Stock Repurchase (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended	88 Months Ended
	Dec. 31, 2016	Dec. 31, 2016	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	10,000,000.0
Stock repurchase program, remaining number of shares authorized to be repurchased						11,400,000	2,500,000
Repurchase of common stock (in shares)	0	0	8,600,000	7,500,000
Value of shares repurchased			$ 363.8	$ 234.7
Treasury stock, number of shares held	21,000,000	21,000,000