Derivatives - Fair Value (Details) - USD ($)	Mar. 31, 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	66,000,000	1,000,000
Collateral deposited with clearinghouses and brokers	94,000,000	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	1,099,000,000	2,392,000,000
Total net fair value, asset	26,000,000	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	19,000,000	6,000,000
Total net fair value, asset	8,000,000	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	(1,099,000,000)	(2,392,000,000)
Total net fair value, liability	91,000,000	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	(19,000,000)	(6,000,000)
Total net fair value, liability	3,000,000	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	1,077,000,000	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	19,000,000	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	1,136,000,000	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	20,000,000	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	48,000,000	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	8,000,000	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	54,000,000	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	2,000,000	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