Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

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Debt (MPLX Senior Notes) (Details) - USD ($) $ in Millions			12 Months Ended
Debt (MPLX Senior Notes) (Details) - USD ($) $ in Millions	Dec. 10, 2018	Feb. 08, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Nov. 15, 2018
Debt Instrument [Line Items]
Loss on extinguishment of debt			$ 64	$ 0	$ 0
MPLX senior notes, 5.500% due February 2023
Debt Instrument [Line Items]
Redemption price, percentage	101.833%
Loss on extinguishment of debt			$ 60
MPLX \| MPLX 364-day term loan
Debt Instrument [Line Items]
Repayments of short-term debt		$ 4,100
MPLX \| Senior Notes
Debt Instrument [Line Items]
Long-term debt outstanding		5,500				$ 2,250
MPLX \| Senior Notes \| MPLX senior notes, 4.800% due February 2029
Debt Instrument [Line Items]
Long-term debt outstanding						$ 750
Debt instrument, interest rate						4.80%
MPLX \| Senior Notes \| MPLX senior notes, 5.500% due February 2049
Debt Instrument [Line Items]
Long-term debt outstanding						$ 1,500
Debt instrument, interest rate						5.50%
MPLX \| Senior Notes \| MPLX senior notes, 5.500% due February 2023
Debt Instrument [Line Items]
Debt instrument, interest rate	5.50%
Repayments of long-term debt	$ 750
MPLX \| Senior Notes \| MPLX senior notes, 3.375% due March 2023
Debt Instrument [Line Items]
Long-term debt outstanding		$ 500
Debt instrument, interest rate		3.375%
MPLX \| Senior Notes \| MPLX senior notes, 4.000% due March 2028
Debt Instrument [Line Items]
Long-term debt outstanding		$ 1,250
Debt instrument, interest rate		4.00%
MPLX \| Senior Notes \| MPLX senior notes, 4.500% due April 2038
Debt Instrument [Line Items]
Long-term debt outstanding		$ 1,750
Debt instrument, interest rate		4.50%
MPLX \| Senior Notes \| MPLX senior notes, 4.700% due April 2048
Debt Instrument [Line Items]
Long-term debt outstanding		$ 1,500
Debt instrument, interest rate		4.70%
MPLX \| Senior Notes \| MPLX senior notes, 4.900% due April 2058
Debt Instrument [Line Items]
Long-term debt outstanding		$ 500
Debt instrument, interest rate		4.90%