Marathon Petroleum (MPC) 10-Q 4 May 15 2015 Q1 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	3 Months Ended
	Mar. 31, 2015	Apr. 30, 2015
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	FALSE
Document Period End Date	31-Mar-15
Document Fiscal Year Focus	2015
Document Fiscal Period Focus (Q1,Q2,Q3,FY)	Q1
Trading Symbol	MPC
Entity Registrant Name	Marathon Petroleum Corp
Entity Central Index Key	1510295
Current Fiscal Year End Date	-19
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		271,637,136

Consolidated_Statements_of_Inc

Consolidated Statements of Income (USD $)	3 Months Ended
In Millions, except Per Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Revenues and other income:
Sales and other operating revenues (including consumer excise taxes)	$17,191	$23,285
Income from equity method investments	15	35
Net gain on disposal of assets	5	1
Other income	29	24
Total revenues and other income	17,240	23,345
Costs and expenses:
Cost of revenues (excludes items below)	13,044	20,540
Purchases from related parties	76	159
Consumer excise taxes	1,832	1,515
Depreciation and amortization	363	320
Selling, general and administrative expenses	358	346
Other taxes	97	104
Total costs and expenses	15,770	22,984
Income from operations	1,470	361
Net interest and other financial income (costs)	-81	-46
Income before income taxes	1,389	315
Provision for income taxes	486	108
Net income	903	207
Less net income attributable to noncontrolling interests	12	8
Net income attributable to MPC	$891	$199
Basic:
Net income attributable to MPC per share	$3.26	$0.68
Weighted average shares outstanding (in shares)	273	293
Diluted:
Net income attributable to MPC per share	$3.24	$0.67
Weighted average shares outstanding (in shares)	275	295
Dividends paid (in USD per share)	$0.50	$0.42

Consolidated_Statements_of_Com

Consolidated Statements of Comprehensive Income (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Statement of Comprehensive Income [Abstract]
Net income	$903	$207
Defined benefit postretirement and post-employment plans:
Actuarial changes, net of tax of $5 and $4	8	7
Prior service costs, net of tax of ($5) and ($5)	-8	-8
Other comprehensive income (loss)	0	-1
Comprehensive income	903	206
Less comprehensive income attributable to noncontrolling interests	12	8
Comprehensive income attributable to MPC	$891	$198

Consolidated_Statements_of_Com1

Consolidated Statements of Comprehensive Income (Parenthetical) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Statement of Comprehensive Income [Abstract]
Actuarial changes, tax	$5	$4
Prior service costs, tax	($5)	($5)

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Current assets:
Cash and cash equivalents	$2,078	$1,494
Receivables, less allowance for doubtful accounts of $12 and $13	3,364	4,058
Inventories	5,437	5,642
Other current assets	174	145
Total current assets	11,053	11,339
Equity method investments	902	865
Property, plant and equipment, net	16,241	16,261
Goodwill	1,566	1,566
Other noncurrent assets	420	429
Total assets	30,182	30,460
Current liabilities:
Accounts payable	5,387	6,661
Payroll and benefits payable	474	427
Consumer excise taxes payable	455	463
Accrued taxes	933	647
Long-term debt due within one year	776	27
Other current liabilities	321	354
Total current liabilities	8,346	8,579
Long-term debt	5,967	6,610
Deferred income taxes	2,019	2,014
Defined benefit postretirement plan obligations	1,123	1,099
Deferred credits and other liabilities	747	768
Total liabilities	18,202	19,070
Commitments and contingencies (see Note 21)
MPC stockholders’ equity:
Preferred stock, no shares issued and outstanding (par value $0.01 per share, 30 million shares authorized)	0	0
Common stock:
Issued – 364 million and 363 million shares (par value $0.01 per share, 1 billion shares authorized)	4	4
Held in treasury, at cost – 92 million and 89 million shares	-6,512	-6,299
Additional paid-in capital	9,890	9,844
Retained earnings	8,269	7,515
Accumulated other comprehensive loss	-313	-313
Total MPC stockholders’ equity	11,338	10,751
Noncontrolling interests	642	639
Total equity	11,980	11,390
Total liabilities and equity	$30,182	$30,460

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, except Share data, unless otherwise specified
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$12	$13
Preferred stock:
Shares issued	0	0
Shares outstanding	0	0
Par value	$0.01
Shares authorized	30,000,000
Common stock:
Shares issued	364,000,000	363,000,000
Par value	$0.01
Shares authorized	1,000,000,000
Treasury stock	-92,000,000	-89,000,000

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Operating activities:
Net income	$903	$207
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	363	320
Pension and other postretirement benefits, net	26	82
Deferred income taxes	-2	-14
Net gain on disposal of assets	-5	-1
Equity method investments, net	2	6
Changes in the fair value of derivative instruments	-12	-25
Changes in:
Current receivables	691	139
Inventories	205	-1,000
Current accounts payable and accrued liabilities	-939	1,011
All other, net	-42	41
Net cash provided by operating activities	1,190	766
Investing activities:
Additions to property, plant and equipment	-389	-267
Disposal of assets	11	2
Investments – acquisitions, loans and contributions	-42	-123
Investments - redemptions, repayments and return of capital	1	0
All other, net	31	28
Net cash used in investing activities	-388	-360
Financing activities:
Long-term debt – borrowings	528	270
Long-term debt – repayments	-421	-6
Debt issuance costs	-4	0
Issuance of common stock	21	13
Common stock repurchased	-209	-689
Dividends paid	-136	-123
Distributions to noncontrolling interests	-9	-6
All other, net	12	9
Net cash used in financing activities	-218	-532
Net increase (decrease) in cash and cash equivalents	584	-126
Cash and cash equivalents at beginning of period	1,494	2,292
Cash and cash equivalents at end of period	$2,078	$2,166

Consolidated_Statements_of_Equ

Consolidated Statements of Equity (USD $)	Total	Common Stock	Treasury Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interests
In Millions, unless otherwise specified
Beginning balance at Dec. 31, 2013	$11,332	$4	($4,155)	$9,768	$5,507	($204)	$412
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	207				199		8
Dividends declared	-124				-124
Distributions to noncontrolling interests	-6						-6
Other comprehensive income	-1					-1
Shares repurchased	-689		-689	0
Shares returned - stock based compensation			-5
Shares issued - stock based compensation				14
Net shares issued - stock based compensation	9
Stock-based compensation	21			21			0
Other	-9				9
Ending balance at Mar. 31, 2014	10,758	4	-4,849	9,803	5,591	-205	414
Beginning balance at Dec. 31, 2014	11,390	4	-6,299	9,844	7,515	-313	639
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	903				891		12
Dividends declared	-137				-137
Distributions to noncontrolling interests	-9						-9
Other comprehensive income	0
Shares repurchased	-209		-209	0
Shares returned - stock based compensation			-4
Shares issued - stock based compensation				21
Net shares issued - stock based compensation	17
Stock-based compensation	25			25			0
Ending balance at Mar. 31, 2015	$11,980	$4	($6,512)	$9,890	$8,269	($313)	$642

Consolidated_Statement_of_Equi

Consolidated Statement of Equity - Shares	Total	Common Stock	Treasury Stock
Number of shares held in treasury (beginning balance) at Dec. 31, 2013			-65,000,000
Number of common shares issued (beginning balance) at Dec. 31, 2013		362,000,000
Number of shares issued - stock-based compensation		1,000,000
Number of shares repurchased	-8,000,000		-8,000,000
Number of shares held in treasury (ending balance) at Mar. 31, 2014			-73,000,000
Number of common shares issued (ending balance) at Mar. 31, 2014		363,000,000
Number of shares held in treasury (beginning balance) at Dec. 31, 2014	-89,000,000		-89,000,000
Number of common shares issued (beginning balance) at Dec. 31, 2014	363,000,000	363,000,000
Number of shares issued - stock-based compensation		1,000,000
Number of shares repurchased	-2,000,000		-3,000,000
Number of shares held in treasury (ending balance) at Mar. 31, 2015	-92,000,000		-92,000,000
Number of common shares issued (ending balance) at Mar. 31, 2015	364,000,000	364,000,000

Description_of_the_Business_an

Description of the Business and Basis of Presentation	3 Months Ended
	Mar. 31, 2015
Accounting Policies [Abstract]
Description of the Business and Basis of Presentation	Description of the Business and Basis of Presentation
	Description of the Business—Our business consists of refining and marketing, retail marketing and pipeline transportation operations conducted primarily in the Midwest, Gulf Coast, East Coast and Southeast regions of the United States, through subsidiaries, including Marathon Petroleum Company LP, Speedway LLC and its subsidiaries (“Speedway”) and MPLX LP and its subsidiaries (“MPLX”).
	See Note 9 for additional information about our operations.
	Basis of Presentation—All significant intercompany transactions and accounts have been eliminated.
	These interim consolidated financial statements are unaudited; however, in the opinion of our management, these statements reflect all adjustments necessary for a fair statement of the results for the periods reported. All such adjustments are of a normal, recurring nature unless otherwise disclosed. These interim consolidated financial statements, including the notes, have been prepared in accordance with the rules of the Securities and Exchange Commission applicable to interim period financial statements and do not include all of the information and disclosures required by United States generally accepted accounting principles (“U.S. GAAP”) for complete financial statements.
	These interim consolidated financial statements should be read in conjunction with the audited consolidated financial statements and notes thereto included in our Annual Report on Form 10-K for the year ended December 31, 2014. The results of operations for the three months ended March 31, 2015 are not necessarily indicative of the results to be expected for the full year.

Accounting_Standards

Accounting Standards	3 Months Ended
	Mar. 31, 2015
Accounting Changes and Error Corrections [Abstract]
Accounting Standards	Accounting Standards
	Recently Adopted
	In June 2014, the Financial Accounting Standards Board (“FASB”) issued an accounting standards update for the elimination of the concept of development stage entity (“DSE”) from U.S. GAAP and removes the related incremental reporting. The standards update eliminates the additional financial statement requirements specific to a DSE and was adopted in the first quarter of 2015. In addition, the portion to amend the consolidation model that eliminates the special provisions in the variable interest entity ("VIE") rules for assessing the sufficiency of the equity of a DSE is effective in the first quarter of 2016. Adoption of this standard update in the first quarter of 2015 and 2016 has not and is not expected to have an impact on our consolidated results of operations, financial position or cash flows.
	In April 2014, the FASB issued an accounting standards update that redefines the criteria for determining discontinued operations and introduces new disclosures related to these disposals. The updated definition of a discontinued operation is the disposal of a component (or components) of an entity or the classification of a component (or components) of an entity as held for sale that represents a strategic shift for an entity and has (or will have) a major impact on an entity’s operations and financial results. The standard requires disclosure of additional financial information for discontinued operations and individually material components not qualifying for discontinued operation presentation, as well as information regarding an entity’s continuing involvement with the discontinued operation. The accounting standards update was effective prospectively for annual periods beginning on or after December 15, 2014, and interim periods within those years. Adoption of this standards update in the first quarter of 2015 did not have an impact on our consolidated results of operations, financial position or cash flows.
	Not Yet Adopted
	In April 2015, the FASB issued an accounting standards update clarifying whether a customer should account for a cloud computing arrangement as an acquisition of a software license or as a service arrangement by providing characteristics that a cloud computing arrangement must have in order to be accounted for as a software license acquisition. The change is effective for fiscal years and interim periods within those fiscal years beginning after December 15, 2015. Retrospective or prospective application is allowed and early adoption is permitted. Adoption of this standard is not expected to have a material impact on our consolidated results of operations, financial position or cash flows.
	In April 2015, the FASB issued an update to simplify the presentation of debt issuance costs. The update requires that all debt issue costs be presented on the balance sheet as a direct reduction of the liability. The change is effective for fiscal years and interim periods within those fiscal years beginning after December 15, 2015. Retrospective application is required and early adoption is permitted. Adoption of this standard is not expected to have a material impact on our consolidated results of operations, financial position or cash flows.
	In February 2015, the FASB issued an accounting standards update making targeted changes to the current consolidation guidance. The new standard changes the way certain decisions are made related to substantive rights, related parties, and decision making fees when applying the VIE consolidation model and eliminates certain guidance for limited partnerships and similar entities under the voting interest consolidation model. The update is effective for fiscal years and interim periods within those fiscal years beginning after December 15, 2015. Early adoption is permitted. At this point, we have not determined the impact of the new standards update on our consolidated financial statements and related disclosures.
	In August 2014, the FASB issued an accounting standards update requiring management to assess an entity’s ability to continue as a going concern and to provide related footnote disclosures in certain circumstances. Management will be required to assess if there is substantial doubt about an entity’s ability to continue as a going concern within one year after the date that the financial statements are issued. Disclosures will be required if conditions give rise to substantial doubt and the type of disclosure will be determined based on whether management’s plans will be able to alleviate the substantial doubt. The accounting standards update will be effective for the first annual period ending after December 15, 2016, and for annual periods and interim periods thereafter with early application permitted.
	In May 2014, the FASB issued an accounting standards update for revenue recognition that is aligned with the International Accounting Standards Board’s revenue recognition standard issued on the same day. The guidance in the update states that revenue is recognized when a customer obtains control of a good or service. Recognition of the revenue will involve a multiple step approach including identifying the contract, identifying the separate performance obligations, determining the transaction price, allocating the price to the performance obligations and then recognizing the revenue as the obligations are satisfied. Additional disclosures will be required to provide adequate information to understand the nature, amount, timing and uncertainty of reported revenues and revenues expected to be recognized. The accounting standards update will be effective on a retrospective or modified retrospective basis for annual reporting periods beginning after December 15, 2016, and interim periods within those years, with no early adoption permitted. At this point, we have not determined the impact of the new standard on our consolidated financial statements.

MPLX_LP

MPLX LP	3 Months Ended
	Mar. 31, 2015
Noncontrolling Interest [Abstract]
MPLX LP	MPLX LP
	MPLX is a publicly traded master limited partnership that was formed by us to own, operate, develop and acquire pipelines and other midstream assets related to the transportation and storage of crude oil, refined products and other hydrocarbon-based products.
	As of March 31, 2015, we owned a 71.5 percent interest in MPLX, including the two percent general partner interest. We consolidate this entity for financial reporting purposes since we have a controlling financial interest, and we record a noncontrolling interest for the interest owned by the public.
	On March 1, 2014, we sold MPLX a 13 percent interest in MPLX Pipe Line Holdings LP (“Pipe Line Holdings”) for $310 million. MPLX financed this transaction with $40 million of cash on-hand and $270 million of borrowings on its bank revolving credit facility.
	On December 1, 2014, we sold and contributed interests in Pipe Line Holdings totaling 30.5 percent to MPLX for $600 million in cash and 2.9 million MPLX common units valued at $200 million. MPLX financed the cash portion of this transaction with $600 million of borrowings on its bank revolving credit facility.
	The sales and contribution of our interests in Pipe Line Holdings to MPLX resulted in a change in our ownership in Pipe Line Holdings, but not a change in control. We accounted for them as transactions between entities under common control and did not record a gain or loss.
	On December 8, 2014, MPLX completed a public offering of 3.5 million common units at a price to the public of $66.68 per common unit, for aggregate net proceeds of $221 million. MPLX used the net proceeds from this offering to repay borrowings under its bank revolving credit facility and for general partnership purposes. On December 10, 2014, we exercised our right to maintain our two percent general partner interest in MPLX by purchasing 130 thousand general partner units for $9 million.
	On February 12, 2015, MPLX completed a public offering of $500 million aggregate principal amount of four percent unsecured senior notes due February 15, 2025 (the “MPLX Senior Notes”). See Note 16 for more information.

