Derivatives (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Net After-tax Derivative Activity recorded in AOCI
Beginning balance-AOCI	$ (11)		$ (66)		$ 1		$ (111)
Unrealized gains (losses) recognized in AOCI	(2)	[1]	24	[1]	10	[1]	20	[1]
Losses (gains) reclassified to income			25		(24)		74
Ending balance - AOCI	(13)		(17)		(13)		(17)
Commodity Contracts - cash-flow hedges
Pre-tax derivative activity
Unrealized gains (losses) recognized in AOCI	(3)		37		17		31
Losses (gains) reclassified to income			39		(38)		115
Losses recognized in income - ineffective portion			$ (1)				$ (1)

[1] Net of tax (expense)/benefit of $1 and $(13) for the three months ended September 30, 2012 and 2011, respectively, and $(7) and $(11) for the nine months ended September 30, 2012 and 2011.