Derivatives - Fair Value (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Gross and net fair values of outstanding derivatives (in millions)
Collateral received netted against derivative assets	$ 23	$ 4
Collateral paid netted against derivative liabilities	2	13
Collateral deposited with clearinghouses and brokers	21	25
Cash-flow hedges | Commodity contracts | Other current assets
Gross and net fair values of outstanding derivatives (in millions)
Total net fair value, asset	1	1
Cash-flow hedges | Commodity contracts | Accrued liabilities
Gross and net fair values of outstanding derivatives (in millions)
Total net fair value, liability		6
Cash-flow hedges | Level 2 | Commodity contracts | Other current assets
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	1	1
Cash-flow hedges | Level 2 | Commodity contracts | Accrued liabilities
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross		6
Not designated as hedging instruments | Commodity contracts | Other current assets
Gross and net fair values of outstanding derivatives (in millions)
Total net fair value, asset	34	27
Netting, asset	(398)	(196)
Not designated as hedging instruments | Commodity contracts | Long-term receivables and other assets, net
Gross and net fair values of outstanding derivatives (in millions)
Total net fair value, asset	2	3
Netting, asset	(15)	(2)
Not designated as hedging instruments | Commodity contracts | Accrued liabilities
Gross and net fair values of outstanding derivatives (in millions)
Netting and collateral, liability	(398)	(196)
Total net fair value, liability	13	27
Not designated as hedging instruments | Commodity contracts | Deferred credits and other liabilities
Gross and net fair values of outstanding derivatives (in millions)
Netting and collateral, liability	(15)	(2)
Total net fair value, liability	4	5
Not designated as hedging instruments | Level 1 | Commodity contracts | Other current assets
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	395	166
Not designated as hedging instruments | Level 1 | Commodity contracts | Long-term receivables and other assets, net
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	16	2
Not designated as hedging instruments | Level 1 | Commodity contracts | Accrued liabilities
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	375	172
Not designated as hedging instruments | Level 1 | Commodity contracts | Deferred credits and other liabilities
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	15	1
Not designated as hedging instruments | Level 2 | Commodity contracts | Other current assets
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	37	57
Not designated as hedging instruments | Level 2 | Commodity contracts | Long-term receivables and other assets, net
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	1	3
Not designated as hedging instruments | Level 2 | Commodity contracts | Accrued liabilities
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	36	51
Not designated as hedging instruments | Level 2 | Commodity contracts | Deferred credits and other liabilities
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	$ 4	$ 6