Stockholders' Equity - Before Tax and After Tax Amounts of Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Before Tax
Other comprehensive income	$ 60.0	$ 103.9
Tax (Expense) Benefit
Other comprehensive income	(0.4)	(0.2)
After Tax
Other comprehensive income	59.6	103.7
Foreign Currency Adjustment
Before Tax
Other comprehensive income	58.5	102.7
Tax (Expense) Benefit
Other comprehensive income	0.0	0.0
After Tax
Other comprehensive income	58.5	102.7
Pension and Postretirement Adjustment
Before Tax
Other comprehensive income (loss) before reclassifications	2.8	2.1
Reclassification from accumulated other comprehensive income	(1.3)	(0.9)
Other comprehensive income	1.5	1.2
Tax (Expense) Benefit
Other comprehensive income (loss) before reclassifications	(0.7)	(0.5)
Reclassification from accumulated other comprehensive income	0.3	0.3
Other comprehensive income	(0.4)	(0.2)
After Tax
Other comprehensive income (loss) before reclassifications	2.1	1.6
Reclassification from accumulated other comprehensive income	(1.0)	(0.6)
Other comprehensive income	$ 1.1	$ 1.0