Acquisitions_and_Investments

Acquisitions and Investments	3 Months Ended
	Mar. 31, 2015
Business Combinations [Abstract]
Acquisitions and Investments	Acquisitions and Investments
	Acquisition of Hess’ Retail Operations and Related Assets
	On September 30, 2014, we acquired from Hess Corporation (“Hess”) all of Hess’ retail locations, transport operations and shipper history on various pipelines, including approximately 40,000 barrels per day on Colonial Pipeline for $2.82 billion. We refer to these assets as “Hess’ Retail Operations and Related Assets.” The transaction was funded with a combination of debt and available cash. The transaction provided for an adjustment for working capital, which was finalized for $3 million during the first quarter of 2015, reducing our total consideration. This amount is consistent with the estimate we used in prior periods and therefore, the fair value of the assets acquired and liabilities assumed remain unchanged from year-end 2014.
	The purchase price allocation resulted in the recognition of $629 million in goodwill by our Speedway segment. The goodwill primarily relates to the expected benefits of a significantly expanded retail platform that should enable growth in new markets, as well as the potential for higher merchandise sales by utilizing Speedway’s marketing approach at the acquired locations. We also expect strategic benefits from the financial and operational scale we expect to realize across our entire retail network. The goodwill is deductible for tax purposes.
	The following unaudited pro forma financial information presents consolidated results assuming Hess’ Retail Operations and Related Assets acquisition occurred on January 1, 2013. The pro forma financial information does not give effect to potential synergies that could result from the acquisition and is not necessarily indicative of the results of future operations.
		Three Months Ended
		March 31,
	(In millions, except per share data)	2014
	Sales and other operating revenues (including consumer excise taxes)	$	26,017
	Net income attributable to MPC	182
	Net income attributable to MPC per share – basic	$	0.62
	Net income attributable to MPC per share – diluted	0.62
	The pro forma information includes adjustments to align accounting policies, an adjustment to depreciation expense to reflect the fair value of property, plant and equipment, increased amortization expense related to identifiable intangible assets, additional interest expense related to financing the acquisition, as well as the related income tax effects.
	Acquisition of Biodiesel Facility
	On April 1, 2014, we purchased a biodiesel facility in Cincinnati, Ohio from Felda Iffco Sdn Bhd, Malaysia for $40 million. The plant currently produces biodiesel, glycerin and other by-products and has a capacity of approximately 60 million gallons per year.
	Neither goodwill nor a gain from a bargain purchase was recognized in conjunction with the acquisition.
	Assuming the acquisition had been made at the beginning of any period presented, the consolidated pro forma results would not be materially different from reported results.
	Investments in Pipeline Companies
	In July 2014, we exercised our option to acquire a 35 percent ownership interest in Enbridge Inc.’s Southern Access Extension pipeline (“SAX”) through our investment in Illinois Extension Pipeline Company, LLC (“Illinois Extension Pipeline”). During the three months ended March 31, 2015, we made contributions of $37 million to Illinois Extension Pipeline to fund our portion of the construction costs for the SAX project. We have contributed $157 million since project inception. We account for our ownership interest in Illinois Extension Pipeline as an equity method investment. See Note 21 for information on future contributions to Illinois Extension Pipeline.
	In March 2014, we acquired from Chevron Raven Ridge Pipe Line Company an additional seven percent interest in Explorer Pipeline Company (“Explorer”) for $77 million, bringing our ownership interest to 25 percent. As a result of this increase in our ownership, we now account for our investment in Explorer using the equity method of accounting rather than the cost method. The cumulative impact of the change was applied as an adjustment to 2014 retained earnings.

Variable_Interest_Entity

Variable Interest Entity	3 Months Ended
	Mar. 31, 2015
Variable Interest Entity [Abstract]
Variable Interest Entity	Variable Interest Entity
	As stated in Note 4, we have a 35 percent ownership interest in Illinois Extension Pipeline through our contributions to the SAX project. Illinois Extension Pipeline Company LLC is considered a VIE because it is a development stage entity and the equity in the entity is not sufficient to fund the current stage of development, which is the construction of the SAX pipeline. Our maximum exposure to loss due to this VIE at March 31, 2015 was $157 million, which equates to our contributions to-date to fund our portion of the construction costs for the project.
	We are not the primary beneficiary of this VIE and, therefore, do not consolidate it because we do not have the power to control the activities that significantly influence the economic activities of the entity. The activities that most significantly impact the VIE’s economic performance during the construction phase are the actual construction costs and risks associated with the construction process. Through our vote, we have shared power to direct the construction activities, but do not have the sole ability to control the construction activities.

Related_Party_Transactions

Related Party Transactions	3 Months Ended
	Mar. 31, 2015
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions
	Our related parties include:
	•	Centennial Pipeline LLC (“Centennial”), in which we have a 50 percent noncontrolling interest. Centennial owns a refined products pipeline and storage facility.
	•	Explorer, in which we have a 25 percent interest. Explorer owns and operates a refined products pipeline.
	•	LOCAP LLC (“LOCAP”), in which we have a 59 percent noncontrolling interest. LOCAP owns and operates a crude oil pipeline.
	•	LOOP LLC (“LOOP”), in which we have a 51 percent noncontrolling interest. LOOP owns and operates the only U.S. deepwater oil port.
	•	TAAE, in which we have a 43 percent noncontrolling interest, TACE, in which we have a 60 percent noncontrolling interest and TAME, in which we have a 67 percent direct and indirect noncontrolling interest. These companies each own an ethanol production facility.
	•	Other equity method investees.
	Sales to related parties, which are included in sales and other operating revenues (including consumer excise taxes) on the consolidated statements of income, were $1 million and $2 million for the three months ended March 31, 2015 and 2014, respectively.
	Purchases from related parties were as follows:
		Three Months Ended
		March 31,
	(In millions)	2015		2014
	Centennial	$	—	$	9
	Explorer	7		13
	LOCAP	5		5
	LOOP	13		53
	TAAE	13		16
	TACE	16		27
	TAME	20		34
	Other equity method investees	2		2
	Total	$	76	$	159
	Related party purchases from Centennial consist primarily of refinery feedstocks and refined product transportation costs. Related party purchases from Explorer consist primarily of refined product transportation costs. Related party purchases from LOCAP, LOOP and other equity method investees consist primarily of crude oil transportation costs and crude oil purchases. Related party purchases from TAAE, TACE and TAME consist of ethanol purchases.
	Receivables from related parties, which are included in receivables, less allowance for doubtful accounts on the consolidated balance sheets, were as follows:
	(In millions)	March 31,		December 31,
		2015		2014
	Centennial	$	—	$	2
	Explorer	—		2
	TAME	—		3
	Other equity method investees	1		—
	Total	$	1	$	7
	Payables to related parties, which are included in accounts payable on the consolidated balance sheets, were as follows:
	(In millions)	March 31,		December 31,
		2015		2014
	Explorer	$	3	$	3
	LOCAP	2		2
	LOOP	5		4
	TAAE	1		2
	TACE	1		2
	TAME	2		5
	Total	$	14	$	18

Income_per_Common_Share

Income per Common Share	3 Months Ended
	Mar. 31, 2015
Earnings Per Share [Abstract]
Income per Common Share	Income per Common Share
	We compute basic earnings per share by dividing net income attributable to MPC by the weighted average number of shares of common stock outstanding. Diluted income per share assumes exercise of certain stock-based compensation awards, provided the effect is not anti-dilutive. The number of shares that were anti-dilutive was immaterial in the three months ended March 31, 2015 and 2014.
	MPC grants certain incentive compensation awards to employees and non-employee directors that are considered to be participating securities. Due to the presence of participating securities, we have calculated our earnings per share using the two-class method.
		Three Months Ended
		March 31,
	(In millions, except per share data)	2015		2014
	Basic earnings per share:
	Allocation of earnings:
	Net income attributable to MPC	$	891	$	199
	Income allocated to participating securities	1		—
	Income available to common stockholders – basic	$	890	$	199
	Weighted average common shares outstanding	273		293
	Basic earnings per share	$	3.26	$	0.68
	Diluted earnings per share:
	Allocation of earnings:
	Net income attributable to MPC	$	891	$	199
	Income allocated to participating securities	1		—
	Income available to common stockholders – diluted	$	890	$	199
	Weighted average common shares outstanding	273		293
	Effect of dilutive securities	2		2
	Weighted average common shares, including dilutive effect	275		295
	Diluted earnings per share	$	3.24	$	0.67

Equity

Equity	3 Months Ended
	Mar. 31, 2015
Equity [Abstract]
Equity	Equity
	As of March 31, 2015, our board of directors had approved $8.0 billion in total share repurchase authorizations. Since January 1, 2012, we have repurchased a total of $6.48 billion of our common stock, leaving $1.52 billion available for repurchases. Through March 31, 2015, we have acquired 92 million shares at an average cost per share of $70.95 under these authorizations.
	We may utilize various methods to effect the repurchases, which could include open market repurchases, negotiated block transactions, accelerated share repurchases or open market solicitations for shares, some of which may be effected through Rule 10b5-1 plans. The timing and amount of future repurchases, if any, will depend upon several factors, including market and business conditions, and such repurchases may be discontinued at any time.
	Total share repurchases were as follows for the three months ended March 31, 2015 and 2014:
		Three Months Ended
		March 31,
	(In millions, except per share data)	2015		2014
	Number of shares repurchased	2		8
	Cash paid for shares repurchased	$	209	$	689
	Effective average cost per delivered share	$	95.03	$	87.6
	At March 31, 2015, we had agreements to acquire 88,394 common shares for $9 million, which were settled in early April 2015.

Segment_Information

Segment Information	3 Months Ended
	Mar. 31, 2015
Segment Reporting [Abstract]
Segment Information	Segment Information
	We have three reportable segments: Refining & Marketing; Speedway; and Pipeline Transportation. Each of these segments is organized and managed based upon the nature of the products and services it offers.
	•	Refining & Marketing – refines crude oil and other feedstocks at our refineries in the Gulf Coast and Midwest regions of the United States, purchases ethanol and refined products for resale and distributes refined products through various means, including barges, terminals and trucks that we own or operate. We sell refined products to wholesale marketing customers domestically and internationally, to buyers on the spot market, to our Speedway segment and to independent entrepreneurs who operate Marathon® retail outlets.
	•	Speedway – sells transportation fuels and convenience products in retail markets in the Midwest, East Coast and Southeast regions of the United States.
	•	Pipeline Transportation – transports crude oil and other feedstocks to our refineries and other locations, delivers refined products to wholesale and retail market areas. This segment includes the aggregated operations of MPLX.
	On September 30, 2014, we acquired Hess’ Retail Operations and Related Assets, substantially all of which are part of the Speedway segment. Segment information for the periods prior to the acquisition do not include amounts for these operations. See Note 4.
	Segment income represents income from operations attributable to the reportable segments. Corporate administrative expenses and costs related to certain non-operating assets are not allocated to the reportable segments. In addition, certain items that affect comparability (as determined by the chief operating decision maker) are not allocated to the reportable segments.
	(In millions)	Refining & Marketing			Speedway			Pipeline Transportation		Total
	Three Months Ended March 31, 2015
	Revenues:
	Customer	$	12,644		$	4,531		$	16	$	17,191
	Intersegment(a)	2,733			—			134		2,867
	Segment revenues	$	15,377		$	4,531		$	150	$	20,058
	Segment income from operations(b)	$	1,316		$	168		$	67	$	1,551
	Income from equity method investments	6			—			9		15
	Depreciation and amortization(c)	267			63			20		350
	Capital expenditures and investments(d)	229			45			81		355
	(In millions)	Refining & Marketing			Speedway			Pipeline Transportation		Total
	Three Months Ended March 31, 2014
	Revenues:
	Customer	$	19,810		$	3,458		$	17	$	23,285
	Intersegment(a)	2,233			1			129		2,363
	Segment revenues	$	22,043		$	3,459		$	146	$	25,648
	Segment income from operations(b)	$	362		$	58		$	72	$	492
	Income from equity method investments	24			—			11		35
	Depreciation and amortization(c)	261			28			19		308
	Capital expenditures and investments(d)	178			32			130		340
	(a)	Management believes intersegment transactions were conducted under terms comparable to those with unaffiliated parties.
	(b)	Corporate overhead expenses attributable to MPLX are included in the Pipeline Transportation segment. Corporate overhead expenses are not allocated to the Refining & Marketing and Speedway segments.
	(c)	Differences between segment totals and MPC totals represent amounts related to unallocated items and are included in “Items not allocated to segments” in the reconciliation below.
	(d)	Capital expenditures include changes in capital accruals, acquisitions and investments in affiliates.
	The following reconciles segment income from operations to income before income taxes as reported in the consolidated statements of income:
		Three Months Ended
		March 31,
	(In millions)	2015			2014
	Segment income from operations	$	1,551		$	492
	Items not allocated to segments:
	Corporate and other unallocated items(a)(b)	(80		)	(67		)
	Pension settlement expenses(c)	(1		)	(64		)
	Net interest and other financial income (costs)	(81		)	(46		)
	Income before income taxes	$	1,389		$	315
	(a)	Corporate and other unallocated items consists primarily of MPC’s corporate administrative expenses and costs related to certain non-operating assets.
	(b)	Corporate overhead expenses attributable to MPLX are included in the Pipeline Transportation segment. Corporate overhead expenses are not allocated to the Refining & Marketing and Speedway segments.
	(c)	See Note 19.
	The following reconciles segment capital expenditures and investments to total capital expenditures:
		Three Months Ended
		March 31,
	(In millions)	2015			2014
	Segment capital expenditures and investments	$	355		$	340
	Less: Investments in equity method investees	42			123
	Plus: Items not allocated to segments:
	Capital expenditures not allocated to segments	21			25
	Capitalized interest	8			6
	Total capital expenditures(a)	$	342		$	248
	(a)	Capital expenditures include changes in capital accruals. See Note 17 for a reconciliation of total capital expenditures to additions to property, plant and equipment as reported in the consolidated statements of cash flows.

Other_Items

Other Items	3 Months Ended
	Mar. 31, 2015
Other Income and Expenses [Abstract]
Other Items	Other Items
	Net interest and other financial income (costs) was:
		Three Months Ended
		March 31,
	(In millions)	2015			2014
	Interest income	$	1		$	2
	Interest expense	(80		)	(49		)
	Interest capitalized	8			6
	Other financial costs	(10		)	(5		)
	Net interest and other financial income (costs)	$	(81	)	$	(46	)

Income_Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2015
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes
	The combined federal, state and foreign income tax rate was 35 percent and 34 percent for the three months ended March 31, 2015 and 2014, respectively. The effective tax rate for the three months ended March 31, 2015 and 2014 is equivalent to or slightly less than the U.S. statutory rate of 35 percent primarily due to certain permanent benefit differences, including the domestic manufacturing deduction, partially offset by state and local tax expense.
	We are continuously undergoing examination of our income tax returns, which have been completed for our U.S. federal and state income tax returns through the 2009 and 2003 tax years, respectively. We had $15 million of unrecognized tax benefits as of March 31, 2015. Pursuant to our tax sharing agreement with Marathon Oil, the unrecognized tax benefits related to pre-spinoff operations for which Marathon Oil was the taxpayer remain the responsibility of Marathon Oil and we have indemnified Marathon Oil accordingly. See Note 21 for indemnification information.

Inventories

Inventories	3 Months Ended
	Mar. 31, 2015
Inventory Disclosure [Abstract]
Inventories	Inventories
	(In millions)	March 31,		December 31,
		2015		2014
	Crude oil and refinery feedstocks	$	2,107	$	2,219
	Refined products	2,862		2,955
	Materials and supplies	302		302
	Merchandise	166		166
	Total (at cost)	$	5,437	$	5,642
	Inventories are carried at the lower of cost or market value. The cost of inventories of crude oil and refinery feedstocks, refined products and merchandise is determined primarily under the last-in, first-out (“LIFO”) method. During the three months ended March 31, 2015, we recorded LIFO liquidations caused by permanently decreased levels in refined products inventory volumes. Cost of revenues increased and income from operations decreased by approximately $30 million for the three months ended March 31, 2015 as a result of the LIFO liquidations. There were no liquidations of LIFO inventories for the three months ended March 31, 2014.

Property_Plant_and_Equipment

Property, Plant and Equipment	3 Months Ended
	Mar. 31, 2015
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	Property, Plant and Equipment
	(In millions)	March 31,		December 31,
		2015		2014
	Refining & Marketing	$	18,225	$	18,001
	Speedway	4,674		4,639
	Pipeline Transportation	2,083		2,044
	Corporate and Other	639		618
	Total	25,621		25,302
	Less accumulated depreciation	9,380		9,041
	Property, plant and equipment, net	$	16,241	$	16,261
	Included in construction in progress at March 31, 2015 is $136 million of costs associated with a residual fuel hydrocracker project at our Garyville refinery, intended to increase margins by upgrading residual fuel to ultra-low sulfur diesel and gas oil. We are deferring a final investment decision on this project as we further evaluate the implications of current market conditions on the project. If a decision is made to not pursue this project, there could be a future impairment of the costs incurred for the project.

