Supplementary Statistics - Operating Statistics (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2014 BPD		Jun. 30, 2013 BPD		Jun. 30, 2014 BPD		Jun. 30, 2013 BPD
Operating Statistics [Line Items ]
MPC Consolidated Refined Product Sales Volumes (thousands of barrels per day)	2,153,000	[1],[2]	2,135,000	[1],[2]	2,059,000	[1],[2]	2,016,000	[1],[2]
Refining & Marketing
Refining & Marketing Operating Statistics
Refining & Marketing refined product sales volume (thousands of barrels per day)	2,145,000	[2],[3]	2,125,000	[2],[3]	2,048,000	[2],[4]	2,004,000	[2],[4]
Refining & Marketing gross margin (dollars per barrel)	16.02	[2],[5]	13.11	[2],[5]	15.28	[2],[5]	14.14	[2],[5]
Crude oil capacity utilization percent	98.00%	[2],[6]	99.00%	[2],[6]	91.00%	[2],[6]	96.00%	[2],[6]
Refinery throughputs (thousands of barrels per day)	1,832,000	[2],[7]	1,864,000	[2],[7]	1,741,000	[2],[7]	1,768,000	[2],[7]
Sour crude oil throughput percent	54.00%	[2]	52.00%	[2]	52.00%	[2]	53.00%	[2]
WTI-priced crude oil throughput percent	17.00%	[2]	22.00%	[2]	19.00%	[2]	22.00%	[2]
Refined product yields (thousands of barrels per day)	1,865,000	[2],[7]	1,897,000	[2],[7]	1,772,000	[2],[7]	1,801,000	[2],[7]
Inter-refinery transfers	43,000		37,000		51,000		33,000
Refinery direct operating costs (dollars per barrel):
Planned turnaround and major maintenance	0.94	[2],[8]	0.73	[2],[8]	1.98	[2],[8]	0.93	[2],[8]
Depreciation and amortization	1.39	[2],[8]	1.28	[2],[8]	1.47	[2],[8]	1.35	[2],[8]
Other manufacturing	4.77	[2],[8],[9]	4.06	[2],[8],[9]	5.32	[2],[8],[9]	3.94	[2],[8],[9]
Total	7.10	[2],[8]	6.07	[2],[8]	8.77		6.22
Refining & Marketing | Crude oil refined
Refining & Marketing Operating Statistics
Refinery throughputs (thousands of barrels per day)	1,674,000	[2],[7]	1,690,000	[2],[7]	1,563,000	[2],[7]	1,562,000	[2],[7]
Refining & Marketing | Other charge and blendstocks
Refining & Marketing Operating Statistics
Refinery throughputs (thousands of barrels per day)	158,000	[2],[7]	174,000	[2],[7]	178,000	[2],[7]	206,000	[2],[7]
Refining & Marketing | Gasoline
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	852,000	[2],[7]	923,000	[2],[7]	844,000	[2],[7]	906,000	[2],[7]
Refining & Marketing | Distillates
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	610,000	[2],[7]	609,000	[2],[7]	562,000	[2],[7]	566,000	[2],[7]
Refining & Marketing | Propane
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	37,000	[2],[7]	40,000	[2],[7]	36,000	[2],[7]	36,000	[2],[7]
Refining & Marketing | Feedstocks and special products
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	288,000	[2],[7]	240,000	[2],[7]	255,000	[2],[7]	212,000	[2],[7]
Refining & Marketing | Heavy fuel oil
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	27,000	[2],[7]	31,000	[2],[7]	28,000	[2],[7]	31,000	[2],[7]
Refining & Marketing | Asphalt
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	51,000	[2],[7]	54,000	[2],[7]	47,000	[2],[7]	50,000	[2],[7]
Refining & Marketing | Gulf Coast:
Refining & Marketing Operating Statistics
Refinery throughputs (thousands of barrels per day)	1,187,000	[10],[2]	1,194,000	[10],[2]	1,129,000	[10],[2]	1,122,000	[10],[2]
Sour crude oil throughput percent	67.00%	[2]	64.00%	[2]	64.00%	[2]	66.00%	[2]
WTI-priced crude oil throughput percent	2.00%	[2]	11.00%	[2]	3.00%	[2]	9.00%	[2]
Refined product yields (thousands of barrels per day)	1,214,000	[10],[2]	1,221,000	[10],[2]	1,155,000	[10],[2]	1,148,000	[10],[2]
Refinery direct operating costs (dollars per barrel):
Planned turnaround and major maintenance	0.57	[2],[8]	0.60	[2],[8]	2.11	[2],[8]	0.72	[2],[8]
Depreciation and amortization	1.13	[2],[8]	1.00	[2],[8]	1.19	[2],[8]	1.06	[2],[8]
Other manufacturing	4.77	[2],[8],[9]	4.01	[2],[8],[9]	5.28	[2],[8],[9]	3.68	[2],[8],[9]
Total	6.47	[2],[8]	5.61	[2],[8]	8.58		5.46
Refining & Marketing | Gulf Coast: | Crude oil refined
Refining & Marketing Operating Statistics
Refinery throughputs (thousands of barrels per day)	1,031,000	[10],[2]	1,037,000	[10],[2]	946,000	[10],[2]	938,000	[10],[2]
Refining & Marketing | Gulf Coast: | Other charge and blendstocks
Refining & Marketing Operating Statistics
Refinery throughputs (thousands of barrels per day)	156,000	[10],[2]	157,000	[10],[2]	183,000	[10],[2]	184,000	[10],[2]
Refining & Marketing | Gulf Coast: | Gasoline
