Derivatives - Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Gross and net fair values of outstanding derivatives (in millions)
Collateral received netted against derivative assets	$ 2	$ 4
Collateral paid netted against derivative liabilities	31	13
Collateral deposited with clearinghouses and brokers	33	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	19	27
Netting, asset	(387)	(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	(29)	(2)
Not designated as hedging instruments | Commodity contracts | Accrued liabilities
Gross and net fair values of outstanding derivatives (in millions)
Netting and collateral, liability	(387)	(196)
Total net fair value, liability	47	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	(29)	(2)
Total net fair value, liability	3	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	345	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	29	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	371	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	27	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	61	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	2	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	63	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	$ 5	$ 6