Fair Value of Financial Instruments Unobservable Input Reconciliation (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Net liabilities from price risk management activities as of beginning of period	$ 79	$ 120
Realized and unrealized losses, net	18	(2)
Purchases	0	(1)
Issues	(1)	0
Settlements	0	(1)
Transfers out of Level 3 to Level 2	(1)	0
Net liabilities from price risk management activities as of end of period	$ 95	$ 116