Debt (MPLX Bank Revolving Credit Facility) (Details) - MPLX - MPLX revolving credit facility due July 2027 $ in Millions	Jul. 07, 2022 USD ($) Period	Dec. 31, 2024 USD ($)
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 2,000
Total capacity		$ 2,000
Number of renewal periods | Period	2
Debt instrument, description of variable rate basis	at MPLX’s election, at either the Adjusted Term SOFR or the Alternate Base Rate, both as defined in the MPLX Credit Agreement, plus an applicable margin
Maximum
Debt Instrument [Line Items]
Line of credit facility additional borrowing capacity	$ 1,000
Number of prior quarterly reporting periods covenant	4
Covenant ratio debt to EBITDA	5.0
Covenant ratio debt to EBITDA post acquisition	5.5
Letter of Credit | Maximum
Debt Instrument [Line Items]
Total capacity	$ 150