Derivative Instruments (Details 3) (USD $) In Millions	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended	6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011 NUGs	Jun. 30, 2010 NUGs	Jun. 30, 2011 NUGs	Jun. 30, 2010 NUGs	Jun. 30, 2011 Other	Jun. 30, 2011 Other	Jun. 30, 2010 Other	Mar. 31, 2010 Other
Reconciliation of changes in the fair value of certain contracts that are deferred
Outstanding net asset (liability), Beginning Balance	$ (362)	$ (580)	$ (335)	$ (425)	$ (362)	$ (590)	$ (345)	$ (444)		$ 10	$ 19	$ 10
Additions/Change in value of existing contracts	(145)	(35)	(234)	(259)	(147)	(35)	(236)	(259)	2	2
Settled contracts	62	68	124	137	62	68	134	146		(10)	(9)
Outstanding net asset (liability), Ending Balance	$ (445)	$ (547)	$ (445)	$ (547)	$ (447)	$ (557)	$ (447)	$ (557)	$ 2	$ 2	$ 10	$ 10