Derivatives - Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Collateral deposited with clearinghouses and brokers	$ 15
Initial margin		$ 65
Interest Rate Swaps
Gross and net fair values of outstanding derivatives (in millions)
Collateral paid netted against derivative liabilities	388	104
Other current assets | Collars and Call Options
Gross and net fair values of outstanding derivatives (in millions)
Netting, asset	0	0
Total net fair value, asset	269	92
Other current assets | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Netting, asset	(1,194)	(973)
Total net fair value, asset	5	51
Other current assets | Interest Rate Swaps
Gross and net fair values of outstanding derivatives (in millions)
Netting, asset		0
Total net fair value, asset		5
Long-term receivables and other assets, net | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Netting, asset	(77)	(4)
Total net fair value, asset	2	12
Long-term receivables and other assets, net | Interest Rate Swaps
Gross and net fair values of outstanding derivatives (in millions)
Netting, asset		0
Total net fair value, asset		5
Accrued liabilities | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Netting and collateral, liability	(1,194)	(973)
Total net fair value, liability	(35)	(79)
Accrued liabilities | Interest Rate Swaps
Gross and net fair values of outstanding derivatives (in millions)
Netting and collateral, liability	0	0
Total net fair value, liability	(1,011)	(657)
Deferred credits and other liabilities - other | Collars and Call Options
Gross and net fair values of outstanding derivatives (in millions)
Netting and collateral, liability	0	0
Total net fair value, liability	(18)	(160)
Deferred credits and other liabilities - other | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Netting and collateral, liability	(77)	(4)
Total net fair value, liability	0	(1)
Deferred credits and other liabilities - other | Interest Rate Swaps
Gross and net fair values of outstanding derivatives (in millions)
Netting and collateral, liability	0	0
Total net fair value, liability	(894)	(776)
Deferred credits and other liabilities - other | Warrant
Gross and net fair values of outstanding derivatives (in millions)
Netting and collateral, liability		0
Total net fair value, liability		(107)
Level 1 | Other current assets | Collars and Call Options
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	0	0
Level 1 | Other current assets | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	1,162	945
Level 1 | Other current assets | Interest Rate Swaps
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross		0
Level 1 | Long-term receivables and other assets, net | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	77	4
Level 1 | Long-term receivables and other assets, net | Interest Rate Swaps
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross		0
Level 1 | Accrued liabilities | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	(1,180)	(1,008)
Level 1 | Accrued liabilities | Interest Rate Swaps
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	0	0
Level 1 | Deferred credits and other liabilities - other | Collars and Call Options
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	0	0
Level 1 | Deferred credits and other liabilities - other | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	(77)	(4)
Level 1 | Deferred credits and other liabilities - other | Interest Rate Swaps
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	0	0
Level 1 | Deferred credits and other liabilities - other | Warrant
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross		0
Level 2 | Other current assets | Collars and Call Options
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	269	92
Level 2 | Other current assets | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	37	79
Level 2 | Other current assets | Interest Rate Swaps
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross		5
Level 2 | Long-term receivables and other assets, net | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	2	12
Level 2 | Long-term receivables and other assets, net | Interest Rate Swaps
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross		5
Level 2 | Accrued liabilities | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	(49)	(44)
Level 2 | Accrued liabilities | Interest Rate Swaps
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	(1,011)	(657)
Level 2 | Deferred credits and other liabilities - other | Collars and Call Options
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	(18)	(160)
Level 2 | Deferred credits and other liabilities - other | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	0	(1)
Level 2 | Deferred credits and other liabilities - other | Interest Rate Swaps
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	(894)	(776)
Level 2 | Deferred credits and other liabilities - other | Warrant
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross		(107)
Level 3 | Other current assets | Collars and Call Options
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	0	0
Level 3 | Other current assets | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	0	0
Level 3 | Other current assets | Interest Rate Swaps
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross		0
Level 3 | Long-term receivables and other assets, net | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	0	0
Level 3 | Long-term receivables and other assets, net | Interest Rate Swaps
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross		0
Level 3 | Accrued liabilities | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	0	0
Level 3 | Accrued liabilities | Interest Rate Swaps
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	0	0
Level 3 | Deferred credits and other liabilities - other | Collars and Call Options
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	0	0
Level 3 | Deferred credits and other liabilities - other | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	0	0
Level 3 | Deferred credits and other liabilities - other | Interest Rate Swaps
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	$ 0	0
Level 3 | Deferred credits and other liabilities - other | Warrant
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross		$ 0