CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net Income	$ 146.3	$ 133.4	$ 425.8	$ 337.8
Other comprehensive income, net of tax:
Foreign exchange translation adjustments	(0.2)	7.9	(6.6)	22.5
Defined benefit plan adjustments gain (loss)	0.0	0.0	0.0	11.9
Income (loss) from derivative agreements	6.6	(2.1)	0.7	(6.1)
Other comprehensive income (loss)	6.4	5.8	(5.9)	28.3
Comprehensive income	$ 152.7	$ 139.2	$ 419.9	$ 366.1