Fair_Value_Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2015
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements
	Fair Values—Recurring
	The following tables present assets and liabilities accounted for at fair value on a recurring basis as of March 31, 2015 and December 31, 2014 by fair value hierarchy level. We have elected to offset the fair value amounts recognized for multiple derivative contracts executed with the same counterparty, including any related cash collateral as shown below; however, fair value amounts by hierarchy level are presented on a gross basis in the following tables.
		March 31, 2015
		Fair Value Hierarchy
	(In millions)	Level 1		Level 2		Level 3		Netting and Collateral(a)			Net Carrying Value on Balance Sheet(b)		Collateral Pledged Not Offset
	Commodity derivative instruments, assets	$	94	$	—	$	—	$	(66	)	$	28	$	40
	Other assets	2		—		—		N/A			2		—
	Total assets at fair value	$	96	$	—	$	—	$	(66	)	$	30	$	40
	Commodity derivative instruments, liabilities	$	79	$	—	$	—	$	(79	)	$	—	$	—
	Contingent consideration, liability(c)	—		—		490		N/A			490		—
	Total liabilities at fair value	$	79	$	—	$	490	$	(79	)	$	490	$	—
		December 31, 2014
		Fair Value Hierarchy
	(In millions)	Level 1		Level 2		Level 3		Netting and Collateral(a)			Net Carrying Value on Balance Sheet(b)		Collateral Pledged Not Offset
	Commodity derivative instruments, assets	$	317	$	—	$	—	$	(258	)	$	59	$	—
	Other assets	2		—		—		N/A			2		—
	Total assets at fair value	$	319	$	—	$	—	$	(258	)	$	61	$	—
	Commodity derivative instruments, liabilities	$	180	$	—	$	—	$	(180	)	$	—	$	—
	Contingent consideration, liability(c)	—		—		478		N/A			478		—
	Total liabilities at fair value	$	180	$	—	$	478	$	(180	)	$	478	$	—
	(a)	Represents the impact of netting assets, liabilities and cash collateral when a legal right of offset exists. As of March 31, 2015, cash collateral of $13 million was netted with the mark-to-market derivative liabilities. As of December 31, 2014, $78 million was netted with mark-to-market derivative assets.
	(b)	We have no derivative contracts that are subject to master netting arrangements that are reflected gross on the balance sheet.
	(c)	Includes $189 million and $174 million classified as current at March 31, 2015 and December 31, 2014, respectively.
	Commodity derivatives in Level 1 are exchange-traded contracts for crude oil and refined products measured at fair value with a market approach using the close-of-day settlement prices for the market. Commodity derivatives are covered under master netting agreements with an unconditional right to offset. Collateral deposits in futures commission merchant accounts covered by master netting agreements related to Level 1 commodity derivatives are classified as Level 1 in the fair value hierarchy.
	The contingent consideration represents the fair value as of March 31, 2015 and December 31, 2014 of the amount we expect to pay to BP related to the earnout provision associated with our 2013 acquisition of BP’s refinery in Texas City, Texas and related logistics and marketing assets. We refer to these assets as the “Galveston Bay Refinery and Related Assets.” The fair value of the contingent consideration was estimated using an income approach and is therefore a Level 3 liability. The amount of cash to be paid under the arrangement is based on both a market-based crack spread and refinery throughput volumes for the months during which the earnout applies, as well as established thresholds that cap the annual and total payment. The earnout payment cannot exceed $200 million per year for the first three years of the arrangement or $250 million per year for the last three years of the arrangement, with the total cumulative payment capped at $700 million over the six-year period commencing in 2014. Any excess or shortfall from the annual cap for a current year’s earnout calculation will not affect subsequent years’ calculations. The fair value calculation used significant unobservable inputs, including: (1) an estimate of monthly refinery throughput volumes; (2) a range of internal and external monthly crack spread forecasts from $9 to $18 per barrel; and (3) a range of risk-adjusted discount rates from five percent to 10 percent. An increase or decrease in crack spread forecasts or refinery throughput volume expectations may result in a corresponding increase or decrease in the fair value. Increases to the fair value as a result of increasing forecasts for both of these unobservable inputs, however, are limited as the earnout payment is subject to annual caps. An increase or decrease in the discount rate may result in a decrease or increase to the fair value, respectively. The fair value of the contingent consideration is reassessed each quarter, with changes in fair value recorded in cost of revenues.
	In 2015, we expect to pay BP approximately $189 million for the second year’s contingent earnout. We paid BP $180 million in the third quarter of 2014 for the first year’s contingent earnout.
	The following is a reconciliation of the beginning and ending balances recorded for liabilities classified as Level 3 in the fair value hierarchy.
		Three Months Ended
		March 31,
	(In millions)	2015		2014
	Beginning balance	$	478	$	625
	Unrealized and realized losses included in net income	12		14
	Ending balance	$	490	$	639
	We did not hold any Level 3 derivative instruments during the three months ended March 31, 2015 and 2014. See Note 15 for the income statement impacts of our derivative instruments.
	Fair Values – Reported
	The following table summarizes financial instruments on the basis of their nature, characteristics and risk at March 31, 2015 and December 31, 2014, excluding the derivative financial instruments and contingent consideration reported above.
		March 31, 2015				December 31, 2014
	(In millions)	Fair Value		Carrying Value		Fair Value		Carrying Value
	Financial assets:
	Investments	$	27	$	2	$	26	$	2
	Other	31		30		32		32
	Total financial assets	$	58	$	32	$	58	$	34
	Financial liabilities:
	Long-term debt(a)	$	6,843	$	6,377	$	6,571	$	6,265
	Deferred credits and other liabilities	20		20		17		17
	Total financial liabilities	$	6,863	$	6,397	$	6,588	$	6,282
	(a)	Excludes capital leases, however, includes amount classified as short-term debt.
	Our current assets and liabilities include financial instruments, the most significant of which are trade accounts receivable and payables. We believe the carrying values of our current assets and liabilities approximate fair value. Our fair value assessment incorporates a variety of considerations, including (1) the short-term duration of the instruments, (2) our investment-grade credit rating and (3) our historical incurrence of and expected future insignificance of bad debt expense, which includes an evaluation of counterparty credit risk.
	Fair values of our financial assets included in investments and other financial assets and of our financial liabilities included in deferred credits and other liabilities are measured primarily using an income approach and most inputs are internally generated, which results in a Level 3 classification. Estimated future cash flows are discounted using a rate deemed appropriate to obtain the fair value. Other financial assets primarily consist of environmental remediation receivables. Deferred credits and other liabilities primarily consist of insurance liabilities and environmental remediation liabilities.
	Fair value of fixed-rate long-term debt is measured using a market approach, based upon the average of quotes from major financial institutions and a third-party service for our debt. Because these quotes cannot be independently verified to the market, they are considered Level 3 inputs. Fair value of variable-rate long-term debt approximates the carrying value.

Derivatives

Derivatives	3 Months Ended
	Mar. 31, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivatives	Derivatives
	For further information regarding the fair value measurement of derivative instruments, including any effect of master netting agreements or collateral, see Note 14. We do not designate any of our commodity derivative instruments as hedges for accounting purposes.
	Derivatives that are not designated as accounting hedges may include commodity derivatives used to hedge price risk on (1) inventories, (2) fixed price sales of refined products, (3) the acquisition of foreign-sourced crude oil and (4) the acquisition of ethanol for blending with refined products.
	The following table presents the gross fair values of derivative instruments, excluding cash collateral, and where they appear on the consolidated balance sheets as of March 31, 2015 and December 31, 2014:
		March 31, 2015
	(In millions)	Asset				Liability			Balance Sheet Location
	Commodity derivatives	$	94			$	79		Other current assets
		December 31, 2014
	(In millions)	Asset				Liability			Balance Sheet Location
	Commodity derivatives	$	317			$	180		Other current assets
	The table below summarizes open commodity derivative contracts as of March 31, 2015.
		Position		Total Barrels (In thousands)
	Crude oil(a)
	Exchange-traded	Long		11,454
	Exchange-traded	Short		(23,733	)
	Refined Products(b)
	Exchange-traded	Long		3,378
	Exchange-traded	Short		(2,402	)
	(a)	96 percent of these contracts expire in the second quarter of 2015.
	(b)	100 percent of these contracts expire in the second quarter of 2015.
	The following table summarizes the effect of all commodity derivative instruments in our consolidated statements of income:
		Gain (Loss)
	(In millions)	Three Months Ended March 31,
	Income Statement Location	2015				2014
	Sales and other operating revenues	$	14			$	10
	Cost of revenues	45				(61		)
	Total	$	59			$	(51	)

Debt

Debt	3 Months Ended
	Mar. 31, 2015
Debt Disclosure [Abstract]
Debt	Debt
	Our outstanding borrowings at March 31, 2015 and December 31, 2014 consisted of the following:
	(In millions)	March 31,			December 31,
		2015			2014
	Marathon Petroleum Corporation:
	Revolving credit agreement due 2017	$	—		$	—
	Term loan agreement due 2019	700			700
	3.500% senior notes due March 1, 2016	750			750
	5.125% senior notes due March 1, 2021	1,000			1,000
	3.625% senior notes due September 15, 2024	750			750
	6.500% senior notes due March 1, 2041	1,250			1,250
	4.750% senior notes due September 15, 2044	800			800
	5.000% senior notes due September 15, 2054	400			400
	Consolidated subsidiaries:
	Capital lease obligations due 2015-2028	366			372
	MPLX bank revolving credit facility due 2019	—			385
	MPLX term loan facility due 2019	250			250
	MPLX 4.000% senior notes due February 15, 2025	500			—
	Trade receivables securitization facility due 2016	—			—
	Total	6,766			6,657
	Unamortized discount	(28		)	(26		)
	Fair value adjustments(a)	5			6
	Amounts due within one year	(776		)	(27		)
	Total long-term debt due after one year	$	5,967		$	6,610
	(a)	The $20 million gain on the termination of our interest rate swap agreements in 2012 is being amortized over the remaining life of the 3.50 percent senior notes.
	MPLX Senior Notes – On February 12, 2015, MPLX completed a public offering of $500 million aggregate principal amount of MPLX Senior Notes, the net proceeds of which were approximately $495 million, after deducting underwriting discounts. The net proceeds of this offering were used to repay the amounts outstanding under the MPLX revolving credit agreement (the “MPLX Credit Agreement”), as well as for general partnership purposes. Interest is payable semi-annually in arrears on February 15 and August 15 of each year, commencing on August 15, 2015.
	There were no borrowings or letters of credit outstanding under the MPC revolving credit facility or the trade receivables securitization facility at March 31, 2015. As of March 31, 2015, eligible trade receivables supported available borrowings of $978 million under the $1.3 billion trade receivables facility. During the three months ended March 31, 2015, MPLX borrowed $30 million under the MPLX Credit Agreement at an average interest rate of 1.5 percent, per annum, and repaid $415 million of these borrowings. At March 31, 2015, MPLX had no borrowings and no letters of credit outstanding under the MPLX Credit Agreement, resulting in total unused loan availability of $1 billion, or 100 percent of the borrowing capacity.

Supplemental_Cash_Flow_Informa

Supplemental Cash Flow Information	3 Months Ended
	Mar. 31, 2015
Supplemental Cash Flow Elements [Abstract]
Supplemental Cash Flow Information	Supplemental Cash Flow Information
		Three Months Ended
		March 31,
	(In millions)	2015			2014
	Net cash provided by operating activities included:
	Interest paid (net of amounts capitalized)	$	128		$	80
	Net income taxes paid to taxing authorities	160			5
	The consolidated statements of cash flows exclude changes to the consolidated balance sheets that did not affect cash. The following is a reconciliation of additions to property, plant and equipment to total capital expenditures:
		Three Months Ended
		March 31,
	(In millions)	2015			2014
	Additions to property, plant and equipment	$	389		$	267
	Decrease in capital accruals	(47		)	(19		)
	Total capital expenditures	$	342		$	248

Accumulated_Other_Comprehensiv

Accumulated Other Comprehensive Loss	3 Months Ended
	Mar. 31, 2015
Equity [Abstract]
Accumulated Other Comprehensive Loss	Accumulated Other Comprehensive Loss
	The following table shows the changes in accumulated other comprehensive loss by component. Amounts in parentheses indicate debits.
	(In millions)	Pension Benefits			Other Benefits			Gain on Cash Flow Hedge		Workers Compensation		Total
	Balance as of December 31, 2013	$	(161	)	$	(50	)	$	4	$	3	$	(204	)
	Other comprehensive income (loss) before reclassifications	(43		)	1			—		—		(42		)
	Amounts reclassified from accumulated other comprehensive loss:
	Amortization – prior service credit(a)	(12		)	(1		)	—		—		(13		)
	– actuarial loss(a)	13			1			—		—		14
	– settlement loss(a)	64			—			—		—		64
	Tax effect	(24		)	—			—		—		(24		)
	Other comprehensive income (loss)	(2		)	1			—		—		(1		)
	Balance as of March 31, 2014	$	(163	)	$	(49	)	$	4	$	3	$	(205	)
	(In millions)	Pension Benefits			Other Benefits			Gain on Cash Flow Hedge		Workers Compensation		Total
	Balance as of December 31, 2014	$	(217	)	$	(104	)	$	4	$	4	$	(313	)
	Other comprehensive loss before reclassifications	(1		)	(1		)	—		—		(2		)
	Amounts reclassified from accumulated other comprehensive loss:
	Amortization – prior service credit(a)	(12		)	(1		)	—		—		(13		)
	– actuarial loss(a)	13			3			—		—		16
	– settlement loss(a)	1			—			—		—		1
	Tax effect	(1		)	(1		)	—		—		(2		)
	Other comprehensive income (loss)	—			—			—		—		—
	Balance as of March 31, 2015	$	(217	)	$	(104	)	$	4	$	4	$	(313	)
	(a)	These accumulated other comprehensive loss components are included in the computation of net periodic benefit cost. See Note 19.

Defined_Benefit_Pension_and_Ot

Defined Benefit Pension and Other Postretirement Plans	3 Months Ended
	Mar. 31, 2015
Compensation and Retirement Disclosure [Abstract]
Defined Benefit Pension and Other Postretirement Plans	Defined Benefit Pension and Other Postretirement Plans
	The following summarizes the components of net periodic benefit costs:
		Three Months Ended March 31,
		Pension Benefits						Other Benefits
	(In millions)	2015			2014			2015			2014
	Components of net periodic benefit cost:
	Service cost	$	23		$	23		$	8		$	7
	Interest cost	18			20			8			8
	Expected return on plan assets	(26		)	(28		)	—			—
	Amortization – prior service credit	(12		)	(12		)	(1		)	(1		)
	– actuarial loss	13			13			3			1
	– settlement loss	1			64			—			—
	Net periodic benefit cost	$	17		$	80		$	18		$	15
	During the three months ended March 31, 2015, we made no contributions to our funded pension plans. We have no required funding for 2015, but may make voluntary contributions at our discretion. Current benefit payments related to unfunded pension and other postretirement benefit plans were $4 million and $5 million, respectively, during the three months ended March 31, 2015.
	During the three months ended March 31, 2015 and 2014, we determined that lump sum payments to employees retiring in the respective years will exceed the plans’ total service and interest costs for the year. Settlement losses are required to be recorded when lump sum payments exceed total service and interest costs. As a result, during the three months ended March 31, 2015 and 2014, we recorded pension settlement expenses of $1 million and $64 million related to our lump sum payments made during the first three months of 2015 and 2014, respectively.

StockBased_Compensation_Plans

Stock-Based Compensation Plans	3 Months Ended
	Mar. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Compensation Plans	Stock-Based Compensation Plans
	Stock Option Awards
	The following table presents a summary of our stock option award activity for the three months ended March 31, 2015:
		Number of Shares		Weighted Average Exercise Price
	Outstanding at December 31, 2014	4,751,438		$	45.47
	Granted	354,001		101.78
	Exercised	(577,831	)	36.13
	Forfeited, canceled or expired	(24,383	)	79.69
	Outstanding at March 31, 2015	4,503,225		50.91
	The grant date fair value of stock option awards granted during the three months ended March 31, 2015 was $27.00 per share. The fair value of stock options granted to our employees is estimated on the date of the grant using the Black Scholes option-pricing model, which employs various assumptions.
	Restricted Stock Awards
	The following table presents a summary of restricted stock award activity for the three months ended March 31, 2015:
		Shares of Restricted Stock (“RS”)				Restricted Stock Units (“RSU”)
		Number of Shares		Weighted Average Grant Date Fair Value		Number of Units		Weighted Average Grant Date Fair Value
	Outstanding at December 31, 2014	515,073		$	77.23	411,093		$	37.3
	Granted	47,969		101.57		6,204		93.19
	RS’s Vested/RSU’s Issued	(68,011	)	63.45		—		—
	Forfeited	(15,374	)	77.07		(425	)	89.54
	Outstanding at March 31, 2015	479,657		81.63		416,872		38.08
	Performance Unit Awards
	The following table presents a summary of the activity for performance unit awards to be settled in shares for the three months ended March 31, 2015:
		Number of Units		Weighted Average Grant Date Fair Value
	Outstanding at December 31, 2014	5,791,825		$	0.88
	Granted	2,389,450		0.95
	Settled	(2,035,833	)	0.85
	Outstanding at March 31, 2015	6,145,442		0.92
	The performance unit awards granted during the three months ended March 31, 2015 have a grant date fair value of $0.95 per unit, as calculated using a Monte Carlo valuation model.
	MPLX Awards
	During the three months ended March 31, 2015, MPLX granted equity-based compensation awards under the MPLX LP 2012 Incentive Compensation Plan. The compensation expense for these awards is not material to our consolidated financial statements.

