Employee Benefit Plans - Estimated Future Benefit Payments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Non-qualified pension plans
Employee benefit plans
Employer contributions	$ 6.3
Expected minimum required funding contributions in 2017	6.0
Postretirement Plans
Employee benefit plans
Other assets	0.0
Unfunded plan direct benefits paid	9.0
Estimated future benefit payments, net of subsidies:
2018	8.9
2019	8.2
2020	7.5
2021	6.9
2022	6.3
Subsequent five years	23.9
United States
Employee benefit plans
Employer contributions	0.0
Other assets	0.0	$ 0.0
Estimated future benefit payments, net of subsidies:
2018	24.8
2019	22.6
2020	23.1
2021	23.3
2022	23.9
Subsequent five years	115.1
Foreign Plan
Employee benefit plans
Employer contributions	3.4
Expected minimum required funding contributions in 2017	2.5
Other assets	8.4	$ 6.3
Estimated future benefit payments, net of subsidies:
2018	4.7
2019	5.5
2020	5.3
2021	5.5
2022	6.4
Subsequent five years	$ 36.1