Postretirement Benefit Plans - Change in Benefit Obligation, Plan Assets, Funded Status, and Balance Sheet Items (Details) - Postretirement Benefit Plans [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.97%	4.39%	3.95%
Discount rate	3.57%	3.97%
Expected long-term return on plan assets	6.00%	6.00%	6.25%
Change in benefit obligation:
Benefit obligation at beginning of year	$ 241.4	$ 262.7
Service cost	0.1	0.3	$ 0.4
Interest cost	9.1	11.0	10.9
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment	1.2	(11.4)
International plan exchange rate change	(0.3)	4.3
Defined Benefit Plan, Plan Assets, Benefits Paid	31.7	25.5
Benefit obligation at end of year	$ 219.8	$ 241.4	$ 262.7