Derivatives - Fair Value (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Marketing Derivatives
Derivatives, Fair Value [Line Items]
Collateral related to marketing derivatives	$ 78	$ 85
Interest Rate Swaps
Derivatives, Fair Value [Line Items]
Collateral paid netted against derivative liabilities	326	374
Accrued liabilities | Collars and Call Options
Derivatives, Fair Value [Line Items]
Netting and collateral, liability	0	0
Total net fair value, liability	(249)	(42)
Accrued liabilities | Marketing Derivatives
Derivatives, Fair Value [Line Items]
Netting and collateral, liability	1,679	1,204
Total net fair value, liability	(130)	(129)
Accrued liabilities | Interest Rate Swaps
Derivatives, Fair Value [Line Items]
Netting and collateral, liability	0	0
Total net fair value, liability	(823)	(936)
Other current assets | Collars and Call Options
Derivatives, Fair Value [Line Items]
Netting, asset		0
Total net fair value, asset		25
Other current assets | Marketing Derivatives
Derivatives, Fair Value [Line Items]
Netting, asset	(1,679)	(1,204)
Total net fair value, asset	17	31
Long-term receivables and other assets, net | Marketing Derivatives
Derivatives, Fair Value [Line Items]
Netting, asset	(100)	(7)
Total net fair value, asset	2	2
Deferred credits and other liabilities - other | Marketing Derivatives
Derivatives, Fair Value [Line Items]
Netting and collateral, liability	100	7
Total net fair value, liability	(1)	0
Deferred credits and other liabilities - other | Interest Rate Swaps
Derivatives, Fair Value [Line Items]
Netting and collateral, liability	0	0
Total net fair value, liability	(710)	(822)
Level 1 | Accrued liabilities | Collars and Call Options
Derivatives, Fair Value [Line Items]
Commodity contract derivative liability, gross	0	0
Level 1 | Accrued liabilities | Marketing Derivatives
Derivatives, Fair Value [Line Items]
Commodity contract derivative liability, gross	(1,696)	(1,252)
Level 1 | Accrued liabilities | Interest Rate Swaps
Derivatives, Fair Value [Line Items]
Commodity contract derivative liability, gross	0	0
Level 1 | Other current assets | Collars and Call Options
Derivatives, Fair Value [Line Items]
Commodity contract derivative asset, gross		0
Level 1 | Other current assets | Marketing Derivatives
Derivatives, Fair Value [Line Items]
Commodity contract derivative asset, gross	1,584	1,155
Level 1 | Long-term receivables and other assets, net | Marketing Derivatives
Derivatives, Fair Value [Line Items]
Commodity contract derivative asset, gross	100	7
Level 1 | Deferred credits and other liabilities - other | Marketing Derivatives
Derivatives, Fair Value [Line Items]
Commodity contract derivative liability, gross	(101)	(7)
Level 1 | Deferred credits and other liabilities - other | Interest Rate Swaps
Derivatives, Fair Value [Line Items]
Commodity contract derivative liability, gross	0	0
Level 2 | Accrued liabilities | Collars and Call Options
Derivatives, Fair Value [Line Items]
Commodity contract derivative liability, gross	(249)	(42)
Level 2 | Accrued liabilities | Marketing Derivatives
Derivatives, Fair Value [Line Items]
Commodity contract derivative liability, gross	(113)	(81)
Level 2 | Accrued liabilities | Interest Rate Swaps
Derivatives, Fair Value [Line Items]
Commodity contract derivative liability, gross	(823)	(936)
Level 2 | Other current assets | Collars and Call Options
Derivatives, Fair Value [Line Items]
Commodity contract derivative asset, gross		25
Level 2 | Other current assets | Marketing Derivatives
Derivatives, Fair Value [Line Items]
Commodity contract derivative asset, gross	112	80
Level 2 | Long-term receivables and other assets, net | Marketing Derivatives
Derivatives, Fair Value [Line Items]
Commodity contract derivative asset, gross	2	2
Level 2 | Deferred credits and other liabilities - other | Marketing Derivatives
Derivatives, Fair Value [Line Items]
Commodity contract derivative liability, gross	0	0
Level 2 | Deferred credits and other liabilities - other | Interest Rate Swaps
Derivatives, Fair Value [Line Items]
Commodity contract derivative liability, gross	(710)	(822)
Level 3 | Accrued liabilities | Collars and Call Options
Derivatives, Fair Value [Line Items]
Commodity contract derivative liability, gross	0	0
Level 3 | Accrued liabilities | Marketing Derivatives
Derivatives, Fair Value [Line Items]
Commodity contract derivative liability, gross	0	0
Level 3 | Accrued liabilities | Interest Rate Swaps
Derivatives, Fair Value [Line Items]
Commodity contract derivative liability, gross	0	0
Level 3 | Other current assets | Collars and Call Options
Derivatives, Fair Value [Line Items]
Commodity contract derivative asset, gross		0
Level 3 | Other current assets | Marketing Derivatives
Derivatives, Fair Value [Line Items]
Commodity contract derivative asset, gross	0	0
Level 3 | Long-term receivables and other assets, net | Marketing Derivatives
Derivatives, Fair Value [Line Items]
Commodity contract derivative asset, gross	0	0
Level 3 | Deferred credits and other liabilities - other | Marketing Derivatives
Derivatives, Fair Value [Line Items]
Commodity contract derivative liability, gross	0	0
Level 3 | Deferred credits and other liabilities - other | Interest Rate Swaps
Derivatives, Fair Value [Line Items]
Commodity contract derivative liability, gross	$ 0	$ 0