Marathon Petroleum (MPC) 10-Q 5 Nov 18 2018 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Nov. 01, 2018
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus (Q1,Q2,Q3,FY)	Q3
Trading Symbol	MPC
Entity Registrant Name	Marathon Petroleum Corp
Entity Central Index Key	1,510,295
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Common Stock, Shares Outstanding		690,853,526

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) shares in Millions, $ in Millions		3 Months Ended				9 Months Ended
		Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2018	Sep. 30, 2017
Revenues and other income:
Sales and other operating revenues, excluding consumer excise taxes		$ 22,787	[1]			$ 63,599
Sales and other operating revenues, including consumer excise taxes				$ 19,053	[1]		$ 53,220
Sales to related parties	[2]	201		157		572	458
Income from equity method investments		96		84		262	224
Net gain on disposal of assets		1		0		6	12
Other income		47		92		122	219
Total revenues and other income		23,132		19,386		64,561	54,133
Costs and expenses:
Cost of revenues (excludes items below)		20,457	[1]	16,617	[1]	57,344	47,664
Purchases from related parties	[3]	149		148		428	420
Depreciation and amortization		555		517		1,616	1,574
Selling, general and administrative expenses		445		411		1,271	1,286
Other taxes		123		116		348	339
Total costs and expenses		21,729		17,809		61,007	51,283
Income from operations		1,403		1,577		3,554	2,850
Net interest and other financial costs		240		158		618	465
Income before income taxes		1,163		1,419		2,936	2,385
Provision for income taxes		222		415		525	706
Net income		941		1,004		2,411	1,679
Less net income attributable to:
Redeemable noncontrolling interest		19		16		55	49
Noncontrolling interests		185		85		527	214
Net income attributable to MPC		$ 737		$ 903		$ 1,829	$ 1,416
Basic:
Net income attributable to MPC per share		$ 1.63		$ 1.79		$ 3.96	$ 2.75
Weighted average shares outstanding (in shares)		451		504		462	514
Diluted:
Net income attributable to MPC per share		$ 1.62		$ 1.77		$ 3.92	$ 2.73
Weighted average shares outstanding (in shares)		456		508		466	518
[1]	The 2018 period reflects an election to present certain taxes on a net basis concurrent with our adoption of ASU 2014-09, Revenue - Revenue from Contracts with Customers (“ASC 606”). See Notes 2 and 3 for further information.
[2]	Sales to related parties consists primarily of sales of refined products to PFJ Southeast, an equity affiliate which owns and operates travel plazas primarily in the Southeast region of the United States.
[3]	We obtain transportation services and purchase ethanol from certain of our equity affiliates, none of which is individually material.

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 941	$ 1,004	$ 2,411	$ 1,679
Defined benefit postretirement and post-employment plans:
Actuarial changes, net of tax of $24, $2, $29 and $9, respectively	75	4	89	15
Prior service costs, net of tax of ($3), ($4), ($7) and ($12), respectively	(7)	(7)	(21)	(20)
Other, net of tax of ($1), $0, ($2) and $0, respectively	(3)	0	(5)	0
Other comprehensive income (loss)	65	(3)	63	(5)
Comprehensive income	1,006	1,001	2,474	1,674
Less comprehensive income attributable to:
Redeemable noncontrolling interest	19	16	55	49
Noncontrolling interests	185	85	527	214
Comprehensive income attributable to MPC	$ 802	$ 900	$ 1,892	$ 1,411

Consolidated Statements of Co_2

Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Actuarial changes, tax	$ 24	$ 2	$ 29	$ 9
Prior service costs, tax	(3)	(4)	(7)	(12)
Other, tax	$ (1)	$ 0	$ (2)	$ 0

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents (MPLX: $37 and $5, respectively)	$ 4,992	$ 3,011
Receivables, less allowance for doubtful accounts of $10 and $11 (MPLX: $462 and $299, respectively)	5,408	4,695
Inventories (MPLX: $81 and $65, respectively)	5,339	5,550
Other current assets (MPLX: $33 and $29, respectively)	134	145
Total current assets	15,873	13,401
Equity method investments (MPLX: $4,104 and $4,010, respectively)	4,910	4,787
Property, plant and equipment, net (MPLX: $14,271 and $12,187, respectively)	27,717	26,443
Goodwill (MPLX: $2,586 and $2,245, respectively)	3,713	3,586
Other noncurrent assets (MPLX: $470 and $479, respectively)	818	830
Total assets	53,031	49,047
Current liabilities:
Accounts payable (MPLX: $757 and $621, respectively)	8,016	8,297
Payroll and benefits payable (MPLX: $2 and $1, respectively)	493	591
Accrued taxes (MPLX: $53 and $38, respectively)	657	670
Debt due within one year (MPLX: $1 and $1, respectively)	26	624
Other current liabilities (MPLX: $224 and $130, respectively)	442	296
Total current liabilities	9,634	10,478
Long-term debt (MPLX: $12,889 and $6,945, respectively)	18,423	12,322
Deferred income taxes (MPLX: $13 and $5, respectively)	3,206	2,654
Defined benefit postretirement plan obligations	1,045	1,099
Deferred credits and other liabilities (MPLX: $274 and $230, respectively)	689	666
Total liabilities	32,997	27,219
Commitments and contingencies (see Note 22)
Redeemable noncontrolling interest	1,003	1,000
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 – 735 million and 734 million shares (par value $0.01 per share, 1 billion shares authorized)	7	7
Held in treasury, at cost – 284 million and 248 million shares	(12,495)	(9,869)
Additional paid-in capital	13,703	11,262
Retained earnings	14,119	12,864
Accumulated other comprehensive loss	(168)	(231)
Total MPC stockholders’ equity	15,166	14,033
Noncontrolling interests	3,865	6,795
Total equity	19,031	20,828
Total liabilities, redeemable noncontrolling interest and equity	$ 53,031	$ 49,047

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 10	$ 11
Preferred stock:
Shares issued	0	0
Shares outstanding	0	0
Par value	$ 0.01
Shares authorized	30,000,000
Common stock:
Shares issued	735,000,000	734,000,000
Par value	$ 0.01
Shares authorized	1,000,000,000
Treasury stock	(284,000,000)	(248,000,000)

Consolidated Balance Sheets (MP

Consolidated Balance Sheets (MPLX Parenthetical) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Assets
Cash and cash equivalents	$ 4,992	$ 3,011
Receivables, less allowance for doubtful accounts	5,408	4,695
Inventories	5,339	5,550
Other current assets	134	145
Equity method investments	4,910	4,787
Property, plant and equipment, net	27,717	26,443
Goodwill	3,713	3,586
Other noncurrent assets	818	830
Liabilities
Accounts payable	8,016	8,297
Payroll and benefits payable	493	591
Accrued taxes	657	670
Debt due within one year	26	624
Other current liabilities	442	296
Total long-term debt due after one year	18,423	12,322
Deferred income taxes (MPLX: $13 and $5, respectively)	3,206	2,654
Defined benefit postretirement plan obligations	1,045	1,099
Deferred credits and other liabilities	689	666
MPLX LP
Assets
Cash and cash equivalents	37	5
Receivables, less allowance for doubtful accounts	462	299
Inventories	81	65
Other current assets	33	29
Equity method investments	4,104	4,010
Property, plant and equipment, net	14,271	12,187
Goodwill	2,586	2,245
Other noncurrent assets	470	479
Liabilities
Accounts payable	757	621
Payroll and benefits payable	2	1
Accrued taxes	53	38
Debt due within one year	1	1
Other current liabilities	224	130
Total long-term debt due after one year	12,889	6,945
Deferred income taxes (MPLX: $13 and $5, respectively)	13	5
Defined benefit postretirement plan obligations	0	0
Deferred credits and other liabilities	$ 274	$ 230

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018		Sep. 30, 2017
Operating activities:
Net income	$ 2,411		$ 1,679
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of deferred financing costs and debt discount	51		46
Depreciation and amortization	1,616		1,574
Pension and other postretirement benefits, net	38		(32)
Deferred income taxes	42		57
Net gain on disposal of assets	(6)		(12)
Income from equity method investments	(262)		(224)
Distributions from equity method investments	345		256
Changes in the fair value of derivative instruments	13		101
Changes in:
Current receivables	(709)		(296)
Inventories	215		163
Current accounts payable and accrued liabilities	(316)		654
All other, net	(7)		(99)
Net cash provided by operating activities	3,431		3,867
Investing activities:
Additions to property, plant and equipment	(2,315)		(1,928)
Acquisitions, net of cash acquired	(453)		(249)
Disposal of assets	19		64
Investments – acquisitions, loans and contributions	(222)		(730)
Investments - redemptions, repayments and return of capital	16		60
All other, net	60		166
Net cash used in investing activities	(2,895)		(2,617)
Financing activities:
Commercial paper – issued	0		300
Commercial paper - repayments	0		(300)
Long-term debt – borrowings	10,735		2,661
Long-term debt – repayments	(5,401)		(470)
Debt issuance costs	(53)		(28)
Issuance of common stock	24		27
Common stock repurchased	(2,612)		(1,622)
Dividends paid	(637)		(578)
Issuance of MPLX LP common units	0		473
Distributions to noncontrolling interests	(599)		(505)
Contributions from noncontrolling interests	9		128
Contingent consideration payment	0		(89)
All other, net	(22)		(44)
Net cash provided by (used in) financing activities	1,444		(47)
Net increase in cash, cash equivalents and restricted cash	1,980		1,203
Cash, cash equivalents and restricted cash at beginning of period	3,015	[1]	892
Cash, cash equivalents and restricted cash at end of period	$ 4,995	[1]	$ 2,095
[1]	As a result of the adoption of ASU 2016-18, the consolidated statements of cash flows now explain the change during the period of both cash and cash equivalents and restricted cash.

Consolidated Statements of Equi

Consolidated Statements of Equity - USD ($) $ in Millions	Total	Common Stock	Treasury Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Non-controlling Interests
Beginning balance at Dec. 31, 2016	$ 20,203	$ 7	$ (7,482)	$ 11,060	$ 10,206	$ (234)	$ 6,646
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	1,630				1,416		214
Dividends declared	(578)				(578)
Distributions to noncontrolling interests	(456)						(456)
Contributions from noncontrolling interests	128						128
Other comprehensive income (loss)	(5)					(5)
Shares repurchased	(1,622)		(1,622)
Shares returned - stock based compensation			(14)
Shares issued - stock based compensation				64
Net shares issued - stock based compensation	55						5
Impact from equity transactions of MPLX LP	447			112			335
Ending balance at Sep. 30, 2017	19,802	7	(9,118)	11,236	11,044	(239)	6,872
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of new accounting principle in period of adoption	64				63		1
Beginning balance at Dec. 31, 2017	20,828	7	(9,869)	11,262	12,864	(231)	6,795
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	2,356				1,829		527
Dividends declared	(637)				(637)
Distributions to noncontrolling interests	(547)						(547)
Contributions from noncontrolling interests	9						9
Other comprehensive income (loss)	63					63
Shares repurchased	(2,612)		(2,612)
Shares returned - stock based compensation			(14)
Shares issued - stock based compensation				59
Net shares issued - stock based compensation	53						8
Impact from equity transactions of MPLX LP	(546)			2,382			(2,928)
Ending balance at Sep. 30, 2018	$ 19,031	$ 7	$ (12,495)	$ 13,703	$ 14,119	$ (168)	$ 3,865

Consolidated Statement of Equit

Consolidated Statement of Equity - Shares - shares shares in Millions	Total	Common Stock	Treasury Stock
Number of common shares issued (beginning balance) at Dec. 31, 2016		731
Number of common shares issued - stock compensation		2
Number of common shares issued (ending balance) at Sep. 30, 2017		733
Number of shares held in treasury (beginning balance) at Dec. 31, 2016			(203)
Number of shares repurchased	(31)		(31)
Number of shares returned - stock compensation			(1)
Number of shares held in treasury (ending balance) at Sep. 30, 2017			(235)
Number of common shares issued (beginning balance) at Dec. 31, 2017	734	734
Number of common shares issued - stock compensation		1
Number of common shares issued (ending balance) at Sep. 30, 2018	735	735
Number of shares held in treasury (beginning balance) at Dec. 31, 2017	(248)		(248)
Number of shares repurchased	(36)		(36)
Number of shares returned - stock compensation			0
Number of shares held in treasury (ending balance) at Sep. 30, 2018	(284)		(284)

Redeemable Noncontrolling Inter

Redeemable Noncontrolling Interest - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Temporary Equity [Abstract]
Beginning balance	$ 1,000	$ 1,000
Net income attributable to redeemable noncontrolling interest	55	49
Distributions to noncontrolling interests	(52)	(49)
Ending balance	$ 1,003	$ 1,000

Description of the Business and

Description of the Business and Basis of Presentation	9 Months Ended
	Sep. 30, 2018
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 and midstream services conducted primarily in the Midwest, Gulf Coast, East Coast, Northeast and Southeast regions of the United States, through subsidiaries, including Marathon Petroleum Company LP (“MPC LP”), Speedway LLC and its subsidiaries (“Speedway”) and MPLX LP and its subsidiaries (“MPLX”). See Note 10 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 SEC applicable to interim period financial statements and do not include all of the information and disclosures required by 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, 2017 . The results of operations for the three and nine months ended September 30, 2018 are not necessarily indicative of the results to be expected for the full year. Certain prior period financial statement amounts have been reclassified to conform to current period presentation.

Summary of Principal Accounting

Summary of Principal Accounting Policies	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Summary of Principal Accounting Policies	SUMMARY OF PRINCIPAL ACCOUNTING POLICIES Revenue Recognition As described in Note 3 , we adopted ASC 606 effective January 1, 2018. We recognize revenue based on consideration specified in contracts or agreements with customers when we satisfy our performance obligations by transferring control over products or services to a customer. Concurrent with our adoption of ASC 606, we made an accounting policy election that all taxes assessed by a governmental authority that are both imposed on and concurrent with a revenue-producing transaction and collected from our customers will be recognized on a net basis within sales and other operating revenues. The adoption of ASC 606 did not materially change our revenue recognition patterns, which are described below by reportable segment: • Refining & Marketing - The vast majority of our Refining & Marketing contracts contain pricing that is based on the market price for the product at the time of delivery. Our obligations to deliver product volumes are typically satisfied and revenue is recognized when control of the product transfers to our customers. Concurrent with the transfer of control, we typically receive the right to payment for the delivered product, the customer accepts the product and the customer has significant risks and rewards of ownership of the product. Payment terms require customers to pay shortly after delivery and do not contain significant financing components. • Speedway - Revenue is recognized when our customers receive control of the transportation fuels or merchandise. Payments from customers are received at the time sales occur in cash or by credit or debit card. Speedway offers a loyalty rewards program to its customers. We defer a minor portion of revenue on sales to the loyalty program participants until the participants redeem their rewards. The related contract liability, as defined in ASC 606, is not material to our financial statements. • Midstream - Midstream revenue transactions typically are defined by contracts under which we sell a product or provide a service. Revenues from sales of product are recognized when control of the product transfers to the customer. Revenues from sales of services are recognized over time when the performance obligation is satisfied as services are provided in a series. We have elected to use the output measure of progress to recognize revenue based on the units delivered, processed or transported. The transaction prices in our Midstream contracts often have both fixed components, related to minimum volume commitments, and variable components, which are primarily dependent on volumes. Variable consideration will generally not be estimated at contract inception as the transaction price is specifically allocable to the services provided at each period end. Refer to Note 10 for disclosure of our revenue disaggregated by segment and product line, as well as a description of our reportable segment operations.

Accounting Standards

Accounting Standards	9 Months Ended
	Sep. 30, 2018
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Recently Adopted	ACCOUNTING STANDARDS Recently Adopted ASU 2014-09, Revenue - Revenue from Contracts with Customers (ASC 606) On January 1, 2018, we adopted the new revenue standard, applying the modified retrospective method, whereby a cumulative effect is recorded to opening retained earnings and ASC 606 is applied prospectively. We recorded a net increase of $1 million to our retained earnings balance as of January 1, 2018 due to the cumulative effect of applying the new revenue standard. Impact of Adoption The adoption of ASC 606 did not materially change our revenue recognition patterns. The most significant impacts of adopting ASC 606 for the three and nine month periods ended September 30, 2018 are as follows: • a reduction of sales and other operating revenues of $1.40 billion for the three months ended September 30, 2018 and $4.01 billion for the nine months ended September 30, 2018 due to our accounting policy election to present taxes incurred concurrently with revenue producing transactions and collected on behalf of our customers on a net basis. For the three and nine months ended September 30, 2017 , taxes are reflected on a gross basis in sales and other operating revenues and cost of revenues, and include $1.34 billion and $3.81 billion , respectively, of taxes that are now subject to our net basis accounting policy election. • an increase to both sales and other operating revenues and cost of revenues of $148 million for the three months ended September 30, 2018 and $388 million for the nine months ended September 30, 2018 related to certain Midstream contract provisions for third-party reimbursements, non-cash consideration and imbalances that require gross presentation under ASC 606. Comparative information continues to be reported under the accounting standards in effect for those periods. Practical Expedients We elected the completed contract practical expedient and only applied ASC 606 to contracts that were not completed as of January 1, 2018. We do not disclose information on the future performance obligations for any contract with expected duration of one year or less at inception. As of September 30, 2018 , we do not have future performance obligations that are material to future periods. Receivables On the accompanying consolidated balance sheets, receivables, less allowance for doubtful accounts primarily consists of customer receivables. Significant, non-customer balances included in our receivables at September 30, 2018 include matching buy/sell receivables of $1.73 billion and income tax receivables of $102 million . ASU 2016-16, Income Taxes - Intra-Entity Transfers of Assets Other Than Inventory We adopted this ASU in the first quarter of 2018 and recorded a $61 million cumulative-effect adjustment as an increase to retained earnings as of January 1, 2018 with the offset recorded as a reduction to deferred income taxes. We also adopted the following ASUs during the first nine months of 2018, none of which had a material impact to our financial statements or financial statement disclosures: ASU Effective Date 2017-09 Stock Compensation - Scope of Modification Accounting January 1, 2018 2017-07 Retirement Benefits - Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Cost January 1, 2018 2017-05 Gains and Losses from the Derecognition of Nonfinancial Assets - Clarifying the Scope of Asset Derecognition Guidance January 1, 2018 2017-01 Business Combinations - Clarifying the Definition of a Business January 1, 2018 2016-18 Statement of Cash Flows - Restricted Cash January 1, 2018 2016-15 Statement of Cash Flows - Classification of Certain Cash Receipts and Cash Payments January 1, 2018 2016-01 Financial Instruments - Recognition and Measurement of Financial Assets and Liabilities January 1, 2018
Not Yet Adopted	Not Yet Adopted ASU 2018-02, Reporting Comprehensive Income - Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income In February 2018, the FASB issued an ASU allowing an entity the choice to reclassify to retained earnings the tax effects related to the TCJA that are stranded in accumulated other comprehensive income. We do not expect adoption of this standard to have a material impact on our financial statements. The amendment is effective beginning in 2019. ASU 2017-12, Derivatives and Hedging - Targeted Improvements to Accounting for Hedging Activities In August 2017, the FASB issued an ASU to amend the hedge accounting rules to simplify the application of hedge accounting guidance and better portray the economic results of risk management activities in the financial statements. The guidance expands the ability to hedge nonfinancial and financial risk components, reduces complexity in fair value hedges of interest rate risk, eliminates the requirement to separately measure and report hedge ineffectiveness and eases certain hedge effectiveness assessment requirements. The guidance is effective beginning in 2019. We are currently evaluating the impact of this guidance, including transition elections and required disclosures, on our financial statements and the timing of adoption. However, since we have not historically designated our commodity derivatives as hedges, we do not expect the adoption of this ASU to have a material impact on our consolidated financial statements. ASU 2017-04, Intangibles - Goodwill and Other - Simplifying the Test for Goodwill Impairment In January 2017, the FASB issued an ASU which simplifies the subsequent measurement of goodwill by eliminating Step 2 from the goodwill impairment test. Under the new guidance, the recognition of an impairment charge is calculated based on the amount by which the carrying amount exceeds the reporting unit’s fair value, which could be different from the amount calculated under the current method using the implied fair value of the goodwill; however, the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. The guidance should be applied on a prospective basis, and is effective for annual or any interim goodwill impairment tests in fiscal years beginning after December 15, 2019. ASU 2016-13, Credit Losses - Measurement of Credit Losses on Financial Instruments In June 2016, the FASB issued an ASU related to the accounting for credit losses on certain financial instruments. The guidance requires that for most financial assets, losses be based on an expected loss approach which includes estimates of losses over the life of exposure that considers historical, current and forecasted information. Expanded disclosures related to the methods used to estimate the losses as well as a specific disaggregation of balances for financial assets are also required. The change is effective for fiscal years beginning after December 15, 2019, and interim periods within those fiscal years, with early adoption permitted for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years. We do not expect application of this ASU to have a material impact on our consolidated financial statements. ASU 2016-02 and 2018-11, Leases In February 2016, the FASB issued an ASU requiring lessees to record virtually all leases on their balance sheets. The ASU also requires expanded disclosures to help financial statement users better understand the amount, timing and uncertainty of cash flows arising from leases. For lessors, this amended guidance modifies the classification criteria and the accounting for sales-type and direct financing leases. The guidance will be effective for fiscal years beginning after December 15, 2018, and interim periods within those years. We will transition to the new guidance by recording leases on our balance sheet as of January 1, 2019. We continue to evaluate the impact of this standard on our financial statements, disclosures, internal controls and accounting policies. This evaluation process includes reviewing all forms of leases, performing a completeness assessment over the lease population and analyzing the practical expedients in order to determine the best path of implementing changes to existing processes and controls. We are implementing a third-party supported lease accounting information system to account for our lease population in accordance with this new standard and establishing internal controls over the new system. We have completed a significant portion of the design and testing of the new system and commenced lease data loading and testing. We believe the adoption of the standard will have a material impact on our consolidated financial statements as virtually all leases will be recognized as a right of use asset and lease obligation.

