Accumulated Other Comprehensive Loss (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Increase (Decrease) in Accumulated Other Comprehensive Income
Balance, at the beginning of period			$ (139)
Current period change	(11)	(27)	(29)	(48)
Balance, at the end of period	(168)		(168)
Commodity Contracts
Increase (Decrease) in Accumulated Other Comprehensive Income
Unrealized derivative gains (losses) after taxes recorded in accumulated other comprehensive loss	7		7
Unrealized gains on cash flow hedges, net of tax, expected to be reclassified into earnings during the next 12 months			3
Interest Rate Contracts
Increase (Decrease) in Accumulated Other Comprehensive Income
Unrealized derivative gains (losses) after taxes recorded in accumulated other comprehensive loss	(79)		(79)
Unrealized Loss on Cash Flow Hedges
Increase (Decrease) in Accumulated Other Comprehensive Income
Balance, at the beginning of period			(34)
Current period change			(38)
Balance, at the end of period	(72)		(72)
Pension and PBOP- Net Gain (Loss)
Increase (Decrease) in Accumulated Other Comprehensive Income
Balance, at the beginning of period			(100)
Current period change			9
Balance, at the end of period	(91)		(91)
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)		$ (5)