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, 2018	Dec. 31, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation
Plan Participant Contributions	$ 0.2	$ 0.2
Defined Benefit Plan, Plan Assets, Benefits Paid	11.1	10.3
Fair Value, Inputs, Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation
Assets Measured with Unobservable Inputs, Beginning Balance	10.5	10.8
Actual Return on Plan Assets Still Held	0.1	0.1
Plan Participant Contributions	10.6	9.9
Defined Benefit Plan, Plan Assets, Benefits Paid	11.1	10.3
Assets Measured with Unobservable Inputs, Ending Balance	$ 10.1	$ 10.5