Employee Benefit Plans and Other Postretirement Benefits (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 6.2	$ 6.1	$ 12.4	$ 12.2
Interest cost	10.6	10.4	21.3	20.8
Expected return on plan assets	(14.2)	(13.5)	(28.3)	(27.0)
Net amortization of unrecognized amounts, Prior service cost	1.8	1.5	3.4	3.0
Net amortization of unrecognized amounts, Actuarial loss (income)	2.3	1.9	4.6	3.7
Net periodic benefit cost	6.7	6.4	13.4	12.7
Postretirement Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.1	0.1	0.2	0.2
Interest cost	0.1	0.2	0.2	0.3
Net amortization of unrecognized amounts, Prior service cost	(0.1)	(0.1)	(0.1)	(0.1)
Net periodic benefit cost	$ 0.1	$ 0.2	$ 0.3	$ 0.4