Accumulated Other Comprehensive Loss (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Increase (Decrease) in Accumulated Other Comprehensive Income
Balance, at the beginning of period	$ (139)
Current period change	21	(1)
Balance, at the end of period	(118)
Cash flow hedge gain (loss) reclassification period (in months)	12 months
Commodity Contracts
Increase (Decrease) in Accumulated Other Comprehensive Income
Unrealized derivative gains (losses) after taxes recorded in accumulated other comprehensive loss	27
Unrealized gains on cash flow hedges, net of tax, expected to be reclassified into earnings during the next 12 months	28
Interest Rate Contracts
Increase (Decrease) in Accumulated Other Comprehensive Income
Unrealized derivative gains (losses) after taxes recorded in accumulated other comprehensive loss	(47)
Unrealized Gain (Loss) on Cash Flow Hedges
Increase (Decrease) in Accumulated Other Comprehensive Income
Balance, at the beginning of period	(34)
Current period change	14
Balance, at the end of period	(20)
Pension and PBOP- Net Loss
Increase (Decrease) in Accumulated Other Comprehensive Income
Balance, at the beginning of period	(100)
Current period change	7
Balance, at the end of period	(93)
Pension and PBOP- Prior Service Cost
Increase (Decrease) in Accumulated Other Comprehensive Income
Balance, at the beginning of period	(5)
Current period change	0
Balance, at the end of period	$ (5)