MPLX LP

MPLX LP	9 Months Ended
	Sep. 30, 2018
Noncontrolling Interest [Abstract]
MPLX LP	MPLX LP MPLX is a diversified, growth-oriented publicly traded master limited partnership formed by us to own, operate, develop and acquire midstream energy infrastructure assets. MPLX is engaged in the gathering, processing and transportation of natural gas; the gathering, transportation, fractionation, storage and marketing of NGLs; and the transportation, storage, distribution and marketing of crude oil and refined petroleum products. As of September 30, 2018 , we owned 63.6 percent of the outstanding MPLX common units and we control MPLX through our ownership of the general partner of MPLX. MPLX is a VIE because the limited partners of MPLX do not have substantive kick-out or substantive participating rights over the general partner. We are the primary beneficiary of MPLX because in addition to our significant economic interest, we also have the power, through our 100 percent ownership of the general partner, to control the decisions that most significantly impact MPLX. We therefore consolidate MPLX and record a noncontrolling interest for the 36.4 percent interest owned by the public. We also record a redeemable noncontrolling interest related to MPLX’s preferred units. The creditors of MPLX do not have recourse to MPC’s general credit through guarantees or other financial arrangements. The assets of MPLX are the property of MPLX and cannot be used to satisfy the obligations of MPC. MPC has effectively guaranteed certain indebtedness of LOOP LLC (“LOOP”) and LOCAP LLC (“LOCAP”), in which MPLX holds an interest. See Note 22 for more information. Dropdowns to MPLX and GP/IDR Exchange On February 1, 2018, we contributed our refining logistics assets and fuels distribution services to MPLX in exchange for $4.1 billion in cash and approximately 112 million common units and 2 million general partner units from MPLX. MPLX financed the cash portion of the transaction with its $4.1 billion 364 -day term loan facility, which was entered into on January 2, 2018. We agreed to waive approximately one-third of the first quarter 2018 distributions on the common units issued in connection with this transaction. The contributions of these assets were accounted for as transactions between entities under common control and we did not record a gain or loss. Immediately following the February 1, 2018 dropdown to MPLX, our IDRs were cancelled and our economic general partner interest was converted into a non-economic general partner interest, all in exchange for 275 million newly issued MPLX common units (“GP/IDR Exchange”). As a result of this transaction, the general partner units and IDRs were eliminated, are no longer outstanding and no longer participate in distributions of cash from MPLX. On September 1, 2017, we contributed our joint-interest ownership in certain pipelines and storage facilities to MPLX in exchange for $420 million in cash and approximately 19 million common units and 378 thousand general partner units from MPLX. We also agreed to waive approximately two-thirds of the third quarter 2017 common unit distributions, IDRs and general partner distributions with respect to the common units issued in this transaction. The contributions of these assets were accounted for as transactions between entities under common control and we did not record a gain or loss. On March 1, 2017, we contributed certain terminal, pipeline and storage assets to MPLX in exchange for $1.5 billion in cash and approximately 13 million common units and 264 thousand general partner units from MPLX. We also agreed to waive two-thirds of the first quarter 2017 common unit distributions, IDRs and general partner distributions with respect to the common units issued in this transaction. The contributions of these assets were accounted for as transactions between entities under common control and we did not record a gain or loss. Noncontrolling Interest in MPLX As a result of equity transactions of MPLX, we are required to adjust non-controlling interest and additional paid-in capital. Changes in MPC’s additional paid-in capital resulting from changes in its ownership interests in MPLX were as follows: Nine Months Ended (In millions) 2018 2017 Increase due to the issuance of MPLX LP common units to the public $ 6 $ 25 Increase due to the issuance of MPLX LP common units and general partner units to MPC 1,114 113 Increase due to GP/IDR Exchange 1,808 — Increase in MPC's additional paid-in capital 2,928 138 Tax impact (546 ) (26 ) Increase in MPC's additional paid-in capital, net of tax $ 2,382 $ 112 Agreements We have various long-term, fee-based commercial agreements with MPLX. Under these agreements, MPLX provides transportation, storage, distribution and marketing services to us. Under certain agreements, we commit to provide MPLX with minimum quarterly throughput and distribution volumes of crude oil and refined products and minimum storage volumes of crude oil, refined products and butane. Under certain other agreements, we commit to pay for 100 percent of available capacity for certain marine transportation and refining logistics assets. We also have agreements with MPLX that establish fees for operational and management services provided between us and MPLX and for executive management services and certain general and administrative services provided by us to MPLX. These transactions are eliminated in consolidation, but are reflected as intersegment transactions between our Refining & Marketing and Midstream segments.

Acquisitions

Acquisitions	9 Months Ended
	Sep. 30, 2018
Business Combinations [Abstract]
Acquisitions and Investments	ACQUISITIONS Acquisition of Andeavor On October 1, 2018, we completed the acquisition of Andeavor . Under the terms of the merger agreement, Andeavor stockholders had the option to choose 1.87 shares of MPC common stock or $152.27 in cash per share of Andeavor common stock. The merger agreement included election proration provisions that resulted in approximately 22.9 million shares of Andeavor common stock being converted into cash consideration and the remaining 128.2 million shares of Andeavor common stock being converted into stock consideration. Andeavor stockholders received in the aggregate approximately 239.8 million shares of MPC common stock valued at $19.8 billion and approximately $3.5 billion in cash in connection with the Andeavor acquisition. We are completing our analysis of the purchase price consideration and estimating the fair value of assets acquired and liabilities assumed in connection with the Andeavor acquisition, which is likely to result in a significant amount of goodwill. We recognized $14 million in transaction costs related to the Andeavor acquisition, which are reflected in selling, general and administrative expenses for the nine months ended September 30, 2018 . Acquisition of Mt. Airy Terminal On September 26, 2018, MPLX acquired an eastern U.S. Gulf Coast export terminal (“Mt. Airy Terminal”) from Pin Oak Holdings, LLC for total consideration of $451 million . The terminal includes 4 million barrels of third-party leased storage capacity and a 120 mbpd dock. The Mt. Airy Terminal is located on the Mississippi River between New Orleans and Baton Rouge, near several Gulf Coast refineries, including our Garyville Refinery, and numerous rail lines and pipelines. The Mt. Airy Terminal will be accounted for within the Midstream segment. MPLX is still in the process of finalizing the fair value of assets acquired and liabilities assumed, however, the provisional amounts that have been recorded are $330 million for property, plant and equipment and $126 million for goodwill with the remaining difference from the acquisition price being attributable primarily to net assumed liabilities. Goodwill represents the significant growth potential of the terminal due to the multiple pipelines and rail lines which cross the property, the terminal’s position as an aggregation point for liquids growth in the region for both ocean-going vessels and inland barges, the proximity of the terminal to our Garyville refinery and other refineries in the region as well as the capability to construct an additional dock at the site. The amount of revenue and income from operations associated with the acquisition from the terminal acquisition date to September 30, 2018 did not have a material impact on the consolidated financial statements. In addition, assuming the terminal acquisition had occurred on January 1, 2017, the consolidated pro forma results would not have been materially different from the reported results. Acquisition of Ozark Pipeline On March 1, 2017, MPLX acquired the Ozark pipeline from Enbridge Pipelines (Ozark) LLC for approximately $219 million , including purchase price adjustments made in the second quarter of 2017. Based on the fair value of assets acquired and liabilities assumed at the acquisition date, the final purchase price was primarily allocated to property, plant and equipment. The Ozark pipeline is a 433 -mile, 22 -inch diameter crude oil pipeline originating in Cushing, Oklahoma, and terminating in Wood River, Illinois, capable of transporting approximately 230 mbpd. We account for the Ozark pipeline within the Midstream segment. Assuming the acquisition of the Ozark pipeline had occurred on January 1, 2016, the consolidated pro forma results would not have been materially different from reported results. Investment in Pipeline Company On February 15, 2017, MPLX acquired a partial, indirect equity interest in the Dakota Access Pipeline (“DAPL”) and Energy Transfer Crude Oil Company Pipeline (“ETCOP”) projects, collectively referred to as the Bakken Pipeline system, through a joint venture with Enbridge Energy Partners L.P. (“Enbridge Energy Partners”). The Bakken Pipeline system is capable of transporting more than 520 mbpd of crude oil from the Bakken/Three Forks production area in North Dakota to the Midwest through Patoka, Illinois and ultimately to the Gulf Coast. MPLX contributed $500 million of the $2 billion purchase price paid by the joint venture, MarEn Bakken Company LLC (“MarEn Bakken”), to acquire a 36.75 percent indirect equity interest in the Bakken Pipeline system from Energy Transfer Partners, L.P. (“ETP”) and Sunoco Logistics Partners, L.P. (“SXL”). MPLX holds, through a subsidiary, a 25 percent interest in MarEn Bakken, which equates to an approximate 9.2 percent indirect equity interest in the Bakken Pipeline system. We account for the investment in MarEn Bakken as part of our Midstream segment using the equity method of accounting. Formation of Gathering and Processing Joint Venture Effective January 1, 2017, MPLX and Antero Midstream formed a joint venture, Sherwood Midstream LLC (“Sherwood Midstream”), to support the development of Antero Resources Corporation’s Marcellus Shale acreage in West Virginia. MPLX has a 50 percent ownership interest in Sherwood Midstream. In connection with this transaction, MPLX contributed assets then under construction at the Sherwood Complex with a fair value of approximately $134 million and cash of approximately $20 million . Antero Midstream made an initial capital contribution of approximately $154 million . Also effective January 1, 2017, MPLX converted all of its ownership interests in MarkWest Ohio Fractionation Company, L.L.C. (“Ohio Fractionation”), a previously wholly-owned subsidiary, to Class A Interests and amended its LLC Agreement to create Class B-3 Interests, which were sold to Sherwood Midstream for $126 million in cash. The Class B-3 Interests provide Sherwood Midstream with the right to fractionation revenue and the obligation to pay expenses related to 20 mbpd of capacity in the Hopedale 3 fractionator. Effective January 1, 2017, MPLX and Sherwood Midstream formed a joint venture, Sherwood Midstream Holdings LLC (“Sherwood Midstream Holdings”), for the purpose of owning, operating and maintaining all of the shared assets for the benefit of and use in the operation of the gas plants and other assets owned by Sherwood Midstream and the gas plants and deethanization facilities owned by MPLX. MPLX contributed certain real property, equipment and facilities with a fair value of approximately $209 million to Sherwood Midstream Holdings in exchange for a 79 percent initial ownership interest. Sherwood Midstream contributed cash of approximately $44 million to Sherwood Midstream Holdings in exchange for a 21 percent initial ownership interest. The net book value of the contributed assets was approximately $203 million . The contribution was determined to be an in-substance sale of real estate. During the nine months ended September 30, 2018 , MPLX sold to Sherwood Midstream six percent of its equity ownership in Sherwood Midstream Holdings for $15 million . We account for our direct interests in Sherwood Midstream and Sherwood Midstream Holdings as part of our Midstream segment using the equity method of accounting. We continue to consolidate Ohio Fractionation and have recognized a noncontrolling interest for Sherwood Midstream’s interest in that entity. See Note 6 for additional information related to the investments in Sherwood Midstream, Ohio Fractionation and Sherwood Midstream Holdings.

Variable Interest Entities

Variable Interest Entities	9 Months Ended
	Sep. 30, 2018
Variable Interest Entity, Not Primary Beneficiary, Disclosures [Abstract]
Variable Interest Entities	VARIABLE INTEREST ENTITIES In addition to MPLX, as described in Note 4 , the following entities are also VIEs. Crowley Coastal Partners In May 2016, Crowley Coastal Partners LLC (“Crowley Coastal Partners”) was formed to own an interest in both Crowley Ocean Partners LLC (“Crowley Ocean Partners”) and Crowley Blue Water Partners LLC (“Crowley Blue Water Partners”). We have determined that Crowley Coastal Partners is a VIE based on the terms of the existing financing arrangements for Crowley Blue Water Partners and Crowley Ocean Partners and the associated debt guarantees by MPC and Crowley. Our maximum exposure to loss at September 30, 2018 was $483 million , which includes our equity method investment in Crowley Coastal Partners and the debt guarantees provided to each of the lenders to Crowley Blue Water Partners and Crowley Ocean Partners. We are not the primary beneficiary of this VIE because we do not have the power to control the activities that significantly influence the economic outcomes of the entity and, therefore, do not consolidate the entity. MarkWest Utica EMG On January 1, 2012, MarkWest Utica Operating Company, LLC (“Utica Operating”), a wholly-owned and consolidated subsidiary of MarkWest, and EMG Utica, LLC (“EMG Utica”), executed agreements to form a joint venture, MarkWest Utica EMG LLC (“MarkWest Utica EMG”), to develop significant natural gas gathering, processing and NGL fractionation, transportation and marketing infrastructure in eastern Ohio. As of September 30, 2018 , MPLX had a 56 percent ownership interest in MarkWest Utica EMG. MarkWest Utica EMG's inability to fund its planned activities without subordinated financial support qualify it as a VIE. Utica Operating is not deemed to be the primary beneficiary due to EMG Utica’s voting rights on significant matters. We account for our ownership interest in MarkWest Utica EMG as an equity method investment. Our maximum exposure to loss as a result of our involvement with MarkWest Utica EMG includes our equity investment, any additional capital contribution commitments and any operating expenses incurred by the subsidiary operator in excess of compensation received for the performance of the operating services. Our equity investment in MarkWest Utica EMG at September 30, 2018 was $2.1 billion . Ohio Gathering Ohio Gathering Company, L.L.C. (“Ohio Gathering”) is a subsidiary of MarkWest Utica EMG and is engaged in providing natural gas gathering services in the Utica Shale in eastern Ohio. Ohio Gathering is a joint venture between MarkWest Utica EMG and Summit Midstream Partners, LLC. As of September 30, 2018 , MPLX had a 34 percent indirect ownership interest in Ohio Gathering. As this entity is a subsidiary of MarkWest Utica EMG, which is accounted for as an equity method investment, MPLX reports its portion of Ohio Gathering’s net assets as a component of its investment in MarkWest Utica EMG. Sherwood Midstream As described in Note 5 , MPLX and Antero Midstream formed a joint venture, Sherwood Midstream, to support the development of Antero Resources Corporation’s Marcellus Shale acreage in West Virginia. As of September 30, 2018 , MPLX had a 50 percent ownership interest in Sherwood Midstream. Sherwood Midstream’s inability to fund its planned activities without additional subordinated financial support qualify it as a VIE. MPLX is not deemed to be the primary beneficiary, due to Antero Midstream’s voting rights on significant matters. We account for our ownership interest in Sherwood Midstream using the equity method of accounting. Our maximum exposure to loss as a result of our involvement with Sherwood Midstream includes our equity investment, any additional capital contribution commitments and any operating expenses incurred by the subsidiary operator in excess of compensation received for the performance of the operating services. Our equity investment in Sherwood Midstream at September 30, 2018 was $325 million . Ohio Fractionation As described in Note 5 , MPLX converted all of its ownership interests in Ohio Fractionation to Class A Interests and amended its LLC Agreement to create Class B-3 Interests, which were sold to Sherwood Midstream, providing it with the right to fractionation revenue and the obligation to pay expenses related to 20 mbpd of capacity in the Hopedale 3 fractionator. Ohio Fractionation’s inability to fund its operations without additional subordinated financial support qualify it as a VIE. MPLX has been deemed to be the primary beneficiary of Ohio Fractionation because it has control over decisions that could significantly impact its financial performance, and as a result, consolidates Ohio Fractionation. Sherwood Midstream Holdings As described in Note 5 , MPLX and Sherwood Midstream entered into a joint venture, Sherwood Midstream Holdings, for the purpose of owning, operating and maintaining all of the shared assets for the benefit of and use in the operation of the gas plants and other assets owned by Sherwood Midstream and the gas plants and deethanization facilities owned by MPLX. MPLX had an initial 79 percent direct ownership in Sherwood Midstream Holdings, in addition to an initial 10.5 percent indirect interest through its ownership in Sherwood Midstream. Sherwood Midstream Holdings’ inability to fund its operations without additional subordinated financial support qualify it as a VIE. We account for our ownership interest in Sherwood Midstream Holdings using the equity method of accounting as Sherwood Midstream is considered to be the general partner and controls all decisions related to Sherwood Midstream Holdings. Our maximum exposure to loss as a result of our involvement with Sherwood Midstream Holdings includes our equity investment, any additional capital contribution commitments and any operating expenses incurred by the subsidiary operator in excess of compensation received for the performance of the operating services. Our equity investment in Sherwood Midstream Holdings at September 30, 2018 was $155 million .

Related Party Transactions

Related Party Transactions	9 Months Ended
	Sep. 30, 2018
Related Party Transactions [Abstract]
Related Party Transactions	RELATED PARTY TRANSACTIONS We believe that transactions with related parties were conducted on terms comparable to those with unaffiliated parties. Significant transactions with related parties were as follows: Three Months Ended Nine Months Ended (In millions) 2018 2017 2018 2017 Sales to related parties (a) $ 201 $ 157 $ 572 $ 458 Purchases from related parties (b) 149 148 428 420 (a) Sales to related parties consists primarily of sales of refined products to PFJ Southeast, an equity affiliate which owns and operates travel plazas primarily in the Southeast region of the United States. (b) We obtain transportation services and purchase ethanol from certain of our equity affiliates, none of which is individually material.

Income per Common Share

Income per Common Share	9 Months Ended
	Sep. 30, 2018
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 less income allocated to participating securities by the weighted average number of shares of common stock outstanding. Since MPC grants certain incentive compensation awards to employees and non-employee directors that are considered to be participating securities, we have calculated our earnings per share using the two-class method. Diluted income per share assumes exercise of certain stock-based compensation awards, provided the effect is not anti-dilutive. Three Months Ended Nine Months Ended (In millions, except per share data) 2018 2017 2018 2017 Basic earnings per share: Allocation of earnings: Net income attributable to MPC $ 737 $ 903 $ 1,829 $ 1,416 Income allocated to participating securities — — 1 1 Income available to common stockholders – basic $ 737 $ 903 $ 1,828 $ 1,415 Weighted average common shares outstanding 451 504 462 514 Basic earnings per share $ 1.63 $ 1.79 $ 3.96 $ 2.75 Diluted earnings per share: Allocation of earnings: Net income attributable to MPC $ 737 $ 903 $ 1,829 $ 1,416 Income allocated to participating securities — — 1 1 Income available to common stockholders – diluted $ 737 $ 903 $ 1,828 $ 1,415 Weighted average common shares outstanding 451 504 462 514 Effect of dilutive securities 5 4 4 4 Weighted average common shares, including dilutive effect 456 508 466 518 Diluted earnings per share $ 1.62 $ 1.77 $ 3.92 $ 2.73 The following table summarizes the shares that were anti-dilutive and, therefore, were excluded from the diluted share calculation. Three Months Ended Nine Months Ended (In millions) 2018 2017 2018 2017 Shares issuable under stock-based compensation plans — 1 — 1

Equity

Equity	9 Months Ended
	Sep. 30, 2018
Equity [Abstract]
Equity	EQUITY As of September 30, 2018 , we had $5.58 billion of share repurchase authorization remaining under authorizations from our board of directors. 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: Three Months Ended Nine Months Ended (In millions, except per share data) 2018 2017 2018 2017 Number of shares repurchased 5 8 36 31 Cash paid for shares repurchased $ 400 $ 452 $ 2,612 $ 1,622 Average cost per share $ 73.03 $ 53.85 $ 71.80 $ 52.16 Our dividend payments were $0.46 and $0.40 per common share for the three months ended September 30, 2018 and 2017 , respectively, and $1.38 and $1.12 per common share for the nine months ended September 30, 2018 and 2017 , respectively.

Segment Information

Segment Information	9 Months Ended
	Sep. 30, 2018
Segment Reporting [Abstract]
Segment Information	SEGMENT INFORMATION We have three reportable segments: Refining & Marketing; Speedway; and Midstream. 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 six refineries in the Gulf Coast and Midwest regions of the United States, purchases refined products and ethanol for resale and distributes refined products through transportation, storage, distribution and marketing services provided by our Midstream segment. We sell refined products to wholesale marketing customers domestically and internationally, to buyers on the spot market, to our Speedway business segment and to independent entrepreneurs who operate Marathon ® retail outlets. • Speedway – sells transportation fuels and convenience merchandise in retail markets in the Midwest, East Coast, Southeast and Gulf Coast regions of the United States. • Midstream – gathers, processes and transports natural gas; gathers, transports, fractionates, stores and markets NGLs; and transports, stores, distributes and markets crude oil and refined products principally for the Refining & Marketing segment via refining logistics assets, pipelines, terminals, towboats and barges. The Midstream segment primarily reflects the results of MPLX, our sponsored master limited partnership. As discussed in Note 4 , on February 1, 2018, we contributed certain refining logistics assets and fuels distribution services to MPLX. The results of these new businesses are reported in the Midstream segment prospectively from February 1, 2018, resulting in a net reduction of $230 million and $643 million to Refining & Marketing segment results and a net increase to Midstream segment results of the same amount for the three and nine months ended September 30, 2018 , respectively. No effect was given to prior periods as these entities were not considered businesses prior to February 1, 2018. Segment income represents income from operations attributable to the reportable segments. Corporate administrative expenses, except for those attributable to MPLX, 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 the third quarter we began reporting segment capital expenditures and investments excluding acquisitions in the current and comparative periods. (In millions) Refining & Marketing Speedway Midstream Total Three Months Ended September 30, 2018 Revenues: Third party $ 16,552 $ 5,393 $ 842 $ 22,787 Intersegment 2,931 1 787 3,719 Related party 199 2 — 201 Segment revenues $ 19,682 $ 5,396 $ 1,629 $ 26,707 Segment income from operations $ 666 $ 161 $ 679 $ 1,506 Income from equity method investments 7 18 71 96 Depreciation and amortization (a) 257 76 205 538 Capital expenditures and investments (b) 226 98 593 917 (In millions) Refining & Marketing Speedway Midstream Total Three Months Ended September 30, 2017 Revenues: Third party $ 13,573 $ 4,895 $ 585 $ 19,053 Intersegment (c) 2,904 1 369 3,274 Related party 155 2 — 157 Segment revenues $ 16,632 $ 4,898 $ 954 $ 22,484 Segment income from operations $ 1,097 $ 208 $ 355 $ 1,660 Income from equity method investments (a) 6 20 57 83 Depreciation and amortization (a) 266 68 169 503 Capital expenditures and investments (b) 198 108 423 729 (In millions) Refining & Marketing Speedway Midstream Total Nine Months Ended September 30, 2018 Revenues: Third party $ 46,069 $ 15,225 $ 2,305 $ 63,599 Intersegment 8,181 4 2,180 10,365 Related party 566 6 — 572 Segment revenues $ 54,816 $ 15,235 $ 4,485 $ 74,536 Segment income from operations $ 1,558 $ 415 $ 1,863 $ 3,836 Income from equity method investments (a) 14 51 196 261 Depreciation and amortization (a) 761 228 577 1,566 Capital expenditures and investments (b) 613 225 1,676 2,514 (In millions) Refining & Marketing Speedway Midstream Total Nine Months Ended September 30, 2017 Revenues: Third party $ 37,485 $ 14,070 $ 1,665 $ 53,220 Intersegment (c) 8,302 3 1,076 9,381 Related party 452 6 — 458 Segment revenues $ 46,239 $ 14,079 $ 2,741 $ 63,059 Segment income from operations $ 1,589 $ 581 $ 996 $ 3,166 Income from equity method investments (a) 10 54 139 203 Depreciation and amortization (a) 805 197 528 1,530 Capital expenditures and investments (b) 570 221 1,267 2,058 (a) Differences between segment totals and MPC totals represent amounts related to corporate and other unallocated items and are included in items not allocated to segments in the reconciliation below. (b) Capital expenditures include changes in capital accruals and investments in affiliates. See reconciliation from segment totals to MPC total capital expenditures below. (c) Management believes intersegment transactions were conducted under terms comparable to those with unaffiliated parties. The following reconciles segment income from operations to income before income taxes as reported in the consolidated statements of income: Three Months Ended Nine Months Ended (In millions) 2018 2017 2018 2017 Segment income from operations $ 1,506 $ 1,660 $ 3,836 $ 3,166 Items not allocated to segments: Corporate and other unallocated items (a) (103 ) (85 ) (283 ) (251 ) Litigation — — — (86 ) Impairments (b) — 2 1 21 Income from operations 1,403 1,577 3,554 2,850 Net interest and other financial costs 240 158 618 465 Income before income taxes $ 1,163 $ 1,419 $ 2,936 $ 2,385 (a) Corporate and other unallocated items consists primarily of MPC’s corporate administrative expenses and costs related to certain non-operating assets, except for corporate overhead expenses attributable to MPLX, which are included in the Midstream segment. Corporate overhead expenses are not allocated to the Refining & Marketing and Speedway segments. (b) Includes MPC’s share of gains from the sale of assets remaining from the canceled Sandpiper pipeline project. The following reconciles segment capital expenditures and investments to total capital expenditures: Three Months Ended Nine Months Ended (In millions) 2018 2017 2018 2017 Segment capital expenditures and investments $ 917 $ 729 $ 2,514 $ 2,058 Less investments in equity method investees 104 53 222 230 Plus items not allocated to segments: Corporate 7 19 42 53 Capitalized interest 21 13 55 39 Total capital expenditures (a) $ 841 $ 708 $ 2,389 $ 1,920 (a) Capital expenditures include changes in capital accruals. See Note 18 for a reconciliation of total capital expenditures to additions to property, plant and equipment as reported in the consolidated statements of cash flows. Revenues by product line were as follows: Three Months Ended Nine Months Ended (In millions) 2018 2017 2018 2017 Refined products $ 19,815 $ 16,374 $ 55,265 $ 45,689 Merchandise 1,340 1,370 3,756 3,905 Crude oil and refinery feedstocks 1,011 878 2,872 2,389 Midstream services, transportation and other 621 431 1,706 1,237 Sales and other operating revenues $ 22,787 $ 19,053 $ 63,599 $ 53,220

Net Interest and Other Financia

Net Interest and Other Financial Costs	9 Months Ended
	Sep. 30, 2018
Other Income and Expenses [Abstract]
Net Interest and Other Financial Costs	NET INTEREST AND OTHER FINANCIAL COSTS Net interest and other financial costs were as follows: Three Months Ended Nine Months Ended (In millions) 2018 2017 2018 2017 Interest income $ (26 ) $ (7 ) $ (71 ) $ (16 ) Interest expense 233 172 675 508 Interest capitalized (21 ) (14 ) (55 ) (47 ) Pension and other postretirement non-service costs (a) 45 1 47 — Loss on extinguishment of debt — — 4 — Other financial costs 9 6 18 20 Net interest and other financial costs $ 240 $ 158 $ 618 $ 465 (a) See Note 20 .

