Risk Management and Hedging Activities Risk Management and Hedging Activities - Not Designated as Hedging Contracts (Details) (Not Designated as Hedging Instrument [Member], Commodity Contract [Member], USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Not Designated as Hedging Instrument [Member] | Commodity Contract [Member]
Regulatory Assets (Liabilities), Net, Derivatives [Roll Forward]
Beginning balance	$ 27	$ 82	$ 55	$ 121
Changes in fair value recognized in regulatory assets	(27)	14	(49)	(5)
Net losses reclassified to operating revenue	0	(2)	(11)	(1)
Net (losses) gains reclassified to energy costs	0	(9)	5	(30)
Ending balance	$ 0	$ 85	$ 0	$ 85