Derivatives - Fair Value (Details) - USD ($)	Jun. 30, 2019	Dec. 31, 2018
Gross and net fair values of outstanding derivatives (in millions)
Collateral received netted against derivative assets	$ 0	$ 45,000,000
Collateral paid netted against derivative liabilities	19,000,000	1,000,000
Collateral deposited with clearinghouses and brokers	43,000,000	178,000,000
Not designated as hedging instruments | Commodity Contract
Gross and net fair values of outstanding derivatives (in millions)
Netting and collateral, liability		0
Total net fair value, liability		2,000,000
Not designated as hedging instruments | Other current assets | Commodity Contract
Gross and net fair values of outstanding derivatives (in millions)
Netting, asset	(1,105,000,000)	(2,392,000,000)
Total net fair value, asset	33,000,000	249,000,000
Not designated as hedging instruments | Long-term receivables and other assets, net | Commodity Contract
Gross and net fair values of outstanding derivatives (in millions)
Netting, asset	(24,000,000)	(6,000,000)
Total net fair value, asset	10,000,000	8,000,000
Not designated as hedging instruments | Accrued liabilities | Commodity Contract
Gross and net fair values of outstanding derivatives (in millions)
Netting and collateral, liability	(1,105,000,000)	(2,392,000,000)
Total net fair value, liability	60,000,000	66,000,000
Not designated as hedging instruments | Deferred credits and other liabilities - other | Commodity Contract
Gross and net fair values of outstanding derivatives (in millions)
Netting and collateral, liability	(24,000,000)	(6,000,000)
Total net fair value, liability	2,000,000	2,000,000
Not designated as hedging instruments | Level 1 | Commodity Contract
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross		0
Not designated as hedging instruments | Level 1 | Other current assets | Commodity Contract
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	1,053,000,000	2,531,000,000
Not designated as hedging instruments | Level 1 | Long-term receivables and other assets, net | Commodity Contract
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	24,000,000	5,000,000
Not designated as hedging instruments | Level 1 | Accrued liabilities | Commodity Contract
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	1,076,000,000	2,357,000,000
Not designated as hedging instruments | Level 1 | Deferred credits and other liabilities - other | Commodity Contract
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	25,000,000	6,000,000
Not designated as hedging instruments | Level 2 | Commodity Contract
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross		2,000,000
Not designated as hedging instruments | Level 2 | Other current assets | Commodity Contract
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	85,000,000	110,000,000
Not designated as hedging instruments | Level 2 | Long-term receivables and other assets, net | Commodity Contract
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	10,000,000	9,000,000
Not designated as hedging instruments | Level 2 | Accrued liabilities | Commodity Contract
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	89,000,000	101,000,000
Not designated as hedging instruments | Level 2 | Deferred credits and other liabilities - other | Commodity Contract
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	1,000,000	2,000,000
Not designated as hedging instruments | Level 3 | Commodity Contract
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross		0
Not designated as hedging instruments | Level 3 | Other current assets | Commodity Contract
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	0	0
Not designated as hedging instruments | Level 3 | Long-term receivables and other assets, net | Commodity Contract
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	0	0
Not designated as hedging instruments | Level 3 | Accrued liabilities | Commodity Contract
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	0	0
Not designated as hedging instruments | Level 3 | Deferred credits and other liabilities - other | Commodity Contract
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	$ 0	$ 0