Risk Management and Hedging Activities Risk Management and Hedging Activities - Designated as Hedging Contracts (Details) (Designated as Hedging Instrument [Member], USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Accumulated Other Comprehensive (Income) Loss, Net, Derivatives [Roll Forward]
Cash flow hedge ineffectiveness	insignificant	insignificant
Cash flow hedge loss to be reclassified within twelve months	$ 14
Commodity derivative [Member]
Accumulated Other Comprehensive (Income) Loss, Net, Derivatives [Roll Forward]
Beginning balance	32	12
Changes in fair value recognized in OCI	(8)	(59)
Net gains reclassified to operating revenue	1	0
Net gains reclassified to cost of sales	2	35
Ending balance	$ 27	(12)