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	500,000	[10],[2]	542,000	[10],[2]	494,000	[10],[2]	536,000	[10],[2]
Refining & Marketing | Gulf Coast: | Distillates
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	390,000	[10],[2]	398,000	[10],[2]	355,000	[10],[2]	360,000	[10],[2]
Refining & Marketing | Gulf Coast: | Propane
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	25,000	[10],[2]	25,000	[10],[2]	23,000	[10],[2]	22,000	[10],[2]
Refining & Marketing | Gulf Coast: | Feedstocks and special products
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	270,000	[10],[2]	223,000	[10],[2]	258,000	[10],[2]	201,000	[10],[2]
Refining & Marketing | Gulf Coast: | Heavy fuel oil
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	16,000	[10],[2]	20,000	[10],[2]	15,000	[10],[2]	19,000	[10],[2]
Refining & Marketing | Gulf Coast: | Asphalt
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	13,000	[10],[2]	13,000	[10],[2]	10,000	[10],[2]	10,000	[10],[2]
Refining & Marketing | Midwest:
Refining & Marketing Operating Statistics
Refinery throughputs (thousands of barrels per day)	688,000	[10]	707,000	[10]	663,000	[10]	679,000	[10]
Sour crude oil throughput percent	34.00%		34.00%		34.00%		35.00%
WTI-priced crude oil throughput percent	40.00%		40.00%		43.00%		42.00%
Refined product yields (thousands of barrels per day)	694,000	[10]	713,000	[10]	668,000	[10]	686,000	[10]
Refinery direct operating costs (dollars per barrel):
Planned turnaround and major maintenance	1.53	[8]	0.90	[8]	1.62	[2],[8]	1.22	[2],[8]
Depreciation and amortization	1.75	[8]	1.68	[8]	1.83	[8]	1.75	[8]
Other manufacturing	4.47	[8],[9]	3.96	[8],[9]	4.97	[2],[8],[9]	4.20	[2],[8],[9]
Total	7.75	[8]	6.54	[8]	8.42		7.17
Refining & Marketing | Midwest: | Crude oil refined
Refining & Marketing Operating Statistics
Refinery throughputs (thousands of barrels per day)	643,000	[10]	653,000	[10]	617,000	[10]	624,000	[10]
Refining & Marketing | Midwest: | Other charge and blendstocks
Refining & Marketing Operating Statistics
Refinery throughputs (thousands of barrels per day)	45,000	[10]	54,000	[10]	46,000	[10]	55,000	[10]
Refining & Marketing | Midwest: | Gasoline
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	352,000	[10]	383,000	[10]	350,000	[10]	371,000	[10]
Refining & Marketing | Midwest: | Distillates
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	220,000	[10]	211,000	[10]	207,000	[10]	206,000	[10]
Refining & Marketing | Midwest: | Propane
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	13,000	[10]	15,000	[10]	14,000	[10]	14,000	[10]
Refining & Marketing | Midwest: | Feedstocks and special products
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	60,000	[10]	52,000	[10]	47,000	[10]	43,000	[10]
Refining & Marketing | Midwest: | Heavy fuel oil
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	11,000	[10]	11,000	[10]	13,000	[10]	12,000	[10]
Refining & Marketing | Midwest: | Asphalt
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	38,000	[10]	41,000	[10]	37,000	[10]	40,000	[10]
Speedway
Speedway Operating Statistics
Convenience stores at period-end	1,492		1,468		1,492		1,468
Gasoline and distillate sales (millions of gallons)	806,000,000		781,000,000		1,579,000,000		1,526,000,000
Gasoline and distillate gross margin (dollars per gallon)	0.1282	[11]	0.1738	[11]	0.1220	[11]	0.1525	[11]
Merchandise sales (in millions)	$ 830		$ 806		$ 1,552		$ 1,517
Merchandise gross margin (in millions)	$ 224		$ 212		$ 416		$ 396
Merchandise margin percent	27.10%		26.30%		26.80%		26.10%
Same store gasoline sales volume (period over period) percentage	(1.50%)		0.00%		(1.10%)		0.30%
Merchandise sales excluding cigarettes (period over period) percentage	4.60%	[12]	4.50%	[12]	4.90%	[12]	2.80%	[12]
Pipeline Transportation
Pipeline Transportation Operating Statistics
Pipeline throughputs (thousands of barrels per day)	2,152,000	[13]	2,293,000	[13]	2,058,000	[13]	2,242,000	[13]
Pipeline Transportation | Crude oil pipelines
Pipeline Transportation Operating Statistics
Pipeline throughputs (thousands of barrels per day)	1,281,000	[13]	1,334,000	[13]	1,213,000	[13]	1,303,000	[13]
Pipeline Transportation | Refined products pipelines
Pipeline Transportation Operating Statistics
Pipeline throughputs (thousands of barrels per day)	871,000	[13]	959,000	[13]	845,000	[13]	939,000	[13]

