Derivatives (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011		Jun. 30, 2012		Jun. 30, 2011
Net After-tax Derivative Activity recorded in AOCI
Beginning balance-AOCI	$ (13)		$ (122)		$ 1		$ (111)
Unrealized gains (losses) recognized in AOCI	(2)	[1]	21	[1]	12	[1]	(4)	[1]
Losses (gains) reclassified to income	4		35		(24)		49
Ending balance - AOCI	(11)		(66)		(11)		(66)
Commodity Contracts - cash-flow hedges
Pre-tax derivative activity
Unrealized gains (losses) recognized in AOCI	(2)		34		20		(6)
Losses (gains) reclassified into income	6		54		(39)		76
Gains recognized in income- ineffective portion			$ 1

[1] Net of tax (expense)/benefit of zero and $(13) for the three months ended June 30, 2012 and 2011, respectively, and $(8) and $2 for the six months ended June 30, 2012 and 2011.