Commitments_and_Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies
	We are the subject of, or a party to, a number of pending or threatened legal actions, contingencies and commitments involving a variety of matters, including laws and regulations relating to the environment. Some of these matters are discussed below. For matters for which we have not recorded an accrued liability, we are unable to estimate a range of possible loss because the issues involved have not been fully developed through pleadings and discovery. However, the ultimate resolution of some of these contingencies could, individually or in the aggregate, be material.
	Environmental matters—We are subject to federal, state, local and foreign laws and regulations relating to the environment. These laws generally provide for control of pollutants released into the environment and require responsible parties to undertake remediation of hazardous waste disposal sites and certain other locations including presently or formerly owned or operated retail marketing sites. Penalties may be imposed for noncompliance.
	At March 31, 2015 and December 31, 2014, accrued liabilities for remediation totaled $177 million and $185 million, respectively. It is not presently possible to estimate the ultimate amount of all remediation costs that might be incurred or the penalties if any that may be imposed. Receivables for recoverable costs from certain states, under programs to assist companies in clean-up efforts related to underground storage tanks at presently or formerly owned or operated retail marketing sites, was $66 million and $67 million at March 31, 2015 and December 31, 2014, respectively.
	We are involved in a number of environmental enforcement matters arising in the ordinary course of business. While the outcome and impact on us cannot be predicted with certainty, management believes the resolution of these environmental matters will not, individually or collectively, have a material adverse effect on our consolidated results of operations, financial position or cash flows.
	Lawsuits—In May 2007, the Kentucky attorney general filed a lawsuit against us and Marathon Oil in state court in Franklin County, Kentucky for alleged violations of Kentucky’s emergency pricing and consumer protection laws following Hurricanes Katrina and Rita in 2005. The lawsuit alleges that we overcharged customers by $89 million during September and October 2005. The complaint seeks disgorgement of these sums, as well as penalties, under Kentucky’s emergency pricing and consumer protection laws. We are vigorously defending this litigation. We believe that this is the first lawsuit for damages and injunctive relief under the Kentucky emergency pricing laws to progress this far and it contains many novel issues. In May 2011, the Kentucky attorney general amended his complaint to include a request for immediate injunctive relief as well as unspecified damages and penalties related to our wholesale gasoline pricing in April and May 2011 under statewide price controls that were activated by the Kentucky governor on April 26, 2011 and which have since expired. The court denied the attorney general’s request for immediate injunctive relief, and the remainder of the 2011 claims likely will be resolved along with those dating from 2005. If the lawsuit is resolved unfavorably in its entirety, it could materially impact our consolidated results of operations, financial position or cash flows. However, management does not believe the ultimate resolution of this litigation will have a material adverse effect.
	We are a defendant in a number of other lawsuits and other proceedings arising in the ordinary course of business. While the ultimate outcome and impact to us cannot be predicted with certainty, we believe that the resolution of these other lawsuits and proceedings will not have a material adverse effect on our consolidated financial position, results of operations or cash flows.
	Guarantees—We have provided certain guarantees, direct and indirect, of the indebtedness of other companies. Under the terms of most of these guarantee arrangements, we would be required to perform should the guaranteed party fail to fulfill its obligations under the specified arrangements. In addition to these financial guarantees, we also have various performance guarantees related to specific agreements.
	Guarantees related to indebtedness of equity method investees—We hold interests in an offshore oil port, LOOP, and a crude oil pipeline system, LOCAP. Both LOOP and LOCAP have secured various project financings with throughput and deficiency agreements. Under the agreements, we are required to advance funds if the investees are unable to service their debt. Any such advances are considered prepayments of future transportation charges. The duration of the agreements vary but tend to follow the terms of the underlying debt, which extend through 2037. Our maximum potential undiscounted payments under these agreements for the debt principal totaled $172 million as of March 31, 2015.
	We hold an interest in a refined products pipeline through our investment in Centennial, and have guaranteed our portion of the payment of Centennial’s principal, interest and prepayment costs, if applicable, under a Master Shelf Agreement, which is scheduled to expire in 2024. The guarantee arose in order for Centennial to obtain adequate financing. Our maximum potential undiscounted payments under this agreement for debt principal totaled $37 million as of March 31, 2015.
	Marathon Oil indemnifications—In conjunction with our spinoff from Marathon Oil, we have entered into arrangements with Marathon Oil providing indemnities and guarantees with recorded values of $2 million as of March 31, 2015, which consist of unrecognized tax benefits related to MPC, its consolidated subsidiaries and the refining, marketing and transportation business operations prior to our spinoff which are not already reflected in the unrecognized tax benefits described in Note 11, and other contingent liabilities Marathon Oil may incur related to taxes. Furthermore, the separation and distribution agreement and other agreements with Marathon Oil to effect our spinoff provide for cross-indemnities between Marathon Oil and us. In general, Marathon Oil is required to indemnify us for any liabilities relating to Marathon Oil’s historical oil and gas exploration and production operations, oil sands mining operations and integrated gas operations, and we are required to indemnify Marathon Oil for any liabilities relating to Marathon Oil’s historical refining, marketing and transportation operations. The terms of these indemnifications are indefinite and the amounts are not capped.
	Other guarantees—We have entered into other guarantees with maximum potential undiscounted payments totaling $82 million as of March 31, 2015, which primarily consist of a commitment to contribute cash to an equity method investee for certain catastrophic events, up to $50 million per event, in lieu of procuring insurance coverage and leases of assets containing general lease indemnities and guaranteed residual values.
	General guarantees associated with dispositions – Over the years, we have sold various assets in the normal course of our business. Certain of the related agreements contain performance and general guarantees, including guarantees regarding inaccuracies in representations, warranties, covenants and agreements, and environmental and general indemnifications that require us to perform upon the occurrence of a triggering event or condition. These guarantees and indemnifications are part of the normal course of selling assets. We are typically not able to calculate the maximum potential amount of future payments that could be made under such contractual provisions because of the variability inherent in the guarantees and indemnities. Most often, the nature of the guarantees and indemnities is such that there is no appropriate method for quantifying the exposure because the underlying triggering event has little or no past experience upon which a reasonable prediction of the outcome can be based.
	Contractual commitments—At March 31, 2015, our contractual commitments to acquire property, plant and equipment and advance funds to equity method investees totaled $2.0 billion, which includes $520 million of contingent consideration associated with the acquisition of the Galveston Bay Refinery and Related Assets, $703 million for contributions to North Dakota Pipeline Company LLC and $148 million for contributions to Illinois Extension Pipeline. See Note 4 for additional information on our investments in the SAX project. See Note 14 for additional information on the contingent consideration.

Subsequent_Events

Subsequent Events	3 Months Ended
	Mar. 31, 2015
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events
	On April 29, 2015, our board of directors authorized the sale of its marine business to MPLX. Subject to the approval of the MPLX board of directors, the negotiation of a definitive agreement and the satisfaction of customary closing conditions, the transaction is expected to close in the next several months. Upon completion, we will account for this sale as a transaction between entities under common control and will not record a gain or loss.
	On April 29, 2015, our Board of Directors approved a two-for-one stock split in the form of a stock dividend, which will be distributed on June 10, 2015 to shareholders of record at the close of business on May 20, 2015. The total number of authorized shares of common stock and common stock par value per share remain unchanged. The stock split will require retroactive restatement of all historical share and per share data beginning in the second quarter ending June 30, 2015. All share and per share data information included in this report are presented on a pre-split basis. The pro forma basic earnings per share on a post-split basis were $1.63 and $0.34 for the three months ended March 31, 2015 and March 31, 2014, respectively, and diluted earnings per share were $1.62 and $0.34 for the same time periods. The stock is expected to trade on a split-adjusted basis beginning June 11, 2015.

Supplementary_Statistics

Supplementary Statistics	3 Months Ended
	Mar. 31, 2015
Text Block [Abstract]
Supplementary Statistics	Supplementary Statistics (Unaudited)
		Three Months Ended
		March 31,
	(In millions)	2015			2014
	Income from Operations by segment
	Refining & Marketing	$	1,316		$	362
	Speedway	168			58
	Pipeline Transportation(a)	67			72
	Items not allocated to segments:
	Corporate and other unallocated items(a)	(80		)	(67		)
	Pension settlement expenses	(1		)	(64		)
	Income from operations	$	1,470		$	361
	Capital Expenditures and Investments(b)
	Refining & Marketing	$	229		$	178
	Speedway	45			32
	Pipeline Transportation	81			130
	Corporate and Other(c)	29			31
	Total	$	384		$	371
	(a)	Corporate overhead expenses attributable to MPLX are included in the Pipeline Transportation segment. Corporate overhead expenses are not allocated to the Refining & Marketing and Speedway segments.
	(b)	Capital expenditures include changes in capital accruals, acquisitions and investments in affiliates.
	(c)	Includes capitalized interest of $8 million and $6 million for the three months ended March 31, 2015 and 2014, respectively.
	Supplementary Statistics (Unaudited)
		Three Months Ended
		March 31,
		2015			2014
	MPC Consolidated Refined Product Sales Volumes (thousands of barrels per day)(a)(b)	2,246			1,964
	Refining & Marketing Operating Statistics
	Refining & Marketing refined product sales volume (thousands of barrels per day)(c)	2,233			1,951
	Refining & Marketing gross margin (dollars per barrel)(d)	$	16.14		$	14.46
	Crude oil capacity utilization percent(e)	97			85
	Refinery throughputs (thousands of barrels per day):(f)
	Crude oil refined	1,672			1,450
	Other charge and blendstocks	180			200
	Total	1,852			1,650
	Sour crude oil throughput percent	56			49
	WTI-priced crude oil throughput percent	20			21
	Refined product yields (thousands of barrels per day):(f)
	Gasoline	911			837
	Distillates	553			514
	Propane	36			34
	Feedstocks and special products	298			220
	Heavy fuel oil	30			30
	Asphalt	50			43
	Total	1,878			1,678
	Refinery direct operating costs (dollars per barrel):(g)
	Planned turnaround and major maintenance	$	0.79		$	3.15
	Depreciation and amortization	1.42			1.55
	Other manufacturing(h)	4.26			5.95
	Total	$	6.47		$	10.65
	Refining & Marketing Operating Statistics By Region - Gulf Coast
	Refinery throughputs (thousands of barrels per day):(i)
	Crude oil refined	1,031			860
	Other charge and blendstocks	179			211
	Total	1,210			1,071
	Sour crude oil throughput percent	70			60
	WTI-priced crude oil throughput percent	5			3
	Refined product yields (thousands of barrels per day):(i)
	Gasoline	523			489
	Distillates	342			319
	Propane	25			21
	Feedstocks and special products	307			245
	Heavy fuel oil	15			15
	Asphalt	14			7
	Total	1,226			1,096
Refinery direct operating costs (dollars per barrel):(g)
Planned turnaround and major maintenance	$	0.8		$	3.83
Depreciation and amortization	1.14			1.25
Other manufacturing(h)	3.99			5.87
Total	$	5.93		$	10.95
Supplementary Statistics (Unaudited)
	Three Months Ended
	March 31,
	2015			2014
Refining & Marketing Operating Statistics By Region – Midwest
Refinery throughputs (thousands of barrels per day):(i)
Crude oil refined	641			590
Other charge and blendstocks	36			48
Total	677			638
Sour crude oil throughput percent	34			34
WTI-priced crude oil throughput percent	43			47
Refined product yields (thousands of barrels per day):(i)
Gasoline	388			348
Distillates	211			195
Propane	13			13
Feedstocks and special products	23			33
Heavy fuel oil	16			16
Asphalt	36			36
Total	687			641
Refinery direct operating costs (dollars per barrel):(g)
Planned turnaround and major maintenance	$	0.73		$	1.71
Depreciation and amortization	1.85			1.91
Other manufacturing(h)	4.51			5.54
Total	$	7.09		$	9.16
Speedway Operating Statistics(b)
Convenience stores at period-end	2,753			1,482
Gasoline and distillate sales (millions of gallons)	1,432			773
Gasoline and distillate gross margin (dollars per gallon)(j)	$	0.197		$	0.1156
Merchandise sales (in millions)	$	1,111		$	722
Merchandise gross margin (in millions)	$	311		$	192
Merchandise gross margin percent	28		%	26.5		%
Same store gasoline sales volume (period over period)(k)	(1.2		%)	(0.7		%)
Same store merchandise sales (period over period)(k)(l)	6.2		%	5.3		%
Pipeline Transportation Operating Statistics
Pipeline throughputs (thousands of barrels per day):(m)
Crude oil pipelines	1,221			1,171
Refined products pipelines	886			819
Total	2,107			1,990
(a)	Total average daily volumes of refined product sales to wholesale, branded and retail (Speedway segment) customers.
(b)	Includes the impact of Hess’ Retail Operations and Related Assets beginning on the September 30, 2014 acquisition date.
(c)	Includes intersegment sales.
(d)	Sales revenue less cost of refinery inputs and purchased products, divided by total refinery throughputs.
(e)	Based on calendar day capacity, which is an annual average that includes downtime for planned maintenance and other normal operating activities.
(f)	Excludes inter-refinery volumes of 35 mbpd and 59 mbpd for the three months ended March 31, 2015 and 2014, respectively.
(g)	Per barrel of total refinery throughputs.
(h)	Includes utilities, labor, routine maintenance and other operating costs.
(i)	Includes inter-refinery transfer volumes.
(j)	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.
(k)	Same store comparison includes only locations owned at least 13 months, and therefore excludes locations acquired from Hess.
(l)	Excludes cigarettes.
(m)	On owned common-carrier pipelines, excluding equity method investments.

Description_of_the_Business_an1

Description of the Business and Basis of Presentation (Policies)	3 Months Ended
	Mar. 31, 2015
Accounting Policies [Abstract]
Use of estimates	These interim consolidated financial statements are unaudited; however, in the opinion of our management, these statements reflect all adjustments necessary for a fair statement of the results for the periods reported. All such adjustments are of a normal, recurring nature unless otherwise disclosed. These interim consolidated financial statements, including the notes, have been prepared in accordance with the rules of the Securities and Exchange Commission applicable to interim period financial statements and do not include all of the information and disclosures required by United States generally accepted accounting principles (“U.S. GAAP”) for complete financial statements.
Inventories	Inventories are carried at the lower of cost or market value. The cost of inventories of crude oil and refinery feedstocks, refined products and merchandise is determined primarily under the last-in, first-out (“LIFO”) method.
Derivative instruments	Derivatives that are not designated as accounting hedges may include commodity derivatives used to hedge price risk on (1) inventories, (2) fixed price sales of refined products, (3) the acquisition of foreign-sourced crude oil and (4) the acquisition of ethanol for blending with refined products.
Stock-based compensation arrangements	The fair value of stock options granted to our employees is estimated on the date of the grant using the Black Scholes option-pricing model, which employs various assumptions.

