Debt (MPC Senior Notes) (Details) - Marathon Petroleum Corporation: - Senior notes - USD ($) $ in Millions			1 Months Ended
	Nov. 02, 2021	Mar. 01, 2021	Jun. 30, 2021
Senior notes, 5.125% due March 2021
Debt Instrument [Line Items]
Repayments of debt		$ 1,000
Senior notes, 5.125% due April 2024
Debt Instrument [Line Items]
Repayments of debt			$ 300
Senior notes, 4.750% due December 2023 | Subsequent Event
Debt Instrument [Line Items]
Repayments of debt	$ 850
Senior notes, 4.500% due May 2023 | Subsequent Event
Debt Instrument [Line Items]
Repayments of debt	$ 1,250