Employee Benefit Plans (Components of AOCI and Regulatory Assets and Liabilities) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	$ (165)	$ (132)	$ (96)
Prior service (credit) cost	(3)	(3)	(3)
Pension Benefits | Scenario, Forecast
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	112
Prior service (credit) cost	3
Other Postretirement Plans
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	(7)	(6)	(12)
Prior service (credit) cost	15	13	13
Other Postretirement Plans | Scenario, Forecast
Defined Benefit Plan Disclosure [Line Items]
Net actuarial loss	2
Prior service (credit) cost	$ (28)