Acquisitions_and_Investments_T

Acquisitions and Investments (Tables)	3 Months Ended
	Mar. 31, 2015
Business Combinations [Abstract]
Business Acquisition, Pro Forma Information [Table Text Block]	The following unaudited pro forma financial information presents consolidated results assuming Hess’ Retail Operations and Related Assets acquisition occurred on January 1, 2013. The pro forma financial information does not give effect to potential synergies that could result from the acquisition and is not necessarily indicative of the results of future operations.
		Three Months Ended
		March 31,
	(In millions, except per share data)	2014
	Sales and other operating revenues (including consumer excise taxes)	$	26,017
	Net income attributable to MPC	182
	Net income attributable to MPC per share – basic	$	0.62
	Net income attributable to MPC per share – diluted	0.62

Related_Party_Transactions_Tab

Related Party Transactions (Tables)	3 Months Ended
	Mar. 31, 2015
Related Party Transactions [Abstract]
Purchases From Related Parties	Purchases from related parties were as follows:
		Three Months Ended
		March 31,
	(In millions)	2015		2014
	Centennial	$	—	$	9
	Explorer	7		13
	LOCAP	5		5
	LOOP	13		53
	TAAE	13		16
	TACE	16		27
	TAME	20		34
	Other equity method investees	2		2
	Total	$	76	$	159
Receivables From Related Parties	Receivables from related parties, which are included in receivables, less allowance for doubtful accounts on the consolidated balance sheets, were as follows:
	(In millions)	March 31,		December 31,
		2015		2014
	Centennial	$	—	$	2
	Explorer	—		2
	TAME	—		3
	Other equity method investees	1		—
	Total	$	1	$	7
Payables To Related Parties	Payables to related parties, which are included in accounts payable on the consolidated balance sheets, were as follows:
	(In millions)	March 31,		December 31,
		2015		2014
	Explorer	$	3	$	3
	LOCAP	2		2
	LOOP	5		4
	TAAE	1		2
	TACE	1		2
	TAME	2		5
	Total	$	14	$	18

Income_per_Common_Share_Tables

Income per Common Share (Tables)	3 Months Ended
	Mar. 31, 2015
Earnings Per Share [Abstract]
Summary of Earnings Per Common Share
		Three Months Ended
		March 31,
	(In millions, except per share data)	2015		2014
	Basic earnings per share:
	Allocation of earnings:
	Net income attributable to MPC	$	891	$	199
	Income allocated to participating securities	1		—
	Income available to common stockholders – basic	$	890	$	199
	Weighted average common shares outstanding	273		293
	Basic earnings per share	$	3.26	$	0.68
	Diluted earnings per share:
	Allocation of earnings:
	Net income attributable to MPC	$	891	$	199
	Income allocated to participating securities	1		—
	Income available to common stockholders – diluted	$	890	$	199
	Weighted average common shares outstanding	273		293
	Effect of dilutive securities	2		2
	Weighted average common shares, including dilutive effect	275		295
	Diluted earnings per share	$	3.24	$	0.67

Equity_Tables

Equity (Tables)	3 Months Ended
	Mar. 31, 2015
Equity [Abstract]
Share Repurchases Transacted Through ASR Programs and Open Market Transactions	Total share repurchases were as follows for the three months ended March 31, 2015 and 2014:
		Three Months Ended
		March 31,
	(In millions, except per share data)	2015		2014
	Number of shares repurchased	2		8
	Cash paid for shares repurchased	$	209	$	689
	Effective average cost per delivered share	$	95.03	$	87.6

Segment_Information_Tables

Segment Information (Tables)	3 Months Ended
	Mar. 31, 2015
Segment Reporting [Abstract]
Income From Operations Attributable To Operating Segments
	(In millions)	Refining & Marketing			Speedway			Pipeline Transportation		Total
	Three Months Ended March 31, 2015
	Revenues:
	Customer	$	12,644		$	4,531		$	16	$	17,191
	Intersegment(a)	2,733			—			134		2,867
	Segment revenues	$	15,377		$	4,531		$	150	$	20,058
	Segment income from operations(b)	$	1,316		$	168		$	67	$	1,551
	Income from equity method investments	6			—			9		15
	Depreciation and amortization(c)	267			63			20		350
	Capital expenditures and investments(d)	229			45			81		355
	(In millions)	Refining & Marketing			Speedway			Pipeline Transportation		Total
	Three Months Ended March 31, 2014
	Revenues:
	Customer	$	19,810		$	3,458		$	17	$	23,285
	Intersegment(a)	2,233			1			129		2,363
	Segment revenues	$	22,043		$	3,459		$	146	$	25,648
	Segment income from operations(b)	$	362		$	58		$	72	$	492
	Income from equity method investments	24			—			11		35
	Depreciation and amortization(c)	261			28			19		308
	Capital expenditures and investments(d)	178			32			130		340
	(a)	Management believes intersegment transactions were conducted under terms comparable to those with unaffiliated parties.
	(b)	Corporate overhead expenses attributable to MPLX are included in the Pipeline Transportation segment. Corporate overhead expenses are not allocated to the Refining & Marketing and Speedway segments.
	(c)	Differences between segment totals and MPC totals represent amounts related to unallocated items and are included in “Items not allocated to segments” in the reconciliation below.
	(d)	Capital expenditures include changes in capital accruals, acquisitions and investments in affiliates.
Reconciliation Of Segment Income From Operations To Income Before Income Taxes	The following reconciles segment income from operations to income before income taxes as reported in the consolidated statements of income:
		Three Months Ended
		March 31,
	(In millions)	2015			2014
	Segment income from operations	$	1,551		$	492
	Items not allocated to segments:
	Corporate and other unallocated items(a)(b)	(80		)	(67		)
	Pension settlement expenses(c)	(1		)	(64		)
	Net interest and other financial income (costs)	(81		)	(46		)
	Income before income taxes	$	1,389		$	315
	(a)	Corporate and other unallocated items consists primarily of MPC’s corporate administrative expenses and costs related to certain non-operating assets.
	(b)	Corporate overhead expenses attributable to MPLX are included in the Pipeline Transportation segment. Corporate overhead expenses are not allocated to the Refining & Marketing and Speedway segments.
	(c)	See Note 19.
Reconciliation Of Segment Capital Expenditures And Investments To Total Capital Expenditures	The following reconciles segment capital expenditures and investments to total capital expenditures:
		Three Months Ended
		March 31,
	(In millions)	2015			2014
	Segment capital expenditures and investments	$	355		$	340
	Less: Investments in equity method investees	42			123
	Plus: Items not allocated to segments:
	Capital expenditures not allocated to segments	21			25
	Capitalized interest	8			6
	Total capital expenditures(a)	$	342		$	248
	(a)	Capital expenditures include changes in capital accruals. See Note 17 for a reconciliation of total capital expenditures to additions to property, plant and equipment as reported in the consolidated statements of cash flows.

Other_Items_Tables

Other Items (Tables)	3 Months Ended
	Mar. 31, 2015
Other Income and Expenses [Abstract]
Net Interest And Other Financial Income (Costs)	Net interest and other financial income (costs) was:
		Three Months Ended
		March 31,
	(In millions)	2015			2014
	Interest income	$	1		$	2
	Interest expense	(80		)	(49		)
	Interest capitalized	8			6
	Other financial costs	(10		)	(5		)
	Net interest and other financial income (costs)	$	(81	)	$	(46	)

Inventories_Tables

Inventories (Tables)	3 Months Ended
	Mar. 31, 2015
Inventory Disclosure [Abstract]
Summary Of Inventories
	(In millions)	March 31,		December 31,
		2015		2014
	Crude oil and refinery feedstocks	$	2,107	$	2,219
	Refined products	2,862		2,955
	Materials and supplies	302		302
	Merchandise	166		166
	Total (at cost)	$	5,437	$	5,642

Property_Plant_and_Equipment_T

Property, Plant and Equipment (Tables)	3 Months Ended
	Mar. 31, 2015
Property, Plant and Equipment [Abstract]
Summary Of Property, Plant And Equipment
	(In millions)	March 31,		December 31,
		2015		2014
	Refining & Marketing	$	18,225	$	18,001
	Speedway	4,674		4,639
	Pipeline Transportation	2,083		2,044
	Corporate and Other	639		618
	Total	25,621		25,302
	Less accumulated depreciation	9,380		9,041
	Property, plant and equipment, net	$	16,241	$	16,261

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2015
Fair Value Disclosures [Abstract]
Assets and Liabilities Accounted for at Fair Value on Recurring Basis	The following tables present assets and liabilities accounted for at fair value on a recurring basis as of March 31, 2015 and December 31, 2014 by fair value hierarchy level. We have elected to offset the fair value amounts recognized for multiple derivative contracts executed with the same counterparty, including any related cash collateral as shown below; however, fair value amounts by hierarchy level are presented on a gross basis in the following tables.
		March 31, 2015
		Fair Value Hierarchy
	(In millions)	Level 1		Level 2		Level 3		Netting and Collateral(a)			Net Carrying Value on Balance Sheet(b)		Collateral Pledged Not Offset
	Commodity derivative instruments, assets	$	94	$	—	$	—	$	(66	)	$	28	$	40
	Other assets	2		—		—		N/A			2		—
	Total assets at fair value	$	96	$	—	$	—	$	(66	)	$	30	$	40
	Commodity derivative instruments, liabilities	$	79	$	—	$	—	$	(79	)	$	—	$	—
	Contingent consideration, liability(c)	—		—		490		N/A			490		—
	Total liabilities at fair value	$	79	$	—	$	490	$	(79	)	$	490	$	—
		December 31, 2014
		Fair Value Hierarchy
	(In millions)	Level 1		Level 2		Level 3		Netting and Collateral(a)			Net Carrying Value on Balance Sheet(b)		Collateral Pledged Not Offset
	Commodity derivative instruments, assets	$	317	$	—	$	—	$	(258	)	$	59	$	—
	Other assets	2		—		—		N/A			2		—
	Total assets at fair value	$	319	$	—	$	—	$	(258	)	$	61	$	—
	Commodity derivative instruments, liabilities	$	180	$	—	$	—	$	(180	)	$	—	$	—
	Contingent consideration, liability(c)	—		—		478		N/A			478		—
	Total liabilities at fair value	$	180	$	—	$	478	$	(180	)	$	478	$	—
	(a)	Represents the impact of netting assets, liabilities and cash collateral when a legal right of offset exists. As of March 31, 2015, cash collateral of $13 million was netted with the mark-to-market derivative liabilities. As of December 31, 2014, $78 million was netted with mark-to-market derivative assets.
	(b)	We have no derivative contracts that are subject to master netting arrangements that are reflected gross on the balance sheet.
	(c)	Includes $189 million and $174 million classified as current at March 31, 2015 and December 31, 2014, respectively.
Reconciliation of Net Beginning and Ending Balances Recorded for Net Assets and Liabilities Classified as Level 3	The following is a reconciliation of the beginning and ending balances recorded for liabilities classified as Level 3 in the fair value hierarchy.
		Three Months Ended
		March 31,
	(In millions)	2015		2014
	Beginning balance	$	478	$	625
	Unrealized and realized losses included in net income	12		14
	Ending balance	$	490	$	639
Financial Instruments at Fair Value, Excluding Derivative Financial Instruments and Contingent Consideration	The following table summarizes financial instruments on the basis of their nature, characteristics and risk at March 31, 2015 and December 31, 2014, excluding the derivative financial instruments and contingent consideration reported above.
		March 31, 2015				December 31, 2014
	(In millions)	Fair Value		Carrying Value		Fair Value		Carrying Value
	Financial assets:
	Investments	$	27	$	2	$	26	$	2
	Other	31		30		32		32
	Total financial assets	$	58	$	32	$	58	$	34
	Financial liabilities:
	Long-term debt(a)	$	6,843	$	6,377	$	6,571	$	6,265
	Deferred credits and other liabilities	20		20		17		17
	Total financial liabilities	$	6,863	$	6,397	$	6,588	$	6,282
	(a)	Excludes capital leases

Derivatives_Tables

Derivatives (Tables)	3 Months Ended
	Mar. 31, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Classification of Fair Values of Derivative Instruments, Excluding Cash Collateral	The following table presents the gross fair values of derivative instruments, excluding cash collateral, and where they appear on the consolidated balance sheets as of March 31, 2015 and December 31, 2014:
		March 31, 2015
	(In millions)	Asset				Liability			Balance Sheet Location
	Commodity derivatives	$	94			$	79		Other current assets
		December 31, 2014
	(In millions)	Asset				Liability			Balance Sheet Location
	Commodity derivatives	$	317			$	180		Other current assets
Open Commodity Derivative Contracts	The table below summarizes open commodity derivative contracts as of March 31, 2015.
		Position		Total Barrels (In thousands)
	Crude oil(a)
	Exchange-traded	Long		11,454
	Exchange-traded	Short		(23,733	)
	Refined Products(b)
	Exchange-traded	Long		3,378
	Exchange-traded	Short		(2,402	)
	(a)	96 percent of these contracts expire in the second quarter of 2015.
	(b)	100 percent of these contracts expire in the second quarter of 2015.
Effect of Commodity Derivative Instruments in Statements of Income	The following table summarizes the effect of all commodity derivative instruments in our consolidated statements of income:
		Gain (Loss)
	(In millions)	Three Months Ended March 31,
	Income Statement Location	2015				2014
	Sales and other operating revenues	$	14			$	10
	Cost of revenues	45				(61		)
	Total	$	59			$	(51	)

Debt_Tables

Debt (Tables)	3 Months Ended
	Mar. 31, 2015
Debt Disclosure [Abstract]
Outstanding Borrowings	Our outstanding borrowings at March 31, 2015 and December 31, 2014 consisted of the following:
	(In millions)	March 31,			December 31,
		2015			2014
	Marathon Petroleum Corporation:
	Revolving credit agreement due 2017	$	—		$	—
	Term loan agreement due 2019	700			700
	3.500% senior notes due March 1, 2016	750			750
	5.125% senior notes due March 1, 2021	1,000			1,000
	3.625% senior notes due September 15, 2024	750			750
	6.500% senior notes due March 1, 2041	1,250			1,250
	4.750% senior notes due September 15, 2044	800			800
	5.000% senior notes due September 15, 2054	400			400
	Consolidated subsidiaries:
	Capital lease obligations due 2015-2028	366			372
	MPLX bank revolving credit facility due 2019	—			385
	MPLX term loan facility due 2019	250			250
	MPLX 4.000% senior notes due February 15, 2025	500			—
	Trade receivables securitization facility due 2016	—			—
	Total	6,766			6,657
	Unamortized discount	(28		)	(26		)
	Fair value adjustments(a)	5			6
	Amounts due within one year	(776		)	(27		)
	Total long-term debt due after one year	$	5,967		$	6,610
	(a)	The $20 million gain on the termination of our interest rate swap agreements in 2012 is being amortized over the remaining life of the 3.50 percent senior notes.

Supplemental_Cash_Flow_Informa1

Supplemental Cash Flow Information (Tables)	3 Months Ended
	Mar. 31, 2015
Supplemental Cash Flow Elements [Abstract]
Summary of Supplemental Cash Flow Information
		Three Months Ended
		March 31,
	(In millions)	2015			2014
	Net cash provided by operating activities included:
	Interest paid (net of amounts capitalized)	$	128		$	80
	Net income taxes paid to taxing authorities	160			5
Reconciliation of Additions to Property, Plant and Equipment to Total Capital Expenditures	The consolidated statements of cash flows exclude changes to the consolidated balance sheets that did not affect cash. The following is a reconciliation of additions to property, plant and equipment to total capital expenditures:
		Three Months Ended
		March 31,
	(In millions)	2015			2014
	Additions to property, plant and equipment	$	389		$	267
	Decrease in capital accruals	(47		)	(19		)
	Total capital expenditures	$	342		$	248

Accumulated_Other_Comprehensiv1

Accumulated Other Comprehensive Loss (Tables)	3 Months Ended
	Mar. 31, 2015
Equity [Abstract]
Changes in Accumulated Other Comprehensive Loss by Component	The following table shows the changes in accumulated other comprehensive loss by component. Amounts in parentheses indicate debits.
	(In millions)	Pension Benefits			Other Benefits			Gain on Cash Flow Hedge		Workers Compensation		Total
	Balance as of December 31, 2013	$	(161	)	$	(50	)	$	4	$	3	$	(204	)
	Other comprehensive income (loss) before reclassifications	(43		)	1			—		—		(42		)
	Amounts reclassified from accumulated other comprehensive loss:
	Amortization – prior service credit(a)	(12		)	(1		)	—		—		(13		)
	– actuarial loss(a)	13			1			—		—		14
	– settlement loss(a)	64			—			—		—		64
	Tax effect	(24		)	—			—		—		(24		)
	Other comprehensive income (loss)	(2		)	1			—		—		(1		)
	Balance as of March 31, 2014	$	(163	)	$	(49	)	$	4	$	3	$	(205	)
	(In millions)	Pension Benefits			Other Benefits			Gain on Cash Flow Hedge		Workers Compensation		Total
	Balance as of December 31, 2014	$	(217	)	$	(104	)	$	4	$	4	$	(313	)
	Other comprehensive loss before reclassifications	(1		)	(1		)	—		—		(2		)
	Amounts reclassified from accumulated other comprehensive loss:
	Amortization – prior service credit(a)	(12		)	(1		)	—		—		(13		)
	– actuarial loss(a)	13			3			—		—		16
	– settlement loss(a)	1			—			—		—		1
	Tax effect	(1		)	(1		)	—		—		(2		)
	Other comprehensive income (loss)	—			—			—		—		—
	Balance as of March 31, 2015	$	(217	)	$	(104	)	$	4	$	4	$	(313	)
	(a)	These accumulated other comprehensive loss components are included in the computation of net periodic benefit cost. See Note 19.

