Postretirement Benefits Other Than Pensions - Actuarial Assumptions of OPEB Expense (Details) (Other Postretirement Benefit Plan, Defined Benefit [Member])	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Other Postretirement Benefit Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount Rate	4.00%	3.15%	4.25%
Rate of Increase in Future Compensation Levels	2.10%	2.10%	2.10%