Derivatives - Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Gross and net fair values of outstanding derivatives (in millions)
Collateral received netted against derivative assets	$ 0	$ 14
Collateral paid netted against derivative liabilities	22	4
Collateral deposited with clearinghouses and brokers	32	3
Commodity contracts
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	184	644
Less: counterparty netting and cash collateral, asset	(149)	(535)
Total net fair value, asset	35	109
Commodity contract derivative liability, gross	460	948
Less: counterparty netting and cash collateral, liability	(171)	(525)
Total net fair value, liability	289	423
Cash-flow hedges \| Commodity contracts \| Other current assets
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross		9
Cash-flow hedges \| Commodity contracts \| Accrued liabilities
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	3	1
Not designated as hedging instruments \| Commodity contracts
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	184	635
Commodity contract derivative liability, gross	457	947
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	171	626
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	13	9
Not designated as hedging instruments \| Commodity contracts \| Accrued liabilities
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	242	672
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	$ 215	$ 275

Amount of obligation to return cash collateral under master netting arrangements offset against derivative assets.

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