Pensions and Other Postretirement Benefits - Pension and Postretirement Expenses (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Pension Benefits
Components of Net Periodic Cost:
Service Cost	$ 2.4	$ 3.9	$ 4.9	$ 7.7
Interest Cost	11.3	13.6	22.4	27.0
Administrative Expenses	0.2	0.2	0.5	0.4
Expected Return on Plan Assets	(15.1)	(18.7)	(30.2)	(37.2)
Amortization:
Prior Service Cost (Credit)	0.2	0.1	0.4	0.3
Actuarial Loss (Gain)	7.1	5.6	11.9	11.1
Net Periodic Cost	6.1	4.7	9.9	9.3
Postretirement Health Care Benefits
Components of Net Periodic Cost:
Service Cost	0.2	0.3	0.4	0.5
Interest Cost	0.4	0.5	0.7	0.9
Administrative Expenses	0.0	0.0	0.0	0.0
Expected Return on Plan Assets	0.0	0.0	0.0	0.0
Amortization:
Prior Service Cost (Credit)	0.0	0.0	(0.1)	(0.1)
Actuarial Loss (Gain)	(0.7)	(0.3)	(1.2)	(0.7)
Net Periodic Cost	$ (0.1)	$ 0.5	$ (0.2)	$ 0.6