Equity (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Feb. 21, 2019
Securities Repurchase Program
Repurchase of common stock	$ 68.9	$ 18.5	$ 173.6
Share Repurchase Program
Securities Repurchase Program
Repurchased shares	1,467,886	302,000	4,512,325
Repurchase of common stock	$ 63.1	$ 12.7	$ 167.9
Repurchased shares, average price (in dollars per share)	$ 43.00	$ 41.95	$ 37.21
Remaining amount authorized to be repurchased	$ 136.9
Amount authorized to be repurchased				$ 200.0
Acquired Employee Equity Awards
Securities Repurchase Program
Repurchased shares	119,608	133,710	144,717
Repurchase of common stock	$ 5.8	$ 5.8	$ 5.7
Repurchased shares, average price (in dollars per share)	$ 48.61	$ 43.28	$ 39.47
Common Stock
Securities Repurchase Program
Repurchased shares	1,587,494	435,710	4,657,042