New Accounting Pronouncements (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Jan. 01, 2017
New Accounting Pronouncements
Income tax expense (benefit)	$ 63.6	$ 75.3	$ 134.6	$ 139.2
Impact of ASU 2016-09
New Accounting Pronouncements
Cumulative-effect adjustment to retained earnings					$ 0.0
Income tax expense (benefit)	$ (21.2)		$ (29.2)
Increase in diluted earnings per share (in dollars per share)	$ 0.07		$ 0.09