MPLX (MPLX) 10-K 28 Feb 20 2019 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2019	Feb. 17, 2020	Jun. 30, 2019
Entity Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2019
Document Transition Report	false
Entity File Number	001-35714
Entity Registrant Name	MPLX LP
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	27-0005456
Entity Address, Address Line One	200 E. Hardin Street
Entity Address, City or Town	Findlay
Entity Address, State or Province	OH
Entity Address, Postal Zip Code	45840-3229
City Area Code	419
Local Phone Number	421-2414
Title of 12(b) Security	Common Units Representing Limited Partnership Interests
Trading Symbol	MPLX
Security Exchange Name	NYSE
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 9.3
Entity Common Stock, Shares Outstanding		1,058,415,865
Amendment Flag	false
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Entity Central Index Key	0001552000
Current Fiscal Year End Date	--12-31

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) shares in Millions, $ in Millions		12 Months Ended
		Dec. 31, 2019		Dec. 31, 2018	Dec. 31, 2017
Revenues and other income:
Revenue from Contract with Customer, Excluding Assessed Tax		$ 7,041		$ 5,449
Rental income		388		352	$ 277
Rental income - related parties		1,196		846	279
Income from equity method investments	[1],[2]	290		247	78
Other income		12		7	6
Other income - related parties		114		99	92
Total revenues and other income		9,041		7,005	3,867
Costs and expenses:
Rental cost of sales		141		135	62
Rental cost of sales - related parties		165		31	2
Purchases - related parties		1,231		925	455
Depreciation and amortization	[3]	1,254		867	683
Impairment expense		1,197		0	0
General and administrative expenses		388		316	241
Other taxes		113		83	54
Total costs and expenses		6,664		4,277	2,676
Income from operations		2,377		2,728	1,191
Related party interest and other financial costs		11		5	2
Interest expense (net of amounts capitalized of $51 million, $37 million and $32 million, respectively)		851		590	296
Other financial costs		53		119	56
Income before income taxes		1,462		2,014	837
Provision for income taxes		0		8	1
Net income		1,462		2,006	836
Less: Net income attributable to noncontrolling interests		28		16	6
Less: Net income attributable to Predecessor		401		172	36
Net income attributable to MPLX LP	[4]	1,033		1,818	794
Less: Series A preferred unit distributions					65
Less: General partner’s interest in net income attributable to MPLX LP		0		0	318
Limited partners’ interest in net income attributable to MPLX LP		$ 935		$ 1,743	$ 411
Weighted average limited partner units outstanding:
Common - basic (in units)		906	[5]	761	393
Common - diluted (in units)		907	[5]	761	396
Preferred Partner [Member]
Costs and expenses:
Net income attributable to MPLX LP	[4]	$ 81		$ 75	$ 65
Limited Partners Common Units
Costs and expenses:
Net income attributable to MPLX LP	[4]	$ 910		$ 1,743	$ 411
Net income attributable to MPLX LP per limited partner unit:
Common - basic (in USD per unit)		$ 1		$ 2.29	$ 1.07
Common - diluted (in USD per unit)		$ 1		$ 2.29	$ 1.06
Weighted average limited partner units outstanding:
Common - basic (in units)		906	[5]	761	385
Common - diluted (in units)		907	[5]	761	388
Service [Member]
Revenues and other income:
Revenue from Contract with Customer, Excluding Assessed Tax		$ 2,498		$ 1,856	$ 1,156
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		3,455		2,404	1,082
Product [Member]
Revenues and other income:
Revenue from Contract with Customer, Excluding Assessed Tax		806		887	889
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties	[6]	142		87	8
Oil and Gas, Refining and Marketing [Member]
Costs and expenses:
Cost of Goods and Services Sold		1,489		1,096	528
Natural Gas, Midstream [Member]
Costs and expenses:
Cost of Goods and Services Sold		686		824	651
Service, Other [Member]
Revenues and other income:
Revenue from Contract with Customer, Excluding Assessed Tax		140		220	0
Series A Preferred Stock [Member] | Preferred Partner [Member]
Costs and expenses:
Less: Series A preferred unit distributions		81		75
Series B Preferred Stock [Member] | Preferred Partner [Member]
Costs and expenses:
Less: Series A preferred unit distributions		$ 17		$ 0	$ 0
[1]	“Income from equity method investments” includes the impact of any basis differential amortization or accretion.
[2]	The financial information for equity method investments for 2019 includes financial information of equity method investments acquired as part of the Merger. The financial information for equity method investments for 2018 includes financial information of equity method investments acquired as part of the Merger for the last three months of 2018. The financial information for equity method investments for 2017 does not include financial information of equity method investments acquired as part of the Merger. See Note 1
[3]	Depreciation and amortization attributable to L&S was $503 million , $308 million and $163 million for the years ended 2019 , 2018 and 2017 , respectively. Depreciation and amortization attributable to G&P was $751 million , $559 million and $520 million for 2019 , 2018 and 2017 , respectively.
[4]	Allocation of net income/(loss) attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.
[5]	The Series B preferred units and the MPLX common units issued in connection with the Merger were not outstanding during the entire year. See Notes 4 and 8 for additional information about the treatment of these units.
[6]	There were additional product sales to MPC that net to zero within the consolidated financial statements as the transactions are recorded net due to the terms of the agreements under which such product was sold. For 2019 , 2018 and 2017 , these sales totaled $1,120 million , $607 million and $254 million , respectively.

Consolidated Statements of In_2

Consolidated Statements of Income Consolidated Statements of Income (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Statement [Abstract]
Interest costs capitalized	$ 51	$ 37	$ 32

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income Statement - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	$ 1,462	$ 2,006	$ 836
Other comprehensive income/(loss), net of tax:
Remeasurements of pension and other postretirement benefits related to equity method investments, net of tax	1	(2)	0
Comprehensive income	1,463	2,004	836
Less comprehensive income attributable to:
Noncontrolling interests	28	16	6
Income attributable to Predecessor	401	172	36
Comprehensive income attributable to MPLX LP	$ 1,034	$ 1,816	$ 794

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions		Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents		$ 15	$ 77
Receivables, net		593	611
Current Assets, Related Parties		656	556
Inventories		110	98
Other current assets		110	98
Total current assets		1,484	1,440
Equity method investments		5,275	4,901
Property, plant and equipment, net		22,145	21,525
Intangibles, net		1,270	1,359
Goodwill		9,536	10,016
Other noncurrent assets		52	60
Total assets		40,430	39,325
Current liabilities:
Accounts payable		242	266
Accrued liabilities		187	272
Accrued property, plant and equipment		283	399
Accrued interest payable		210	184
Operating Lease, Liability, Current		66	0
Other current liabilities		136	645
Total current liabilities		2,132	2,268
Long-term deferred revenue		217	132
Liabilities, Related Parties, Noncurrent		290	46
Long-term debt		19,704	17,922
Deferred income taxes		12	14
Operating Lease, Liability, Noncurrent		302	0
Deferred credits and other liabilities		192	208
Total liabilities		22,849	20,590
Commitments and contingencies (see Note 23)
Series A preferred units		968	1,004
Equity
Total MPLX LP partners’ capital		16,364	17,575
Accumulated other comprehensive loss	[1]	(15)	(16)
Noncontrolling interests		249	156
Total equity		16,613	17,731
Total liabilities, preferred units and equity		40,430	39,325
Operating Lease, Right-of-Use Asset		365	0
Other Assets, Related Parties, Noncurrent		303	24
Current Liabilities, Related Parties		1,008	502
MPC
Current liabilities:
Operating Lease, Liability, Current		1	0
Operating Lease, Liability, Noncurrent		230	0
Equity
Operating Lease, Right-of-Use Asset		232	0
Limited Partners Common Units | Public
Equity
Total MPLX LP partners’ capital		10,800	8,336
Total equity		10,800	8,336
Limited Partners Common Units | MPC
Equity
Total MPLX LP partners’ capital		4,968	(1,612)
Total equity		4,968	(1,612)
Series B Preferred Stock [Member]
Equity
Total MPLX LP partners’ capital		611	0
LOOP and Explorer
Equity
Accumulated other comprehensive loss		(15)	(16)
Retained Earnings [Member] | MPC
Equity
Total equity		$ 0	$ 10,867
[1]	These components of “Accumulated other comprehensive loss” are included in the computation of net periodic benefit cost by LOOP and Explorer and are therefore included on the Consolidated Statements of Income under the caption “Income/(loss) from equity method investments.”

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - shares shares in Millions	Dec. 31, 2019	Dec. 31, 2018
Limited Partners Common Units | Public
Units issued	392	289
Units outstanding	392	289
Limited Partners Common Units | MPC
Units issued	666	505
Units outstanding	666	505
Series B Preferred Stock [Member]
Units issued	0.6	0
Units outstanding	0.6	0

Consolidated Statements of Cash

Consolidated Statements of Cash Flows $ in Millions	12 Months Ended
	Dec. 31, 2019USD ($)		Dec. 31, 2018USD ($)		Dec. 31, 2017USD ($)
Operating activities:
Net income	$ 1,462		$ 2,006		$ 836
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of deferred financing costs	42		55		53
Depreciation and amortization	1,254	[1]	867	[1]	683	[1]
Impairment expense	1,197		0		0
Deferred income taxes	(2)		8		(1)
Asset retirement expenditures	(1)		(7)		(2)
Gain on disposal of assets	(6)		3		0
Income from equity method investments	(290)	[2],[3]	(247)	[2],[3]	(78)	[2],[3]
Distributions from unconsolidated affiliates	525		412		241
Changes in:
Current receivables	17		(104)		8
Inventories	(9)		(5)		(3)
Fair value of derivatives	2		(10)		6
Current accounts payable and accrued liabilities	(59)		88		48
Current assets/current liabilities - related parties	(163)		(61)		55
Increase (Decrease) in Other Operating Assets and Liabilities, Net	4		0		0
Deferred revenue	100		61		33
All other, net	9		5		28
Net cash provided by operating activities	4,082		3,071		1,907
Investing activities:
Additions to property, plant and equipment	(2,408)		(2,111)		(1,411)
Proceeds from Contributions from Affiliates	6
Acquisitions, net of cash acquired			(451)		(249)
Investments - net related party loans	0		0		80
Disposal of assets	30		8		7
Investments in unconsolidated affiliates	(713)		(341)		(761)
Distributions from unconsolidated affiliates - return of capital	18		16		26
All other, net	4		1		0
Net cash used in investing activities	(3,063)		(2,878)		(2,308)
Financing activities:
Long-term debt - borrowings	9,174		13,476		2,911
Long-term debt - repayments	(7,924)		(6,946)		(416)
Related party debt - borrowings	9,313		3,962		2,369
Related party debt - repayments	(8,719)		(4,347)		(1,983)
Debt issuance costs	(20)		(76)		(29)
Net proceeds from equity offerings	0		0		483
Distributions to Series A preferred unitholders					(65)
Distributions to MPC for acquisitions	0		(4,111)		(1,951)
Distributions to MPC from Predecessor	0		0		113
Distributions to unitholders and general partner	(2,435)		(1,819)		(1,120)
Distributions to noncontrolling interests	(30)		(17)		(7)
Contributions from MPC	74		41		0
Contributions from noncontrolling interests	95		11		129
Consideration payment to Class B unitholders	0		0		(25)
All other, net	(13)		19		(12)
Net Cash Provided by (Used in) Financing Activities	(1,089)		(117)		171
Net (decrease)/increase in cash, cash equivalents and restricted cash	(70)		76		(230)
Cash, cash equivalents and restricted cash at beginning of period	15		85		9
Cash, cash equivalents and restricted cash at end of period	15		85		9
Series A Preferred Stock [Member] | Preferred Partner [Member]
Financing activities:
Distributions to Series A preferred unitholders	(81)		(71)
Series B Preferred Stock [Member] | Preferred Partner [Member]
Financing activities:
Distributions to Series A preferred unitholders	(21)		0		0
Payments of Distributions on Preferred Units from Predecessor	$ (502)		$ (239)		$ 0
[1]	Depreciation and amortization attributable to L&S was $503 million , $308 million and $163 million for the years ended 2019 , 2018 and 2017 , respectively. Depreciation and amortization attributable to G&P was $751 million , $559 million and $520 million for 2019 , 2018 and 2017 , respectively.
[2]	“Income from equity method investments” includes the impact of any basis differential amortization or accretion.
[3]	The financial information for equity method investments for 2019 includes financial information of equity method investments acquired as part of the Merger. The financial information for equity method investments for 2018 includes financial information of equity method investments acquired as part of the Merger for the last three months of 2018. The financial information for equity method investments for 2017 does not include financial information of equity method investments acquired as part of the Merger. See Note 1

Consolidated Statements of Equi

Consolidated Statements of Equity - USD ($) $ in Millions	Total	Preferred Partner [Member]	PublicLimited Partners Common Units	PublicLimited Partners Class B Units	MPCLimited Partners Common Units	MPCGeneral Partner	AOCI Attributable to Parent	Noncontrolling Interest	Equity of PredecessorMPC
Beginning balance at Dec. 31, 2016	$ 11,110	$ 0	$ 8,086	$ 133	$ 1,069	$ 1,013	$ 0	$ 18	$ 791
Distributions to MPC from Predecessor	(113)	0	0	0	0	0	0	0	(113)
Distribution declared, general partner	(32)	0	0	0	0	(32)	0	0	0
Contribution from MPC	(675)	0	0	0	0	0	(14)	0	(689)
Unit issuances under ATM Program	483	0	473	0	0	10	0	0	0
Stockholders' Equity, Other	8	0	8	0	0	0	0	0	0
Net income (loss)	(771)	0	(301)	0	(110)	(318)	0	(6)	(36)
Allocation of MPC's net investment at acquisition	0	0	0	0	(1,669)	266	0	0	1,403
Distribution to MPC for acquisitions	(1,931)	0	0	0	(537)	(1,394)	0	0	0
Noncontrolling interests	(1,120)	0	(622)	0	(212)	(286)	0	0	0
(Placeholder)	(7)	0	0	0	0	0	0	(7)	0
Contributions from noncontrolling interests	129	0	0	0	0	0	0	129	0
Unit conversion	0	0	(133)	133	0	0	0	0	0
Ending balance at Dec. 31, 2017	9,973	0	8,379	0	2,099	(637)	(14)	146	0
Distributions to MPC from Predecessor	0
Contribution from MPC	(11,980)	0	0	0	0	0	0	0	(11,980)
Stockholders' Equity, Other	11	0	12	0	0	1	(2)	0	0
Net income (loss)	(1,931)	0	(667)	0	(1,076)	0	0	(16)	(172)
Allocation of MPC's net investment at acquisition	0	0	0	0	(5,172)	4,126	0	0	1,046
Distribution to MPC for acquisitions	(4,100)	0	0	0	(936)	(3,164)	0	0	0
Noncontrolling interests	(2,058)	0	(722)	0	(1,097)	0	0	0	(239)
(Placeholder)	(17)	0	0	0	0	0	0	(17)	0
Contributions from noncontrolling interests	11	0	0	0	0	0	0	11	0
Unit conversion	0	0	0	0	(7,926)	7,926	0	0	0
Ending balance at Dec. 31, 2018	17,731	0	8,336	0	(1,612)	0	(16)	156	10,867
Distributions to MPC from Predecessor	0
Contribution from MPC	(346)	0	0	0	(315)	0	0	0	(31)
Stockholders' Equity, Other	13	0	12	0	0	0	1	0	0
Net income (loss)	(1,381)	(17)	(340)	0	(595)	0	0	(28)	(401)
Allocation of MPC's net investment at acquisition	0	(615)	(2,983)	0	(7,199)	0	0	0	10,797
Noncontrolling interests	(2,959)	(21)	(907)	0	(1,529)	0	0	0	(502)
(Placeholder)	(30)	0	0	0	0	0	0	(30)	0
Contributions from noncontrolling interests	95	0	0	0	0	0	0	95	0
Unit conversion	36	0	36	0	0	0	0	0	0
Ending balance at Dec. 31, 2019	$ 16,613	$ 611	$ 10,800	$ 0	$ 4,968	$ 0	$ (15)	$ 249	$ 0

Description of the Business and

Description of the Business and Basis of Presentation	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Business Description and Basis of Presentation [Text Block]	Description of the Business and Basis of Presentation Description of the Business – MPLX LP is a diversified, large-cap master limited partnership formed by Marathon Petroleum Corporation (“MPC”) that owns and operates midstream energy infrastructure and logistics assets, and provides fuels distribution services. References in this report to “MPLX LP,” “MPLX,” “the Partnership,” “we,” “ours,” “us,” or like terms refer to MPLX LP and its subsidiaries. References to “MPC” refer collectively to Marathon Petroleum Corporation as our sponsor and its subsidiaries, other than the Partnership. We are engaged in the transportation, storage and distribution of crude oil, asphalt and refined petroleum products; the gathering, processing and transportation of natural gas; and the gathering, transportation, fractionation, storage and marketing of NGLs. MPLX’s principal executive office is located in Findlay, Ohio. MPLX was formed on March 27, 2012 as a Delaware limited partnership and completed its Initial Offering on October 31, 2012 . MPLX’s business consists of two segments based on the nature of services it offers: Logistics and Storage (“L&S”), which relates primarily to crude oil and refined petroleum products; and Gathering and Processing (“G&P”), which relates primarily to natural gas and NGLs. See Note 10 for additional information regarding the operations and results of these segments. On July 30, 2019, MPLX completed its acquisition by merger (the “Merger”) of Andeavor Logistics LP (“ANDX”). At the effective time of the Merger, each common unit held by ANDX’s public unitholders was converted into the right to receive 1.135 MPLX common units. ANDX common units held by certain affiliates of MPC were converted into the right to receive 1.0328 MPLX common units. See Note 4 for additional information regarding the Merger. Basis of Presentation – The consolidated financial statements include all majority-owned and controlled subsidiaries. For non-wholly-owned consolidated subsidiaries, the interests owned by third parties have been recorded as “Noncontrolling interests” on the accompanying Consolidated Balance Sheets. Intercompany investments, accounts and transactions have been eliminated. MPLX’s investments in which MPLX exercises significant influence but does not control and does not have a controlling financial interest are accounted for using the equity method. MPLX’s investments in a VIE in which MPLX exercises significant influence but does not control and is not the primary beneficiary are also accounted for using the equity method. In relation to the Merger described above and in Note 4 , ANDX’s assets, liabilities and results of operations prior to the Merger are collectively included in what we refer to as the “Predecessor” from October 1, 2018, which was the date that MPC acquired Andeavor. MPLX’s acquisition of ANDX is considered a transfer between entities under common control due to MPC’s relationship with ANDX prior to the Merger. As an entity under common control with MPC, MPLX recorded the assets acquired and liabilities assumed on its consolidated balance sheets at MPC’s historical carrying value. Transfers of businesses between entities under common control require prior periods to be retrospectively adjusted for those dates that the entity was under common control. Accordingly, the accompanying financial statements and related notes of MPLX LP have been retrospectively adjusted to include the historical results of ANDX beginning October 1, 2018. Certain prior period financial statement amounts have been reclassified to conform to current period presentation. The accompanying consolidated financial statements of MPLX have been prepared in accordance with GAAP.

Summary of Principal Accounting

Summary of Principal Accounting Policies	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Summary of Principal Accounting Policies	Summary of Principal Accounting Policies Use of Estimates – The preparation of financial statements in accordance with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities as of the date of the consolidated financial statements and the reported amounts of revenues and expenses during the respective reporting periods. Actual results could differ materially from those estimates. Estimates are subject to uncertainties due to the levels of subjectivity and judgment necessary to account for highly uncertain matters or the susceptibility of such matters to change and affect items such as valuing identified intangible assets; determining the fair value of derivative instruments; evaluating impairments of long-lived assets, goodwill and equity investments; establishing estimated useful lives for long-lived assets; acquisition accounting; recognizing share-based compensation expense; estimating revenues, expense accruals and capital expenditures; valuing AROs; and determining liabilities, if any, for environmental and legal contingencies. Revenue Recognition – Revenue is measured based on consideration specified in a contract with a customer. MPLX recognizes revenue when it satisfies a performance obligation by transferring control over a product or providing services to a customer. MPLX enters into a variety of contract types in order to generate “Product sales” and “Service revenue.” MPLX provides services under the following types of arrangements: • Fee-based arrangements – Under fee-based arrangements, MPLX receives a fee or fees for one or more of the following services: gathering, processing and transportation of natural gas; gathering, transportation, fractionation, exchange and storage of NGLs; and transportation, storage and distribution of crude oil, refined products and other hydrocarbon-based products. The revenue MPLX earns from these arrangements is generally directly related to the volume of natural gas, NGLs, refined products or crude oil that is handled by or flows through MPLX’s systems and facilities and is not normally directly dependent on commodity prices. In certain cases, MPLX’s arrangements provide for minimum annual payments or fixed demand charges. Fee-based arrangements are reported as “Service revenue” on the Consolidated Statements of Income. Revenue is recognized over time as services are performed. In certain instances when specifically stated in the contract terms, MPLX purchases product after fee-based services have been provided. Revenue from the sale of products purchased after services are provided is reported as “Product sales” on the Consolidated Statements of Income and recognized on a gross basis, as MPLX takes control of the product and is the principal in the transaction. • Percent-of-proceeds arrangements – Under percent-of-proceeds arrangements, MPLX: gathers and processes natural gas on behalf of producers; sells the resulting residue gas, condensate and NGLs at market prices; and remits to producers an agreed-upon percentage of the proceeds. In other cases, instead of remitting cash payments to the producer, MPLX delivers an agreed-upon percentage of the residue gas and NGLs to the producer (take-in-kind arrangements) and sells the volumes MPLX retains to third parties or related parties. Revenue is recognized on a net basis when MPLX acts as an agent and does not have control of the gross amount of gas and/or NGLs prior to it being sold. Percent-of-proceeds revenue is reported as “Service revenue - product related” on the Consolidated Statements of Income. • Keep-whole arrangements – Under keep-whole arrangements, MPLX gathers natural gas from the producer, processes the natural gas and sells the resulting condensate and NGLs to third parties at market prices. Because the extraction of the condensate and NGLs from the natural gas during processing reduces the Btu content of the natural gas, MPLX must either purchase natural gas at market prices for return to producers or make cash payment to the producers equal to the value of the energy content of this natural gas. Certain keep-whole arrangements also have provisions that require MPLX to share a percentage of the keep-whole profits with the producers based on the oil to gas ratio or the NGL to gas ratio. “Service revenue - product related” is recorded based on the value of the NGLs received on the date the services are performed. Natural gas purchased to return to the producer and shared NGL profits are recorded as a reduction of “Service revenue - product related” on the Consolidated Statements of Income on the date the services are performed. Sales of NGLs under these arrangements are reported as “Product sales” on the Consolidated Statements of Income and are reported on a gross basis as MPLX is the principal in the arrangement and controls the product prior to sale. The sale of the NGLs may occur shortly after services are performed at the tailgate of the plant, or after a period of time as determined by MPLX. • Purchase arrangements – Under purchase arrangements, MPLX purchases natural gas at either the wellhead or the tailgate of a plant. MPLX then gathers and delivers the natural gas to pipelines where MPLX may resell the natural gas. Wellhead purchase arrangements represent an arrangement with a supplier and are recorded in “Purchased product costs.” Often, MPLX earns fees for services performed prior to taking control of the product in these arrangements and “Service revenue” is recorded for these fees. Revenue generated from the sale of product obtained in tailgate purchase arrangements is reported as “Product sales” on the Consolidated Statements of Income and is recognized on a gross basis as MPLX purchases and takes control of the product prior to sale and is the principal in the transaction. In many cases, MPLX provides services under contracts that contain a combination of more than one of the arrangements described above. When fees are charged (in addition to product received) under percent-of-proceeds arrangements, keep-whole arrangements or purchase arrangements, MPLX records such fees as “Service revenue” on the Consolidated Statements of Income. The terms of MPLX’s contracts vary based on gas quality conditions, the competitive environment when the contracts are signed and customer requirements. Performance obligations are determined based on the specific terms of the arrangements, economics of the geographical regions, and the services offered and whether they are deemed distinct. MPLX allocates the consideration earned between the performance obligations based on the stand-alone selling price when multiple performance obligations are identified. Revenue from MPLX’s service arrangements will generally be recognized over time as the performance obligation is satisfied as services are provided. MPLX has elected to use the output measure of progress to recognize revenue based on the units delivered, processed or transported. The transaction price has 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 each period. In instances in which tiered pricing structures do not reflect our efforts to perform, MPLX will estimate variable consideration at contract inception. “Product sales” will be recognized at a point in time when control of the product transfers to the customer. Minimum volume commitments may create contract liabilities or deferred credits if current period payments can be used for future services. Breakage is estimated and recognized into service revenue in instances where it is probable the customer will not use the credit in future periods. Amounts billed to customers for shipping and handling, electricity, and other costs to perform services are included in “Service revenue” on the Consolidated Statements of Income. Shipping and handling costs associated with product sales are included in “Purchased product costs” on the Consolidated Statements of Income. Facility expenses, costs of revenues and depreciation represent those expenses related to operating our various facilities and are necessary to provide both “Product sales” and “Service revenue.” Customers usually pay monthly based on the products purchased or services performed that month. Taxes collected from customers and remitted to the appropriate taxing authority are excluded from revenue. Based on the terms of certain natural gas gathering, transportation and processing agreements, MPLX is considered to be the lessor under several implicit operating lease arrangements in accordance with GAAP. Revenue and costs related to the portion of the revenue earned under these contracts considered to be implicit leases are recorded as “Rental income” and “Rental cost of sales,” respectively, on the Consolidated Statements of Income. Revenue and Expense Accruals – MPLX routinely makes accruals based on estimates for both revenues and expenses due to the timing of compiling billing information, receiving certain third-party information and reconciling MPLX’s records with those of third parties. The delayed information from third parties includes, among other things, actual volumes purchased, transported or sold, adjustments to inventory and invoices for purchases, actual natural gas and NGL deliveries and other operating expenses. MPLX makes accruals to reflect estimates for these items based on its internal records and information from third parties. Estimated accruals are adjusted when actual information is received from third parties and MPLX’s internal records have been reconciled. Cash and Cash Equivalents – Cash and cash equivalents include cash on hand and on deposit and investments in highly liquid debt instruments with initial maturities of three months or less. Restricted Cash – Restricted cash consists of cash and investments that must be maintained as collateral for letters of credit issued to certain third-party producer customers. The balances will be outstanding until certain capital projects are completed and the third party releases the restriction. Restricted cash also consists of cash advances to be used for the operation and maintenance of an operated pipeline system. Restricted cash is included in “ Other current assets ” on the Consolidated Balance Sheets. Receivables – Receivables primarily consist of customer accounts receivable, which are recorded at the invoiced amount and generally do not bear interest. Allowances for doubtful accounts are generally recorded when it becomes probable that the receivable will not be collected and are recorded to bad debt expense. We review the allowance quarterly with past-due balances over 90 days and other higher-risk amounts being reviewed individually for collectability. Balances that remain outstanding after reasonable collection efforts have been unsuccessful are written off through a charge to the valuation allowance and a credit to accounts receivable. Lease Receivables - Lease receivables are the present value of the sum of the future minimum lease payments and the unguaranteed residual value of the leased assets under arrangements where MPLX is the lessor. Management assesses these lease receivables for recoverability quarterly. Inventories – Inventories consist primarily of natural gas, propane, other NGLs and materials and supplies to be used in operations. Natural gas, propane, and other NGLs are valued at the lower of cost or market value. Materials and supplies are stated at the lower of cost or market value. Cost for materials and supplies are determined primarily using the weighted-average cost method. Imbalances – Within our pipelines and storage assets, we experience volume gains and losses due to pressure and temperature changes, evaporation and variances in meter readings and other measurement methods. Until settled, positive imbalances are recorded as other current assets and negative imbalances are recorded as accounts payable. Positive and negative product imbalances are settled in cash, settled by physical delivery of gas from a different source, or tracked and settled in the future. Property, Plant and Equipment – Property, plant and equipment are recorded at cost and depreciated on a straight-line basis over the estimated useful lives of the assets. Expenditures that extend the useful lives of assets are capitalized. Such assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. If the sum of the expected undiscounted future cash flows from the use of the asset and its eventual disposition is less than the carrying amount of the asset, an impairment assessment is performed and the excess of the book value over the fair value is recorded as an impairment loss. When items of property, plant and equipment are sold or otherwise disposed of, any gains or losses are reported on the Consolidated Statements of Income. Gains on the disposal of property, plant and equipment are recognized when they occur, which is generally at the time of closing. If a loss on disposal is expected, such losses are recognized when the assets are classified as held for sale. Interest costs for the construction or development of long-lived assets are capitalized and amortized over the related asset’s estimated useful life. Goodwill and Intangibles – Goodwill represents the excess of the purchase price over the estimated fair value of the net assets acquired in the acquisition of a business. Goodwill is not amortized, but rather is tested for impairment annually and when events or changes in circumstances indicate that the fair value of a reporting unit with goodwill has been reduced below carrying value. The impairment test requires allocating goodwill and other assets and liabilities to reporting units. The fair value of each reporting unit is determined using an income and/or market approach which is compared to the carrying value of the reporting unit. The fair value under the income approach is calculated using the expected present value of future cash flows method. Significant assumptions used in the cash flow forecasts include future operating performance, future volumes, discount rates, and future capital requirements. If the fair value of the reporting unit is less than the carrying value, including goodwill, the excess, if any, of the book value over the fair value of the reporting unit up to the amount of goodwill recorded is charged to net income as an impairment expense. Amortization of intangibles with definite lives is calculated using the straight-line method which is reflective of the benefit pattern in which the estimated economic benefit is expected to be received over the estimated useful life of the intangible asset. Intangibles subject to amortization are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of the intangible may not be recoverable. If the sum of the expected undiscounted future cash flows related to the asset is less than the carrying amount of the asset, an impairment loss is recognized based on the fair value of the asset. Intangibles not subject to amortization are tested for impairment annually and when circumstances indicate that the fair value is less than the carrying amount of the intangible. If the fair value is less than the carrying value, an impairment is recorded for the difference. As a result of MPLX’s November 30, 2019 annual goodwill impairment analysis, we recorded an impairment charge of approximately $1.2 billion , which resulted in a goodwill balance of $9.5 billion at December 31, 2019. See Note 14 for further details. No impairments were recorded as a result of our 2018 annual goodwill impairment analysis. Other Taxes – Other taxes primarily include real estate taxes. Environmental Costs – Environmental expenditures are capitalized if the costs mitigate or prevent future contamination or if the costs improve environmental safety or efficiency of the existing assets. MPLX recognizes remediation costs and penalties when the responsibility to remediate is probable and the amount of associated costs can be reasonably estimated. The timing of remediation accruals coincides with completion of a feasibility study or the commitment to a formal plan of action. Remediation liabilities are accrued based on estimates of known environmental exposure and are discounted when the estimated amounts are reasonably fixed and determinable. If recoveries of remediation costs from third parties are probable, a receivable is recorded and is discounted when the estimated amount is reasonably fixed and determinable. Asset Retirement Obligations – An ARO is a legal obligation associated with the retirement of tangible long-lived assets that generally result from the acquisition, construction, development or normal operation of the asset. AROs are recorded at fair value in the period in which they are incurred, if a reasonable estimate of fair value can be made, and added to the carrying amount of the associated asset. This additional carrying amount is then depreciated over the life of the asset. The liability is determined using a credit adjusted risk free interest rate and increases due to the passage of time based on the time value of money until the obligation is settled. MPLX recognizes a liability of a conditional ARO as soon as the fair value of the liability can be reasonably estimated. A conditional ARO is defined as an unconditional legal obligation to perform an asset retirement activity in which the timing and/or method of settlement are conditional on a future event that may or may not be within the control of the entity. AROs have not been recognized for certain assets because the fair value cannot be reasonably estimated since the settlement dates of the obligations are indeterminate. Such obligations will be recognized in the period when sufficient information becomes available to estimate a range of potential settlement dates. Investment in Unconsolidated Affiliates – Equity investments in which MPLX exercises significant influence, but does not control and is not the primary beneficiary, are accounted for using the equity method and are reported in “ Equity method investments ” on the accompanying Consolidated Balance Sheets. This includes entities in which we hold majority ownership but the minority shareholders have substantive participating rights. Differences in the basis of the investments and the separate net asset values of the investees, if any, are amortized into net income over the remaining useful lives of the underlying assets and liabilities, except for the excess related to goodwill. MPLX believes the equity method is an appropriate means for it to recognize increases or decreases measured by GAAP in the economic resources underlying the investments. Regular evaluation of these investments is appropriate to evaluate any potential need for impairment. MPLX uses evidence of a loss in value to identify if an investment has an other than a temporary decline. During the fourth quarter of 2019, two of the joint ventures in which we have an interest recorded impairments, which impacted the amount of income from equity method investments during the period by approximately $28 million . For one of the joint ventures, we also had a basis difference which was being amortized over the life of the underlying assets. As a result of the impairment recorded by the joint venture, we also assessed this basis difference for impairment and recorded approximately $14 million of impairment during the quarter related to this investment, which was recorded through “Income from equity method investments”. This impairment was largely due to a reduction in forecasted volumes of the joint venture related to the loss of one of its customers. Deferred Financing Costs – Deferred financing costs are an asset for credit facility costs and netted against debt for senior notes. These costs are amortized over the contractual term of the related obligations using the effective interest method or, in certain circumstances, accelerated if the obligation is refinanced. Derivative Instruments – MPLX may use commodity derivatives to economically hedge a portion of its exposure to commodity price risk. All derivative instruments (including derivatives embedded in other contracts) are recorded at fair value. Certain commodity derivatives are reflected on the consolidated balance sheets on a net basis by counterparty as they are governed by master netting arrangements. MPLX discloses the fair value of all derivative instruments under the captions “ Other noncurrent assets ,” “ Other current liabilities ” and “ Deferred credits and other liabilities ” on the Consolidated Balance Sheets. Changes in the fair value of derivative instruments are reported on the Consolidated Statements of Income in accounts related to the item whose value or cash flows are being managed. All derivative instruments are marked to market through “ Product sales ,” “ Purchased product costs ,” or “Cost of revenues” on the Consolidated Statements of Income. Revenue gains and losses relate to contracts utilized to manage the cash flow for the sale of a product, typically NGLs. Purchased product costs gains and losses relate to contracts utilized to manage the cost of natural gas purchases, typically related to keep-whole arrangements. Cost of revenues gains and losses relate to a contract utilized to manage electricity costs. Changes in risk management for unrealized activities are reported as an adjustment to net income in computing cash flow from operating activities on the accompanying Consolidated Statements of Cash Flows. During the years ended December 31, 2019 , 2018 and 2017 , MPLX did not elect hedge accounting for any derivatives. MPLX has elected the normal purchases and normal sales designation for certain contracts related to the physical purchase of electric power and the sale of some commodities. Fair Value of Financial Instruments – Management believes the carrying amount of financial instruments, including cash and cash equivalents, receivables, receivables from related parties, other current assets, accounts payable, accounts payable to related parties and accrued liabilities approximate fair value because of the short-term maturity of these instruments. The recorded value of the amounts outstanding under the bank revolving credit facility, if any, approximate fair value due to the variable interest rate that approximates current market rates (see Note 15 ). Derivative instruments are recorded at fair value, based on available market information (see Note 16 ). Fair Value Measurement – Financial assets and liabilities recorded at fair value in the Consolidated Balance Sheets are categorized based upon the fair value hierarchy established by GAAP, which classifies the inputs used to measure fair value into Level 1, Level 2 or Level 3. A financial instrument’s categorization within the valuation hierarchy is based upon the lowest level of input that is significant to the fair value measurement. The methods and assumptions utilized may produce a fair value that may not be realized in future periods upon settlement. Furthermore, while MPLX believes its valuation methods are appropriate and consistent with other market participants, the use of different methodologies or assumptions to determine the fair value of certain financial instruments could result in a different estimate of fair value at the reporting date. For further discussion see Note 15 . Equity-Based Compensation Arrangements – MPLX issues phantom units under its share-based compensation plan as described further in Note 21 . A phantom unit entitles the grantee a right to receive a common unit upon the issuance of the phantom unit. The fair value of phantom unit awards granted to employees and non-employee directors is based on the fair market value of MPLX LP common units on the date of grant. The fair value of the units awarded is amortized into earnings using a straight-line amortization schedule over the period of service corresponding with the vesting period. For phantom units that vest immediately and are not forfeitable, equity-based compensation expense is recognized at the time of grant. Performance units paying out in cash are accounted for as liability awards and recorded at fair value with a mark-to-market adjustment made each quarter. The performance units paying out in units are accounted for as equity awards and use a Monte Carlo valuation model to calculate a grant date fair value. To satisfy common unit awards, MPLX may issue new common units, acquire common units in the open market or use common units already owned by the general partner. Tax Effects of Share-Based Compensation – MPLX elected to adopt the simplified method to establish the beginning balance of the additional paid-in capital pool (“APIC Pool”) related to the tax effects of employee share-based compensation and to determine the subsequent impact on the APIC Pool and Consolidated Statements of Cash Flows of the tax effects of share-based compensation awards that were outstanding upon adoption. Additional paid-in capital is reported as “Common unitholders - public ” on the accompanying Consolidated Balance Sheets. Income Taxes – MPLX is not a taxable entity for United States federal income tax purposes or for the majority of the states that impose an income tax. Taxes on MPLX’s net income generally are borne by its partners through the allocation of taxable income. MPLX’s taxable income or loss, which may vary substantially from the net income or loss reported on the Consolidated Statements of Income, is includable in the federal income tax returns of each partner. MPLX and certain legal entities are, however, taxable entities under certain state jurisdictions. MPLX accounts for income taxes under the asset and liability method. Deferred income taxes are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax basis, capital loss carryforwards and net operating loss and credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates applied to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect of any tax rate change on deferred taxes is recognized as tax expense/(benefit) from continuing operations in the period that includes the enactment date of the tax rate change. Realizability of deferred tax assets is assessed and, if not more likely than not, a valuation allowance is recorded to reflect the deferred tax assets at net realizable value as determined by management. All deferred tax balances are classified as long-term in the accompanying Consolidated Balance Sheets. All changes in the tax bases of assets and liabilities are allocated among operations and items charged or credited directly to equity. Distributions – In preparing the Consolidated Statements of Equity, net income attributable to MPLX LP is allocated to Series A and Series B preferred unitholders based on a fixed distribution schedule, as discussed in Notes 8 and 9 , and subsequently allocated to the general partner and limited partner unitholders. Distributions, although earned, are not accrued as a liability until declared. However, when distributions related to the eliminated IDRs were made, earnings equal to the amount of those distributions were first allocated to the general partner before the remaining earnings are allocated to the limited partner unitholders based on their respective ownership percentages. The allocation of net income attributable to MPLX LP for purposes of calculating net income per limited partner unit is described in below. Net Income Per Limited Partner Unit – MPLX uses the two-class method when calculating the net income per unit applicable to limited partners, because there is more than one class of participating security. The classes of participating securities include common units, general partner units, Series A and Series B preferred units, certain equity-based compensation awards and eliminated IDRs. Class B units were considered to be a separate class of common units that did not participate in distributions. Net income attributable to MPLX LP is allocated to the unitholders differently for preparation of the Consolidated Statements of Equity and the calculation of net income per limited partner unit. In preparing the Consolidated Statements of Equity, net income attributable to MPLX LP is allocated to Series A and Series B preferred unitholders based on a fixed distribution schedule and subsequently allocated to remaining unitholders in accordance with their respective ownership percentages. However, prior to 2018 when distributions related to the eliminated IDRs were made, earnings equal to the amount of those distributions are first allocated to the general partner before the remaining earnings are allocated to the unitholders, except Class B unitholders, based on their respective ownership percentages. Subsequent to the conversion of the general partner to a non-economic interest as described in Note 8 , no earnings are allocated to the general partner. Distributions, although earned, are not accrued until declared. The allocation of net income attributable to MPLX LP for purposes of calculating net income per limited partner unit is described in Note 7 . In preparing net income per limited partner units, during periods in which a net loss attributable to MPLX is reported or periods in which the total distributions exceed the reported net income attributable to MPLX’s unitholders, the amount allocable to certain equity-based compensation awards is based on actual distributions to the equity-based compensation awards. Diluted earnings per unit is calculated by dividing net income attributable to MPLX’s common unitholders, after deducting amounts allocable to other participating securities, by the weighted average number of common units and potential common units outstanding during the period. Potential common units are excluded from the calculation of diluted earnings per unit during periods in which net income attributable to MPLX’s unitholders, after deducting amounts that are allocable to the outstanding equity-based compensation awards, preferred units, and eliminated IDRs, is a loss as the impact would be anti-dilutive. Business Combinations – MPLX recognizes and measures the assets acquired and liabilities assumed in a business combination based on their estimated fair values at the acquisition date, with any remaining difference recorded as goodwill or gain from a bargain purchase. Depending on the nature of the transaction, management may engage an independent valuation specialist to assist with the determination of fair value of the assets acquired, liabilities assumed, noncontrolling interests, if any, and goodwill, based on recognized business valuation methodologies. If the initial accounting for the business combination is incomplete by the end of the reporting period in which the acquisition occurs, an estimate will be recorded. Subsequent to the acquisition, and not later than one year from the acquisition date, MPLX will record any material adjustments to the initial estimate based on new information obtained that would have existed as of the acquisition date. An adjustment that arises from information obtained that did not exist as of the date of the acquisition will be recorded in the period of the adjustment. An income, market or cost valuation method may be utilized to estimate the fair value of the assets acquired, liabilities assumed, and noncontrolling interests, if any, in a business combination. The income valuation method represents the present value of future cash flows over the life of the asset using: (i) discrete financial forecasts, which rely on management’s estimates of volumes, NGL prices, revenue and operating expenses; (ii) long-term growth rates; and (iii) appropriate discount rates. The market valuation method uses prices paid for a reasonably similar asset by other purchasers in the market, with adjustments relating to any differences between the assets. The cost valuation method is based on the replacement cost of a comparable

Accounting Standards

Accounting Standards	12 Months Ended
	Dec. 31, 2019
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Accounting Standards	Accounting Standards Recently Adopted ASU 2016-02, Leases We adopted ASU No. 2016-02, Leases (Topic 842), as of January 1, 2019, electing the transition method, which permits entities to adopt the provisions of the standard using the modified retrospective approach without adjusting comparative periods. We also elected the package of practical expedients permitted under the transition guidance within the new standard, which among other things, allowed us to grandfather the historical accounting conclusions until a reassessment event is present. We have also elected the practical expedient to not recognize short-term leases on the balance sheet, the practical expedient related to right of way permits and land easements which allows us to carry forward our accounting treatment for those existing agreements, and the practical expedient to combine lease and non-lease components for the majority of our underlying classes of assets except for our third-party contractor service and equipment agreements and boat and barge equipment agreements in which we are the lessee. We did not elect the practical expedient to combine lease and non-lease components for arrangements in which we are the lessor. In instances where the practical expedient was not elected, lease and non-lease consideration is allocated based on relative standalone selling price. Right of use (“ROU”) assets represent our right to use an underlying asset in which we obtain substantially all of the economic benefits and the right to direct the use of the asset during the lease term. Lease liabilities represent our obligation to make lease payments arising from the lease. Operating lease ROU assets and lease liabilities are recognized at the commencement date based on the present value of lease payments over the lease term. We recognize ROU assets and lease liabilities on the balance sheet for leases with a lease term of greater than one year. Payments that are not fixed at the commencement of the lease are considered variable and are excluded from the ROU asset and lease liability calculations. In the measurement of our ROU assets and lease liabilities, the fixed lease payments in the agreement are discounted using a secured incremental borrowing rate for a term similar to the duration of the lease, as our leases do not provide implicit rates. Operating lease expense is recognized on a straight-line basis over the lease term. Adoption of the new standard resulted in the recording of ROU assets and lease liabilities of approximately $629 million and $629 million , respectively, as of January 1, 2019. This is inclusive of ROU assets and lease liabilities related to ANDX of $124 million and $127 million , respectively. The standard did not materially impact our consolidated statements of income, cash flows or equity as a result of adoption. As a lessor under ASC 842, MPLX may be required to re-classify existing operating leases to sales-type leases upon modification and related reassessment of the leases. See Note 22 for further information regarding our ongoing evaluation of the impacts of lease reassessments as modifications occur. ASU 2017-04, Intangibles - Goodwill and Other - Simplifying the Test for Goodwill Impairment In connection with our annual goodwill impairment test, we adopted ASU 2017-04 prospectively during the fourth quarter of 2019. Under ASU 2017-04, 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 former 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. During the fourth quarter of 2019, we recorded certain goodwill impairment charges as described in Note 14 . We also adopted the following standard during 2019 , which did not have a material impact to our financial statements or financial statement disclosures: ASU Effective Date 2017-12 Derivatives and Hedging - Targeted Improvements to Accounting for Hedging Activities January 1, 2019

