Segment Information (Reconciliation Of Segment Income From Operations To Income Before Income Taxes) (Detail) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Income from operations		$ 2,017	$ 1,403	$ 1,711	$ 440	$ 1,168	$ 1,577	$ 982	$ 291	$ 5,571	$ 4,018		$ 2,386
Net interest and other financial costs										1,003	674		564
Income before income taxes										4,568	3,344		1,822
Operating Segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Income from operations										6,261	4,389		3,138
Corporate and Other
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Income from operations										(502)	(365)	[1]	(266)
Segment Reconciling Items
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Transaction-related costs										(197)	0		0
Litigation										0	(29)		0
Impairment	[2]									$ 9	$ 23		$ (486)

[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 and ANDX, which are included in the Midstream segment. Corporate overhead expenses are not allocated to the Refining & Marketing and Retail segments.

[2] 2017 includes MPC’s share of gains from the the sale of assets remaining from the canceled Sandpiper pipeline project. 2016 includes impairments of goodwill and equity method investments. See Note 17.