Pensions and Other Postretirement Benefits - Pension and Postretirement Expenses (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Pension Benefits
Components of Net Periodic Cost:
Service Cost	$ 2.6	$ 2.5
Interest Cost	10.6	11.1
Administrative Expenses	0.0	0.3
Expected Return on Plan Assets	(16.0)	(15.1)
Amortization:
Prior Service Cost (Credit)	0.1	0.2
Actuarial Loss (Gain)	1.7	4.8
Net Periodic (Benefit) Cost	(1.0)	3.8
Postretirement Health Care Benefits
Components of Net Periodic Cost:
Service Cost	0.2	0.2
Interest Cost	0.3	0.3
Administrative Expenses	0.0	0.0
Expected Return on Plan Assets	0.0	0.0
Amortization:
Prior Service Cost (Credit)	(0.1)	(0.1)
Actuarial Loss (Gain)	(0.5)	(0.5)
Net Periodic (Benefit) Cost	$ (0.1)	$ (0.1)