Derivatives - Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Gross and net fair values of outstanding derivatives (in millions)
Collateral received netted against derivative assets	$ 6	$ 4
Collateral paid netted against derivative liabilities	1	13
Collateral deposited with clearinghouses and brokers	25	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
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
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	23	27
Netting, asset	(308)	(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	3	3
Netting, asset	(3)	(2)
Not designated as hedging instruments | Commodity contracts | Accrued liabilities
Gross and net fair values of outstanding derivatives (in millions)
Netting and collateral, liability	(308)	(196)
Total net fair value, liability	8	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	(3)	(2)
Total net fair value, liability	6	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	285	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	4	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	282	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	3	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	46	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	34	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	$ 6	$ 6