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Income Taxes	INCOME TAXES The combined federal, state and foreign income tax rate was 19 percent and 29 percent for the three months ended September 30, 2018 and 2017 , respectively, and 18 percent and 30 percent for the nine months ended September 30, 2018 and 2017 , respectively. The effective tax rate for the three and nine months ended September 30, 2018 was less than the U.S. statutory rate of 21 percent primarily due to certain permanent tax differences related to net income attributable to noncontrolling interest offset by state and local tax expense. The effective tax rate for the three and nine months ended September 30, 2017 was less than the then applicable U.S. statutory rate of 35 percent primarily due to certain permanent tax differences related to net income attributable to noncontrolling interest, the domestic manufacturing deduction and equity compensation offset by state and local tax expense. We are continuously undergoing examination of our income tax returns, which have been completed through the 2007 tax year for state returns and the 2009 tax year for our U.S. federal return. As of September 30, 2018 , we had $21 million of unrecognized tax benefits. Prior to its spin-off on June 30, 2011, Marathon Petroleum Corporation was included in the Marathon Oil Corporation (“Marathon Oil”) federal income tax returns for all applicable years. During the third quarter of 2017, Marathon Oil received a notice of Final Partnership Administrative Adjustment (“FPAA”) from the U.S. Internal Revenue Service for taxable year 2010, relating to certain pre-spinoff transactions. Marathon Oil filed a U.S. Tax Court petition disputing these adjustments during the fourth quarter of 2017. We received an FPAA for taxable years 2011-2014 for items resulting from this matter and filed a U.S. Tax Court petition for tax years 2011-2014 to dispute these corollary adjustments in the fourth quarter of 2017. We continue to believe that the issue in dispute is more likely than not to be fully sustained and, therefore, no liability has been accrued for this matter. 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 22 for indemnification information.

Inventories

Inventories	9 Months Ended
	Sep. 30, 2018
Inventory Disclosure [Abstract]
Inventories	INVENTORIES (In millions) September 30, December 31, Crude oil and refinery feedstocks $ 1,717 $ 2,056 Refined products 3,005 2,839 Materials and supplies 465 494 Merchandise 152 161 Total $ 5,339 $ 5,550 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 LIFO method. There were no material LIFO inventory liquidations recognized for the nine months ended September 30, 2018 .

Property, Plant and Equipment

Property, Plant and Equipment	9 Months Ended
	Sep. 30, 2018
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	PROPERTY, PLANT AND EQUIPMENT (In millions) September 30, December 31, Refining & Marketing (a) $ 18,708 $ 19,490 Speedway 5,520 5,358 Midstream (a) 18,213 14,898 Corporate and Other 835 792 Total 43,276 40,538 Less accumulated depreciation 15,559 14,095 Property, plant and equipment, net $ 27,717 $ 26,443 (a) On February 1, 2018, we contributed certain refining logistics assets and fuels distribution services to MPLX. In connection with this transaction, approximately $830 million of net property, plant and equipment was recorded to the Midstream segment with an offsetting reduction to the Refining & Marketing segment . We own a 33 percent undivided joint interest in the Capline Pipeline System (“Capline”), a crude oil pipeline that runs from St. James, Louisiana to Patoka, Illinois. We account for this undivided joint interest by recognizing our proportionate share of Capline’s assets on our balance sheet, which are primarily classified as property, plant and equipment. Capline experienced a significant reduction in shipment volumes in the second quarter of 2018 primarily due to recently completed competing pipelines. The pipeline’s owners are proceeding with planning for the reversal of the pipeline to support southbound movements of crude oil as supported by shipper interest indicated during a non-binding open season conducted in 2017. Pending agreement among the owners, southbound service is estimated to commence by the second half of 2022. In the second quarter of 2018, we evaluated our share of Capline assets for impairment in accordance with ASC 360, and determined no impairment existed due to the probability of continuing future cash flows associated with a reversed Capline. We continue to monitor developments in the commercial outlook for Capline and noted no significant changes in the third quarter. As of September 30, 2018 , our carrying value was $154 million .

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2018
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 September 30, 2018 and December 31, 2017 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. September 30, 2018 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 $ 62 $ — $ — $ (62 ) $ — $ 20 Other assets 3 — — N/A 3 — Total assets at fair value $ 65 $ — $ — $ (62 ) $ 3 $ 20 Commodity derivative instruments, liabilities $ 99 $ — $ 2 $ (99 ) $ 2 $ — Embedded derivatives in commodity contracts — — 82 — 82 — Total liabilities at fair value $ 99 $ — $ 84 $ (99 ) $ 84 $ — December 31, 2017 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 $ 127 $ — $ — $ (118 ) $ 9 $ 8 Other assets 3 — — N/A 3 — Total assets at fair value $ 130 $ — $ — $ (118 ) $ 12 $ 8 Commodity derivative instruments, liabilities $ 126 $ — $ 2 $ (126 ) $ 2 $ — Embedded derivatives in commodity contracts — — 64 — 64 — Total liabilities at fair value $ 126 $ — $ 66 $ (126 ) $ 66 $ — (a) Represents the impact of netting assets, liabilities and cash collateral when a legal right of offset exists. As of September 30, 2018 , cash collateral of $37 million was netted with the mark-to-market derivative liabilities. As of December 31, 2017 , $8 million was netted with mark-to-market derivative liabilities. (b) We have no derivative contracts that are subject to master netting arrangements reflected gross on the balance sheet. 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. Level 3 instruments are OTC NGL contracts and embedded derivatives in commodity contracts. The embedded derivative liability relates to a natural gas purchase agreement embedded in a keep‑whole processing agreement. The fair value calculation for these Level 3 instruments used significant unobservable inputs including: (1) NGL prices interpolated and extrapolated due to inactive markets ranging from $0.78 to $1.65 per gallon and (2) the probability of renewal of 80 percent for the first five -year term and 70 percent for the second five -year term of the natural gas purchase agreement and the related keep-whole processing agreement. For these contracts, increases in forward NGL prices result in a decrease in the fair value of the derivative assets and an increase in the fair value of the derivative liabilities. The forward prices for the individual NGL products generally increase or decrease in a positive correlation with one another. Increases or decreases in forward NGL prices result in an increase or decrease in the fair value of the embedded derivative liability. An increase in the probability of renewal would result in an increase in the fair value of the related embedded derivative liability. 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 Nine Months Ended (In millions) 2018 2017 2018 2017 Beginning balance $ 68 $ 41 $ 66 $ 190 Contingent consideration payment — — — (131 ) Unrealized and realized losses included in net income 20 22 29 8 Settlements of derivative instruments (4 ) (6 ) (11 ) (10 ) Ending balance $ 84 $ 57 $ 84 $ 57 The amount of total losses for the period included in earnings attributable to the change in unrealized losses relating to assets still held at the end of period: Derivative instruments $ 21 $ 17 $ 22 $ 8 Contingent consideration agreement — — — 1 Total $ 21 $ 17 $ 22 $ 9 Fair Values – Reported The following table summarizes financial instruments on the basis of their nature, characteristics and risk at September 30, 2018 and December 31, 2017 , excluding the derivative financial instruments and contingent consideration reported above. September 30, 2018 December 31, 2017 (In millions) Fair Value Carrying Value Fair Value Carrying Value Financial assets: Environmental receivables and misc. deposits 23 23 17 17 Total financial assets $ 23 $ 23 $ 17 $ 17 Financial liabilities: Long-term debt (a) $ 18,421 $ 18,036 $ 13,893 $ 12,642 Deferred credits and other liabilities 115 107 122 109 Total financial liabilities $ 18,536 $ 18,143 $ 14,015 $ 12,751 (a) Excludes capital leases and debt issuance costs; includes amount classified as debt due within one year. Our current assets and liabilities include financial instruments, the most significant of which are trade accounts receivable and payables. Fair values of our 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. Deferred credits and other liabilities primarily consist of a liability resulting from a financing arrangement for the construction of MPLX’s steam methane reformer at the Javelina gas processing and fractionation complex in Corpus Christi, Texas, insurance liabilities and environmental remediation liabilities. Fair value of fixed-rate long-term debt is measured using Level 3 inputs. Fair value of variable-rate long-term debt approximates the carrying value.

Derivatives

Derivatives	9 Months Ended
	Sep. 30, 2018
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 15 . 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, (4) the acquisition of ethanol for blending with refined products, (5) the sale of NGLs and (6) the purchase of natural gas. 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 September 30, 2018 and December 31, 2017 : (In millions) September 30, 2018 Balance Sheet Location Asset Liability Commodity derivatives Other current assets $ 62 $ 99 Other current liabilities (a) — 17 Deferred credits and other liabilities (a) — 67 (In millions) December 31, 2017 Balance Sheet Location Asset Liability Commodity derivatives Other current assets $ 127 $ 126 Other current liabilities (a) — 14 Deferred credits and other liabilities (a) — 52 (a) Includes embedded derivatives. The tables below summarize open commodity derivative contracts for crude oil and refined products as of September 30, 2018 . Position Total Barrels (In thousands) Crude Oil (a) Exchange-traded Long 14,052 Exchange-traded Short (16,782 ) (a) 98.7 percent of the exchange-traded contracts expire in the fourth quarter of 2018 . Position Total Gallons (In thousands) Refined Products (a) Exchange-traded Long 135,408 Exchange-traded Short (320,250 ) OTC Short (28,980 ) (a) 97.1 percent of the exchange-traded contracts expire in the fourth quarter of 2018 . The following table summarizes the effect of all commodity derivative instruments in our consolidated statements of income: Gain (Loss) Gain (Loss) (In millions) Three Months Ended September 30, Nine Months Ended September 30, Income Statement Location 2018 2017 2018 2017 Sales and other operating revenues $ 3 $ (10 ) $ 1 $ 8 Cost of revenues (69 ) 1 (152 ) (30 ) Total $ (66 ) $ (9 ) $ (151 ) $ (22 )

Debt

Debt	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
Debt	DEBT Our outstanding borrowings at September 30, 2018 and December 31, 2017 consisted of the following: (In millions) September 30, December 31, Marathon Petroleum Corporation: Commercial paper $ — $ — 364-day bank revolving credit facility due July 2018 (a) — — Trade receivables securitization facility due July 2019 — — Bank revolving credit facility due 2022 — — Senior notes, 2.700% due December 2018 — 600 Senior notes, 3.400% due December 2020 650 650 Senior notes, 5.125% due March 2021 1,000 1,000 Senior notes, 3.625%, due September 2024 750 750 Senior notes, 6.500%, due March 2041 1,250 1,250 Senior notes, 4.750%, due September 2044 800 800 Senior notes, 5.850% due December 2045 250 250 Senior notes, 5.000%, due September 2054 400 400 Capital lease obligations due 2018-2033 511 356 MPLX LP: MPLX bank revolving credit facility due 2022 1,000 505 MPLX senior notes, 5.500%, due February 2023 710 710 MPLX senior notes, 3.375%, due March 2023 500 — MPLX senior notes, 4.500%, due July 2023 989 989 MPLX senior notes, 4.875%, due December 2024 1,149 1,149 MPLX senior notes, 4.000%, due February 2025 500 500 MPLX senior notes, 4.875%, due June 2025 1,189 1,189 MarkWest senior notes, 4.500% - 5.500%, due 2023 - 2025 63 63 MPLX senior notes, 4.125%, due March 2027 1,250 1,250 MPLX senior notes, 4.000%, due March 2028 1,250 — MPLX senior notes, 4.500%, due April 2038 1,750 — MPLX senior notes, 5.200%, due March 2047 1,000 1,000 MPLX senior notes, 4.700%, due April 2048 1,500 — MPLX senior notes, 4.900%, due April 2058 500 — MPLX capital lease obligations due 2020 7 7 Total 18,968 13,418 Unamortized debt issuance costs (105 ) (59 ) Unamortized discount (414 ) (413 ) Amounts due within one year (26 ) (624 ) Total long-term debt due after one year $ 18,423 $ 12,322 (a) The 364-day facility expired on July 20, 2018. Commercial Paper During the nine months ended September 30, 2018 , we had no borrowings or repayments under the commercial paper program. At September 30, 2018 , we had no amounts outstanding under the commercial paper program. Trade Receivables Securitization Facility At September 30, 2018 , we had no amounts outstanding under our trade receivables securitization facility. MPC Revolving Credit Agreements There were no borrowings or letters of credit outstanding under the MPC bank revolving credit facility at September 30, 2018 . MPC Senior Notes On March 15, 2018, we redeemed all of the $600 million outstanding aggregate principal amount of our 2.700 percent senior notes due December 2018. The 2018 senior notes were redeemed at a price equal to par plus a make whole premium, plus accrued and unpaid interest. The make whole premium of $2.5 million was calculated based on the market yield of the applicable treasury issue as of the redemption date as determined in accordance with the indenture governing the 2018 senior notes. MPLX Credit Agreement During the nine months ended September 30, 2018 , MPLX borrowed $1.175 billion under the MPLX bank revolving credit facility, at an average interest rate of 3.1 percent , and repaid $680 million . At September 30, 2018 , MPLX had $1 billion outstanding borrowings and $3 million letters of credit outstanding under the MPLX bank revolving credit facility, resulting in total availability of approximately $1.247 billion . MPLX 364-Day Term Loan On January 2, 2018, MPLX entered into a term loan agreement with a syndicate of lenders providing for a $4.1 billion , 364 -day term loan facility. MPLX drew the entire amount of the term loan facility in a single borrowing to fund the cash portion of the consideration for the February 1, 2018 dropdown. On February 8, 2018, MPLX used $4.1 billion of the net proceeds from the issuance of MPLX senior notes to repay the 364 -day term-loan facility. MPLX Senior Notes On February 8, 2018, MPLX issued $5.5 billion in aggregate principal amount of senior notes in a public offering, consisting of $500 million aggregate principal amount of 3.375 percent unsecured senior notes due March 2023, $1.25 billion aggregate principal amount of 4.000 percent unsecured senior notes due March 2028, $1.75 billion aggregate principal amount of 4.500 percent unsecured senior notes due April 2038, $1.5 billion aggregate principal amount of 4.700 percent unsecured senior notes due April 2048, and $500 million aggregate principal amount of 4.900 percent unsecured senior notes due April 2058. MPLX used $4.1 billion of the net proceeds of the offering to repay the 364-day term-loan facility. The remaining proceeds were used to repay outstanding borrowings under MPLX’s revolving credit facility and intercompany loan agreement with us and for general partnership purposes.

Supplemental Cash Flow Informat

Supplemental Cash Flow Information	9 Months Ended
	Sep. 30, 2018
Supplemental Cash Flow Elements [Abstract]
Supplemental Cash Flow Information	SUPPLEMENTAL CASH FLOW INFORMATION Nine Months Ended (In millions) 2018 2017 Net cash provided by operating activities included: Interest paid (net of amounts capitalized) $ 520 $ 446 Income taxes paid to taxing authorities 153 383 Non-cash investing and financing activities: Capital leases 171 — Contribution of assets to joint venture (a) — 337 (a) MarkWest’s contribution of assets to Sherwood Midstream and Sherwood Midstream Holdings. See Note 5 . (In millions) September 30, December 31, Cash and cash equivalents $ 4,992 $ 3,011 Restricted cash (a) 3 4 Cash, cash equivalents and restricted cash (b) $ 4,995 $ 3,015 (a) The restricted cash balance is included within other current assets on the consolidated balance sheets. (b) As a result of the adoption of ASU 2016-18, the consolidated statements of cash flows now explain the change during the period of both cash and cash equivalents and restricted cash. 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 per the consolidated statements of cash flows to total capital expenditures: Nine Months Ended (In millions) 2018 2017 Additions to property, plant and equipment per the consolidated statements of cash flows $ 2,315 $ 1,928 Asset retirement expenditures 7 1 Increase (decrease) in capital accruals 67 (9 ) Total capital expenditures $ 2,389 $ 1,920

Accumulated Other Comprehensive

Accumulated Other Comprehensive Loss	9 Months Ended
	Sep. 30, 2018
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, 2016 $ (233 ) $ (7 ) $ 4 $ 2 $ (234 ) Other comprehensive loss before reclassifications (2 ) — — — (2 ) Amounts reclassified from accumulated other comprehensive loss: Amortization – prior service credit (a) (29 ) (2 ) — — (31 ) – actuarial loss/(gain) (a) 27 (1 ) — — 26 – settlement loss (a) 2 — — — 2 Other (b) — — — (2 ) (2 ) Tax effect — 1 — 1 2 Other comprehensive loss (2 ) (2 ) — (1 ) (5 ) Balance as of September 30, 2017 $ (235 ) $ (9 ) $ 4 $ 1 $ (239 ) (In millions) Pension Benefits Other Benefits Gain on Cash Flow Hedge Workers Compensation Total Balance as of December 31, 2017 $ (190 ) $ (48 ) $ 4 $ 3 $ (231 ) Other comprehensive income (loss) before reclassifications 35 (1 ) (2 ) — 32 Amounts reclassified from accumulated other comprehensive loss: Amortization – prior service credit (a) (25 ) (2 ) — — (27 ) – actuarial loss/(gain) (a) 26 (1 ) — — 25 – settlement loss (a) 47 — — — 47 Other (b) — — — (4 ) (4 ) Tax effect (12 ) 1 — 1 (10 ) Other comprehensive income (loss) 71 (3 ) (2 ) (3 ) 63 Balance as of September 30, 2018 $ (119 ) $ (51 ) $ 2 $ — $ (168 ) (a) These accumulated other comprehensive loss components are included in the computation of net periodic benefit cost. See Note 20 . (b) This amount was reclassified out of accumulated other comprehensive loss and is included in selling, general and administrative expenses on the consolidated statements of income.

Defined Benefit Pension and Oth

Defined Benefit Pension and Other Postretirement Plans	9 Months Ended
	Sep. 30, 2018
Retirement Benefits [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 September 30, Pension Benefits Other Benefits (In millions) 2018 2017 2018 2017 Components of net periodic benefit cost: Service cost $ 36 $ 33 $ 7 $ 6 Interest cost 18 19 7 8 Expected return on plan assets (25 ) (25 ) — — Amortization – prior service credit (9 ) (10 ) — — – actuarial loss (gain) 9 9 (1 ) — – settlement loss 45 1 — — Net periodic benefit cost $ 74 $ 27 $ 13 $ 14 Nine Months Ended September 30, Pension Benefits Other Benefits (In millions) 2018 2017 2018 2017 Components of net periodic benefit cost: Service cost $ 107 $ 99 $ 22 $ 19 Interest cost 54 56 22 23 Expected return on plan assets (75 ) (75 ) — — Amortization – prior service credit (25 ) (29 ) (2 ) (2 ) – actuarial loss (gain) 26 27 (1 ) (1 ) – settlement loss 47 2 — — Net periodic benefit cost $ 134 $ 80 $ 41 $ 39 The components of net periodic benefit cost other than the service cost component are included in net interest and other financial costs on the consolidated statements of income. During the nine months ended September 30, 2018 , we chose to make a $100 million voluntary contribution to our funded pension plans. Benefit payments related to unfunded pension and other postretirement benefit plans were $13 million and $25 million , respectively, during the nine months ended September 30, 2018 .