Acquisitions

Acquisitions	12 Months Ended
	Dec. 31, 2019
Business Combinations [Abstract]
Acquisitions	Acquisitions Acquisition of Andeavor Logistics LP On May 7, 2019, ANDX, Tesoro Logistics GP, LLC, then the general partner of ANDX (“TLGP”), MPLX, MPLX GP LLC, the general partner of MPLX (“MPLX GP”), and MPLX MAX LLC, a wholly-owned subsidiary of MPLX (“Merger Sub”), entered into an Agreement and Plan of Merger (the “Merger Agreement”) that provided for, among other things, the merger of Merger Sub with and into ANDX. On July 30, 2019, the Merger was completed, and ANDX survived the Merger as a wholly-owned subsidiary of MPLX. At the effective time of the Merger, each common unit held by ANDX’s public unitholders was converted into the right to receive 1.135 MPLX common units. ANDX common units held by certain affiliates of MPC were converted into the right to receive 1.0328 MPLX common units. See Note 8 for information on common units issued in connection with the Merger as well as Series B preferred units. Additionally, as a result of the Merger, each ANDX TexNew Mex Unit issued and outstanding immediately prior to the effective time of the Merger was converted into a right for Western Refining Southwest, Inc. (“Southwest, Inc.”), a wholly-owned subsidiary of MPC, as the holder of all such units, to receive a unit representing a substantially equivalent limited partner interest in MPLX (the “MPLX TexNew Mex Units”). By virtue of the conversion, all ANDX TexNew Mex Units were cancelled and ceased to exist as of the effective time of the Merger. The MPLX TexNew Mex Units are a new class of units in MPLX substantially equivalent to the ANDX TexNew Mex Units, including substantially equivalent rights, powers, duties and obligations that the ANDX TexNew Mex Units had immediately prior to the closing of the Merger. As a result of the Merger, the ANDX Special Limited Partner Interest outstanding immediately prior to the effective time of the Merger was converted into a right for Southwest Inc., as the holder of all such interest, to receive a substantially equivalent special limited partner interest in MPLX (the “MPLX Special Limited Partner Interest”). By virtue of the conversion, the ANDX Special Limited Partner Interest was cancelled and ceased to exist as of the effective time of the Merger. For information on ANDX’s preferred units, please see Note 8 . The assets of ANDX consist of a network of owned and operated crude oil, refined product and natural gas pipelines; crude oil and water gathering systems; refining logistics assets; terminals with crude oil and refined products storage capacity; rail facilities; marine terminals including storage; bulk petroleum distribution facilities; a trucking fleet; and natural gas processing and fractionation complexes. The assets are located in the western and inland regions of the United States and complement MPLX’s existing business and assets. MPC accounted for its October 1, 2018 acquisition of Andeavor (including acquiring control of ANDX), using the acquisition method of accounting, which required Andeavor assets and liabilities to be recorded by MPC at the acquisition date fair value. The Merger was closed on July 30, 2019, and the results of ANDX have been incorporated into the results of MPLX as of October 1, 2018, which is the date that common control was established. As a result of MPC’s relationship with both MPLX and ANDX, the Merger has been treated as a common control transaction, which requires the recasting of MPLX’s historical results and the recognition of assets acquired and liabilities assumed using MPC’s historical carrying value. The fair value of assets acquired and liabilities assumed shown below represents MPC’s historical carrying values as of October 1, 2018. (In millions) As Originally Reported Adjustments (1) As Adjusted Cash and cash equivalents $ 83 $ (53 ) $ 30 Receivables, net 241 259 500 Inventories 21 — 21 Other current assets (2) 59 (7 ) 52 Equity method investments 731 (89 ) 642 Property, plant and equipment, net 6,709 (427 ) 6,282 Intangibles, net (3) 960 74 1,034 Other noncurrent assets (4) 31 (8 ) 23 Total assets acquired 8,835 (251 ) 8,584 Accounts payable 198 265 463 Other current liabilities (5) 188 (41 ) 147 Long-term debt 4,916 — 4,916 Deferred credits and other long-term liabilities (6) 75 1 76 Total liabilities assumed 5,377 225 5,602 Net assets acquired excluding goodwill 3,458 (476 ) 2,982 Goodwill 7,428 724 8,152 Total purchase price $ 10,886 $ 248 $ 11,134 (1) Inclusive of activity recorded subsequent to the acquisition of ANDX on July 30, 2019, a portion of which was recorded as a non-cash contribution from MPC. (2) Includes both related party and third party other current assets. (3) Includes approximately $4 million of favorable lease assets. In connection with the implementation of ASC 842, this balance was reclassed to “Right of use assets” on the Consolidated Balance Sheets during 2019. (4) Includes both related party and third party other noncurrent assets as well as right of use assets associated with leases. (5) Includes accrued liabilities, operating lease liabilities, long-term debt due within one year, as well as related party and third party other current liabilities. (6) Includes deferred revenue and deferred income taxes, as well as related party and third party other noncurrent liabilities. Details of our valuation methodology and significant inputs for fair value measurements are included by asset class below. The fair value measurements for equity method investments; property, plant and equipment; intangible assets and long-term debt are based on significant inputs that are not observable in the market and, therefore, represent Level 3 measurements. Goodwill The purchase consideration allocation resulted in the recognition of $ 8.2 billion in goodwill, which has been allocated between the L&S segment and the G&P segment at $7.2 billion and $ 1.0 billion , respectively. See Note 14 for further information related to goodwill. Inventory The fair value of inventory was recorded at cost as of October 1, 2018, as these items are related to spare parts as well as materials and supplies and approximate fair value. Equity Method Investments The fair value of the equity method investments was $642 million , which was determined based on applying income and market approaches. The income approach relied on the discounted cash flow method and the market approach relied on a market multiple approach considering historical and projected financial results. Discount rates for the discounted cash flow models were based on capital structures for similar market participants and included various risk premiums that account for risks associated with the specific investments. Property, Plant and Equipment The fair value of property, plant and equipment was $6.3 billion , which was based primarily on the cost approach. Key assumptions in the cost approach include determining the replacement cost by evaluating recent purchases of similar assets or published data, and adjusting replacement cost for economic and functional obsolescence, location, normal useful lives, and capacity (if applicable). Acquired Intangible Assets The fair value of the acquired identifiable intangible assets was $1.0 billion , which represents the value of various customer contracts and relationships and other intangible assets. The fair value of customer contracts and relationships was $950 million , which was valued by applying the multi-period excess earnings method, which is an income approach. Key assumptions in the income approach include the underlying contract cash flow estimates, remaining contract term, probability of renewal, growth rates and discount rates. The intangible assets are all finite lived and will be amortized over two to 10 years. Debt The fair value of the ANDX notes was measured using a market approach, based upon the average of quotes for the acquired debt from major financial institutions and a third-party valuation service. Additionally, approximately $1.1 billion of borrowings under revolving credit agreements approximated fair value. The ANDX revolving credit facilities with total capacity of $2.1 billion were terminated upon closing of the Merger and were repaid with borrowings under the MPLX revolving credit facility. Acquisition Costs We recognized $14 million in acquisition costs during 2019, which are reflected in general and administrative expenses. ANDX Revenue and Net Income For the year ended December 31, 2019 , we recognized $2,400 million of revenues and other income related to ANDX and $266 million of net loss related to ANDX, which was impacted by the goodwill impairment discussed in Note 14 . For the year ended December 31, 2018 , we recognized $580 million of revenues and other income related to ANDX and $172 million of net income related to ANDX. Pro Forma Financial Information The following unaudited pro forma information combines the historical operations of MPLX and ANDX, giving effect to the Merger as if it had been consummated on January 1, 2018, the beginning of the earliest period presented. (In millions) 2019 2018 Total revenues and other income $ 9,041 $ 8,666 Net income attributable to MPLX LP $ 1,434 $ 2,446 The pro forma information includes adjustments to align accounting policies, which include adjustments for capitalization of assets and treatment of planned major maintenance costs. The pro forma information also includes adjustments related to: eliminating transactions between MPLX and ANDX, which previously would have been recorded as transactions between related parties; basis differences on equity method investments as a result of recognition of MPC’s investments in ANDX’s equity method investments; depreciation and amortization expense to reflect the increased fair value of property, plant and equipment and increased amortization expense related to identifiable intangible assets, as well as adjustments to interest expense for the amortization of fair value adjustments over the remaining term of ANDX’s outstanding debt, reversal of ANDX’s historical amortization of debt issuance costs and debt discounts and to adjust for the difference in the weighted average interest rate between MPLX’s revolving credit facility and ANDX’s revolving credit facilities. The following table presents MPLX’s previously reported Consolidated Balance Sheet Data as of December 31, 2018 retrospectively adjusted for the Merger: December 31, 2018 (In millions) MPLX LP (Previously Reported) Predecessor MPLX LP (Currently Reported) Assets Current assets: Cash and cash equivalents $ 68 $ 9 $ 77 Receivables, net 417 194 611 Current assets - related parties 290 266 556 Inventories 77 21 98 Other current assets 45 53 98 Total current assets 897 543 1,440 Equity method investments 4,174 727 4,901 Property, plant and equipment, net 14,639 6,886 21,525 Intangibles, net 424 935 1,359 Goodwill 2,586 7,430 10,016 Noncurrent assets - related parties 24 — 24 Other noncurrent assets 35 25 60 Total assets 22,779 16,546 39,325 Liabilities Current liabilities: Accounts payable 162 104 266 Accrued liabilities 250 22 272 Current liabilities - related parties 254 248 502 Accrued property, plant and equipment 294 105 399 Accrued interest payable 143 41 184 Other current liabilities 83 562 645 Total current liabilities 1,186 1,082 2,268 Long-term deferred revenue 80 52 132 Long-term liabilities - related parties 43 3 46 Long-term debt 13,392 4,530 17,922 Deferred income taxes 13 1 14 Deferred credits and other liabilities 197 11 208 Total liabilities 14,911 5,679 20,590 Commitments and contingencies (see Note 20) Series A preferred units 1,004 — 1,004 Equity Common unitholders - public 8,336 — 8,336 Common unitholder - MPC (1,612 ) — (1,612 ) Equity of Predecessor — 10,867 10,867 Accumulated other comprehensive loss (16 ) — (16 ) Total MPLX LP partners’ capital 6,708 10,867 17,575 Noncontrolling interests 156 — 156 Total equity 6,864 10,867 17,731 Total liabilities, preferred units and equity $ 22,779 $ 16,546 $ 39,325 Mt. Airy Terminal On September 26, 2018, MPLX acquired an eastern U.S. Gulf Coast export terminal (the “Mt. Airy Terminal”) from Pin Oak Holdings, LLC for total consideration of $451 million . At the time of the acquisition, the terminal included tanks with 4 million barrels of third-party leased storage capacity and a dock with 120 mbpd of capacity. The Mt. Airy Terminal is located on the Mississippi River between New Orleans and Baton Rouge, is in close proximity to several Gulf Coast refineries including MPC’s Garyville Refinery and is near numerous rail lines and pipelines. The Mt. Airy Terminal is accounted for within the L&S segment. In the first quarter of 2019, an adjustment to the initial purchase price was made for approximately $5 million related to the final settlement of the acquisition, which was paid in the first six months of 2019 as shown on the statement of cash flow. This reduced the total purchase price to $446 million and resulted in $336 million of property, plant and equipment, $121 million of goodwill and the remainder being attributable to net liabilities assumed. Based on the fair value estimates of assets acquired and liabilities assumed at the acquisition date, the purchase price was allocated as follows: (In millions) Balance as of September 26, 2018 Receivables, net $ 3 Other current assets 1 Property, plant and equipment, net 336 Intangibles, net 9 Goodwill 121 Accounts payable (17 ) Other current liabilities (7 ) Net assets acquired $ 446 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 export vessels and inland barges, the proximity of the terminal to MPC’s Garyville refinery and other refineries in the region as well as the opportunity to construct an additional dock at the site. The amount of revenue and income from operations associated with the acquisition of the Mt. Airy Terminal included on the Consolidated Statement of Income since the September 26, 2018 acquisition date was not material to the financial statements. Assuming the acquisition had occurred on January 1, 2017, the consolidated pro forma results would not have been materially different from the reported results. Refining Logistics and Fuels Distribution Acquisition On February 1, 2018 , MPC and MPLX LP closed on an agreement for the dropdown of refining logistics assets and fuels distribution services to MPLX LP. MPC contributed these assets and services in exchange for $4.1 billion in cash and a fixed number of MPLX LP common units and general partner units of 111,611,111 and 2,277,778 , respectively. The fair value of the common and general partner units issued as of the acquisition date was $4.3 billion based on the closing common unit price as of February 1, 2018 , as recorded on the Consolidated Statements of Equity, for a total purchase price of $8.4 billion . The equity issued consisted of: (i) 85,610,278 common units to MPLX GP LLC (“MPLX GP”), (ii) 18,176,666 common units to MPLX Logistics Holdings LLC (“MPLX Logistics”) and (iii) 7,824,167 common units to MPLX Holdings Inc. (“MPLX Holdings”). MPLX also issued 2,277,778 general partner units to MPLX GP in order to maintain its two percent general partner interest (“GP Interest”) in MPLX. MPC agreed to waive approximately one-third of the first quarter 2018 distributions on the common units issued in connection with this transaction. As a result of this waiver, MPC did not receive $23.7 million of the distributions that would have otherwise accrued on such common units with respect to the first quarter 2018. Immediately following this transaction, the GP Interest was converted into a non-economic general partner interest as discussed in Note 8 . MPLX recorded this transaction on a historical basis as required for transactions between entities under common control. No effect was given to the prior periods as these entities were not considered businesses prior to the February 1, 2018 dropdown. In connection with the dropdown, approximately $830 million of net property, plant and equipment was recorded in addition to $85 million and $130 million of goodwill allocated to MPLX Refining Logistics LLC (“Refining Logistics”) and MPLX Fuels Distribution LLC (“Fuels Distribution”), respectively. Both the Refining Logistics assets and the Fuels Distribution services are accounted for within the L&S segment. As of the transaction date, the Refining Logistics assets included 619 tanks with approximately 56 million barrels of storage capacity (crude, finished products and intermediates), 32 rail and truck racks, 18 docks, and gasoline blenders. These assets generate revenue through storage services agreements with MPC. Refining Logistics provides certain services to MPC related to the receipt, storage, throughput, custody and delivery of petroleum products in and through certain storage and logistical facilities and assets associated with MPC’s refineries. Fuels Distribution, which is a wholly owned subsidiary of MPLXT, generates revenue through a Fuels Distribution Services Agreement with MPC. Fuels Distribution is structured to provide a broad range of scheduling and marketing services as MPC’s agent. The amounts of revenue and income from operations associated with these investments included on the Consolidated Statements of Income, since the February 1, 2018 acquisition date, were as follows: (In millions) Twelve Months Ended Revenues and other income $ 1,359 Income from operations $ 874 Joint-Interest Acquisition On September 1, 2017 , MPLX entered into a Membership Interests and Shares Contributions Agreement with MPLX GP, MPLX Logistics, MPLX Holdings and MPC Investment LLC (“MPC Investment”), each a wholly-owned subsidiary of MPC, whereby MPLX agreed to acquire certain ownership interests in joint venture entities indirectly held by MPC. Pursuant to the agreement, MPC Investment agreed to contribute: all of the membership interests of Lincoln Pipeline LLC, which holds a 35 percent interest in Illinois Extension; all of the membership interests of MPL Louisiana Holdings LLC, which holds a 41 percent interest in LOOP; a 59 percent interest in LOCAP; and a 25 percent interest in Explorer, through a series of intercompany contributions to MPLX for an agreed upon purchase price of approximately $420 million in cash and equity consideration valued at approximately $630 million , for total consideration of $1.05 billion (collectively, the “Joint-Interest Acquisition”). The number of common units representing the equity consideration was then determined by dividing the contribution amount by the simple average of the ten-day trailing volume weighted average NYSE price of a common unit for the ten trading days ending at market close on August 31, 2017. The fair value of the common and general partner units issued was approximately $653 million based on the closing common unit price as of September 1, 2017, as recorded on the Consolidated Statements of Equity, for a total purchase price of $1.07 billion . The equity issued consisted of: (i) 13,719,017 common units to MPLX GP; (ii) 3,350,893 common units to MPLX Logistics and (iii) 1,441,224 common units to MPLX Holdings. MPLX also issued 377,778 general partner units to MPLX GP in order to maintain its two percent GP Interest in MPLX. Illinois Extension operates the 168 -mile, 24 -inch diameter Southern Access Extension crude oil pipeline from Flanagan, Illinois to Patoka, Illinois, as well as additional tankage and two pump stations. LOOP owns and operates midstream crude oil infrastructure, including a deep-water oil port offshore of Louisiana, pipelines and onshore storage facilities. LOOP also manages the operations of LOCAP, an affiliate pipeline system. LOCAP owns and operates a crude oil pipeline and tank facility in St. James, Louisiana, that distributes oil received from LOOP’s storage facilities and other connecting pipelines to nearby refineries and into the Mid-Continent region of the United States. Explorer owns and operates an approximate 1,830 - mile common carrier pipeline that primarily transports gasoline, diesel, diluent and jet fuel from the Gulf Coast region to the Midwest United States. MPLX accounts for the Joint-Interest Acquisition entities as equity method investments within its L&S segment. As a transfer between entities under common control, MPLX recorded the Joint-Interest Acquisition on its Consolidated Balance Sheets at MPC’s historical basis, which included accumulated other comprehensive loss. MPLX recognizes an “Accumulated other comprehensive loss” on its Consolidated Balance Sheets relating to pension and other post-retirement benefits provided by the LOOP and Explorer joint-interests to their employees. MPLX is not a sponsor of these benefit plans. Distributions of cash received from the entities and interests acquired in the Joint-Interest Acquisition related to periods prior to the acquisition were prorated on a daily basis with MPLX retaining the portion of distributions beginning on the closing date. All amounts distributed to MPLX related to periods before the acquisition have been paid to MPC. Additionally, MPLX agreed to pay MPC for any distributions of cash from LOOP related to the sale of LOOP’s excess crude oil inventory. Because the future distributions or payments could not be reasonably quantified, a liability was not recorded in connection with the acquisition. MPLX subsequently received distributions related to the time period prior to the acquisition, which it remitted to MPC and recorded a corresponding decrease to the general partner’s equity for $32 million . MPLX accounts for the interests acquired in the Joint-Interest Acquisition one month in arrears, which is the most recently available information. The amount of income associated with these investments included on the Consolidated Statements of Income under the caption “ Income from equity method investments ” for the twelve months ended December 31, 2019 , December 31, 2018 and December 31, 2017 totaled $110 million , $118 million and $21 million , respectively. MPC agreed to waive approximately two-thirds of the third quarter 2017 distributions on the common units issued in connection with the Joint-Interest Acquisition. As a result of this waiver, MPC did not receive approximately two-thirds of the distributions or IDRs that would have otherwise accrued on such common units with respect to the third quarter 2017 distributions. The value of these waived distributions was $10 million . Acquisition of Hardin Street Transportation LLC, Woodhaven Cavern LLC and MPLX Terminals LLC MPC contributed the assets of HST, WHC and MPLXT to newly created and wholly-owned subsidiaries and entered into commercial agreements related to services provided by these new entities to MPC on January 1, 2015 for HST and WHC and April 1, 2016 for MPLXT. Pursuant to a Membership Interests Contributions Agreement entered into on March 1, 2017 by MPLX with MPLX GP, MPLX Logistics, MPLX Holdings and MPC Investment (each a wholly-owned subsidiary of MPC), MPC Investment agreed to contribute the outstanding membership interests in HST, WHC and MPLXT through a series of intercompany contributions to MPLX for approximately $1.5 billion in cash and equity consideration valued at approximately $504 million . The number of common units representing the equity consideration was determined by dividing the contribution amount by the simple average of the ten-day trailing volume weighted average NYSE price of a common unit for the ten trading days ending at market close on February 28, 2017. The fair value of the common and general partner units issued was approximately $503 million , and consisted of (i) 9,197,900 common units to MPLX GP, (ii) 2,630,427 common units to MPLX Logistics and (iii) 1,132,049 common units to MPLX Holdings. MPLX also issued 264,497 general partner units to MPLX GP in order to maintain its two percent GP Interest in MPLX. MPC agreed to waive two-thirds of the first quarter 2017 distributions on the common units issued in connection with the Transaction. As a result of this waiver, MPC did not receive two-thirds of the general partner distributions or IDRs that would have otherwise accrued on such common units with respect to the first quarter 2017 distributions. The value of these waived distributions was $6 million . HST owns and operates various private crude oil and refined product pipeline systems and associated storage tanks. As of the acquisition date, these pipeline systems consisted of 174 miles of crude oil pipelines and 430 miles of refined products pipelines. WHC owns and operates eight butane and propane storage caverns located in Michigan with approximately 1.8 million barrels of NGL storage capacity. As of the acquisition date, MPLXT owned and operated 59 terminals for the receipt, storage, blending, additization, handling and redelivery of refined petroleum products. Additionally, MPLXT operated one leased terminal and had partial ownership interest in two terminals. Collectively, these 62 terminals have a combined shell capacity of approximately 23.6 million barrels. The terminal facilities are located primarily in the Midwest, Gulf Coast and Southeast regions of the United States. MPLX accounts for these businesses within its L&S segment. MPLX retrospectively adjusted the historical financial results for all periods to give effect to the acquisition of HST and WHC effective January 1, 2015, and the acquisition of MPLXT effective April 1, 2016, as required for transactions between entities under common control. Prior to these dates, these entities were not considered businesses and, therefore, there are no financial results from which to recast. 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 final fair value estimates of assets acquired and liabilities assumed at the acquisition date, the purchase price was primarily allocated to property, plant and equipment. The Ozark pipeline is a 433 -mile, 22 -inch crude oil pipeline originating in Cushing, Oklahoma, and terminating in Wood River, Illinois, capable of transporting approximately 230 mbpd. MPLX accounts for the Ozark pipeline within its L&S segment. The amounts of revenue and income from operations associated with the acquisition included on the Consolidated Statements of Income, since the March 1, 2017 acquisition date are as follows: (In millions) Twelve Months Ended December 31, 2017 Revenues and other income $ 64 Income from operations $ 20 Assuming the acquisition of the Ozark pipeline had occurred on January 1, 2017, the consolidated pro forma results would not have been materially different from reported results. MarEn Bakken On February 15, 2017, MPLX closed on a joint venture, MarEn Bakken Company, LLC (“MarEn Bakken”), with Enbridge Energy Partners L.P. in which MPLX LP acquired a partial, indirect interest in the Dakota Access Pipeline and Energy Transfer Crude Oil Company Pipeline projects, collectively referred to as the Bakken Pipeline system, from Energy Transfer Partners, L.P. and Sunoco Logistics Partners, LP. 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 $2.0 billion purchase price paid by MarEn Bakken to acquire a 37 percent indirect interest in the Bakken Pipeline system. MPLX holds, through a subsidiary, a 25 percent interest in MarEn Bakken, which equates to an approximate 9 percent indirect interest in the Bakken Pipeline system. MPLX accounts for its investment in MarEn Bakken as an equity method investment and bases the equity method accounting for this joint venture one month in arrears which is the most recently available information. The amount of income or loss associated with these investments included on the Consolidated Statements of Income under the caption “ Income from equity method investments ” for the twelve months ended December 31, 2019 , December 31, 2018 and December 31, 2017 totaled $72 million , $48 million and $15 million , respectively. In connection with MPLX’s acquisition of a partial, indirect equity interest in the Bakken Pipeline system, MPC agreed to waive its right to receive incentive distributions of $1.6 million per quarter for twelve consecutive quarters, beginning with distributions declared in the first quarter of 2017 and paid to MPC in the second quarter of 2017, which was prorated to $0.8 million

Investments and Noncontrolling

Investments and Noncontrolling Interests	12 Months Ended
	Dec. 31, 2019
Equity Method Investments and Joint Ventures [Abstract]
Investments and Noncontrolling Interests	Investments and Noncontrolling Interests The following table presents MPLX’s equity method investments at the dates indicated: Ownership as of Carrying value at December 31, December 31, (In millions, except ownership percentages) 2019 2019 2018 L&S MarEn Bakken Company LLC 25% $ 481 $ 498 Illinois Extension Pipeline Company, L.L.C. 35% 265 275 LOOP LLC 41% 238 226 Andeavor Logistics Rio Pipeline LLC (1) 67% 202 181 Minnesota Pipe Line Company, LLC (1) 17% 190 197 Whistler Pipeline LLC 38% 134 — Wink to Webster Pipeline LLC 15% 126 — Explorer Pipeline Company 25% 83 90 Other (1) 55 51 Total L&S 1,774 1,518 G&P MarkWest Utica EMG, L.L.C. 56% 1,984 2,039 Sherwood Midstream LLC 50% 537 366 MarkWest EMG Jefferson Dry Gas Gathering Company, L.L.C. 67% 302 236 Rendezvous Gas Services, L.L.C. (1) 78% 170 248 Sherwood Midstream Holdings LLC 53% 157 157 Centrahoma Processing LLC 40% 153 160 Other (1) 198 177 Total G&P 3,501 3,383 Total $ 5,275 $ 4,901 (1) These investments as well as certain investments included within “Other” for both L&S and G&P are investments acquired as part of the Merger. The December 31, 2019 balance reflects all purchase accounting adjustments identified by MPC as part of its acquisition of Andeavor. As a result of the Merger, MPLX acquired an ownership interest in Rendezvous Gas Services, L.L.C. (“RGS”), Minnesota Pipe Line Company, LLC (“MNPL”) and Andeavor Logistics Rio Pipeline LLC (“ALRP”), among others. RGS and ALRP have been deemed to be VIEs; however, neither MPLX nor any of its subsidiaries have been deemed to be the primary beneficiary due to voting rights on significant matters. For all of the investments acquired through the Merger, we have the ability to exercise influence through participation in the management committees which make all significant decisions. However, since we have equal or proportionate influence over each committee as a joint interest partner and all significant decisions require the consent of the other investors without regard to economic interest, we have determined that these entities should not be consolidated and apply the equity method of accounting with respect to our investments in each entity. In addition to the investments acquired through the Merger, MarkWest Utica EMG, L.L.C. (“MarkWest Utica EMG”), Sherwood Midstream LLC (“Sherwood Midstream”), MarkWest EMG Jefferson Dry Gas Gathering Company, L.L.C. (“Jefferson Dry Gas”) and Sherwood Midstream Holdings LLC (“Sherwood Midstream Holdings”) are also deemed to be VIEs. However, consistent with the investments above, neither MPLX nor any of its subsidiaries are deemed to be the primary beneficiary due to voting rights on significant matters. Sherwood Midstream has been deemed the primary beneficiary of Sherwood Midstream Holdings due to its controlling financial interest through its authority to manage the joint venture. As a result, Sherwood Midstream consolidates Sherwood Midstream Holdings. Therefore, MPLX also reports its portion of Sherwood Midstream Holdings’ net assets as a component of its investment in Sherwood Midstream. As of December 31, 2019 , MPLX has a 23.7 percent indirect ownership interest in Sherwood Midstream Holdings through Sherwood Midstream. During 2019, MPLX acquired equity interests in Whistler Pipeline LLC and Wink to Webster Pipeline LLC. Both joint ventures are located in the Permian Basin and will transport crude oil or natural gas to the U.S. Gulf Coast. These investments are deemed to be VIEs; however, MPLX does not operate these joint ventures and is not deemed to be the primary beneficiary due to voting rights on significant matters as described above. MPLX’s maximum exposure to loss as a result of its involvement with equity method investments includes its equity investment, any additional capital contribution commitments and any operating expenses incurred by the subsidiary operator in excess of its compensation received for the performance of the operating services. MPLX did not provide any financial support to equity method investments that it was not contractually obligated to provide during the years ended December 31, 2019 , 2018 and 2017 . During the fourth quarter of 2019, two joint ventures in which we have an interest recorded impairments, which impacted the amount of income from equity method investments during the period by approximately $28 million and took the carrying value of one of the investments to zero. For the other joint venture, we had a basis difference recorded which was being amortized over the life of the underlying assets. As a result of the impairment recorded by the joint venture, we assessed our investment, including the related basis difference, for impairment and recorded an additional $14 million of impairment during the quarter related to our basis difference. The fair value of the investment was determined based upon applying the discounted cash flow method, which is an income approach. The discounted cash flow fair value estimate is based on known or knowable information at the interim measurement date. The significant assumptions that were used to develop the estimate of the fair value under the discounted cash flow method include management’s best estimates of the expected future results using a probability-weighted average set of cash flow forecasts and the discount rate. Fair value determinations require considerable judgment and are sensitive to changes in underlying assumptions and factors. As such, the fair value of these equity method investments represents a Level 3 measurement. As a result, there can be no assurance that the estimates and assumptions made for purposes of the impairment test will prove to be an accurate prediction of the future. The impairment of the basis difference was also recorded through “Income from equity method investments” for a total impact during the quarter of approximately $42 million . The impairments were largely due to a reduction in forecasted volumes of the joint ventures. Summarized financial information for MPLX’s equity method investments for the years ended December 31, 2019 , 2018 and 2017 is as follows: December 31, 2019 (1) (In millions) Other VIEs Non-VIEs Total Revenues and other income $ 650 $ 1,417 $ 2,067 Costs and expenses 375 568 943 Income from operations 275 849 1,124 Net income 215 752 967 Income from equity method investments (2) $ 103 $ 187 $ 290 December 31, 2018 (1) (In millions) Other VIEs Non-VIEs Total Revenues and other income $ 484 $ 1,421 $ 1,905 Costs and expenses 286 738 1,024 Income from operations 198 683 881 Net income 197 606 803 Income from equity method investments (2) $ 67 $ 180 $ 247 December 31, 2017 (1) (In millions) Other VIEs Non-VIEs Total Revenues and other income $ 273 $ 954 $ 1,227 Costs and expenses 139 520 659 Income from operations 134 434 568 Net income 133 345 478 Income from equity method investments (2) $ 30 $ 48 $ 78 (1) The financial information for equity method investments for 2019 includes financial information of equity method investments acquired as part of the Merger. The financial information for equity method investments for 2018 includes financial information of equity method investments acquired as part of the Merger for the last three months of 2018. The financial information for equity method investments for 2017 does not include financial information of equity method investments acquired as part of the Merger. See Note 1 for additional information. (2) “Income from equity method investments” includes the impact of any basis differential amortization or accretion. Summarized balance sheet information for MPLX’s equity method investments as of December 31, 2019 and 2018 is as follows: December 31, 2019 (In millions) Other VIEs Non-VIEs Total Current assets $ 534 $ 330 $ 864 Noncurrent assets 5,862 5,134 10,996 Current liabilities 192 245 437 Noncurrent liabilities $ 305 $ 822 $ 1,127 December 31, 2018 (In millions) Other VIEs Non-VIEs Total Current assets $ 252 $ 415 $ 667 Noncurrent assets 3,796 5,290 9,086 Current liabilities 158 280 438 Noncurrent liabilities $ 191 $ 845 $ 1,036 As of December 31, 2019 and 2018 , the carrying value of MPLX’s equity method investments in the G&P segment exceeded the underlying net assets of its investees by $ 1.0 billion and $1.3 billion , respectively. As of December 31, 2019 and 2018 , the carrying value of MPLX’s equity method investments in the L&S segment exceeded the underlying net assets of its investees by $329 million and $187 million , respectively. This basis difference is being amortized into net income over the remaining estimated useful lives of the underlying net assets, except for $ 498 million and $167 million of excess related to goodwill for the G&P and L&S segments, respectively, as of December 31, 2019 and $542 million and $167 million of excess related to goodwill for the G&P and L&S segments, respectively, as of December 31, 2018.

Related Party Agreements and Tr

Related Party Agreements and Transactions	12 Months Ended
	Dec. 31, 2019
Related Party Transactions [Abstract]
Related Party Agreements and Transactions	Related Party Agreements and Transactions MPLX engages in transactions with both MPC and certain of its equity method investments as part of its normal business; however, transactions with MPC make up the majority of MPLX’s related party transactions. Transactions with related parties are further described below. MPLX has various long-term, fee-based commercial agreements with MPC. Under these agreements, MPLX provides transportation, terminal, fuels distribution, marketing, storage, management, operational and other services to MPC. MPC has committed to provide MPLX with minimum quarterly throughput volumes on crude oil and refined products and other fees for storage capacity; operating and management fees; as well as reimbursements for certain direct and indirect costs. MPC has also committed to provide a fixed fee for 100 percent of available capacity for boats, barges and third-party chartered equipment under the marine transportation service agreement. In addition, MPLX has obligations to MPC for services provided to MPLX by MPC under omnibus and employee services type agreements as well as other various agreements as discussed below. The commercial agreements with MPC include: • MPLX has fuels distribution agreements with MPC under which MPC pays MPLX for marketing and selling MPC’s products. This can include MPC paying MPLX a tiered monthly fee based on the volume of products sold or thought margin support under a related product supply agreement. Agreements are subject to minimum volume commitments and are subject various terms and renewal periods. • MPLX has various pipeline transportation agreements under which MPC pays MPLX fees for transporting crude and refined products on MPLX’s pipeline systems. These agreements are subject to minimum throughput volumes under which MPC will pay MPLX deficiency payments for any period in which they do not ship the minimum committed volume. These deficiency payments can be applied as credits to future periods in which MPC ships volumes in excess of the minimum volume, subject to a limited period of time. These agreements are subject to various terms and renewal periods. • MPLX has a six-year marine transportation agreement under which MPC pays MPLX fees for providing marine transportation of crude oil, feedstock and refined petroleum products, and related services. • MPLX has various trucking transportation services agreements with terms ranging from month-to-month to 10 years , under which MPC pays MPLX fees for gathering barrels and providing trucking, dispatch, delivery and data services. Most of these agreements are subject to minimum volume commitments and have various terms regarding carry-forward of deficiency payments as credits towards excess volumes shipped in future periods. These agreements are subject to various terms and renewal periods. • MPLX has numerous storage services agreements governing storage services at various types of facilities including terminals, pipeline tank farms, caverns and refineries, under which MPC pays MPLX per-barrel fees for providing storage services. Some of these agreements provide MPC with exclusive access to storage at certain locations, such as storage located at MPC’s refineries or storage in certain caverns. Under these agreements, MPC pays MPLX a per-barrel fee for such storage capacity, regardless of whether MPC fully utilizes the available capacity. Many of the refinery storage agreements also contain provisions for logistical services to be provided by MPLX, for which MPC pays monthly fees. These agreements are subject to terms ranging from three to 17 years and are subject to various renewal periods. • MPLX has a 10-year terminal services agreement governing certain terminals under which MPC pays MPLX fees for terminal storage for refined petroleum products. Under this agreement MPC pays MPLX agreed upon fees relating to MPC product deliveries as well as any viscosity surcharges, loading, handling, transfers or other related charges. This agreement is subject to minimum volume throughput commitments under which MPC pays a deficiency payment for any period in which they do not meet the minimum committed volume. The terminal services agreement with MPC includes automatic renewal terms ranging from one to five years . MPLX also has numerous additional terminal services agreements governing terminals acquired through the Merger. Under these agreements, MPC pays MPLX agreed upon fees relating to various terminal activities including throughput, blending, on and offloading and additives. Many of these agreements contain various minimum commitments for some or all of these activities. Some of these agreements allow for deficiency payments to be applied as credits to future periods with excess throughput volumes. These agreements have terms ranging from one to 10 years with varying renewal terms. • MPLX has a year to year keep-whole commodity agreement with MPC under which MPC pays us a processing fee for NGL’s related to keep-whole agreements and delivers shrink gas to the producers on our behalf. We pay MPC a marketing fee in exchange for assuming the commodity risk. The pricing structure under this agreement provides for a base volume subject to a base rate and incremental volumes subject to variable rates which are calculated with reference to certain of our costs incurred as processor of the volumes. The pricing for both the base and incremental volumes are subject to revision each year. In many cases, agreements are location-based hybrid agreements, containing provisions relating to multiple of the types of agreements and services described above. Operating Agreements MPLX operates various pipelines owned by MPC under operating services agreements. Under these operating services agreements, MPLX receives an operating fee for operating the assets and is reimbursed for all direct and indirect costs associated with operating the assets. Most of these agreements are indexed for inflation. These agreements range from one to five years in length and automatically renew unless terminated by either party. Co-location Services Agreements MPLX is party to co-location services agreements with MPC’s refineries, under which MPC provides management, operational and other services to the subsidiaries of Refining Logistics. Refining Logistics pays MPC monthly fixed fees and direct reimbursements for such services calculated as set forth in the agreements. These agreements have initial terms of 50 years . Ground Lease Agreements MPLX is party to ground lease agreements with certain of MPC’s refineries under which MPLX is the lessor of certain sections of property which contain facilities owned by Refining Logistics and are within the premises of MPC’s refineries. Refining Logistics pays MPC monthly fixed fees under these ground leases. These agreements have initial terms of 50 years . Management Services Agreement MPLX, through its subsidiary, HSM, has a management services agreement with MPC under which it provides management services to assist MPC in the oversight and management of the marine business. HSM receives a fixed annual fee for providing the required management services. This fee is adjusted annually on the anniversary of the contract for inflation and any changes in the scope of the management services provided. This agreement is set to expire on January 1, 2021 and automatically renews for two additional renewal terms of 5 years each unless terminated by either party. Omnibus Agreements MPLX has omnibus agreements with MPC that address MPLX’s payment of fixed annual fees to MPC for the provision of executive management services by certain executive officers of the general partner and MPLX’s reimbursement of MPC for the provision of certain general and administrative services to it. They also provide for MPC’s indemnification to MPLX for certain matters, including environmental, title and tax matters; as well as our indemnification of MPC for certain matters under these agreements. Certain environmental indemnifications related to the Los Angeles Logistics Assets Acquisition are excluded from coverage under omnibus agreements and are instead covered by a Carson Assets Indemnity Agreement. Employee Services Agreements MPLX has various employee services agreements and secondment agreements with MPC under which MPLX reimburses MPC for employee benefit expenses, along with the provision of operational and management services in support of both our L&S and G&P segments’ operations. Loan Agreement MPLX is party to a loan agreement with MPC Investment (the “MPC Loan Agreement”). Under the terms of the agreement, MPC Investment makes a loan or loans to MPLX on a revolving basis as requested by MPLX and as agreed to by MPC Investment. On April 27, 2018, MPLX and MPC Investment entered into an amendment to the MPC Loan Agreement to increase the borrowing capacity under the MPC Loan Agreement from $500 million to $1 billion . In connection with the Merger, on July 31, 2019, MPLX and MPC Investment entered into a second amendment to the MPC Loan Agreement to increase the borrowing capacity under the MPC Loan Agreement to $1.5 billion in aggregate principal amount of all loans outstanding at any one time. The entire unpaid principal amount of the loan, together with all accrued and unpaid interest and other amounts (if any), shall become due and payable on July 31, 2024, provided that MPC Investment may demand payment of all or any portion of the outstanding principal amount of the loan, together with all accrued and unpaid interest and other amounts (if any), at any time prior to July 31, 2024. Borrowings under the MPC Loan Agreement prior to July 31, 2019 bore interest at LIBOR plus 1.50 percent , while borrowings as of and after July 31, 2019 will bear interest at LIBOR plus 1.25 percent or such lower rate as would be applicable to such loans under the MPLX Credit Agreement. Activity on the MPC Loan Agreement was as follows: (In millions) December 31, 2019 December 31, 2018 Borrowings $ 8,540 $ 3,962 Average interest rate of borrowings 3.441 % 3.473 % Repayments $ 7,946 $ 4,347 Outstanding balance at end of period $ 594 $ — Prior to the Merger, ANDX was also party to a loan agreement with MPC (“ANDX-MPC Loan Agreement”). This facility was entered into on December 21, 2018, with a borrowing capacity of $500 million . In connection with the Merger, on July 31, 2019, MPLX repaid the entire outstanding balance and terminated the ANDX-MPC Loan Agreement. There was no activity on the ANDX-MPC Loan Agreement in 2018. Activity on the agreement during 2019 prior to the Merger was as follows: (In millions) December 31, 2019 Borrowings $ 773 Average interest rate of borrowings 4.249 % Repayments $ 773 Outstanding balance at end of period $ — Related Party Revenue Related party sales to MPC consist of crude oil and refined products pipeline and trucking transportation services based on tariff/contracted rates; storage, terminal and fuels distribution services based on contracted rates; and marine transportation services. Related party sales to MPC also consist of revenue related to volume deficiency credits. MPLX also has operating agreements with MPC under which it receives a fee for operating MPC’s retained pipeline assets and a fixed annual fee for providing oversight and management services required to run the marine business. MPLX also receives management fee revenue for engineering, construction and administrative services for operating certain of its equity method investments. Revenue received from related parties included on the Consolidated Statements of Income was as follows: (In millions) 2019 2018 2017 Service revenue MPC $ 3,455 $ 2,404 $ 1,082 Rental income MPC 1,196 846 279 Product sales (1) MPC 140 87 8 Other 2 — — Total Product sales - related parties 142 87 8 Other income MPC 47 41 40 Other 67 58 52 Total Other income - related parties $ 114 $ 99 $ 92 (1) There were additional product sales to MPC that net to zero within the consolidated financial statements as the transactions are recorded net due to the terms of the agreements under which such product was sold. For 2019 , 2018 and 2017 , these sales totaled $1,120 million , $607 million and $254 million , respectively. Related Party Expenses MPC provides executive management services and certain general and administrative services to MPLX under the terms of our omnibus agreements. Omnibus charges included in “Rental cost of sales - related parties” primarily relate to services that support MPLX’s rental operations and maintenance of assets available for rent. Omnibus charges included in “Purchases - related parties” primarily relate to services that support MPLX’s operations and maintenance activities, as well as compensation expenses. Omnibus charges included in “General and administrative expenses” primarily relate to services that support MPLX’s executive management, accounting and human resources activities. MPLX also obtains employee services from MPC under employee services agreements (“ESA charges”). ESA charges for personnel directly involved in or supporting operations and maintenance activities related to rental services are classified as “Rental cost of sales - related parties.” ESA charges for personnel directly involved in or supporting operations and maintenance activities related to other services are classified as “Purchases - related parties.” ESA charges for personnel involved in executive management, accounting and human resources activities are classified as “General and administrative expenses.” In addition to these agreements, MPLX purchases products from MPC, makes payments to MPC in its capacity as general contractor to MPLX, and has certain rent and lease agreements with MPC. Expenses incurred from MPC under the omnibus and employee services agreements as well as other purchases from MPC included on the Consolidated Statements of Income are as follows: (In millions) 2019 2018 2017 Rental cost of sales - related parties $ 165 $ 31 $ 2 Purchases - related parties MPC 1,210 919 455 Other 21 6 — General and administrative expenses 243 199 138 Total $ 1,639 $ 1,155 $ 595 Some charges incurred under the omnibus and ESA agreements are related to engineering services and are associated with assets under construction. These charges are added to “Property, plant and equipment, net” on the Consolidated Balance Sheets. For 2019 , 2018 and 2017 , these charges totaled $169 million , $152 million and $42 million , respectively. Related Party Assets and Liabilities December 31, (In millions) 2019 2018 Current assets - related parties Receivables - MPC $ 621 $ 542 Receivables - Other 22 9 Prepaid - MPC 9 5 Lease Receivables - MPC 4 — Total 656 556 Noncurrent assets - related parties Long-term receivables - MPC 21 24 Right of use assets - MPC 232 — Long-term lease receivables - MPC 43 — Unguaranteed residual asset - MPC 7 — Total 303 24 Current liabilities - related parties Payables - MPC 911 360 Payables - Other 37 76 Operating lease liabilities - MPC 1 — Deferred revenue - Minimum volume deficiencies - MPC 42 57 Deferred revenue - Project reimbursements - MPC 16 9 Deferred revenue - Project reimbursements - Other 1 — Total 1,008 502 Long-term liabilities - related parties Long-term operating lease liabilities - MPC 230 — Long-term deferred revenue - Project reimbursements - MPC 53 46 Long-term deferred revenue - Project reimbursements - Other 7 — Total $ 290 $ 46 From time to time, MPLX may also sell to or purchase from related parties assets and inventory at the lesser of average unit cost or net realizable value. Sales to related parties during the years ended December 31, 2019 and 2018 were $10 million and $6 million , respectively. Purchases from related parties during the years ended December 31, 2019 and 2018 were approximately $5 million and $8 million , respectively.

