Supplementary Data Share Repurchase Program (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Feb. 10, 2017	Feb. 12, 2016
Disclosure of Repurchase Agreements [Abstract]
Stock repurchase program, authorized amount			$ 300.0	$ 300.0
Number of shares repurchased	9.4	8.5
Aggregate cost, including fees	$ 216.0	$ 193.3
Average price per share, including fees	$ 22.92	$ 22.69
Stock repurchase program, remaining authorized repurchase amount, excluding fees	$ 239.5