Stock-Based Compensation Plans

Stock-Based Compensation Plans	9 Months Ended
	Sep. 30, 2018
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 nine months ended September 30, 2018 : Number of Shares Weighted Average Exercise Price Outstanding at December 31, 2017 8,465,398 $ 33.74 Granted 903,797 67.71 Exercised (905,914 ) 26.30 Forfeited or expired (28,664 ) 47.54 Outstanding at September 30, 2018 8,434,617 38.13 The grant date fair value of stock option awards granted during the nine months ended September 30, 2018 was $17.21 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 nine months ended September 30, 2018 : 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, 2017 1,188,662 $ 45.07 285,164 $ 29.95 Granted 438,209 70.39 19,173 70.99 RS Vested/RSUs Issued (552,217 ) 44.88 (151,170 ) 22.95 Forfeited (51,645 ) 49.33 — — Outstanding at September 30, 2018 1,023,009 55.80 153,167 42.00 Performance Unit Awards The following table presents a summary of the activity for performance unit awards to be settled in shares for the nine months ended September 30, 2018 : Number of Units Weighted Average Grant Date Fair Value Outstanding at December 31, 2017 6,851,542 $ 0.81 Granted 3,830,000 0.83 Vested (2,052,959 ) 0.95 Forfeited (10,000 ) 0.92 Outstanding at September 30, 2018 8,618,583 0.79 The performance unit awards granted during the nine months ended September 30, 2018 have a grant date fair value of $0.83 per unit, as calculated using a Monte Carlo valuation model. MPLX Awards During the nine months ended September 30, 2018 , MPLX granted equity-based compensation awards under the MPLX LP 2018 and MPLX LP 2012 Incentive Compensation Plans. The compensation expense for these awards is not material to our consolidated financial statements.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2018
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 a liability, we are unable to estimate a range of possible loss because the issues involved have not been fully developed through pleadings, discovery or court proceedings. 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 September 30, 2018 and December 31, 2017 , accrued liabilities for remediation totaled $104 million and $114 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, were $36 million and $45 million at September 30, 2018 and December 31, 2017 , 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. Litigation Relating to the Acquisition of Andeavor Between June 20 and July 11, 2018, six putative class actions (the “Actions”) were filed against some or all of Andeavor, the directors of Andeavor, and MPC, Mahi Inc. (“Merger Sub 1”) and Mahi LLC (n/k/a Andeavor LLC) (“Merger Sub 2” and, together with MPC and Merger Sub 1, the “MPC Defendants”), relating to the Andeavor merger. Two complaints, Malka Raul v. Andeavor, et al., and Stephen Bushansky v. Andeavor, et al., were filed in the U.S. District Court for the Western District of Texas. Four complaints, captioned The Vladimir Gusinsky Rev. Trust v. Andeavor, et al., Lawrence Zucker v. Andeavor, et al., Mel Gross v. Andeavor, et al., and Hudson v. Andeavor, et al. were filed in the U.S. District Court for the District of Delaware. The Actions generally alleged that Andeavor, the directors of Andeavor and the MPC Defendants disseminated a false or misleading registration statement regarding the merger in violation of Section 14(a) of the Securities Exchange Act of 1934 (“the “Exchange Act”) and Rule 14a-9 promulgated thereunder. Specifically, the Actions alleged that the registration statement filed by MPC misstated or omitted material information regarding the parties’ financial projections and the analyses performed by Andeavor’s and MPC’s respective financial advisors, and that disclosure of material information was necessary in light of preclusive deal protection provisions in the merger agreement, the financial interests of Andeavor’s officers and directors in completing the deal, and the financial interests of Andeavor’s and MPC’s respective financial advisors. The Actions further alleged that the directors of Andeavor and/or the MPC Defendants were liable for these violations as “controlling persons” of Andeavor under Section 20(a) of the Exchange Act. The Actions sought injunctive relief, including to enjoin and/or rescind the merger, damages in the event the merger is consummated, and an award of attorneys’ fees, in addition to other relief. On July 5 and July 20, 2018, MPC filed amendments to its Registration Statement on Form S-4, which included certain supplemental disclosures responding to allegations made by the plaintiffs. On August 3, 2018, Andeavor filed its proxy statement, and after that date, the parties had numerous discussions regarding the adequacy of disclosures. The parties ultimately reached an agreement in principle to resolve the Actions in exchange for the supplemental disclosures. Consistent with that agreement, Andeavor and MPC each filed a Current Report on Form 8-K on September 14, 2018 that included certain additional disclosures in response to plaintiffs’ allegations. Between September 21 and September 28, 2018, all the Actions were dismissed as moot, and the parties reserved their rights in the event of any dispute over attorneys’ fees and expenses. The Company does not believe the ultimate resolution of these fee issues will be material. Other Lawsuits In May 2015, the Kentucky attorney general filed a lawsuit against our wholly-owned subsidiary, MPC LP, in the United States District Court for the Western District of Kentucky asserting claims under federal and state antitrust statutes, the Kentucky Consumer Protection Act, and state common law. The complaint, as amended in July 2015, alleges that MPC LP used deed restrictions, supply agreements with customers and exchange agreements with competitors to unreasonably restrain trade in areas within Kentucky and seeks declaratory relief, unspecified damages, civil penalties, restitution and disgorgement of profits. At this stage, the ultimate outcome of this litigation remains uncertain, and neither the likelihood of an unfavorable outcome nor the ultimate liability, if any, can be determined, and we are unable to estimate a reasonably possible loss (or range of loss) for this matter. We intend to vigorously defend ourselves in this matter. 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 on our consolidated financial position, results of operations, or cash flows. We are also a party to 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 —MPC and MPLX hold interests in an offshore oil port, LOOP, and MPLX holds an interest in a crude oil pipeline system, LOCAP. Both LOOP and LOCAP have secured various project financings with throughput and deficiency agreements. Under the agreements, MPC, as a shipper, is 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 $160 million as of September 30, 2018 . We hold an interest in a refined products pipeline through our investment in Centennial Pipeline LLC (“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 $22 million as of September 30, 2018 . In connection with our 50 percent indirect interest in Crowley Ocean Partners, we have agreed to conditionally guarantee our portion of the obligations of the joint venture and its subsidiaries under a senior secured term loan agreement. The term loan agreement provides for loans of up to $325 million to finance the acquisition of four product tankers. MPC’s liability under the guarantee for each vessel is conditioned upon the occurrence of certain events, including if we cease to maintain an investment grade credit rating or the charter for the relevant product tanker ceases to be in effect and is not replaced by a charter with an investment grade company on certain defined commercial terms. As of September 30, 2018 , our maximum potential undiscounted payments under this agreement for debt principal totaled $163 million . In connection with our 50 percent indirect interest in Crowley Blue Water Partners, we have agreed to provide a conditional guarantee of up to 50 percent of its outstanding debt balance in the event there is no charter agreement in place with an investment grade customer for the entity’s three vessels as well as other financial support in certain circumstances. The maximum exposure under these arrangements is 50 percent of the amount of the debt, which was $128 million as of September 30, 2018 . 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 $3 million as of September 30, 2018 , 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 12 , 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 $92 million as of September 30, 2018 , 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, a commitment to fund a share of the bonds issued by a government entity for construction of public utilities in the event that other industrial users of the facility default on their utility payments 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 and Contingencies At September 30, 2018 , our contractual commitments to acquire property, plant and equipment and advance funds to equity method investees totaled $1.03 billion . Certain natural gas processing and gathering arrangements require us to construct natural gas processing plants, natural gas gathering pipelines and NGL pipelines and contain certain fees and charges if specified construction milestones are not achieved for reasons other than force majeure. In certain cases, certain producer customers may have the right to cancel the processing arrangements with us if there are significant delays that are not due to force majeure.

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2018
Subsequent Events [Abstract]
Subsequent Events	SUBSEQUENT EVENTS Acquisition of Andeavor See Note 5 for additional information on the Andeavor acquisition. Authorized Shares of MPC Common Stock On October 1, 2018, in connection with the Andeavor acquisition, we amended our certification of incorporation to increase the number of authorized shares of MPC common stock from one billion to two billion , as approved by MPC stockholders at MPC’s September 24, 2018 special meeting of stockholders. MPC Revolving Credit Agreements On August 28, 2018, we entered into credit agreements with a syndicate of lenders to replace MPC’s previous five -year $2.5 billion bank revolving credit facility due in 2022 and our previous 364 -day $1 billion bank revolving agreement that expired in July 2018. The new credit agreements, which became effective October 1, 2018 in connection with the Andeavor acquisition, provide for a $5 billion five -year revolving credit agreement that expires in 2023 (“new MPC five-year credit agreement”) and a $1 billion 364 -day revolving credit agreement that expires in 2019 (“new MPC 364-day credit agreement” and together with the new MPC five-year credit agreement, the “new MPC credit agreements”). MPC has an option under the new MPC five-year credit agreement to increase the aggregate commitments by up to an additional $1 billion , subject to, among other conditions, the consent of the lenders whose commitments would be increased. In addition, MPC may request up to two one -year extensions of the maturity date of the new MPC five-year credit agreement subject to, among other conditions, the consent of lenders holding a majority of the commitments, provided that the commitments of any non-consenting lenders will terminate on the then-effective maturity date. The new MPC five-year credit agreement includes sub-facilities for swing-line loans of up to $250 million and letters of credit of up to $2.2 billion (which may be increased to up to $3 billion upon receipt of additional letter of credit issuing commitments). The financial covenants and the interest rate terms contained in the new credit agreements are substantially the same as those contained in the previous bank revolving credit facilities. MPC Senior Notes As a result of the completion of the Andeavor acquisition, we assumed an aggregate principal amount of $3.375 billion senior notes issued by Andeavor. On October 2, 2018, approximately $2.905 billion aggregate principal amount of Andeavor ’s outstanding senior notes were exchanged for new unsecured senior notes issued by MPC having the same maturity and interest rates as the Andeavor senior notes and cash in an exchange offer and consent solicitation undertaken by MPC and Andeavor.

Supplementary Statistics

Supplementary Statistics	9 Months Ended
	Sep. 30, 2018
Text Block [Abstract]
Supplementary Statistics	SUPPLEMENTARY STATISTICS (UNAUDITED) Three Months Ended Nine Months Ended (In millions) 2018 2017 2018 2017 Income from Operations by Segment Refining & Marketing (a) $ 666 $ 1,097 $ 1,558 $ 1,589 Speedway 161 208 415 581 Midstream (a) 679 355 1,863 996 Items not allocated to segments: Corporate and other unallocated items (103 ) (85 ) (283 ) (251 ) Litigation — — — (86 ) Impairments (b) — 2 1 21 Income from operations $ 1,403 $ 1,577 $ 3,554 $ 2,850 Capital Expenditures and Investments (c) Refining & Marketing $ 226 $ 198 $ 613 $ 570 Speedway 98 108 225 221 Midstream 593 423 1,676 1,267 Corporate and Other (d) 28 32 97 92 Total capital expenditures and investments $ 945 $ 761 $ 2,611 $ 2,150 (a) On February 1, 2018, we contributed certain refining logistics assets and fuels distributions services to MPLX. The results of these new businesses are reported in the Midstream segment prospectively from February 1, resulting in a net reduction of $230 million and $643 million to Refining & Marketing segment results and a net increase to Midstream segment results of the same amount for the three and nine months ended September 30, 2018 , respectively. No effect was given to prior periods as these entities were not considered businesses prior to February 1, 2018. (b) Includes MPC’s share of gains from the sales of assets remaining from the canceled Sandpiper pipeline project. (c) Capital expenditures include changes in capital accruals and investments in affiliates and excludes acquisitions. (d) Includes capitalized interest of $21 million and $13 million for the three months ended September 30, 2018 and 2017 , respectively, and $55 million and $39 million for the nine months ended September 30, 2018 and 2017 , respectively. SUPPLEMENTARY STATISTICS (UNAUDITED) Three Months Ended Nine Months Ended 2018 2017 2018 2017 MPC Consolidated Refined Product Sales Volumes (mbpd) (a) 2,394 2,357 2,358 2,272 Refining & Marketing Operating Statistics Refining & Marketing refined product sales volume (mbpd) (b) 2,382 2,357 2,346 2,263 Export sales volume (mbpd) (c) 280 331 289 291 Refining & Marketing margin (dollars per barrel) (d) $ 14.25 $ 14.14 $ 13.48 $ 12.42 Crude oil capacity utilization percent (e) 97.4 101.5 96.7 95.8 Refinery throughputs (mbpd): (f) Crude oil refined 1,833 1,845 1,819 1,741 Other charge and blendstocks 199 172 173 176 Total 2,032 2,017 1,992 1,917 Sour crude oil throughput percent 52 57 53 61 WTI-priced crude oil throughput percent 30 23 28 20 Refined product yields (mbpd): (f) Gasoline 942 939 942 910 Distillates 676 673 659 627 Propane 40 38 37 35 Feedstocks and special products 313 298 294 285 Heavy fuel oil 29 45 30 36 Asphalt 73 67 68 64 Total 2,073 2,060 2,030 1,957 Refinery direct operating costs (dollars per barrel): (g) Planned turnaround and major maintenance $ 1.77 $ 1.20 $ 1.64 $ 1.69 Depreciation and amortization 1.29 1.34 1.31 1.44 Other manufacturing (h) 3.54 3.83 3.71 4.10 Total $ 6.60 $ 6.37 $ 6.66 $ 7.23 Refining & Marketing Operating Statistics By Region - Gulf Coast Refinery throughputs (mbpd): (i) Crude oil refined 1,150 1,123 1,121 1,041 Other charge and blendstocks 204 217 187 219 Total 1,354 1,340 1,308 1,260 Sour crude oil throughput percent 63 69 62 75 WTI-priced crude oil throughput percent 17 14 15 10 Refined product yields (mbpd): (i) Gasoline 567 538 557 525 Distillates 442 438 421 393 Propane 27 25 24 25 Feedstocks and special products 314 326 301 310 Heavy fuel oil 16 31 18 24 Asphalt 22 19 21 17 Total 1,388 1,377 1,342 1,294 Three Months Ended Nine Months Ended 2018 2017 2018 2017 Refinery direct operating costs (dollars per barrel): (g) Planned turnaround and major maintenance $ 0.64 $ 0.90 $ 1.30 $ 1.86 Depreciation and amortization 1.03 1.05 1.03 1.15 Other manufacturing (h) 3.20 3.52 3.43 3.81 Total $ 4.87 $ 5.47 $ 5.76 $ 6.82 Refining & Marketing Operating Statistics By Region – Midwest Refinery throughputs (mbpd): (i) Crude oil refined 683 722 698 700 Other charge and blendstocks 49 35 39 31 Total 732 757 737 731 Sour crude oil throughput percent 34 38 37 41 WTI-priced crude oil throughput percent 52 38 49 34 Refined product yields (mbpd): (i) Gasoline 375 401 385 385 Distillates 234 235 238 234 Propane 13 14 13 11 Feedstocks and special products 53 50 46 47 Heavy fuel oil 13 15 12 13 Asphalt 51 48 47 47 Total 739 763 741 737 Refinery direct operating costs (dollars per barrel): (g) Planned turnaround and major maintenance $ 3.74 $ 1.60 $ 2.13 $ 1.22 Depreciation and amortization 1.68 1.72 1.70 1.80 Other manufacturing (h) 3.89 3.96 3.96 4.19 Total $ 9.31 $ 7.28 $ 7.79 $ 7.21 Speedway Operating Statistics Convenience stores at period-end 2,745 2,734 Gasoline and distillate sales (millions of gallons) 1,474 1,464 4,317 4,332 Gasoline and distillate margin (dollars per gallon) (j) $ 0.1651 $ 0.1772 $ 0.1620 $ 0.1727 Merchandise sales (in millions) $ 1,339 $ 1,295 $ 3,753 $ 3,693 Merchandise margin (in millions) $ 384 $ 374 $ 1,069 $ 1,065 Merchandise margin percent 28.7 % 28.9 % 28.5 % 28.8 % Same store gasoline sales volume (period over period) (k) (1.2 %) (3.1 %) (1.8 %) (1.6 %) Same store merchandise sales (period over period) (k)(l) 4.9 % 0.3 % 3.4 % 1.5 % Midstream Operating Statistics Crude oil and refined product pipeline throughputs (mbpd) (m) 3,829 3,562 3,694 3,299 Terminal throughput (mbpd) 1,474 1,496 1,468 1,470 Gathering system throughput (MMcf/d) (n) 4,737 3,729 4,403 3,415 Natural gas processed (MMcf/d) (n) 7,171 6,581 6,874 6,336 C2 (ethane) + NGLs (natural gas liquids) fractionated (mbpd) (n) 488 397 451 384 (a) Total average daily volumes of refined product sales to wholesale, branded and retail customers. (b) Includes intersegment sales. (c) Represents fully loaded export cargoes for each time period. These sales volumes are included in the total sales volume amounts. (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 down time for planned maintenance and other normal operating activities. (f) Excludes inter-refinery volumes of 54 mbpd and 80 mbpd for the three months ended September 30, 2018 and 2017 , respectively, and 53 mbpd and 74 mbpd for the nine months ended September 30, 2018 and 2017 , respectively. (g) Per barrel of total refinery throughputs. Effective with the February 1, 2018 dropdown, direct operating costs related to certain refining logistics assets are now reported in the Midstream segment. No effect was given to prior periods as this entity was not considered a business prior to February 1, 2018. (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 bank card processing fees, divided by gasoline and distillate sales volume. (k) Same store comparison includes only locations owned at least 13 months. (l) Excludes cigarettes. (m) Includes common-carrier pipelines and private pipelines owned or operated by MPLX, excluding equity method investments. (n) Includes amounts related to unconsolidated equity method investments on a 100 percent basis.

Summary of Principal Accountin

Summary of Principal Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2018
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 SEC applicable to interim period financial statements and do not include all of the information and disclosures required by GAAP for complete financial statements.
Revenue recognition	Revenue Recognition As described in Note 3 , we adopted ASC 606 effective January 1, 2018. We recognize revenue based on consideration specified in contracts or agreements with customers when we satisfy our performance obligations by transferring control over products or services to a customer. Concurrent with our adoption of ASC 606, we made an accounting policy election that all taxes assessed by a governmental authority that are both imposed on and concurrent with a revenue-producing transaction and collected from our customers will be recognized on a net basis within sales and other operating revenues. The adoption of ASC 606 did not materially change our revenue recognition patterns, which are described below by reportable segment: • Refining & Marketing - The vast majority of our Refining & Marketing contracts contain pricing that is based on the market price for the product at the time of delivery. Our obligations to deliver product volumes are typically satisfied and revenue is recognized when control of the product transfers to our customers. Concurrent with the transfer of control, we typically receive the right to payment for the delivered product, the customer accepts the product and the customer has significant risks and rewards of ownership of the product. Payment terms require customers to pay shortly after delivery and do not contain significant financing components. • Speedway - Revenue is recognized when our customers receive control of the transportation fuels or merchandise. Payments from customers are received at the time sales occur in cash or by credit or debit card. Speedway offers a loyalty rewards program to its customers. We defer a minor portion of revenue on sales to the loyalty program participants until the participants redeem their rewards. The related contract liability, as defined in ASC 606, is not material to our financial statements. • Midstream - Midstream revenue transactions typically are defined by contracts under which we sell a product or provide a service. Revenues from sales of product are recognized when control of the product transfers to the customer. Revenues from sales of services are recognized over time when the performance obligation is satisfied as services are provided in a series. We have elected to use the output measure of progress to recognize revenue based on the units delivered, processed or transported. The transaction prices in our Midstream contracts often have both fixed components, related to minimum volume commitments, and variable components, which are primarily dependent on volumes. Variable consideration will generally not be estimated at contract inception as the transaction price is specifically allocable to the services provided at each period end. Refer to Note 10 for disclosure of our revenue disaggregated by segment and product line, as well as a description of our reportable segment operations.
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 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, (4) the acquisition of ethanol for blending with refined products, (5) the sale of NGLs and (6) the purchase of natural gas.
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.

MPLX LP (Tables)

MPLX LP (Tables)	9 Months Ended
	Sep. 30, 2018
Noncontrolling Interest [Abstract]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net	As a result of equity transactions of MPLX, we are required to adjust non-controlling interest and additional paid-in capital. Changes in MPC’s additional paid-in capital resulting from changes in its ownership interests in MPLX were as follows: Nine Months Ended (In millions) 2018 2017 Increase due to the issuance of MPLX LP common units to the public $ 6 $ 25 Increase due to the issuance of MPLX LP common units and general partner units to MPC 1,114 113 Increase due to GP/IDR Exchange 1,808 — Increase in MPC's additional paid-in capital 2,928 138 Tax impact (546 ) (26 ) Increase in MPC's additional paid-in capital, net of tax $ 2,382 $ 112

Related Party Transactions (Tab

Related Party Transactions (Tables)	9 Months Ended
	Sep. 30, 2018
Related Party Transactions [Abstract]
Sales to Related Parties	Significant transactions with related parties were as follows: Three Months Ended Nine Months Ended (In millions) 2018 2017 2018 2017 Sales to related parties (a) $ 201 $ 157 $ 572 $ 458 Purchases from related parties (b) 149 148 428 420 (a) Sales to related parties consists primarily of sales of refined products to PFJ Southeast, an equity affiliate which owns and operates travel plazas primarily in the Southeast region of the United States. (b) We obtain transportation services and purchase ethanol from certain of our equity affiliates, none of which is individually material.

Income per Common Share (Tables

Income per Common Share (Tables)	9 Months Ended
	Sep. 30, 2018
Earnings Per Share [Abstract]
Summary of Earnings Per Common Share	We compute basic earnings per share by dividing net income attributable to MPC less income allocated to participating securities by the weighted average number of shares of common stock outstanding. Since MPC grants certain incentive compensation awards to employees and non-employee directors that are considered to be participating securities, we have calculated our earnings per share using the two-class method. Diluted income per share assumes exercise of certain stock-based compensation awards, provided the effect is not anti-dilutive. Three Months Ended Nine Months Ended (In millions, except per share data) 2018 2017 2018 2017 Basic earnings per share: Allocation of earnings: Net income attributable to MPC $ 737 $ 903 $ 1,829 $ 1,416 Income allocated to participating securities — — 1 1 Income available to common stockholders – basic $ 737 $ 903 $ 1,828 $ 1,415 Weighted average common shares outstanding 451 504 462 514 Basic earnings per share $ 1.63 $ 1.79 $ 3.96 $ 2.75 Diluted earnings per share: Allocation of earnings: Net income attributable to MPC $ 737 $ 903 $ 1,829 $ 1,416 Income allocated to participating securities — — 1 1 Income available to common stockholders – diluted $ 737 $ 903 $ 1,828 $ 1,415 Weighted average common shares outstanding 451 504 462 514 Effect of dilutive securities 5 4 4 4 Weighted average common shares, including dilutive effect 456 508 466 518 Diluted earnings per share $ 1.62 $ 1.77 $ 3.92 $ 2.73
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	The following table summarizes the shares that were anti-dilutive and, therefore, were excluded from the diluted share calculation. Three Months Ended Nine Months Ended (In millions) 2018 2017 2018 2017 Shares issuable under stock-based compensation plans — 1 — 1

Equity (Tables)

Equity (Tables)	9 Months Ended
	Sep. 30, 2018
Equity [Abstract]
Share Repurchases	Total share repurchases were as follows: Three Months Ended Nine Months Ended (In millions, except per share data) 2018 2017 2018 2017 Number of shares repurchased 5 8 36 31 Cash paid for shares repurchased $ 400 $ 452 $ 2,612 $ 1,622 Average cost per share $ 73.03 $ 53.85 $ 71.80 $ 52.16

Segment Information (Tables)

Segment Information (Tables)	9 Months Ended
	Sep. 30, 2018
Segment Reporting [Abstract]
Income From Operations Attributable To Operating Segments	Segment income represents income from operations attributable to the reportable segments. Corporate administrative expenses, except for those attributable to MPLX, 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 the third quarter we began reporting segment capital expenditures and investments excluding acquisitions in the current and comparative periods. (In millions) Refining & Marketing Speedway Midstream Total Three Months Ended September 30, 2018 Revenues: Third party $ 16,552 $ 5,393 $ 842 $ 22,787 Intersegment 2,931 1 787 3,719 Related party 199 2 — 201 Segment revenues $ 19,682 $ 5,396 $ 1,629 $ 26,707 Segment income from operations $ 666 $ 161 $ 679 $ 1,506 Income from equity method investments 7 18 71 96 Depreciation and amortization (a) 257 76 205 538 Capital expenditures and investments (b) 226 98 593 917 (In millions) Refining & Marketing Speedway Midstream Total Three Months Ended September 30, 2017 Revenues: Third party $ 13,573 $ 4,895 $ 585 $ 19,053 Intersegment (c) 2,904 1 369 3,274 Related party 155 2 — 157 Segment revenues $ 16,632 $ 4,898 $ 954 $ 22,484 Segment income from operations $ 1,097 $ 208 $ 355 $ 1,660 Income from equity method investments (a) 6 20 57 83 Depreciation and amortization (a) 266 68 169 503 Capital expenditures and investments (b) 198 108 423 729 (In millions) Refining & Marketing Speedway Midstream Total Nine Months Ended September 30, 2018 Revenues: Third party $ 46,069 $ 15,225 $ 2,305 $ 63,599 Intersegment 8,181 4 2,180 10,365 Related party 566 6 — 572 Segment revenues $ 54,816 $ 15,235 $ 4,485 $ 74,536 Segment income from operations $ 1,558 $ 415 $ 1,863 $ 3,836 Income from equity method investments (a) 14 51 196 261 Depreciation and amortization (a) 761 228 577 1,566 Capital expenditures and investments (b) 613 225 1,676 2,514 (In millions) Refining & Marketing Speedway Midstream Total Nine Months Ended September 30, 2017 Revenues: Third party $ 37,485 $ 14,070 $ 1,665 $ 53,220 Intersegment (c) 8,302 3 1,076 9,381 Related party 452 6 — 458 Segment revenues $ 46,239 $ 14,079 $ 2,741 $ 63,059 Segment income from operations $ 1,589 $ 581 $ 996 $ 3,166 Income from equity method investments (a) 10 54 139 203 Depreciation and amortization (a) 805 197 528 1,530 Capital expenditures and investments (b) 570 221 1,267 2,058 (a) Differences between segment totals and MPC totals represent amounts related to corporate and other unallocated items and are included in items not allocated to segments in the reconciliation below. (b) Capital expenditures include changes in capital accruals and investments in affiliates. See reconciliation from segment totals to MPC total capital expenditures below. (c) Management believes intersegment transactions were conducted under terms comparable to those with unaffiliated parties.
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 Nine Months Ended (In millions) 2018 2017 2018 2017 Segment income from operations $ 1,506 $ 1,660 $ 3,836 $ 3,166 Items not allocated to segments: Corporate and other unallocated items (a) (103 ) (85 ) (283 ) (251 ) Litigation — — — (86 ) Impairments (b) — 2 1 21 Income from operations 1,403 1,577 3,554 2,850 Net interest and other financial costs 240 158 618 465 Income before income taxes $ 1,163 $ 1,419 $ 2,936 $ 2,385 (a) Corporate and other unallocated items consists primarily of MPC’s corporate administrative expenses and costs related to certain non-operating assets, except for corporate overhead expenses attributable to MPLX, which are included in the Midstream segment. Corporate overhead expenses are not allocated to the Refining & Marketing and Speedway segments. (b) Includes MPC’s share of gains from the sale of assets remaining from the canceled Sandpiper pipeline project.
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 Nine Months Ended (In millions) 2018 2017 2018 2017 Segment capital expenditures and investments $ 917 $ 729 $ 2,514 $ 2,058 Less investments in equity method investees 104 53 222 230 Plus items not allocated to segments: Corporate 7 19 42 53 Capitalized interest 21 13 55 39 Total capital expenditures (a) $ 841 $ 708 $ 2,389 $ 1,920 (a) Capital expenditures include changes in capital accruals. See Note 18 for a reconciliation of total capital expenditures to additions to property, plant and equipment as reported in the consolidated statements of cash flows.
Revenue from External Customers by Products and Services	Revenues by product line were as follows: Three Months Ended Nine Months Ended (In millions) 2018 2017 2018 2017 Refined products $ 19,815 $ 16,374 $ 55,265 $ 45,689 Merchandise 1,340 1,370 3,756 3,905 Crude oil and refinery feedstocks 1,011 878 2,872 2,389 Midstream services, transportation and other 621 431 1,706 1,237 Sales and other operating revenues $ 22,787 $ 19,053 $ 63,599 $ 53,220

Net Interest and Other Financ_2

Net Interest and Other Financial Costs (Tables)	9 Months Ended
	Sep. 30, 2018
Other Income and Expenses [Abstract]
Net Interest And Other Financial Income (Costs)	Net interest and other financial costs were as follows: Three Months Ended Nine Months Ended (In millions) 2018 2017 2018 2017 Interest income $ (26 ) $ (7 ) $ (71 ) $ (16 ) Interest expense 233 172 675 508 Interest capitalized (21 ) (14 ) (55 ) (47 ) Pension and other postretirement non-service costs (a) 45 1 47 — Loss on extinguishment of debt — — 4 — Other financial costs 9 6 18 20 Net interest and other financial costs $ 240 $ 158 $ 618 $ 465 (a) See Note 20 .

