Subsequent Events - Available capacity, excluding MPLX (Details) - USD ($) $ in Millions			1 Months Ended	3 Months Ended
		May 05, 2020	Apr. 30, 2020	Mar. 31, 2020
MPC 364-day bank revolving credit facility due September 2020
Subsequent Event [Line Items]
Total Capacity				$ 1,000
Outstanding Borrowings				0
Outstanding Letters of Credit				0
Available Capacity				1,000
MPC bank revolving credit facility
Subsequent Event [Line Items]
Total Capacity				5,000
Outstanding Borrowings	[1]			2,000
Outstanding Letters of Credit				1
Available Capacity				2,999
Borrowings				2,000
MPC trade receivables securitization facility
Subsequent Event [Line Items]
Total Capacity				750
Outstanding Borrowings	[2],[3]			0
Outstanding Letters of Credit				0
Available Capacity				750
Borrowings				925
Repayments				$ 925
Subsequent Event
Subsequent Event [Line Items]
Available Capacity		$ 6,766
Subsequent Event | MPC 364-day bank revolving credit facility due September 2020
Subsequent Event [Line Items]
Total Capacity		1,000
Outstanding Borrowings		0
Outstanding Letters of Credit		0
Available Capacity		1,000
Subsequent Event | MPC 364-day bank revolving credit facility
Subsequent Event [Line Items]
Total Capacity		1,000
Outstanding Borrowings		0
Outstanding Letters of Credit		0
Available Capacity		1,000
Subsequent Event | MPC bank revolving credit facility
Subsequent Event [Line Items]
Total Capacity		5,000
Outstanding Borrowings	[4]	750
Outstanding Letters of Credit		1
Available Capacity		4,249
Borrowings			$ 1,500
Repayments		2,750
Subsequent Event | MPC trade receivables securitization facility
Subsequent Event [Line Items]
Total Capacity		517
Outstanding Borrowings		0
Outstanding Letters of Credit		0
Available Capacity		517
Maximum borrowing capacity		$ 750

[1] Borrowed $2 billion on March 30, 2020.

[2] Borrowed $925 million and repaid $925 million during the three months ended March 31, 2020.

[3] Availability under our $750 million trade receivables facility is a function of eligible trade receivables, which will be lower in a sustained lower price environment for refined products. As of April 30, 2020 eligible trade receivables supported borrowings of approximately $517 million

[4] Borrowed $2 billion on March 30, 2020 and $1.5 billion in April. Repaid $2.75 billion in May.