Revenue Disaggregation of Revenue (Details) - USD ($) $ in Millions		3 Months Ended											12 Months Ended
		Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	[1]	Mar. 31, 2019	[1]	Dec. 31, 2018	[1]	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													$ 7,041	$ 5,449
Other Operating Income													(5)	(3)	$ (24)
Total revenues and other income		$ 2,316	$ 2,280	$ 2,210		$ 2,235		$ 2,295		$ 1,712	$ 1,578	$ 1,420	9,041	7,005	3,867
Other income													12	7	6
Service [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													2,498	1,856	1,156
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties													3,455	2,404	1,082
Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													140	220	0
Product [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													806	887	889
Revenue from Contract with Customer, excluding Assessed Tax and Non-ASC 606 Revenue													806	882
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties	[2]												142	87	$ 8
Logistics and Storage [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													3,856	2,598
Logistics and Storage [Member] | Service [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													346	174
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties													3,419	2,401
Logistics and Storage [Member] | Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													0	0
Logistics and Storage [Member] | Product [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, excluding Assessed Tax and Non-ASC 606 Revenue													65	12
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties													26	11
Gathering and Processing [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													3,185	2,851
Gathering and Processing [Member] | Service [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													2,152	1,682
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties													36	3
Gathering and Processing [Member] | Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													140	220
Gathering and Processing [Member] | Product [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, excluding Assessed Tax and Non-ASC 606 Revenue													741	870
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties													116	76
Other Income [Member]
Disaggregation of Revenue [Line Items]
Other Operating Income													0	5
Other income	[3]												$ 2,000	$ 1,556

[1] As discussed in Note 1, MPLX’s acquisition of ANDX is considered a transfer between entities under common control due to MPC’s prior relationship with ANDX. Transfers of businesses between entities under common control require prior periods to be retrospectively adjusted for those dates that the entity was under common control. Accordingly, the tables above include the historical results of ANDX beginning October 1, 2018. Amounts shown for the fourth quarter of 2018 as well as the first and second quarters of 2019 are different than amounts previously reported for Total revenues and other income, Income from operations and Net income as a results of this retrospective adjustment for ANDX. Total revenues and other income originally reported for the fourth quarter of 2018 and the first and second quarters of 2019 was $1,715 million, $1,646 million and $1,629 million, respectively. Income from operations originally reported for the fourth quarter of 2018 and the first and second quarters of 2019 was $666 million, $678 million and $659 million, respectively. Net income originally reported for the fourth quarter of 2018 and the first and second quarters of 2019 was $439 million, $509 million and $488 million, respectively.

[2] There were additional product sales to MPC that net to zero within the consolidated financial statements as the transactions are recorded net due to the terms of the agreements under which such product was sold. For 2019, 2018 and 2017, these sales totaled $1,120 million, $607 million and $254 million, respectively.

[3] Non-ASC 606 Revenue includes rental income, income from equity method investments, derivative gains and losses, mark-to-market adjustments, and other income.