Net Income (Loss) Per Limited P

Net Income (Loss) Per Limited Partner Unit	12 Months Ended
	Dec. 31, 2019
Earnings Per Share [Abstract]
Net Income (Loss) Per Limited Partner Unit	Net Income/(Loss) Per Limited Partner Unit Net income/(loss) per unit applicable to common limited partner units is computed by dividing net income/(loss) attributable to MPLX LP less income/(loss) allocated to participating securities by the weighted average number of common units outstanding. Additional MPLX common units and MPLX Series B preferred units were issued on July 30, 2019 as a result of the merger with ANDX as discussed in Note 4. Distributions declared on these newly issued common and Series B preferred units are a reduction to income available to MPLX common unit holders due to their participation in distributions of income. Classes of participating securities for 2019, 2018 and 2017 include: 2019 2018 2017 Common Units ü ü ü Equity-based compensation awards ü ü ü Series A preferred units ü ü ü Series B preferred units ü General partner units and IDRs ü The HST, WHC and MPLXT acquisitions and the Merger were transfers between entities under common control as discussed in Note 4 . As entities under common control with MPC, prior periods were retrospectively adjusted to furnish comparative information. Accordingly, the prior period earnings have been allocated to the general partner and do not affect the net income/(loss) per unit calculation. The earnings for the entities acquired under common control will be included in the net income/(loss) per unit calculation prospectively as described above. In 2019 and 2018 , MPLX had dilutive potential common units consisting of certain equity-based compensation awards. In 2017 , MPLX had dilutive potential common units consisting of certain equity-based compensation awards and Class B units. Potential common units omitted from the diluted earnings per unit calculation for the years ended December 31, 2019 , 2018 and 2017 were less than 1 million . (In millions) 2019 2018 2017 Net income attributable to MPLX LP $ 1,033 $ 1,818 $ 794 Less: Distributions declared on Series A preferred units (1) 81 75 65 Distributions declared on Series B preferred units (1) 42 — — General partner’s distributions declared (includes IDRs) (1)(2) — — 328 Limited partners’ distributions declared on MPLX common units (including common units of general partner) (1) 2,635 1,985 895 Undistributed net loss attributable to MPLX LP $ (1,725 ) $ (242 ) $ (494 ) (1) See Note 8 for distribution information. (2) Distributions declared on January 25, 2018 on general partner common units issued on February 1, 2018 in exchange for the economic general partner interest, including IDRs, are shown as general partner distributions declared. 2019 (In millions, except per unit data) Limited Partners’ Common Units Series A Preferred Units Series B Preferred Units Total Basic and diluted net income attributable to MPLX LP per unit: Net income attributable to MPLX LP: Distributions declared $ 2,635 $ 81 $ 42 $ 2,758 Undistributed net loss attributable to MPLX LP (1,725 ) — — (1,725 ) Net income attributable to MPLX LP (1) $ 910 $ 81 $ 42 $ 1,033 Weighted average units outstanding: Basic (2) 906 906 Diluted (2) 907 907 Net income attributable to MPLX LP per limited partner unit: Basic $ 1.00 Diluted $ 1.00 2018 (In millions, except per unit data) Limited Partners’ Common Units Series A Preferred Units Total Basic and diluted net income attributable to MPLX LP per unit: Net income attributable to MPLX LP: Distributions declared $ 1,985 $ 75 $ 2,060 Undistributed net loss attributable to MPLX LP (242 ) — (242 ) Net income attributable to MPLX LP (1) $ 1,743 $ 75 $ 1,818 Weighted average units outstanding: Basic 761 761 Diluted 761 761 Net income attributable to MPLX LP per limited partner unit: Basic $ 2.29 Diluted $ 2.29 2017 (In millions, except per unit data) General Partner Limited Partners’ Common Units Series A Preferred Units Total Basic and diluted net income attributable to MPLX LP per unit: Net income attributable to MPLX LP: Distribution declared (including IDRs) $ 328 $ 895 $ 65 $ 1,288 Undistributed net loss attributable to MPLX LP (10 ) (484 ) — (494 ) Net income attributable to MPLX LP (1) $ 318 $ 411 $ 65 $ 794 Weighted average units outstanding: Basic 8 385 393 Diluted 8 388 396 Net income attributable to MPLX LP per limited partner unit: Basic $ 1.07 Diluted $ 1.06 (1) Allocation of net income/(loss) attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period. (2) The Series B preferred units and the MPLX common units issued in connection with the Merger were not outstanding during the entire year. See Notes 4 and 8 for additional information about the treatment of these units.

Equity

Equity	12 Months Ended
	Dec. 31, 2019
Equity [Abstract]
Equity	Equity Units Outstanding – MPLX had 1,058,355,471 common units outstanding as of December 31, 2019 . Of that number, 665,997,540 were owned by MPC, which also owns the non-economic GP interest as described below. MPLX had 600,000 Series B preferred units outstanding as of December 31, 2019 . The sections below describe activities and events which impacted our unit balances throughout the year. Merger - In connection with the Merger and as discussed in Note 4, each common unit held by ANDX’s public unitholders was converted into the right to receive 1.135 MPLX common units while ANDX common units held by certain affiliates of MPC were converted into the right to receive 1.0328 MPLX common units. This resulted in the issuance of MPLX common units of approximately 102 million units to public unitholders and approximately 161 million units to MPC in connection with MPLX's acquisition of ANDX on July 30, 2019. Series A Redeemable Preferred Unit Conversions - During 2019, certain holders of Series A preferred units exercised their rights to convert their Series A preferred units into approximately 1.2 million common units as discussed in Note 9 . GP/IDR Exchange – On February 1, 2018, MPC cancelled its IDRs and converted its economic GP Interest in MPLX LP to a non-economic general partner interest in exchange for 275 million newly issued MPLX LP common units. These units had a fair value of $10.4 billion as of the transaction date as recorded on the Consolidated Statements of Equity. 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. MPC continues to own the non-economic GP Interest in MPLX LP. See Note 7 for more information on the net income per unit calculation. Class B Conversions - On July 1, 2016 and July 1, 2017, each Class B unit of MPLX LP was converted, in two equal installments, into 1.09 MPLX LP common units and the right to receive $6.20 in cash. Upon the conversion of each tranche of the Class B units, the right of the unitholder, M&R MWE Liberty LLC and certain of its affiliates (“M&R”), to vote as a common unitholder of MPLX was limited to a maximum of five percent of MPLX’s outstanding common units. Additionally, M&R was given the right with respect to such converted units to participate in MPLX’s underwritten offerings of our common units including continuous equity or similar programs in an amount up to 20 percent of the total number of common units offered by MPLX. M&R may freely transfer such converted units, and M&R has the right to demand that MPLX conduct up to three underwritten offerings beginning in 2017, but restricted to no more than one offering in any twelve-month period. Following the July 1, 2017 conversion, all MPLX Class B units were eliminated, are no longer outstanding and no longer participate in distributions of cash from MPLX. ATM Program – On March 13, 2018, MPLX entered into a Third Amended and Restated Distribution Agreement, providing for the at-the-market issuances of common units having an aggregate offering price of up to approximately $ 1.7 billion , in amounts, at prices and on terms determined by market conditions and other factors at the time of the offerings (such continuous offering program, or at-the-market program is referred to as the “ATM Program”). During the years ended December 31, 2019 and 2018 , MPLX issued no common units under the ATM Program. During the year ended December 31, 2017 , MPLX issued an aggregate of 13,846,998 common units under the ATM Program generating net proceeds of approximately $473 million . MPLX used the net proceeds from sales under the ATM Program for general business purposes, including repayment or refinancing of debt, and funding for acquisitions, working capital requirements and capital expenditures. The table below summarizes the changes in the number of units outstanding for the years ended December 31, 2017 , 2018 , and 2019 : (In units) Common Class B General Partner (1) Total Balance at December 31, 2016 357,193,288 3,990,878 7,371,105 368,555,271 Unit-based compensation awards 268,167 — 5,472 273,639 Issuance of units under the ATM Program 13,846,998 — 282,591 14,129,589 Contribution of HST/WHC/MPLXT (See Note 4) 12,960,376 — 264,497 13,224,873 Contribution of the Joint-Interest Acquisition (See Note 4) 18,511,134 — 377,778 18,888,912 Class B Conversion 4,350,057 (3,990,878 ) 7,330 366,509 Balance at December 31, 2017 407,130,020 — 8,308,773 415,438,793 Unit-based compensation awards 348,387 — 140 348,527 Contribution of Refining Logistics and Fuels Distribution (See Note 4) 111,611,111 — 2,277,778 113,888,889 Conversion of GP economic interests 275,000,000 — (10,586,691 ) 264,413,309 Balance at December 31, 2018 794,089,518 — — 794,089,518 Unit-based compensation awards 288,031 — — 288,031 Issuance of units in connection with the Merger 262,829,592 — — 262,829,592 Conversion of Series A preferred units 1,148,330 — — 1,148,330 Balance at December 31, 2019 1,058,355,471 — — 1,058,355,471 (1) Changes to the number of general partner units outstanding, other than changes due to contributions made to MPC for the acquisitions of HSM, HST, WHC, MPLXT, the Joint-Interest Acquisition and Refining Logistics and Fuels Distribution, are the result of cash contributions made by the general partner in order to maintain its two percent GP Interest. Series B Preferred Units - Prior to the Merger, ANDX issued 600,000 units of 6.875 percent Fixed-to-Floating Rate Cumulative Redeemable Perpetual Preferred Units representing limited partner interests of ANDX at a price to the public of $1,000 per unit. Upon completion of the Merger, the ANDX preferred units converted to preferred units of MPLX representing substantially equivalent limited partnership interests in MPLX (the “Series B preferred units”). The Series B preferred units are pari passu with the Series A preferred units with respect to distribution rights and rights upon liquidation. Distributions on the Series B preferred units are payable semi-annually in arrears on the 15th day, or the first business day thereafter, of February and August of each year up to and including February 15, 2023. After February 15, 2023, the holders of Series B preferred units are entitled to receive cumulative, quarterly distributions payable in arrears on the 15th day of February, May, August and November of each year, or the first business day thereafter, based on a floating annual rate equal to the three-month LIBOR plus 4.652 percent . The changes in the Series B preferred unit balance from the Merger through December 31, 2019 are summarized below and are included in the Consolidated Balance Sheets and Consolidated Statements of Equity within “Equity of Predecessor” for the period prior to the Merger and within “Series B preferred units” for the period following the Merger. The Series B preferred units are recorded at fair value as of July 30, 2019. (In millions) Series B Preferred Units Beginning Balance at the Merger date $ 615 Net income allocated 17 Distributions received by Series B preferred unitholders (21 ) Balance at December 31, 2019 $ 611 TexNew Mex Units - Prior to the Merger, MPC held 80,000 Andeavor Logistics TexNew Mex units, representing all outstanding units. At the time of the Merger, each Andeavor Logistics TexNew Mex unit was automatically converted into TexNew Mex units of MPLX with substantially the same rights and obligations as the Andeavor Logistics TexNew Mex units. The TexNew Mex units represent the right to receive quarterly distribution payments in an amount calculated using the distributable cash flow generated by a particular portion of the TexNew Mex pipeline system, in excess of a base amount and adjusted for previously agreed upon stipulations and contingencies. No distributions were payable to TexNew Mex unitholders for distributable cash flow generated during the post-Merger period in 2018. In 2019, distributions of less than $1 million were earned by the TexNew Mex units, which were declared in January of 2020 and paid in February 2020. Issuance of Additional Securities – The Partnership Agreement authorizes MPLX to issue an unlimited number of additional securities for the consideration and on the terms and conditions determined by the general partner without the approval of the unitholders. Net Income Allocation – In preparing the Consolidated Statements of Equity, net income attributable to MPLX LP is allocated to Series A and Series B preferred unitholders first and subsequently allocated to the limited partner unitholders in accordance with their respective ownership percentages. Prior to 2018, when distributions related to the IDRs were made, earnings equal to the amount of those distributions were first allocated to the general partner before the remaining earnings are allocated to the unitholders, based on their respective ownership percentages. The following table presents the allocation of the general partner’s GP Interest in net income attributable to MPLX, for income statement periods occurring prior to the exchange of the GP economic interests: (In millions) 2017 Net income attributable to MPLX LP $ 794 Less: Preferred unit distributions 65 General partner's IDRs and other 310 Net income attributable to MPLX LP available to general and limited partners 419 General partner's two percent GP Interest in net income attributable to MPLX LP 8 General partner's IDRs and other 310 General partner's GP Interest in net income attributable to MPLX LP $ 318 Cash Distributions – The Partnership Agreement sets forth the calculation to be used to determine the amount and priority of cash distributions that the common unitholders and preferred unitholders will receive. In accordance with the Partnership Agreement, on January 23, 2020 , MPLX declared a quarterly cash distribution, based on the results of the fourth quarter of 2019 , totaling $715 million , or $0.6875 per common unit. This rate was also received by Series A preferred unitholders. These distributions were paid on February 14, 2020 to unitholders of record on February 4, 2020 . Distributions for the fourth quarter of 2018 were $0.6475 per common unit while distributions for the twelve months ended December 31, 2019 and 2018 were $2.6900 and $2.5300 per common unit, respectively. The $715 million of common unit distributions is net of $12.5 million in quarterly distributions waived by MPC. This waiver was instituted in 2017 under the terms of ANDX’s historical partnership agreement with Andeavor. The waiver is no longer applicable after 2019 based on the original term in the waiver agreement. Additionally, as a result of the Merger, 600,000 ANDX preferred units were converted into 600,000 Series B preferred units of MPLX. Series B preferred unitholders are entitled to receive, when and if declared by the board, a fixed distribution of $68.75 per unit, per annum, payable semi-annually in arrears on February 15 and August 15, or the first business day thereafter, up to and including February 15, 2023. After February 15, 2023, the holders of Series B preferred units are entitled to receive cumulative, quarterly distributions payable in arrears on the 15th day of February, May, August and November of each year, or the first business day thereafter, based on a floating annual rate equal to the three-month LIBOR plus 4.652 percent . MPLX made a cash distribution to holders of the Series B preferred unitholders on February 15, 2020 for approximately $21 million . The allocation of total quarterly cash distributions to general, limited, and preferred unitholders is as follows for the years ended December 31, 2019 , 2018 and 2017 . MPLX’s distributions are declared subsequent to quarter end; therefore, the following table represents total cash distributions applicable to the period in which the distributions were earned. (In millions) 2019 2018 2017 General partner's distributions: General partner's distributions on general partner units $ — $ — $ 25 General partner's distributions on IDRs (1) — — 303 Total distribution on general partner units and IDRs — — 328 Limited partners' distributions: Common unitholders, includes common units of general partner 2,635 1,985 895 Series A preferred unit distributions 81 75 65 Series B preferred unit distribution 42 — — Total cash distributions declared $ 2,758 $ 2,060 $ 1,288 (1) Includes distributions of fourth quarter 2017 income declared on general partner common units issued February 1, 2018 in exchange for the economic general partner interest. The distribution on common units for the year ended December 31, 2019 includes the impact of the issuance of approximately 102 million units issued to public unitholders and approximately 161 million units issued to MPC in connection with the Merger. Due to the timing of the closing, distributions presented in the table above include second quarter distributions on MPLX common units issued to former ANDX unitholders in connection with the Merger. Due to the waiver mentioned above, the distributions on common units exclude $12.5 million of waived distributions for the three months ended December 31, 2019 and $37.5 million of waived distributions for the year ended December 31, 2019. Also included in the table above is $21 million of distributions earned by the Series B preferred units for 2019 as well as $21 million

Redeemable Preferred Units

Redeemable Preferred Units	12 Months Ended
	Dec. 31, 2019
Redeemable Preferred Units Disclosure [Abstract]
Redeemable Preferred Units	Series A Preferred Units Private Placement of Preferred Units – On May 13, 2016, MPLX completed the private placement of approximately 30.8 million 6.5 percent Series A Convertible preferred units for a cash purchase price of $32.50 per unit. The aggregate net proceeds of approximately $984 million from the sale of the Series A preferred units were used for capital expenditures, repayment of debt and general business purposes. Preferred Unit Distribution Rights - The Series A preferred units rank senior to all common units and pari passu with all Series B preferred units with respect to distributions and rights upon liquidation. The holders of the Series A preferred units received cumulative quarterly distributions equal to $0.528125 per unit for each quarter prior to the second quarter of 2018. Beginning with the second quarter of 2018, the holders of the Series A preferred units are entitled to receive, when and if declared by the board, a quarterly distribution equal to the greater of $0.528125 per unit or the amount of distributions they would have received on an as converted basis. On January 23, 2020 , MPLX declared a quarterly cash distribution of $0.6875 per common unit for the fourth quarter of 2019. Holders of the Series A preferred units will receive the common unit rate in lieu of the lower $0.528125 base amount. The holders may convert their Series A preferred units into common units at any time, in full or in part, subject to minimum conversion amounts and conditions. After the fourth anniversary of the issuance date, MPLX may convert the Series A preferred units into common units at any time, in whole or in part, subject to certain minimum conversion amounts and conditions, if the closing price of MPLX common units is greater than $48.75 for the 20-day trading period immediately preceding the conversion notice date. The conversion rate for the Series A preferred units shall be the quotient of (a) the sum of (i) $32.50, plus (ii) any unpaid cash distributions on the applicable preferred unit, divided by (b) $32.50, subject to adjustment for unit distributions, unit splits and similar transactions. The holders of the Series A preferred units are entitled to vote on an as-converted basis with the common unitholders and have certain other class voting rights with respect to any amendment to the MPLX partnership agreement that would adversely affect any rights, preferences or privileges of the preferred units. In addition, upon certain events involving a change of control, the holders of preferred units may elect, among other potential elections, to convert their Series A preferred units to common units at the then applicable change of control conversion rate. On September 20, 2019, certain holders exercised their right to convert a total of 1.2 million Series A preferred units into common units. As a result of the transaction, approximately 29.6 million Series A preferred units remain outstanding as of December 31, 2019. The changes in the redeemable preferred balance for 2019 and 2018 are summarized below: (In millions) 2019 2018 Balance at beginning of period $ 1,004 $ 1,000 Net income allocated 81 75 Distributions received by preferred unitholders (81 ) (71 ) Conversion of preferred units to common units (36 ) — Balance at end of period $ 968 $ 1,004 The Series A preferred units are considered redeemable securities under GAAP due to the existence of redemption provisions upon a deemed liquidation event, which is outside MPLX’s control. Therefore, they are presented as temporary equity in the mezzanine section of the Consolidated Balance Sheets. The Series A preferred units have been recorded at their issuance date fair value, net of issuance costs. Income allocations increase the carrying value and declared distributions decrease the carrying value of the Series A preferred units. As the Series A preferred units are not currently redeemable and not probable of becoming redeemable, adjustment to the initial carrying amount is not necessary and would only be required if it becomes probable that the Series A preferred units would become redeemable.

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2019
Segment Reporting [Abstract]
Segment Information	Segment Information MPLX’s chief operating decision maker is the chief executive officer (“CEO”) of its general partner. The CEO reviews MPLX’s discrete financial information, makes operating decisions, assesses financial performance and allocates resources on a type of service basis. MPLX has two reportable segments: L&S and G&P. Each of these segments is organized and managed based upon the nature of the products and services it offers. • L&S – transports, stores, distributes and markets crude oil, asphalt, refined petroleum products and water. Also includes an inland marine business, terminals, rail facilities, storage caverns and refining logistics. • G&P – gathers, processes and transports natural gas; gathers, transports, fractionates, stores and markets NGLs. During the second quarter of 2018, our CEO began to evaluate the performance of our segments using Segment Adjusted EBITDA. We have modified our presentation of segment performance metrics to be consistent with this change, including prior periods presented for consistent and comparable presentation. Amounts included in net income and excluded from Segment Adjusted EBITDA include: (i) depreciation and amortization; (ii) provision/(benefit) for income taxes; (iii) amortization of deferred financing costs; (iv) extinguishment of debt; (v) non-cash equity-based compensation; (vi) impairment expense; (vii) net interest and other financial costs; (viii) income/(loss) from equity method investments; (ix) distributions and adjustments related to equity method investments; (x) unrealized derivative gains/(losses); (xi) acquisition costs; (xii) noncontrolling interests; and (xiii) other adjustments as deemed necessary. These items are either: (i) believed to be non-recurring in nature; (ii) not believed to be allocable or controlled by the segment; or (iii) are not tied to the operational performance of the segment. The tables below present information about revenues and other income, capital expenditures and investments in unconsolidated affiliates for the years ended December 31, 2019, 2018 and 2017 as well as total assets for our reportable segments as of December 31, 2019 and 2018: (In millions) 2019 2018 2017 L&S Service revenue $ 3,765 $ 2,575 $ 1,200 Rental income 1,235 856 279 Product related revenue 91 23 — Income from equity method investments 200 171 36 Other income 61 47 47 Total segment revenues and other income (1) 5,352 3,672 1,562 Segment Adjusted EBITDA (2) 2,748 2,057 775 Capital expenditures 1,060 708 512 Investments in unconsolidated affiliates 289 3 533 G&P Service revenue 2,188 1,685 1,038 Rental income 349 342 277 Product related revenue 997 1,171 897 Income from equity method investments 90 76 42 Other income 65 59 51 Total segment revenues and other income (1) 3,689 3,333 2,305 Segment Adjusted EBITDA (2) 1,586 1,418 1,229 Capital expenditures 1,203 1,545 972 Investments in unconsolidated affiliates $ 424 $ 338 $ 228 (1) Within the total segment revenues and other income amounts presented above, third party revenues for the L&S segment were $660 million , $371 million and $160 million for 2019 , 2018 and 2017 , respectively. Third party revenues for the G&P segment were $3,474 million , $3,198 million and $2,246 million for 2019 , 2018 and 2017 , respectively. (2) See below for the reconciliation from Segment Adjusted EBITDA to “Net income.” December 31, (In millions) 2019 2018 Segment Assets Cash and cash equivalents $ 15 $ 77 L&S 20,810 19,963 G&P 19,605 19,285 Total assets $ 40,430 $ 39,325 The table below provides a reconciliation between “Net income” and Segment Adjusted EBITDA. (In millions) 2019 2018 2017 Reconciliation to Net income: L&S Segment Adjusted EBITDA $ 2,748 $ 2,057 $ 775 G&P Segment Adjusted EBITDA 1,586 1,418 1,229 Total reportable segments 4,334 3,475 2,004 Depreciation and amortization (1) (1,254 ) (867 ) (683 ) (Provision)/benefit for income taxes — (8 ) (1 ) Amortization of deferred financing costs (42 ) (55 ) (53 ) Loss on extinguishment of debt — (46 ) — Non-cash equity-based compensation (22 ) (23 ) (15 ) Impairment expense (1,197 ) — — Net interest and other financial costs (873 ) (613 ) (301 ) Income from equity method investments 290 247 78 Distributions/adjustments related to equity method investments (562 ) (458 ) (231 ) Unrealized derivative gains/(losses) (2) 1 5 (6 ) Acquisition costs (14 ) (4 ) (11 ) Other (1 ) — — Adjusted EBITDA attributable to noncontrolling interests 32 18 8 Adjusted EBITDA attributable to Predecessor (3) 770 335 47 Net income $ 1,462 $ 2,006 $ 836 (1) Depreciation and amortization attributable to L&S was $503 million , $308 million and $163 million for the years ended 2019 , 2018 and 2017 , respectively. Depreciation and amortization attributable to G&P was $751 million , $559 million and $520 million for 2019 , 2018 and 2017 , respectively. (2) MPLX makes a distinction between realized or unrealized gains and losses on derivatives. During the period when a derivative contract is outstanding, changes in the fair value of the derivative are recorded as an unrealized gain or loss. When a derivative contract matures or is settled, the previously recorded unrealized gain or loss is reversed and the realized gain or loss of the contract is recorded. (3) The Adjusted EBITDA adjustments related to Predecessor are excluded from Adjusted EBITDA attributable to MPLX LP prior to the acquisition date.

Major Customers and Concentrati

Major Customers and Concentration of Credit Risk	12 Months Ended
	Dec. 31, 2019
Risks and Uncertainties [Abstract]
Major Customers and Concentration of Credit Risk	Major Customers and Concentration of Credit Risk The table below shows, by segment, the percentage of operating revenues as well as total revenues and other income with MPC which is our most significant customer and our largest concentration of credit risk. 2019 (1) 2018 (1) 2017 (1) Operating revenues (2) L&S 91 % 94 % 92 % G&P 4 % 3 % 0 % Total 56 % 50 % 37 % Total revenues and other income L&S 88 % 90 % 90 % G&P 4 % 2 % 0 % Total 54 % 48 % 36 % (1) The percent calculations exclude revenues attributable to volumes shipped by MPC under joint tariffs with third parties, which are treated as third-party revenue for accounting purposes. (2) Operating revenues consist of service revenue, service revenue - product related, rental income and product sales. MPLX has a concentration of trade receivables due from customers in the same industry: MPC, integrated oil companies, independent refining companies and other pipeline companies. These concentrations of customers may impact MPLX’s overall exposure to credit risk as they may be similarly affected by changes in economic, regulatory and other factors. MPLX manages its exposure to credit risk through credit analysis, credit limit approvals and monitoring procedures; and for certain transactions, it may request letters of credit, prepayments or guarantees.

Inventories

Inventories	12 Months Ended
	Dec. 31, 2019
Inventory Disclosure [Abstract]
Inventories	Inventories Inventories consist of the following: December 31, (In millions) 2019 2018 NGLs $ 5 $ 9 Line fill 10 9 Spare parts, materials and supplies 95 80 Total inventories $ 110 $ 98

Property, Plant and Equipment

Property, Plant and Equipment	12 Months Ended
	Dec. 31, 2019
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	Property, Plant and Equipment Property, plant and equipment with associated accumulated depreciation is shown below: Estimated Useful Lives December 31, (In millions) 2019 2018 Natural gas gathering and NGL transportation pipelines and facilities 5 - 40 years $ 7,037 $ 6,349 Processing, fractionation and storage facilities 5 - 46 years 6,410 6,045 Pipelines and related assets 2 - 51 years 5,117 5,111 Barges and towing vessels 15 - 20 years 739 621 Terminals and related assets 4 - 45 years 2,222 2,757 Refinery related assets 13 - 38 years 1,383 1,447 Land, building, office equipment and other 2 - 45 years 2,554 1,562 Construction-in-progress 1,405 1,321 Total 26,867 25,213 Less accumulated depreciation 4,722 3,688 Property, plant and equipment, net $ 22,145 $ 21,525

Goodwill and Intangibles

Goodwill and Intangibles	12 Months Ended
	Dec. 31, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangibles	Goodwill and Intangibles Goodwill MPLX annually evaluates goodwill for impairment as of November 30, as well as whenever events or changes in circumstances indicate it is more likely than not that the fair value of a reporting unit with goodwill is less than its carrying amount. As a result of the Merger and subsequent changes to our internal organization structure, the number of reporting units was reduced from 12 to 6 in conjunction with our annual impairment test, however, this change in structure did not have an impact on our operating segments. Our reporting units are one level below our operating segments and are determined based on the way in which segment management operates and reviews each operating segment. As a result of our change in reporting units, we performed our goodwill impairment assessment prior to the change in reporting units in addition to performing an impairment assessment immediately following the change in our reporting units. Significant assumptions used to estimate the reporting units’ fair value include the discount rate as well as estimates of future cash flows, which are impacted primarily by producer customers’ development plans, which impact future volumes and capital requirements. After performing our evaluations related to the impairment of goodwill, we recorded an impairment of $1,156 million prior to our change in reporting units and an additional impairment of $41 million subsequent to our change in reporting units, both within the G&P operating segment. The remainder of the reporting units fair values were in excess of their carrying values. The impairment was primarily driven by updated guidance related to the slowing of drilling activity which has reduced production growth forecasts from our producer customers. This resulted in goodwill totaling approximately $9.5 billion as of December 31, 2019, with all but one of our six reporting units having goodwill. The fair value of the reporting units for the interim goodwill impairment analysis described above was determined based on applying both a discounted cash flow or income approach as well as a market approach. The discounted cash flow fair value estimate is based on known or knowable information at the measurement date. The significant assumptions that were used to develop the estimates of the fair values under the discounted cash flow method included management’s best estimates of the expected future results and discount rates, which range from 9.0 percent to 10.0 percent . Fair value determinations require considerable judgment and are sensitive to changes in underlying assumptions and factors. As a result, there can be no assurance that the estimates and assumptions made for purposes of the interim goodwill impairment test will prove to be an accurate prediction of the future. The fair value measurements for the individual reporting units’ overall fair values, and the fair values of the goodwill assigned thereto, represent Level 3 measurements. The changes in carrying amount of goodwill were as follows for the periods presented: (In millions) L&S G&P Total Gross goodwill as of December 31, 2017 $ 162 $ 2,213 $ 2,375 Accumulated impairment losses — (130 ) (130 ) Balance as of December 31, 2017 162 2,083 2,245 Acquisitions (1) 7,072 699 7,771 Balance as of December 31, 2018 7,234 2,782 10,016 Impairment losses — (1,197 ) (1,197 ) Acquisitions (1) 488 229 717 Balance as of December 31, 2019 7,722 1,814 9,536 Gross goodwill as of December 31, 2019 7,722 3,141 10,863 Accumulated impairment losses — (1,327 ) (1,327 ) Balance as of December 31, 2019 $ 7,722 $ 1,814 $ 9,536 (1) Acquisitions in 2018 are inclusive of the Mt. Airy Terminal acquisition as well as the Merger while acquisitions in 2019 are inclusive of measurement period adjustments related to the previously mentioned transactions. Intangible Assets MPLX’s intangible assets are comprised of customer contracts and relationships. The weighted average amortization period for intangible assets acquired during 2019 was approximately 9 years . Gross intangible assets with accumulated amortization as of December 31, 2019 and 2018 is shown below: December 31, 2019 December 31, 2018 (In millions) Useful Life Gross Accumulated Amortization (1) Net Gross Accumulated Amortization (1) Net L&S 6 - 8 years $ 283 $ (45 ) $ 238 $ 249 $ (14 ) $ 235 G&P 6 - 25 years 1,288 (256 ) 1,032 1,253 (129 ) 1,124 $ 1,571 $ (301 ) $ 1,270 $ 1,502 $ (143 ) $ 1,359 (1) Amortization expense attributable to the G&P segment for the years ended December 31, 2019 and 2018 was $127 million and $49 million , respectively. Amortization expense attributable to the L&S segment for the year ended December 31, 2019 and 2018 was $31 million and $14 million , respectively. Estimated future amortization expense related to the intangible assets at December 31, 2019 is as follows: (In millions) 2020 $ 155 2021 155 2022 155 2023 155 2024 150 Thereafter 500 Total $ 1,270

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements Fair Values – Recurring Fair value measurements and disclosures relate primarily to MPLX’s derivative positions as discussed in Note 16 . The following table presents the financial instruments carried at fair value on a recurring basis as of December 31, 2019 and 2018 by fair value hierarchy level. MPLX has elected to offset the fair value amounts recognized for multiple derivative contracts executed with the same counterparty. December 31, 2019 2018 (In millions) Assets Liabilities Assets Liabilities Significant unobservable inputs (Level 3) Embedded derivatives in commodity contracts $ — $ (60 ) $ — $ (61 ) Total carrying value on Consolidated Balance Sheets $ — $ (60 ) $ — $ (61 ) Level 3 instruments include all NGL transactions and embedded derivatives in commodity contracts. The embedded derivative liability relates to a natural gas purchase commitment 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 $0.43 to $1.23 and (2) the probability of renewal of 94 percent for the first five-year term and 83 percent for the second five-year term of the gas purchase commitment and related keep-whole processing agreement. Increases or decreases in the fractionation spread result in an increase or decrease in the fair value of the embedded derivative liability, respectively. An increase in the probability of renewal would result in an increase in the fair value of the related embedded derivative liability. Beyond the embedded derivative discussed above, we had no outstanding commodity contracts as of December 31, 2019 or December 31, 2018 . Changes in Level 3 Fair Value Measurements The following table is a reconciliation of the net beginning and ending balances recorded for net assets and liabilities classified as Level 3 in the fair value hierarchy. 2019 2018 (In millions) Commodity Derivative Contracts (net) Embedded Derivatives in Commodity Contracts (net) Commodity Derivative Contracts (net) Embedded Derivatives in Commodity Contracts (net) Fair value at beginning of period $ — $ (61 ) $ (2 ) $ (64 ) Total gains/(losses) (realized and unrealized) included in earnings (1) — (5 ) 6 (9 ) Settlements — 6 (4 ) 12 Fair value at end of period — (60 ) — (61 ) The amount of total losses for the period included in earnings attributable to the change in unrealized gains or losses relating to liabilities still held at end of period $ — $ (5 ) $ — $ (8 ) (1) Gains and losses on commodity derivatives classified as Level 3 are recorded in “Product sales” on the Consolidated Statements of Income. Gains and losses on derivatives embedded in commodity contracts are recorded in “Purchased product costs” and “Cost of revenues” on the Consolidated Statements of Income. Fair Values – Reported MPLX’s primary financial instruments are cash and cash equivalents, receivables, receivables from related parties, lease receivables from related parties, accounts payable, payables to related parties and long-term debt. MPLX’s fair value assessment incorporates a variety of considerations, including (1) the duration of the instruments, (2) MPC’s investment-grade credit rating and (3) the historical incurrence of and expected future insignificance of bad debt expense, which includes an evaluation of counterparty credit risk. MPLX believes the carrying values of its current assets and liabilities approximate fair value. The recorded value of the amounts outstanding under the bank revolving credit facility, if any, approximates fair value due to the variable interest rate that approximates current market rates. Derivative instruments are recorded at fair value, based on available market information (see Note 16 ). The fair value of MPLX’s long-term debt is estimated based on recent market non-binding indicative quotes. The fair value of the SMR liability is estimated using a discounted cash flow approach based on the contractual cash flows and MPLX’s unsecured borrowing rate. The long-term debt and SMR liability fair values are considered Level 3 measurements. The following table summarizes the fair value and carrying value of the long-term debt, excluding finance leases, and SMR liability. December 31, 2019 2018 (In millions) Fair Value Carrying Value Fair Value Carrying Value Long-term debt $ 21,054 $ 19,800 $ 18,070 $ 18,511 SMR liability $ 90 $ 80 $ 92 $ 86

Derivative Financial Instrument

Derivative Financial Instruments	12 Months Ended
	Dec. 31, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Financial Instruments	Derivative Financial Instruments As of December 31, 2019 , MPLX had no outstanding commodity contracts. Embedded Derivative - MPLX has a natural gas purchase commitment embedded in a keep-whole processing agreement with a producer customer in the Southern Appalachian region expiring in December 2022. The customer has the unilateral option to extend the agreement for two consecutive five-year terms through December 2032. For accounting purposes, the natural gas purchase commitment and term extending options have been aggregated into a single compound embedded derivative. The probability of the customer exercising its options is determined based on assumptions about the customer’s potential business strategy decision points that may exist at the time they would elect whether to renew the contract. The changes in fair value of this compound embedded derivative are based on the difference between the contractual and index pricing, the probability of the producer customer exercising its option to extend and the estimated favorability of these contracts compared to current market conditions. The changes in fair value are recorded in earnings through “Purchased product costs” on the Consolidated Statements of Income. As of December 31, 2019 and 2018 , the estimated fair value of this contract was a liability of $60 million and $61 million , respectively. Certain derivative positions are subject to master netting agreements; therefore, MPLX has elected to offset derivative assets and liabilities that are legally permissible to be offset. As of December 31, 2019 and 2018 , there were no derivative assets or liabilities that were offset on the Consolidated Balance Sheets. The impact of MPLX’s derivative instruments on its Consolidated Balance Sheets is summarized below: December 31, (In millions) 2019 2018 Derivative contracts not designated as hedging instruments and their balance sheet location Asset Liability Asset Liability Commodity contracts (1) Other current assets /Other current liabilities $ — $ (5 ) $ — $ (7 ) Other noncurrent assets /Deferred credits and other liabilities — (55 ) — (54 ) Total $ — $ (60 ) $ — $ (61 ) (1) Includes embedded derivatives in commodity contracts as discussed above. For further information regarding the fair value measurement of derivative instruments, including the effect of master netting arrangements or collateral, see Note 15 . See Note 2 for a discussion of derivatives MPLX may use and the reasons for them. The impact of MPLX’s derivative contracts not designated as hedging instruments and the location of gains and losses recognized on the Consolidated Statements of Income is summarized below: (In millions) 2019 2018 2017 Product sales Realized gains/(losses) $ — $ 4 $ (9 ) Unrealized gains — 2 4 Total derivative gains/(losses) related to product sales — 6 (5 ) Purchased product costs Realized losses (6 ) (12 ) (9 ) Unrealized gains/(losses) 1 3 (10 ) Total derivative loss related to purchased product costs (5 ) (9 ) (19 ) Cost of revenues Realized gains/(losses) — — — Unrealized gains/(losses) — — — Total derivative losses related to cost of revenues — — — Total derivative losses $ (5 ) $ (3 ) $ (24 )

