Financial Instruments, Derivatives, Guarantees and Concentration of Credit Risk (Details) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2010	Dec. 31, 2009
Asset (Liability)
Cash and cash equivalents	$ 1,166	$ 795	$ 1,601	$ 1,867
Carrying Amount
Asset (Liability)
Cash and cash equivalents	1,166	795
Restricted cash (current and noncurrent)	29	28
ARO Trust investments	40	40
Long-term debt, including current portion	(9,305)	(9,104)
Guarantee	(34)	(35)
Other	42	(23)
Net energy derivatives:
Energy commodity cash flow hedges	182	266
Other energy derivatives	3	18
Fair Value
Asset (Liability)
Cash and cash equivalents	1,166	795
Restricted cash (current and noncurrent)	29	28
ARO Trust investments	40	40
Long-term debt, including current portion	(10,325)	(9,990)
Guarantee	(32)	(34)
Other	41	(25)
Net energy derivatives:
Energy commodity cash flow hedges	182	266
Other energy derivatives	$ 3	$ 18