Inventories (Tables)

Inventories (Tables)	9 Months Ended
	Sep. 30, 2018
Inventory Disclosure [Abstract]
Summary Of Inventories	(In millions) September 30, December 31, Crude oil and refinery feedstocks $ 1,717 $ 2,056 Refined products 3,005 2,839 Materials and supplies 465 494 Merchandise 152 161 Total $ 5,339 $ 5,550

Property, Plant and Equipment (

Property, Plant and Equipment (Tables)	9 Months Ended
	Sep. 30, 2018
Property, Plant and Equipment [Abstract]
Summary Of Property, Plant And Equipment	(In millions) September 30, December 31, Refining & Marketing (a) $ 18,708 $ 19,490 Speedway 5,520 5,358 Midstream (a) 18,213 14,898 Corporate and Other 835 792 Total 43,276 40,538 Less accumulated depreciation 15,559 14,095 Property, plant and equipment, net $ 27,717 $ 26,443 (a) On February 1, 2018, we contributed certain refining logistics assets and fuels distribution services to MPLX. In connection with this transaction, approximately $830 million of net property, plant and equipment was recorded to the Midstream segment with an offsetting reduction to the Refining & Marketing segment .

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2018
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 September 30, 2018 and December 31, 2017 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. September 30, 2018 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 $ 62 $ — $ — $ (62 ) $ — $ 20 Other assets 3 — — N/A 3 — Total assets at fair value $ 65 $ — $ — $ (62 ) $ 3 $ 20 Commodity derivative instruments, liabilities $ 99 $ — $ 2 $ (99 ) $ 2 $ — Embedded derivatives in commodity contracts — — 82 — 82 — Total liabilities at fair value $ 99 $ — $ 84 $ (99 ) $ 84 $ — December 31, 2017 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 $ 127 $ — $ — $ (118 ) $ 9 $ 8 Other assets 3 — — N/A 3 — Total assets at fair value $ 130 $ — $ — $ (118 ) $ 12 $ 8 Commodity derivative instruments, liabilities $ 126 $ — $ 2 $ (126 ) $ 2 $ — Embedded derivatives in commodity contracts — — 64 — 64 — Total liabilities at fair value $ 126 $ — $ 66 $ (126 ) $ 66 $ — (a) Represents the impact of netting assets, liabilities and cash collateral when a legal right of offset exists. As of September 30, 2018 , cash collateral of $37 million was netted with the mark-to-market derivative liabilities. As of December 31, 2017 , $8 million was netted with mark-to-market derivative liabilities. (b) We have no derivative contracts that are subject to master netting arrangements reflected gross on the balance sheet.
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 Nine Months Ended (In millions) 2018 2017 2018 2017 Beginning balance $ 68 $ 41 $ 66 $ 190 Contingent consideration payment — — — (131 ) Unrealized and realized losses included in net income 20 22 29 8 Settlements of derivative instruments (4 ) (6 ) (11 ) (10 ) Ending balance $ 84 $ 57 $ 84 $ 57 The amount of total losses for the period included in earnings attributable to the change in unrealized losses relating to assets still held at the end of period: Derivative instruments $ 21 $ 17 $ 22 $ 8 Contingent consideration agreement — — — 1 Total $ 21 $ 17 $ 22 $ 9
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 September 30, 2018 and December 31, 2017 , excluding the derivative financial instruments and contingent consideration reported above. September 30, 2018 December 31, 2017 (In millions) Fair Value Carrying Value Fair Value Carrying Value Financial assets: Environmental receivables and misc. deposits 23 23 17 17 Total financial assets $ 23 $ 23 $ 17 $ 17 Financial liabilities: Long-term debt (a) $ 18,421 $ 18,036 $ 13,893 $ 12,642 Deferred credits and other liabilities 115 107 122 109 Total financial liabilities $ 18,536 $ 18,143 $ 14,015 $ 12,751 (a) Excludes capital leases and debt issuance costs; includes amount classified as debt due within one year.

Derivatives (Tables)

Derivatives (Tables)	9 Months Ended
	Sep. 30, 2018
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 September 30, 2018 and December 31, 2017 : (In millions) September 30, 2018 Balance Sheet Location Asset Liability Commodity derivatives Other current assets $ 62 $ 99 Other current liabilities (a) — 17 Deferred credits and other liabilities (a) — 67 (In millions) December 31, 2017 Balance Sheet Location Asset Liability Commodity derivatives Other current assets $ 127 $ 126 Other current liabilities (a) — 14 Deferred credits and other liabilities (a) — 52 (a) Includes embedded derivatives.
Open Commodity Derivative Contracts	The tables below summarize open commodity derivative contracts for crude oil and refined products as of September 30, 2018 . Position Total Barrels (In thousands) Crude Oil (a) Exchange-traded Long 14,052 Exchange-traded Short (16,782 ) (a) 98.7 percent of the exchange-traded contracts expire in the fourth quarter of 2018 . Position Total Gallons (In thousands) Refined Products (a) Exchange-traded Long 135,408 Exchange-traded Short (320,250 ) OTC Short (28,980 ) (a) 97.1 percent of the exchange-traded contracts expire in the fourth quarter of 2018 .
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) Gain (Loss) (In millions) Three Months Ended September 30, Nine Months Ended September 30, Income Statement Location 2018 2017 2018 2017 Sales and other operating revenues $ 3 $ (10 ) $ 1 $ 8 Cost of revenues (69 ) 1 (152 ) (30 ) Total $ (66 ) $ (9 ) $ (151 ) $ (22 )

Debt (Tables)

Debt (Tables)	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
Outstanding Borrowings	Our outstanding borrowings at September 30, 2018 and December 31, 2017 consisted of the following: (In millions) September 30, December 31, Marathon Petroleum Corporation: Commercial paper $ — $ — 364-day bank revolving credit facility due July 2018 (a) — — Trade receivables securitization facility due July 2019 — — Bank revolving credit facility due 2022 — — Senior notes, 2.700% due December 2018 — 600 Senior notes, 3.400% due December 2020 650 650 Senior notes, 5.125% due March 2021 1,000 1,000 Senior notes, 3.625%, due September 2024 750 750 Senior notes, 6.500%, due March 2041 1,250 1,250 Senior notes, 4.750%, due September 2044 800 800 Senior notes, 5.850% due December 2045 250 250 Senior notes, 5.000%, due September 2054 400 400 Capital lease obligations due 2018-2033 511 356 MPLX LP: MPLX bank revolving credit facility due 2022 1,000 505 MPLX senior notes, 5.500%, due February 2023 710 710 MPLX senior notes, 3.375%, due March 2023 500 — MPLX senior notes, 4.500%, due July 2023 989 989 MPLX senior notes, 4.875%, due December 2024 1,149 1,149 MPLX senior notes, 4.000%, due February 2025 500 500 MPLX senior notes, 4.875%, due June 2025 1,189 1,189 MarkWest senior notes, 4.500% - 5.500%, due 2023 - 2025 63 63 MPLX senior notes, 4.125%, due March 2027 1,250 1,250 MPLX senior notes, 4.000%, due March 2028 1,250 — MPLX senior notes, 4.500%, due April 2038 1,750 — MPLX senior notes, 5.200%, due March 2047 1,000 1,000 MPLX senior notes, 4.700%, due April 2048 1,500 — MPLX senior notes, 4.900%, due April 2058 500 — MPLX capital lease obligations due 2020 7 7 Total 18,968 13,418 Unamortized debt issuance costs (105 ) (59 ) Unamortized discount (414 ) (413 ) Amounts due within one year (26 ) (624 ) Total long-term debt due after one year $ 18,423 $ 12,322 (a) The 364-day facility expired on July 20, 2018.

Supplemental Cash Flow Inform_2

Supplemental Cash Flow Information (Tables)	9 Months Ended
	Sep. 30, 2018
Supplemental Cash Flow Elements [Abstract]
Summary of Supplemental Cash Flow Information	Nine Months Ended (In millions) 2018 2017 Net cash provided by operating activities included: Interest paid (net of amounts capitalized) $ 520 $ 446 Income taxes paid to taxing authorities 153 383 Non-cash investing and financing activities: Capital leases 171 — Contribution of assets to joint venture (a) — 337 (a) MarkWest’s contribution of assets to Sherwood Midstream and Sherwood Midstream Holdings. See Note 5 .
Schedule of Cash and Cash Equivalents	(In millions) September 30, December 31, Cash and cash equivalents $ 4,992 $ 3,011 Restricted cash (a) 3 4 Cash, cash equivalents and restricted cash (b) $ 4,995 $ 3,015 (a) The restricted cash balance is included within other current assets on the consolidated balance sheets. (b) As a result of the adoption of ASU 2016-18, the consolidated statements of cash flows now explain the change during the period of both cash and cash equivalents and restricted cash.
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 per the consolidated statements of cash flows to total capital expenditures: Nine Months Ended (In millions) 2018 2017 Additions to property, plant and equipment per the consolidated statements of cash flows $ 2,315 $ 1,928 Asset retirement expenditures 7 1 Increase (decrease) in capital accruals 67 (9 ) Total capital expenditures $ 2,389 $ 1,920

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Loss (Tables)	9 Months Ended
	Sep. 30, 2018
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, 2016 $ (233 ) $ (7 ) $ 4 $ 2 $ (234 ) Other comprehensive loss before reclassifications (2 ) — — — (2 ) Amounts reclassified from accumulated other comprehensive loss: Amortization – prior service credit (a) (29 ) (2 ) — — (31 ) – actuarial loss/(gain) (a) 27 (1 ) — — 26 – settlement loss (a) 2 — — — 2 Other (b) — — — (2 ) (2 ) Tax effect — 1 — 1 2 Other comprehensive loss (2 ) (2 ) — (1 ) (5 ) Balance as of September 30, 2017 $ (235 ) $ (9 ) $ 4 $ 1 $ (239 ) (In millions) Pension Benefits Other Benefits Gain on Cash Flow Hedge Workers Compensation Total Balance as of December 31, 2017 $ (190 ) $ (48 ) $ 4 $ 3 $ (231 ) Other comprehensive income (loss) before reclassifications 35 (1 ) (2 ) — 32 Amounts reclassified from accumulated other comprehensive loss: Amortization – prior service credit (a) (25 ) (2 ) — — (27 ) – actuarial loss/(gain) (a) 26 (1 ) — — 25 – settlement loss (a) 47 — — — 47 Other (b) — — — (4 ) (4 ) Tax effect (12 ) 1 — 1 (10 ) Other comprehensive income (loss) 71 (3 ) (2 ) (3 ) 63 Balance as of September 30, 2018 $ (119 ) $ (51 ) $ 2 $ — $ (168 ) (a) These accumulated other comprehensive loss components are included in the computation of net periodic benefit cost. See Note 20 . (b) This amount was reclassified out of accumulated other comprehensive loss and is included in selling, general and administrative expenses on the consolidated statements of income.

Defined Benefit Pension and O_2

Defined Benefit Pension and Other Postretirement Plans (Tables)	9 Months Ended
	Sep. 30, 2018
Retirement Benefits [Abstract]
Components of Net Periodic Benefit Costs	The following summarizes the components of net periodic benefit costs: Three Months Ended September 30, Pension Benefits Other Benefits (In millions) 2018 2017 2018 2017 Components of net periodic benefit cost: Service cost $ 36 $ 33 $ 7 $ 6 Interest cost 18 19 7 8 Expected return on plan assets (25 ) (25 ) — — Amortization – prior service credit (9 ) (10 ) — — – actuarial loss (gain) 9 9 (1 ) — – settlement loss 45 1 — — Net periodic benefit cost $ 74 $ 27 $ 13 $ 14 Nine Months Ended September 30, Pension Benefits Other Benefits (In millions) 2018 2017 2018 2017 Components of net periodic benefit cost: Service cost $ 107 $ 99 $ 22 $ 19 Interest cost 54 56 22 23 Expected return on plan assets (75 ) (75 ) — — Amortization – prior service credit (25 ) (29 ) (2 ) (2 ) – actuarial loss (gain) 26 27 (1 ) (1 ) – settlement loss 47 2 — — Net periodic benefit cost $ 134 $ 80 $ 41 $ 39

Stock-Based Compensation Plans

Stock-Based Compensation Plans (Tables)	9 Months Ended
	Sep. 30, 2018
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 nine months ended September 30, 2018 : Number of Shares Weighted Average Exercise Price Outstanding at December 31, 2017 8,465,398 $ 33.74 Granted 903,797 67.71 Exercised (905,914 ) 26.30 Forfeited or expired (28,664 ) 47.54 Outstanding at September 30, 2018 8,434,617 38.13
Summary of Restricted Stock Award Activity	The following table presents a summary of restricted stock award activity for the nine months ended September 30, 2018 : 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, 2017 1,188,662 $ 45.07 285,164 $ 29.95 Granted 438,209 70.39 19,173 70.99 RS Vested/RSUs Issued (552,217 ) 44.88 (151,170 ) 22.95 Forfeited (51,645 ) 49.33 — — Outstanding at September 30, 2018 1,023,009 55.80 153,167 42.00
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 nine months ended September 30, 2018 : Number of Units Weighted Average Grant Date Fair Value Outstanding at December 31, 2017 6,851,542 $ 0.81 Granted 3,830,000 0.83 Vested (2,052,959 ) 0.95 Forfeited (10,000 ) 0.92 Outstanding at September 30, 2018 8,618,583 0.79

Supplementary Statistics (Table

Supplementary Statistics (Tables)	9 Months Ended
	Sep. 30, 2018
Text Block [Abstract]
Supplementary Statistics	Three Months Ended Nine Months Ended (In millions) 2018 2017 2018 2017 Income from Operations by Segment Refining & Marketing (a) $ 666 $ 1,097 $ 1,558 $ 1,589 Speedway 161 208 415 581 Midstream (a) 679 355 1,863 996 Items not allocated to segments: Corporate and other unallocated items (103 ) (85 ) (283 ) (251 ) Litigation — — — (86 ) Impairments (b) — 2 1 21 Income from operations $ 1,403 $ 1,577 $ 3,554 $ 2,850 Capital Expenditures and Investments (c) Refining & Marketing $ 226 $ 198 $ 613 $ 570 Speedway 98 108 225 221 Midstream 593 423 1,676 1,267 Corporate and Other (d) 28 32 97 92 Total capital expenditures and investments $ 945 $ 761 $ 2,611 $ 2,150 (a) On February 1, 2018, we contributed certain refining logistics assets and fuels distributions services to MPLX. The results of these new businesses are reported in the Midstream segment prospectively from February 1, resulting in a net reduction of $230 million and $643 million to Refining & Marketing segment results and a net increase to Midstream segment results of the same amount for the three and nine months ended September 30, 2018 , respectively. No effect was given to prior periods as these entities were not considered businesses prior to February 1, 2018. (b) Includes MPC’s share of gains from the sales of assets remaining from the canceled Sandpiper pipeline project. (c) Capital expenditures include changes in capital accruals and investments in affiliates and excludes acquisitions. (d) Includes capitalized interest of $21 million and $13 million for the three months ended September 30, 2018 and 2017 , respectively, and $55 million and $39 million for the nine months ended September 30, 2018 and 2017 , respectively.
Operating Statistics	Three Months Ended Nine Months Ended 2018 2017 2018 2017 MPC Consolidated Refined Product Sales Volumes (mbpd) (a) 2,394 2,357 2,358 2,272 Refining & Marketing Operating Statistics Refining & Marketing refined product sales volume (mbpd) (b) 2,382 2,357 2,346 2,263 Export sales volume (mbpd) (c) 280 331 289 291 Refining & Marketing margin (dollars per barrel) (d) $ 14.25 $ 14.14 $ 13.48 $ 12.42 Crude oil capacity utilization percent (e) 97.4 101.5 96.7 95.8 Refinery throughputs (mbpd): (f) Crude oil refined 1,833 1,845 1,819 1,741 Other charge and blendstocks 199 172 173 176 Total 2,032 2,017 1,992 1,917 Sour crude oil throughput percent 52 57 53 61 WTI-priced crude oil throughput percent 30 23 28 20 Refined product yields (mbpd): (f) Gasoline 942 939 942 910 Distillates 676 673 659 627 Propane 40 38 37 35 Feedstocks and special products 313 298 294 285 Heavy fuel oil 29 45 30 36 Asphalt 73 67 68 64 Total 2,073 2,060 2,030 1,957 Refinery direct operating costs (dollars per barrel): (g) Planned turnaround and major maintenance $ 1.77 $ 1.20 $ 1.64 $ 1.69 Depreciation and amortization 1.29 1.34 1.31 1.44 Other manufacturing (h) 3.54 3.83 3.71 4.10 Total $ 6.60 $ 6.37 $ 6.66 $ 7.23 Refining & Marketing Operating Statistics By Region - Gulf Coast Refinery throughputs (mbpd): (i) Crude oil refined 1,150 1,123 1,121 1,041 Other charge and blendstocks 204 217 187 219 Total 1,354 1,340 1,308 1,260 Sour crude oil throughput percent 63 69 62 75 WTI-priced crude oil throughput percent 17 14 15 10 Refined product yields (mbpd): (i) Gasoline 567 538 557 525 Distillates 442 438 421 393 Propane 27 25 24 25 Feedstocks and special products 314 326 301 310 Heavy fuel oil 16 31 18 24 Asphalt 22 19 21 17 Total 1,388 1,377 1,342 1,294 Three Months Ended Nine Months Ended 2018 2017 2018 2017 Refinery direct operating costs (dollars per barrel): (g) Planned turnaround and major maintenance $ 0.64 $ 0.90 $ 1.30 $ 1.86 Depreciation and amortization 1.03 1.05 1.03 1.15 Other manufacturing (h) 3.20 3.52 3.43 3.81 Total $ 4.87 $ 5.47 $ 5.76 $ 6.82 Refining & Marketing Operating Statistics By Region – Midwest Refinery throughputs (mbpd): (i) Crude oil refined 683 722 698 700 Other charge and blendstocks 49 35 39 31 Total 732 757 737 731 Sour crude oil throughput percent 34 38 37 41 WTI-priced crude oil throughput percent 52 38 49 34 Refined product yields (mbpd): (i) Gasoline 375 401 385 385 Distillates 234 235 238 234 Propane 13 14 13 11 Feedstocks and special products 53 50 46 47 Heavy fuel oil 13 15 12 13 Asphalt 51 48 47 47 Total 739 763 741 737 Refinery direct operating costs (dollars per barrel): (g) Planned turnaround and major maintenance $ 3.74 $ 1.60 $ 2.13 $ 1.22 Depreciation and amortization 1.68 1.72 1.70 1.80 Other manufacturing (h) 3.89 3.96 3.96 4.19 Total $ 9.31 $ 7.28 $ 7.79 $ 7.21 Speedway Operating Statistics Convenience stores at period-end 2,745 2,734 Gasoline and distillate sales (millions of gallons) 1,474 1,464 4,317 4,332 Gasoline and distillate margin (dollars per gallon) (j) $ 0.1651 $ 0.1772 $ 0.1620 $ 0.1727 Merchandise sales (in millions) $ 1,339 $ 1,295 $ 3,753 $ 3,693 Merchandise margin (in millions) $ 384 $ 374 $ 1,069 $ 1,065 Merchandise margin percent 28.7 % 28.9 % 28.5 % 28.8 % Same store gasoline sales volume (period over period) (k) (1.2 %) (3.1 %) (1.8 %) (1.6 %) Same store merchandise sales (period over period) (k)(l) 4.9 % 0.3 % 3.4 % 1.5 % Midstream Operating Statistics Crude oil and refined product pipeline throughputs (mbpd) (m) 3,829 3,562 3,694 3,299 Terminal throughput (mbpd) 1,474 1,496 1,468 1,470 Gathering system throughput (MMcf/d) (n) 4,737 3,729 4,403 3,415 Natural gas processed (MMcf/d) (n) 7,171 6,581 6,874 6,336 C2 (ethane) + NGLs (natural gas liquids) fractionated (mbpd) (n) 488 397 451 384 (a) Total average daily volumes of refined product sales to wholesale, branded and retail customers. (b) Includes intersegment sales. (c) Represents fully loaded export cargoes for each time period. These sales volumes are included in the total sales volume amounts. (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 down time for planned maintenance and other normal operating activities. (f) Excludes inter-refinery volumes of 54 mbpd and 80 mbpd for the three months ended September 30, 2018 and 2017 , respectively, and 53 mbpd and 74 mbpd for the nine months ended September 30, 2018 and 2017 , respectively. (g) Per barrel of total refinery throughputs. Effective with the February 1, 2018 dropdown, direct operating costs related to certain refining logistics assets are now reported in the Midstream segment. No effect was given to prior periods as this entity was not considered a business prior to February 1, 2018. (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 bank card processing fees, divided by gasoline and distillate sales volume. (k) Same store comparison includes only locations owned at least 13 months. (l) Excludes cigarettes. (m) Includes common-carrier pipelines and private pipelines owned or operated by MPLX, excluding equity method investments. (n) Includes amounts related to unconsolidated equity method investments on a 100 percent basis.