Debt

Debt	12 Months Ended
	Dec. 31, 2019
Debt Disclosure [Abstract]
Debt	Debt MPLX’s outstanding borrowings at December 31, 2019 and 2018 consisted of the following: December 31, (In millions) 2019 2018 MPLX LP: Bank revolving credit facility due 2024 $ — $ — Term loan facility due 2021 1,000 — Floating rate senior notes due September 2021 1,000 — Floating rate senior notes due September 2022 1,000 — 6.250% senior notes due October 2022 266 — 3.500% senior notes due December 2022 486 — 3.375% senior notes due March 2023 500 500 4.500% senior notes due July 2023 989 989 6.375% senior notes due May 2024 381 — 4.875% senior notes due December 2024 1,149 1,149 5.250% senior notes due January 2025 708 — 4.000% senior notes due February 2025 500 500 4.875% senior notes due June 2025 1,189 1,189 4.125% senior notes due March 2027 1,250 1,250 4.250% senior notes due December 2027 732 — 4.000% senior notes due March 2028 1,250 1,250 4.800% senior notes due February 2029 750 750 4.500% senior notes due April 2038 1,750 1,750 5.200% senior notes due March 2047 1,000 1,000 5.200% senior notes due December 2047 487 — 4.700% senior notes due April 2048 1,500 1,500 5.500% senior notes due February 2049 1,500 1,500 4.900% senior notes due April 2058 500 500 Consolidated subsidiaries: MarkWest - 4.500% - 4.875% senior notes, due 2023-2025 23 23 ANDX - 3.500% - 6.375% senior notes, due 2019-2047 190 3,750 ANDX credit facilities — 1,245 Financing lease obligations (1) 19 21 Total 20,119 18,866 Unamortized debt issuance costs (106 ) (97 ) Unamortized discount/premium (300 ) (334 ) Amounts due within one year (9 ) (513 ) Total long-term debt due after one year $ 19,704 $ 17,922 (1) See Note 22 for lease information. The following table shows five years of scheduled debt payments, including payments on finance lease obligations: (In millions) 2020 $ 10 2021 2,002 2022 1,802 2023 1,502 2024 $ 1,601 Credit Agreements MPLX Credit Agreement Effective July 30, 2019, in connection with the closing of the Merger, MPLX amended and restated its existing revolving credit facility (the “MPLX Credit Agreement”) to, among other things, increase borrowing capacity to up to $3.5 billion , extend its term from July 2022 to July 2024, increase the letter of credit issuing capacity to $300 million and increase the swingline capacity to $150 million . The financial covenants and the interest rate terms contained in the new credit agreement are substantially the same as those contained in the previous bank revolving credit facility. The borrowing capacity under the MPLX Credit Agreement may be increased by up to an additional $1 billion , subject to certain conditions, including the consent of lenders whose commitments would increase. In addition, the maturity date may be extended, for up to two additional one-year periods, subject to, among other conditions, the approval of lenders holding the majority of the commitments then outstanding, provided that the commitments of any non-consenting lenders will terminate on the then-effective maturity date. Borrowings under the MPLX Credit Agreement bear interest at either the Adjusted LIBOR or the Alternate Base Rate (as defined in the MPLX Credit Agreement), at our election, plus a specified margin . MPLX is charged various fees and expenses in connection with the agreement, including administrative agent fees, commitment fees on the unused portion of the facility and fees with respect to issued and outstanding letters of credit. The applicable margins to the benchmark interest rates and certain fees fluctuate based on the credit ratings in effect from time to time on MPLX’s long-term debt. The MPLX Credit Agreement contains certain representations and warranties, affirmative and restrictive covenants and events of default that MPLX considers to be usual and customary for an agreement of this type, including a financial covenant that requires MPLX to maintain a ratio of Consolidated Total Debt as of the end of each fiscal quarter to Consolidated EBITDA (both as defined in the MPLX Credit Agreement) for the prior four fiscal quarters of no greater than 5.0 to 1.0 (or 5.5 to 1.0 for up to two fiscal quarters following certain acquisitions). Consolidated EBITDA is subject to adjustments for certain acquisitions and dispositions completed and capital projects undertaken during the relevant period. Other covenants restrict MPLX and/or certain of its subsidiaries from incurring debt, creating liens on our assets and entering into transactions with affiliates. As of December 31, 2019 , MPLX was in compliance with the covenants contained in the MPLX Credit Agreement. During the year ended December 31, 2019 , MPLX borrowed $5,310 million under the MPLX Credit Agreement, at a weighted average interest rate of 3.547 percent , and repaid $5,310 million of these borrowings. At December 31, 2019 , MPLX had no outstanding borrowings under the new facility and less than $1 million in letters of credit outstanding under this facility, resulting in total availability of $3.5 billion , or almost 100.0 percent of the borrowing capacity . During the year ended December 31, 2018 , MPLX borrowed $1,410 million under the MPLX Credit Agreement, at a weighted average interest rate of 3.464 percent , and repaid $1,915 million of these borrowings. At December 31, 2018 , MPLX had no outstanding borrowings and $3 million in letters of credit outstanding under this facility, resulting in total availability of $2.2 billion , or 99.9 percent of the borrowing capacity. ANDX Credit Facilities Prior to the Merger, ANDX had revolving credit facilities (the “ANDX credit facilities”) totaling $2.1 billion in borrowing capacity which were set to mature January 29, 2021. The ANDX credit facilities were terminated upon closing of the Merger and repaid with borrowings under the MPLX revolving credit facility. During the year ended December 31, 2019 , there were borrowings of $864 million under the ANDX credit facilities, at an average interest rate of 4.129 percent , and repayments of $2.1 billion . On October 1, 2018, the date on which common control was established, there were outstanding borrowings on the ANDX credit facilities of $1.1 billion . From October 1, 2018 through December 31, 2018, ANDX borrowed $760 million at an average interest rate of 4.061 percent and repaid $635 million , resulting in a balance of $1.2 billion at December 31, 2018. Term Loan Agreement On September 26, 2019, MPLX entered into a Term Loan Agreement, which provides for a committed term loan facility for up to an aggregate of $1 billion . Borrowings under the Term Loan Agreement bear interest, at MPLX’s election, at either (i) the Adjusted LIBO Rate (as defined in the Term Loan Agreement) plus a margin ranging from 75.0 basis points to 100.0 basis points per annum, depending on MPLX’s credit ratings, or (ii) the Alternate Base Rate (as defined in the Term Loan Agreement) . The proceeds from borrowings under the Term Loan Agreement are to be used to fund the repayment of MPLX’s existing indebtedness and/or for general business purposes. Amounts borrowed under the Term Loan Agreement will be due and payable on September 26, 2021 . As of December 31, 2019 , MPLX had drawn $1.0 billion on the term loan at an average interest rate of 2.561 percent . The Term Loan Agreement contains representations and warranties, affirmative and negative covenants and events of default that we consider to be customary for an agreement of this type and are substantially similar to those contained in the MPLX Credit Agreement, including a covenant that requires MPLX’s ratio of Consolidated Total Debt to Consolidated EBITDA (as both terms are defined in the Term Loan Agreement) for the four prior fiscal quarters not to exceed 5.0 to 1.0 as of the last day of each fiscal quarter (or during the six-month period following certain acquisitions, 5.5 to 1.0 ). Consolidated EBITDA is subject to adjustments for certain acquisitions completed and capital projects undertaken during the relevant period. Floating Rate Senior Notes On September 9, 2019, MPLX issued $2.0 billion aggregate principal amount of floating rate senior notes in a public offering, consisting of $1.0 billion aggregate principal amount of notes due September 2021 and $1.0 billion aggregate principal amount of notes due September 2022 (collectively, the “Floating Rate Senior Notes”). The Floating Rate Senior Notes were offered at a price to the public of 100 percent of par. The Floating Rate Senior Notes are callable, in whole or in part, at par plus accrued and unpaid interest at any time on or after September 10, 2020. The net proceeds were used to repay MPLX’s existing indebtedness and/or for general business purposes. Interest on the Floating Rate Senior Notes is payable quarterly in March, June, September and December, commencing on December 9, 2019. The interest rate applicable to the floating rate senior notes due September 2021 is LIBOR plus 0.9 percent per annum . The interest rate applicable to the floating rate senior notes due September 2022 is LIBOR plus 1.1 percent per annum . Fixed Rate Senior Notes Interest on each series of MPLX LP, MarkWest and ANDX senior notes is payable semi-annually in arrears, according to the table below. Senior Notes Interest payable semi-annually in arrears 6.250% senior notes due October 2022 April 15 th and October 15 th 3.500% senior notes due December 2022 June 1 st and December 1 st 3.375% senior notes due March 2023 March 15 th and September 15 th 4.500% senior notes due July 2023 January 15 th and July 15 th 6.375% senior notes due May 2024 May 1 st and November 1 st 4.875% senior notes due December 2024 June 1 st and December 1 st 5.250% senior notes due January 2025 January 15 th and July 15 th 4.000% senior notes due February 2025 February 15 th and August 15 th 4.875% senior notes due June 2025 June 1 st and December 1 st 4.125% senior notes due March 2027 March 1 st and September 1 st 4.250% senior notes due December 2027 June 1 st and December 1 st 4.000% senior notes due March 2028 March 15 th and September 15 th 4.800% senior notes due February 2029 February 15 th and August 15 th 4.500% senior notes due April 2038 April 15 th and October 15 th 5.200% senior notes due March 2047 March 1 st and September 1 st 5.200% senior notes due December 2047 June 1 st and December 1 st 4.700% senior notes due April 2048 April 15 th and October 15 th 5.500% senior notes due February 2049 February 15 th and August 15 th 4.900% senior notes due April 2058 April 15 th and October 15 th In connection with the Merger, MPLX assumed ANDX’s outstanding senior notes, which had an aggregate principal amount of $3.75 billion , interest rates ranging from 3.5 percent to 6.375 percent and maturity dates ranging from 2019 to 2047. On September 23, 2019, $3.06 billion aggregate principal amount of ANDX’s outstanding senior notes were exchanged for an aggregate principal amount of $3.06 billion unsecured senior notes (the “Exchange Notes”) issued by MPLX in an exchange offer and consent solicitation undertaken by MPLX, leaving $690 million aggregate principal of outstanding senior notes issued by ANDX. Of this, $500 million aggregate principal amount is related to ANDX 5.5 percent senior notes due 2019. The aggregate principal amount of $500 million and accrued interest of $13.75 million was paid on October 15, 2019 using net proceeds from the Floating Rate Senior Notes and borrowings under the Term Loan Agreement discussed above and includes interest through the payoff date. The Exchange Notes consist of $266 million in aggregate principal amount of 6.25 percent senior notes due October 2022, $486 million in aggregate principal amount of 3.5 percent senior notes due December 2022, $381 million in aggregate principal amount of 6.375 percent senior notes due May 2024, $708 million in aggregate principal amount of 5.25 percent senior notes due January 2025, $732 million in aggregate principal amount of 4.25 percent senior notes due December 2027 and $487 million in aggregate principal amount of 5.2 percent senior notes due December 2047. Interest on each series of Exchange Notes is payable semi-annually in arrears according to the table above. On December 10, 2018, MPLX redeemed all of the $750 million aggregate principal amount of 5.5 percent senior notes due February 15, 2023, $40 million of which was issued by the MarkWest subsidiary. These notes were redeemed at 101.833 percent of the aggregate principal amount, which resulted in a payment of $14 million related to the note premium and the immediate recognition of $46 million of unamortized debt issuance costs. On November 15, 2018, MPLX issued $2.25 billion aggregate principal amount of senior notes in a public offering, consisting of $750 million aggregate principal amount of 4.8 percent senior notes due February 2029 and $1.5 billion aggregate principal amount of 5.5 percent senior notes due February 2049 (collectively, the “November 2018 New Senior Notes”). The November 2018 New Senior Notes were offered at a price to the public of 99.432 percent and 98.031 percent of par, respectively. The net proceeds were used to repay outstanding borrowings under the MPLX Credit Agreement and the MPC Loan Agreement and to redeem the $750 million aggregate principal amount of 5.5 percent senior notes due February 2023, as well as for general business purposes. Interest on each series of notes in the November 2018 New Senior Notes is payable semi-annually in arrears, commencing on February 15, 2019. On February 8, 2018 , MPLX issued $5.5 billion aggregate principal amount of senior notes in a public offering, consisting of $500 million aggregate principal amount of 3.375 percent senior notes due March 2023 , $1.25 billion aggregate principal amount of 4.0 percent senior notes due March 2028 , $1.75 billion aggregate principal amount of 4.5 percent senior notes due April 2038 , $1.5 billion aggregate principal amount of 4.7 percent senior notes due April 2048 , and $500 million aggregate principal amount of 4.9 percent senior notes due April 2058 (collectively, the “February 2018 New Senior Notes”). The February 2018 New Senior Notes were offered at a price to the public of 99.931 percent , 99.551 percent , 98.811 percent , 99.348 percent , and 99.289 percent of par, respectively. Also on February 8, 2018 , $4.1 billion of the net proceeds from the offering were used to repay the 364-day term loan facility, which was drawn on February 1, 2018 to fund the cash portion of the dropdown consideration for Refining Logistics and Fuels Distribution. The remaining net proceeds were used to repay outstanding borrowings under the MPLX Credit Agreement and the MPC Loan Agreement, as well as for general business purposes. Interest on each series of notes due in 2023 and 2028 is payable semi-annually in arrears, commencing on September 15, 2018. Interest on each series of notes due in 2038, 2048 and 2058 is payable semi-annually in arrears, commencing on October 15, 2018. SMR Transaction On September 1, 2009, MarkWest completed the sale of the SMR (the “SMR Transaction”). At that time, MarkWest had begun constructing the SMR at its Javelina gas processing and fractionation complex in Corpus Christi, Texas. Under the terms of the agreement, MarkWest received proceeds of $73 million and the purchaser completed the construction of the SMR. MarkWest and the purchaser also executed a related product supply agreement under which MPLX will receive the entire product produced by the SMR through 2030 in exchange for processing fees and the reimbursement of certain other expenses. The processing fee payments began when the SMR commenced operations in March 2010. MarkWest was deemed to have continuing involvement with the SMR as a result of certain provisions in the related agreements. Therefore, the transaction is treated as a financing arrangement under GAAP. MPLX imputes interest on the SMR liability at 6.39 percent annually, its incremental borrowing rate at the time of the purchase accounting valuation. Each processing fee payment has multiple elements: reduction of principal of the SMR liability, interest expense associated with the SMR liability and facility expense related to the operation of the SMR. As part of purchase accounting, the SMR Transaction has been recorded at fair value. As of December 31, 2019 and 2018 , the following amounts related to the SMR are included in the accompanying Consolidated Balance Sheets: December 31, (In millions) 2019 2018 Assets Property, plant and equipment, net $ 46 $ 51 Liabilities Other current liabilities 5 5 Deferred credits and other liabilities $ 75 $ 81

Revenue Revenue

Revenue Revenue	12 Months Ended
	Dec. 31, 2019
Revenue from Contract with Customer [Abstract]
Revenue from Contract with Customer [Text Block]	Revenue Disaggregation of Revenue The following table represents a disaggregation of revenue for each reportable segment for the years ended December 31, 2019 and 2018 : 2019 (In millions) L&S G&P Total Revenues and other income: Service revenue $ 346 $ 2,152 $ 2,498 Service revenue - related parties 3,419 36 3,455 Service revenue - product related — 140 140 Product sales (1) 65 741 806 Product sales - related parties 26 116 142 Total revenues from contracts with customers $ 3,856 $ 3,185 7,041 Non-ASC 606 revenue (2) 2,000 Total revenues and other income $ 9,041 2018 (In millions) L&S G&P Total Revenues and other income: Service revenue $ 174 $ 1,682 $ 1,856 Service revenue - related parties 2,401 3 2,404 Service revenue - product related — 220 220 Product sales (1) 12 870 882 Product sales - related parties 11 76 87 Total revenues from contracts with customers $ 2,598 $ 2,851 5,449 Non-ASC 606 revenue (2) 1,556 Total revenues and other income $ 7,005 (1) G&P “Product sales” for the year ended December 31, 2018 was adjusted in the table above by $5 million related to derivative gains and mark-to-market adjustments. There were no adjustments for the year ended December 31, 2019 . (2) Non-ASC 606 Revenue includes rental income, income from equity method investments, derivative gains and losses, mark-to-market adjustments, and other income. Contract Balances Contract assets typically relate to aid in construction agreements where the revenue recognized and MPLX’s rights to consideration for work completed exceeds the amount billed to the customer. Contract assets are generally classified as current and included in “Other current assets” on the Consolidated Balance Sheets. Contract liabilities, which we refer to as “Deferred revenue” and “Long-term deferred revenue,” typically relate to advance payments for aid in construction agreements and deferred customer credits associated with makeup rights and minimum volume commitments. Related to minimum volume commitments, breakage is estimated and recognized into service revenue in instances where it is probable the customer will not use the credit in future periods. We classify contract liabilities as current or long-term based on the timing of when we expect to recognize revenue. “Receivables, net” primarily relate to our commodity sales. Portions of the “Receivables, net” balance are attributed to the sale of commodity product controlled by MPLX prior to sale while a significant portion of the balance relates to the sale of commodity product on behalf of our producer customers. The sales and related “Receivables, net” are commingled and excluded from the table below. MPLX remits the net sales price back to our producer customers upon completion of the sale. Each period end, certain amounts within accounts payable relate to our payments to producer customers. Such amounts are not deemed material at period end as a result of when we settle with each producer. The table below reflects the changes in our contract balances for the years ended December 31, 2019 and 2018 : (In millions) Balance at December 31, 2018 (1) Additions/ (Deletions) Revenue Recognized (2) Balance at December 31, 2019 Contract assets $ 36 $ 5 $ (2 ) $ 39 Deferred revenue 13 17 (7 ) 23 Deferred revenue - related parties 65 55 (67 ) 53 Long-term deferred revenue 56 34 — 90 Long-term deferred revenue - related parties $ 52 $ 3 $ — $ 55 (In millions) Balance at January 1, 2018 (1) Additions/ (Deletions) (3) Revenue Recognized (2) Balance at December 31, 2018 Contract assets $ 4 $ 32 $ — $ 36 Deferred revenue 5 19 (11 ) 13 Deferred revenue - related parties 42 60 (37 ) 65 Long-term deferred revenue 5 51 — 56 Long-term deferred revenue - related parties $ 43 $ 9 $ — $ 52 (1) Balance represents ASC 606 portion of each respective line item. (2) No significant revenue was recognized related to past performance obligations for the years ended December 31, 2019 and 2018 . (3) Includes opening balances related to the Merger. Remaining Performance Obligations The table below includes estimated revenue expected to be recognized in the future related to performance obligations that are unsatisfied (or partially unsatisfied) at the end of the reporting period. As of December 31, 2019 , the amounts allocated to contract assets and contract liabilities on the Consolidated Balance Sheets are $220 million and are reflected in the amounts below. This will be recognized as revenue as the obligations are satisfied, which is expected to occur over the next 24 years . Further, MPLX does not disclose variable consideration due to volume variability in the table below. (In millions) 2020 $ 1,717 2022 1,693 2022 1,640 2023 1,555 2024 and thereafter 5,317 Total revenue on remaining performance obligations (1)(2)(3) $ 11,922 (1) All fixed consideration from contracts with customers is included in the amounts presented above. Variable consideration that is constrained or not required to be estimated as it reflects our efforts to perform is excluded. (2) Arrangements deemed implicit leases are included in “Rental income” and are excluded from this table. (3) Only minimum volume commitments that are deemed fixed are included in the table above. MPLX has various minimum volume commitments in processing arrangements that vary based on the actual Btu content of the gas received. These amounts are deemed variable consideration and are excluded from the table above. We do not disclose information on the future performance obligations for any contract with an original expected duration of one year or less.

Supplemental Cash Flow Informat

Supplemental Cash Flow Information	12 Months Ended
	Dec. 31, 2019
Supplemental Cash Flow Elements [Abstract]
Supplemental Cash Flow Information	Supplemental Cash Flow Information December 31, (In millions) 2019 2018 Cash and cash equivalents $ 15 $ 77 Restricted cash (1) — 8 Cash, cash equivalents and restricted cash $ 15 $ 85 (1) The restricted cash balance is included within “Other current assets” on the Consolidated Balance Sheets. (In millions) 2019 2018 2017 Net cash provided by operating activities included: Interest paid (net of amounts capitalized) $ 835 $ 568 $ 263 Income taxes paid 1 1 3 Cash paid for amounts included in the measurement of lease liabilities Payments on operating leases 85 — — Interest payment under finance lease obligations 1 — — Net cash provided by financing activities included Principal payments under finance lease obligations 5 — — Non-cash investing and financing activities: Net transfers of property, plant and equipment from materials and supplies inventories 2 2 6 MPLX terminal lease classification change 21 — — ROU assets obtained in exchange for new operating lease obligations 26 — — ROU assets obtained in exchange for new finance lease obligations 4 — — Contribution - fixed assets to joint venture (1) — — 337 Contribution - common units issued (2) $ 7,722 $ 4,236 $ 1,133 (1) Contribution of assets to Sherwood Midstream and Sherwood Midstream Holdings. (2) For 2017, includes limited and general partner units issued to MPC as consideration in the acquisitions of the joint-interests, HST, WHC and MPLXT. For 2018, includes limited and general partner units issued to MPC as consideration in the acquisition of Refining Logistics and Fuels Distribution. For 2019, includes limited partner units issued to MPC and public unitholders as consideration in the Merger. See Note 4 . At December 31, 2017, “Payables - related parties” per the Consolidated Balance Sheets included an $11 million payable to MPC for distributions of cash received from Joint-Interest Acquisition entities that did not affect cash. The Consolidated Statements of Cash Flows exclude changes to the Consolidated Balance Sheets that did not affect cash. The following is the change of additions to property, plant and equipment related to capital accruals: (In millions) 2019 2018 2017 Increase/(decrease) in capital accruals $ (146 ) $ 135 $ 71

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income Accumulated Other Comprehensive Income	12 Months Ended
	Dec. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]	Accumulated Other Comprehensive Loss MPLX records an accumulated other comprehensive loss on the Consolidated Balance Sheets relating to pension and other post-retirement benefits provided by LOOP and Explorer to their employees. MPLX is not a sponsor of these benefit plans. As a transfer between entities under common control, MPLX recorded the Joint-Interest Acquisition from MPC on the Consolidated Balance Sheets at MPC’s historical basis, which included accumulated other comprehensive loss. MPLX’s assumption of the accumulated other comprehensive loss balance had no effect on MPLX’s comprehensive income during the period as the balance was accumulated while under the ownership of MPC. The following table shows the changes in “Accumulated other comprehensive loss” by component during the period December 31, 2017 through December 31, 2019 : (In millions) Pension Benefits Other Post-Retirement Benefits Total Balance at December 31, 2017 (1) $ (13 ) $ (1 ) $ (14 ) Other comprehensive loss - remeasurements (2) (1 ) (1 ) (2 ) Balance at December 31, 2018 (1) (14 ) (2 ) (16 ) Other comprehensive income - remeasurements (2) — 1 1 Balance as of December 31, 2019 (1) $ (14 ) $ (1 ) $ (15 ) (1) These components of “Accumulated other comprehensive loss” are included in the computation of net periodic benefit cost by LOOP and Explorer and are therefore included on the Consolidated Statements of Income under the caption “Income/(loss) from equity method investments.” (2)

Equity-Based Compensation

Equity-Based Compensation	12 Months Ended
	Dec. 31, 2019
Share-based Payment Arrangement [Abstract]
Equity-Based Compensation	Equity-Based Compensation Description of the Plan Effective March 15, 2018 , the MPLX LP 2012 Incentive Compensation Plan (“MPLX 2012 Plan”) was replaced by the MPLX LP 2018 Incentive Compensation Plan (“MPLX 2018 Plan”). The MPLX 2018 Plan will continue in effect until February 28, 2028 , unless terminated earlier. Subject to customary anti-dilution adjustments, the MPLX 2018 Plan allows for no more than 16 million common units representing limited partnership interests in MPLX to be delivered under the plan. The MPLX LP 2012 Plan allowed for no more than 2.75 million MPLX LP common limited partner units to be delivered. Consistent with the MPLX 2012 Plan, the MPLX 2018 Plan authorizes the MPLX GP board of directors (the “Board”) to grant unit options, unit appreciation rights, restricted units and phantom units, distribution equivalent rights, unit awards, profits interest units, performance units and other unit-based awards to the employees, officers and directors of the General Partner, MPLX, or any of their affiliates, including MPC. Common units delivered pursuant to an award granted under the MPLX 2018 Plan may be newly issued common units or acquired in the open market or from any other person, including an affiliate of MPLX, as determined by the Board. Unit-based Awards under the Plan MPLX expenses all unit-based payments to employees and non-employee directors based on the grant date fair value of the awards over the requisite service period, adjusted for estimated forfeitures. Phantom Units – MPLX has granted phantom units under the MPLX 2018 Plan and the MPLX 2012 Plan to non-employee directors of MPLX LP’s general partner and of MPC. Awards to non-employee directors are accounted for as non-employee awards. Phantom units granted to non-employee directors vest immediately at the time of the grant, as they are non-forfeitable, but are not issued until the director’s departure from the board of directors. Prior to issuance, non-employee directors do not have the right to vote such units and cash distribution equivalents accrue in the form of additional phantom units and will be issued when the director departs from the board of directors. MPLX has granted phantom units under the MPLX 2018 Plan and the MPLX 2012 Plan to certain officers and non-officers of MPLX, MPLX’s general partner and MPC who make significant contributions to our business. These grants are accounted for as employee awards. In general, these phantom units will vest over a requisite service period of up to three years . Prior to vesting, these phantom unit recipients will not have the right to vote such units and cash distributions declared will be accrued and paid upon vesting. The accrued distributions at December 31, 2019 and 2018 were $6 million and $4 million , respectively. The fair values of phantom units are based on the fair value of MPLX common units on the grant date. Performance Units – MPLX has granted performance units under the MPLX 2018 Plan and the MPLX 2012 Plan to certain officers of the general partner and certain eligible MPC officers who make significant contributions to our business. Performance units are designed to pay out 75 percent in cash and 25 percent in MPLX common units. The performance units paying out in cash are accounted for as liability awards and recorded at fair value with a mark-to-market adjustment made each quarter. The performance units paying out in units are accounted for as equity awards. The performance units granted in 2017 are hybrid awards having a three-year performance period of January 1, 2017 through December 31, 2019. The payout of the award is dependent on two independent conditions, each constituting 50 percent of the overall target units granted. The awards have a performance condition based on MPLX’s DCF during the last twelve months of the performance period, and a market condition based on MPLX’s total unitholder return over the entire three-year performance period. During the first quarter of 2018, a performance award was granted; however, a grant date could not be established based on the nature of the award terms. Given that a grant date cannot be established, no expense or units have been recorded. When a grant date is established, the fair value of the award will be recognized over the remaining service period. The performance units granted in 2019 are hybrid awards having a three-year performance period of January 1, 2019 through December 31, 2021. The payout of the award is dependent on two independent conditions, each constituting 50 percent of the overall target units granted. The awards have a performance condition based on MPLX’s DCF during the performance period and a market condition based on MPLX’s total unitholder return over the performance period. The market condition was valued using a Monte Carlo valuation, resulting in a grant date fair value of $0.68 per unit for the 2019 equity-classified performance units. Grant date fair value of the performance condition is based on potential payouts per unit of up to $2.00 per unit. Compensation cost associated with the performance condition is based on the grant date fair value of the payout deemed most probable to occur and is adjusted as the expectation for payout changes. Outstanding Phantom Unit Awards The following is a summary of phantom unit award activity of MPLX common units in 2019 : Phantom Units Number of Units Weighted Average Fair Value Aggregate Intrinsic Value (In millions) Outstanding at December 31, 2018 1,154,335 $ 34.34 Granted 219,488 32.62 Legacy ANDX phantom units converted to MPLX phantom units at the Merger 208,533 43.64 Settled (426,451 ) 33.84 Forfeited (46,337 ) 33.63 Outstanding at December 31, 2019 1,109,568 35.97 Vested and expected to vest at December 31, 2019 1,104,552 35.98 $ 28 Non-forfeitable at December 31, 2019 (1) 507,471 $ 37.32 $ 13 (1) Represents a subset of phantom units held by our non-employee directors and certain of our officers and non-officer employees that are generally non-forfeitable and that would be paid out as common units upon the holder’s separation from service. The following is a summary of the values related to phantom units: Phantom Units Intrinsic Value of Units Issued During the Period (in millions) Weighted Average Grant Date Fair Value of Units Granted During the Period 2019 $ 14 $ 32.62 2018 18 33.84 2017 $ 15 $ 36.26 As of December 31, 2019 , unrecognized compensation cost related to phantom unit awards was $9 million , which is expected to be recognized over a weighted average period of 1.3 years . Outstanding Performance Unit Awards The following table presents a summary of the 2019 activity for performance unit awards to be settled in MPLX common units: Performance Units Number of Units Weighted Outstanding at December 31, 2018 1,941,750 $ 0.80 Granted 987,994 0.76 Settled (772,397 ) 0.63 Forfeited — — Outstanding at December 31, 2019 2,157,347 $ 0.84 The number of common units that would be issued upon target vesting, using the closing price of our common units on December 31, 2019 would be 84,735 common units. As of December 31, 2019 , unrecognized compensation cost related to equity-classified performance unit awards was $1 million which is expected to be recognized over a weighted average period of 2.0 years . Performance units paying out in MPLX common units have a grant date fair value calculated using a Monte Carlo valuation model, which requires the input of subjective assumptions. The following table provides a summary of the weighted average inputs used for these assumptions: 2019 2018 2017 Risk-free interest rate 2.51% N/A 1.52% Look-back period 2.84 years N/A 2.83 years Expected volatility 25.01% N/A 49.34% Grant date fair value of performance units granted $0.76 N/A $0.90 The assumption for expected volatility of our unit price reflects the historical volatility of MPLX common units. The look-back period reflects the remaining performance period at the grant date. The risk-free interest rate for the remaining performance period as of the grant date is based on the U.S. Treasury yield curve in effect at the time of the grant. No grant date fair value has been calculated for performance units granted in 2018, since due to the award terms, a grant date has not yet been established. Total Unit-Based Compensation Expense Total unit-based compensation expense for awards settling in MPLX common units was $22 million in 2019 , $24 million in 2018 and $18 million in 2017 . MPC’s Stock-based Compensation Stock-based compensation expenses charged to MPLX under our employee services agreement with MPC were $10 million , $8 million and $2 million for 2019 , 2018 and 2017 , respectively.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies MPLX is 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 MPLX has not recorded an accrued liability, MPLX is unable to estimate a range of possible losses for the reasons discussed in more detail below. However, the ultimate resolution of some of these contingencies could, individually or in the aggregate, be material. Environmental Matters – MPLX is subject to federal, state and local 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. Penalties may be imposed for non-compliance. At December 31, 2019 and 2018 , accrued liabilities for remediation totaled $19 million and $20 million , respectively. However, it is not presently possible to estimate the ultimate amount of all remediation costs that might be incurred or the penalties, if any, which may be imposed. At December 31, 2019 and 2018 , there were no balances with MPC for indemnification of environmental costs. MarkWest Liberty Midstream, Ohio Fractionation and MarkWest Utica EMG, together with other MarkWest affiliates, agreed to pay a penalty of approximately $0.9 million , undertake certain monitoring and emission reduction projects at certain facilities with an estimated cost of approximately $3.3 million , and implement certain process enhancements for its and its affiliates’ leak detection and repair programs at its gas processing and fractionation sites. On November 1, 2018, MPLX and 11 of its subsidiaries entered into a Consent Decree with the EPA, the State of Oklahoma, the Pennsylvania Department of Environmental Protection and the State of West Virginia resolving these issues. The Consent Decree was approved by the court on January 8, 2019 and the penalty has been paid. MPLX is involved in environmental enforcement matters arising in the ordinary course of business. While the outcome and impact on MPLX cannot be predicted with certainty, management believes the resolution of these environmental matters will not, individually or collectively, have a material adverse effect on its consolidated results of operations, financial position or cash flows. Other Lawsuits – MPLX, MarkWest, MarkWest Liberty Midstream, MarkWest Liberty Bluestone, L.L.C., Ohio Fractionation and MarkWest Utica EMG (collectively, the “MPLX Parties”) were parties to various lawsuits with Bilfinger Westcon, Inc. (“Westcon”) that were instituted in 2016 and 2017 in the Court of Common Pleas in Butler County, Pennsylvania, the Circuit Court in Wetzel County, West Virginia, and the Court of Common Pleas in Harrison County, Ohio. The lawsuits related to disputes regarding construction work performed by Westcon at the Bluestone, Mobley and Cadiz processing complexes in Pennsylvania, West Virginia and Ohio, respectively, and the Hopedale fractionation complex in Ohio. As previously disclosed in our Quarterly Report on Form 10-Q for the quarter ended June 30, 2019, in July 2019, Westcon and the MPLX Parties reached an agreement to resolve the disputes among those parties relating to the Bluestone processing complex in Pennsylvania. In the quarter ended December 31, 2019, Westcon and the MPLX Parties reached agreements to resolve the remaining disputes among those parties relating to the Mobley and Cadiz processing complexes in West Virginia and Ohio, respectively, and the Hopedale fractionation complex in Ohio. The settlements will not have a material adverse effect on MPLX’s consolidated financial position, results of operations or cash flows. MPLX is 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. While it is possible that an adverse result in one or more of the lawsuits or proceedings in which we are a defendant could be material to us, based upon current information and our experience as a defendant in other matters, we believe that these lawsuits and proceedings, individually or in the aggregate, will not have a material adverse effect on our consolidated results of operations, financial position or cash flows. Guarantees – Over the years, MPLX has sold various assets in the normal course of its 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 MPLX to perform upon the occurrence of a triggering event or condition. These guarantees and indemnifications are part of the normal course of selling assets. MPLX is 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. In connection with our approximate 9 percent indirect interest in a joint venture that owns and operates the Dakota Access Pipeline and Energy Transfer Crude Oil Pipeline projects, collectively referred to as the Bakken Pipeline system, we have entered into a Contingent Equity Contribution Agreement whereby MPLX LP, along with the other joint venture owners in the Bakken Pipeline system, have agreed to make equity contributions to the joint venture upon certain events occurring to allow the entities that own and operate the Bakken Pipeline system to satisfy their senior note payment obligations. The senior notes were issued to repay amounts owed by the pipeline companies to fund the cost of construction of Bakken Pipeline system. At December 31, 2019 , our maximum potential undiscounted payments under the Contingent Equity Contribution Agreement was approximately $230 million . Contractual Commitments and Contingencies – At December 31, 2019 , MPLX’s contractual commitments to acquire property, plant and equipment totaled $753 million . These commitments were primarily related to G&P plant expansion, terminal, pipeline and refining logistics projects. In addition, from time to time and in the ordinary course of business, MPLX and its affiliates provide guarantees of MPLX’s subsidiaries payment and performance obligations in the G&P segment. Certain natural gas processing and gathering arrangements require MPLX to construct new 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 producers may have the right to cancel the processing arrangements if there are significant delays that are not due to force majeure. As of December 31, 2019 , management does not believe there are any indications that MPLX will not be able to meet the construction milestones, that force majeure does not apply or that such fees and charges will otherwise be triggered. Other Contractual Obligations – MPLX executed transportation and terminalling agreements that obligate us to minimum volume, throughput or payment commitments over the terms of the agreements, which range from four to 20 years . After the minimum volume commitments are met in the transportation and terminalling agreements, MPLX pays additional amounts based on throughput. There are escalation clauses in the transportation and terminalling agreements, which are based on Consumer Price Index adjustments. The minimum future payments under these agreements as of December 31, 2019 are as follows: (In millions) 2020 $ 2,246 2021 2,222 2022 2,199 2023 2,200 2024 1,753 2025 and thereafter 191 Total $ 10,811 SMR Transaction – On September 1, 2009, MarkWest entered into a product supply agreement creating a long-term contractual obligation for the payment of processing fees in exchange for the entire product processed by the SMR. See Note 17 for additional discussion. The product received under this agreement is sold to a refinery customer pursuant to a corresponding long-term agreement. The minimum amounts payable annually under the product supply agreement, excluding the potential impact of inflation adjustments per the agreement, are as follows: (In millions) 2020 $ 17 2021 17 2022 17 2023 17 2024 17 2024 and thereafter 92 Total minimum payments 177 Less: Services element 68 Less: Interest 29 Total SMR liability 80 Less: Current portion of SMR liability 5 Long-term portion of SMR liability $ 75

Select Quarterly Financial Data

Select Quarterly Financial Data	12 Months Ended
	Dec. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Select Quarterly Financial Data	Select Quarterly Financial Data (Unaudited) 2019 (In millions, except per unit data) 1st Qtr. (1) 2nd Qtr. (1) 3rd Qtr. 4th Qtr. Total revenues and other income $ 2,235 $ 2,210 $ 2,280 $ 2,316 Income from operations 912 885 926 (346 ) Net income 689 657 689 (573 ) Net income attributable to MPLX LP 503 482 629 (581 ) Net income attributable to MPLX LP per limited partner unit: Common - basic 0.61 0.56 0.61 (0.58 ) Common - diluted 0.61 0.55 0.61 (0.58 ) Cash distributions declared per limited partner common unit 0.6575 0.6675 0.6775 0.6875 Distributions declared: Limited partner units - Public 191 261 266 270 Limited partner units - MPC 332 431 438 446 Series A preferred units 20 21 20 20 Series B preferred units — 21 10 11 Total distributions declared $ 543 $ 734 $ 734 $ 747 2018 (In millions, except per unit data) 1st Qtr. 2nd Qtr. 3rd Qtr. 4th Qtr. (1) Total revenues and other income $ 1,420 $ 1,578 $ 1,712 $ 2,295 Income from operations 557 608 672 891 Net income 423 456 516 611 Net income attributable to MPLX LP 421 453 510 434 Net income attributable to MPLX LP per limited partner unit: Common - basic 0.61 0.55 0.62 0.52 Common - diluted 0.61 0.55 0.62 0.52 Cash distributions declared per limited partner common unit 0.6175 0.6275 0.6375 0.6475 Distributions declared: Limited partner units - Public 179 181 185 187 Limited partner units - MPC 288 316 322 327 Series A preferred units 16 20 19 20 Total distributions declared $ 483 $ 517 $ 526 $ 534 (1) As discussed in Note 1, MPLX’s acquisition of ANDX is considered a transfer between entities under common control due to MPC’s prior relationship with ANDX. Transfers of businesses between entities under common control require prior periods to be retrospectively adjusted for those dates that the entity was under common control. Accordingly, the tables above include the historical results of ANDX beginning October 1, 2018. Amounts shown for the fourth quarter of 2018 as well as the first and second quarters of 2019 are different than amounts previously reported for Total revenues and other income, Income from operations and Net income as a results of this retrospective adjustment for ANDX. Total revenues and other income originally reported for the fourth quarter of 2018 and the first and second quarters of 2019 was $1,715 million , $1,646 million and $1,629 million , respectively. Income from operations originally reported for the fourth quarter of 2018 and the first and second quarters of 2019 was $666 million , $678 million and $659 million , respectively. Net income originally reported for the fourth quarter of 2018 and the first and second quarters of 2019 was $439 million , $509 million and $488 million , respectively.

Description of the Business a_2

Description of the Business and Basis of Presentation (Policies)	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Basis of presentation	Basis of Presentation – The consolidated financial statements include all majority-owned and controlled subsidiaries. For non-wholly-owned consolidated subsidiaries, the interests owned by third parties have been recorded as “Noncontrolling interests” on the accompanying Consolidated Balance Sheets. Intercompany investments, accounts and transactions have been eliminated. MPLX’s investments in which MPLX exercises significant influence but does not control and does not have a controlling financial interest are accounted for using the equity method. MPLX’s investments in a VIE in which MPLX exercises significant influence but does not control and is not the primary beneficiary are also accounted for using the equity method. In relation to the Merger described above and in Note 4 , ANDX’s assets, liabilities and results of operations prior to the Merger are collectively included in what we refer to as the “Predecessor” from October 1, 2018, which was the date that MPC acquired Andeavor. MPLX’s acquisition of ANDX is considered a transfer between entities under common control due to MPC’s relationship with ANDX prior to the Merger. As an entity under common control with MPC, MPLX recorded the assets acquired and liabilities assumed on its consolidated balance sheets at MPC’s historical carrying value. Transfers of businesses between entities under common control require prior periods to be retrospectively adjusted for those dates that the entity was under common control. Accordingly, the accompanying financial statements and related notes of MPLX LP have been retrospectively adjusted to include the historical results of ANDX beginning October 1, 2018. Certain prior period financial statement amounts have been reclassified to conform to current period presentation. The accompanying consolidated financial statements of MPLX have been prepared in accordance with GAAP.