[1] Total average daily volumes of refined product sales to wholesale, branded and retail (Speedway segment) customers.

[2] Includes the impact of the Galveston Bay Refinery and Related Assets beginning on the February 1, 2013 acquisition date.

[3] Includes intersegment sales.

[4] The six months ended June 30, 2013 includes the acquisition of the Galveston Bay Refinery and Related Assets, comprised of total consideration, excluding inventory and other current assets, plus assumed liabilities. Total consideration includes the base purchase price and a fair-value estimate of $600 million for the contingent consideration. See Note 4 to the unaudited consolidated financial statements.

[5] Sales revenue less cost of refinery inputs and purchased products, divided by total refinery throughputs.

[6] Based on calendar day capacity, which is an annual average that includes downtime for planned maintenance and other normal operating activities.

[7] Excludes inter-refinery volumes of 43 mbpd and 37 mbpd for the three months ended June 30, 2014 and 2013, respectively, and 51 mbpd and 33 mbpd for the six months ended June 30, 2014 and 2013, respectively.

[8] Per barrel of total refinery throughputs.

[9] Includes utilities, labor, routine maintenance and other operating costs.

[10] Includes inter-refinery transfer volumes.

[11] The price paid by consumers less the cost of refined products, including transportation, consumer excise taxes and bankcard processing fees, divided by gasoline and distillate sales volume.

[12] Excludes cigarettes.

[13] On owned common-carrier pipelines, excluding equity method investments.