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, 2016	Dec. 31, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation
Contributions by Plan Participants	$ 4.0	$ 4.6
Net Benefit Expenses Paid	(15.6)	(16.2)
Fair Value, Inputs, Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation
Beginning Balance of Assets Measured with Unobservable Inputs	11.2	11.3
Actual Return on Plan Assets Still Held	0.1	0.3
Contributions by Plan Participants	15.1	15.8
Net Benefit Expenses Paid	(15.6)	(16.2)
Ending Balance of Assets Measured with Unobservable Inputs	$ 10.8	$ 11.2