Incentive Compensation Plans Stock Option Activity (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stock-based Payment Award
Intrinsic value of stock options exercised	$ 15.1	$ 15.2	$ 16.1
Proceeds from stock options exercised including taxes withheld	$ 20.0	$ 18.2	$ 20.4
Employee Stock Option
Stock-based Payment Award
Stock options outstanding as of January 1, 2017	4.8
Stock options outstanding as of Jan 1, 2017, Weighted-average exercise price	$ 9.83
Exercised	(1.1)	(1.2)	(1.4)
Exercised, weighted-average exercise price	$ 11.15
Stock options outstanding as of December 31, 2017	3.7	4.8
Stock options outstanding as of Dec 31, 2017, Weighted-average exercise price	$ 9.44	$ 9.83
Options outstanding, weighted average remaining contractual term	2 years 7 months
Stock options outstanding, aggregate intrinsic value	$ 39.2