Debt (MPLX Senior Notes) (Details) - USD ($) $ in Millions		2 Months Ended	3 Months Ended	12 Months Ended
	Feb. 15, 2023	Mar. 31, 2023	Sep. 30, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Feb. 09, 2023	Aug. 11, 2022	Mar. 14, 2022
Debt Instrument [Line Items]
Redemption of preferred units				$ 600	$ 0	$ 0
Loss on extinguishment of debt				9	2	$ 133
MPLX | Series B Preferred Stock
Debt Instrument [Line Items]
Redemption of preferred units	$ 600
Senior Notes | Senior notes, 4.500% due July 2023
Debt Instrument [Line Items]
Loss on extinguishment of debt				9
MPLX | MPLX | Series B Preferred Stock
Debt Instrument [Line Items]
Redemption of preferred units	$ 600
MPLX | Senior Notes
Debt Instrument [Line Items]
Long-term debt outstanding				20,700	20,100
Debt instrument, face amount							$ 1,600
MPLX | Senior Notes | Senior notes, 4.500% due July 2023
Debt Instrument [Line Items]
Long-term debt outstanding				0	989
Repayments of debt		$ 1,000
MPLX | Senior Notes | Senior notes, 4.875% due December 2024
Debt Instrument [Line Items]
Long-term debt outstanding				1,149	1,149
MPLX | Senior Notes | Senior notes, 4.000% due February 2025
Debt Instrument [Line Items]
Long-term debt outstanding				500	500
MPLX | Senior Notes | Senior notes, 4.875% due June 2025
Debt Instrument [Line Items]
Long-term debt outstanding				1,189	1,189
MPLX | Senior Notes | Senior notes, 1.750% due March 2026
Debt Instrument [Line Items]
Long-term debt outstanding				1,500	1,500
MPLX | Senior Notes | Senior notes, 4.125% due March 2027
Debt Instrument [Line Items]
Long-term debt outstanding				1,250	1,250
MPLX | Senior Notes | Senior notes, 4.250% due December 2027
Debt Instrument [Line Items]
Long-term debt outstanding				732	732
MPLX | Senior Notes | Senior notes, 4.000% due March 2028
Debt Instrument [Line Items]
Long-term debt outstanding				1,250	1,250
MPLX | Senior Notes | Senior notes, 4.800% due February 2029
Debt Instrument [Line Items]
Long-term debt outstanding				750	750
MPLX | Senior Notes | Senior notes, 2.650% due August 2030
Debt Instrument [Line Items]
Long-term debt outstanding				1,500	1,500
MPLX | Senior Notes | Senior notes, 4.950% due September 2032
Debt Instrument [Line Items]
Long-term debt outstanding				1,000	1,000
Debt instrument, face amount								$ 1,000
MPLX | Senior Notes | Senior notes, 5.000% due March 2033
Debt Instrument [Line Items]
Long-term debt outstanding				1,100	0
Debt instrument, face amount							1,100
MPLX | Senior Notes | Senior notes, 4.500% due April 2038
Debt Instrument [Line Items]
Long-term debt outstanding				1,750	1,750
MPLX | Senior Notes | Senior notes, 5.200% due March 2047
Debt Instrument [Line Items]
Long-term debt outstanding				1,000	1,000
MPLX | Senior Notes | Senior notes, 5.200% due December 2047
Debt Instrument [Line Items]
Long-term debt outstanding				487	487
MPLX | Senior Notes | Senior notes, 4.700% due April 2048
Debt Instrument [Line Items]
Long-term debt outstanding				1,500	1,500
MPLX | Senior Notes | Senior notes, 5.500% due February 2049
Debt Instrument [Line Items]
Long-term debt outstanding				1,500	1,500
MPLX | Senior Notes | Senior notes, 4.950% due March 2052
Debt Instrument [Line Items]
Long-term debt outstanding				1,500	1,500
Debt instrument, face amount									$ 1,500
MPLX | Senior Notes | Senior notes, 5.65% due March 2053
Debt Instrument [Line Items]
Long-term debt outstanding				500	0
Debt instrument, face amount							$ 500
MPLX | Senior Notes | Senior notes, 4.900% due April 2058
Debt Instrument [Line Items]
Long-term debt outstanding				500	500
MPLX | Senior Notes | Senior notes, 3.500% due December 2022
Debt Instrument [Line Items]
Repayments of debt			$ 500
MPLX | Senior Notes | Senior notes, 3.500% due December 2022 | ANDX
Debt Instrument [Line Items]
Repayments of debt			14
MPLX | Senior Notes | Senior notes, 3.375% due March 2023
Debt Instrument [Line Items]
Repayments of debt			$ 500
MPLX | Senior Notes | MarkWest | MarkWest senior notes, 4.500% - 4.875% due 2023 - 2025
Debt Instrument [Line Items]
Long-term debt outstanding				12	23
MPLX | Senior Notes | ANDX | ANDX senior notes, 4.250% - 5.200% due 2027 - 2047
Debt Instrument [Line Items]
Long-term debt outstanding				$ 31	$ 31