Stock-Based Compensation - Schedule of Other Stock Option Statistics (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Other disclosures
Total unrecognized compensation cost on nonvested options	$ 7.2
Non-qualified stock options
Other disclosures
Aggregate intrinsic value of outstanding options	53.1	$ 57.2
Aggregate intrinsic value of exercisable options	45.8	53.2
Total intrinsic value of options exercised	$ 25.6	$ 6.7
Total number of options exercisable (in shares)	1.3	1.8
Weighted average exercise price of options exercisable (in dollars per share)	$ 25.27	$ 21.99
Total unrecognized compensation cost on nonvested options	$ 1.2	$ 1.1