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Debt (MPLX Senior Notes) (Details) - USD ($) $ in Millions			3 Months Ended
Debt (MPLX Senior Notes) (Details) - USD ($) $ in Millions	Mar. 13, 2023	Feb. 15, 2023	Mar. 31, 2023	Mar. 31, 2022	Feb. 09, 2023
Debt Instrument [Line Items]
Redemption of noncontrolling interests - preferred units			$ 600	$ 0
Loss on extinguishment of debt			9	$ 0
MPLX \| Series B Preferred Stock
Debt Instrument [Line Items]
Redemption of noncontrolling interests - preferred units		$ 600
MPLX LP: \| MPLX \| Series B Preferred Stock
Debt Instrument [Line Items]
Redemption of noncontrolling interests - preferred units		$ 600
Senior notes \| MPLX LP:
Debt Instrument [Line Items]
Debt instrument, face amount					$ 1,600
Senior notes \| 5.000% senior notes due March 2033 \| MPLX LP:
Debt Instrument [Line Items]
Debt instrument, face amount					1,100
Senior notes \| 5.650% senior notes due March 2053 \| MPLX LP:
Debt Instrument [Line Items]
Debt instrument, face amount					$ 500
Senior notes \| 4.500% senior notes due July 2023
Debt Instrument [Line Items]
Loss on extinguishment of debt			$ 9
Senior notes \| 4.500% senior notes due July 2023 \| MPLX LP:
Debt Instrument [Line Items]
Repayments of debt	$ 1,000