Segment Information (Reconciliation Of Segment Income From Operations To Income Before Income Taxes) (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Income from operations		$ 841	$ 2,024	$ 2,042	$ 669	$ 2,017	$ 1,403	$ 1,711	$ 440	$ 5,576		$ 5,571		$ 4,018
Net interest and other financial costs										1,247		1,003		674
Income before income taxes										4,329		4,568		3,344
Operating Segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Income from operations										7,543		6,261		4,389
Corporate and Other
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Income from operations	[1]									(805)		(502)		(365)
Segment Reconciling Items
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Equity method investment restructuring gains										259	[2]	0		0
Transaction-related costs										(160)	[3]	(197)	[3]	0
Litigation										(22)		0		(29)
Impairment	[4]									$ (1,239)		$ 9		$ 23

[1] Corporate and other unallocated items consists primarily of MPC’s corporate administrative expenses and costs related to certain non-operating assets, except for corporate overhead expenses attributable to MPLX, which are included in the Midstream segment. Corporate overhead expenses are not allocated to the Refining & Marketing and Retail segments.

[2] Includes gains related to The Andersons Marathon Holdings LLC and Capline Pipeline Company LLC. See Note 14.

[3] 2019 includes costs incurred in connection with the proposed Speedway separation, Midstream strategic review and other related efforts. Both 2019 and 2018 include employee severance, retention and other costs related to the acquisition of Andeavor. Effective October 1, 2019, we have discontinued reporting Andeavor transaction-related costs as one year has passed since the Andeavor acquisition. The post October 1, 2019 transaction costs are immaterial and reported in corporate and other unallocated items.

[4] 2018 and 2017 includes MPC’s share of gains from the sale of assets remaining from the Sandpiper pipeline project, which was cancelled and impaired in 2016.