Summary of Principal Accounti_2

Summary of Principal Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2019
Accounting Policies [Abstract]
Use of estimates	Use of Estimates – The preparation of financial statements in accordance with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities as of the date of the consolidated financial statements and the reported amounts of revenues and expenses during the respective reporting periods. Actual results could differ materially from those estimates. Estimates are subject to uncertainties due to the levels of subjectivity and judgment necessary to account for highly uncertain matters or the susceptibility of such matters to change and affect items such as valuing identified intangible assets; determining the fair value of derivative instruments; evaluating impairments of long-lived assets, goodwill and equity investments; establishing estimated useful lives for long-lived assets; acquisition accounting; recognizing share-based compensation expense; estimating revenues, expense accruals and capital expenditures; valuing AROs; and determining liabilities, if any, for environmental and legal contingencies.
Revenue recognition	Revenue Recognition – Revenue is measured based on consideration specified in a contract with a customer. MPLX recognizes revenue when it satisfies a performance obligation by transferring control over a product or providing services to a customer. MPLX enters into a variety of contract types in order to generate “Product sales” and “Service revenue.” MPLX provides services under the following types of arrangements: • Fee-based arrangements – Under fee-based arrangements, MPLX receives a fee or fees for one or more of the following services: gathering, processing and transportation of natural gas; gathering, transportation, fractionation, exchange and storage of NGLs; and transportation, storage and distribution of crude oil, refined products and other hydrocarbon-based products. The revenue MPLX earns from these arrangements is generally directly related to the volume of natural gas, NGLs, refined products or crude oil that is handled by or flows through MPLX’s systems and facilities and is not normally directly dependent on commodity prices. In certain cases, MPLX’s arrangements provide for minimum annual payments or fixed demand charges. Fee-based arrangements are reported as “Service revenue” on the Consolidated Statements of Income. Revenue is recognized over time as services are performed. In certain instances when specifically stated in the contract terms, MPLX purchases product after fee-based services have been provided. Revenue from the sale of products purchased after services are provided is reported as “Product sales” on the Consolidated Statements of Income and recognized on a gross basis, as MPLX takes control of the product and is the principal in the transaction. • Percent-of-proceeds arrangements – Under percent-of-proceeds arrangements, MPLX: gathers and processes natural gas on behalf of producers; sells the resulting residue gas, condensate and NGLs at market prices; and remits to producers an agreed-upon percentage of the proceeds. In other cases, instead of remitting cash payments to the producer, MPLX delivers an agreed-upon percentage of the residue gas and NGLs to the producer (take-in-kind arrangements) and sells the volumes MPLX retains to third parties or related parties. Revenue is recognized on a net basis when MPLX acts as an agent and does not have control of the gross amount of gas and/or NGLs prior to it being sold. Percent-of-proceeds revenue is reported as “Service revenue - product related” on the Consolidated Statements of Income. • Keep-whole arrangements – Under keep-whole arrangements, MPLX gathers natural gas from the producer, processes the natural gas and sells the resulting condensate and NGLs to third parties at market prices. Because the extraction of the condensate and NGLs from the natural gas during processing reduces the Btu content of the natural gas, MPLX must either purchase natural gas at market prices for return to producers or make cash payment to the producers equal to the value of the energy content of this natural gas. Certain keep-whole arrangements also have provisions that require MPLX to share a percentage of the keep-whole profits with the producers based on the oil to gas ratio or the NGL to gas ratio. “Service revenue - product related” is recorded based on the value of the NGLs received on the date the services are performed. Natural gas purchased to return to the producer and shared NGL profits are recorded as a reduction of “Service revenue - product related” on the Consolidated Statements of Income on the date the services are performed. Sales of NGLs under these arrangements are reported as “Product sales” on the Consolidated Statements of Income and are reported on a gross basis as MPLX is the principal in the arrangement and controls the product prior to sale. The sale of the NGLs may occur shortly after services are performed at the tailgate of the plant, or after a period of time as determined by MPLX. • Purchase arrangements – Under purchase arrangements, MPLX purchases natural gas at either the wellhead or the tailgate of a plant. MPLX then gathers and delivers the natural gas to pipelines where MPLX may resell the natural gas. Wellhead purchase arrangements represent an arrangement with a supplier and are recorded in “Purchased product costs.” Often, MPLX earns fees for services performed prior to taking control of the product in these arrangements and “Service revenue” is recorded for these fees. Revenue generated from the sale of product obtained in tailgate purchase arrangements is reported as “Product sales” on the Consolidated Statements of Income and is recognized on a gross basis as MPLX purchases and takes control of the product prior to sale and is the principal in the transaction. In many cases, MPLX provides services under contracts that contain a combination of more than one of the arrangements described above. When fees are charged (in addition to product received) under percent-of-proceeds arrangements, keep-whole arrangements or purchase arrangements, MPLX records such fees as “Service revenue” on the Consolidated Statements of Income. The terms of MPLX’s contracts vary based on gas quality conditions, the competitive environment when the contracts are signed and customer requirements. Performance obligations are determined based on the specific terms of the arrangements, economics of the geographical regions, and the services offered and whether they are deemed distinct. MPLX allocates the consideration earned between the performance obligations based on the stand-alone selling price when multiple performance obligations are identified. Revenue from MPLX’s service arrangements will generally be recognized over time as the performance obligation is satisfied as services are provided. MPLX has elected to use the output measure of progress to recognize revenue based on the units delivered, processed or transported. The transaction price has 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 each period. In instances in which tiered pricing structures do not reflect our efforts to perform, MPLX will estimate variable consideration at contract inception. “Product sales” will be recognized at a point in time when control of the product transfers to the customer. Minimum volume commitments may create contract liabilities or deferred credits if current period payments can be used for future services. Breakage is estimated and recognized into service revenue in instances where it is probable the customer will not use the credit in future periods. Amounts billed to customers for shipping and handling, electricity, and other costs to perform services are included in “Service revenue” on the Consolidated Statements of Income. Shipping and handling costs associated with product sales are included in “Purchased product costs” on the Consolidated Statements of Income. Facility expenses, costs of revenues and depreciation represent those expenses related to operating our various facilities and are necessary to provide both “Product sales” and “Service revenue.” Customers usually pay monthly based on the products purchased or services performed that month. Taxes collected from customers and remitted to the appropriate taxing authority are excluded from revenue. Based on the terms of certain natural gas gathering, transportation and processing agreements, MPLX is considered to be the lessor under several implicit operating lease arrangements in accordance with GAAP. Revenue and costs related to the portion of the revenue earned under these contracts considered to be implicit leases are recorded as “Rental income” and “Rental cost of sales,” respectively, on the Consolidated Statements of Income.
Revenue and expense accruals	Revenue and Expense Accruals – MPLX routinely makes accruals based on estimates for both revenues and expenses due to the timing of compiling billing information, receiving certain third-party information and reconciling MPLX’s records with those of third parties. The delayed information from third parties includes, among other things, actual volumes purchased, transported or sold, adjustments to inventory and invoices for purchases, actual natural gas and NGL deliveries and other operating expenses. MPLX makes accruals to reflect estimates for these items based on its internal records and information from third parties. Estimated accruals are adjusted when actual information is received from third parties and MPLX’s internal records have been reconciled.
Cash and cash equivalents	Cash and Cash Equivalents – Cash and cash equivalents include cash on hand and on deposit and investments in highly liquid debt instruments with initial maturities of three months or less.
Restricted cash	Restricted Cash – Restricted cash consists of cash and investments that must be maintained as collateral for letters of credit issued to certain third-party producer customers. The balances will be outstanding until certain capital projects are completed and the third party releases the restriction. Restricted cash also consists of cash advances to be used for the operation and maintenance of an operated pipeline system. Restricted cash is included in “ Other current assets ” on the Consolidated Balance Sheets.
Receivables	Receivables – Receivables primarily consist of customer accounts receivable, which are recorded at the invoiced amount and generally do not bear interest. Allowances for doubtful accounts are generally recorded when it becomes probable that the receivable will not be collected and are recorded to bad debt expense. We review the allowance quarterly with past-due balances over 90 days and other higher-risk amounts being reviewed individually for collectability. Balances that remain outstanding after reasonable collection efforts have been unsuccessful are written off through a charge to the valuation allowance and a credit to accounts receivable.
Inventories	Inventories – Inventories consist primarily of natural gas, propane, other NGLs and materials and supplies to be used in operations. Natural gas, propane, and other NGLs are valued at the lower of cost or market value. Materials and supplies are stated at the lower of cost or market value. Cost for materials and supplies are determined primarily using the weighted-average cost method.
Imbalances	Imbalances – Within our pipelines and storage assets, we experience volume gains and losses due to pressure and temperature changes, evaporation and variances in meter readings and other measurement methods. Until settled, positive imbalances are recorded as other current assets and negative imbalances are recorded as accounts payable. Positive and negative product imbalances are settled in cash, settled by physical delivery of gas from a different source, or tracked and settled in the future.
Property, plant and equipment	Property, Plant and Equipment – Property, plant and equipment are recorded at cost and depreciated on a straight-line basis over the estimated useful lives of the assets. Expenditures that extend the useful lives of assets are capitalized. Such assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. If the sum of the expected undiscounted future cash flows from the use of the asset and its eventual disposition is less than the carrying amount of the asset, an impairment assessment is performed and the excess of the book value over the fair value is recorded as an impairment loss. When items of property, plant and equipment are sold or otherwise disposed of, any gains or losses are reported on the Consolidated Statements of Income. Gains on the disposal of property, plant and equipment are recognized when they occur, which is generally at the time of closing. If a loss on disposal is expected, such losses are recognized when the assets are classified as held for sale. Interest costs for the construction or development of long-lived assets are capitalized and amortized over the related asset’s estimated useful life.
Intangibles	Goodwill and Intangibles – Goodwill represents the excess of the purchase price over the estimated fair value of the net assets acquired in the acquisition of a business. Goodwill is not amortized, but rather is tested for impairment annually and when events or changes in circumstances indicate that the fair value of a reporting unit with goodwill has been reduced below carrying value. The impairment test requires allocating goodwill and other assets and liabilities to reporting units. The fair value of each reporting unit is determined using an income and/or market approach which is compared to the carrying value of the reporting unit. The fair value under the income approach is calculated using the expected present value of future cash flows method. Significant assumptions used in the cash flow forecasts include future operating performance, future volumes, discount rates, and future capital requirements. If the fair value of the reporting unit is less than the carrying value, including goodwill, the excess, if any, of the book value over the fair value of the reporting unit up to the amount of goodwill recorded is charged to net income as an impairment expense. Amortization of intangibles with definite lives is calculated using the straight-line method which is reflective of the benefit pattern in which the estimated economic benefit is expected to be received over the estimated useful life of the intangible asset. Intangibles subject to amortization are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of the intangible may not be recoverable. If the sum of the expected undiscounted future cash flows related to the asset is less than the carrying amount of the asset, an impairment loss is recognized based on the fair value of the asset. Intangibles not subject to amortization are tested for impairment annually and when circumstances indicate that the fair value is less than the carrying amount of the intangible. If the fair value is less than the carrying value, an impairment is recorded for the difference. As a result of MPLX’s November 30, 2019 annual goodwill impairment analysis, we recorded an impairment charge of approximately $1.2 billion , which resulted in a goodwill balance of $9.5 billion at December 31, 2019. See Note 14 for further details. No impairments were recorded as a result of our 2018 annual goodwill impairment analysis.
Goodwill	Goodwill and Intangibles – Goodwill represents the excess of the purchase price over the estimated fair value of the net assets acquired in the acquisition of a business. Goodwill is not amortized, but rather is tested for impairment annually and when events or changes in circumstances indicate that the fair value of a reporting unit with goodwill has been reduced below carrying value. The impairment test requires allocating goodwill and other assets and liabilities to reporting units. The fair value of each reporting unit is determined using an income and/or market approach which is compared to the carrying value of the reporting unit. The fair value under the income approach is calculated using the expected present value of future cash flows method. Significant assumptions used in the cash flow forecasts include future operating performance, future volumes, discount rates, and future capital requirements. If the fair value of the reporting unit is less than the carrying value, including goodwill, the excess, if any, of the book value over the fair value of the reporting unit up to the amount of goodwill recorded is charged to net income as an impairment expense. Amortization of intangibles with definite lives is calculated using the straight-line method which is reflective of the benefit pattern in which the estimated economic benefit is expected to be received over the estimated useful life of the intangible asset. Intangibles subject to amortization are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of the intangible may not be recoverable. If the sum of the expected undiscounted future cash flows related to the asset is less than the carrying amount of the asset, an impairment loss is recognized based on the fair value of the asset. Intangibles not subject to amortization are tested for impairment annually and when circumstances indicate that the fair value is less than the carrying amount of the intangible. If the fair value is less than the carrying value, an impairment is recorded for the difference. As a result of MPLX’s November 30, 2019 annual goodwill impairment analysis, we recorded an impairment charge of approximately $1.2 billion , which resulted in a goodwill balance of $9.5 billion at December 31, 2019. See Note 14 for further details. No impairments were recorded as a result of our 2018 annual goodwill impairment analysis.
Other taxes	Other Taxes – Other taxes primarily include real estate taxes.
Environmental costs	Environmental Costs – Environmental expenditures are capitalized if the costs mitigate or prevent future contamination or if the costs improve environmental safety or efficiency of the existing assets. MPLX recognizes remediation costs and penalties when the responsibility to remediate is probable and the amount of associated costs can be reasonably estimated. The timing of remediation accruals coincides with completion of a feasibility study or the commitment to a formal plan of action. Remediation liabilities are accrued based on estimates of known environmental exposure and are discounted when the estimated amounts are reasonably fixed and determinable. If recoveries of remediation costs from third parties are probable, a receivable is recorded and is discounted when the estimated amount is reasonably fixed and determinable.
Asset retirement obligations	Asset Retirement Obligations – An ARO is a legal obligation associated with the retirement of tangible long-lived assets that generally result from the acquisition, construction, development or normal operation of the asset. AROs are recorded at fair value in the period in which they are incurred, if a reasonable estimate of fair value can be made, and added to the carrying amount of the associated asset. This additional carrying amount is then depreciated over the life of the asset. The liability is determined using a credit adjusted risk free interest rate and increases due to the passage of time based on the time value of money until the obligation is settled. MPLX recognizes a liability of a conditional ARO as soon as the fair value of the liability can be reasonably estimated. A conditional ARO is defined as an unconditional legal obligation to perform an asset retirement activity in which the timing and/or method of settlement are conditional on a future event that may or may not be within the control of the entity. AROs have not been recognized for certain assets because the fair value cannot be reasonably estimated since the settlement dates of the obligations are indeterminate. Such obligations will be recognized in the period when sufficient information becomes available to estimate a range of potential settlement dates.
Investment in unconsolidated affiliates	Investment in Unconsolidated Affiliates – Equity investments in which MPLX exercises significant influence, but does not control and is not the primary beneficiary, are accounted for using the equity method and are reported in “ Equity method investments ” on the accompanying Consolidated Balance Sheets. This includes entities in which we hold majority ownership but the minority shareholders have substantive participating rights. Differences in the basis of the investments and the separate net asset values of the investees, if any, are amortized into net income over the remaining useful lives of the underlying assets and liabilities, except for the excess related to goodwill. MPLX believes the equity method is an appropriate means for it to recognize increases or decreases measured by GAAP in the economic resources underlying the investments. Regular evaluation of these investments is appropriate to evaluate any potential need for impairment. MPLX uses evidence of a loss in value to identify if an investment has an other than a temporary decline. During the fourth quarter of 2019, two of the joint ventures in which we have an interest recorded impairments, which impacted the amount of income from equity method investments during the period by approximately $28 million . For one of the joint ventures, we also had a basis difference which was being amortized over the life of the underlying assets. As a result of the impairment recorded by the joint venture, we also assessed this basis difference for impairment and recorded approximately $14 million
Deferred financing costs	Deferred Financing Costs – Deferred financing costs are an asset for credit facility costs and netted against debt for senior notes. These costs are amortized over the contractual term of the related obligations using the effective interest method or, in certain circumstances, accelerated if the obligation is refinanced.
Derivative instruments	Derivative Instruments – MPLX may use commodity derivatives to economically hedge a portion of its exposure to commodity price risk. All derivative instruments (including derivatives embedded in other contracts) are recorded at fair value. Certain commodity derivatives are reflected on the consolidated balance sheets on a net basis by counterparty as they are governed by master netting arrangements. MPLX discloses the fair value of all derivative instruments under the captions “ Other noncurrent assets ,” “ Other current liabilities ” and “ Deferred credits and other liabilities ” on the Consolidated Balance Sheets. Changes in the fair value of derivative instruments are reported on the Consolidated Statements of Income in accounts related to the item whose value or cash flows are being managed. All derivative instruments are marked to market through “ Product sales ,” “ Purchased product costs ,” or “Cost of revenues” on the Consolidated Statements of Income. Revenue gains and losses relate to contracts utilized to manage the cash flow for the sale of a product, typically NGLs. Purchased product costs gains and losses relate to contracts utilized to manage the cost of natural gas purchases, typically related to keep-whole arrangements. Cost of revenues gains and losses relate to a contract utilized to manage electricity costs. Changes in risk management for unrealized activities are reported as an adjustment to net income in computing cash flow from operating activities on the accompanying Consolidated Statements of Cash Flows. During the years ended December 31, 2019 , 2018 and 2017 , MPLX did not elect hedge accounting for any derivatives. MPLX has elected the normal purchases and normal sales designation for certain contracts related to the physical purchase of electric power and the sale of some commodities.
Fair value of financial instruments	Fair Value of Financial Instruments – Management believes the carrying amount of financial instruments, including cash and cash equivalents, receivables, receivables from related parties, other current assets, accounts payable, accounts payable to related parties and accrued liabilities approximate fair value because of the short-term maturity of these instruments. The recorded value of the amounts outstanding under the bank revolving credit facility, if any, approximate fair value due to the variable interest rate that approximates current market rates (see Note 15 ). Derivative instruments are recorded at fair value, based on available market information (see Note 16 ).
Fair value measurement	Fair Value Measurement – Financial assets and liabilities recorded at fair value in the Consolidated Balance Sheets are categorized based upon the fair value hierarchy established by GAAP, which classifies the inputs used to measure fair value into Level 1, Level 2 or Level 3. A financial instrument’s categorization within the valuation hierarchy is based upon the lowest level of input that is significant to the fair value measurement. The methods and assumptions utilized may produce a fair value that may not be realized in future periods upon settlement. Furthermore, while MPLX believes its valuation methods are appropriate and consistent with other market participants, the use of different methodologies or assumptions to determine the fair value of certain financial instruments could result in a different estimate of fair value at the reporting date. For further discussion see Note 15 .
Equity-based compensation arrangements	Equity-Based Compensation Arrangements – MPLX issues phantom units under its share-based compensation plan as described further in Note 21 . A phantom unit entitles the grantee a right to receive a common unit upon the issuance of the phantom unit. The fair value of phantom unit awards granted to employees and non-employee directors is based on the fair market value of MPLX LP common units on the date of grant. The fair value of the units awarded is amortized into earnings using a straight-line amortization schedule over the period of service corresponding with the vesting period. For phantom units that vest immediately and are not forfeitable, equity-based compensation expense is recognized at the time of grant. Performance units paying out in cash are accounted for as liability awards and recorded at fair value with a mark-to-market adjustment made each quarter. The performance units paying out in units are accounted for as equity awards and use a Monte Carlo valuation model to calculate a grant date fair value. To satisfy common unit awards, MPLX may issue new common units, acquire common units in the open market or use common units already owned by the general partner.
Tax effects of share-based compensation	Tax Effects of Share-Based Compensation – MPLX elected to adopt the simplified method to establish the beginning balance of the additional paid-in capital pool (“APIC Pool”) related to the tax effects of employee share-based compensation and to determine the subsequent impact on the APIC Pool and Consolidated Statements of Cash Flows of the tax effects of share-based compensation awards that were outstanding upon adoption. Additional paid-in capital is reported as “Common unitholders - public ” on the accompanying Consolidated Balance Sheets.
Income taxes	Income Taxes – MPLX is not a taxable entity for United States federal income tax purposes or for the majority of the states that impose an income tax. Taxes on MPLX’s net income generally are borne by its partners through the allocation of taxable income. MPLX’s taxable income or loss, which may vary substantially from the net income or loss reported on the Consolidated Statements of Income, is includable in the federal income tax returns of each partner. MPLX and certain legal entities are, however, taxable entities under certain state jurisdictions. MPLX accounts for income taxes under the asset and liability method. Deferred income taxes are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax basis, capital loss carryforwards and net operating loss and credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates applied to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect of any tax rate change on deferred taxes is recognized as tax expense/(benefit) from continuing operations in the period that includes the enactment date of the tax rate change. Realizability of deferred tax assets is assessed and, if not more likely than not, a valuation allowance is recorded to reflect the deferred tax assets at net realizable value as determined by management. All deferred tax balances are classified as long-term in the accompanying Consolidated Balance Sheets. All changes in the tax bases of assets and liabilities are allocated among operations and items charged or credited directly to equity.
Distributions	Distributions – In preparing the Consolidated Statements of Equity, net income attributable to MPLX LP is allocated to Series A and Series B preferred unitholders based on a fixed distribution schedule, as discussed in Notes 8 and 9 , and subsequently allocated to the general partner and limited partner unitholders. Distributions, although earned, are not accrued as a liability until declared. However, when distributions related to the eliminated IDRs were made, earnings equal to the amount of those distributions were first allocated to the general partner before the remaining earnings are allocated to the limited partner unitholders based on their respective ownership percentages. The allocation of net income attributable to MPLX LP for purposes of calculating net income per limited partner unit is described in below.
Net income per limited partner unit	Net Income Per Limited Partner Unit – MPLX uses the two-class method when calculating the net income per unit applicable to limited partners, because there is more than one class of participating security. The classes of participating securities include common units, general partner units, Series A and Series B preferred units, certain equity-based compensation awards and eliminated IDRs. Class B units were considered to be a separate class of common units that did not participate in distributions. Net income attributable to MPLX LP is allocated to the unitholders differently for preparation of the Consolidated Statements of Equity and the calculation of net income per limited partner unit. In preparing the Consolidated Statements of Equity, net income attributable to MPLX LP is allocated to Series A and Series B preferred unitholders based on a fixed distribution schedule and subsequently allocated to remaining unitholders in accordance with their respective ownership percentages. However, prior to 2018 when distributions related to the eliminated IDRs were made, earnings equal to the amount of those distributions are first allocated to the general partner before the remaining earnings are allocated to the unitholders, except Class B unitholders, based on their respective ownership percentages. Subsequent to the conversion of the general partner to a non-economic interest as described in Note 8 , no earnings are allocated to the general partner. Distributions, although earned, are not accrued until declared. The allocation of net income attributable to MPLX LP for purposes of calculating net income per limited partner unit is described in Note 7 . In preparing net income per limited partner units, during periods in which a net loss attributable to MPLX is reported or periods in which the total distributions exceed the reported net income attributable to MPLX’s unitholders, the amount allocable to certain equity-based compensation awards is based on actual distributions to the equity-based compensation awards. Diluted earnings per unit is calculated by dividing net income attributable to MPLX’s common unitholders, after deducting amounts allocable to other participating securities, by the weighted average number of common units and potential common units outstanding during the period. Potential common units are excluded from the calculation of diluted earnings per unit during periods in which net income attributable to MPLX’s unitholders, after deducting amounts that are allocable to the outstanding equity-based compensation awards, preferred units, and eliminated IDRs, is a loss as the impact would be anti-dilutive.
Business combinations	Business Combinations – MPLX recognizes and measures the assets acquired and liabilities assumed in a business combination based on their estimated fair values at the acquisition date, with any remaining difference recorded as goodwill or gain from a bargain purchase. Depending on the nature of the transaction, management may engage an independent valuation specialist to assist with the determination of fair value of the assets acquired, liabilities assumed, noncontrolling interests, if any, and goodwill, based on recognized business valuation methodologies. If the initial accounting for the business combination is incomplete by the end of the reporting period in which the acquisition occurs, an estimate will be recorded. Subsequent to the acquisition, and not later than one year from the acquisition date, MPLX will record any material adjustments to the initial estimate based on new information obtained that would have existed as of the acquisition date. An adjustment that arises from information obtained that did not exist as of the date of the acquisition will be recorded in the period of the adjustment. An income, market or cost valuation method may be utilized to estimate the fair value of the assets acquired, liabilities assumed, and noncontrolling interests, if any, in a business combination. The income valuation method represents the present value of future cash flows over the life of the asset using: (i) discrete financial forecasts, which rely on management’s estimates of volumes, NGL prices, revenue and operating expenses; (ii) long-term growth rates; and (iii) appropriate discount rates. The market valuation method uses prices paid for a reasonably similar asset by other purchasers in the market, with adjustments relating to any differences between the assets. The cost valuation method is based on the replacement cost of a comparable asset at prices at the time of the acquisition reduced for depreciation of the asset. Acquisition-related costs are expensed as incurred in connection with each business combination. Acquisitions in which the company or business being acquired by MPLX had an existing relationship with MPC may result in the transaction being considered a transfer between entities under common control. In this situations, MPLX records the assets acquired and liabilities assumed on its consolidated balance sheets at MPC’s historical carrying value. Transfers of businesses between entities under common control require prior periods to be retrospectively adjusted for those dates that the entity was under common control. See Note 4 for more information about the acquisitions.
Accounting for changes in ownership interests in subsidiaries	Accounting for Changes in Ownership Interests in Subsidiaries – MPLX’s ownership interest in a consolidated subsidiary may change if it sells a portion of its interest or acquires additional interest or if the subsidiary issues or repurchases its own shares. If the transaction does not result in a change in control over the subsidiary, the transaction is accounted for as an equity transaction. If a sale results in a loss of control, it would result in the deconsolidation of a subsidiary with a gain or loss recognized on the Consolidated Statements of Income unless the subsidiary meets the definition of in-substance real estate. Deconsolidation of in-substance real estate is recorded at cost with no gain or loss recognized. If the purchase of additional interest occurs that changes the acquirer’s ownership interest from noncontrolling to controlling, the acquirer’s preexisting interest in the acquiree is remeasured to its fair value, with a resulting gain or loss recorded in earnings upon consummation of the business combination. Once an entity has control of a subsidiary, its acquisitions of some or all of the noncontrolling interests in that subsidiary are accounted for as equity transactions and are not considered to be a business combination.

Accounting Standards New Accoun

Accounting Standards New Accounting Pronouncements Not yet Adopted (Tables)	12 Months Ended
	Dec. 31, 2019
ASUs not yet adopted [Abstract]
Description of New Accounting Pronouncements Not yet Adopted [Text Block]	Not Yet Adopted 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. The application of this ASU will not have a material impact on our consolidated financial statements.

Acquisitions (Tables)

Acquisitions (Tables)	12 Months Ended
	Dec. 31, 2019
ANDX LP [Member]
Business Acquisition [Line Items]
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed	The fair value of assets acquired and liabilities assumed shown below represents MPC’s historical carrying values as of October 1, 2018. (In millions) As Originally Reported Adjustments (1) As Adjusted Cash and cash equivalents $ 83 $ (53 ) $ 30 Receivables, net 241 259 500 Inventories 21 — 21 Other current assets (2) 59 (7 ) 52 Equity method investments 731 (89 ) 642 Property, plant and equipment, net 6,709 (427 ) 6,282 Intangibles, net (3) 960 74 1,034 Other noncurrent assets (4) 31 (8 ) 23 Total assets acquired 8,835 (251 ) 8,584 Accounts payable 198 265 463 Other current liabilities (5) 188 (41 ) 147 Long-term debt 4,916 — 4,916 Deferred credits and other long-term liabilities (6) 75 1 76 Total liabilities assumed 5,377 225 5,602 Net assets acquired excluding goodwill 3,458 (476 ) 2,982 Goodwill 7,428 724 8,152 Total purchase price $ 10,886 $ 248 $ 11,134 (1) Inclusive of activity recorded subsequent to the acquisition of ANDX on July 30, 2019, a portion of which was recorded as a non-cash contribution from MPC. (2) Includes both related party and third party other current assets. (3) Includes approximately $4 million of favorable lease assets. In connection with the implementation of ASC 842, this balance was reclassed to “Right of use assets” on the Consolidated Balance Sheets during 2019. (4) Includes both related party and third party other noncurrent assets as well as right of use assets associated with leases. (5) Includes accrued liabilities, operating lease liabilities, long-term debt due within one year, as well as related party and third party other current liabilities. (6) Includes deferred revenue and deferred income taxes, as well as related party and third party other noncurrent liabilities.
Business Acquisition, Pro Forma Information	The following unaudited pro forma information combines the historical operations of MPLX and ANDX, giving effect to the Merger as if it had been consummated on January 1, 2018, the beginning of the earliest period presented. (In millions) 2019 2018 Total revenues and other income $ 9,041 $ 8,666 Net income attributable to MPLX LP $ 1,434 $ 2,446
Mt. Airy Terminal [Member]
Business Acquisition [Line Items]
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed	Based on the fair value estimates of assets acquired and liabilities assumed at the acquisition date, the purchase price was allocated as follows: (In millions) Balance as of September 26, 2018 Receivables, net $ 3 Other current assets 1 Property, plant and equipment, net 336 Intangibles, net 9 Goodwill 121 Accounts payable (17 ) Other current liabilities (7 ) Net assets acquired $ 446
Business Acquisition, Pro Forma Information	Assuming the acquisition had occurred on January 1, 2017, the consolidated pro forma results would not have been materially different from the reported results.
Ozark Pipeline
Business Acquisition [Line Items]
Business Acquisition, Pro Forma Information	Assuming the acquisition of the Ozark pipeline had occurred on January 1, 2017, the consolidated pro forma results would not have been materially different from reported results.

Investments and Noncontrollin_2

Investments and Noncontrolling Interests (Tables)	12 Months Ended
	Dec. 31, 2019
Equity Method Investments and Joint Ventures [Abstract]
Equity Method Investments	The following table presents MPLX’s equity method investments at the dates indicated: Ownership as of Carrying value at December 31, December 31, (In millions, except ownership percentages) 2019 2019 2018 L&S MarEn Bakken Company LLC 25% $ 481 $ 498 Illinois Extension Pipeline Company, L.L.C. 35% 265 275 LOOP LLC 41% 238 226 Andeavor Logistics Rio Pipeline LLC (1) 67% 202 181 Minnesota Pipe Line Company, LLC (1) 17% 190 197 Whistler Pipeline LLC 38% 134 — Wink to Webster Pipeline LLC 15% 126 — Explorer Pipeline Company 25% 83 90 Other (1) 55 51 Total L&S 1,774 1,518 G&P MarkWest Utica EMG, L.L.C. 56% 1,984 2,039 Sherwood Midstream LLC 50% 537 366 MarkWest EMG Jefferson Dry Gas Gathering Company, L.L.C. 67% 302 236 Rendezvous Gas Services, L.L.C. (1) 78% 170 248 Sherwood Midstream Holdings LLC 53% 157 157 Centrahoma Processing LLC 40% 153 160 Other (1) 198 177 Total G&P 3,501 3,383 Total $ 5,275 $ 4,901 (1) These investments as well as certain investments included within “Other” for both L&S and G&P are investments acquired as part of the Merger. The December 31, 2019 balance reflects all purchase accounting adjustments identified by MPC as part of its acquisition of Andeavor.
Summarized Financial Information For Equity Method Investees Table	Summarized financial information for MPLX’s equity method investments for the years ended December 31, 2019 , 2018 and 2017 is as follows: December 31, 2019 (1) (In millions) Other VIEs Non-VIEs Total Revenues and other income $ 650 $ 1,417 $ 2,067 Costs and expenses 375 568 943 Income from operations 275 849 1,124 Net income 215 752 967 Income from equity method investments (2) $ 103 $ 187 $ 290 December 31, 2018 (1) (In millions) Other VIEs Non-VIEs Total Revenues and other income $ 484 $ 1,421 $ 1,905 Costs and expenses 286 738 1,024 Income from operations 198 683 881 Net income 197 606 803 Income from equity method investments (2) $ 67 $ 180 $ 247 December 31, 2017 (1) (In millions) Other VIEs Non-VIEs Total Revenues and other income $ 273 $ 954 $ 1,227 Costs and expenses 139 520 659 Income from operations 134 434 568 Net income 133 345 478 Income from equity method investments (2) $ 30 $ 48 $ 78 (1) The financial information for equity method investments for 2019 includes financial information of equity method investments acquired as part of the Merger. The financial information for equity method investments for 2018 includes financial information of equity method investments acquired as part of the Merger for the last three months of 2018. The financial information for equity method investments for 2017 does not include financial information of equity method investments acquired as part of the Merger. See Note 1 for additional information. (2) “Income from equity method investments” includes the impact of any basis differential amortization or accretion. Summarized balance sheet information for MPLX’s equity method investments as of December 31, 2019 and 2018 is as follows: December 31, 2019 (In millions) Other VIEs Non-VIEs Total Current assets $ 534 $ 330 $ 864 Noncurrent assets 5,862 5,134 10,996 Current liabilities 192 245 437 Noncurrent liabilities $ 305 $ 822 $ 1,127 December 31, 2018 (In millions) Other VIEs Non-VIEs Total Current assets $ 252 $ 415 $ 667 Noncurrent assets 3,796 5,290 9,086 Current liabilities 158 280 438 Noncurrent liabilities $ 191 $ 845 $ 1,036

Related Party Agreements and _2

Related Party Agreements and Transactions (Tables)	12 Months Ended
	Dec. 31, 2019
Related Party Transaction [Line Items]
Schedule Of Entity Wide Information Allocated Related Party Employee Benefit Costs By Income Statement Line [Table Text Block]	Related Party Expenses MPC provides executive management services and certain general and administrative services to MPLX under the terms of our omnibus agreements. Omnibus charges included in “Rental cost of sales - related parties” primarily relate to services that support MPLX’s rental operations and maintenance of assets available for rent. Omnibus charges included in “Purchases - related parties” primarily relate to services that support MPLX’s operations and maintenance activities, as well as compensation expenses. Omnibus charges included in “General and administrative expenses” primarily relate to services that support MPLX’s executive management, accounting and human resources activities. MPLX also obtains employee services from MPC under employee services agreements (“ESA charges”). ESA charges for personnel directly involved in or supporting operations and maintenance activities related to rental services are classified as “Rental cost of sales - related parties.” ESA charges for personnel directly involved in or supporting operations and maintenance activities related to other services are classified as “Purchases - related parties.” ESA charges for personnel involved in executive management, accounting and human resources activities are classified as “General and administrative expenses.” In addition to these agreements, MPLX purchases products from MPC, makes payments to MPC in its capacity as general contractor to MPLX, and has certain rent and lease agreements with MPC. Expenses incurred from MPC under the omnibus and employee services agreements as well as other purchases from MPC included on the Consolidated Statements of Income are as follows: (In millions) 2019 2018 2017 Rental cost of sales - related parties $ 165 $ 31 $ 2 Purchases - related parties MPC 1,210 919 455 Other 21 6 — General and administrative expenses 243 199 138 Total $ 1,639 $ 1,155 $ 595 Some charges incurred under the omnibus and ESA agreements are related to engineering services and are associated with assets under construction. These charges are added to “Property, plant and equipment, net” on the Consolidated Balance Sheets. For 2019 , 2018 and 2017 , these charges totaled $169 million , $152 million and $42 million , respectively.
Related Party Agreements and Transactions	Related Party Agreements and Transactions MPLX engages in transactions with both MPC and certain of its equity method investments as part of its normal business; however, transactions with MPC make up the majority of MPLX’s related party transactions. Transactions with related parties are further described below. MPLX has various long-term, fee-based commercial agreements with MPC. Under these agreements, MPLX provides transportation, terminal, fuels distribution, marketing, storage, management, operational and other services to MPC. MPC has committed to provide MPLX with minimum quarterly throughput volumes on crude oil and refined products and other fees for storage capacity; operating and management fees; as well as reimbursements for certain direct and indirect costs. MPC has also committed to provide a fixed fee for 100 percent of available capacity for boats, barges and third-party chartered equipment under the marine transportation service agreement. In addition, MPLX has obligations to MPC for services provided to MPLX by MPC under omnibus and employee services type agreements as well as other various agreements as discussed below. The commercial agreements with MPC include: • MPLX has fuels distribution agreements with MPC under which MPC pays MPLX for marketing and selling MPC’s products. This can include MPC paying MPLX a tiered monthly fee based on the volume of products sold or thought margin support under a related product supply agreement. Agreements are subject to minimum volume commitments and are subject various terms and renewal periods. • MPLX has various pipeline transportation agreements under which MPC pays MPLX fees for transporting crude and refined products on MPLX’s pipeline systems. These agreements are subject to minimum throughput volumes under which MPC will pay MPLX deficiency payments for any period in which they do not ship the minimum committed volume. These deficiency payments can be applied as credits to future periods in which MPC ships volumes in excess of the minimum volume, subject to a limited period of time. These agreements are subject to various terms and renewal periods. • MPLX has a six-year marine transportation agreement under which MPC pays MPLX fees for providing marine transportation of crude oil, feedstock and refined petroleum products, and related services. • MPLX has various trucking transportation services agreements with terms ranging from month-to-month to 10 years , under which MPC pays MPLX fees for gathering barrels and providing trucking, dispatch, delivery and data services. Most of these agreements are subject to minimum volume commitments and have various terms regarding carry-forward of deficiency payments as credits towards excess volumes shipped in future periods. These agreements are subject to various terms and renewal periods. • MPLX has numerous storage services agreements governing storage services at various types of facilities including terminals, pipeline tank farms, caverns and refineries, under which MPC pays MPLX per-barrel fees for providing storage services. Some of these agreements provide MPC with exclusive access to storage at certain locations, such as storage located at MPC’s refineries or storage in certain caverns. Under these agreements, MPC pays MPLX a per-barrel fee for such storage capacity, regardless of whether MPC fully utilizes the available capacity. Many of the refinery storage agreements also contain provisions for logistical services to be provided by MPLX, for which MPC pays monthly fees. These agreements are subject to terms ranging from three to 17 years and are subject to various renewal periods. • MPLX has a 10-year terminal services agreement governing certain terminals under which MPC pays MPLX fees for terminal storage for refined petroleum products. Under this agreement MPC pays MPLX agreed upon fees relating to MPC product deliveries as well as any viscosity surcharges, loading, handling, transfers or other related charges. This agreement is subject to minimum volume throughput commitments under which MPC pays a deficiency payment for any period in which they do not meet the minimum committed volume. The terminal services agreement with MPC includes automatic renewal terms ranging from one to five years . MPLX also has numerous additional terminal services agreements governing terminals acquired through the Merger. Under these agreements, MPC pays MPLX agreed upon fees relating to various terminal activities including throughput, blending, on and offloading and additives. Many of these agreements contain various minimum commitments for some or all of these activities. Some of these agreements allow for deficiency payments to be applied as credits to future periods with excess throughput volumes. These agreements have terms ranging from one to 10 years with varying renewal terms. • MPLX has a year to year keep-whole commodity agreement with MPC under which MPC pays us a processing fee for NGL’s related to keep-whole agreements and delivers shrink gas to the producers on our behalf. We pay MPC a marketing fee in exchange for assuming the commodity risk. The pricing structure under this agreement provides for a base volume subject to a base rate and incremental volumes subject to variable rates which are calculated with reference to certain of our costs incurred as processor of the volumes. The pricing for both the base and incremental volumes are subject to revision each year. In many cases, agreements are location-based hybrid agreements, containing provisions relating to multiple of the types of agreements and services described above. Operating Agreements MPLX operates various pipelines owned by MPC under operating services agreements. Under these operating services agreements, MPLX receives an operating fee for operating the assets and is reimbursed for all direct and indirect costs associated with operating the assets. Most of these agreements are indexed for inflation. These agreements range from one to five years in length and automatically renew unless terminated by either party. Co-location Services Agreements MPLX is party to co-location services agreements with MPC’s refineries, under which MPC provides management, operational and other services to the subsidiaries of Refining Logistics. Refining Logistics pays MPC monthly fixed fees and direct reimbursements for such services calculated as set forth in the agreements. These agreements have initial terms of 50 years . Ground Lease Agreements MPLX is party to ground lease agreements with certain of MPC’s refineries under which MPLX is the lessor of certain sections of property which contain facilities owned by Refining Logistics and are within the premises of MPC’s refineries. Refining Logistics pays MPC monthly fixed fees under these ground leases. These agreements have initial terms of 50 years . Management Services Agreement MPLX, through its subsidiary, HSM, has a management services agreement with MPC under which it provides management services to assist MPC in the oversight and management of the marine business. HSM receives a fixed annual fee for providing the required management services. This fee is adjusted annually on the anniversary of the contract for inflation and any changes in the scope of the management services provided. This agreement is set to expire on January 1, 2021 and automatically renews for two additional renewal terms of 5 years each unless terminated by either party. Omnibus Agreements MPLX has omnibus agreements with MPC that address MPLX’s payment of fixed annual fees to MPC for the provision of executive management services by certain executive officers of the general partner and MPLX’s reimbursement of MPC for the provision of certain general and administrative services to it. They also provide for MPC’s indemnification to MPLX for certain matters, including environmental, title and tax matters; as well as our indemnification of MPC for certain matters under these agreements. Certain environmental indemnifications related to the Los Angeles Logistics Assets Acquisition are excluded from coverage under omnibus agreements and are instead covered by a Carson Assets Indemnity Agreement. Employee Services Agreements MPLX has various employee services agreements and secondment agreements with MPC under which MPLX reimburses MPC for employee benefit expenses, along with the provision of operational and management services in support of both our L&S and G&P segments’ operations. Loan Agreement MPLX is party to a loan agreement with MPC Investment (the “MPC Loan Agreement”). Under the terms of the agreement, MPC Investment makes a loan or loans to MPLX on a revolving basis as requested by MPLX and as agreed to by MPC Investment. On April 27, 2018, MPLX and MPC Investment entered into an amendment to the MPC Loan Agreement to increase the borrowing capacity under the MPC Loan Agreement from $500 million to $1 billion . In connection with the Merger, on July 31, 2019, MPLX and MPC Investment entered into a second amendment to the MPC Loan Agreement to increase the borrowing capacity under the MPC Loan Agreement to $1.5 billion in aggregate principal amount of all loans outstanding at any one time. The entire unpaid principal amount of the loan, together with all accrued and unpaid interest and other amounts (if any), shall become due and payable on July 31, 2024, provided that MPC Investment may demand payment of all or any portion of the outstanding principal amount of the loan, together with all accrued and unpaid interest and other amounts (if any), at any time prior to July 31, 2024. Borrowings under the MPC Loan Agreement prior to July 31, 2019 bore interest at LIBOR plus 1.50 percent , while borrowings as of and after July 31, 2019 will bear interest at LIBOR plus 1.25 percent or such lower rate as would be applicable to such loans under the MPLX Credit Agreement. Activity on the MPC Loan Agreement was as follows: (In millions) December 31, 2019 December 31, 2018 Borrowings $ 8,540 $ 3,962 Average interest rate of borrowings 3.441 % 3.473 % Repayments $ 7,946 $ 4,347 Outstanding balance at end of period $ 594 $ — Prior to the Merger, ANDX was also party to a loan agreement with MPC (“ANDX-MPC Loan Agreement”). This facility was entered into on December 21, 2018, with a borrowing capacity of $500 million . In connection with the Merger, on July 31, 2019, MPLX repaid the entire outstanding balance and terminated the ANDX-MPC Loan Agreement. There was no activity on the ANDX-MPC Loan Agreement in 2018. Activity on the agreement during 2019 prior to the Merger was as follows: (In millions) December 31, 2019 Borrowings $ 773 Average interest rate of borrowings 4.249 % Repayments $ 773 Outstanding balance at end of period $ — Related Party Revenue Related party sales to MPC consist of crude oil and refined products pipeline and trucking transportation services based on tariff/contracted rates; storage, terminal and fuels distribution services based on contracted rates; and marine transportation services. Related party sales to MPC also consist of revenue related to volume deficiency credits. MPLX also has operating agreements with MPC under which it receives a fee for operating MPC’s retained pipeline assets and a fixed annual fee for providing oversight and management services required to run the marine business. MPLX also receives management fee revenue for engineering, construction and administrative services for operating certain of its equity method investments. Revenue received from related parties included on the Consolidated Statements of Income was as follows: (In millions) 2019 2018 2017 Service revenue MPC $ 3,455 $ 2,404 $ 1,082 Rental income MPC 1,196 846 279 Product sales (1) MPC 140 87 8 Other 2 — — Total Product sales - related parties 142 87 8 Other income MPC 47 41 40 Other 67 58 52 Total Other income - related parties $ 114 $ 99 $ 92 (1) There were additional product sales to MPC that net to zero within the consolidated financial statements as the transactions are recorded net due to the terms of the agreements under which such product was sold. For 2019 , 2018 and 2017 , these sales totaled $1,120 million , $607 million and $254 million , respectively. Related Party Expenses MPC provides executive management services and certain general and administrative services to MPLX under the terms of our omnibus agreements. Omnibus charges included in “Rental cost of sales - related parties” primarily relate to services that support MPLX’s rental operations and maintenance of assets available for rent. Omnibus charges included in “Purchases - related parties” primarily relate to services that support MPLX’s operations and maintenance activities, as well as compensation expenses. Omnibus charges included in “General and administrative expenses” primarily relate to services that support MPLX’s executive management, accounting and human resources activities. MPLX also obtains employee services from MPC under employee services agreements (“ESA charges”). ESA charges for personnel directly involved in or supporting operations and maintenance activities related to rental services are classified as “Rental cost of sales - related parties.” ESA charges for personnel directly involved in or supporting operations and maintenance activities related to other services are classified as “Purchases - related parties.” ESA charges for personnel involved in executive management, accounting and human resources activities are classified as “General and administrative expenses.” In addition to these agreements, MPLX purchases products from MPC, makes payments to MPC in its capacity as general contractor to MPLX, and has certain rent and lease agreements with MPC. Expenses incurred from MPC under the omnibus and employee services agreements as well as other purchases from MPC included on the Consolidated Statements of Income are as follows: (In millions) 2019 2018 2017 Rental cost of sales - related parties $ 165 $ 31 $ 2 Purchases - related parties MPC 1,210 919 455 Other 21 6 — General and administrative expenses 243 199 138 Total $ 1,639 $ 1,155 $ 595 Some charges incurred under the omnibus and ESA agreements are related to engineering services and are associated with assets under construction. These charges are added to “Property, plant and equipment, net” on the Consolidated Balance Sheets. For 2019 , 2018 and 2017 , these charges totaled $169 million , $152 million and $42 million , respectively. Related Party Assets and Liabilities December 31, (In millions) 2019 2018 Current assets - related parties Receivables - MPC $ 621 $ 542 Receivables - Other 22 9 Prepaid - MPC 9 5 Lease Receivables - MPC 4 — Total 656 556 Noncurrent assets - related parties Long-term receivables - MPC 21 24 Right of use assets - MPC 232 — Long-term lease receivables - MPC 43 — Unguaranteed residual asset - MPC 7 — Total 303 24 Current liabilities - related parties Payables - MPC 911 360 Payables - Other 37 76 Operating lease liabilities - MPC 1 — Deferred revenue - Minimum volume deficiencies - MPC 42 57 Deferred revenue - Project reimbursements - MPC 16 9 Deferred revenue - Project reimbursements - Other 1 — Total 1,008 502 Long-term liabilities - related parties Long-term operating lease liabilities - MPC 230 — Long-term deferred revenue - Project reimbursements - MPC 53 46 Long-term deferred revenue - Project reimbursements - Other 7 — Total $ 290 $ 46 From time to time, MPLX may also sell to or purchase from related parties assets and inventory at the lesser of average unit cost or net realizable value. Sales to related parties during the years ended December 31, 2019 and 2018 were $10 million and $6 million , respectively. Purchases from related parties during the years ended December 31, 2019 and 2018 were approximately $5 million and $8 million , respectively.
Schedule of Long-term Debt Instruments [Table Text Block]	Loan Agreement MPLX is party to a loan agreement with MPC Investment (the “MPC Loan Agreement”). Under the terms of the agreement, MPC Investment makes a loan or loans to MPLX on a revolving basis as requested by MPLX and as agreed to by MPC Investment. On April 27, 2018, MPLX and MPC Investment entered into an amendment to the MPC Loan Agreement to increase the borrowing capacity under the MPC Loan Agreement from $500 million to $1 billion . In connection with the Merger, on July 31, 2019, MPLX and MPC Investment entered into a second amendment to the MPC Loan Agreement to increase the borrowing capacity under the MPC Loan Agreement to $1.5 billion in aggregate principal amount of all loans outstanding at any one time. The entire unpaid principal amount of the loan, together with all accrued and unpaid interest and other amounts (if any), shall become due and payable on July 31, 2024, provided that MPC Investment may demand payment of all or any portion of the outstanding principal amount of the loan, together with all accrued and unpaid interest and other amounts (if any), at any time prior to July 31, 2024. Borrowings under the MPC Loan Agreement prior to July 31, 2019 bore interest at LIBOR plus 1.50 percent , while borrowings as of and after July 31, 2019 will bear interest at LIBOR plus 1.25 percent or such lower rate as would be applicable to such loans under the MPLX Credit Agreement. Activity on the MPC Loan Agreement was as follows: (In millions) December 31, 2019 December 31, 2018 Borrowings $ 8,540 $ 3,962 Average interest rate of borrowings 3.441 % 3.473 % Repayments $ 7,946 $ 4,347 Outstanding balance at end of period $ 594 $ — Prior to the Merger, ANDX was also party to a loan agreement with MPC (“ANDX-MPC Loan Agreement”). This facility was entered into on December 21, 2018, with a borrowing capacity of $500 million . In connection with the Merger, on July 31, 2019, MPLX repaid the entire outstanding balance and terminated the ANDX-MPC Loan Agreement. There was no activity on the ANDX-MPC Loan Agreement in 2018. Activity on the agreement during 2019 prior to the Merger was as follows: (In millions) December 31, 2019 Borrowings $ 773 Average interest rate of borrowings 4.249 % Repayments $ 773 Outstanding balance at end of period $ —
Revenue from Related Parties	Related Party Revenue Related party sales to MPC consist of crude oil and refined products pipeline and trucking transportation services based on tariff/contracted rates; storage, terminal and fuels distribution services based on contracted rates; and marine transportation services. Related party sales to MPC also consist of revenue related to volume deficiency credits. MPLX also has operating agreements with MPC under which it receives a fee for operating MPC’s retained pipeline assets and a fixed annual fee for providing oversight and management services required to run the marine business. MPLX also receives management fee revenue for engineering, construction and administrative services for operating certain of its equity method investments. Revenue received from related parties included on the Consolidated Statements of Income was as follows: (In millions) 2019 2018 2017 Service revenue MPC $ 3,455 $ 2,404 $ 1,082 Rental income MPC 1,196 846 279 Product sales (1) MPC 140 87 8 Other 2 — — Total Product sales - related parties 142 87 8 Other income MPC 47 41 40 Other 67 58 52 Total Other income - related parties $ 114 $ 99 $ 92 (1) There were additional product sales to MPC that net to zero within the consolidated financial statements as the transactions are recorded net due to the terms of the agreements under which such product was sold. For 2019 , 2018 and 2017 , these sales totaled $1,120 million , $607 million and $254 million , respectively.

Net Income (Loss) Per Limited_2

Net Income (Loss) Per Limited Partner Unit (Tables)	12 Months Ended
	Dec. 31, 2019
Earnings Per Share [Abstract]
Schedule of Net Income Per Limited Partner Unit	Potential common units omitted from the diluted earnings per unit calculation for the years ended December 31, 2019 , 2018 and 2017 were less than 1 million . (In millions) 2019 2018 2017 Net income attributable to MPLX LP $ 1,033 $ 1,818 $ 794 Less: Distributions declared on Series A preferred units (1) 81 75 65 Distributions declared on Series B preferred units (1) 42 — — General partner’s distributions declared (includes IDRs) (1)(2) — — 328 Limited partners’ distributions declared on MPLX common units (including common units of general partner) (1) 2,635 1,985 895 Undistributed net loss attributable to MPLX LP $ (1,725 ) $ (242 ) $ (494 ) (1) See Note 8 for distribution information. (2) Distributions declared on January 25, 2018 on general partner common units issued on February 1, 2018 in exchange for the economic general partner interest, including IDRs, are shown as general partner distributions declared.
Schedule of Basic and Diluted Earnings Per Unit	2019 (In millions, except per unit data) Limited Partners’ Common Units Series A Preferred Units Series B Preferred Units Total Basic and diluted net income attributable to MPLX LP per unit: Net income attributable to MPLX LP: Distributions declared $ 2,635 $ 81 $ 42 $ 2,758 Undistributed net loss attributable to MPLX LP (1,725 ) — — (1,725 ) Net income attributable to MPLX LP (1) $ 910 $ 81 $ 42 $ 1,033 Weighted average units outstanding: Basic (2) 906 906 Diluted (2) 907 907 Net income attributable to MPLX LP per limited partner unit: Basic $ 1.00 Diluted $ 1.00 2018 (In millions, except per unit data) Limited Partners’ Common Units Series A Preferred Units Total Basic and diluted net income attributable to MPLX LP per unit: Net income attributable to MPLX LP: Distributions declared $ 1,985 $ 75 $ 2,060 Undistributed net loss attributable to MPLX LP (242 ) — (242 ) Net income attributable to MPLX LP (1) $ 1,743 $ 75 $ 1,818 Weighted average units outstanding: Basic 761 761 Diluted 761 761 Net income attributable to MPLX LP per limited partner unit: Basic $ 2.29 Diluted $ 2.29 2017 (In millions, except per unit data) General Partner Limited Partners’ Common Units Series A Preferred Units Total Basic and diluted net income attributable to MPLX LP per unit: Net income attributable to MPLX LP: Distribution declared (including IDRs) $ 328 $ 895 $ 65 $ 1,288 Undistributed net loss attributable to MPLX LP (10 ) (484 ) — (494 ) Net income attributable to MPLX LP (1) $ 318 $ 411 $ 65 $ 794 Weighted average units outstanding: Basic 8 385 393 Diluted 8 388 396 Net income attributable to MPLX LP per limited partner unit: Basic $ 1.07 Diluted $ 1.06 (1) Allocation of net income/(loss) attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period. (2) The Series B preferred units and the MPLX common units issued in connection with the Merger were not outstanding during the entire year. See Notes 4 and 8 for additional information about the treatment of these units.

