Risk Management and Hedging Activities Risk Management and Hedging Activities - Not Designated as Hedging Contracts (Details) (Not Designated as Hedging Instrument [Member], Commodity derivative [Member], USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Not Designated as Hedging Instrument [Member] | Commodity derivative [Member]
Regulatory Assets (Liabilities), Net, Derivatives [Roll Forward]
Beginning balance	$ 182	$ 235
Changes in fair value recognized in net regulatory assets	4	(19)
Net (losses) gains reclassified to operating revenue	(30)	4
Net gains (losses) reclassified to cost of sales	3	(46)
Ending balance	$ 159	$ 174