Ended	88 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Jan. 18, 2016	May 15, 2015	Dec. 11, 2007
Equity [Abstract]
Stock repurchase program, number of shares authorized to be repurchased			15,000,000.0	20,000,000.0	10,000,000
Repurchased shares under authorization (in shares)	8,600,000	7,500,000
Amount of repurchased shares under authorization	$ 363.8	$ 234.7
Stock repurchase program, remaining number of shares authorized to be repurchased				11,400,000	2,500,000