Employee Benefit Plans OPEB Changes in Assets Measured at Fair Value Using Signficant Unobservable Inputs (Details) - Other Postretirement Benefit Plans - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation
Fair Value of Plan Assets at Beginning of Year	$ 9.9	$ 10.1
Fair Value of Plan Assets at End of Year	9.3	9.9
Fair Value, Inputs, Level 3 | Life Insurance Contracts
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation
Fair Value of Plan Assets at Beginning of Year	9.9	10.1
Actual Return on Plan Assets Still Held	0.1	0.2
Plan Participant Contributions	9.9	10.8
Defined Benefit Plan, Plan Assets, Benefits Paid	10.6	11.2
Fair Value of Plan Assets at End of Year	$ 9.3	$ 9.9