Equity (Tables)

Equity (Tables)	12 Months Ended
	Dec. 31, 2019
Equity [Abstract]
Schedule of Stockholders Equity	The table below summarizes the changes in the number of units outstanding for the years ended December 31, 2017 , 2018 , and 2019 : (In units) Common Class B General Partner (1) Total Balance at December 31, 2016 357,193,288 3,990,878 7,371,105 368,555,271 Unit-based compensation awards 268,167 — 5,472 273,639 Issuance of units under the ATM Program 13,846,998 — 282,591 14,129,589 Contribution of HST/WHC/MPLXT (See Note 4) 12,960,376 — 264,497 13,224,873 Contribution of the Joint-Interest Acquisition (See Note 4) 18,511,134 — 377,778 18,888,912 Class B Conversion 4,350,057 (3,990,878 ) 7,330 366,509 Balance at December 31, 2017 407,130,020 — 8,308,773 415,438,793 Unit-based compensation awards 348,387 — 140 348,527 Contribution of Refining Logistics and Fuels Distribution (See Note 4) 111,611,111 — 2,277,778 113,888,889 Conversion of GP economic interests 275,000,000 — (10,586,691 ) 264,413,309 Balance at December 31, 2018 794,089,518 — — 794,089,518 Unit-based compensation awards 288,031 — — 288,031 Issuance of units in connection with the Merger 262,829,592 — — 262,829,592 Conversion of Series A preferred units 1,148,330 — — 1,148,330 Balance at December 31, 2019 1,058,355,471 — — 1,058,355,471 (1) Changes to the number of general partner units outstanding, other than changes due to contributions made to MPC for the acquisitions of HSM, HST, WHC, MPLXT, the Joint-Interest Acquisition and Refining Logistics and Fuels Distribution, are the result of cash contributions made by the general partner in order to maintain its two percent GP Interest.
Schedule Of Calculation Of Net Income Applicable to Partners	Net Income Allocation – In preparing the Consolidated Statements of Equity, net income attributable to MPLX LP is allocated to Series A and Series B preferred unitholders first and subsequently allocated to the limited partner unitholders in accordance with their respective ownership percentages. Prior to 2018, when distributions related to the IDRs were made, earnings equal to the amount of those distributions were first allocated to the general partner before the remaining earnings are allocated to the unitholders, based on their respective ownership percentages. The following table presents the allocation of the general partner’s GP Interest in net income attributable to MPLX, for income statement periods occurring prior to the exchange of the GP economic interests: (In millions) 2017 Net income attributable to MPLX LP $ 794 Less: Preferred unit distributions 65 General partner's IDRs and other 310 Net income attributable to MPLX LP available to general and limited partners 419 General partner's two percent GP Interest in net income attributable to MPLX LP 8 General partner's IDRs and other 310 General partner's GP Interest in net income attributable to MPLX LP $ 318
Distributions Made to Limited Partner, by Distribution	e allocation of total quarterly cash distributions to general, limited, and preferred unitholders is as follows for the years ended December 31, 2019 , 2018 and 2017 . MPLX’s distributions are declared subsequent to quarter end; therefore, the following table represents total cash distributions applicable to the period in which the distributions were earned. (In millions) 2019 2018 2017 General partner's distributions: General partner's distributions on general partner units $ — $ — $ 25 General partner's distributions on IDRs (1) — — 303 Total distribution on general partner units and IDRs — — 328 Limited partners' distributions: Common unitholders, includes common units of general partner 2,635 1,985 895 Series A preferred unit distributions 81 75 65 Series B preferred unit distribution 42 — — Total cash distributions declared $ 2,758 $ 2,060 $ 1,288 (1) Includes distributions of fourth quarter 2017 income declared on general partner common units issued February 1, 2018 in exchange for the economic general partner interest. The distribution on common units for the year ended December 31, 2019 includes the impact of the issuance of approximately 102 million units issued to public unitholders and approximately 161 million units issued to MPC in connection with the Merger. Due to the timing of the closing, distributions presented in the table above include second quarter distributions on MPLX common units issued to former ANDX unitholders in connection with the Merger. Due to the waiver mentioned above, the distributions on common units exclude $12.5 million of waived distributions for the three months ended December 31, 2019 and $37.5 million of waived distributions for the year ended December 31, 2019. Also included in the table above is $21 million of distributions earned by the Series B preferred units for 2019 as well as $21 million

Redeemable Preferred Units (Tab

Redeemable Preferred Units (Tables)	12 Months Ended
	Dec. 31, 2019
Redeemable Preferred Units Disclosure [Abstract]
Rollforward of Redeemable Preferred Units	The changes in the redeemable preferred balance for 2019 and 2018 are summarized below: (In millions) 2019 2018 Balance at beginning of period $ 1,004 $ 1,000 Net income allocated 81 75 Distributions received by preferred unitholders (81 ) (71 ) Conversion of preferred units to common units (36 ) — Balance at end of period $ 968 $ 1,004

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2019
Segment Reporting [Abstract]
Reconciliation of Other Significant Reconciling Items from Segments to Consolidated [Table Text Block]	The table below provides a reconciliation between “Net income” and Segment Adjusted EBITDA. (In millions) 2019 2018 2017 Reconciliation to Net income: L&S Segment Adjusted EBITDA $ 2,748 $ 2,057 $ 775 G&P Segment Adjusted EBITDA 1,586 1,418 1,229 Total reportable segments 4,334 3,475 2,004 Depreciation and amortization (1) (1,254 ) (867 ) (683 ) (Provision)/benefit for income taxes — (8 ) (1 ) Amortization of deferred financing costs (42 ) (55 ) (53 ) Loss on extinguishment of debt — (46 ) — Non-cash equity-based compensation (22 ) (23 ) (15 ) Impairment expense (1,197 ) — — Net interest and other financial costs (873 ) (613 ) (301 ) Income from equity method investments 290 247 78 Distributions/adjustments related to equity method investments (562 ) (458 ) (231 ) Unrealized derivative gains/(losses) (2) 1 5 (6 ) Acquisition costs (14 ) (4 ) (11 ) Other (1 ) — — Adjusted EBITDA attributable to noncontrolling interests 32 18 8 Adjusted EBITDA attributable to Predecessor (3) 770 335 47 Net income $ 1,462 $ 2,006 $ 836 (1) Depreciation and amortization attributable to L&S was $503 million , $308 million and $163 million for the years ended 2019 , 2018 and 2017 , respectively. Depreciation and amortization attributable to G&P was $751 million , $559 million and $520 million for 2019 , 2018 and 2017 , respectively. (2) MPLX makes a distinction between realized or unrealized gains and losses on derivatives. During the period when a derivative contract is outstanding, changes in the fair value of the derivative are recorded as an unrealized gain or loss. When a derivative contract matures or is settled, the previously recorded unrealized gain or loss is reversed and the realized gain or loss of the contract is recorded. (3) The Adjusted EBITDA adjustments related to Predecessor are excluded from Adjusted EBITDA attributable to MPLX LP prior to the acquisition date.
Reconciliation of Assets from Segment to Consolidated [Table Text Block]	December 31, (In millions) 2019 2018 Segment Assets Cash and cash equivalents $ 15 $ 77 L&S 20,810 19,963 G&P 19,605 19,285 Total assets $ 40,430 $ 39,325
Schedule of Segment Reporting Information, by Segment [Table Text Block]	The tables below present information about revenues and other income, capital expenditures and investments in unconsolidated affiliates for the years ended December 31, 2019, 2018 and 2017 as well as total assets for our reportable segments as of December 31, 2019 and 2018: (In millions) 2019 2018 2017 L&S Service revenue $ 3,765 $ 2,575 $ 1,200 Rental income 1,235 856 279 Product related revenue 91 23 — Income from equity method investments 200 171 36 Other income 61 47 47 Total segment revenues and other income (1) 5,352 3,672 1,562 Segment Adjusted EBITDA (2) 2,748 2,057 775 Capital expenditures 1,060 708 512 Investments in unconsolidated affiliates 289 3 533 G&P Service revenue 2,188 1,685 1,038 Rental income 349 342 277 Product related revenue 997 1,171 897 Income from equity method investments 90 76 42 Other income 65 59 51 Total segment revenues and other income (1) 3,689 3,333 2,305 Segment Adjusted EBITDA (2) 1,586 1,418 1,229 Capital expenditures 1,203 1,545 972 Investments in unconsolidated affiliates $ 424 $ 338 $ 228 (1) Within the total segment revenues and other income amounts presented above, third party revenues for the L&S segment were $660 million , $371 million and $160 million for 2019 , 2018 and 2017 , respectively. Third party revenues for the G&P segment were $3,474 million , $3,198 million and $2,246 million for 2019 , 2018 and 2017 , respectively. (2) See below for the reconciliation from Segment Adjusted EBITDA to “Net income.”

Inventories (Tables)

Inventories (Tables)	12 Months Ended
	Dec. 31, 2019
Inventory Disclosure [Abstract]
Summary of Inventories	Inventories consist of the following: December 31, (In millions) 2019 2018 NGLs $ 5 $ 9 Line fill 10 9 Spare parts, materials and supplies 95 80 Total inventories $ 110 $ 98

Property, Plant and Equipment (

Property, Plant and Equipment (Tables)	12 Months Ended
	Dec. 31, 2019
Property, Plant and Equipment [Abstract]
Summary of Property, Plant and Equipment	Property, plant and equipment with associated accumulated depreciation is shown below: Estimated Useful Lives December 31, (In millions) 2019 2018 Natural gas gathering and NGL transportation pipelines and facilities 5 - 40 years $ 7,037 $ 6,349 Processing, fractionation and storage facilities 5 - 46 years 6,410 6,045 Pipelines and related assets 2 - 51 years 5,117 5,111 Barges and towing vessels 15 - 20 years 739 621 Terminals and related assets 4 - 45 years 2,222 2,757 Refinery related assets 13 - 38 years 1,383 1,447 Land, building, office equipment and other 2 - 45 years 2,554 1,562 Construction-in-progress 1,405 1,321 Total 26,867 25,213 Less accumulated depreciation 4,722 3,688 Property, plant and equipment, net $ 22,145 $ 21,525

Goodwill and Intangibles (Table

Goodwill and Intangibles (Tables)	12 Months Ended
	Dec. 31, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill	The changes in carrying amount of goodwill were as follows for the periods presented: (In millions) L&S G&P Total Gross goodwill as of December 31, 2017 $ 162 $ 2,213 $ 2,375 Accumulated impairment losses — (130 ) (130 ) Balance as of December 31, 2017 162 2,083 2,245 Acquisitions (1) 7,072 699 7,771 Balance as of December 31, 2018 7,234 2,782 10,016 Impairment losses — (1,197 ) (1,197 ) Acquisitions (1) 488 229 717 Balance as of December 31, 2019 7,722 1,814 9,536 Gross goodwill as of December 31, 2019 7,722 3,141 10,863 Accumulated impairment losses — (1,327 ) (1,327 ) Balance as of December 31, 2019 $ 7,722 $ 1,814 $ 9,536 (1) Acquisitions in 2018 are inclusive of the Mt. Airy Terminal acquisition as well as the Merger while acquisitions in 2019 are inclusive of measurement period adjustments related to the previously mentioned transactions.
Schedule of Acquired Finite-Lived Intangible Assets by Major Class	MPLX’s intangible assets are comprised of customer contracts and relationships. The weighted average amortization period for intangible assets acquired during 2019 was approximately 9 years . Gross intangible assets with accumulated amortization as of December 31, 2019 and 2018 is shown below: December 31, 2019 December 31, 2018 (In millions) Useful Life Gross Accumulated Amortization (1) Net Gross Accumulated Amortization (1) Net L&S 6 - 8 years $ 283 $ (45 ) $ 238 $ 249 $ (14 ) $ 235 G&P 6 - 25 years 1,288 (256 ) 1,032 1,253 (129 ) 1,124 $ 1,571 $ (301 ) $ 1,270 $ 1,502 $ (143 ) $ 1,359 (1) Amortization expense attributable to the G&P segment for the years ended December 31, 2019 and 2018 was $127 million and $49 million , respectively. Amortization expense attributable to the L&S segment for the year ended December 31, 2019 and 2018 was $31 million and $14 million , respectively.
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense	Estimated future amortization expense related to the intangible assets at December 31, 2019 is as follows: (In millions) 2020 $ 155 2021 155 2022 155 2023 155 2024 150 Thereafter 500 Total $ 1,270

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block]	The following table presents the financial instruments carried at fair value on a recurring basis as of December 31, 2019 and 2018 by fair value hierarchy level. MPLX has elected to offset the fair value amounts recognized for multiple derivative contracts executed with the same counterparty. December 31, 2019 2018 (In millions) Assets Liabilities Assets Liabilities Significant unobservable inputs (Level 3) Embedded derivatives in commodity contracts $ — $ (60 ) $ — $ (61 ) Total carrying value on Consolidated Balance Sheets $ — $ (60 ) $ — $ (61 )
Fair Value Inputs Assets and Liabilities Quantitative Information [Table Text Block]	Level 3 instruments include all NGL transactions and embedded derivatives in commodity contracts. The embedded derivative liability relates to a natural gas purchase commitment 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 $0.43 to $1.23 and (2) the probability of renewal of 94 percent for the first five-year term and 83 percent for the second five-year term of the gas purchase commitment and related keep-whole processing agreement. Increases or decreases in the fractionation spread result in an increase or decrease in the fair value of the embedded derivative liability, respectively. An increase in the probability of renewal would result in an increase in the fair value of the related embedded derivative liability. Beyond the embedded derivative discussed above, we had no outstanding commodity contracts as of December 31, 2019 or December 31, 2018 .
Schedule of changes in Level 3 fair value measurements [Table Text Block]	The following table is a reconciliation of the net beginning and ending balances recorded for net assets and liabilities classified as Level 3 in the fair value hierarchy. 2019 2018 (In millions) Commodity Derivative Contracts (net) Embedded Derivatives in Commodity Contracts (net) Commodity Derivative Contracts (net) Embedded Derivatives in Commodity Contracts (net) Fair value at beginning of period $ — $ (61 ) $ (2 ) $ (64 ) Total gains/(losses) (realized and unrealized) included in earnings (1) — (5 ) 6 (9 ) Settlements — 6 (4 ) 12 Fair value at end of period — (60 ) — (61 ) The amount of total losses for the period included in earnings attributable to the change in unrealized gains or losses relating to liabilities still held at end of period $ — $ (5 ) $ — $ (8 ) (1) Gains and losses on commodity derivatives classified as Level 3 are recorded in “Product sales” on the Consolidated Statements of Income. Gains and losses on derivatives embedded in commodity contracts are recorded in “Purchased product costs” and “Cost of revenues” on the Consolidated Statements of Income.
Fair Value, by Balance Sheet Grouping [Table Text Block]	The following table summarizes the fair value and carrying value of the long-term debt, excluding finance leases, and SMR liability. December 31, 2019 2018 (In millions) Fair Value Carrying Value Fair Value Carrying Value Long-term debt $ 21,054 $ 19,800 $ 18,070 $ 18,511 SMR liability $ 90 $ 80 $ 92 $ 86

Derivative Financial Instrume_2

Derivative Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block]	As of December 31, 2019 , MPLX had no outstanding commodity contracts.
Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block]	The impact of MPLX’s derivative instruments on its Consolidated Balance Sheets is summarized below: December 31, (In millions) 2019 2018 Derivative contracts not designated as hedging instruments and their balance sheet location Asset Liability Asset Liability Commodity contracts (1) Other current assets /Other current liabilities $ — $ (5 ) $ — $ (7 ) Other noncurrent assets /Deferred credits and other liabilities — (55 ) — (54 ) Total $ — $ (60 ) $ — $ (61 ) (1) Includes embedded derivatives in commodity contracts as discussed above.
Derivative Instruments, Gain (Loss) [Table Text Block]	The impact of MPLX’s derivative contracts not designated as hedging instruments and the location of gains and losses recognized on the Consolidated Statements of Income is summarized below: (In millions) 2019 2018 2017 Product sales Realized gains/(losses) $ — $ 4 $ (9 ) Unrealized gains — 2 4 Total derivative gains/(losses) related to product sales — 6 (5 ) Purchased product costs Realized losses (6 ) (12 ) (9 ) Unrealized gains/(losses) 1 3 (10 ) Total derivative loss related to purchased product costs (5 ) (9 ) (19 ) Cost of revenues Realized gains/(losses) — — — Unrealized gains/(losses) — — — Total derivative losses related to cost of revenues — — — Total derivative losses $ (5 ) $ (3 ) $ (24 )

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2019
Extinguishment of Debt [Line Items]
Schedule of Extinguishment of Debt [Table Text Block]	On December 10, 2018, MPLX redeemed all of the $750 million aggregate principal amount of 5.5 percent senior notes due February 15, 2023, $40 million of which was issued by the MarkWest subsidiary. These notes were redeemed at 101.833 percent of the aggregate principal amount, which resulted in a payment of $14 million related to the note premium and the immediate recognition of $46 million of unamortized debt issuance costs.
Summary of Outstanding Borrowings	MPLX’s outstanding borrowings at December 31, 2019 and 2018 consisted of the following: December 31, (In millions) 2019 2018 MPLX LP: Bank revolving credit facility due 2024 $ — $ — Term loan facility due 2021 1,000 — Floating rate senior notes due September 2021 1,000 — Floating rate senior notes due September 2022 1,000 — 6.250% senior notes due October 2022 266 — 3.500% senior notes due December 2022 486 — 3.375% senior notes due March 2023 500 500 4.500% senior notes due July 2023 989 989 6.375% senior notes due May 2024 381 — 4.875% senior notes due December 2024 1,149 1,149 5.250% senior notes due January 2025 708 — 4.000% senior notes due February 2025 500 500 4.875% senior notes due June 2025 1,189 1,189 4.125% senior notes due March 2027 1,250 1,250 4.250% senior notes due December 2027 732 — 4.000% senior notes due March 2028 1,250 1,250 4.800% senior notes due February 2029 750 750 4.500% senior notes due April 2038 1,750 1,750 5.200% senior notes due March 2047 1,000 1,000 5.200% senior notes due December 2047 487 — 4.700% senior notes due April 2048 1,500 1,500 5.500% senior notes due February 2049 1,500 1,500 4.900% senior notes due April 2058 500 500 Consolidated subsidiaries: MarkWest - 4.500% - 4.875% senior notes, due 2023-2025 23 23 ANDX - 3.500% - 6.375% senior notes, due 2019-2047 190 3,750 ANDX credit facilities — 1,245 Financing lease obligations (1) 19 21 Total 20,119 18,866 Unamortized debt issuance costs (106 ) (97 ) Unamortized discount/premium (300 ) (334 ) Amounts due within one year (9 ) (513 ) Total long-term debt due after one year $ 19,704 $ 17,922
Schedule of Debt Payments	The following table shows five years of scheduled debt payments, including payments on finance lease obligations: (In millions) 2020 $ 10 2021 2,002 2022 1,802 2023 1,502 2024 $ 1,601
Schedule of interest payable dates	Interest on each series of MPLX LP, MarkWest and ANDX senior notes is payable semi-annually in arrears, according to the table below. Senior Notes Interest payable semi-annually in arrears 6.250% senior notes due October 2022 April 15 th and October 15 th 3.500% senior notes due December 2022 June 1 st and December 1 st 3.375% senior notes due March 2023 March 15 th and September 15 th 4.500% senior notes due July 2023 January 15 th and July 15 th 6.375% senior notes due May 2024 May 1 st and November 1 st 4.875% senior notes due December 2024 June 1 st and December 1 st 5.250% senior notes due January 2025 January 15 th and July 15 th 4.000% senior notes due February 2025 February 15 th and August 15 th 4.875% senior notes due June 2025 June 1 st and December 1 st 4.125% senior notes due March 2027 March 1 st and September 1 st 4.250% senior notes due December 2027 June 1 st and December 1 st 4.000% senior notes due March 2028 March 15 th and September 15 th 4.800% senior notes due February 2029 February 15 th and August 15 th 4.500% senior notes due April 2038 April 15 th and October 15 th 5.200% senior notes due March 2047 March 1 st and September 1 st 5.200% senior notes due December 2047 June 1 st and December 1 st 4.700% senior notes due April 2048 April 15 th and October 15 th 5.500% senior notes due February 2049 February 15 th and August 15 th 4.900% senior notes due April 2058 April 15 th and October 15 th
Schedule of amounts related to the SMR included in the Balance Sheet	As of December 31, 2019 and 2018 , the following amounts related to the SMR are included in the accompanying Consolidated Balance Sheets: December 31, (In millions) 2019 2018 Assets Property, plant and equipment, net $ 46 $ 51 Liabilities Other current liabilities 5 5 Deferred credits and other liabilities $ 75 $ 81

Revenue Revenue (Tables)

Revenue Revenue (Tables)	12 Months Ended
	Dec. 31, 2019
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue [Table Text Block]	The following table represents a disaggregation of revenue for each reportable segment for the years ended December 31, 2019 and 2018 : 2019 (In millions) L&S G&P Total Revenues and other income: Service revenue $ 346 $ 2,152 $ 2,498 Service revenue - related parties 3,419 36 3,455 Service revenue - product related — 140 140 Product sales (1) 65 741 806 Product sales - related parties 26 116 142 Total revenues from contracts with customers $ 3,856 $ 3,185 7,041 Non-ASC 606 revenue (2) 2,000 Total revenues and other income $ 9,041 2018 (In millions) L&S G&P Total Revenues and other income: Service revenue $ 174 $ 1,682 $ 1,856 Service revenue - related parties 2,401 3 2,404 Service revenue - product related — 220 220 Product sales (1) 12 870 882 Product sales - related parties 11 76 87 Total revenues from contracts with customers $ 2,598 $ 2,851 5,449 Non-ASC 606 revenue (2) 1,556 Total revenues and other income $ 7,005 (1) G&P “Product sales” for the year ended December 31, 2018 was adjusted in the table above by $5 million related to derivative gains and mark-to-market adjustments. There were no adjustments for the year ended December 31, 2019 . (2) Non-ASC 606 Revenue includes rental income, income from equity method investments, derivative gains and losses, mark-to-market adjustments, and other income.
Contract with Customer, Asset and Liability [Table Text Block]	The table below reflects the changes in our contract balances for the years ended December 31, 2019 and 2018 : (In millions) Balance at December 31, 2018 (1) Additions/ (Deletions) Revenue Recognized (2) Balance at December 31, 2019 Contract assets $ 36 $ 5 $ (2 ) $ 39 Deferred revenue 13 17 (7 ) 23 Deferred revenue - related parties 65 55 (67 ) 53 Long-term deferred revenue 56 34 — 90 Long-term deferred revenue - related parties $ 52 $ 3 $ — $ 55 (In millions) Balance at January 1, 2018 (1) Additions/ (Deletions) (3) Revenue Recognized (2) Balance at December 31, 2018 Contract assets $ 4 $ 32 $ — $ 36 Deferred revenue 5 19 (11 ) 13 Deferred revenue - related parties 42 60 (37 ) 65 Long-term deferred revenue 5 51 — 56 Long-term deferred revenue - related parties $ 43 $ 9 $ — $ 52 (1) Balance represents ASC 606 portion of each respective line item. (2) No significant revenue was recognized related to past performance obligations for the years ended December 31, 2019 and 2018 .
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table Text Block]	The table below includes estimated revenue expected to be recognized in the future related to performance obligations that are unsatisfied (or partially unsatisfied) at the end of the reporting period. As of December 31, 2019 , the amounts allocated to contract assets and contract liabilities on the Consolidated Balance Sheets are $220 million and are reflected in the amounts below. This will be recognized as revenue as the obligations are satisfied, which is expected to occur over the next 24 years . Further, MPLX does not disclose variable consideration due to volume variability in the table below. (In millions) 2020 $ 1,717 2022 1,693 2022 1,640 2023 1,555 2024 and thereafter 5,317 Total revenue on remaining performance obligations (1)(2)(3) $ 11,922 (1) All fixed consideration from contracts with customers is included in the amounts presented above. Variable consideration that is constrained or not required to be estimated as it reflects our efforts to perform is excluded. (2) Arrangements deemed implicit leases are included in “Rental income” and are excluded from this table. (3) Only minimum volume commitments that are deemed fixed are included in the table above. MPLX has various minimum volume commitments in processing arrangements that vary based on the actual Btu content of the gas received. These amounts are deemed variable consideration and are excluded from the table above.

Supplemental Cash Flow Inform_2

Supplemental Cash Flow Information (Tables)	12 Months Ended
	Dec. 31, 2019
Supplemental Cash Flow Elements [Abstract]
Summary of Supplemental Cash Flow Information	December 31, (In millions) 2019 2018 Cash and cash equivalents $ 15 $ 77 Restricted cash (1) — 8 Cash, cash equivalents and restricted cash $ 15 $ 85 (1) The restricted cash balance is included within “Other current assets” on the Consolidated Balance Sheets. (In millions) 2019 2018 2017 Net cash provided by operating activities included: Interest paid (net of amounts capitalized) $ 835 $ 568 $ 263 Income taxes paid 1 1 3 Cash paid for amounts included in the measurement of lease liabilities Payments on operating leases 85 — — Interest payment under finance lease obligations 1 — — Net cash provided by financing activities included Principal payments under finance lease obligations 5 — — Non-cash investing and financing activities: Net transfers of property, plant and equipment from materials and supplies inventories 2 2 6 MPLX terminal lease classification change 21 — — ROU assets obtained in exchange for new operating lease obligations 26 — — ROU assets obtained in exchange for new finance lease obligations 4 — — Contribution - fixed assets to joint venture (1) — — 337 Contribution - common units issued (2) $ 7,722 $ 4,236 $ 1,133 (1) Contribution of assets to Sherwood Midstream and Sherwood Midstream Holdings. (2) For 2017, includes limited and general partner units issued to MPC as consideration in the acquisitions of the joint-interests, HST, WHC and MPLXT. For 2018, includes limited and general partner units issued to MPC as consideration in the acquisition of Refining Logistics and Fuels Distribution. For 2019, includes limited partner units issued to MPC and public unitholders as consideration in the Merger. See Note 4
Summary of Changes in Capital Accruals	The Consolidated Statements of Cash Flows exclude changes to the Consolidated Balance Sheets that did not affect cash. The following is the change of additions to property, plant and equipment related to capital accruals: (In millions) 2019 2018 2017 Increase/(decrease) in capital accruals $ (146 ) $ 135 $ 71

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income Accumulated Other Comprehensive Income (Tables)	12 Months Ended
	Dec. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]	The following table shows the changes in “Accumulated other comprehensive loss” by component during the period December 31, 2017 through December 31, 2019 : (In millions) Pension Benefits Other Post-Retirement Benefits Total Balance at December 31, 2017 (1) $ (13 ) $ (1 ) $ (14 ) Other comprehensive loss - remeasurements (2) (1 ) (1 ) (2 ) Balance at December 31, 2018 (1) (14 ) (2 ) (16 ) Other comprehensive income - remeasurements (2) — 1 1 Balance as of December 31, 2019 (1) $ (14 ) $ (1 ) $ (15 ) (1) These components of “Accumulated other comprehensive loss” are included in the computation of net periodic benefit cost by LOOP and Explorer and are therefore included on the Consolidated Statements of Income under the caption “Income/(loss) from equity method investments.” (2)

Equity-Based Compensation (Tabl

Equity-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2019
Phantom Units
Equity-Based Compensation [Line Items]
Summary of Unit Award Activity	The following is a summary of phantom unit award activity of MPLX common units in 2019 : Phantom Units Number of Units Weighted Average Fair Value Aggregate Intrinsic Value (In millions) Outstanding at December 31, 2018 1,154,335 $ 34.34 Granted 219,488 32.62 Legacy ANDX phantom units converted to MPLX phantom units at the Merger 208,533 43.64 Settled (426,451 ) 33.84 Forfeited (46,337 ) 33.63 Outstanding at December 31, 2019 1,109,568 35.97 Vested and expected to vest at December 31, 2019 1,104,552 35.98 $ 28 Non-forfeitable at December 31, 2019 (1) 507,471 $ 37.32 $ 13
Schedule of Share-based Compensation Arrangement by Share-based Payment Award, Restricted Stock Units, Vested and Expected to Vest	The following is a summary of the values related to phantom units: Phantom Units Intrinsic Value of Units Issued During the Period (in millions) Weighted Average Grant Date Fair Value of Units Granted During the Period 2019 $ 14 $ 32.62 2018 18 33.84 2017 $ 15 $ 36.26
Performance Shares
Equity-Based Compensation [Line Items]
Summary of Unit Award Activity	The following table presents a summary of the 2019 activity for performance unit awards to be settled in MPLX common units: Performance Units Number of Units Weighted Outstanding at December 31, 2018 1,941,750 $ 0.80 Granted 987,994 0.76 Settled (772,397 ) 0.63 Forfeited — — Outstanding at December 31, 2019 2,157,347 $ 0.84
Schedule of Share-based Compensation, Performance Unit Awards, Valuation Assumptions	The following table provides a summary of the weighted average inputs used for these assumptions: 2019 2018 2017 Risk-free interest rate 2.51% N/A 1.52% Look-back period 2.84 years N/A 2.83 years Expected volatility 25.01% N/A 49.34% Grant date fair value of performance units granted $0.76 N/A $0.90

Leases Lessee Disclosure (Table

Leases Lessee Disclosure (Tables)	12 Months Ended
	Dec. 31, 2019
Lessee, Lease, Description [Line Items]
Lessee, Finance Leases [Text Block]	Lessee We lease a wide variety of facilities and equipment under leases from third parties, including land and building space, office and field equipment, storage facilities and transportation equipment, while our related party leases primarily relate to ground leases associated with our refining logistics assets. Our remaining lease terms range from less than one to 59 years . Some long-term leases include renewal options ranging from one to 50 years and, in certain leases, also include purchase options. Renewal options and termination options were not included in the measurement of ROU assets and lease liabilities since it was determined they were not reasonably certain to be exercised. Under ASC 840, operating lease costs were $89 million in 2018 and $64 million in 2017 . Under ASC 842, the components of lease cost were as follows: 2019 (In millions) Related Party Third Party Components of lease costs: Operating lease costs $ 14 $ 75 Finance lease cost: Amortization of ROU assets — 5 Interest on lease liabilities — 1 Total finance lease cost — 6 Variable lease cost 1 11 Short-term lease cost — 80 Total lease cost $ 15 $ 172 Supplemental balance sheet data related to leases were as follows: December 31, 2019 (In millions) Related Party Third Party Operating leases Assets Right of use assets $ 232 $ 365 Liabilities Operating lease liabilities 1 66 Long-term operating lease liabilities 230 302 Total operating lease liabilities $ 231 $ 368 Weighted average remaining lease term 47.20 years 8.59 years Weighted average discount rate 5.80 % 4.38 % Finance leases Assets Property, plant and equipment, gross $ 46 Accumulated depreciation 19 Property, plant and equipment, net 27 Liabilities Other current liabilities 9 Long-term debt 10 Total finance lease liabilities $ 19 Weighted average remaining lease term 10.16 years Weighted average discount rate 5.87 % As of December 31, 2019 , maturities of lease liabilities for operating lease obligations and finance lease obligations having initial or remaining non-cancellable lease terms in excess of one year are as follows: (In millions) Related Party Operating Third Party Operating Finance 2020 $ 14 $ 78 $ 10 2021 14 73 2 2022 14 63 2 2023 14 56 2 2024 14 36 1 2025 and thereafter 605 139 10 Gross lease payments 675 445 27 Less: Imputed interest 444 77 8 Total lease liabilities $ 231 $ 368 $ 19 Future minimum commitments as of December 31, 2018, for capital lease obligations and for operating lease obligations having initial or remaining non-cancellable lease terms in excess of one year are as follows: (In millions) Operating Capital Lease Obligations 2019 $ 90 $ 5 2020 88 8 2021 83 3 2022 76 2 2023 70 2 2024 and thereafter 825 4 Total minimum lease payments $ 1,232 24 Less: imputed interest costs 3 Present value of net minimum lease payments $ 21
Lease, Cost [Table Text Block]	Under ASC 840, operating lease costs were $89 million in 2018 and $64 million in 2017 . Under ASC 842, the components of lease cost were as follows: 2019 (In millions) Related Party Third Party Components of lease costs: Operating lease costs $ 14 $ 75 Finance lease cost: Amortization of ROU assets — 5 Interest on lease liabilities — 1 Total finance lease cost — 6 Variable lease cost 1 11 Short-term lease cost — 80 Total lease cost $ 15 $ 172
Supplemental Balance Sheet Disclosures [Text Block]	Supplemental balance sheet data related to leases were as follows: December 31, 2019 (In millions) Related Party Third Party Operating leases Assets Right of use assets $ 232 $ 365 Liabilities Operating lease liabilities 1 66 Long-term operating lease liabilities 230 302 Total operating lease liabilities $ 231 $ 368 Weighted average remaining lease term 47.20 years 8.59 years Weighted average discount rate 5.80 % 4.38 % Finance leases Assets Property, plant and equipment, gross $ 46 Accumulated depreciation 19 Property, plant and equipment, net 27 Liabilities Other current liabilities 9 Long-term debt 10 Total finance lease liabilities $ 19 Weighted average remaining lease term 10.16 years Weighted average discount rate 5.87 %
Schedule of Future Minimum Lease Payments for Operating and Finance Leases [Table Text Block]	As of December 31, 2019 , maturities of lease liabilities for operating lease obligations and finance lease obligations having initial or remaining non-cancellable lease terms in excess of one year are as follows: (In millions) Related Party Operating Third Party Operating Finance 2020 $ 14 $ 78 $ 10 2021 14 73 2 2022 14 63 2 2023 14 56 2 2024 14 36 1 2025 and thereafter 605 139 10 Gross lease payments 675 445 27 Less: Imputed interest 444 77 8 Total lease liabilities $ 231 $ 368 $ 19 Future minimum commitments as of December 31, 2018, for capital lease obligations and for operating lease obligations having initial or remaining non-cancellable lease terms in excess of one year are as follows: (In millions) Operating Capital Lease Obligations 2019 $ 90 $ 5 2020 88 8 2021 83 3 2022 76 2 2023 70 2 2024 and thereafter 825 4 Total minimum lease payments $ 1,232 24 Less: imputed interest costs 3 Present value of net minimum lease payments $ 21

Leases Lessor Disclosures (Tabl

Leases Lessor Disclosures (Tables)	12 Months Ended
	Dec. 31, 2019
Lessor, Lease, Description [Line Items]
Lessor, Operating Lease, Payments to be Received, Maturity [Table Text Block]	The following is a schedule of minimum future rental revenue on the non-cancellable operating leases as of December 31, 2019 : (In millions) Related Party Third Party Total 2020 $ 1,134 $ 186 $ 1,320 2021 1,130 179 1,309 2022 1,127 177 1,304 2023 1,074 170 1,244 2024 1,015 167 1,182 2025 and thereafter 2,699 1,072 3,771 Total minimum future rentals $ 8,179 $ 1,951 $ 10,130
Schedule of Future Minimum Rental Payments Receivable for Operating Leases [Table Text Block]	The following is a schedule of minimum future rental revenue on the non-cancellable operating leases as of December 31, 2018: (In millions) Related Party Third Party Total 2019 $ 1,277 $ 171 $ 1,448 2020 1,275 163 1,438 2021 1,146 154 1,300 2022 1,143 151 1,294 2023 1,094 145 1,239 2024 and thereafter 3,786 1,114 4,900 Total minimum future rentals $ 9,721 $ 1,898 $ 11,619
Sales-type Lease, Lease Income [Table Text Block]	Lessor Based on the terms of fee-based transportation and storage services agreements with MPC and third parties , MPLX is considered to be the lessor under several operating lease arrangements in accordance with GAAP. These agreements have remaining terms ranging from less than 1 year to 11 years with renewal options ranging from 1 year to 5 years , with some agreements having multiple renewal options. We are also considered to be the lessor under operating lease agreements related to certain fee-based natural gas gathering, transportation and processing agreements. MPLX’s primary natural gas lease operations relate to a natural gas gathering agreement in the Marcellus Shale for which it earns a fixed-fee for providing gathering services to a single producer using a dedicated gathering system. As the gathering system is expanded, the fixed-fee charged to the producer is adjusted to include the additional gathering assets in the lease. The primary term of the natural gas gathering arrangement expires in 2038 and will continue thereafter on a year-to-year basis until terminated by either party. Other significant natural gas implicit leases relate to a natural gas processing agreement in the Marcellus Shale and a natural gas processing agreement in the Southern Appalachia region for which MPLX earns minimum monthly fees for providing processing services to a single producer using a dedicated processing plant. The primary term of these natural gas processing agreements expires during 2023 and 2033, these contracts will continue thereafter on a year-to-year basis until terminated by either party. MPLX did not elect to use the practical expedient to combine lease and non-lease components for lessor arrangements. The tables below represent the portion of the contract allocated to the lease component based on relative standalone selling price. Lessor agreements are currently deemed operating, as we elected the practical expedient to carry forward historical classification conclusions. If and when a modification of an existing agreement occurs and the agreement is required to be assessed under ASC 842, MPLX assesses the amended agreement and makes a determination as to whether a reclassification of the lease is required. During the year ended December 31, 2019 , there was a modification to MPLX terminal agreements with MPC. Based on the modification, certain terminals within the MPLX terminal agreement were reclassified from operating leases to sales-type leases. As a result, the underlying assets previously shown on the Consolidated Balance Sheets associated with the sales-type leases were derecognized and the net investment in the lease (i.e., the sum of the present value of the future lease payments and the unguaranteed residual value of the assets) was recorded as a lease receivable. When determining the net investment in the lease, certain variable payments were excluded from the total contract consideration, primarily related to fees for which there are no minimum volume commitments. The difference between the net book value of the underlying assets and the net investment in the lease has been recorded through equity given that the dropdown of MPLXT was a common control transaction. During the year, MPLX derecognized approximately $29 million of property, plant and equipment, derecognized approximately $3 million of existing deferred rent receivable, recorded a lease receivable of approximately $47 million , recorded an unguaranteed residual asset of approximately $6 million and equity of $21 million . Under ASC 840, MPLX’s revenue from its implicit lease arrangements, excluding executory costs, totaled approximately $1,032 million in 2018 and $601 million in 2017 . Lease revenues included on the Consolidated Statements of Income during 2019 were as follows: 2019 (In millions) Related Party Third Party Operating leases: Operating lease revenue (1) $ 1,020 $ 257 Sales-type leases: Profit/(loss) recognized at the commencement date — N/A Interest income (Sales-type rental revenue- fixed minimum) 6 N/A Interest income (Revenue from variable lease payments) $ 1 N/A (1) These amounts are presented net of executory costs. The following is a schedule of minimum future rental revenue on the non-cancellable operating leases as of December 31, 2019 : (In millions) Related Party Third Party Total 2020 $ 1,134 $ 186 $ 1,320 2021 1,130 179 1,309 2022 1,127 177 1,304 2023 1,074 170 1,244 2024 1,015 167 1,182 2025 and thereafter 2,699 1,072 3,771 Total minimum future rentals $ 8,179 $ 1,951 $ 10,130 The following is a schedule of minimum future rental revenue on the non-cancellable operating leases as of December 31, 2018: (In millions) Related Party Third Party Total 2019 $ 1,277 $ 171 $ 1,448 2020 1,275 163 1,438 2021 1,146 154 1,300 2022 1,143 151 1,294 2023 1,094 145 1,239 2024 and thereafter 3,786 1,114 4,900 Total minimum future rentals $ 9,721 $ 1,898 $ 11,619 The following is a schedule of minimum future revenue on the sales-type leases with MPC as of December 31, 2019 : (In millions) Related Party 2020 $ 14 2021 14 2022 14 2023 15 2024 15 2025 and thereafter 20 Total minimum future rentals 92 Less: present value discount 45 Lease receivable $ 47 The following schedule summarizes MPLX’s investment in assets held for operating lease by major classes as of December 31, 2019 and 2018 : December 31, (In millions) 2019 2018 Natural gas gathering and NGL transportation pipelines and facilities $ 1,120 $ 964 Processing, fractionation and storage facilities 2,176 1,670 Pipelines and related assets 362 376 Barges and towing vessels 738 619 Terminals and related assets 1,232 1,415 Refinery related assets 1,083 981 Land, building, office equipment and other 236 187 Total 6,947 6,212 Less accumulated depreciation 2,355 2,074 Property, plant and equipment, net $ 4,592 $ 4,138
Sales-type and Direct Financing Leases, Lease Receivable, Maturity [Table Text Block]	The following is a schedule of minimum future revenue on the sales-type leases with MPC as of December 31, 2019 : (In millions) Related Party 2020 $ 14 2021 14 2022 14 2023 15 2024 15 2025 and thereafter 20 Total minimum future rentals 92 Less: present value discount 45 Lease receivable $ 47
Schedule of Property Subject to or Available for Operating Lease [Table Text Block]	The following schedule summarizes MPLX’s investment in assets held for operating lease by major classes as of December 31, 2019 and 2018 : December 31, (In millions) 2019 2018 Natural gas gathering and NGL transportation pipelines and facilities $ 1,120 $ 964 Processing, fractionation and storage facilities 2,176 1,670 Pipelines and related assets 362 376 Barges and towing vessels 738 619 Terminals and related assets 1,232 1,415 Refinery related assets 1,083 981 Land, building, office equipment and other 236 187 Total 6,947 6,212 Less accumulated depreciation 2,355 2,074 Property, plant and equipment, net $ 4,592 $ 4,138
Lessor, Operating Leases [Text Block]	Lessor Based on the terms of fee-based transportation and storage services agreements with MPC and third parties , MPLX is considered to be the lessor under several operating lease arrangements in accordance with GAAP. These agreements have remaining terms ranging from less than 1 year to 11 years with renewal options ranging from 1 year to 5 years , with some agreements having multiple renewal options. We are also considered to be the lessor under operating lease agreements related to certain fee-based natural gas gathering, transportation and processing agreements. MPLX’s primary natural gas lease operations relate to a natural gas gathering agreement in the Marcellus Shale for which it earns a fixed-fee for providing gathering services to a single producer using a dedicated gathering system. As the gathering system is expanded, the fixed-fee charged to the producer is adjusted to include the additional gathering assets in the lease. The primary term of the natural gas gathering arrangement expires in 2038 and will continue thereafter on a year-to-year basis until terminated by either party. Other significant natural gas implicit leases relate to a natural gas processing agreement in the Marcellus Shale and a natural gas processing agreement in the Southern Appalachia region for which MPLX earns minimum monthly fees for providing processing services to a single producer using a dedicated processing plant. The primary term of these natural gas processing agreements expires during 2023 and 2033, these contracts will continue thereafter on a year-to-year basis until terminated by either party. MPLX did not elect to use the practical expedient to combine lease and non-lease components for lessor arrangements. The tables below represent the portion of the contract allocated to the lease component based on relative standalone selling price. Lessor agreements are currently deemed operating, as we elected the practical expedient to carry forward historical classification conclusions. If and when a modification of an existing agreement occurs and the agreement is required to be assessed under ASC 842, MPLX assesses the amended agreement and makes a determination as to whether a reclassification of the lease is required. During the year ended December 31, 2019 , there was a modification to MPLX terminal agreements with MPC. Based on the modification, certain terminals within the MPLX terminal agreement were reclassified from operating leases to sales-type leases. As a result, the underlying assets previously shown on the Consolidated Balance Sheets associated with the sales-type leases were derecognized and the net investment in the lease (i.e., the sum of the present value of the future lease payments and the unguaranteed residual value of the assets) was recorded as a lease receivable. When determining the net investment in the lease, certain variable payments were excluded from the total contract consideration, primarily related to fees for which there are no minimum volume commitments. The difference between the net book value of the underlying assets and the net investment in the lease has been recorded through equity given that the dropdown of MPLXT was a common control transaction. During the year, MPLX derecognized approximately $29 million of property, plant and equipment, derecognized approximately $3 million of existing deferred rent receivable, recorded a lease receivable of approximately $47 million , recorded an unguaranteed residual asset of approximately $6 million and equity of $21 million . Under ASC 840, MPLX’s revenue from its implicit lease arrangements, excluding executory costs, totaled approximately $1,032 million in 2018 and $601 million in 2017 . Lease revenues included on the Consolidated Statements of Income during 2019 were as follows: 2019 (In millions) Related Party Third Party Operating leases: Operating lease revenue (1) $ 1,020 $ 257 Sales-type leases: Profit/(loss) recognized at the commencement date — N/A Interest income (Sales-type rental revenue- fixed minimum) 6 N/A Interest income (Revenue from variable lease payments) $ 1 N/A (1) These amounts are presented net of executory costs. The following is a schedule of minimum future rental revenue on the non-cancellable operating leases as of December 31, 2019 : (In millions) Related Party Third Party Total 2020 $ 1,134 $ 186 $ 1,320 2021 1,130 179 1,309 2022 1,127 177 1,304 2023 1,074 170 1,244 2024 1,015 167 1,182 2025 and thereafter 2,699 1,072 3,771 Total minimum future rentals $ 8,179 $ 1,951 $ 10,130 The following is a schedule of minimum future rental revenue on the non-cancellable operating leases as of December 31, 2018: (In millions) Related Party Third Party Total 2019 $ 1,277 $ 171 $ 1,448 2020 1,275 163 1,438 2021 1,146 154 1,300 2022 1,143 151 1,294 2023 1,094 145 1,239 2024 and thereafter 3,786 1,114 4,900 Total minimum future rentals $ 9,721 $ 1,898 $ 11,619 The following is a schedule of minimum future revenue on the sales-type leases with MPC as of December 31, 2019 : (In millions) Related Party 2020 $ 14 2021 14 2022 14 2023 15 2024 15 2025 and thereafter 20 Total minimum future rentals 92 Less: present value discount 45 Lease receivable $ 47 The following schedule summarizes MPLX’s investment in assets held for operating lease by major classes as of December 31, 2019 and 2018 : December 31, (In millions) 2019 2018 Natural gas gathering and NGL transportation pipelines and facilities $ 1,120 $ 964 Processing, fractionation and storage facilities 2,176 1,670 Pipelines and related assets 362 376 Barges and towing vessels 738 619 Terminals and related assets 1,232 1,415 Refinery related assets 1,083 981 Land, building, office equipment and other 236 187 Total 6,947 6,212 Less accumulated depreciation 2,355 2,074 Property, plant and equipment, net $ 4,592 $ 4,138