Defined_Benefit_Pension_and_Ot1

Defined Benefit Pension and Other Postretirement Plans (Tables)	3 Months Ended
	Mar. 31, 2015
Compensation and Retirement Disclosure [Abstract]
Components of Net Periodic Benefit Costs	The following summarizes the components of net periodic benefit costs:
		Three Months Ended March 31,
		Pension Benefits						Other Benefits
	(In millions)	2015			2014			2015			2014
	Components of net periodic benefit cost:
	Service cost	$	23		$	23		$	8		$	7
	Interest cost	18			20			8			8
	Expected return on plan assets	(26		)	(28		)	—			—
	Amortization – prior service credit	(12		)	(12		)	(1		)	(1		)
	– actuarial loss	13			13			3			1
	– settlement loss	1			64			—			—
	Net periodic benefit cost	$	17		$	80		$	18		$	15

StockBased_Compensation_Plans_

Stock-Based Compensation Plans (Tables)	3 Months Ended
	Mar. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of Stock Option Award Activity	The following table presents a summary of our stock option award activity for the three months ended March 31, 2015:
		Number of Shares		Weighted Average Exercise Price
	Outstanding at December 31, 2014	4,751,438		$	45.47
	Granted	354,001		101.78
	Exercised	(577,831	)	36.13
	Forfeited, canceled or expired	(24,383	)	79.69
	Outstanding at March 31, 2015	4,503,225		50.91
Summary of Restricted Stock Award Activity	The following table presents a summary of restricted stock award activity for the three months ended March 31, 2015:
		Shares of Restricted Stock (“RS”)				Restricted Stock Units (“RSU”)
		Number of Shares		Weighted Average Grant Date Fair Value		Number of Units		Weighted Average Grant Date Fair Value
	Outstanding at December 31, 2014	515,073		$	77.23	411,093		$	37.3
	Granted	47,969		101.57		6,204		93.19
	RS’s Vested/RSU’s Issued	(68,011	)	63.45		—		—
	Forfeited	(15,374	)	77.07		(425	)	89.54
	Outstanding at March 31, 2015	479,657		81.63		416,872		38.08
Schedule of Performance Unit Awards	The following table presents a summary of the activity for performance unit awards to be settled in shares for the three months ended March 31, 2015:
		Number of Units		Weighted Average Grant Date Fair Value
	Outstanding at December 31, 2014	5,791,825		$	0.88
	Granted	2,389,450		0.95
	Settled	(2,035,833	)	0.85
	Outstanding at March 31, 2015	6,145,442		0.92

Supplementary_Statistics_Table

Supplementary Statistics (Tables)	3 Months Ended
	Mar. 31, 2015
Text Block [Abstract]
Supplementary Statistics	Supplementary Statistics (Unaudited)
		Three Months Ended
		March 31,
	(In millions)	2015			2014
	Income from Operations by segment
	Refining & Marketing	$	1,316		$	362
	Speedway	168			58
	Pipeline Transportation(a)	67			72
	Items not allocated to segments:
	Corporate and other unallocated items(a)	(80		)	(67		)
	Pension settlement expenses	(1		)	(64		)
	Income from operations	$	1,470		$	361
	Capital Expenditures and Investments(b)
	Refining & Marketing	$	229		$	178
	Speedway	45			32
	Pipeline Transportation	81			130
	Corporate and Other(c)	29			31
	Total	$	384		$	371
	(a)	Corporate overhead expenses attributable to MPLX are included in the Pipeline Transportation segment. Corporate overhead expenses are not allocated to the Refining & Marketing and Speedway segments.
	(b)	Capital expenditures include changes in capital accruals, acquisitions and investments in affiliates.
	(c)	Includes capitalized interest of $8 million and $6 million for the three months ended March 31, 2015 and 2014, respectively.
Operating Statistics	Supplementary Statistics (Unaudited)
		Three Months Ended
		March 31,
		2015			2014
	MPC Consolidated Refined Product Sales Volumes (thousands of barrels per day)(a)(b)	2,246			1,964
	Refining & Marketing Operating Statistics
	Refining & Marketing refined product sales volume (thousands of barrels per day)(c)	2,233			1,951
	Refining & Marketing gross margin (dollars per barrel)(d)	$	16.14		$	14.46
	Crude oil capacity utilization percent(e)	97			85
	Refinery throughputs (thousands of barrels per day):(f)
	Crude oil refined	1,672			1,450
	Other charge and blendstocks	180			200
	Total	1,852			1,650
	Sour crude oil throughput percent	56			49
	WTI-priced crude oil throughput percent	20			21
	Refined product yields (thousands of barrels per day):(f)
	Gasoline	911			837
	Distillates	553			514
	Propane	36			34
	Feedstocks and special products	298			220
	Heavy fuel oil	30			30
	Asphalt	50			43
	Total	1,878			1,678
	Refinery direct operating costs (dollars per barrel):(g)
	Planned turnaround and major maintenance	$	0.79		$	3.15
	Depreciation and amortization	1.42			1.55
	Other manufacturing(h)	4.26			5.95
	Total	$	6.47		$	10.65
	Refining & Marketing Operating Statistics By Region - Gulf Coast
	Refinery throughputs (thousands of barrels per day):(i)
	Crude oil refined	1,031			860
	Other charge and blendstocks	179			211
	Total	1,210			1,071
	Sour crude oil throughput percent	70			60
	WTI-priced crude oil throughput percent	5			3
	Refined product yields (thousands of barrels per day):(i)
	Gasoline	523			489
	Distillates	342			319
	Propane	25			21
	Feedstocks and special products	307			245
	Heavy fuel oil	15			15
	Asphalt	14			7
	Total	1,226			1,096
	Refinery direct operating costs (dollars per barrel):(g)
	Planned turnaround and major maintenance	$	0.8		$	3.83
	Depreciation and amortization	1.14			1.25
	Other manufacturing(h)	3.99			5.87
	Total	$	5.93		$	10.95
	Supplementary Statistics (Unaudited)
		Three Months Ended
		March 31,
		2015			2014
	Refining & Marketing Operating Statistics By Region – Midwest
	Refinery throughputs (thousands of barrels per day):(i)
	Crude oil refined	641			590
	Other charge and blendstocks	36			48
	Total	677			638
	Sour crude oil throughput percent	34			34
	WTI-priced crude oil throughput percent	43			47
	Refined product yields (thousands of barrels per day):(i)
	Gasoline	388			348
	Distillates	211			195
	Propane	13			13
	Feedstocks and special products	23			33
Heavy fuel oil	16			16
Asphalt	36			36
Total	687			641
Refinery direct operating costs (dollars per barrel):(g)
Planned turnaround and major maintenance	$	0.73		$	1.71
Depreciation and amortization	1.85			1.91
Other manufacturing(h)	4.51			5.54
Total	$	7.09		$	9.16
Speedway Operating Statistics(b)
Convenience stores at period-end	2,753			1,482
Gasoline and distillate sales (millions of gallons)	1,432			773
Gasoline and distillate gross margin (dollars per gallon)(j)	$	0.197		$	0.1156
Merchandise sales (in millions)	$	1,111		$	722
Merchandise gross margin (in millions)	$	311		$	192
Merchandise gross margin percent	28		%	26.5		%
Same store gasoline sales volume (period over period)(k)	(1.2		%)	(0.7		%)
Same store merchandise sales (period over period)(k)(l)	6.2		%	5.3		%
Pipeline Transportation Operating Statistics
Pipeline throughputs (thousands of barrels per day):(m)
Crude oil pipelines	1,221			1,171
Refined products pipelines	886			819
Total	2,107			1,990
(a)	Total average daily volumes of refined product sales to wholesale, branded and retail (Speedway segment) customers.
(b)	Includes the impact of Hess’ Retail Operations and Related Assets beginning on the September 30, 2014 acquisition date.
(c)	Includes intersegment sales.
(d)	Sales revenue less cost of refinery inputs and purchased products, divided by total refinery throughputs.
(e)	Based on calendar day capacity, which is an annual average that includes downtime for planned maintenance and other normal operating activities.
(f)	Excludes inter-refinery volumes of 35 mbpd and 59 mbpd for the three months ended March 31, 2015 and 2014, respectively.
(g)	Per barrel of total refinery throughputs.
(h)	Includes utilities, labor, routine maintenance and other operating costs.
(i)	Includes inter-refinery transfer volumes.
(j)	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.
(k)	Same store comparison includes only locations owned at least 13 months, and therefore excludes locations acquired from Hess.
(l)	Excludes cigarettes.
(m)	On owned common-carrier pipelines, excluding equity method investments.

MPLX_LP_Detail

MPLX LP (Detail) (USD $)	0 Months Ended			3 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 01, 2014	Mar. 01, 2014	Dec. 08, 2014	Mar. 31, 2015	Dec. 10, 2014	Feb. 12, 2015
MPLX Pipe Line Holdings LP
Noncontrolling Interest [Line Items]
Additional interest sold	30.50%	13.00%
Proceeds from sale of ownership interest	$600	$310
MPLX LP
Noncontrolling Interest [Line Items]
Proceeds from issuance of common limited partners units			221
General partners' capital account, units issued					130,000
General partners' contributed capital					9
MPLX LP | MPLX Revolver
Noncontrolling Interest [Line Items]
Cash paid for acquisition	600	270
MPLX LP | 4.000% senior notes due two thousand twenty five | Senior Notes
Noncontrolling Interest [Line Items]
Debt instrument, face amount						500
Debt instrument, interest rate				4.00%
Debt instrument, maturity date				15-Feb-25
MPLX LP | Cash and cash equivalents
Noncontrolling Interest [Line Items]
Cash paid for acquisition		40
MPLX LP | General Partner and Limited Partner
Noncontrolling Interest [Line Items]
MPC's partnership interest in MPLX (in percentage)				71.50%
MPLX LP | General Partner
Noncontrolling Interest [Line Items]
MPC's partnership interest in MPLX (in percentage)				2.00%
MPLX LP | Limited Partner
Noncontrolling Interest [Line Items]
Equity interest issued or issuable, number of shares	2,900,000
Equity interest issued or issuable, value assigned	$200
Units sold in public offering			3,500,000
Shares issued, price per share			$66.68

Acquisitions_and_Investments_A

Acquisitions and Investments (Acquisition of Hess' Retail Operations and Related Assets) (Details) (USD $)	0 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Mar. 31, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Goodwill		$1,566	$1,566
Hess' Retail Operations and Related Assets
Business Acquisition [Line Items]
Allocation of space on Colonial Pipeline (in barrels per day)	40,000
Cash paid for acquisition	2,820
Net working capital adjustment estimate	-3
Goodwill	$629

Acquisitions_and_Investments_S

Acquisitions and Investments (Schedule of Acquisition Related Pro Forma Financial Information) (Details) (USD $)	3 Months Ended
In Millions, except Per Share data, unless otherwise specified	Mar. 31, 2014
Business Combinations [Abstract]
Sales and other operating revenues (including consumer excise taxes)	$26,017
Net income attributable to MPC	$182
Net income attributable to MPC per share – basic	$0.62
Net income attributable to MPC per share – diluted	$0.62

Acquisitions_and_Investments_A1

Acquisitions and Investments (Acquisition of Biodiesel Facility) (Details) (Felda Iffco Sdn Bhd [Member], USD $)	1 Months Ended
In Millions, unless otherwise specified	Apr. 30, 2014	Apr. 01, 2014
		gallons_per_year
Felda Iffco Sdn Bhd [Member]
Business Acquisition [Line Items]
Cash paid for acquisition	$40
Plant capacity volume		60,000,000

Acquisitions_and_Investments_I

Acquisitions and Investments (Investments in Pipeline Companies) (Details) (USD $)	3 Months Ended	9 Months Ended	0 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2015	Mar. 04, 2014	Jul. 01, 2014
Illinois Extension Pipeline Company LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments, ownership percentage				35.00%
Cash paid to acquire equity method investments	$37	$157
Explorer
Schedule of Equity Method Investments [Line Items]
Equity method investments, ownership percentage	25.00%	25.00%
Cash paid to acquire equity method investments			$77
Ownership percentage acquired			7.00%

Variable_Interest_Entity_Detai

Variable Interest Entity (Details) (Illinois Extension Pipeline Company LLC, Variable Interest Entity, Not Primary Beneficiary, USD $)	Mar. 31, 2015
In Millions, unless otherwise specified
Illinois Extension Pipeline Company LLC | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
VIE, maximum loss exposure, amount	$157

Related_Party_Transactions_Add

Related Party Transactions - Additional Information (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Centennial
Related Party Transaction [Line Items]
Equity method investments, ownership percentage	50.00%
Explorer
Related Party Transaction [Line Items]
Equity method investments, ownership percentage	25.00%
LOCAP
Related Party Transaction [Line Items]
Equity method investments, ownership percentage	59.00%
LOOP
Related Party Transaction [Line Items]
Equity method investments, ownership percentage	51.00%
TAAE
Related Party Transaction [Line Items]
Equity method investments, ownership percentage	43.00%
TACE
Related Party Transaction [Line Items]
Equity method investments, ownership percentage	60.00%
TAME
Related Party Transaction [Line Items]
Equity method investments, ownership percentage	67.00%
Other equity method investees
Related Party Transaction [Line Items]
Sales to related parties	$1	$2

Related_Party_Transactions_Pur

Related Party Transactions - Purchases from Related Parties (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Related Party Transaction [Line Items]
Purchases from related parties	$76	$159
Centennial
Related Party Transaction [Line Items]
Purchases from related parties	0	9
Explorer
Related Party Transaction [Line Items]
Purchases from related parties	7	13
LOCAP
Related Party Transaction [Line Items]
Purchases from related parties	5	5
LOOP
Related Party Transaction [Line Items]
Purchases from related parties	13	53
TAAE
Related Party Transaction [Line Items]
Purchases from related parties	13	16
TACE
Related Party Transaction [Line Items]
Purchases from related parties	16	27
TAME
Related Party Transaction [Line Items]
Purchases from related parties	20	34
Other equity method investees
Related Party Transaction [Line Items]
Purchases from related parties	$2	$2

Related_Party_Transactions_Rec

Related Party Transactions - Receivables From Related Parties (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Related Party Transaction [Line Items]
Current receivables from related parties	$1	$7
Centennial
Related Party Transaction [Line Items]
Current receivables from related parties	0	2
Explorer
Related Party Transaction [Line Items]
Current receivables from related parties	0	2
TAME
Related Party Transaction [Line Items]
Current receivables from related parties	0	3
Other equity method investees
Related Party Transaction [Line Items]
Current receivables from related parties	$1	$0

Related_Party_Transactions_Pay

Related Party Transactions - Payables To Related Parties (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Related Party Transaction [Line Items]
Payables to related parties	$14	$18
Explorer
Related Party Transaction [Line Items]
Payables to related parties	3	3
LOCAP
Related Party Transaction [Line Items]
Payables to related parties	2	2
LOOP
Related Party Transaction [Line Items]
Payables to related parties	5	4
TAAE
Related Party Transaction [Line Items]
Payables to related parties	1	2
TACE
Related Party Transaction [Line Items]
Payables to related parties	1	2
TAME
Related Party Transaction [Line Items]
Payables to related parties	$2	$5

Income_Per_Common_Share_Summar

Income Per Common Share - Summary of Earnings Per Common Share (Detail) (USD $)	3 Months Ended
In Millions, except Per Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Basic earnings per share:
Net income attributable to MPC	$891	$199
Income allocated to participating securities	1	0
Income available to common stockholders – basic	890	199
Weighted average common shares outstanding (in shares)	273	293
Basic (in USD per share)	$3.26	$0.68
Diluted earnings per share:
Net income attributable to MPC	891	199
Income allocated to participating securities	1	0
Income available to common stockholders – diluted	$890	$199
Weighted average common shares outstanding (in shares)	273	293
Effect of dilutive securities (in shares)	2	2
Weighted average common shares, including dilutive effect (in shares)	275	295
Diluted (in USD per share)	$3.24	$0.67

Equity_Additional_Information_

Equity - Additional Information (Detail) (USD $)	3 Months Ended		39 Months Ended	1 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Apr. 30, 2015
Equity, Class of Treasury Stock [Line Items]
Stock repurchase plan authorized amount	$8,000,000,000		$8,000,000,000
Cash paid for shares repurchased	209,000,000	689,000,000	6,480,000,000
Stock repurchase plan remaining authorized amount	1,520,000,000		1,520,000,000
Number of shares repurchased	2,000,000	8,000,000	92,000,000
Effective average cost per delivered share	$95.03	$87.60	$70.95
Scenario, Forecast
Equity, Class of Treasury Stock [Line Items]
Cash paid for shares repurchased				$9,000,000
Number of shares repurchased				88,394

Equity_Share_Repurchases_Detai

Equity - Share Repurchases (Detail) (USD $)	3 Months Ended		39 Months Ended
In Millions, except Per Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015
Equity [Abstract]
Number of shares repurchased	2	8	92
Cash paid for shares repurchased	$209	$689	$6,480
Effective average cost per delivered share	$95.03	$87.60	$70.95

Segment_Information_Additional

Segment Information - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2015
	Segment
Segment Reporting [Abstract]
Number of reportable segments	3

Segment_Information_Income_Fro

Segment Information - Income From Operations Attributable To Operating Segments (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015		Mar. 31, 2014
Segment Reporting Information [Line Items]
Revenues	$17,191		$23,285
Income from operations	1,470		361
Income from equity method investments	15		35
Depreciation and amortization	363		320
Capital expenditures and investments	384	[1],[2]	371	[1],[2]
Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenues	2,867	[3]	2,363	[3]
Operating Segments
Segment Reporting Information [Line Items]
Revenues	20,058		25,648
Income from operations	1,551	[4]	492	[4]
Income from equity method investments	15		35
Depreciation and amortization	350	[5]	308	[5]
Capital expenditures and investments	355	[2]	340	[2]
Refining & Marketing
Segment Reporting Information [Line Items]
Revenues	12,644		19,810
Refining & Marketing | Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenues	2,733		2,233
Refining & Marketing | Operating Segments
Segment Reporting Information [Line Items]
Revenues	15,377		22,043
Income from operations	1,316		362
Income from equity method investments	6		24
Depreciation and amortization	267		261
Capital expenditures and investments	229		178
Speedway
Segment Reporting Information [Line Items]
Revenues	4,531		3,458
Speedway | Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenues	0		1
Speedway | Operating Segments
Segment Reporting Information [Line Items]
Revenues	4,531		3,459
Income from operations	168		58
Income from equity method investments	0		0
Depreciation and amortization	63		28
Capital expenditures and investments	45		32
Pipeline Transportation
Segment Reporting Information [Line Items]
Revenues	16		17
Pipeline Transportation | Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenues	134		129
Pipeline Transportation | Operating Segments
Segment Reporting Information [Line Items]
Revenues	150		146
Income from operations	67	[4]	72	[4]
Income from equity method investments	9		11
Depreciation and amortization	20		19
Capital expenditures and investments	81		130
Reportable Segment
Segment Reporting Information [Line Items]
Revenues	$17,191		$23,285
[1]	Includes capitalized interest of $8 million and $6 million for the three months ended March 31, 2015 and 2014, respectively.
[2]	Capital expenditures include changes in capital accruals, acquisitions and investments in affiliates.
[3]	Management believes intersegment transactions were conducted under terms comparable to those with unaffiliated parties
[4]	Corporate overhead expenses attributable to MPLX are included in the Pipeline Transportation segment. Corporate overhead expenses are not allocated to the Refining & Marketing and Speedway segments.
[5]	Differences between segment totals and MPC totals represent amounts related to unallocated items and are included in “Items not allocated to segments” in the reconciliation below.

