Derivatives (Details 4) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Gross and net fair values of outstanding derivatives (in millions)
Less: counterparty netting and cash collateral, asset	$ (750)	$ (301)
Less: counterparty netting and cash collateral, liability	(784)	(371)
Total net fair value, asset	115	118
Total net fair value, liability	84	126
Collateral received netted against derivative assets	13	25
Collateral paid netted against derivative liabilities	47	95
Collateral deposited with clearinghouses and brokers	85	116
Credit risk contingent features
Net derivative liabilities with credit-risk-contingent features	19	34
Amount of collateral posted	28	64
Commodity Contracts
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	865	419
Commodity contract derivative liability, gross	868	497
Cash-flow hedges | Commodity Contracts
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	4	11
Commodity contract derivative liability, gross	1	2
Cash-flow hedges | Commodity Contracts | Other current assets
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	4	11
Cash-flow hedges | Commodity Contracts | Accrued liabilities
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	1	1
Cash-flow hedges | Commodity Contracts | Deferred credits and other liabilities
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross		1
Not designated as hedging instruments | Commodity Contracts
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	861	408
Commodity contract derivative liability, gross	867	495
Not designated as hedging instruments | Commodity Contracts | Other current assets
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	841	386
Not designated as hedging instruments | Commodity Contracts | Long-term receivables and other assets, net
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	20	22
Not designated as hedging instruments | Commodity Contracts | Accrued liabilities
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	850	479
Not designated as hedging instruments | Commodity Contracts | Deferred credits and other liabilities
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	$ 17	$ 16