Accumulated Other Comprehensive Loss (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Increase (Decrease) in Accumulated Other Comprehensive Income
Balance, at the beginning of period	$ (76)	$ 37
Current period change	(63)	(113)	(130)
Balance, at the end of period	(139)	(76)	37
Cash Flow Hedge Gain (Loss) Reclassification Period	12 months
Commodity Contracts
Increase (Decrease) in Accumulated Other Comprehensive Income
Unrealized derivative gains (losses) after taxes recorded in accumulated other comprehensive loss	21
Unrealized gains on cash flow hedges, net of tax, expected to be reclassified into earnings during the next 12 months	22
Interest Rate Contracts
Increase (Decrease) in Accumulated Other Comprehensive Income
Unrealized derivative gains (losses) after taxes recorded in accumulated other comprehensive loss	(55)
Cash Flow Hedges - Net Unrealized Gain (Loss)
Increase (Decrease) in Accumulated Other Comprehensive Income
Balance, at the beginning of period	16	105
Current period change	(50)	(89)
Balance, at the end of period	(34)	16
Pension and PBOP- Net Gain (Loss)
Increase (Decrease) in Accumulated Other Comprehensive Income
Balance, at the beginning of period	(87)	(70)
Current period change	(13)	(17)
Balance, at the end of period	(100)	(87)
Pension and PBOP- Prior Service Cost
Increase (Decrease) in Accumulated Other Comprehensive Income
Balance, at the beginning of period	(5)	2
Current period change	0	(7)
Balance, at the end of period	$ (5)	$ (5)