ASU 2014-09, Revenue - Revenue

ASU 2014-09, Revenue - Revenue from Contracts with Customers (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption							$ 64
Sales and other operating revenues, excluding consumer excise taxes	$ 22,787	[1]			$ 63,599
Cost of revenues	20,457	[1]	$ 16,617	[1]	57,344	$ 47,664
Matching buy/sell receivables	1,730				1,730
Income taxes receivables	102				102
Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption							$ 1
Consumer Excise Tax | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Sales and other operating revenues, excluding consumer excise taxes	1,400				4,010
Cost of revenues	1,400				4,010
Third Party Reimbursements, Noncash Consideration and Imbalances | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Sales and other operating revenues, excluding consumer excise taxes	148				388
Cost of revenues	$ 148				$ 388
Revenue from Contract with Customer | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Excise and sales taxes			1,340			3,810
Cost of Goods, Total | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Excise and sales taxes			$ 1,340			$ 3,810
[1]	The 2018 period reflects an election to present certain taxes on a net basis concurrent with our adoption of ASU 2014-09, Revenue - Revenue from Contracts with Customers (“ASC 606”). See Notes 2 and 3 for further information.

ASU 2016-16, Income Taxes - Int

ASU 2016-16, Income Taxes - Intra-Entity Transfers of Assets Other Than Inventory (Details) $ in Millions	Dec. 31, 2017USD ($)
Cumulative effect of new accounting principle in period of adoption	$ 64
Accounting Standards Update 2016-16
Cumulative effect of new accounting principle in period of adoption	$ 61

MPLX LP (Detail)

MPLX LP (Detail) - MPLX LP	Sep. 30, 2018
Noncontrolling Interest [Line Items]
MPC's partnership interest in MPLX (in percentage)	63.60%
Ownership percentage of general partner interest	100.00%
Public's ownership interest in MPLX (in percentage)	36.40%

MPLX LP - Dropdowns to MPLX and

MPLX LP - Dropdowns to MPLX and GP/IDR Exchange (Details) - MPLX LP - USD ($) shares in Thousands, $ in Millions	Feb. 01, 2018	Jan. 02, 2018	Sep. 01, 2017	Mar. 01, 2017
MPLX 364-day term loan
Noncontrolling Interest [Line Items]
Maximum borrowing capacity	$ 4,100	$ 4,100
Debt instrument, term	364 days	364 days
Cash and Cash Equivalents
Noncontrolling Interest [Line Items]
Cash consideration	$ 4,100		$ 420	$ 1,500
Limited Partner
Noncontrolling Interest [Line Items]
Units issued, number of units	112,000		19,000	13,000
Conversion of stock, shares issued	275,000
General Partner
Noncontrolling Interest [Line Items]
Units issued, number of units	2,000		378	264

MPLX LP - Noncontrolling Intere

MPLX LP - Noncontrolling Interest in MPLX (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Increase in MPC's additional paid-in capital, net of tax	$ (546)	$ 447
Additional Paid-in Capital
Increase due to the issuance of MPLX LP common units to the public	6	25
Increase due to the issuance of MPLX LP common units and general partner units to MPC	1,114	113
Increase due to GP/IDR Exchange	1,808	0
Increase in MPC's additional paid-in capital	2,928	138
Tax impact	(546)	(26)
Increase in MPC's additional paid-in capital, net of tax	$ 2,382	$ 112

Acquisitions - Acquisition of A

Acquisitions - Acquisition of Andeavor (Details) - Andeavor - USD ($) $ / shares in Units, $ in Millions	Oct. 01, 2018	Sep. 30, 2018
Business Acquisition [Line Items]
Shares converted to cash	22,900,000
Shares converted	128,200,000
Shares issued, number of shares	239,800,000
Consideration transferred, equity interests issued and issuable	$ 19,768
Cash payment to Andeavor stockholders	$ 3,485
Transaction costs		$ 14
Subsequent Event
Business Acquisition [Line Items]
Share conversion rate	1.87
Cash consideration to unitholders (per share)	$ 152.27

Acquisitions - Acquisition of M

Acquisitions - Acquisition of Mt. Airy Terminal (Details) bbl / d in Thousands, bbl in Millions, $ in Millions	Sep. 26, 2018USD ($)bbl / dbbl	Sep. 30, 2018USD ($)	Dec. 31, 2017USD ($)
Goodwill		$ 3,713	$ 3,586
Mt. Airy Terminal
Storage capacity | bbl	4
Barrels handled | bbl / d	120
MPLX LP
Goodwill		$ 2,586	$ 2,245
MPLX LP | Mt. Airy Terminal
Cash consideration	$ 451
Property, plant, and equipment acquired	330
Goodwill	$ 126

Acquisitions - Acquisition of O

Acquisitions - Acquisition of Ozark Pipeline (Details) - Ozark Pipeline bbl / d in Thousands, $ in Millions	Mar. 01, 2017USD ($)bbl / dinmi
Business Acquisition [Line Items]
Pipeline length | mi	433
Pipeline diameter | in	22
Crude oil throughput | bbl / d	230
MPLX LP
Business Acquisition [Line Items]
Cash consideration | $	$ 219

Acquisitions - Investment in Pi

Acquisitions - Investment in Pipeline Company (Details) bbl / d in Thousands, $ in Millions	Feb. 15, 2017USD ($)bbl / d
Bakken Pipeline System
Schedule of Equity Method Investments [Line Items]
Crude oil throughput | bbl / d	520
MPLX LP | Bakken Pipeline System
Schedule of Equity Method Investments [Line Items]
Equity method investments, ownership percentage	9.20%
MPLX LP | MarEn Bakken
Schedule of Equity Method Investments [Line Items]
Cash paid to acquire equity method investments	$ 500
Equity method investments, ownership percentage	25.00%
MPC & Enbridge Energy Partners | Bakken Pipeline System
Schedule of Equity Method Investments [Line Items]
Percentage of ownership interest in joint venture acquired	36.75%
MPC & Enbridge Energy Partners | MarEn Bakken
Schedule of Equity Method Investments [Line Items]
Cash paid to acquire equity method investments	$ 2,000

Acquisitions - Formation of Gat

Acquisitions - Formation of Gathering and Processing Joint Venture (Details) bbl / d in Thousands, $ in Millions	Jan. 01, 2017USD ($)bbl / d	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	[1]
Schedule of Equity Method Investments [Line Items]
Contribution of assets to joint venture		$ 0	$ 337
Sherwood Midstream
Schedule of Equity Method Investments [Line Items]
Equity method investments, ownership percentage		50.00%
Sherwood Midstream | MPLX LP
Schedule of Equity Method Investments [Line Items]
Contribution of assets to joint venture	$ 134
Payments to acquire interest in joint venture	20
Sherwood Midstream | Antero Midstream Partners L.P.
Schedule of Equity Method Investments [Line Items]
Payments to acquire interest in joint venture	$ 154
Ohio Fractionation
Schedule of Equity Method Investments [Line Items]
Capacity | bbl / d	20
Ohio Fractionation | Sherwood Midstream
Schedule of Equity Method Investments [Line Items]
Payments to acquire interest in joint venture	$ 126
Sherwood Midstream Holdings
Schedule of Equity Method Investments [Line Items]
Ownership interest In assets sold by company in affiliate		6.00%
Proceeds from sale of ownership interest in assets sold by company in affiliate		$ 15
Sherwood Midstream Holdings | Direct Ownership Interest
Schedule of Equity Method Investments [Line Items]
Equity method investments, ownership percentage	79.00%
Sherwood Midstream Holdings | MPLX LP
Schedule of Equity Method Investments [Line Items]
Contribution of assets to joint venture	$ 203
Fair value of assets contributed	$ 209
Sherwood Midstream Holdings | Sherwood Midstream
Schedule of Equity Method Investments [Line Items]
Equity method investments, ownership percentage	21.00%
Payments to acquire interest in joint venture	$ 44
[1]	MarkWest’s contribution of assets to Sherwood Midstream and Sherwood Midstream Holdings. See Note 5.

Variable Interest Entities (Det

Variable Interest Entities (Details) bbl / d in Thousands, $ in Millions	Sep. 30, 2018USD ($)	Dec. 31, 2017USD ($)	Jan. 01, 2017bbl / d
Variable Interest Entity [Line Items]
Equity method investments	$ 4,910	$ 4,787
Crowley Coastal Partners
Variable Interest Entity [Line Items]
VIE, maximum loss exposure, amount	$ 483
MarkWest Utica EMG
Variable Interest Entity [Line Items]
Equity method investments, ownership percentage	56.00%
Equity method investments	$ 2,100
Ohio Gathering
Variable Interest Entity [Line Items]
Equity method investments, ownership percentage	34.00%
Sherwood Midstream
Variable Interest Entity [Line Items]
Equity method investments, ownership percentage	50.00%
Equity method investments	$ 325
Ohio Fractionation
Variable Interest Entity [Line Items]
Capacity | bbl / d			20
Sherwood Midstream Holdings
Variable Interest Entity [Line Items]
Equity method investments	$ 155
Sherwood Midstream Holdings | Direct Ownership Interest
Variable Interest Entity [Line Items]
Equity method investments, ownership percentage			79.00%
Sherwood Midstream Holdings | Indirect Ownership Interest
Variable Interest Entity [Line Items]
Equity method investments, ownership percentage			10.50%

Related Party Transactions (Det

Related Party Transactions (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Related Party Transactions [Abstract]
Sales to related parties	[1]	$ 201	$ 157	$ 572	$ 458
Purchases from related parties	[2]	$ 149	$ 148	$ 428	$ 420
[1]	Sales to related parties consists primarily of sales of refined products to PFJ Southeast, an equity affiliate which owns and operates travel plazas primarily in the Southeast region of the United States.
[2]	We obtain transportation services and purchase ethanol from certain of our equity affiliates, none of which is individually material.

Income Per Common Share - Summa

Income Per Common Share - Summary of Earnings Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Basic earnings per share:
Net income attributable to MPC	$ 737	$ 903	$ 1,829	$ 1,416
Income allocated to participating securities	0	0	1	1
Income available to common stockholders – basic	$ 737	$ 903	$ 1,828	$ 1,415
Weighted average common shares outstanding (in shares)	451	504	462	514
Basic (in USD per share)	$ 1.63	$ 1.79	$ 3.96	$ 2.75
Diluted earnings per share:
Net income attributable to MPC	$ 737	$ 903	$ 1,829	$ 1,416
Income allocated to participating securities	0	0	1	1
Income available to common stockholders – diluted	$ 737	$ 903	$ 1,828	$ 1,415
Weighted average common shares outstanding (in shares)	451	504	462	514
Effect of dilutive securities (in shares)	5	4	4	4
Weighted average common shares, including dilutive effect (in shares)	456	508	466	518
Diluted (in USD per share)	$ 1.62	$ 1.77	$ 3.92	$ 2.73

Income Per Common Share - Anti-

Income Per Common Share - Anti-dilutive Shares (Details) - shares shares in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Stock Based Compensation Expense [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Shares issuable under stock-based compensation plans	0	1	0	1

Equity - Additional Information

Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Equity [Abstract]
Stock repurchase program, remaining authorized repurchase amount	$ 5,580		$ 5,580
Dividends paid (in USD per share)	$ 0.46	$ 0.40	$ 1.38	$ 1.12

Equity - Share Repurchases (Det

Equity - Share Repurchases (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Equity [Abstract]
Number of shares repurchased	5	8	36	31
Cash paid for shares repurchased	$ 400	$ 452	$ 2,612	$ 1,622
Average cost per share	$ 73.03	$ 53.85	$ 71.80	$ 52.16

Segment Information - Additiona

Segment Information - Additional Information (Detail) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2018USD ($)Segmentrefinery	Sep. 30, 2017USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | Segment			3
Number of refineries | refinery			6
Income from operations	$ 1,403	$ 1,577	$ 3,554	$ 2,850
Refining Logistics & Fuels Distribution [Member] | Midstream
Segment Reporting Information [Line Items]
Income from operations	230		643
Refining Logistics & Fuels Distribution [Member] | Refining & Marketing
Segment Reporting Information [Line Items]
Income from operations	$ (230)		$ (643)

Segment Information - Income Fr

Segment Information - Income From Operations Attributable To Operating Segments (Detail) - USD ($) $ in Millions		3 Months Ended				9 Months Ended
		Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2018		Sep. 30, 2017
Segment Reporting Information [Line Items]
Sales and other operating revenues, excluding consumer excise taxes		$ 22,787	[1]			$ 63,599
Sales and other operating revenues, including consumer excise taxes				$ 19,053	[1]			$ 53,220
Sales to related parties	[2]	201		157		572		458
Income from operations		1,403		1,577		3,554		2,850
Income from equity method investments		96		84		262		224
Depreciation and amortization		555		517		1,616		1,574
Capital expenditures and investments	[3]	945		761		2,611		2,150
Intersegment Eliminations
Segment Reporting Information [Line Items]
Sales and other operating revenues, excluding consumer excise taxes		3,719				10,365
Sales and other operating revenues, including consumer excise taxes	[4]			3,274				9,381
Operating Segments
Segment Reporting Information [Line Items]
Sales and other operating revenues, excluding consumer excise taxes		26,707				74,536
Sales and other operating revenues, including consumer excise taxes				22,484				63,059
Income from operations		1,506		1,660		3,836		3,166
Income from equity method investments		96		83	[5]	261	[5]	203	[5]
Depreciation and amortization	[5]	538		503		1,566		1,530
Capital expenditures and investments	[6]	917		729		2,514		2,058
Refining & Marketing
Segment Reporting Information [Line Items]
Sales and other operating revenues, excluding consumer excise taxes		16,552				46,069
Sales and other operating revenues, including consumer excise taxes				13,573				37,485
Sales to related parties		199		155		566		452
Refining & Marketing | Intersegment Eliminations
Segment Reporting Information [Line Items]
Sales and other operating revenues, excluding consumer excise taxes		2,931				8,181
Sales and other operating revenues, including consumer excise taxes				2,904				8,302
Refining & Marketing | Operating Segments
Segment Reporting Information [Line Items]
Sales and other operating revenues, excluding consumer excise taxes		19,682				54,816
Sales and other operating revenues, including consumer excise taxes				16,632				46,239
Income from operations		666	[7]	1,097		1,558	[7]	1,589
Income from equity method investments		7		6		14		10
Depreciation and amortization		257		266		761		805
Capital expenditures and investments		226		198		613		570
Speedway
Segment Reporting Information [Line Items]
Sales and other operating revenues, excluding consumer excise taxes		5,393				15,225
Sales and other operating revenues, including consumer excise taxes				4,895				14,070
Sales to related parties		2		2		6		6
Speedway | Intersegment Eliminations
Segment Reporting Information [Line Items]
Sales and other operating revenues, excluding consumer excise taxes		1				4
Sales and other operating revenues, including consumer excise taxes				1				3
Speedway | Operating Segments
Segment Reporting Information [Line Items]
Sales and other operating revenues, excluding consumer excise taxes		5,396				15,235
Sales and other operating revenues, including consumer excise taxes				4,898				14,079
Income from operations		161		208		415		581
Income from equity method investments		18		20		51		54
Depreciation and amortization		76		68		228		197
Capital expenditures and investments		98		108		225		221
Midstream
Segment Reporting Information [Line Items]
Sales and other operating revenues, excluding consumer excise taxes		842				2,305
Sales and other operating revenues, including consumer excise taxes				585				1,665
Sales to related parties		0		0		0		0
Midstream | Intersegment Eliminations
Segment Reporting Information [Line Items]
Sales and other operating revenues, excluding consumer excise taxes		787				2,180
Sales and other operating revenues, including consumer excise taxes				369				1,076
Midstream | Operating Segments
Segment Reporting Information [Line Items]
Sales and other operating revenues, excluding consumer excise taxes		1,629				4,485
Sales and other operating revenues, including consumer excise taxes				954				2,741
Income from operations		679	[7]	355		1,863	[7]	996
Income from equity method investments		71		57		196		139
Depreciation and amortization		205		169		577		528
Capital expenditures and investments		593		423		1,676		1,267
Reportable Segment
Segment Reporting Information [Line Items]
Sales and other operating revenues, excluding consumer excise taxes		$ 22,787				$ 63,599
Sales and other operating revenues, including consumer excise taxes				$ 19,053				$ 53,220
[1]	The 2018 period reflects an election to present certain taxes on a net basis concurrent with our adoption of ASU 2014-09, Revenue - Revenue from Contracts with Customers (“ASC 606”). See Notes 2 and 3 for further information.
[2]	Sales to related parties consists primarily of sales of refined products to PFJ Southeast, an equity affiliate which owns and operates travel plazas primarily in the Southeast region of the United States.
[3]	Capital expenditures include changes in capital accruals and investments in affiliates and excludes acquisitions.
[4]	Management believes intersegment transactions were conducted under terms comparable to those with unaffiliated parties.
[5]	Differences between segment totals and MPC totals represent amounts related to corporate and other unallocated items and are included in items not allocated to segments in the reconciliation below.
[6]	Capital expenditures include changes in capital accruals and investments in affiliates. See reconciliation from segment totals to MPC total capital expenditures below.
[7]	On February 1, 2018, we contributed certain refining logistics assets and fuels distributions services to MPLX. The results of these new businesses are reported in the Midstream segment prospectively from February 1, resulting in a net reduction of $230 million and $643 million to Refining & Marketing segment results and a net increase to Midstream segment results of the same amount for the three and nine months ended September 30, 2018, respectively. No effect was given to prior periods as these entities were not considered businesses prior to February 1, 2018.

Segment Information - Reconcili

Segment Information - Reconciliation Of Segment Income From Operations To Income Before Income Taxes (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Income from operations		$ 1,403	$ 1,577	$ 3,554	$ 2,850
Net interest and other financial income (costs)		240	158	618	465
Income before income taxes		1,163	1,419	2,936	2,385
Operating Segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Income from operations		1,506	1,660	3,836	3,166
Corporate and Other
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Income from operations	[1]	(103)	(85)	(283)	(251)
Segment Reconciling Items
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Litigation		0	0	0	(86)
Impairments	[2]	$ 0	$ 2	$ 1	$ 21
[1]	Corporate and other unallocated items consists primarily of MPC’s corporate administrative expenses and costs related to certain non-operating assets, except for corporate overhead expenses attributable to MPLX, which are included in the Midstream segment. Corporate overhead expenses are not allocated to the Refining & Marketing and Speedway segments.
[2]	Includes MPC’s share of gains from the sale of assets remaining from the canceled Sandpiper pipeline project

Segment Information - Reconci_2

Segment Information - Reconciliation Of Segment Capital Expenditures And Investments To Total Capital Expenditures (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Reconciliation Of Segment Capital Expenditures And Investments To Total Capital Expenditures [Line Items]
Capital expenditures and investments	[1]	$ 945	$ 761	$ 2,611	$ 2,150
Plus items not allocated to segments:
Capital expenditures	[2]	841	708	2,389	1,920
Operating Segments
Reconciliation Of Segment Capital Expenditures And Investments To Total Capital Expenditures [Line Items]
Capital expenditures and investments	[3]	917	729	2,514	2,058
Less investments in equity method investees		104	53	222	230
Corporate and Other
Reconciliation Of Segment Capital Expenditures And Investments To Total Capital Expenditures [Line Items]
Capital expenditures and investments	[4]	28	32	97	92
Plus items not allocated to segments:
Corporate		7	19	42	53
Capitalized interest		$ 21	$ 13	$ 55	$ 39
[1]	Capital expenditures include changes in capital accruals and investments in affiliates and excludes acquisitions.
[2]	Capital expenditures include changes in capital accruals. See Note 18 for a reconciliation of total capital expenditures to additions to property, plant and equipment as reported in the consolidated statements of cash flows.
[3]	Capital expenditures include changes in capital accruals and investments in affiliates. See reconciliation from segment totals to MPC total capital expenditures below.
[4]	Includes capitalized interest of $21 million and $13 million for the three months ended September 30, 2018 and 2017, respectively, and $55 million and $39 million for the nine months ended September 30, 2018 and 2017, respectively.

Segment Information - Revenues

Segment Information - Revenues by Product Line (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2018	Sep. 30, 2017
Revenue from External Customer [Line Items]
Sales and other operating revenues, excluding consumer excise taxes	$ 22,787	[1]			$ 63,599
Sales and other operating revenues, including consumer excise taxes			$ 19,053	[1]		$ 53,220
Refined products
Revenue from External Customer [Line Items]
Sales and other operating revenues, excluding consumer excise taxes	19,815				55,265
Sales and other operating revenues, including consumer excise taxes			16,374			45,689
Merchandise
Revenue from External Customer [Line Items]
Sales and other operating revenues, excluding consumer excise taxes	1,340				3,756
Sales and other operating revenues, including consumer excise taxes			1,370			3,905
Crude oil and refinery feedstocks
Revenue from External Customer [Line Items]
Sales and other operating revenues, excluding consumer excise taxes	1,011				2,872
Sales and other operating revenues, including consumer excise taxes			878			2,389
Midstream services, transportation and other
Revenue from External Customer [Line Items]
Sales and other operating revenues, excluding consumer excise taxes	$ 621				$ 1,706
Sales and other operating revenues, including consumer excise taxes			$ 431			$ 1,237
[1]	The 2018 period reflects an election to present certain taxes on a net basis concurrent with our adoption of ASU 2014-09, Revenue - Revenue from Contracts with Customers (“ASC 606”). See Notes 2 and 3 for further information.

Net Interest And Other Financ_3

Net Interest And Other Financial Costs (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Other Income and Expenses [Abstract]
Interest income		$ (26)	$ (7)	$ (71)	$ (16)
Interest expense		233	172	675	508
Interest capitalized		(21)	(14)	(55)	(47)
Pension and other postretirement non-service costs	[1]	45	1	47	0
Loss on extinguishment of debt		0	0	4	0
Other financial costs		9	6	18	20
Net interest and other financial costs		$ 240	$ 158	$ 618	$ 465
[1]	See Note 20.

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Combined federal, state and foreign income tax rate	19.00%	29.00%	18.00%	30.00%
Statutory rate applied to income before income taxes			21.00%	35.00%
Unrecognized benefits	$ 21		$ 21

Inventories - Summary Of Invent

Inventories - Summary Of Inventories (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Inventory Disclosure [Abstract]
Crude oil and refinery feedstocks	$ 1,717	$ 2,056
Refined products	3,005	2,839
Materials and supplies	465	494
Merchandise	152	161
Total	$ 5,339	$ 5,550

Inventories - Additional Inform

Inventories - Additional Information (Detail) $ in Millions	9 Months Ended
	Sep. 30, 2018USD ($)
Inventory Disclosure [Abstract]
Impact on income as a result of LIFO liquidations	$ 0

Property, Plant And Equipment -

Property, Plant And Equipment - Summary Of Property, Plant And Equipment (Detail) - USD ($) $ in Millions	Feb. 01, 2018	Sep. 30, 2018		Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		$ 43,276		$ 40,538
Less accumulated depreciation		15,559		14,095
Property, plant and equipment, net		$ 27,717		26,443
Undivided joint interest, ownership percentage		33.00%
Undivided joint interest		$ 154
Refining & Marketing
Property, Plant and Equipment [Line Items]
Property, plant and equipment, transfers	$ (830)
Midstream
Property, Plant and Equipment [Line Items]
Property, plant and equipment, transfers	$ 830
Operating Segments | Refining & Marketing
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		18,708	[1]	19,490
Operating Segments | Speedway
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		5,520		5,358
Operating Segments | Midstream
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		18,213	[1]	14,898
Corporate and Other
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		$ 835		$ 792
[1]	On February 1, 2018, we contributed certain refining logistics assets and fuels distribution services to MPLX. In connection with this transaction, approximately $830 million of net property, plant and equipment was recorded to the Midstream segment with an offsetting reduction to the Refining & Marketing segment.We own a 33 percent undivided joint interest in the Capline Pipeline System (“Capline”), a crude oil pipeline that runs from St. James, Louisiana to Patoka, Illinois. We account for this undivided joint interest by recognizing our proportionate share of Capline’s assets on our balance sheet, which are primarily classified as property, plant and equipment. Capline experienced a significant reduction in shipment volumes in the second quarter of 2018 primarily due to recently completed competing pipelines. The pipeline’s owners are proceeding with planning for the reversal of the pipeline to support southbound movements of crude oil as supported by shipper interest indicated during a non-binding open season conducted in 2017. Pending agreement among the owners, southbound service is estimated to commence by the second half of 2022. In the second quarter of 2018, we evaluated our share of Capline assets for impairment in accordance with ASC 360, and determined no impairment existed due to the probability of continuing future cash flows associated with a reversed Capline. We continue to monitor developments in the commercial outlook for Capline and noted no significant changes in the third quarter. As of September 30, 2018, our carrying value was $154 million.

