Risk Management and Hedging Activities Risk Management and Hedging Activities - Not Designated as Hedging Activities (Details) (Not Designated as Hedging Instrument [Member], Commodity Contract [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Not Designated as Hedging Instrument [Member] | Commodity Contract [Member]
Regulatory Assets (Liabilities), Net, Derivatives [Roll Forward]
Beginning balance	$ 121	$ 264
Changes in fair value recognized in regulatory assets	15	45
Net gains reclassified to operating revenue	9	38
Net losses reclassified to energy costs	(90)	(226)
Ending balance	$ 55	$ 121