Summary of Significant Accounting Policies - Changes in the Components of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Pension and OPEB liability adjustments, pre-tax	$ 15.4	$ 3.4	$ 1.9
Unrealized gain (loss) on financial instruments, pre-tax	5.1	23.0	(13.6)
Unrealized foreign currency translation adjustments, pre-tax	31.5	(16.7)	(54.4)
Total other comprehensive income (loss), pre-tax	52.0	9.7	(66.1)
Pension and OPEB liability adjustments, Tax	(3.8)	(4.3)	0.9
Unrealized gain (loss) on financial instruments, Tax	(2.8)	(3.3)	0.3
Unrealized foreign currency translation adjustments, Tax	4.5	0.0	0.0
Total other comprehensive income (loss), Tax	(2.1)	(7.6)	1.2
Pension and OPEB liability adjustments, Net of Tax	11.6	(0.9)	2.8
Unrealized gain (loss) on financial instruments, Net of Tax	2.3	19.7	(13.3)
Unrealized foreign currency translation adjustments, Net of Tax	36.0	(16.7)	(54.4)
Other comprehensive income (loss)	$ 49.9	$ 2.1	$ (64.9)