Segment_Information_Reconcilia

Segment Information - Reconciliation Of Segment Income From Operations To Income Before Income Taxes (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015		Mar. 31, 2014
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Income from operations	$1,470		$361
Net interest and other financial income (costs)	81		46
Income before income taxes	1,389		315
Operating Segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Income from operations	1,551	[1]	492	[1]
Corporate and Other
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Income from operations	-80	[1],[2]	-67	[1],[2]
Segment Reconciling Items
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Pension settlement expenses	($1)	[3]	($64)	[3]
[1]	Corporate overhead expenses attributable to MPLX are included in the Pipeline Transportation segment. Corporate overhead expenses are not allocated to the Refining & Marketing and Speedway segments.
[2]	Corporate and other unallocated items consists primarily of MPC’s corporate administrative expenses and costs related to certain non-operating assets.
[3]	See Note 19.

Segment_Information_Reconcilia1

Segment Information - Reconciliation Of Segment Capital Expenditures And Investments To Total Capital Expenditures (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015		Mar. 31, 2014
Reconciliation Of Segment Capital Expenditures And Investments To Total Capital Expenditures [Line Items]
Capital expenditures and investments	$384	[1],[2]	$371	[1],[2]
Plus: Items not allocated to segments:
Capital expenditures	342	[3]	248	[3]
Operating Segments
Reconciliation Of Segment Capital Expenditures And Investments To Total Capital Expenditures [Line Items]
Capital expenditures and investments	355	[2]	340	[2]
Less: Investments in equity method investees	-42		-123
Corporate and Other
Reconciliation Of Segment Capital Expenditures And Investments To Total Capital Expenditures [Line Items]
Capital expenditures and investments	29	[1]	31	[1]
Plus: Items not allocated to segments:
Capital expenditures not allocated to segments	21		25
Capitalized interest	$8		$6
[1]	Includes capitalized interest of $8 million and $6 million for the three months ended March 31, 2015 and 2014, respectively.
[2]	Capital expenditures include changes in capital accruals, acquisitions and investments in affiliates.
[3]	Capital expenditures include changes in capital accruals. See Note 17 for a reconciliation of total capital expenditures to additions to property, plant and equipment as reported in the consolidated statements of cash flows.

Other_Items_Net_Interest_And_O

Other Items - Net Interest And Other Financial Income (Costs) (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Other Income and Expenses [Abstract]
Interest income	$1	$2
Interest expense	-80	-49
Interest capitalized	8	6
Other financial costs	-10	-5
Net interest and other financial income (costs)	$81	$46

Income_Taxes_Additional_Inform

Income Taxes - Additional Information (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Income Tax Disclosure [Abstract]
Combined federal, state and foreign income tax rate	35.00%	34.00%
Statutory rate applied to income before income taxes	35.00%
Unrecognized benefits	$15

Inventories_Summary_Of_Invento

Inventories - Summary Of Inventories (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Inventory Disclosure [Abstract]
Crude oil and refinery feedstocks	$2,107	$2,219
Refined products	2,862	2,955
Materials and supplies	302	302
Merchandise	166	166
Total (at cost)	$5,437	$5,642

Inventories_Additional_Informa

Inventories - Additional Information (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Inventory Disclosure [Abstract]
Impact on revenues and costs as a result of LIFO liquidations	($30)	$0

Property_Plant_And_Equipment_S

Property, Plant And Equipment - Summary Of Property, Plant And Equipment (Detail) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$25,621	$25,302
Less accumulated depreciation	9,380	9,041
Net property, plant and equipment	16,241	16,261
Operating Segments | Refining & Marketing
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	18,225	18,001
Operating Segments | Speedway
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	4,674	4,639
Operating Segments | Pipeline Transportation
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,083	2,044
Corporate and Other
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$639	$618

Property_Plant_and_Equipment_P

Property, Plant and Equipment Property, Plant and Equipment (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$25,621	$25,302
Residual Fuel Hydrocracker - Garyville | Construction in Progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$136

Fair_Value_Measurements_Assets

Fair Value Measurements - Assets and Liabilities Accounted for at Fair Value on Recurring Basis (Detail) (USD $)	Mar. 31, 2015		Dec. 31, 2014
In Millions, unless otherwise specified
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash collateral netted with derivative liabilities	$13
Cash collateral netted with derivative assets			-78
Liabilities, current	189		174
Fair Value, Measurements, Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commodity derivative instruments, assets - netting and collateral	-66	[1]	-258	[1]
Commodity derivative instruments, assets - net	28	[2]	59	[2]
Commodity derivative instruments, assets - collateral pledged not offset	40		0
Other assets	2		2
Total assets at fair value	30		61
Commodity derivative instruments, liabilities - netting and collateral	-79	[1]	-180	[1]
Commodity derivative instruments, liabilities - net	0	[2]	0	[2]
Commodity derivative instruments, liabilities - collateral pledged not offset	0		0
Contingent consideration, liability	490	[3]	478	[3]
Total liabilities at fair value	490		478
Fair Value, Measurements, Recurring | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commodity derivative instruments, assets - gross	94		317
Other assets	2		2
Total assets at fair value	96		319
Commodity derivative instruments, liabilities - gross	79		180
Contingent consideration, liability	0		0
Total liabilities at fair value	79		180
Fair Value, Measurements, Recurring | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commodity derivative instruments, assets - gross	0		0
Other assets	0		0
Total assets at fair value	0		0
Commodity derivative instruments, liabilities - gross	0		0
Contingent consideration, liability	0		0
Total liabilities at fair value	0		0
Fair Value, Measurements, Recurring | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commodity derivative instruments, assets - gross	0		0
Other assets	0		0
Total assets at fair value	0		0
Commodity derivative instruments, liabilities - gross	0		0
Contingent consideration, liability	490	[3]	478	[3]
Total liabilities at fair value	$490		$478
[1]	Represents the impact of netting assets, liabilities and cash collateral when a legal right of offset exists. As of March 31, 2015, cash collateral of $13 million was netted with the mark-to-market derivative liabilities. As of December 31, 2014, $78 million was netted with mark-to-market derivative assets.
[2]	We have no derivative contracts that are subject to master netting arrangements that are reflected gross on the balance sheet.
[3]	Includes $189 million and $174 million classified as current at March 31, 2015 and December 31, 2014, respectively.

Fair_Value_Measurements_Narrat

Fair Value Measurements - Narrative (Detail) (USD $)	3 Months Ended		12 Months Ended	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014	Jun. 30, 2015	Feb. 01, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized and realized losses included in net income	$12,000,000	$14,000,000
Fair Value, Measurements, Recurring | Derivative
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized and realized losses included in net income	0	0
Fair Value, Measurements, Recurring | Contingent Consideration
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unrealized and realized losses included in net income	12,000,000	14,000,000
Galveston Bay Refinery and Related Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Maximum earnout payment, year one					200,000,000
Maximum earnout payment, year two					200,000,000
Maximum earnout payment, year three					200,000,000
Maximum earnout payment, year four					250,000,000
Maximum earnout payment, year five					250,000,000
Maximum earnout payment, year six					250,000,000
Total cumulative payment capped over six-year period					700,000,000
Cash paid for acquisition			180,000,000
Galveston Bay Refinery and Related Assets | Scenario, Forecast
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash paid for acquisition				$189,000,000
Galveston Bay Refinery and Related Assets | Fair Value, Measurements, Recurring | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range of internal and external crack spread forecast per barrel	9
Discount rate	5.00%
Galveston Bay Refinery and Related Assets | Fair Value, Measurements, Recurring | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Range of internal and external crack spread forecast per barrel	18
Discount rate	10.00%

Fair_Value_Measurements_Reconc

Fair Value Measurements - Reconciliation of Net Beginning and Ending Balances Recorded for Net Assets and Liabilities Classified as Level 3 (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$478	$625
Unrealized and realized losses included in net income	12	14
Ending balance	$490	$639

Fair_Value_Measurements_Financ

Fair Value Measurements - Financial Instruments at Fair Value, Excluding Derivative Financial Instruments and Contingent Consideration (Detail) (USD $)	Mar. 31, 2015		Dec. 31, 2014
In Millions, unless otherwise specified
Fair Value
Financial assets:
Investments	$27		$26
Other assets	31		32
Total financial assets	58		58
Financial liabilities:
Long-term debt	6,843	[1]	6,571	[1]
Deferred credits and other liabilities	20		17
Total financial liabilities	6,863		6,588
Carrying Value
Financial assets:
Investments	2		2
Other assets	30		32
Total financial assets	32		34
Financial liabilities:
Long-term debt	6,377	[1]	6,265	[1]
Deferred credits and other liabilities	20		17
Total financial liabilities	$6,397		$6,282
[1]	Excludes capital leases

Derivatives_Classification_of_

Derivatives - Classification of Gross Fair Values of Derivative Instruments, Excluding Cash Collateral (Detail) (Commodity derivatives, Other current assets, USD $)	Mar. 31, 2015	Dec. 31, 2014
In Millions, unless otherwise specified
Commodity derivatives | Other current assets
Derivatives, Fair Value [Line Items]
Asset	$94	$317
Liability	$79	$180

Derivatives_Open_Commodity_Der

Derivatives - Open Commodity Derivative Contracts (Detail)	3 Months Ended
	Mar. 31, 2015
Derivative [Line Items]
Derivative contract expiration date	30-Jun-15
Crude Oil Exchange-Traded
Derivative [Line Items]
Percentage of derivative contracts expiring in the period	96.00%
Crude Oil Exchange-Traded | Long
Derivative [Line Items]
Notional contracts (in thousands of Total Barrels)	11,454,000	[1]
Crude Oil Exchange-Traded | Short
Derivative [Line Items]
Notional contracts (in thousands of Total Barrels)	23,733,000	[1]
Refined Products Exchange-Traded
Derivative [Line Items]
Percentage of derivative contracts expiring in the period	100.00%
Refined Products Exchange-Traded | Long
Derivative [Line Items]
Notional contracts (in thousands of Total Barrels)	3,378,000	[2]
Refined Products Exchange-Traded | Short
Derivative [Line Items]
Notional contracts (in thousands of Total Barrels)	2,402,000	[2]
[1]	96 percent of these contracts expire in the second quarter of 2015.
[2]	100 percent of these contracts expire in the second quarter of 2015.

Derivatives_Effect_of_Commodit

Derivatives - Effect of Commodity Derivative Instruments in Statements of Income (Detail) (Commodity derivatives, USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss)	$59	($51)
Sales and other operating revenues
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss)	14	10
Cost of revenues
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss)	$45	($61)

Debt_Outstanding_Borrowings_De

Debt - Outstanding Borrowings (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Debt Instrument [Line Items]
Total	$6,766		$6,657
Unamortized discount	-28		-26
Fair value adjustments	5	[1]	6	[1]
Amounts due within one year	-776		-27
Total long-term debt due after one year	5,967		6,610
Interest Rate Swap
Debt Instrument [Line Items]
Deferred gain on discontinuation of interest rate fair value hedge	20
Consolidated subsidiaries: | Capital Lease Obligations
Debt Instrument [Line Items]
Capital lease obligations	366		372
Debt instrument maturity year, start	1-Jan-15
Debt instrument maturity year, end	31-Dec-28
MPC Revolver | Line of Credit
Debt Instrument [Line Items]
Long-term debt, gross	0		0
Line of credit facility, expiration date	14-Sep-17
MPC Term Loan | Unsecured Debt
Debt Instrument [Line Items]
Long-term debt, gross	700		700
Line of credit facility, expiration date	30-Sep-19
3.500% senior notes due March 1, 2016 | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross	750		750
Debt instrument, maturity date	1-Mar-16
Debt instrument, interest rate	3.50%
5.125% senior notes due March 1, 2021 | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross	1,000		1,000
Debt instrument, maturity date	1-Mar-21
Debt instrument, interest rate	5.13%
3.625% senior notes due September 15, 2024 | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross	750		750
Debt instrument, maturity date	15-Sep-24
Debt instrument, interest rate	3.63%
6.500% senior notes due March 1, 2041 | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross	1,250		1,250
Debt instrument, maturity date	1-Mar-41
Debt instrument, interest rate	6.50%
4.750% senior notes due September 15, 2044 | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross	800		800
Debt instrument, maturity date	15-Sep-44
Debt instrument, interest rate	4.75%
5.000% senior notes due September 15, 2054 | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross	400		400
Debt instrument, maturity date	15-Sep-54
Debt instrument, interest rate	5.00%
5.000% senior notes due September 15, 2054 | MPLX LP | Senior Notes
Debt Instrument [Line Items]
Debt instrument, maturity date	15-Feb-25
Debt instrument, interest rate	4.00%
MPLX Revolver | MPLX LP | Line of Credit
Debt Instrument [Line Items]
Long-term debt, gross	0		385
MPLX Term Loan | MPLX LP | Unsecured Debt
Debt Instrument [Line Items]
Long-term debt, gross	250		250
Line of credit facility, expiration date	20-Dec-19
4.000% senior notes due two thousand twenty five | MPLX LP | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross	500		0
Debt instrument, maturity date	15-Feb-25
Debt instrument, interest rate	4.00%
Trade Receivables Securitization | Consolidated subsidiaries: | Secured Debt
Debt Instrument [Line Items]
Long-term debt, gross	$0		$0
Line of credit facility, expiration date	31-Dec-16
[1]	The $20 million gain on the termination of our interest rate swap agreements in 2012 is being amortized over the remaining life of the 3.50 percent senior notes.

Debt_MPLX_Senior_Notes_Details

Debt MPLX Senior Notes (Details) (MPLX LP, Senior Notes, USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Feb. 12, 2015
Debt Instrument [Line Items]
Proceeds from (repayments of) debt	$495
4.000% senior notes due two thousand twenty five
Debt Instrument [Line Items]
Debt instrument, face amount		$500

Debt_Additional_Information_De

Debt - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
MPC Revolver | Line of Credit
Line of Credit Facility [Line Items]
Long-term debt, gross	$0	$0
Trade Receivables Securitization
Line of Credit Facility [Line Items]
Current borrowing capacity	978,000,000
Maximum borrowing capacity	1,300,000,000
MPLX Revolver | MPLX LP
Line of Credit Facility [Line Items]
Borrowings during period	30,000,000
Interest rate during period	1.50%
Repayments during period	415,000,000
Remaining borrowing capacity	1,000,000,000
Remaining borrowing capacity, percentage	100.00%
MPLX Revolver | MPLX LP | Letter of Credit
Line of Credit Facility [Line Items]
Borrowings outstanding	0
MPLX Revolver | MPLX LP | Line of Credit
Line of Credit Facility [Line Items]
Long-term debt, gross	$0	$385,000,000

Supplemental_Cash_Flow_Informa2

Supplemental Cash Flow Information - Summary of Supplemental Cash Flow Information (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Net cash provided by operating activities included:
Interest paid (net of amounts capitalized)	$128	$80
Net income taxes paid to taxing authorities	$160	$5

Supplemental_Cash_Flow_Informa3

Supplemental Cash Flow Information - Reconciliation of Additions to Property, Plant and Equipment to Total Capital Expenditures (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Supplemental Cash Flow Elements [Abstract]
Additions to property, plant and equipment	$389	$267
Decrease in capital accruals	-47	-19
Total capital expenditures	$342	$248

Accumulated_Other_Comprehensiv2

Accumulated Other Comprehensive Loss - Changes in Accumulated Other Comprehensive Loss by Component (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015		Mar. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	($313)		($204)
Other comprehensive loss before reclassifications	-2		-42
Amounts reclassified from accumulated other comprehensive loss:
Amortization - prior service credit	-13	[1]	-13	[1]
Amortization - actuarial loss	16	[1]	14	[1]
Amortization - settlement loss	1	[1]	64	[1]
Tax effect	-2		-24
Other comprehensive income (loss)	0		-1
Ending balance	-313		-205
Accumulated Defined Benefit Plans Adjustment | Pension Benefits
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	-217		-161
Other comprehensive loss before reclassifications	-1		-43
Amounts reclassified from accumulated other comprehensive loss:
Amortization - prior service credit	-12	[1]	-12	[1]
Amortization - actuarial loss	13	[1]	13	[1]
Amortization - settlement loss	1	[1]	64	[1]
Tax effect	-1		-24
Other comprehensive income (loss)	0		-2
Ending balance	-217		-163
Accumulated Defined Benefit Plans Adjustment | Other Benefits
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	-104		-50
Other comprehensive loss before reclassifications	-1		1
Amounts reclassified from accumulated other comprehensive loss:
Amortization - prior service credit	-1	[1]	-1	[1]
Amortization - actuarial loss	3	[1]	1	[1]
Amortization - settlement loss	0		0
Tax effect	-1		0
Other comprehensive income (loss)	0		1
Ending balance	-104		-49
Gain on Cash Flow Hedge
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	4		4
Other comprehensive loss before reclassifications	0		0
Amounts reclassified from accumulated other comprehensive loss:
Tax effect	0		0
Other comprehensive income (loss)	0		0
Ending balance	4		4
Workers Compensation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	4		3
Other comprehensive loss before reclassifications	0		0
Amounts reclassified from accumulated other comprehensive loss:
Tax effect	0		0
Other comprehensive income (loss)	0		0
Ending balance	$4		$3
[1]	These accumulated other comprehensive loss components are included in the computation of net periodic benefit cost. See Note 19.

