Debt (MPLX Senior Notes) (Details) - MPLX LP: - Senior notes - USD ($) $ in Millions	2 Months Ended	5 Months Ended
	Dec. 01, 2024	Feb. 15, 2025	May 20, 2024
Senior notes, 5.50% due June 2034
Debt Instrument [Line Items]
Debt instrument, face amount			$ 1,650
Senior notes, 4.875% due December 2024 | Forecast
Debt Instrument [Line Items]
Repayments of debt	$ 1,149
Senior notes, 4.875% due December 2024 | Forecast | MarkWest
Debt Instrument [Line Items]
Repayments of debt	$ 1
Senior notes, 4.000% due February 2025 | Forecast
Debt Instrument [Line Items]
Repayments of debt		$ 500