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Contractual Obligation, Fiscal Year Maturity Schedule	MPLX executed transportation and terminalling agreements that obligate us to minimum volume, throughput or payment commitments over the terms of the agreements, which range from four to 20 years . After the minimum volume commitments are met in the transportation and terminalling agreements, MPLX pays additional amounts based on throughput. There are escalation clauses in the transportation and terminalling agreements, which are based on Consumer Price Index adjustments. The minimum future payments under these agreements as of December 31, 2019 are as follows: (In millions) 2020 $ 2,246 2021 2,222 2022 2,199 2023 2,200 2024 1,753 2025 and thereafter 191 Total $ 10,811
Schedule of Minimum Amounts Payable Annually Under the Product Supply Agreement	On September 1, 2009, MarkWest entered into a product supply agreement creating a long-term contractual obligation for the payment of processing fees in exchange for the entire product processed by the SMR. See Note 17 for additional discussion. The product received under this agreement is sold to a refinery customer pursuant to a corresponding long-term agreement. The minimum amounts payable annually under the product supply agreement, excluding the potential impact of inflation adjustments per the agreement, are as follows: (In millions) 2020 $ 17 2021 17 2022 17 2023 17 2024 17 2024 and thereafter 92 Total minimum payments 177 Less: Services element 68 Less: Interest 29 Total SMR liability 80 Less: Current portion of SMR liability 5 Long-term portion of SMR liability $ 75

Select Quarterly Financial Da_2

Select Quarterly Financial Data (Tables)	12 Months Ended
	Dec. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Summary of Quarterly Financial Data	2019 (In millions, except per unit data) 1st Qtr. (1) 2nd Qtr. (1) 3rd Qtr. 4th Qtr. Total revenues and other income $ 2,235 $ 2,210 $ 2,280 $ 2,316 Income from operations 912 885 926 (346 ) Net income 689 657 689 (573 ) Net income attributable to MPLX LP 503 482 629 (581 ) Net income attributable to MPLX LP per limited partner unit: Common - basic 0.61 0.56 0.61 (0.58 ) Common - diluted 0.61 0.55 0.61 (0.58 ) Cash distributions declared per limited partner common unit 0.6575 0.6675 0.6775 0.6875 Distributions declared: Limited partner units - Public 191 261 266 270 Limited partner units - MPC 332 431 438 446 Series A preferred units 20 21 20 20 Series B preferred units — 21 10 11 Total distributions declared $ 543 $ 734 $ 734 $ 747 2018 (In millions, except per unit data) 1st Qtr. 2nd Qtr. 3rd Qtr. 4th Qtr. (1) Total revenues and other income $ 1,420 $ 1,578 $ 1,712 $ 2,295 Income from operations 557 608 672 891 Net income 423 456 516 611 Net income attributable to MPLX LP 421 453 510 434 Net income attributable to MPLX LP per limited partner unit: Common - basic 0.61 0.55 0.62 0.52 Common - diluted 0.61 0.55 0.62 0.52 Cash distributions declared per limited partner common unit 0.6175 0.6275 0.6375 0.6475 Distributions declared: Limited partner units - Public 179 181 185 187 Limited partner units - MPC 288 316 322 327 Series A preferred units 16 20 19 20 Total distributions declared $ 483 $ 517 $ 526 $ 534 (1) As discussed in Note 1, MPLX’s acquisition of ANDX is considered a transfer between entities under common control due to MPC’s prior relationship with ANDX. Transfers of businesses between entities under common control require prior periods to be retrospectively adjusted for those dates that the entity was under common control. Accordingly, the tables above include the historical results of ANDX beginning October 1, 2018. Amounts shown for the fourth quarter of 2018 as well as the first and second quarters of 2019 are different than amounts previously reported for Total revenues and other income, Income from operations and Net income as a results of this retrospective adjustment for ANDX. Total revenues and other income originally reported for the fourth quarter of 2018 and the first and second quarters of 2019 was $1,715 million , $1,646 million and $1,629 million , respectively. Income from operations originally reported for the fourth quarter of 2018 and the first and second quarters of 2019 was $666 million , $678 million and $659 million , respectively. Net income originally reported for the fourth quarter of 2018 and the first and second quarters of 2019 was $439 million , $509 million and $488 million , respectively.

Description of the Business a_3

Description of the Business and Basis of Presentation (Detail)	Jul. 30, 2019shares	Oct. 31, 2012	Mar. 27, 2012	Dec. 31, 2019
Description Of Business And Basis Of Presentation [Line Items]
Date of partnership formation			Mar. 27, 2012
Date for initial public offering completed		Oct. 31, 2012
Number of reportable segments				2
ANDX LP [Member] | Nonpublic [Member]
Description Of Business And Basis Of Presentation [Line Items]
Common Units Conversion Ratio - ANDX to MPLX	1.0328
ANDX LP [Member] | Public
Description Of Business And Basis Of Presentation [Line Items]
Common Units Conversion Ratio - ANDX to MPLX	1.135

Summary of Principal Accounti_3

Summary of Principal Accounting Policies (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Income (Loss) from Equity Method Investments from Asset Impairment and Elimination of Basis Differential	$ 42
Impairment expense	1,197	$ 0	$ 0
Goodwill	$ 9,536	$ 10,016	$ 2,245

Accounting Standards ASU 2016-0

Accounting Standards ASU 2016-02 Leases and related updates (Details) - Accounting Standards Update 2016-02 [Member] $ in Millions	Jan. 01, 2019USD ($)
Operating Lease Right Of Use Asset [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	$ 629
Operating Lease Liability [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	629
ANDX LP [Member] | Operating Lease Right Of Use Asset [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	124
ANDX LP [Member] | Operating Lease Liability [Member]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	$ 127

Acquisitions Acquisitions (Ande

Acquisitions Acquisitions (Andeavor Logistics LP) (Details) - USD ($) $ in Millions		Jul. 30, 2019	Oct. 01, 2018		Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019		Mar. 31, 2019		Dec. 31, 2018		Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017		Sep. 09, 2019	Jul. 29, 2019	Dec. 31, 2016
Business Acquisition [Line Items]
Cash and cash equivalents					$ 15						$ 77						$ 15		$ 77
Total revenues and other income					2,316	$ 2,280	$ 2,210	[1]	$ 2,235	[1]	2,295	[1]	$ 1,712	$ 1,578	$ 1,420		9,041		7,005		$ 3,867
Net income					(573)	689	657	[1]	689	[1]	611	[1]	516	456	423		1,462		2,006		836
Goodwill, Purchase Accounting Adjustments									(5)
Goodwill					9,536						10,016						9,536		10,016		2,245
Net income attributable to MPLX LP					(581)	$ 629	482	[1]	503	[1]	434	[1]	$ 510	$ 453	$ 421		1,033	[2]	1,818	[2]	794	[2]
Acquisition Costs, Period Cost																	14		4		11
Receivables, net					593						611						593		611
Current Assets, Related Parties					656						556						656		556
Inventory, Gross					110						98						110		98
Other current assets					110						98						110		98
Assets, Current					1,484						1,440						1,484		1,440
Equity method investments					5,275						4,901						5,275		4,901
Property, plant and equipment, net					22,145						21,525						22,145		21,525
Intangibles, net					1,270						1,359						1,270		1,359
Other Assets, Related Parties, Noncurrent					303						24						303		24
Other noncurrent assets					52						60						52		60
Total assets					40,430						39,325						40,430		39,325
Accounts payable					242						266						242		266
Accrued liabilities					187						272						187		272
Current Liabilities, Related Parties					1,008						502						1,008		502
Accrued property, plant and equipment					283						399						283		399
Accrued interest payable					210						184						210		184
Other current liabilities					136						645						136		645
Liabilities, Current					2,132						2,268						2,132		2,268
Long-term deferred revenue					217						132						217		132
Liabilities, Related Parties, Noncurrent					290						46						290		46
Long-term debt					19,704						17,922						19,704		17,922
Deferred income taxes					12						14						12		14
Deferred credits and other liabilities					192						208						192		208
Liabilities					22,849						20,590						22,849		20,590
Series A preferred units					968						1,004						968		1,004
Total MPLX LP partners’ capital					16,364						17,575						16,364		17,575
Partners' Capital, Including Portion Attributable to Noncontrolling Interest					16,613						17,731						16,613		17,731		9,973				$ 11,110
Accumulated other comprehensive loss	[3]				(15)						(16)						(15)		(16)		(14)
Noncontrolling interests					249						156						249		156
Liabilities and Equity					40,430						39,325						40,430		39,325
Andeavor Logistics [Member]
Business Acquisition [Line Items]
Total revenues and other income																	2,400		580
Net income																	266		172
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents			$ 30
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Receivables			500
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Inventory			21
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Other	[4]		52
Business Combination, Recognized Identifiable Assets Acquired, Equity Method Investments			642
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment			6,282
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill			1,034
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets	[5]		23
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets			8,584
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable			463
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Other	[6]		147
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt			4,916
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other	[7]		76
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities			5,602
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net			2,982
Goodwill			8,152
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest			11,134
Net income attributable to MPLX LP																	1,434		2,446
Acquisition Costs, Period Cost																$ 14
ANDX LP [Member] | Public
Business Acquisition [Line Items]
Common Units Conversion Ratio - ANDX to MPLX		1.135
ANDX LP [Member] | Nonpublic [Member]
Business Acquisition [Line Items]
Common Units Conversion Ratio - ANDX to MPLX		1.0328
Operating Lease Right Of Use Asset [Member] | Andeavor Logistics [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill	[8],[9]		4
Logistics and Storage [Member]
Business Acquisition [Line Items]
Goodwill					7,722						7,234						7,722		7,234		162
Intangibles, net					238						235						238		235
Logistics and Storage [Member] | Andeavor Logistics [Member]
Business Acquisition [Line Items]
Goodwill			7,200
Gathering and Processing [Member]
Business Acquisition [Line Items]
Goodwill					1,814						2,782						1,814		2,782		2,083
Intangibles, net					1,032						1,124						$ 1,032		1,124
Gathering and Processing [Member] | Andeavor Logistics [Member]
Business Acquisition [Line Items]
Goodwill			1,000
Previously Reported [Member]
Business Acquisition [Line Items]
Cash and cash equivalents											68								68
Total revenues and other income	[1]						1,629		1,646		1,715
Net income	[1]						$ 488		$ 509		439
Goodwill											2,586								2,586
Receivables, net											417								417
Current Assets, Related Parties											290								290
Inventory, Gross											77								77
Other current assets											45								45
Assets, Current											897								897
Equity method investments											4,174								4,174
Property, plant and equipment, net											14,639								14,639
Intangibles, net											424								424
Other Assets, Related Parties, Noncurrent											24								24
Other noncurrent assets											35								35
Total assets											22,779								22,779
Accounts payable											162								162
Accrued liabilities											250								250
Current Liabilities, Related Parties											254								254
Accrued property, plant and equipment											294								294
Accrued interest payable											143								143
Other current liabilities											83								83
Liabilities, Current											1,186								1,186
Long-term deferred revenue											80								80
Liabilities, Related Parties, Noncurrent											43								43
Long-term debt											13,392								13,392
Deferred income taxes											13								13
Deferred credits and other liabilities											197								197
Liabilities											14,911								14,911
Series A preferred units											1,004								1,004
Total MPLX LP partners’ capital											6,708								6,708
Partners' Capital, Including Portion Attributable to Noncontrolling Interest											6,864								6,864
Noncontrolling interests											156								156
Liabilities and Equity											22,779								22,779
Previously Reported [Member] | Andeavor Logistics [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents			83
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Receivables			241
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Inventory			21
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Other	[4]		59
Business Combination, Recognized Identifiable Assets Acquired, Equity Method Investments			731
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment			6,709
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill			960
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets	[5]		31
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets			8,835
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable			198
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Other	[6]		188
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt			4,916
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other	[7]		75
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities			5,377
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net			3,458
Goodwill			7,428
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest			10,886
Restatement Adjustment [Member] | Andeavor Logistics [Member]
Business Acquisition [Line Items]
Cash and cash equivalents											9								9
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents	[9]		(53)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Receivables	[9]		259
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Inventory	[9]		0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Other	[4],[9]		(7)
Business Combination, Recognized Identifiable Assets Acquired, Equity Method Investments	[9]		(89)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment	[9]		(427)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill	[8],[9]		74
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets	[5],[9]		(8)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets	[9]		(251)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable	[9]		265
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Other	[6],[9]		(41)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt	[9]		0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other	[7],[9]		1
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities	[9]		225
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net	[9]		(476)
Goodwill			724	[9]							7,430								7,430
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest	[9]		248
Receivables, net											194								194
Current Assets, Related Parties											266								266
Inventory, Gross											21								21
Other current assets											53								53
Assets, Current											543								543
Equity method investments											727								727
Property, plant and equipment, net											6,886								6,886
Intangibles, net											935								935
Other Assets, Related Parties, Noncurrent											0								0
Other noncurrent assets											25								25
Total assets											16,546								16,546
Accounts payable											104								104
Accrued liabilities											22								22
Current Liabilities, Related Parties											248								248
Accrued property, plant and equipment											105								105
Accrued interest payable											41								41
Other current liabilities											562								562
Liabilities, Current											1,082								1,082
Long-term deferred revenue											52								52
Liabilities, Related Parties, Noncurrent											3								3
Long-term debt											4,530								4,530
Deferred income taxes											1								1
Deferred credits and other liabilities											11								11
Liabilities											5,679								5,679
Series A preferred units											0								0
Total MPLX LP partners’ capital											10,867								10,867
Partners' Capital, Including Portion Attributable to Noncontrolling Interest											10,867								10,867
Noncontrolling interests											0								0
Liabilities and Equity											16,546								16,546
Customer Contracts [Member] | Andeavor Logistics [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill			$ 950
Minimum | Andeavor Logistics [Member]
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life			2 years
Minimum | Logistics and Storage [Member]
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life																	6 years
Minimum | Gathering and Processing [Member]
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life																	6 years
Maximum | Andeavor Logistics [Member]
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life			10 years
Maximum | Logistics and Storage [Member]
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life																	8 years
Maximum | Gathering and Processing [Member]
Business Acquisition [Line Items]
Finite-Lived Intangible Asset, Useful Life																	25 years
Senior Notes
Business Acquisition [Line Items]
Long-term debt, gross																							$ 2,000
Senior Notes | Andeavor Logistics [Member]
Business Acquisition [Line Items]
Long-term debt, gross			$ 1,100
Andeavor Logistics [Member] | ANDX Bank Revolving Credit Facilities [Member]
Business Acquisition [Line Items]
Long-term debt, gross			$ 1,100								1,200								1,200
Line of Credit Facility, Current Borrowing Capacity																								$ 2,100
Limited Partners Common Units
Business Acquisition [Line Items]
Net income attributable to MPLX LP	[2]																$ 910		1,743		411
Limited Partners Common Units | Public
Business Acquisition [Line Items]
Total MPLX LP partners’ capital					10,800						8,336						10,800		8,336
Partners' Capital, Including Portion Attributable to Noncontrolling Interest					10,800						8,336						10,800		8,336		8,379				8,086
Limited Partners Common Units | Public | Previously Reported [Member]
Business Acquisition [Line Items]
Total MPLX LP partners’ capital											8,336								8,336
Limited Partners Common Units | Public | Restatement Adjustment [Member] | Andeavor Logistics [Member]
Business Acquisition [Line Items]
Total MPLX LP partners’ capital											0								0
Marathon Petroleum Corporation [Member] | Limited Partners Common Units
Business Acquisition [Line Items]
Total MPLX LP partners’ capital					4,968						(1,612)						4,968		(1,612)
Partners' Capital, Including Portion Attributable to Noncontrolling Interest					4,968						(1,612)						4,968		(1,612)		2,099				1,069
Marathon Petroleum Corporation [Member] | Limited Partners Common Units | Previously Reported [Member]
Business Acquisition [Line Items]
Total MPLX LP partners’ capital											(1,612)								(1,612)
Marathon Petroleum Corporation [Member] | Limited Partners Common Units | Restatement Adjustment [Member] | Andeavor Logistics [Member]
Business Acquisition [Line Items]
Total MPLX LP partners’ capital											0								0
Retained Earnings [Member] | Marathon Petroleum Corporation [Member]
Business Acquisition [Line Items]
Partners' Capital, Including Portion Attributable to Noncontrolling Interest					0						10,867						0		10,867		$ 0				$ 791
Retained Earnings [Member] | Marathon Petroleum Corporation [Member] | Previously Reported [Member]
Business Acquisition [Line Items]
Partners' Capital, Including Portion Attributable to Noncontrolling Interest											0								0
Retained Earnings [Member] | Marathon Petroleum Corporation [Member] | Restatement Adjustment [Member] | Andeavor Logistics [Member]
Business Acquisition [Line Items]
Partners' Capital, Including Portion Attributable to Noncontrolling Interest											10,867								10,867
LOOP and Explorer
Business Acquisition [Line Items]
Accumulated other comprehensive loss					$ (15)						(16)						$ (15)		(16)
LOOP and Explorer | Previously Reported [Member]
Business Acquisition [Line Items]
Accumulated other comprehensive loss											(16)								(16)
LOOP and Explorer | Restatement Adjustment [Member] | Andeavor Logistics [Member]
Business Acquisition [Line Items]
Accumulated other comprehensive loss											$ 0								0
Pro Forma [Member] | Andeavor Logistics [Member]
Business Acquisition [Line Items]
Total revenues and other income																			$ 8,666
[1]	As discussed in Note 1, MPLX’s acquisition of ANDX is considered a transfer between entities under common control due to MPC’s prior relationship with ANDX. Transfers of businesses between entities under common control require prior periods to be retrospectively adjusted for those dates that the entity was under common control. Accordingly, the tables above include the historical results of ANDX beginning October 1, 2018. Amounts shown for the fourth quarter of 2018 as well as the first and second quarters of 2019 are different than amounts previously reported for Total revenues and other income, Income from operations and Net income as a results of this retrospective adjustment for ANDX. Total revenues and other income originally reported for the fourth quarter of 2018 and the first and second quarters of 2019 was $1,715 million , $1,646 million and $1,629 million , respectively. Income from operations originally reported for the fourth quarter of 2018 and the first and second quarters of 2019 was $666 million , $678 million and $659 million , respectively. Net income originally reported for the fourth quarter of 2018 and the first and second quarters of 2019 was $439 million , $509 million and $488 million , respectively.
[2]	Allocation of net income/(loss) attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.
[3]	These components of “Accumulated other comprehensive loss” are included in the computation of net periodic benefit cost by LOOP and Explorer and are therefore included on the Consolidated Statements of Income under the caption “Income/(loss) from equity method investments.”
[4]	Includes both related party and third party other current assets.
[5]	Includes both related party and third party other noncurrent assets as well as right of use assets associated with leases.
[6]	Includes accrued liabilities, operating lease liabilities, long-term debt due within one year, as well as related party and third party other current liabilities.
[7]	Includes deferred revenue and deferred income taxes, as well as related party and third party other noncurrent liabilities.
[8]	Includes approximately $4 million of favorable lease assets. In connection with the implementation of ASC 842, this balance was reclassed to “Right of use assets” on the Consolidated Balance Sheets during 2019.
[9]	Inclusive of activity recorded subsequent to the acquisition of ANDX on July 30, 2019, a portion of which was recorded as a non-cash contribution from MPC.

Acquisitions Acquisitions (Acqu

Acquisitions Acquisitions (Acquisition Mt. Airy Terminal) (Details) bbl / d in Thousands, bbl in Millions, $ in Millions		Sep. 26, 2018USD ($)bbl / dbbl	Mar. 31, 2019USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Business Acquisition [Line Items]
Intangibles, net				$ 1,270	$ 1,359
Goodwill				9,536	10,016	$ 2,245
Income from equity method investments	[1],[2]			$ 290	$ 247	$ 78
Mt. Airy Terminal [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Receivables		$ 3
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Other		1
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment		336	$ 336
Intangibles, net		9
Goodwill		121	121
Payments to Acquire Businesses, Gross		$ 451	$ 446
Storage Capacity | bbl		4
Barrels Handled | bbl / d		120
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable		$ (17)
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Other		(7)
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest		$ 446
[1]	“Income from equity method investments” includes the impact of any basis differential amortization or accretion.
[2]	The financial information for equity method investments for 2019 includes financial information of equity method investments acquired as part of the Merger. The financial information for equity method investments for 2018 includes financial information of equity method investments acquired as part of the Merger for the last three months of 2018. The financial information for equity method investments for 2017 does not include financial information of equity method investments acquired as part of the Merger. See Note 1

Acquisitions Acquisitions (Refi

Acquisitions Acquisitions (Refining Logistics and Fuels Distribution) (Details) bbl in Millions, $ in Millions		Feb. 01, 2018USD ($)Tanksharesbbl	Sep. 01, 2017USD ($)shares	Mar. 01, 2017USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)shares	Dec. 31, 2017USD ($)
Business Acquisition [Line Items]
Limited Liability Company (LLC) or Limited Partnership (LP), Managing Member or General Partner, Ownership Interest		2.00%		2.00%			2.00%
Contribution from MPC							$ 346	$ 11,980	$ 675
Property, plant and equipment, net					$ 21,525	$ 21,525	22,145	21,525
Goodwill					10,016	10,016	9,536	$ 10,016	2,245
Number of storage tanks | Tank		619
Number of rail and truck racks		32
Number of docks and gasoline blenders		18
Refining Logistics & Fuels Distribution [Member]
Business Acquisition [Line Items]
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual						1,359
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual						$ 874
Payments to Acquire Businesses, Gross		$ 4,100
Partners' Capital Account, Units, Acquisitions | shares								113,888,889
Equity interest issued or issuable, fair value assigned		4,300
Business Acquisition, Total Consideration, Fair Value Assigned		8,400
Property, plant and equipment, net		830
Refining Logistics [Member]
Business Acquisition [Line Items]
Goodwill		85
Fuels Distribution [Member]
Business Acquisition [Line Items]
Goodwill		$ 130
Limited Partners Common Units | Refining Logistics & Fuels Distribution [Member]
Business Acquisition [Line Items]
Partners' Capital Account, Units, Acquisitions | shares								111,611,111
Limited Partners Common Units | MPLX LP [Member] | Refining Logistics & Fuels Distribution [Member]
Business Acquisition [Line Items]
Partners' Capital Account, Units, Acquisitions | shares		111,611,111
Limited Partners Common Units | MPLX Logistics LLC | Refining Logistics & Fuels Distribution [Member]
Business Acquisition [Line Items]
Partners' Capital Account, Units, Acquisitions | shares		18,176,666
Limited Partners Common Units | MPLX Holdings Inc | Refining Logistics & Fuels Distribution [Member]
Business Acquisition [Line Items]
Partners' Capital Account, Units, Acquisitions | shares		7,824,167
General Partner Units | Refining Logistics & Fuels Distribution [Member]
Business Acquisition [Line Items]
Partners' Capital Account, Units, Acquisitions | shares	[1]							2,277,778
General Partner Units | MPLX LP [Member] | Refining Logistics & Fuels Distribution [Member]
Business Acquisition [Line Items]
Partners' Capital Account, Units, Acquisitions | shares		2,277,778
General Partner Common Units | Refining Logistics & Fuels Distribution [Member]
Business Acquisition [Line Items]
Partners' Capital Account, Units, Acquisitions | shares		85,610,278
LOOP LOCAP SAX and Explorer
Business Acquisition [Line Items]
Equity interest issued or issuable, fair value assigned			$ 653
Business Acquisition, Total Consideration, Fair Value Assigned			$ 1,070
Limited Liability Company (LLC) or Limited Partnership (LP), Managing Member or General Partner, Ownership Interest			2.00%
LOOP LOCAP SAX and Explorer | Limited Partners Common Units | MPLX Logistics LLC
Business Acquisition [Line Items]
Partners' Capital Account, Units, Acquisitions | shares			3,350,893
LOOP LOCAP SAX and Explorer | Limited Partners Common Units | MPLX Holdings Inc
Business Acquisition [Line Items]
Partners' Capital Account, Units, Acquisitions | shares			1,441,224
LOOP LOCAP SAX and Explorer | General Partner Units
Business Acquisition [Line Items]
Partners' Capital Account, Units, Acquisitions | shares			377,778
LOOP LOCAP SAX and Explorer | General Partner Common Units
Business Acquisition [Line Items]
Partners' Capital Account, Units, Acquisitions | shares			13,719,017
Marathon Petroleum Corporation [Member]
Business Acquisition [Line Items]
Contribution from MPC				$ 6
Marathon Petroleum Corporation [Member] | Refining Logistics & Fuels Distribution [Member]
Business Acquisition [Line Items]
Contribution from MPC		$ 23.7
Marathon Petroleum Corporation [Member] | Limited Partners Common Units
Business Acquisition [Line Items]
Contribution from MPC							$ 315	$ 0	$ 0
Marathon Petroleum Corporation [Member] | LOOP LOCAP SAX and Explorer
Business Acquisition [Line Items]
Contribution from MPC					$ 10
Crude Oil
Business Acquisition [Line Items]
Storage Capacity | bbl		56
[1]	Changes to the number of general partner units outstanding, other than changes due to contributions made to MPC for the acquisitions of HSM, HST, WHC, MPLXT, the Joint-Interest Acquisition and Refining Logistics and Fuels Distribution, are the result of cash contributions made by the general partner in order to maintain its two percent GP Interest.

Acquisitions (Joint-Interest Ac

Acquisitions (Joint-Interest Acquisition) (Details) $ in Millions		Feb. 01, 2018	Sep. 01, 2017USD ($)inmishares	Mar. 01, 2017USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Schedule of Equity Method Investments [Line Items]
Aggregate percentage of general partner interest		2.00%		2.00%		2.00%
Income from equity method investments	[1],[2]					$ 290	$ 247	$ 78
Contribution from MPC						346	11,980	675
MPC
Schedule of Equity Method Investments [Line Items]
Contribution from MPC				$ 6
MPC | Limited Partners Common Units
Schedule of Equity Method Investments [Line Items]
Contribution from MPC						315	0	0
MPC | General Partner
Schedule of Equity Method Investments [Line Items]
Contribution from MPC						$ 0	0	0
Illinois Extension
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage			35.00%			35.00%
Pipeline length | mi			168
Pipeline diameter | in			24
Number of pump stations			2
LOOP
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage			41.00%			41.00%
LOCAP
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage			59.00%
Explorer
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage			25.00%			25.00%
Pipeline length | mi			1,830
LOOP LOCAP SAX and Explorer
Schedule of Equity Method Investments [Line Items]
Payments to acquire interest in joint venture			$ 420
Equity interest issued or issuable, value assigned			630
Total consideration, value assigned			1,050
Equity interest issued or issuable, fair value assigned			653
Business Acquisition, Total Consideration, Fair Value Assigned			$ 1,070
Aggregate percentage of general partner interest			2.00%
Income from equity method investments						$ 110	$ 118	$ 21
LOOP LOCAP SAX and Explorer | General Partner Common Units
Schedule of Equity Method Investments [Line Items]
Units, acquisitions | shares			13,719,017
LOOP LOCAP SAX and Explorer | General Partner Units
Schedule of Equity Method Investments [Line Items]
Units, acquisitions | shares			377,778
LOOP LOCAP SAX and Explorer | MPLX Holdings Inc | Limited Partners Common Units
Schedule of Equity Method Investments [Line Items]
Units, acquisitions | shares			1,441,224
LOOP LOCAP SAX and Explorer | MPLX Logistics LLC | Limited Partners Common Units
Schedule of Equity Method Investments [Line Items]
Units, acquisitions | shares			3,350,893
LOOP LOCAP SAX and Explorer | MPC
Schedule of Equity Method Investments [Line Items]
Contribution from MPC					$ 10
LOOP LOCAP SAX and Explorer | MPC | General Partner
Schedule of Equity Method Investments [Line Items]
Payments of Distributions to Affiliates						$ 32
[1]	“Income from equity method investments” includes the impact of any basis differential amortization or accretion.
[2]	The financial information for equity method investments for 2019 includes financial information of equity method investments acquired as part of the Merger. The financial information for equity method investments for 2018 includes financial information of equity method investments acquired as part of the Merger for the last three months of 2018. The financial information for equity method investments for 2017 does not include financial information of equity method investments acquired as part of the Merger. See Note 1

Acquisitions (Acquisition of HS

Acquisitions (Acquisition of HST, WHC & MPLXT) (Details) bbl in Millions, $ in Millions	Feb. 01, 2018	Mar. 01, 2017USD ($)misharesbbl	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)shares
Business Acquisition [Line Items]
Aggregate percentage of general partner interest	2.00%	2.00%	2.00%
Contribution from MPC | $			$ 346	$ 11,980	$ 675
Number of natural gas liquids storage caverns		8
Number of light product terminals		62
Wholly Owned Properties
Business Acquisition [Line Items]
Number of light product terminals		59
Property Subject to Operating Lease
Business Acquisition [Line Items]
Number of light product terminals		1
Partially Owned Properties
Business Acquisition [Line Items]
Number of light product terminals		2
Natural gas liquids storage caverns
Business Acquisition [Line Items]
Storage Capacity | bbl		1.8
Light-product terminal
Business Acquisition [Line Items]
Storage Capacity | bbl		23.6
Crude Oil
Business Acquisition [Line Items]
Miles of pipeline | mi		174
Refined products
Business Acquisition [Line Items]
Miles of pipeline | mi		430
MPC
Business Acquisition [Line Items]
Contribution from MPC | $		$ 6
Limited Partners Common Units | MPC
Business Acquisition [Line Items]
Contribution from MPC | $			$ 315	$ 0	$ 0
HST & WHC & MPLXT
Business Acquisition [Line Items]
Equity interest issued or issuable, value assigned | $		504
Equity interest issued or issuable, fair value assigned | $		$ 503
Units, acquisitions | shares					13,224,873
HST & WHC & MPLXT | General Partner Common Units
Business Acquisition [Line Items]
Units, acquisitions | shares		9,197,900
HST & WHC & MPLXT | Limited Partners Common Units
Business Acquisition [Line Items]
Units, acquisitions | shares					12,960,376
HST & WHC & MPLXT | Limited Partners Common Units | MPLX Logistics LLC
Business Acquisition [Line Items]
Units, acquisitions | shares		2,630,427
HST & WHC & MPLXT | Limited Partners Common Units | MPLX Holdings Inc
Business Acquisition [Line Items]
Units, acquisitions | shares		1,132,049
HST & WHC & MPLXT | General Partner Units
Business Acquisition [Line Items]
Units, acquisitions | shares		264,497			264,497	[1]
HST & WHC & MPLXT | Cash and Cash Equivalents [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross | $		$ 1,500
[1]	Changes to the number of general partner units outstanding, other than changes due to contributions made to MPC for the acquisitions of HSM, HST, WHC, MPLXT, the Joint-Interest Acquisition and Refining Logistics and Fuels Distribution, are the result of cash contributions made by the general partner in order to maintain its two percent GP Interest.

Acquisitions (Acquisition of Oz

Acquisitions (Acquisition of Ozark Pipeline) (Details) bbl / d in Thousands, $ in Millions	Mar. 01, 2017USD ($)bbl / dinmi	Dec. 31, 2017USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Business Acquisition [Line Items]
Payments to acquire property, plant, and equipment			$ 2,408	$ 2,111	$ 1,411
Ozark Pipeline
Business Acquisition [Line Items]
Payments to acquire property, plant, and equipment	$ 219
Pipeline length | mi	433
Pipeline diameter | in	22
Pipeline barrels handled | bbl / d	230
Revenues and other income		$ 64
Income from operations		$ 20

Acquisitions (Acquisition of Ma

Acquisitions (Acquisition of MarEn Bakken) (Details) bbl / d in Thousands, $ in Millions		Feb. 15, 2017USD ($)Quarterly_reporting_periodbbl / d	Dec. 31, 2017USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Schedule of Equity Method Investments [Line Items]
Payments to acquire equity method investments				$ 713	$ 341	$ 761
Income from equity method investments	[1],[2]			290	247	$ 78
MPC
Schedule of Equity Method Investments [Line Items]
Incentive distribution rights forfeited per quarter		$ 1.6
Number of quarters IDRs forfeited | Quarterly_reporting_period		12
Prorated incentive distribution rights forfeited		$ 0.8
MarEn Bakken
Schedule of Equity Method Investments [Line Items]
Payments to acquire equity method investments		$ 2,000
MarEn Bakken
Schedule of Equity Method Investments [Line Items]
Barrels Handled | bbl / d		520
Payments to acquire equity method investments		$ 500
Percentage of ownership interest in joint venture acquired		25.00%
Income from equity method investments			$ 15	$ 72	$ 48
Bakken Pipeline System
Schedule of Equity Method Investments [Line Items]
Percentage of ownership interest in joint venture acquired		37.00%
Equity method investment, ownership percentage		9.00%
[1]	“Income from equity method investments” includes the impact of any basis differential amortization or accretion.
[2]	The financial information for equity method investments for 2019 includes financial information of equity method investments acquired as part of the Merger. The financial information for equity method investments for 2018 includes financial information of equity method investments acquired as part of the Merger for the last three months of 2018. The financial information for equity method investments for 2017 does not include financial information of equity method investments acquired as part of the Merger. See Note 1

Investments and Noncontrollin_3

Investments and Noncontrolling Interest (Equity Method Investments) (Details) - USD ($) $ in Millions		Dec. 31, 2019	Dec. 31, 2018	Sep. 01, 2017
Schedule of Equity Method Investments [Line Items]
Equity method investments		$ 5,275	$ 4,901
Whistler Pipeline LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		38.00%
Wink to Webster Pipeline LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		15.00%
Centrahoma Processing LLC
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		40.00%
Explorer
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		25.00%		25.00%
Illinois Extension
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		35.00%		35.00%
LOOP
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		41.00%		41.00%
MarEn Bakken
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		25.00%
MarkWest EMG Jefferson Dry Gas Gathering Company, L.L.C. [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		67.00%
Rendezvous Gas Services, L.L.C. [Member] | Direct Ownership Interest
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage	[1]	78.00%
MarkWest Utica EMG
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		56.00%
Sherwood Midstream LLC
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		50.00%
Sherwood Midstream Holdings | Direct Ownership Interest
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		53.00%
Andeavor Logistics Rio Pipeline [Member] | Direct Ownership Interest
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage	[1]	67.00%
Minnesota Pipe Line Company, LLC [Member] | Direct Ownership Interest
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage	[1]	17.00%
Logistics and Storage [Member] | Whistler Pipeline LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments		$ 134	0
Logistics and Storage [Member] | Wink to Webster Pipeline LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments		126	0
Logistics and Storage [Member] | Explorer
Schedule of Equity Method Investments [Line Items]
Equity method investments		83	90
Logistics and Storage [Member] | Illinois Extension
Schedule of Equity Method Investments [Line Items]
Equity method investments		265	275
Logistics and Storage [Member] | LOOP
Schedule of Equity Method Investments [Line Items]
Equity method investments		238	226
Logistics and Storage [Member] | MarEn Bakken
Schedule of Equity Method Investments [Line Items]
Equity method investments		481	498
Logistics and Storage [Member] | Other VIEs and Non-VIEs [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments	[1]	55	51
Logistics and Storage [Member] | Andeavor Logistics Rio Pipeline [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments	[1]	202	181
Logistics and Storage [Member] | Minnesota Pipe Line Company, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments	[1]	190	197
Gathering and Processing [Member] | Centrahoma Processing LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments		153	160
Gathering and Processing [Member] | MarkWest EMG Jefferson Dry Gas Gathering Company, L.L.C. [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments		302	236
Gathering and Processing [Member] | Rendezvous Gas Services, L.L.C. [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments	[1]	170	248
Gathering and Processing [Member] | MarkWest Utica EMG
Schedule of Equity Method Investments [Line Items]
Equity method investments		1,984	2,039
Gathering and Processing [Member] | Sherwood Midstream LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments		537	366
Gathering and Processing [Member] | Sherwood Midstream Holdings
Schedule of Equity Method Investments [Line Items]
Equity method investments		157	157
Gathering and Processing [Member] | Other VIEs and Non-VIEs [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments	[1]	198	177
Operating Segments | Logistics and Storage [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments		1,774	1,518
Operating Segments | Gathering and Processing [Member]
Schedule of Equity Method Investments [Line Items]
Equity method investments		$ 3,501	$ 3,383
[1]	These investments as well as certain investments included within “Other” for both L&S and G&P are investments acquired as part of the Merger. The December 31, 2019 balance reflects all purchase accounting adjustments identified by MPC as part of its acquisition of Andeavor.

Investments and Noncontrollin_4

Investments and Noncontrolling Interests (Summary of Equity Method Investment Financial Information) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Revenue and other income	[1]	$ 2,067	$ 1,905	$ 1,227
Costs and expenses	[1]	943	1,024	659
Income (loss) from operations	[1]	1,124	881	568
Net income (loss)	[1]	967	803	478
Income from equity method investments	[1],[2]	290	247	78
Income (Loss) from Equity Method Investments from Asset Impairment and Elimination of Basis Differential		42
Current assets		864	667
Noncurrent assets		10,996	9,086
Current liabilities		437	438
Noncurrent liabilities		1,127	1,036
Other VIEs
Schedule of Equity Method Investments [Line Items]
Revenue and other income	[1]	650	484	273
Costs and expenses	[1]	375	286	139
Income (loss) from operations	[1]	275	198	134
Net income (loss)	[1]	215	197	133
Income from equity method investments	[1],[2]	103	67	30
Current assets		534	252
Noncurrent assets		5,862	3,796
Current liabilities		192	158
Noncurrent liabilities		305	191
Non-VIEs
Schedule of Equity Method Investments [Line Items]
Revenue and other income	[1]	1,417	1,421	954
Costs and expenses	[1]	568	738	520
Income (loss) from operations	[1]	849	683	434
Net income (loss)	[1]	752	606	345
Income from equity method investments	[1],[2]	187	180	$ 48
Current assets		330	415
Noncurrent assets		5,134	5,290
Current liabilities		245	280
Noncurrent liabilities		$ 822	$ 845
[1]	The financial information for equity method investments for 2019 includes financial information of equity method investments acquired as part of the Merger. The financial information for equity method investments for 2018 includes financial information of equity method investments acquired as part of the Merger for the last three months of 2018. The financial information for equity method investments for 2017 does not include financial information of equity method investments acquired as part of the Merger. See Note 1
[2]	“Income from equity method investments” includes the impact of any basis differential amortization or accretion.