Defined_Benefit_Pension_and_Ot2

Defined Benefit Pension and Other Postretirement Plans - Components of Net Periodic Benefit Costs (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Pension Benefits
Components of net periodic benefit cost:
Service cost	$23	$23
Interest cost	18	20
Expected return on plan assets	-26	-28
Amortization – prior service credit	-12	-12
Amortization – actuarial loss	13	13
Amortization - settlement loss	1	64
Net periodic benefit cost	17	80
Other Benefits
Components of net periodic benefit cost:
Service cost	8	7
Interest cost	8	8
Expected return on plan assets	0	0
Amortization – prior service credit	-1	-1
Amortization – actuarial loss	3	1
Amortization - settlement loss	0	0
Net periodic benefit cost	$18	$15

Defined_Benefit_Pension_and_Ot3

Defined Benefit Pension and Other Postretirement Plans - Additional Information (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$0
Pension settlement expenses	1	64
Other Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Benefits paid	4
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Benefits paid	5
Pension settlement expenses	$0	$0

StockBased_Compensation_Plans_1

Stock-Based Compensation Plans - Summary of Stock Option Award Activity (Detail) (Stock Options, USD $)	3 Months Ended
	Mar. 31, 2015
Stock Options
Number of Shares
Outstanding, beginning balance	4,751,438
Granted	354,001
Exercised	-577,831
Forfeited, canceled or expired	-24,383
Outstanding, ending balance	4,503,225
Weighted Average Exercise Price
Outstanding, beginning balance (in USD per share)	$45.47
Granted (in USD per share)	$101.78
Exercised (in USD per share)	$36.13
Forfeited, canceled or expired (in USD per share)	$79.69
Outstanding, ending balance (in USD per share)	$50.91

StockBased_Compensation_Plans_2

Stock-Based Compensation Plans - Narrative (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date fair value (in USD per share)	$27
Performance Unit Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in USD per share)	$0.95

StockBased_Compensation_Plans_3

Stock-Based Compensation Plans - Summary of Restricted Stock Award Activity (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015
Restricted Stock
Number of Shares
Outstanding, beginning balance	515,073
Granted	47,969
RS’s Vested/RSU’s Issued	-68,011
Forfeited	-15,374
Outstanding, ending balance	479,657
Weighted Average Grant Date Fair Value
Outstanding, beginning balance (in USD per share)	$77.23
Granted (in USD per share)	$101.57
RS's Vested/RSU's Issued (in USD per share)	$63.45
Forfeited (in USD per share)	$77.07
Outstanding, ending balance (in USD per share)	$81.63
Restricted Stock Units
Number of Shares
Outstanding, beginning balance	411,093
Granted	6,204
RS’s Vested/RSU’s Issued	0
Forfeited	-425
Outstanding, ending balance	416,872
Weighted Average Grant Date Fair Value
Outstanding, beginning balance (in USD per share)	$37.30
Granted (in USD per share)	$93.19
RS's Vested/RSU's Issued (in USD per share)	$0
Forfeited (in USD per share)	$89.54
Outstanding, ending balance (in USD per share)	$38.08

StockBased_Compensation_Plans_4

Stock-Based Compensation Plans - Summary of Performance Unit Awards (Detail) (Performance Unit Awards, USD $)	3 Months Ended
	Mar. 31, 2015
Performance Unit Awards
Number of Units
Outstanding, beginning balance	5,791,825
Granted	2,389,450
Settled	-2,035,833
Outstanding, ending balance	6,145,442
Weighted Average Grant Date Fair Value
Outstanding, beginning balance (in USD per share)	$0.88
Granted (in USD per share)	$0.95
Settled (in USD per share)	$0.85
Outstanding, ending balance (in USD per share)	$0.92

Commitments_and_Contingencies_

Commitments and Contingencies (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Loss Contingencies [Line Items]
Accrued liabilities for remediation	$177	$185
Receivables for recoverable costs	66	67
Contractual commitments to acquire property, plant and equipment and advance funds to equity method investees	2,000
Galveston Bay Refinery and Related Assets
Loss Contingencies [Line Items]
Contractual commitments to acquire property, plant and equipment and advance funds to equity method investees	520
North Dakota Pipeline
Loss Contingencies [Line Items]
Contractual commitments to acquire property, plant and equipment and advance funds to equity method investees	703
Illinois Extension Pipeline Company LLC
Loss Contingencies [Line Items]
Contractual commitments to acquire property, plant and equipment and advance funds to equity method investees	148
Indemnification Agreement | Marathon Oil Companies
Loss Contingencies [Line Items]
Guarantee obligation current carrying value	2
Other Guarantees | Equity method investees
Loss Contingencies [Line Items]
Maximum potential undiscounted payments	82
Guarantee obligations maximum exposure per event	50
Guarantee of Indebtedness of Others | Financial Guarantee | LOOP and LOCAP LLC
Loss Contingencies [Line Items]
Line of credit facility, expiration date	31-Dec-37
Maximum potential undiscounted payments	172
Master Shelf Agreement | Financial Guarantee | Centennial
Loss Contingencies [Line Items]
Line of credit facility, expiration date	31-Dec-24
Maximum potential undiscounted payments	37
Pending Litigation
Loss Contingencies [Line Items]
Loss contingency, inestimable loss	For matters for which we have not recorded an accrued liability, we are unable to estimate a range of possible loss because the issues involved have not been fully developed through pleadings and discovery.
Pending Litigation | Emergency Pricing And Consumer Protection Laws
Loss Contingencies [Line Items]
Alleged amount overcharged from customers	$89
Loss contingency, period of occurrence	during September and October 2005
Plaintiff	Commonwealth of Kentucky

Subsequent_Events_Subsequent_E

Subsequent Events Subsequent Events (Details) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Subsequent Events [Abstract]
Basic earnings per share on a post-split basis	$1.63	$0.34
Diluted earnings per share on a post-split basis	$1.62	$0.34

Supplementary_Statistics_Suppl

Supplementary Statistics - Supplementary Statistics (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015		Mar. 31, 2014
Supplementary Statistics [Line Items]
Income from operations	$1,470		$361
Capital expenditures and investments	384	[1],[2]	371	[1],[2]
Operating Segments
Supplementary Statistics [Line Items]
Income from operations	1,551	[3]	492	[3]
Capital expenditures and investments	355	[2]	340	[2]
Operating Segments | Refining & Marketing
Supplementary Statistics [Line Items]
Income from operations	1,316		362
Capital expenditures and investments	229		178
Operating Segments | Speedway
Supplementary Statistics [Line Items]
Income from operations	168		58
Capital expenditures and investments	45		32
Operating Segments | Pipeline Transportation
Supplementary Statistics [Line Items]
Income from operations	67	[3]	72	[3]
Capital expenditures and investments	81		130
Corporate and Other
Supplementary Statistics [Line Items]
Income from operations	-80	[3],[4]	-67	[3],[4]
Capital expenditures and investments	29	[1]	31	[1]
Capitalized interest	8		6
Segment Reconciling Items
Supplementary Statistics [Line Items]
Pension settlement expenses	($1)	[5]	($64)	[5]
[1]	Includes capitalized interest of $8 million and $6 million for the three months ended March 31, 2015 and 2014, respectively.
[2]	Capital expenditures include changes in capital accruals, acquisitions and investments in affiliates.
[3]	Corporate overhead expenses attributable to MPLX are included in the Pipeline Transportation segment. Corporate overhead expenses are not allocated to the Refining & Marketing and Speedway segments.
[4]	Corporate and other unallocated items consists primarily of MPC’s corporate administrative expenses and costs related to certain non-operating assets.
[5]	See Note 19.

Supplementary_Statistics_Opera

Supplementary Statistics - Operating Statistics (Detail) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2015		Mar. 31, 2014
Operating Statistics [Line Items ]
MPC Consolidated Refined Product Sales Volumes (thousands of barrels per day)	2,246,000	[1],[2]	1,964,000	[1],[2]
Refining & Marketing
Refining & Marketing Operating Statistics
Refining & Marketing refined product sales volume (thousands of barrels per day)	2,233,000	[3]	1,951,000	[3]
Refining & Marketing gross margin (dollars per barrel)	16.14	[4]	14.46	[4]
Crude oil capacity utilization percent	97.00%	[5]	85.00%	[5]
Refinery throughputs (thousands of barrels per day)	1,852,000	[6]	1,650,000	[6]
Sour crude oil throughput percent	56.00%		49.00%
WTI-priced crude oil throughput percent	20.00%		21.00%
Refined product yields (thousands of barrels per day)	1,878,000	[6]	1,678,000	[6]
Inter-refinery transfers	35,000		59,000
Refinery direct operating costs (dollars per barrel):
Planned turnaround and major maintenance	0.79	[7]	3.15	[7]
Depreciation and amortization	1.42	[7]	1.55	[7]
Other manufacturing	4.26	[7],[8]	5.95	[7],[8]
Total	6.47	[7]	10.65	[7]
Refining & Marketing | Crude oil refined
Refining & Marketing Operating Statistics
Refinery throughputs (thousands of barrels per day)	1,672,000	[6]	1,450,000	[6]
Refining & Marketing | Other charge and blendstocks
Refining & Marketing Operating Statistics
Refinery throughputs (thousands of barrels per day)	180,000	[6]	200,000	[6]
Refining & Marketing | Gasoline
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	911,000	[6]	837,000	[6]
Refining & Marketing | Distillates
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	553,000	[6]	514,000	[6]
Refining & Marketing | Propane
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	36,000	[6]	34,000	[6]
Refining & Marketing | Feedstocks and special products
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	298,000	[6]	220,000	[6]
Refining & Marketing | Heavy fuel oil
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	30,000	[6]	30,000	[6]
Refining & Marketing | Asphalt
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	50,000	[6]	43,000	[6]
Refining & Marketing | Gulf Coast:
Refining & Marketing Operating Statistics
Refinery throughputs (thousands of barrels per day)	1,210,000	[9]	1,071,000	[9]
Sour crude oil throughput percent	70.00%		60.00%
WTI-priced crude oil throughput percent	5.00%		3.00%
Refined product yields (thousands of barrels per day)	1,226,000	[9]	1,096,000	[9]
Refinery direct operating costs (dollars per barrel):
Planned turnaround and major maintenance	0.8	[7]	3.83	[7]
Depreciation and amortization	1.14	[7]	1.25	[7]
Other manufacturing	3.99	[7],[8]	5.87	[7],[8]
Total	5.93	[7]	10.95	[7]
Refining & Marketing | Gulf Coast: | Crude oil refined
Refining & Marketing Operating Statistics
Refinery throughputs (thousands of barrels per day)	1,031,000	[9]	860,000	[9]
Refining & Marketing | Gulf Coast: | Other charge and blendstocks
Refining & Marketing Operating Statistics
Refinery throughputs (thousands of barrels per day)	179,000	[9]	211,000	[9]
Refining & Marketing | Gulf Coast: | Gasoline
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	523,000	[9]	489,000	[9]
Refining & Marketing | Gulf Coast: | Distillates
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	342,000	[9]	319,000	[9]
Refining & Marketing | Gulf Coast: | Propane
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	25,000	[9]	21,000	[9]
Refining & Marketing | Gulf Coast: | Feedstocks and special products
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	307,000	[9]	245,000	[9]
Refining & Marketing | Gulf Coast: | Heavy fuel oil
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	15,000	[9]	15,000	[9]
Refining & Marketing | Gulf Coast: | Asphalt
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	14,000	[9]	7,000	[9]
Refining & Marketing | Midwest:
Refining & Marketing Operating Statistics
Refinery throughputs (thousands of barrels per day)	677,000	[9]	638,000	[9]
Sour crude oil throughput percent	34.00%		34.00%
WTI-priced crude oil throughput percent	43.00%		47.00%
Refined product yields (thousands of barrels per day)	687,000	[9]	641,000	[9]
Refinery direct operating costs (dollars per barrel):
Planned turnaround and major maintenance	0.73	[7]	1.71	[7]
Depreciation and amortization	1.85	[7]	1.91	[7]
Other manufacturing	4.51	[7],[8]	5.54	[7],[8]
Total	7.09	[7]	9.16	[7]
Refining & Marketing | Midwest: | Crude oil refined
Refining & Marketing Operating Statistics
Refinery throughputs (thousands of barrels per day)	641,000	[9]	590,000	[9]
Refining & Marketing | Midwest: | Other charge and blendstocks
Refining & Marketing Operating Statistics
Refinery throughputs (thousands of barrels per day)	36,000	[9]	48,000	[9]
Refining & Marketing | Midwest: | Gasoline
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	388,000	[9]	348,000	[9]
Refining & Marketing | Midwest: | Distillates
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	211,000	[9]	195,000	[9]
Refining & Marketing | Midwest: | Propane
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	13,000	[9]	13,000	[9]
Refining & Marketing | Midwest: | Feedstocks and special products
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	23,000	[9]	33,000	[9]
Refining & Marketing | Midwest: | Heavy fuel oil
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	16,000	[9]	16,000	[9]
Refining & Marketing | Midwest: | Asphalt
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	36,000	[9]	36,000	[9]
Speedway
Speedway Operating Statistics(b)
Convenience stores at period-end	2,753	[1]	1,482
Gasoline and distillate sales (millions of gallons)	1,432,000,000		773,000,000
Gasoline and distillate gross margin (dollars per gallon)	0.197	[10]	0.1156	[11]
Merchandise sales (in millions)	1,111		722
Merchandise gross margin (in millions)	311		192
Merchandise margin percent	28.00%		26.50%
Same store gasoline sales volume (period over period) percentage	-1.20%	[12]	-0.70%	[12]
Merchandise sales excluding cigarettes (period over period) percentage	6.20%	[11],[12]	5.30%	[11],[12]
Pipeline Transportation
Pipeline Transportation Operating Statistics
Pipeline throughputs (thousands of barrels per day)	2,107,000	[13]	1,990,000	[13]
Pipeline Transportation | Crude oil pipelines
Pipeline Transportation Operating Statistics
Pipeline throughputs (thousands of barrels per day)	1,221,000	[13]	1,171,000	[13]
Pipeline Transportation | Refined products pipelines
Pipeline Transportation Operating Statistics
Pipeline throughputs (thousands of barrels per day)	886,000	[13]	819,000	[13]
[1]	Includes the impact of Hess’ Retail Operations and Related Assets beginning on the September 30, 2014 acquisition date.
[2]	Total average daily volumes of refined product sales to wholesale, branded and retail (Speedway segment) customers.
[3]	Includes intersegment sales.
[4]	Sales revenue less cost of refinery inputs and purchased products, divided by total refinery throughputs.
[5]	Based on calendar day capacity, which is an annual average that includes downtime for planned maintenance and other normal operating activities.
[6]	Excludes inter-refinery volumes of 35 mbpd and 59 mbpd for the three months ended March 31, 2015 and 2014, respectively.
[7]	Per barrel of total refinery throughputs.
[8]	Includes utilities, labor, routine maintenance and other operating costs.
[9]	Includes inter-refinery transfer volumes.
[10]	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.
[11]	Excludes cigarettes.
[12]	Same store comparison includes only locations owned at least 13 months
[13]	On owned common-carrier pipelines, excluding equity method investments.