Pensions and Other Postretirement Benefits - Pension and Postretirement Expenses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Pension Benefits
Components of Net Periodic Cost:
Service Cost	$ 3.7	$ 3.5	$ 11.5	$ 10.5
Interest Cost	2.8	11.5	10.5	34.5
Administrative Expenses	0.0	0.0	0.2	0.2
Expected Return on Plan Assets	(4.1)	(13.6)	(15.7)	(41.1)
Net Settlement Loss	0.0	0.0	152.5	0.0
Defined Benefit Plan, Additional Information [Abstract]
Prior Service Credit	0.0	0.0	0.0	0.0
Actuarial Loss (Gain)	1.4	2.5	4.1	7.6
Net Periodic Cost (Benefit)	3.8	3.9	163.1	11.7
Postretirement Health Care Benefits
Components of Net Periodic Cost:
Service Cost	0.1	0.1	0.4	0.4
Interest Cost	0.2	0.3	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
Net Settlement Loss	0.0	0.0	0.0	0.0
Defined Benefit Plan, Additional Information [Abstract]
Prior Service Credit	(0.1)	(0.1)	(0.2)	(0.2)
Actuarial Loss (Gain)	(0.4)	(0.6)	(1.3)	(1.8)
Net Periodic Cost (Benefit)	$ (0.2)	$ (0.3)	$ (0.4)	$ (0.7)