Fair Value Measurements - Narrative (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021 USD ($) bblPerDay	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) bblPerDay $ / bbl	Sep. 30, 2020 USD ($) $ / bbl	May 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Purchase contract, amount of barrel to be purchased and sold | bblPerDay	50,000		50,000
Long-term purchase commitment, period			6 years
South Texas deficiency fee obligation	$ 0	$ 0	$ 0	$ 69
South Texas divestiture
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
South Texas deficiency fee obligation				$ 69
Marketing derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative, fair value input, WASP differential deduction | $ / bbl			2.07	1.97
Annual discount rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration, cash payment, measurement input					0.036
Contingent consideration, cash receipt, measurement input					0.032