Supplementary Data Share Repurchase Program (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Feb. 14, 2018	Feb. 10, 2017
Disclosure of Repurchase Agreements [Abstract]
Stock repurchase program, authorized amount			$ 300.0	$ 300.0
Number of shares repurchased	2.4	2.3
Aggregate cost, including fees	$ 54.9	$ 55.0
Average price per share, including fees	$ 22.59	$ 23.85
Stock repurchase program, remaining authorized repurchase amount, excluding fees	$ 400.6