Benefit Plans and Other Postretirement Benefits (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Pension Benefits
Components of net pension expense:
Service cost	$ 2.4	$ 2.3	$ 4.9	$ 4.6
Interest cost	4.9	4.8	9.9	10.6
Expected return on plan assets	(7.7)	(7.7)	(15.5)	(15.2)
Amortization of prior service cost	0.7	0.5	1.4	1.1
Amortization of actuarial losses	5.7	4.9	11.4	11.2
Net pension expense	6.0	4.8	12.1	12.3
U.S. Plans, Pension Benefits
Components of net pension expense:
Estimated cash contribution to the Plans in 2017 based on current actuarial calculations			25.0
Other Postretirement Benefits
Components of net pension expense:
Interest cost	0.1	0.1	0.2	0.2
Amortization of actuarial losses	0.2	0.2	0.3	0.3
Net pension expense	$ 0.3	$ 0.3	$ 0.5	$ 0.5