Derivatives - Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Collateral related to marketing derivatives	$ 202	$ 85
Interest Rate Swaps
Gross and net fair values of outstanding derivatives (in millions)
Collateral paid netted against derivative liabilities	282	374
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	8	25
Other current assets | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Netting, asset	(1,732)	(1,204)
Total net fair value, asset	53	31
Long-term receivables and other assets, net | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Netting, asset	(38)	(7)
Total net fair value, asset	2	2
Accrued liabilities | Collars and Call Options
Gross and net fair values of outstanding derivatives (in millions)
Netting and collateral, liability		0
Total net fair value, liability		(42)
Accrued liabilities | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Netting and collateral, liability	1,732	1,204
Total net fair value, liability	(223)	(129)
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	(708)	(936)
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
Total net fair value, liability	(98)
Deferred credits and other liabilities - other | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Netting and collateral, liability	38	7
Total net fair value, liability	0	0
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	(604)	(822)
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	1,649	1,155
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	38	7
Level 1 | Accrued liabilities | Collars and Call Options
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross		0
Level 1 | Accrued liabilities | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	(1,861)	(1,252)
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
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	(38)	(7)
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 2 | Other current assets | Collars and Call Options
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	8	25
Level 2 | Other current assets | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative asset, gross	136	80
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	2
Level 2 | Accrued liabilities | Collars and Call Options
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross		(42)
Level 2 | Accrued liabilities | Marketing Derivatives
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	(94)	(81)
Level 2 | Accrued liabilities | Interest Rate Swaps
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, gross	(708)	(936)
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	(98)
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	0
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	(604)	(822)
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 | 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 | Accrued liabilities | Collars and Call Options
Gross and net fair values of outstanding derivatives (in millions)
Commodity contract derivative liability, 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
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