Fair Value Measurements - Asset

Fair Value Measurements - Assets and Liabilities Accounted for at Fair Value on Recurring Basis (Detail) - USD ($) $ in Millions		Sep. 30, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash collateral netted with derivative liabilities		$ 37	$ 8
Fair Value, Measurements, Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commodity derivative instruments, assets - netting and collateral		(62)	(118)
Commodity derivative instruments, assets - collateral pledged not offset		20	8
Other assets		3	3
Total assets at fair value		3	12
Commodity derivative instruments, liabilities - netting and collateral		(99)	(126)
Commodity derivative instruments, liabilities - collateral pledged not offset		0	0
Total liabilities at fair value		84	66
Fair Value, Measurements, Recurring | Commodity derivatives
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commodity derivative instruments, assets - netting and collateral	[1]	(62)	(118)
Commodity derivative instruments, assets - net carrying value on balance sheet	[2]	0	9
Commodity derivative instruments, assets - collateral pledged not offset		20	8
Commodity derivative instruments, liabilities - netting and collateral	[1]	(99)	(126)
Commodity derivative instruments, liabilities - net carrying value on balance sheet	[2]	2	2
Commodity derivative instruments, liabilities - collateral pledged not offset		0	0
Fair Value, Measurements, Recurring | Embedded derivatives in commodity contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commodity derivative instruments, liabilities - netting and collateral		0	0
Commodity derivative instruments, liabilities - net carrying value on balance sheet	[2]	82	64
Commodity derivative instruments, liabilities - collateral pledged not offset		0	0
Fair Value, Measurements, Recurring | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other assets		3	3
Total assets at fair value		65	130
Total liabilities at fair value		99	126
Fair Value, Measurements, Recurring | Level 1 | Commodity derivatives
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commodity derivative instruments, assets - gross		62	127
Commodity derivative instruments, liabilities - gross		99	126
Fair Value, Measurements, Recurring | Level 1 | Embedded derivatives in commodity contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commodity derivative instruments, liabilities - gross		0	0
Fair Value, Measurements, Recurring | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other assets		0	0
Total assets at fair value		0	0
Total liabilities at fair value		0	0
Fair Value, Measurements, Recurring | Level 2 | Commodity derivatives
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commodity derivative instruments, assets - gross		0	0
Commodity derivative instruments, liabilities - gross		0	0
Fair Value, Measurements, Recurring | Level 2 | Embedded derivatives in commodity contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commodity derivative instruments, liabilities - gross		0	0
Fair Value, Measurements, Recurring | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Other assets		0	0
Total assets at fair value		0	0
Total liabilities at fair value		84	66
Fair Value, Measurements, Recurring | Level 3 | Commodity derivatives
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commodity derivative instruments, assets - gross		0	0
Commodity derivative instruments, liabilities - gross		2	2
Fair Value, Measurements, Recurring | Level 3 | Embedded derivatives in commodity contracts
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commodity derivative instruments, liabilities - gross		$ 82	$ 64
[1]	Represents the impact of netting assets, liabilities and cash collateral when a legal right of offset exists. As of September 30, 2018, cash collateral of $37 million was netted with the mark-to-market derivative liabilities. As of December 31, 2017, $8 million was netted with mark-to-market derivative liabilities.
[2]	We have no derivative contracts that are subject to master netting arrangements reflected gross on the balance sheet.

Fair Value Measurements - Recur

Fair Value Measurements - Recurring Narrative (Detail)	9 Months Ended
	Sep. 30, 2018USD ($)
Commodity derivatives | Level 3 | Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Forward commodity price	$ 0.78
Commodity derivatives | Level 3 | Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Forward commodity price	$ 1.65
Embedded derivatives in commodity contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Embedded derivative renewal term	5 years
Embedded derivatives in commodity contracts | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Probability of renewal first term	80.00%
Probability of renewal second term	70.00%

Fair Value Measurements - Recon

Fair Value Measurements - Reconciliation of Net Beginning and Ending Balances Recorded for Net Assets and Liabilities Classified as Level 3 (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 68	$ 41	$ 66	$ 190
Contingent consideration payment	0	0	0	(131)
Unrealized and realized losses included in net income	20	22	29	8
Settlements of derivative instruments	(4)	(6)	(11)	(10)
Ending balance	$ 84	$ 57	$ 84	$ 57

Fair Value Measurements - Losse

Fair Value Measurements - Losses Included in Earnings Relating to Assets Still Held at End of Period (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
The amount of total losses for the period included in earnings attributable to the change in unrealized losses relating to assets still held at the end of period:	$ 21	$ 17	$ 22	$ 9
Derivative
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
The amount of total losses for the period included in earnings attributable to the change in unrealized losses relating to assets still held at the end of period:	21	17	22	8
Contingent Consideration
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
The amount of total losses for the period included in earnings attributable to the change in unrealized losses relating to assets still held at the end of period:	$ 0	$ 0	$ 0	$ 1

Fair Value Measurements - Finan

Fair Value Measurements - Financial Instruments at Fair Value, Excluding Derivative Financial Instruments and Contingent Consideration (Detail) - USD ($) $ in Millions		Sep. 30, 2018	Dec. 31, 2017
Fair Value
Financial assets:
Environmental receivables and misc. deposits		$ 23	$ 17
Total financial assets		23	17
Financial liabilities:
Long-term debt	[1]	18,421	13,893
Deferred credits and other liabilities		115	122
Total financial liabilities		18,536	14,015
Carrying Value
Financial assets:
Environmental receivables and misc. deposits		23	17
Total financial assets		23	17
Financial liabilities:
Long-term debt	[1]	18,036	12,642
Deferred credits and other liabilities		107	109
Total financial liabilities		$ 18,143	$ 12,751
[1]	Excludes capital leases and debt issuance costs; includes amount classified as debt due within one year.

Derivatives - Classification of

Derivatives - Classification of Gross Fair Values of Derivative Instruments, Excluding Cash Collateral (Detail) - Commodity derivatives - USD ($) $ in Millions		Sep. 30, 2018	Dec. 31, 2017
Other current assets
Derivatives, Fair Value [Line Items]
Asset		$ 62	$ 127
Liability		99	126
Other current liabilities(a)
Derivatives, Fair Value [Line Items]
Asset		0	0
Liability	[1]	17	14
Deferred credits and other liabilities
Derivatives, Fair Value [Line Items]
Asset		0	0
Liability	[1]	$ 67	$ 52
[1]	Includes embedded derivatives.

Derivatives - Open Commodity De

Derivatives - Open Commodity Derivative Contracts - Crude Oil (Details) - Crude Oil - Exchange Traded bbl in Thousands	3 Months Ended
	Sep. 30, 2018bbl
Derivative [Line Items]
Percentage of derivative contracts expiring in the period	98.70%
Derivative contract expiration date	Dec. 31, 2018
Long
Derivative [Line Items]
Notional contracts (in thousands of Total Barrels)	14,052	[1]
Short
Derivative [Line Items]
Notional contracts (in thousands of Total Barrels)	16,782	[1]
[1]	of the exchange-traded contracts expire in the fourth quarter of 2018.

Derivatives - Open Commodity _2

Derivatives - Open Commodity Derivative Contracts - Refined Products (Detail) - Refined products gal in Thousands	3 Months Ended
	Sep. 30, 2018gal
Exchange Traded
Derivative [Line Items]
Percentage of derivative contracts expiring in the period	97.10%
Derivative contract expiration date	Dec. 31, 2018
Exchange Traded | Long
Derivative [Line Items]
Notional contracts (in thousands of Total Gallons)	135,408	[1]
Exchange Traded | Short
Derivative [Line Items]
Notional contracts (in thousands of Total Gallons)	320,250	[1]
Over the Counter | Short
Derivative [Line Items]
Notional contracts (in thousands of Total Gallons)	28,980	[1]
[1]	of the exchange-traded contracts expire in the fourth quarter of 2018.

Derivatives - Effect of Commodi

Derivatives - Effect of Commodity Derivative Instruments in Statements of Income (Detail) - Commodity derivatives - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss)	$ (66)	$ (9)	$ (151)	$ (22)
Sales and other operating revenues
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss)	3	(10)	1	8
Cost of revenues
Derivative Instruments, Gain (Loss) [Line Items]
Gain (Loss)	$ (69)	$ 1	$ (152)	$ (30)

Debt - Outstanding Borrowings (

Debt - Outstanding Borrowings (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018		Dec. 31, 2017
Debt Instrument [Line Items]
Total	$ 18,968		$ 13,418
Unamortized debt issuance costs	(105)		(59)
Unamortized discount	(414)		(413)
Amounts due within one year	(26)		(624)
Total long-term debt due after one year	18,423		12,322
Marathon Petroleum Corporation
Debt Instrument [Line Items]
Commercial paper	0		0
Marathon Petroleum Corporation | Capital Lease Obligations
Debt Instrument [Line Items]
Capital lease obligations	$ 511		356
Debt instrument maturity year, start	Oct. 1, 2018
Debt instrument maturity year, end	Mar. 31, 2033
Marathon Petroleum Corporation | 364-day revolver due July 2018 | Line of Credit
Debt Instrument [Line Items]
Long-term debt, gross	$ 0	[1]	0
Line of credit facility, expiration date	Jul. 20, 2018
Marathon Petroleum Corporation | Trade receivables securitization facility due July 2019 | Secured Debt
Debt Instrument [Line Items]
Long-term debt, gross	$ 0		0
Line of credit facility, expiration date	Jul. 19, 2019
Marathon Petroleum Corporation | Bank revolving credit facility due 2022 | Line of Credit
Debt Instrument [Line Items]
Long-term debt, gross	$ 0		0
Line of credit facility, expiration date	Jul. 21, 2022
Marathon Petroleum Corporation | Senior notes, 2.700% due December 2018 | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 0		600
Debt instrument, maturity date	Dec. 14, 2018
Debt instrument, interest rate	2.70%
Marathon Petroleum Corporation | Senior notes, 3.400% due December 2020 | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 650		650
Debt instrument, maturity date	Dec. 15, 2020
Debt instrument, interest rate	3.40%
Marathon Petroleum Corporation | Senior notes, 5.125% due March 2021 | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 1,000		1,000
Debt instrument, maturity date	Mar. 1, 2021
Debt instrument, interest rate	5.125%
Marathon Petroleum Corporation | Senior notes, 3.625%, due September 2024 | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 750		750
Debt instrument, maturity date	Sep. 15, 2024
Debt instrument, interest rate	3.625%
Marathon Petroleum Corporation | Senior notes, 6.500%, due March 2041 | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 1,250		1,250
Debt instrument, maturity date	Mar. 1, 2041
Debt instrument, interest rate	6.50%
Marathon Petroleum Corporation | Senior notes, 4.750%, due September 2044 | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 800		800
Debt instrument, maturity date	Sep. 15, 2044
Debt instrument, interest rate	4.75%
Marathon Petroleum Corporation | Senior notes, 5.850% due December 2045 | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 250		250
Debt instrument, maturity date	Dec. 15, 2045
Debt instrument, interest rate	5.85%
Marathon Petroleum Corporation | Senior notes, 5.000%, due September 2054 | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 400		400
Debt instrument, maturity date	Sep. 15, 2054
Debt instrument, interest rate	5.00%
MPLX LP | Senior Notes | MarkWest
Debt Instrument [Line Items]
Long-term debt, gross	$ 63		63
MPLX LP | Capital Lease Obligations
Debt Instrument [Line Items]
Capital lease obligations	$ 7		7
Debt instrument maturity year, start	Oct. 1, 2018
Debt instrument maturity year, end	Mar. 31, 2020
MPLX LP | MPLX bank revolving credit facility due 2022 | Line of Credit
Debt Instrument [Line Items]
Long-term debt, gross	$ 1,000		505
Line of credit facility, expiration date	Jul. 21, 2022
MPLX LP | MPLX senior notes, 5.500%, due February 2023 | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 710		710
Debt instrument, maturity date	Feb. 15, 2023
Debt instrument, interest rate	5.50%
MPLX LP | MPLX senior notes, 5.500%, due February 2023 | Senior Notes | MarkWest
Debt Instrument [Line Items]
Debt instrument, maturity date	Feb. 15, 2023
Debt instrument, interest rate	5.50%
MPLX LP | MPLX senior notes, 3.375%, due March 2023 | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 500		0
Debt instrument, maturity date	Mar. 15, 2023
Debt instrument, interest rate	3.375%
MPLX LP | MPLX senior notes, 4.500%, due July 2023 | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 989		989
Debt instrument, maturity date	Jul. 15, 2023
Debt instrument, interest rate	4.50%
MPLX LP | MPLX senior notes, 4.500%, due July 2023 | Senior Notes | MarkWest
Debt Instrument [Line Items]
Debt instrument, maturity date	Jul. 15, 2023
Debt instrument, interest rate	4.50%
MPLX LP | MPLX senior notes, 4.875%, due December 2024 | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 1,149		1,149
Debt instrument, maturity date	Dec. 1, 2024
Debt instrument, interest rate	4.875%
MPLX LP | MPLX senior notes, 4.875%, due December 2024 | Senior Notes | MarkWest
Debt Instrument [Line Items]
Debt instrument, maturity date	Dec. 1, 2024
Debt instrument, interest rate	4.875%
MPLX LP | MPLX senior notes, 4.000%, due February 2025 | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 500		500
Debt instrument, maturity date	Feb. 15, 2025
Debt instrument, interest rate	4.00%
MPLX LP | MPLX senior notes, 4.875%, due June 2025 | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 1,189		1,189
Debt instrument, maturity date	Jun. 1, 2025
Debt instrument, interest rate	4.875%
MPLX LP | MPLX senior notes, 4.875%, due June 2025 | Senior Notes | MarkWest
Debt Instrument [Line Items]
Debt instrument, maturity date	Jun. 1, 2025
Debt instrument, interest rate	4.875%
MPLX LP | MPLX senior notes, 4.125%, due March 2027 | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 1,250		1,250
Debt instrument, maturity date	Mar. 1, 2027
Debt instrument, interest rate	4.125%
MPLX LP | MPLX senior notes, 4.000%, due March 2028 | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 1,250		0
Debt instrument, maturity date	Mar. 15, 2028
Debt instrument, interest rate	4.00%
MPLX LP | MPLX senior notes, 4.500%, due April 2038 | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 1,750		0
Debt instrument, maturity date	Apr. 15, 2038
Debt instrument, interest rate	4.50%
MPLX LP | MPLX senior notes, 5.200%, due March 2047 | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 1,000		1,000
Debt instrument, maturity date	Mar. 1, 2047
Debt instrument, interest rate	5.20%
MPLX LP | MPLX senior notes, 4.700%, due April 2048 | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 1,500		0
Debt instrument, maturity date	Apr. 15, 2048
Debt instrument, interest rate	4.70%
MPLX LP | MPLX senior notes, 4.900%, due April 2058 | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross	$ 500		$ 0
Debt instrument, maturity date	Apr. 15, 2058
Debt instrument, interest rate	4.90%
[1]	The 364-day facility expired on July 20, 2018.

Debt - Commercial Paper (Detail

Debt - Commercial Paper (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Debt Instrument [Line Items]
Commercial paper – issued	$ 0	$ 300
Commercial paper - repayments	0	$ 300
Marathon Petroleum Corporation
Debt Instrument [Line Items]
Commercial paper, outstanding balance	$ 0		$ 0

Debt - Trade Receivables Securi

Debt - Trade Receivables Securitization Facility (Details) - Trade receivables securitization facility due July 2019 - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Borrowings	$ 0
Repayments	0
Marathon Petroleum Corporation | Secured Debt
Debt Instrument [Line Items]
Long-term debt, gross	0	$ 0
Marathon Petroleum Corporation | Letter of Credit
Debt Instrument [Line Items]
Long-term line of credit	$ 0

Debt - MPC Revolving Credit Agr

Debt - MPC Revolving Credit Agreements (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018		Dec. 31, 2017
364-day revolver due July 2018
Debt Instrument [Line Items]
Borrowings	$ 0
Repayments	0
Bank revolving credit facility due 2022
Debt Instrument [Line Items]
Repayments	0
Marathon Petroleum Corporation | 364-day revolver due July 2018 | Letter of Credit
Debt Instrument [Line Items]
Long-term line of credit	0
Marathon Petroleum Corporation | 364-day revolver due July 2018 | Line of Credit
Debt Instrument [Line Items]
Long-term debt, gross	0	[1]	$ 0
Marathon Petroleum Corporation | Bank revolving credit facility due 2022 | Letter of Credit
Debt Instrument [Line Items]
Long-term line of credit	0
Marathon Petroleum Corporation | Bank revolving credit facility due 2022 | Line of Credit
Debt Instrument [Line Items]
Long-term debt, gross	$ 0		$ 0
[1]	The 364-day facility expired on July 20, 2018.

Debt - MPC Senior Notes (Detail

Debt - MPC Senior Notes (Details) - Senior notes, 2.700% due December 2018 $ in Millions	Mar. 15, 2018USD ($)
Debt Instrument [Line Items]
Repayments of long-term debt	$ 600
Make whole premium	$ 2.5

Debt - MPLX Credit Agreement (D

Debt - MPLX Credit Agreement (Details) - MPLX LP - MPLX bank revolving credit facility due 2022 $ in Millions	9 Months Ended
	Sep. 30, 2018USD ($)
Debt Instrument [Line Items]
Borrowings	$ 1,175
Interest rate during period	3.10%
Repayments	$ 680
Remaining borrowing capacity	1,247
Letter of Credit
Debt Instrument [Line Items]
Long-term line of credit	$ 3

Debt - MPLX 364-Day Term Loan (

Debt - MPLX 364-Day Term Loan (Details) - MPLX LP - MPLX 364-day term loan - USD ($) $ in Billions	Feb. 08, 2018	Feb. 01, 2018	Jan. 02, 2018
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 4.1	$ 4.1
Debt instrument, term		364 days	364 days
Proceeds from issuance of debt		$ 4.1
Repayments of short-term debt	$ 4.1

Debt - MPLX Senior Notes (Detai

Debt - MPLX Senior Notes (Details) - MPLX LP $ in Millions	Feb. 08, 2018USD ($)
MPLX 364-day term loan
Debt Instrument [Line Items]
Repayments of short-term debt	$ 4,100
Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross	5,500
Senior Notes | MPLX senior notes, 3.375%, due March 2023
Debt Instrument [Line Items]
Long-term debt, gross	$ 500
Debt instrument, interest rate	3.375%
Senior Notes | MPLX senior notes, 4.000%, due March 2028
Debt Instrument [Line Items]
Long-term debt, gross	$ 1,250
Debt instrument, interest rate	4.00%
Senior Notes | MPLX senior notes, 4.500%, due April 2038
Debt Instrument [Line Items]
Long-term debt, gross	$ 1,750
Debt instrument, interest rate	4.50%
Senior Notes | MPLX senior notes, 4.700%, due April 2048
Debt Instrument [Line Items]
Long-term debt, gross	$ 1,500
Debt instrument, interest rate	4.70%
Senior Notes | MPLX senior notes, 4.900%, due April 2058
Debt Instrument [Line Items]
Long-term debt, gross	$ 500
Debt instrument, interest rate	4.90%

Supplemental Cash Flow Inform_3

Supplemental Cash Flow Information - Summary of Supplemental Cash Flow Information (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Net cash provided by operating activities included:
Interest paid (net of amounts capitalized)	$ 520	$ 446
Income taxes paid to taxing authorities	153	383
Non-cash investing and financing activities:
Capital leases	171	0
Contribution of assets to joint venture	$ 0	$ 337	[1]
[1]	MarkWest’s contribution of assets to Sherwood Midstream and Sherwood Midstream Holdings. See Note 5.

Supplemental Cash Flow Inform_4

Supplemental Cash Flow Information - Cash, Cash Equalivalents and Restricted Cash (Details) - USD ($) $ in Millions		Sep. 30, 2018		Dec. 31, 2017		Sep. 30, 2017	Dec. 31, 2016
Supplemental Cash Flow Elements [Abstract]
Cash and cash equivalents		$ 4,992		$ 3,011
Restricted cash	[1]	3		4
Cash, cash equivalents and restricted cash		$ 4,995	[2]	$ 3,015	[2]	$ 2,095	$ 892
[1]	The restricted cash balance is included within other current assets on the consolidated balance sheets
[2]	As a result of the adoption of ASU 2016-18, the consolidated statements of cash flows now explain the change during the period of both cash and cash equivalents and restricted cash.

Supplemental Cash Flow Inform_5

Supplemental Cash Flow Information - Reconciliation of Additions to Property, Plant and Equipment to Total Capital Expenditures (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Supplemental Cash Flow Elements [Abstract]
Additions to property, plant and equipment per the consolidated statements of cash flows				$ 2,315	$ 1,928
Asset retirement expenditures				7	1
Increase (decrease) in capital accruals				67	(9)
Capital expenditures	[1]	$ 841	$ 708	$ 2,389	$ 1,920
[1]	Capital expenditures include changes in capital accruals. See Note 18 for a reconciliation of total capital expenditures to additions to property, plant and equipment as reported in the consolidated statements of cash flows.

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Loss - Changes in Accumulated Other Comprehensive Loss by Component (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance				$ (231)	$ (234)
Other comprehensive loss before reclassifications				32	(2)
Amounts reclassified from accumulated other comprehensive loss:
Amortization - prior service credit				(27)	(31)
Amortization - actuarial loss/(gain)				25	26
Amortization - settlement loss				47	2
Other				(4)	(2)
Tax effect				(10)	2
Other comprehensive income (loss)		$ 65	$ (3)	63	(5)
Ending balance		(168)	(239)	(168)	(239)
Accumulated Defined Benefit Plans Adjustment | Pension Benefits
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance				(190)	(233)
Other comprehensive loss before reclassifications				35	(2)
Amounts reclassified from accumulated other comprehensive loss:
Amortization - prior service credit	[1]			(25)	(29)
Amortization - actuarial loss/(gain)	[1]			26	27
Amortization - settlement loss	[1]			47	2
Tax effect				(12)	0
Other comprehensive income (loss)				71	(2)
Ending balance		(119)	(235)	(119)	(235)
Accumulated Defined Benefit Plans Adjustment | Other Benefits
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance				(48)	(7)
Other comprehensive loss before reclassifications				(1)	0
Amounts reclassified from accumulated other comprehensive loss:
Amortization - prior service credit	[1]			(2)	(2)
Amortization - actuarial loss/(gain)	[1]			(1)	(1)
Amortization - settlement loss				0	0
Tax effect				1	1
Other comprehensive income (loss)				(3)	(2)
Ending balance		(51)	(9)	(51)	(9)
Gain on Cash Flow Hedge
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance				4	4
Other comprehensive loss before reclassifications				(2)	0
Amounts reclassified from accumulated other comprehensive loss:
Tax effect				0	0
Other comprehensive income (loss)				(2)	0
Ending balance		2	4	2	4
Workers Compensation
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance				3	2
Other comprehensive loss before reclassifications				0	0
Amounts reclassified from accumulated other comprehensive loss:
Other				(4)	(2)
Tax effect				1	1
Other comprehensive income (loss)				(3)	(1)
Ending balance		$ 0	$ 1	$ 0	$ 1
[1]	These accumulated other comprehensive loss components are included in the computation of net periodic benefit cost. See Note 20.

