Employee Benefit Plans OPEB Changes in Assets Measured at Fair Value Using Signficant Unobservable Inputs (Details) (Other Postretirement Benefit Plans, USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation
Contributions by Plan Participants	$ 4.1	$ 3.9
Defined Benefit Plan, Benefits Paid	(16.6)	(15.9)
Fair Value, Inputs, Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation
Assets Measured with Unobservable Inputs, Beginning Balance	11.4	11.5
Defined Benefit Plan, Actual Return on Plan Assets Still Held	0.4	0.2
Contributions by Plan Participants	16.1	15.6
Defined Benefit Plan, Benefits Paid	(16.6)	(15.9)
Assets Measured with Unobservable Inputs, Ending Balance	$ 11.3	$ 11.4