Benefit Plans and Other Postretirement Benefits, Net pension expense (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Pension Benefits
Components of net pension expense:
Service cost	$ 2.5	$ 2.3	$ 7.3	$ 6.9
Interest cost	5.0	5.2	14.9	15.8
Expected return on plan assets	(7.8)	(7.6)	(23.2)	(22.7)
Amortization of transition obligation				(0.1)
Amortization of prior service cost	0.7	0.6	2.1	1.7
Amortization of net actuarial losses	5.8	5.6	17.2	16.7
Net pension expense	6.2	6.1	18.3	18.3
Estimated cash contribution to the Plans in 2017 based on current actuarial calculations	25.0		25.0
Pension Benefits | U.S. Plans
Components of net pension expense:
Plan contributions by employer			17.0
Other Postretirement Benefits
Components of net pension expense:
Service cost				0.1
Interest cost	0.1	0.1	0.3	0.3
Amortization of net actuarial losses	0.2	0.2	0.5	0.5
Net pension expense	$ 0.3	$ 0.3	$ 0.8	$ 0.9