Defined Benefit Pension and O_3

Defined Benefit Pension and Other Postretirement Plans - Components of Net Periodic Benefit Costs (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Pension Benefits
Components of net periodic benefit cost:
Service cost	$ 36	$ 33	$ 107	$ 99
Interest cost	18	19	54	56
Expected return on plan assets	(25)	(25)	(75)	(75)
Amortization – prior service credit	(9)	(10)	(25)	(29)
Amortization – actuarial loss (gain)	9	9	26	27
Amortization - settlement loss	45	1	47	2
Net periodic benefit cost	74	27	134	80
Other Benefits
Components of net periodic benefit cost:
Service cost	7	6	22	19
Interest cost	7	8	22	23
Expected return on plan assets	0	0	0	0
Amortization – prior service credit	0	0	(2)	(2)
Amortization – actuarial loss (gain)	(1)	0	(1)	(1)
Amortization - settlement loss	0	0	0	0
Net periodic benefit cost	$ 13	$ 14	$ 41	$ 39

Defined Benefit Pension and O_4

Defined Benefit Pension and Other Postretirement Plans - Additional Information (Detail) $ in Millions	9 Months Ended
	Sep. 30, 2018USD ($)
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 100
Other Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Benefits paid	13
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Benefits paid	$ 25

Stock-Based Compensation Plan_2

Stock-Based Compensation Plans - Summary of Stock Option Award Activity (Detail) - Stock Options	9 Months Ended
	Sep. 30, 2018$ / sharesshares
Number of Shares
Outstanding, beginning balance | shares	8,465,398
Granted | shares	903,797
Exercised | shares	(905,914)
Forfeited or expired | shares	(28,664)
Outstanding, ending balance | shares	8,434,617
Weighted Average Exercise Price
Outstanding, beginning balance (in USD per share) | $ / shares	$ 33.74
Granted (in USD per share) | $ / shares	67.71
Exercised (in USD per share) | $ / shares	26.30
Forfeited or expired (in USD per share) | $ / shares	47.54
Outstanding, ending balance (in USD per share) | $ / shares	$ 38.13

Stock-Based Compensation Plan_3

Stock-Based Compensation Plans - Narrative (Detail)	9 Months Ended
	Sep. 30, 2018$ / shares
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant date fair value (in USD per share)	$ 17.21
Performance Unit Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in USD per share)	$ 0.83

Stock-Based Compensation Plan_4

Stock-Based Compensation Plans - Summary of Restricted Stock Award Activity (Detail)	9 Months Ended
	Sep. 30, 2018$ / sharesshares
Restricted Stock
Number of Shares
Outstanding, beginning balance | shares	1,188,662
Granted | shares	438,209
RS Vested/RSUs Issued | shares	(552,217)
Forfeited | shares	(51,645)
Outstanding, ending balance | shares	1,023,009
Weighted Average Grant Date Fair Value
Outstanding, beginning balance (in USD per share) | $ / shares	$ 45.07
Granted (in USD per share) | $ / shares	70.39
RS's Vested/RSU's Issued (in USD per share) | $ / shares	44.88
Forfeited (in USD per share) | $ / shares	49.33
Outstanding, ending balance (in USD per share) | $ / shares	$ 55.80
Restricted Stock Units
Number of Shares
Outstanding, beginning balance | shares	285,164
Granted | shares	19,173
RS Vested/RSUs Issued | shares	(151,170)
Forfeited | shares	0
Outstanding, ending balance | shares	153,167
Weighted Average Grant Date Fair Value
Outstanding, beginning balance (in USD per share) | $ / shares	$ 29.95
Granted (in USD per share) | $ / shares	70.99
RS's Vested/RSU's Issued (in USD per share) | $ / shares	22.95
Forfeited (in USD per share) | $ / shares	0
Outstanding, ending balance (in USD per share) | $ / shares	$ 42

Stock-Based Compensation Plan_5

Stock-Based Compensation Plans - Summary of Performance Unit Awards (Detail) - Performance Unit Awards	9 Months Ended
	Sep. 30, 2018$ / sharesshares
Number of Units
Outstanding, beginning balance | shares	6,851,542
Granted | shares	3,830,000
Vested | shares	(2,052,959)
Forfeited | shares	(10,000)
Outstanding, ending balance | shares	8,618,583
Weighted Average Grant Date Fair Value
Outstanding, beginning balance (in USD per share) | $ / shares	$ 0.81
Granted (in USD per share) | $ / shares	0.83
Vested (in USD per share) | $ / shares	0.95
Forfeited (in USD per share) | $ / shares	0.92
Outstanding, ending balance (in USD per share) | $ / shares	$ 0.79

Commitments and Contingencies (

Commitments and Contingencies (Detail)	9 Months Ended
	Sep. 30, 2018
Pending Litigation
Loss Contingencies [Line Items]
Loss contingency, inestimable loss	<div style="line-height:120%;padding-top:6px;font-size:10pt;"><font style="font-family:inherit;font-size:10pt;">For matters for which we have not recorded a liability, we are unable to estimate a range of possible loss because the issues involved have not been fully developed through pleadings, discovery or court proceedings.</font></div></div>" id="sjs-B5">&lt;div style="font-family:Times New Roman;font-size:10pt;">&lt;div style="line-height:120%;padding-top:6px;font-size:10pt;">&lt;font style="font-family:inherit;font-size:10pt;">For matters for which we have not recorded a liability, we are unable to estimate a range of possible loss because the issues involved have not been fully developed through pleadings, discovery or court proceedings.&lt;/font>&lt;/div>&lt;/div>

Commitments and Contingencies -

Commitments and Contingencies - Environmental Matters (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Accrued liabilities for remediation	$ 104	$ 114
Receivables for recoverable costs	$ 36	$ 45

Commitments and Contingencies_2

Commitments and Contingencies - Other Lawsuits (Details) - Pending Litigation - Emergency Pricing And Consumer Protection Laws $ in Millions	9 Months Ended
	Sep. 30, 2018USD ($)
Loss Contingencies [Line Items]
Plaintiff	Commonwealth of Kentucky
Damages sought	$ 89
Loss contingency, period of occurrence	during September and October 2005

Commitments and Contingencies_3

Commitments and Contingencies - Guarantees (Details) $ in Millions	9 Months Ended
	Sep. 30, 2018USD ($)
Other Guarantees
Loss Contingencies [Line Items]
Maximum potential undiscounted payments	$ 92
Guarantee obligations maximum exposure per event	$ 50
LOOP and LOCAP LLC | Guarantee of Indebtedness of Others | Financial Guarantee
Loss Contingencies [Line Items]
Line of credit facility, expiration date	Dec. 31, 2037
Maximum potential undiscounted payments	$ 160
Centennial | Guarantee of Indebtedness of Others | Financial Guarantee
Loss Contingencies [Line Items]
Maximum potential undiscounted payments	$ 22
Centennial | Master Shelf Agreement [Member] | Financial Guarantee
Loss Contingencies [Line Items]
Line of credit facility, expiration date	Dec. 31, 2024
Crowley Ocean Partners
Loss Contingencies [Line Items]
Equity method investments, ownership percentage	50.00%
Crowley Ocean Partners | Guarantee of Indebtedness of Others | Financial Guarantee
Loss Contingencies [Line Items]
Maximum potential undiscounted payments	$ 163
Crowley Ocean Partners | Guarantee of Indebtedness of Others | Financial Guarantee | Crowley Term Loan
Loss Contingencies [Line Items]
Maximum borrowing capacity	$ 325
Crowley Blue Water Partners
Loss Contingencies [Line Items]
Equity method investments, ownership percentage	50.00%
Crowley Blue Water Partners | Guarantee of Indebtedness of Others | Financial Guarantee
Loss Contingencies [Line Items]
Maximum potential undiscounted payments	$ 128
Marathon Oil Companies | Indemnification Agreement
Loss Contingencies [Line Items]
Guarantee obligation current carrying value	$ 3

Commitments and Contingencies_4

Commitments and Contingencies - Contractual Commitments and Contingencies (Details) $ in Millions	9 Months Ended
	Sep. 30, 2018USD ($)
Commitments and Contingencies Disclosure [Abstract]
Contractual commitments to acquire property, plant and equipment and advance funds to equity method investees	$ 1,030

Subsequent Events - Authorized

Subsequent Events - Authorized Shares of MPC Common Stock (Details) - shares	Oct. 01, 2018	Sep. 30, 2018
Subsequent Event [Line Items]
Shares authorized		1,000,000,000
Subsequent Event
Subsequent Event [Line Items]
Shares authorized	2,000,000,000

Subsequent Events - MPC Revolvi

Subsequent Events - MPC Revolving Credit Agreements (Details) $ in Millions	Oct. 01, 2018USD ($)Period	Jul. 20, 2016USD ($)
Bank revolving credit facility due 2022
Subsequent Event [Line Items]
Debt instrument, term		5 years
Maximum borrowing capacity		$ 2,500
364-day revolver due July 2018
Subsequent Event [Line Items]
Debt instrument, term		364 days
Maximum borrowing capacity		$ 1,000
Bank revolving credit facility due 2023 | Subsequent Event
Subsequent Event [Line Items]
Debt instrument, term	5 years
Maximum borrowing capacity	$ 5,000
Number of renewal periods | Period	2
Line of credit facility, duration of renewal period	1 year
Bank revolving credit facility due 2023 | Subsequent Event | Letter of Credit
Subsequent Event [Line Items]
Line of credit facility, current borrowing capacity	$ 2,200
Bank revolving credit facility due 2023 | Subsequent Event | Line of Credit
Subsequent Event [Line Items]
Line of credit facility, expiration date	Oct. 1, 2023
Bank revolving credit facility due 2023 | Subsequent Event | Maximum
Subsequent Event [Line Items]
Line of credit facility, additional borrowing capacity	$ 1,000
Bank revolving credit facility due 2023 | Subsequent Event | Maximum | Bridge Loan
Subsequent Event [Line Items]
Line of credit facility, current borrowing capacity	250
Bank revolving credit facility due 2023 | Subsequent Event | Maximum | Letter of Credit
Subsequent Event [Line Items]
Line of credit facility, current borrowing capacity	$ 3,000
364-day bank revolving credit facility due September 2019 | Subsequent Event
Subsequent Event [Line Items]
Debt instrument, term	364 days
Maximum borrowing capacity	$ 1,000
364-day bank revolving credit facility due September 2019 | Subsequent Event | Line of Credit
Subsequent Event [Line Items]
Line of credit facility, expiration date	Sep. 30, 2019

Subsequent Events - MPC Senior

Subsequent Events - MPC Senior Notes (Details) - Subsequent Event - Andeavor - Senior Notes $ in Millions	Oct. 01, 2018USD ($)
Subsequent Event [Line Items]
Long-term debt assumed	$ 3,375
Debt instrument, face amount	$ 2,905

Supplementary Statistics - Supp

Supplementary Statistics - Supplementary Statistics (Detail) - USD ($) $ in Millions		3 Months Ended			9 Months Ended
		Sep. 30, 2018		Sep. 30, 2017	Sep. 30, 2018		Sep. 30, 2017
Supplementary Statistics [Line Items]
Income from operations		$ 1,403		$ 1,577	$ 3,554		$ 2,850
Capital expenditures and investments	[1]	945		761	2,611		2,150
Refining & Marketing | Refining Logistics & Fuels Distribution [Member]
Supplementary Statistics [Line Items]
Income from operations		(230)			(643)
Midstream | Refining Logistics & Fuels Distribution [Member]
Supplementary Statistics [Line Items]
Income from operations		230			643
Operating Segments
Supplementary Statistics [Line Items]
Income from operations		1,506		1,660	3,836		3,166
Capital expenditures and investments	[2]	917		729	2,514		2,058
Operating Segments | Refining & Marketing
Supplementary Statistics [Line Items]
Income from operations		666	[3]	1,097	1,558	[3]	1,589
Capital expenditures and investments		226		198	613		570
Operating Segments | Speedway
Supplementary Statistics [Line Items]
Income from operations		161		208	415		581
Capital expenditures and investments		98		108	225		221
Operating Segments | Midstream
Supplementary Statistics [Line Items]
Income from operations		679	[3]	355	1,863	[3]	996
Capital expenditures and investments		593		423	1,676		1,267
Corporate and Other
Supplementary Statistics [Line Items]
Income from operations	[4]	(103)		(85)	(283)		(251)
Capital expenditures and investments	[5]	28		32	97		92
Capitalized interest		21		13	55		39
Segment Reconciling Items
Supplementary Statistics [Line Items]
Litigation		0		0	0		(86)
Impairments	[6]	$ 0		$ 2	$ 1		$ 21
[1]	Capital expenditures include changes in capital accruals and investments in affiliates and excludes acquisitions.
[2]	Capital expenditures include changes in capital accruals and investments in affiliates. See reconciliation from segment totals to MPC total capital expenditures below.
[3]	On February 1, 2018, we contributed certain refining logistics assets and fuels distributions services to MPLX. The results of these new businesses are reported in the Midstream segment prospectively from February 1, resulting in a net reduction of $230 million and $643 million to Refining & Marketing segment results and a net increase to Midstream segment results of the same amount for the three and nine months ended September 30, 2018, respectively. No effect was given to prior periods as these entities were not considered businesses prior to February 1, 2018.
[4]	Corporate and other unallocated items consists primarily of MPC’s corporate administrative expenses and costs related to certain non-operating assets, except for corporate overhead expenses attributable to MPLX, which are included in the Midstream segment. Corporate overhead expenses are not allocated to the Refining & Marketing and Speedway segments.
[5]	Includes capitalized interest of $21 million and $13 million for the three months ended September 30, 2018 and 2017, respectively, and $55 million and $39 million for the nine months ended September 30, 2018 and 2017, respectively.
[6]	Includes MPC’s share of gains from the sale of assets remaining from the canceled Sandpiper pipeline project

Supplementary Statistics - Oper

Supplementary Statistics - Operating Statistics (Detail) bbl / d in Thousands, gal in Millions, CFPD in Millions, $ in Millions		3 Months Ended			9 Months Ended
		Sep. 30, 2018USD ($)bbl / dCFPDStore$ / bbl$ / galgal	Sep. 30, 2017USD ($)bbl / dCFPDStore$ / bbl$ / galgal		Sep. 30, 2018USD ($)bbl / dCFPDStore$ / bbl$ / galgal	Sep. 30, 2017USD ($)bbl / dCFPDStore$ / bbl$ / galgal
Operating Statistics [Line Items ]
MPC Consolidated Refined Product Sales Volumes (thousands of barrels per day)	[1]	2,394	2,357		2,358	2,272
Speedway Operating Statistics
Sales and other operating revenues, including consumer excise taxes | $			$ 19,053	[2]		$ 53,220
Merchandise
Speedway Operating Statistics
Sales and other operating revenues, including consumer excise taxes | $			$ 1,370			$ 3,905
Refining & Marketing
Refining & Marketing Operating Statistics
Refining & Marketing refined product sales volume (thousands of barrels per day)	[3]	2,382	2,357		2,346	2,263
Export sales volume (thousands of barrels per day)		280	331		289	291
Refining & Marketing margin (dollars per barrel) | $ / bbl	[4]	14.25	14.14		13.48	12.42
Crude oil capacity utilization percent	[5]	97.40%	101.50%		96.70%	95.80%
Refinery throughputs (thousands of barrels per day)	[6]	2,032	2,017		1,992	1,917
Sour crude oil throughput percent		52.00%	57.00%		53.00%	61.00%
WTI-priced crude oil throughput percent		30.00%	23.00%		28.00%	20.00%
Refined product yields (thousands of barrels per day)	[6]	2,073	2,060		2,030	1,957
Inter-refinery transfers		54	80		53	74
Refinery direct operating costs (dollars per barrel):
Planned turnaround and major maintenance | $ / bbl	[7]	1.77	1.20		1.64	1.69
Depreciation and amortization | $ / bbl	[7]	1.29	1.34		1.31	1.44
Other manufacturing | $ / bbl	[7],[8]	3.54	3.83		3.71	4.10
Total | $ / bbl	[7]	6.60	6.37		6.66	7.23
Speedway Operating Statistics
Sales and other operating revenues, including consumer excise taxes | $			$ 13,573			$ 37,485
Refining & Marketing | Crude oil refined
Refining & Marketing Operating Statistics
Refinery throughputs (thousands of barrels per day)	[6]	1,833	1,845		1,819	1,741
Refining & Marketing | Other charge and blendstocks
Refining & Marketing Operating Statistics
Refinery throughputs (thousands of barrels per day)	[6]	199	172		173	176
Refining & Marketing | Gasoline
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	[6]	942	939		942	910
Refining & Marketing | Distillates
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	[6]	676	673		659	627
Refining & Marketing | Propane
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	[6]	40	38		37	35
Refining & Marketing | Feedstocks and special products
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	[6]	313	298		294	285
Refining & Marketing | Heavy fuel oil
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	[6]	29	45		30	36
Refining & Marketing | Asphalt
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	[6]	73	67		68	64
Refining & Marketing | Gulf Coast:
Refining & Marketing Operating Statistics
Refinery throughputs (thousands of barrels per day)	[9]	1,354	1,340		1,308	1,260
Sour crude oil throughput percent		63.00%	69.00%		62.00%	75.00%
WTI-priced crude oil throughput percent		17.00%	14.00%		15.00%	10.00%
Refined product yields (thousands of barrels per day)	[9]	1,388	1,377		1,342	1,294
Refinery direct operating costs (dollars per barrel):
Planned turnaround and major maintenance | $ / bbl	[7]	0.64	0.90		1.30	1.86
Depreciation and amortization | $ / bbl	[7]	1.03	1.05		1.03	1.15
Other manufacturing | $ / bbl	[7],[8]	3.20	3.52		3.43	3.81
Total | $ / bbl	[7]	4.87	5.47		5.76	6.82
Refining & Marketing | Gulf Coast: | Crude oil refined
Refining & Marketing Operating Statistics
Refinery throughputs (thousands of barrels per day)	[9]	1,150	1,123		1,121	1,041
Refining & Marketing | Gulf Coast: | Other charge and blendstocks
Refining & Marketing Operating Statistics
Refinery throughputs (thousands of barrels per day)	[9]	204	217		187	219
Refining & Marketing | Gulf Coast: | Gasoline
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	[9]	567	538		557	525
Refining & Marketing | Gulf Coast: | Distillates
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	[9]	442	438		421	393
Refining & Marketing | Gulf Coast: | Propane
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	[9]	27	25		24	25
Refining & Marketing | Gulf Coast: | Feedstocks and special products
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	[9]	314	326		301	310
Refining & Marketing | Gulf Coast: | Heavy fuel oil
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	[9]	16	31		18	24
Refining & Marketing | Gulf Coast: | Asphalt
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	[9]	22	19		21	17
Refining & Marketing | Midwest:
Refining & Marketing Operating Statistics
Refinery throughputs (thousands of barrels per day)	[9]	732	757		737	731
Sour crude oil throughput percent		34.00%	38.00%		37.00%	41.00%
WTI-priced crude oil throughput percent		52.00%	38.00%		49.00%	34.00%
Refined product yields (thousands of barrels per day)	[9]	739	763		741	737
Refinery direct operating costs (dollars per barrel):
Planned turnaround and major maintenance | $ / bbl	[7]	3.74	1.60		2.13	1.22
Depreciation and amortization | $ / bbl	[7]	1.68	1.72		1.70	1.80
Other manufacturing | $ / bbl	[7],[8]	3.89	3.96		3.96	4.19
Total | $ / bbl	[7]	9.31	7.28		7.79	7.21
Refining & Marketing | Midwest: | Crude oil refined
Refining & Marketing Operating Statistics
Refinery throughputs (thousands of barrels per day)	[9]	683	722		698	700
Refining & Marketing | Midwest: | Other charge and blendstocks
Refining & Marketing Operating Statistics
Refinery throughputs (thousands of barrels per day)	[9]	49	35		39	31
Refining & Marketing | Midwest: | Gasoline
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	[9]	375	401		385	385
Refining & Marketing | Midwest: | Distillates
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	[9]	234	235		238	234
Refining & Marketing | Midwest: | Propane
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	[9]	13	14		13	11
Refining & Marketing | Midwest: | Feedstocks and special products
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	[9]	53	50		46	47
Refining & Marketing | Midwest: | Heavy fuel oil
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	[9]	13	15		12	13
Refining & Marketing | Midwest: | Asphalt
Refining & Marketing Operating Statistics
Refined product yields (thousands of barrels per day)	[9]	51	48		47	47
Speedway
Speedway Operating Statistics
Convenience stores at period-end | Store		2,745	2,734		2,745	2,734
Gasoline and distillate sales (millions of gallons) | gal		1,474	1,464		4,317	4,332
Gasoline and distillate margin (dollars per gallon) | $ / gal	[10]	0.1651	0.1772		0.1620	0.1727
Sales and other operating revenues, including consumer excise taxes | $			$ 4,895			$ 14,070
Merchandise margin (in millions) | $		$ 384	$ 374		$ 1,069	$ 1,065
Merchandise margin percent		28.70%	28.90%		28.50%	28.80%
Same store gasoline sales volume (period over period) percentage	[11]	(1.20%)	(3.10%)		(1.80%)	(1.60%)
Merchandise sales excluding cigarettes (period over period) percentage	[12]	4.90%	0.30%		3.40%	1.50%
Speedway | Merchandise
Speedway Operating Statistics
Sales and other operating revenues, including consumer excise taxes | $		$ 1,339	$ 1,295		$ 3,753	$ 3,693
Midstream
Speedway Operating Statistics
Sales and other operating revenues, including consumer excise taxes | $			$ 585			$ 1,665
Midstream Operating Statistics
Crude oil and refined product pipeline throughputs (thousands of barrels per day)	[13]	3,829	3,562		3,694	3,299
Terminal throughput (thousands of barrels per day)		1,474	1,496		1,468	1,470
Gathering system throughput (MMcf/d) | CFPD	[14]	4,737	3,729		4,403	3,415
Natural gas processed (MMcf/d) | CFPD	[14]	7,171	6,581		6,874	6,336
C2 and NGLs fractionated (thousands barrels per day)	[14]	488	397		451	384
[1]	Total average daily volumes of refined product sales to wholesale, branded and retail customers.
[2]	The 2018 period reflects an election to present certain taxes on a net basis concurrent with our adoption of ASU 2014-09, Revenue - Revenue from Contracts with Customers (“ASC 606”). See Notes 2 and 3 for further information.
[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 down time for planned maintenance and other normal operating activities.
[6]	Excludes inter-refinery volumes of 54 mbpd and 80 mbpd for the three months ended September 30, 2018 and 2017, respectively, and 53 mbpd and 74 mbpd for the nine months ended September 30, 2018 and 2017, respectively.
[7]	Per barrel of total refinery throughputs. Effective with the February 1, 2018 dropdown, direct operating costs related to certain refining logistics assets are now reported in the Midstream segment. No effect was given to prior periods as this entity was not considered a business prior to February 1, 2018.
[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 bank card processing fees, divided by gasoline and distillate sales volume.
[11]	Same store comparison includes only locations owned at least 13 months.
[12]	Excludes cigarettes.
[13]	Includes common-carrier pipelines and private pipelines owned or operated by MPLX, excluding equity method investments.
[14]	Includes amounts related to unconsolidated equity method investments on a 100 percent basis.