Investments and Noncontrollin_5

Investments and Noncontrolling Interests (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]
Income (Loss) from Equity Method Investments from Asset Impairment	$ 28
Equity Method Investment, Other than Temporary Impairment	14
Income (Loss) from Equity Method Investments from Asset Impairment and Elimination of Basis Differential	$ 42
MarkWest Utica EMG
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage	56.00%
Sherwood Midstream LLC
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage	50.00%
Sherwood Midstream Holdings | Direct Ownership Interest
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage	53.00%
Sherwood Midstream Holdings | Indirect Ownership Interest
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage	23.70%
Gathering and Processing [Member]
Schedule of Equity Method Investments [Line Items]
Basis difference	$ 1,000	$ 1,300
Basis difference, not amortized	498	542
Logistics and Storage [Member]
Schedule of Equity Method Investments [Line Items]
Basis difference	329	187
Basis difference, not amortized	$ 167	$ 167

Related Party Agreements and _3

Related Party Agreements and Transactions (Narrative) (Detail) - USD ($) $ in Millions	Jul. 31, 2019	Apr. 27, 2018	Dec. 31, 2019	Dec. 31, 2018	Apr. 26, 2018
Loan Agreement [Abstract]
Revenue from related parties			$ 10	$ 6
Purchases from related parties			5	8
MPC
Loan Agreement [Abstract]
Prepaid insurance			9	5
MPC Investment | Related Party Revolving Credit Agreement
Loan Agreement [Abstract]
Line of Credit Facility, Current Borrowing Capacity	$ 1,500	$ 1,000			$ 500
Debt Instrument, Description of Variable Rate Basis	LIBOR plus 1.25 percent	LIBOR plus 1.50 percent
Proceeds from lines of credit			8,540	3,962
Repayments of lines of credit			7,946	4,347
Outstanding balance			$ 594	$ 0
Interest rate during period			3.441%	3.473%
Commercial Agreements | MPC | Six Year Transportation Services Agreement [Member] | Providing marine transportation of crude oil, feedstocks and refined petroleum products, and related services [Member]
Commercial Agreements
Term Of Agreements			6 years
Commercial Agreements | MPC | Trucking Services Agreement [Member] | Refined products
Commercial Agreements
Term Of Agreements			10 years
Commercial Agreements | MPC | Storage Services Agreements | Minimum | Refined products
Commercial Agreements
Term Of Agreements			3 years
Commercial Agreements | MPC | Storage Services Agreements | Maximum | Refined products
Commercial Agreements
Term Of Agreements			17 years
Commercial Agreements | MPC | Ten Year Terminal Services Agreement [Member] | Refined products
Commercial Agreements
Term Of Agreements			10 years
Commercial Agreements | MPC | Terminal Services Agreements | Minimum | Refined products
Commercial Agreements
Term Of Agreements			1 year
Automatic renewal term agreement			1 year
Commercial Agreements | MPC | Terminal Services Agreements | Maximum | Refined products
Commercial Agreements
Term Of Agreements			10 years
Automatic renewal term agreement			5 years
Commercial Agreements | MPC | Management Services Agreements [Member] | Co-location Agreements [Member]
Commercial Agreements
Term Of Agreements			50 years
Commercial Agreements | MPC | Management Services Agreements [Member] | Marine Management Services [Member]
Commercial Agreements
Automatic renewal term agreement			5 years
Number of renewals			2
Commercial Agreements | MPC | Lease Agreements [Member] | Management Services Agreements [Member]
Commercial Agreements
Term Of Agreements			50 years
Operating Agreements [Member] | MPC | Minimum
Commercial Agreements
Term Of Agreements			1 year
Operating Agreements [Member] | MPC | Maximum
Commercial Agreements
Term Of Agreements			5 years
MarkWest Utica EMG
Related Party Transaction [Line Items]
Equity method investment, ownership percentage			56.00%
Sherwood Midstream LLC
Related Party Transaction [Line Items]
Equity method investment, ownership percentage			50.00%
MarkWest EMG Jefferson Dry Gas Gathering Company, L.L.C. [Member]
Related Party Transaction [Line Items]
Equity method investment, ownership percentage			67.00%

Related Party Agreements and _4

Related Party Agreements and Transactions (Intercompany Loans with Related Parties) (Detail) - USD ($) $ in Millions	Jul. 31, 2019	Apr. 27, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 21, 2018	Apr. 26, 2018
Related Party Transaction [Line Items]
Revenue from related parties			$ 10	$ 6
Purchases from related parties			5	8
MPC
Related Party Transaction [Line Items]
Current liabilities - related parties			911	360
Other
Related Party Transaction [Line Items]
Current liabilities - related parties			37	76
MPC Investment | Related Party Revolving Credit Agreement
Related Party Transaction [Line Items]
Line of Credit Facility, Current Borrowing Capacity	$ 1,500	$ 1,000				$ 500
Debt Instrument, Description of Variable Rate Basis	LIBOR plus 1.25 percent	LIBOR plus 1.50 percent
Proceeds from lines of credit			$ 8,540	$ 3,962
Interest rate during period			3.441%	3.473%
Repayments of lines of credit			$ 7,946	$ 4,347
Outstanding balance			594	$ 0
ANDX LP [Member] | MPC Investment | Related Party Revolving Credit Agreement
Related Party Transaction [Line Items]
Line of Credit Facility, Current Borrowing Capacity					$ 500
Proceeds from lines of credit			$ 773
Interest rate during period			4.249%
Repayments of lines of credit			$ 773
Outstanding balance			$ 0

Related Party Agreements and _5

Related Party Agreements and Transactions (Summary of Revenue by Income Statement RP Line Item) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Related Party Transaction [Line Items]
Rental income - related parties		$ 1,196	$ 846	$ 279
Related Party Transaction, Other Revenues from Transactions with Related Party		114	99	92
MPC
Related Party Transaction [Line Items]
Rental income - related parties		1,196	846	279
Sales Revenue, Goods, Related Party, Net Zero		1,120	607	254
Related Party Transaction, Other Revenues from Transactions with Related Party		47	41	40
Other Affiliates [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Other Revenues from Transactions with Related Party		67	58	52
Service [Member]
Related Party Transaction [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		3,455	2,404	1,082
Service [Member] | MPC
Related Party Transaction [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties		3,455	2,404	1,082
Product [Member]
Related Party Transaction [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties	[1]	142	87	8
Product [Member] | MPC
Related Party Transaction [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties	[1]	140	87	8
Product [Member] | Other Affiliates [Member]
Related Party Transaction [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties	[1]	$ 2	$ 0	$ 0
[1]	There were additional product sales to MPC that net to zero within the consolidated financial statements as the transactions are recorded net due to the terms of the agreements under which such product was sold. For 2019 , 2018 and 2017 , these sales totaled $1,120 million , $607 million and $254 million , respectively.

Related Party Agreements and _6

Related Party Agreements and Transactions (Summary of Expenses by Income Statement RP Line Item) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
MPC
Related Party Transaction [Line Items]
Expenses incurred under employee services agreements	$ 1,639	$ 1,155	$ 595
MPC | Rental cost of sales - related parties [Member]
Related Party Transaction [Line Items]
Expenses incurred under employee services agreements	165	31	2
MPC | Purchases - related parties
Related Party Transaction [Line Items]
Expenses incurred under employee services agreements	1,210	919	455
MPC | General and Administrative Expense - Related Party [Member]
Related Party Transaction [Line Items]
Expenses incurred under employee services agreements	243	199	138
Other Affiliates [Member] | Purchases - related parties
Related Party Transaction [Line Items]
Expenses incurred under employee services agreements	21	6	0
Construction-in-progress | MPC
Related Party Transaction [Line Items]
Property, Plant and Equipment, Additions	$ 169	$ 152	$ 42

Related Party Agreements and _7

Related Party Agreements and Transactions (Summary of Balance Sheet by RP Line Item) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Related Party Transaction [Line Items]
Current Assets, Related Parties	$ 656		$ 556
Operating Lease, Right-of-Use Asset	365		0
Other Assets, Related Parties, Noncurrent	303		24
Operating Lease, Liability, Current	66		0
Current Liabilities, Related Parties	1,008		502
Operating Lease, Liability, Noncurrent	302		0
Liabilities, Related Parties, Noncurrent	290		46
Other Affiliates [Member]
Related Party Transaction [Line Items]
Accounts Receivable, Related Parties, Current	22		9
Due to Related Parties, Current	37		76
MPC
Related Party Transaction [Line Items]
Accounts Receivable, Related Parties, Current	621		542
Prepaid insurance	9		5
Net Investment in Lease, Current	4		0
Due from Related Parties, Noncurrent	21		24
Operating Lease, Right-of-Use Asset	232		0
Net Investment in Lease, Noncurrent	43		0
Sales-type Lease, Unguaranteed Residual Asset	7	$ 6	0
Due to Related Parties, Current	911		360
Operating Lease, Liability, Current	1		0
Operating Lease, Liability, Noncurrent	230		0
MPC | Minimum Committed Volume Contracts [Member]
Related Party Transaction [Line Items]
Deferred revenue related parties	42		57
MPC | Reimbursable Projects
Related Party Transaction [Line Items]
Deferred revenue related parties	16		9
Deferred Revenue, Noncurrent, Related Parties	53		46
MPC | Other current liabilities
Related Party Transaction [Line Items]
Deferred revenue related parties	1		0
MPC | Other Noncurrent Liabilities [Member]
Related Party Transaction [Line Items]
Deferred Revenue, Noncurrent, Related Parties	$ 7		$ 0

Net Income (Loss) Per Limited_3

Net Income (Loss) Per Limited Partner Unit (Schedule of Distributions by Partner Class) (Detail) - USD ($) shares in Millions, $ in Millions

3 Months Ended

12 Months Ended

Dec. 31, 2019

Sep. 30, 2019

Jun. 30, 2019

[1]

Mar. 31, 2019

[1]

Dec. 31, 2018

[1]

Sep. 30, 2018

Jun. 30, 2018

Mar. 31, 2018

Dec. 31, 2019

Dec. 31, 2018

Dec. 31, 2017

Net Income Per Share [Line Items]

Potentially dilutive securities

1

1

1

Net income attributable to MPLX LP

$ (581)

$ 629

$ 482

$ 503

$ 434

$ 510

$ 453

$ 421

$ 1,033

[2]

$ 1,818

[2]

$ 794

[2]

Total cash distributions declared

2,758

2,060

1,288

Undistributed net loss attributable to MPLX LP

(1,725)

(242)

(494)

Preferred Partner [Member]

Net Income Per Share [Line Items]

Net income attributable to MPLX LP

[2]

81

75

65

Total cash distributions declared

[3]

65

General Partner

Net Income Per Share [Line Items]

Net income attributable to MPLX LP

[2]

318

Total cash distributions declared

[3],[4]

0

0

328

Limited Partners Common Units

Net Income Per Share [Line Items]

Net income attributable to MPLX LP

[2]

910

1,743

411

Total cash distributions declared

[3]

2,635

1,985

895

Series A Preferred Stock [Member] | Preferred Partner [Member]

Net Income Per Share [Line Items]

Total cash distributions declared

[3]

81

75

Series B Preferred Stock [Member] | Preferred Partner [Member]

Net Income Per Share [Line Items]

Total cash distributions declared

[3]

$ 42

[2]

$ 0

$ 0

[1]

As discussed in Note 1, MPLX’s acquisition of ANDX is considered a transfer between entities under common control due to MPC’s prior relationship with ANDX. Transfers of businesses between entities under common control require prior periods to be retrospectively adjusted for those dates that the entity was under common control. Accordingly, the tables above include the historical results of ANDX beginning October 1, 2018. Amounts shown for the fourth quarter of 2018 as well as the first and second quarters of 2019 are different than amounts previously reported for Total revenues and other income, Income from operations and Net income as a results of this retrospective adjustment for ANDX. Total revenues and other income originally reported for the fourth quarter of 2018 and the first and second quarters of 2019 was $1,715 million , $1,646 million and $1,629 million , respectively. Income from operations originally reported for the fourth quarter of 2018 and the first and second quarters of 2019 was $666 million , $678 million and $659 million , respectively. Net income originally reported for the fourth quarter of 2018 and the first and second quarters of 2019 was $439 million , $509 million and $488 million , respectively.

[2]

Allocation of net income/(loss) attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.

[3]

See Note 8 for distribution information.

[4]

Distributions declared on January 25, 2018 on general partner common units issued on February 1, 2018 in exchange for the economic general partner interest, including IDRs, are shown as general partner distributions declared.

Net Income (Loss) Per Limited_4

Net Income (Loss) Per Limited Partner Unit (Basic and Diluted Earnings Per Unit) (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended											12 Months Ended
		Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019		Mar. 31, 2019		Dec. 31, 2018		Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Net income attributable to MPLX LP:
Total cash distributions declared													$ 2,758		$ 2,060		$ 1,288
Undistributed net income loss attributable to MPLX LP													(1,725)		(242)		(494)
Net income attributable to MPLX LP		$ (581)	$ 629	$ 482	[1]	$ 503	[1]	$ 434	[1]	$ 510	$ 453	$ 421	$ 1,033	[2]	$ 1,818	[2]	$ 794	[2]
Weighted average units outstanding:
Basic (shares)													906	[3]	761		393
Diluted (shares)													907	[3]	761		396
General Partner
Net income attributable to MPLX LP:
Total cash distributions declared	[4],[5]												$ 0		$ 0		$ 328
Undistributed net income loss attributable to MPLX LP																	(10)
Net income attributable to MPLX LP	[2]																$ 318
Weighted average units outstanding:
Basic (shares)																	8
Diluted (shares)																	8
Limited Partners Common Units
Net income attributable to MPLX LP:
Total cash distributions declared	[5]												2,635		1,985		$ 895
Undistributed net income loss attributable to MPLX LP													(1,725)		(242)		(484)
Net income attributable to MPLX LP	[2]												$ 910		$ 1,743		$ 411
Weighted average units outstanding:
Basic (shares)													906	[3]	761		385
Diluted (shares)													907	[3]	761		388
Net income attributable to MPLX LP subsequent to initial public offering per limited partner unit:
Basic (in USD per unit)		$ (0.58)	$ 0.61	$ 0.56		$ 0.61		$ 0.52		$ 0.62	$ 0.55	$ 0.61	$ 1		$ 2.29		$ 1.07
Diluted (in USD per unit)		$ (0.58)	$ 0.61	$ 0.55		$ 0.61		$ 0.52		$ 0.62	$ 0.55	$ 0.61	$ 1		$ 2.29		$ 1.06
Preferred Partner [Member]
Net income attributable to MPLX LP:
Total cash distributions declared	[5]																$ 65
Undistributed net income loss attributable to MPLX LP																	0
Net income attributable to MPLX LP	[2]												$ 81		$ 75		65
Series A Preferred Stock [Member] | Preferred Partner [Member]
Net income attributable to MPLX LP:
Total cash distributions declared	[5]												81		75
Undistributed net income loss attributable to MPLX LP													0		0
Series B Preferred Stock [Member] | Preferred Partner [Member]
Net income attributable to MPLX LP:
Total cash distributions declared	[5]												42	[2]	$ 0		$ 0
Undistributed net income loss attributable to MPLX LP													$ 0
[1]	As discussed in Note 1, MPLX’s acquisition of ANDX is considered a transfer between entities under common control due to MPC’s prior relationship with ANDX. Transfers of businesses between entities under common control require prior periods to be retrospectively adjusted for those dates that the entity was under common control. Accordingly, the tables above include the historical results of ANDX beginning October 1, 2018. Amounts shown for the fourth quarter of 2018 as well as the first and second quarters of 2019 are different than amounts previously reported for Total revenues and other income, Income from operations and Net income as a results of this retrospective adjustment for ANDX. Total revenues and other income originally reported for the fourth quarter of 2018 and the first and second quarters of 2019 was $1,715 million , $1,646 million and $1,629 million , respectively. Income from operations originally reported for the fourth quarter of 2018 and the first and second quarters of 2019 was $666 million , $678 million and $659 million , respectively. Net income originally reported for the fourth quarter of 2018 and the first and second quarters of 2019 was $439 million , $509 million and $488 million , respectively.
[2]	Allocation of net income/(loss) attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.
[3]	The Series B preferred units and the MPLX common units issued in connection with the Merger were not outstanding during the entire year. See Notes 4 and 8 for additional information about the treatment of these units.
[4]	Distributions declared on January 25, 2018 on general partner common units issued on February 1, 2018 in exchange for the economic general partner interest, including IDRs, are shown as general partner distributions declared.
[5]	See Note 8 for distribution information.

Equity (Units Outstanding) (Det

Equity (Units Outstanding) (Details) - USD ($) $ in Millions		Sep. 20, 2019	Jul. 30, 2019	Feb. 01, 2018	Mar. 01, 2017	May 13, 2016	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017		Dec. 31, 2016
Stockholders Equity [Line Items]
Number of units outstanding							1,058,355,471				794,089,518				1,058,355,471	794,089,518	415,438,793		368,555,271
Aggregate percentage of general partner interest				2.00%	2.00%										2.00%
Partners' Capital Account, Units, Converted															(1,148,330)	(264,413,309)	(366,509)
Total cash distributions declared															$ 2,758	$ 2,060	$ 1,288
Partners' Capital Account, Unit-based Payment Arrangement, Number of Units															288,031	348,527	273,639
Units issued																	14,129,589
Limited Partners Common Units
Stockholders Equity [Line Items]
Number of units outstanding							1,058,355,471				794,089,518				1,058,355,471	794,089,518	407,130,020		357,193,288
Partners' Capital Account, Units, Converted				(275,000,000)											(1,148,330)	(275,000,000)	(4,350,057)
Total cash distributions declared	[1]														$ 2,635	$ 1,985	$ 895
Partners' Capital Account, Unit-based Payment Arrangement, Number of Units															288,031	348,387	268,167
Units issued															0		13,846,998
Limited Partners Common Units | MPC
Stockholders Equity [Line Items]
Common units outstanding							666,000,000				505,000,000				666,000,000	505,000,000
Limited Partners' Capital Account, Units Issued			161,000,000				666,000,000				505,000,000				666,000,000	505,000,000
Total cash distributions declared							$ 446	$ 438	$ 431	$ 332	$ 327	$ 322	$ 316	$ 288
General Partner And Limited Partner Units | MPC
Stockholders Equity [Line Items]
Common units outstanding							665,997,540								665,997,540
General Partner Units
Stockholders Equity [Line Items]
Number of units outstanding	[2]						0				0				0	0	8,308,773		7,371,105
Partners' Capital Account, Units, Converted	[2]														0	(10,586,691)	(7,330)
Partners' Capital Account, Unit-based Payment Arrangement, Number of Units	[2]														0	140	5,472
Units issued	[2]																282,591
Class B Units
Stockholders Equity [Line Items]
Number of units outstanding							0				0				0	0	0		3,990,878
Partners' Capital Account, Units, Converted																	(3,990,878)
ANDX LP [Member] | Public
Stockholders Equity [Line Items]
Common Units Conversion Ratio - ANDX to MPLX			1.135
ANDX LP [Member] | Nonpublic [Member]
Stockholders Equity [Line Items]
Common Units Conversion Ratio - ANDX to MPLX			1.0328
Public | Limited Partners Common Units
Stockholders Equity [Line Items]
Common units outstanding							392,000,000				289,000,000				392,000,000	289,000,000
Limited Partners' Capital Account, Units Issued			102,000,000				392,000,000				289,000,000				392,000,000	289,000,000
Total cash distributions declared							$ 270	$ 266	$ 261	$ 191	$ 187	$ 185	$ 181	$ 179
Series A Convertible Preferred Units
Stockholders Equity [Line Items]
Number of units outstanding							29,600,000								29,600,000
Partners' Capital Account, Units, Converted		(1,200,000)
Units issued						30,800,000
Series B Preferred Stock [Member] | MPLX LP [Member]
Stockholders Equity [Line Items]
Preferred Units, Outstanding			600,000				600,000								600,000
TexNew Mex units [Member] | MPLX LP [Member]
Stockholders Equity [Line Items]
Common units outstanding			80,000
Total cash distributions declared											$ 0				$ 1
HST & WHC & MPLXT
Stockholders Equity [Line Items]
Partners' Capital Account, Units, Acquisitions																	13,224,873
HST & WHC & MPLXT | Limited Partners Common Units
Stockholders Equity [Line Items]
Partners' Capital Account, Units, Acquisitions																	12,960,376
HST & WHC & MPLXT | General Partner Units
Stockholders Equity [Line Items]
Partners' Capital Account, Units, Acquisitions					264,497												264,497	[2]
LOOP LOCAP SAX and Explorer Llc [Member]
Stockholders Equity [Line Items]
Partners' Capital Account, Units, Acquisitions																	18,888,912
LOOP LOCAP SAX and Explorer Llc [Member] | Limited Partners Common Units
Stockholders Equity [Line Items]
Partners' Capital Account, Units, Acquisitions																	18,511,134
LOOP LOCAP SAX and Explorer Llc [Member] | General Partner Units
Stockholders Equity [Line Items]
Partners' Capital Account, Units, Acquisitions	[2]																377,778
Refining Logistics & Fuels Distribution [Member]
Stockholders Equity [Line Items]
Partners' Capital Account, Units, Acquisitions																113,888,889
Refining Logistics & Fuels Distribution [Member] | Limited Partners Common Units
Stockholders Equity [Line Items]
Partners' Capital Account, Units, Acquisitions																111,611,111
Refining Logistics & Fuels Distribution [Member] | General Partner Units
Stockholders Equity [Line Items]
Partners' Capital Account, Units, Acquisitions	[2]															2,277,778
Refining Logistics & Fuels Distribution [Member] | MPLX LP [Member] | Limited Partners Common Units
Stockholders Equity [Line Items]
Partners' Capital Account, Units, Acquisitions				111,611,111
Refining Logistics & Fuels Distribution [Member] | MPLX LP [Member] | General Partner Units
Stockholders Equity [Line Items]
Partners' Capital Account, Units, Acquisitions				2,277,778
Andeavor Logistics [Member]
Stockholders Equity [Line Items]
Partners' Capital Account, Units, Acquisitions															262,829,592
Andeavor Logistics [Member] | Limited Partners Common Units
Stockholders Equity [Line Items]
Partners' Capital Account, Units, Acquisitions															262,829,592
Andeavor Logistics [Member] | General Partner Units
Stockholders Equity [Line Items]
Partners' Capital Account, Units, Acquisitions	[2]														0
[1]	See Note 8 for distribution information.
[2]	Changes to the number of general partner units outstanding, other than changes due to contributions made to MPC for the acquisitions of HSM, HST, WHC, MPLXT, the Joint-Interest Acquisition and Refining Logistics and Fuels Distribution, are the result of cash contributions made by the general partner in order to maintain its two percent GP Interest.

Equity (Reorganization Transact

Equity (Reorganization Transactions) (Details) $ / shares in Units, $ in Millions		Jul. 29, 2019$ / sharesshares	Feb. 01, 2018USD ($)shares	Jul. 01, 2017Agreement$ / sharesshares	Mar. 01, 2017USD ($)	Jul. 01, 2016Agreement$ / sharesshares	Sep. 30, 2019USD ($)	Dec. 31, 2019USD ($)$ / sharesshares	Sep. 30, 2019USD ($)$ / shares	Jun. 30, 2019USD ($)$ / shares	Mar. 31, 2019$ / shares	Dec. 31, 2018USD ($)$ / shares	Sep. 30, 2018$ / shares	Jun. 30, 2018$ / shares	Mar. 31, 2018$ / shares	Dec. 31, 2019USD ($)$ / sharesshares	Dec. 31, 2018USD ($)$ / sharesshares	Dec. 31, 2017USD ($)shares	Jul. 30, 2019USD ($)shares	Dec. 31, 2016USD ($)
Class of Stock [Line Items]
Contribution from MPC																$ 346	$ 11,980	$ 675
Partners' Capital, Including Portion Attributable to Noncontrolling Interest								$ 16,613				$ 17,731				$ 16,613	$ 17,731	$ 9,973		$ 11,110
Partners' Capital Account, Units, Converted | shares																1,148,330	264,413,309	366,509
Partners' Capital Account, Exchanges and Conversions																$ (36)	$ 0	$ 0
Net income (loss)																(1,381)	(1,931)	(771)
(Placeholder)																$ (30)	$ (17)	$ (7)
MPC
Class of Stock [Line Items]
Contribution from MPC					$ 6
Limited Partners Common Units
Class of Stock [Line Items]
Cash distributions declared per limited partner common unit | $ / shares								$ 0.6875	$ 0.6775	$ 0.6675	$ 0.6575	$ 0.6475	$ 0.6375	$ 0.6275	$ 0.6175	$ 2.6900	$ 2.5300
Partners' Capital Account, Units, Converted | shares			275,000,000													1,148,330	275,000,000	4,350,057
Partners' Capital Account, Exchanges and Conversions			$ 10,400
Limited Partners Common Units | MPC
Class of Stock [Line Items]
Contribution from MPC																$ 315	$ 0	$ 0
Partners' Capital, Including Portion Attributable to Noncontrolling Interest								$ 4,968				$ (1,612)				4,968	(1,612)	2,099		$ 1,069
Partners' Capital Account, Exchanges and Conversions																0	7,926	0
Net income (loss)																(595)	(1,076)	(110)
(Placeholder)																$ 0	$ 0	$ 0
Class B Units
Class of Stock [Line Items]
Partners' Capital Account, Units, Converted | shares																		3,990,878
General Partner Units
Class of Stock [Line Items]
Partners' Capital Account, Units, Converted | shares	[1]															0	10,586,691	7,330
MarkWest
Class of Stock [Line Items]
Common Units Conversion Ratio | shares				1.09		1.09
Cash consideration to unitholders | $ / shares				$ 6.20		$ 6.20
ANDX LP [Member] | MPC
Class of Stock [Line Items]
Contribution from MPC								$ 12.5	$ 12.5							$ 37.5
Andeavor Logistics [Member]
Class of Stock [Line Items]
Preferred Units, Outstanding | shares		600,000																	600,000
ANDX LP [Member]
Class of Stock [Line Items]
Preferred Stock, Dividend Rate, Percentage		6.875%
Units issued, price per unit | $ / shares		$ 1,000
Maximum | M&R MWE Liberty LLC [Member]
Class of Stock [Line Items]
Number of Underwritten Offerings Allowable to be Demanded | Agreement				3		3
Number of Underwritten Offerings Allowable to be Demanded in 12 Month Period | Agreement				1		1
Maximum | M&R MWE Liberty LLC [Member] | Limited Partners Common Units
Class of Stock [Line Items]
Percentage of Limited Partners' Capital Account, Units Outstanding				5.00%		5.00%
Maximum | M&R MWE Liberty LLC [Member] | Class B Units
Class of Stock [Line Items]
Percentage of Units Sold in Public Offering				20.00%		20.00%
Series B Preferred Stock [Member] | MPLX LP [Member]
Class of Stock [Line Items]
Preferred Units, Outstanding | shares								600,000								600,000			600,000
Preferred Stock, Dividend Rate, Percentage																4.652%
Preferred Class B [Member] | Preferred Partner [Member]
Class of Stock [Line Items]
Partners' Capital, Including Portion Attributable to Noncontrolling Interest								$ 611								$ 611			$ 615
Cash distributions declared per limited partner common unit | $ / shares								$ 68.75
Net income (loss)							$ 17
(Placeholder)							$ (21)	$ 21	$ 21	$ 21
[1]	Changes to the number of general partner units outstanding, other than changes due to contributions made to MPC for the acquisitions of HSM, HST, WHC, MPLXT, the Joint-Interest Acquisition and Refining Logistics and Fuels Distribution, are the result of cash contributions made by the general partner in order to maintain its two percent GP Interest.

Equity (ATM Program) (Details)

Equity (ATM Program) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2017
Stockholders Equity [Line Items]
Common Stock, Monetary Value of Shares Authorized	$ 1,700
Units issued		14,129,589
ATM Program
Stockholders Equity [Line Items]
Net proceeds		$ 473
Limited Partners Common Units
Stockholders Equity [Line Items]
Units issued	0	13,846,998

Equity (Changes in Partners Cap

Equity (Changes in Partners Capital, Unit Rollforward) (Details) - shares		Feb. 01, 2018	Sep. 01, 2017	Mar. 01, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stockholders Equity [Line Items]
Beginning balance, number of units					794,089,518	415,438,793	368,555,271
Unit-based compensation awards, in units					288,031	348,527	273,639
Units issued							14,129,589
Unit conversion					1,148,330	264,413,309	366,509
Ending balance, number of units					1,058,355,471	794,089,518	415,438,793
Aggregate percentage of general partner interest		2.00%		2.00%	2.00%
LOOP LOCAP SAX and Explorer
Stockholders Equity [Line Items]
Aggregate percentage of general partner interest			2.00%
Refining Logistics & Fuels Distribution [Member]
Stockholders Equity [Line Items]
Units, acquisitions						113,888,889
HST & WHC & MPLXT
Stockholders Equity [Line Items]
Units, acquisitions							13,224,873
LOOP LOCAP SAX and Explorer
Stockholders Equity [Line Items]
Units, acquisitions							18,888,912
Andeavor Logistics [Member]
Stockholders Equity [Line Items]
Units, acquisitions					262,829,592
Limited Partners Common Units
Stockholders Equity [Line Items]
Beginning balance, number of units					794,089,518	407,130,020	357,193,288
Unit-based compensation awards, in units					288,031	348,387	268,167
Units issued					0		13,846,998
Unit conversion		275,000,000			1,148,330	275,000,000	4,350,057
Ending balance, number of units					1,058,355,471	794,089,518	407,130,020
Limited Partners Common Units | Refining Logistics & Fuels Distribution [Member]
Stockholders Equity [Line Items]
Units, acquisitions						111,611,111
Limited Partners Common Units | HST & WHC & MPLXT
Stockholders Equity [Line Items]
Units, acquisitions							12,960,376
Limited Partners Common Units | LOOP LOCAP SAX and Explorer
Stockholders Equity [Line Items]
Units, acquisitions							18,511,134
Limited Partners Common Units | Andeavor Logistics [Member]
Stockholders Equity [Line Items]
Units, acquisitions					262,829,592
Class B Units
Stockholders Equity [Line Items]
Beginning balance, number of units					0	0	3,990,878
Unit conversion							3,990,878
Ending balance, number of units					0	0	0
General Partner Units
Stockholders Equity [Line Items]
Beginning balance, number of units	[1]				0	8,308,773	7,371,105
Unit-based compensation awards, in units	[1]				0	140	5,472
Units issued	[1]						282,591
Unit conversion	[1]				0	10,586,691	7,330
Ending balance, number of units	[1]				0	0	8,308,773
General Partner Units | LOOP LOCAP SAX and Explorer
Stockholders Equity [Line Items]
Units, acquisitions			377,778
General Partner Units | Refining Logistics & Fuels Distribution [Member]
Stockholders Equity [Line Items]
Units, acquisitions	[1]					2,277,778
General Partner Units | HST & WHC & MPLXT
Stockholders Equity [Line Items]
Units, acquisitions				264,497			264,497	[1]
General Partner Units | LOOP LOCAP SAX and Explorer
Stockholders Equity [Line Items]
Units, acquisitions	[1]						377,778
General Partner Units | Andeavor Logistics [Member]
Stockholders Equity [Line Items]
Units, acquisitions	[1]				0
[1]	Changes to the number of general partner units outstanding, other than changes due to contributions made to MPC for the acquisitions of HSM, HST, WHC, MPLXT, the Joint-Interest Acquisition and Refining Logistics and Fuels Distribution, are the result of cash contributions made by the general partner in order to maintain its two percent GP Interest.

Equity (Net Income Allocation)

Equity (Net Income Allocation) (Details) - USD ($) $ in Millions

3 Months Ended

12 Months Ended

Dec. 31, 2019

Sep. 30, 2019

Jun. 30, 2019

[1]

Mar. 31, 2019

[1]

Dec. 31, 2018

[1]

Sep. 30, 2018

Jun. 30, 2018

Mar. 31, 2018

Dec. 31, 2019

Dec. 31, 2018

Dec. 31, 2017

Equity [Abstract]

Net income attributable to MPLX LP

$ (581)

$ 629

$ 482

$ 503

$ 434

$ 510

$ 453

$ 421

$ 1,033

[2]

$ 1,818

[2]

$ 794

[2]

Distributions to preferred unitholders

(65)

General partner's IDRs and other

310

Net income attributable to MPLX LP available to general and limited partners

419

General partner's two percent GP Interest in net income attributable to MPLX LP

8

General partner's GP Interest in net income attributable to MPLX LP

$ 0

$ 0

$ 318

[1]

As discussed in Note 1, MPLX’s acquisition of ANDX is considered a transfer between entities under common control due to MPC’s prior relationship with ANDX. Transfers of businesses between entities under common control require prior periods to be retrospectively adjusted for those dates that the entity was under common control. Accordingly, the tables above include the historical results of ANDX beginning October 1, 2018. Amounts shown for the fourth quarter of 2018 as well as the first and second quarters of 2019 are different than amounts previously reported for Total revenues and other income, Income from operations and Net income as a results of this retrospective adjustment for ANDX. Total revenues and other income originally reported for the fourth quarter of 2018 and the first and second quarters of 2019 was $1,715 million , $1,646 million and $1,629 million , respectively. Income from operations originally reported for the fourth quarter of 2018 and the first and second quarters of 2019 was $666 million , $678 million and $659 million , respectively. Net income originally reported for the fourth quarter of 2018 and the first and second quarters of 2019 was $439 million , $509 million and $488 million , respectively.

[2]

Allocation of net income/(loss) attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.

Equity (Cash Distributions) (De

Equity (Cash Distributions) (Details) - USD ($) $ / shares in Units, $ in Millions

Jan. 23, 2020

Dec. 31, 2019

Sep. 30, 2019

Jun. 30, 2019

Mar. 31, 2019

Dec. 31, 2018

Sep. 30, 2018

Jun. 30, 2018

Mar. 31, 2018

Dec. 31, 2019

Dec. 31, 2018

Dec. 31, 2017

Incentive Distribution Made to Managing Member or General Partner [Line Items]

Distributions to preferred units

$ 2,758

$ 2,060

$ 1,288

Subsequent Event

Incentive Distribution Made to Managing Member or General Partner [Line Items]

Distribution made to limited partner, declaration date

Jan. 23, 2020

Distributions to preferred units

$ 715

Cash distributions declared per limited partner common unit

$ 0.6875

Distribution made to limited partner, distribution date

Feb. 14, 2020

Distribution made to limited partner, date of record

Feb. 4, 2020

Limited Partners Common Units

Incentive Distribution Made to Managing Member or General Partner [Line Items]

Distributions to preferred units

[1]

$ 2,635

$ 1,985

$ 895

Cash distributions declared per limited partner common unit

$ 0.6875

$ 0.6775

$ 0.6675

$ 0.6575

$ 0.6475

$ 0.6375

$ 0.6275

$ 0.6175

$ 2.6900

$ 2.5300

[1]

See Note 8 for distribution information.

Equity (Cash Distributions Appl

Equity (Cash Distributions Applicable to Period the Distributions Were Earned) (Details) - USD ($) shares in Millions, $ in Millions		Mar. 01, 2017	Sep. 30, 2019	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019		Dec. 31, 2018	Dec. 31, 2017	Jul. 30, 2019
Class of Stock [Line Items]
General partner's distributions on general partner units												$ 0		$ 0	$ 25
General partner's distributions on IDRs	[1]											0		0	303
Total distribution on general partner units and IDRs												0		0	328
Total cash distributions declared												2,758		2,060	1,288
Contribution from MPC												346		11,980	675
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders												30		17	7
Preferred Class A [Member]
Class of Stock [Line Items]
Limited partners' distributions				$ 20	$ 20	$ 21	$ 20	$ 20	$ 19	$ 20	$ 16	81		75	65
Limited Partners Common Units
Class of Stock [Line Items]
Limited partners' distributions												2,635		1,985	895
Preferred Class B [Member]
Class of Stock [Line Items]
Limited partners' distributions				11	10	21	0					42		0	0
Preferred Partner [Member]
Class of Stock [Line Items]
Total cash distributions declared	[2]														65
Preferred Partner [Member] | Preferred Class B [Member]
Class of Stock [Line Items]
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders			$ 21	$ (21)	(21)	(21)
Preferred Partner [Member] | Series B Preferred Stock [Member]
Class of Stock [Line Items]
Total cash distributions declared	[2]											42	[3]	0	0
Limited Partners Common Units
Class of Stock [Line Items]
Total cash distributions declared	[2]											$ 2,635		$ 1,985	895
Public | Limited Partners Common Units
Class of Stock [Line Items]
Limited Partners' Capital Account, Units Issued				392				289				392		289		102
Total cash distributions declared				$ 270	266	261	191	$ 187	185	181	179
Contribution from MPC												$ 0		$ 0	0
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders												$ 0		$ 0	0
Marathon Petroleum Corporation [Member]
Class of Stock [Line Items]
Contribution from MPC		$ 6
Marathon Petroleum Corporation [Member] | Limited Partners Common Units
Class of Stock [Line Items]
Limited Partners' Capital Account, Units Issued				666				505				666		505		161
Total cash distributions declared				$ 446	438	$ 431	$ 332	$ 327	$ 322	$ 316	$ 288
Contribution from MPC												$ 315		$ 0	0
Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders												0		$ 0	$ 0
ANDX LP [Member] | Marathon Petroleum Corporation [Member]
Class of Stock [Line Items]
Contribution from MPC				$ 12.5	$ 12.5							$ 37.5
MPLX LP [Member] | Series B Preferred Stock [Member]
Class of Stock [Line Items]
Preferred Stock, Dividend Payment Rate, Variable												LIBOR plus
Preferred Stock, Dividend Rate, Percentage												4.652%
[1]	cludes distributions of fourth quarter 2017 income declared on general partner common units issued February 1, 2018 in exchange for the economic general partner interest.
[2]	See Note 8 for distribution information.
[3]	Allocation of net income/(loss) attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.

Redeemable Preferred Units (Nar

Redeemable Preferred Units (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	Jan. 23, 2020	Sep. 20, 2019	May 13, 2016	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Redeemable Noncontrolling Interest [Line Items]
Issuance of preferred units						14,129,589
Partners' Capital Account, Units, Converted				1,148,330	264,413,309	366,509
Partners' Capital Account, Units				1,058,355,471	794,089,518	415,438,793	368,555,271
Series A Convertible Preferred Units
Redeemable Noncontrolling Interest [Line Items]
Issuance of preferred units			30,800,000
Preferred Stock, Dividend Rate, Percentage			6.50%
Units issued, price per unit			$ 32.50
Issuance of redeemable preferred units			$ 984
Preferred units, dividend rate, per-dollar-amount			$ 0.528125
Preferred units, description			The holders may convert their Series A preferred units into common units at any time, in full or in part, subject to minimum conversion amounts and conditions. After the fourth anniversary of the issuance date, MPLX may convert the Series A preferred units into common units at any time, in whole or in part, subject to certain minimum conversion amounts and conditions, if the closing price of MPLX common units is greater than $48.75 for the 20-day trading period immediately preceding the conversion notice date. The conversion rate for the Series A preferred units shall be the quotient of (a) the sum of (i) $32.50, plus (ii) any unpaid cash distributions on the applicable preferred unit, divided by (b) $32.50, subject to adjustment for unit distributions, unit splits and similar transactions. The holders of the Series A preferred units are entitled to vote on an as-converted basis with the common unitholders and have certain other class voting rights with respect to any amendment to the MPLX partnership agreement that would adversely affect any rights, preferences or privileges of the preferred units. In addition, upon certain events involving a change of control, the holders of preferred units may elect, among other potential elections, to convert their Series A preferred units to common units at the then applicable change of control conversion rate.
Partners' Capital Account, Units, Converted		1,200,000
Partners' Capital Account, Units				29,600,000
Subsequent Event
Redeemable Noncontrolling Interest [Line Items]
Distribution made to limited partner, declaration date	Jan. 23, 2020
Cash distributions declared per limited partner common unit	$ 0.6875

Redeemable Preferred Units (Rol

Redeemable Preferred Units (Rollforward of Redeemable Preferred Units) (Details) - USD ($) $ in Millions	May 13, 2016	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Redeemable Noncontrolling Interest [Line Items]
Redeemable preferred units, beginning balance		$ 1,004
Distributions to unitholders and general partner		(2,435)	$ (1,819)	$ (1,120)
Redeemable preferred units, ending balance		968	1,004
Series A Convertible Preferred Units
Redeemable Noncontrolling Interest [Line Items]
Redeemable preferred units, beginning balance		1,004	1,000
Issuance of redeemable preferred units	$ 984
Net income allocated		81	75
Distributions to unitholders and general partner		(81)	(71)
Redeemable preferred units, ending balance		968	1,004	$ 1,000
Convertible Preferred Stock Converted to Other Securities		$ (36)	$ 0

Segment Information (Details)

Segment Information (Details)	12 Months Ended
	Dec. 31, 2019
Segment Reporting Information [Line Items]
Number of reportable segments	2

Segment Information - Revenues

Segment Information - Revenues and Adjusted EBITDA (Details) - USD ($) $ in Millions		3 Months Ended											12 Months Ended
		Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	[1]	Mar. 31, 2019	[1]	Dec. 31, 2018	[1]	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting, Revenue Reconciling Item [Line Items]
Total segment revenues and other income		$ 2,316	$ 2,280	$ 2,210		$ 2,235		$ 2,295		$ 1,712	$ 1,578	$ 1,420	$ 9,041	$ 7,005	$ 3,867
Revenue from Contract with Customer, Excluding Assessed Tax													7,041	5,449
Rental income													388	352	277
Income (Loss) from Equity Method Investments	[2],[3]												290	247	78
Other income													12	7	6
Investments in unconsolidated affiliates													(713)	(341)	(761)
Revenues	[4]														(6)
Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Adjusted EBITDA													4,334	3,475	2,004
Logistics and Storage [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													3,856	2,598
Investments in unconsolidated affiliates													289	3	533
Logistics and Storage [Member] | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total segment revenues and other income	[5]												5,352	3,672	1,562
Rental income													1,235	856	279
Income (Loss) from Equity Method Investments													200	171	36
Other income													61	47	47
Adjusted EBITDA	[6]												2,748	2,057	775
Capital Expenditure													1,060	708	512
Gathering and Processing [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													3,185	2,851
Investments in unconsolidated affiliates													424	338	228
Gathering and Processing [Member] | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Total segment revenues and other income	[5]												3,689	3,333	2,305
Rental income													349	342	277
Income (Loss) from Equity Method Investments													90	76	42
Other income													65	59	51
Adjusted EBITDA	[6]												1,586	1,418	1,229
Capital Expenditure													1,203	1,545	972
Service [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													2,498	1,856	1,156
Service [Member] | Logistics and Storage [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													346	174
Service [Member] | Logistics and Storage [Member] | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													3,765	2,575	1,200
Service [Member] | Gathering and Processing [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													2,152	1,682
Service [Member] | Gathering and Processing [Member] | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													2,188	1,685	1,038
Product [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													806	887	889
Product [Member] | Logistics and Storage [Member] | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													91	23	0
Product [Member] | Gathering and Processing [Member] | Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													997	1,171	897
Third Party | Logistics and Storage [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total segment revenues and other income													660	371	160
Third Party | Gathering and Processing [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total segment revenues and other income													$ 3,474	$ 3,198	$ 2,246
[1]	As discussed in Note 1, MPLX’s acquisition of ANDX is considered a transfer between entities under common control due to MPC’s prior relationship with ANDX. Transfers of businesses between entities under common control require prior periods to be retrospectively adjusted for those dates that the entity was under common control. Accordingly, the tables above include the historical results of ANDX beginning October 1, 2018. Amounts shown for the fourth quarter of 2018 as well as the first and second quarters of 2019 are different than amounts previously reported for Total revenues and other income, Income from operations and Net income as a results of this retrospective adjustment for ANDX. Total revenues and other income originally reported for the fourth quarter of 2018 and the first and second quarters of 2019 was $1,715 million , $1,646 million and $1,629 million , respectively. Income from operations originally reported for the fourth quarter of 2018 and the first and second quarters of 2019 was $666 million , $678 million and $659 million , respectively. Net income originally reported for the fourth quarter of 2018 and the first and second quarters of 2019 was $439 million , $509 million and $488 million , respectively.
[2]	“Income from equity method investments” includes the impact of any basis differential amortization or accretion.
[3]	The financial information for equity method investments for 2019 includes financial information of equity method investments acquired as part of the Merger. The financial information for equity method investments for 2018 includes financial information of equity method investments acquired as part of the Merger for the last three months of 2018. The financial information for equity method investments for 2017 does not include financial information of equity method investments acquired as part of the Merger. See Note 1
[4]	MPLX makes a distinction between realized or unrealized gains and losses on derivatives. During the period when a derivative contract is outstanding, changes in the fair value of the derivative are recorded as an unrealized gain or loss. When a derivative contract matures or is settled, the previously recorded unrealized gain or loss is reversed and the realized gain or loss of the contract is recorded.
[5]	Within the total segment revenues and other income amounts presented above, third party revenues for the L&S segment were $660 million , $371 million and $160 million for 2019 , 2018 and 2017 , respectively. Third party revenues for the G&P segment were $3,474 million , $3,198 million and $2,246 million for 2019 , 2018 and 2017 , respectively.
[6]	See below for the reconciliation from Segment Adjusted EBITDA to “Net income.”

Segment Information - Assets by

Segment Information - Assets by Segment (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting, Asset Reconciling Item [Line Items]
Cash and cash equivalents	$ 15	$ 77
Total assets	40,430	39,325
Operating Segments | Logistics and Storage [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	20,810	19,963
Operating Segments | Gathering and Processing [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Total assets	$ 19,605	$ 19,285

Segment Information - Reconcili

Segment Information - Reconciliation Adjusted EBITDA to Net income (Details) - USD ($) $ in Millions		3 Months Ended											12 Months Ended
		Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	[5]	Mar. 31, 2019	[5]	Dec. 31, 2018	[5]	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Depreciation and amortization	[1]												$ 1,254	$ 867	$ 683
Provision for income taxes													0	8	1
Amortization of deferred financing costs													42	55	53
Extinguishment of Debt, Gain (Loss), Net of Tax													0	(46)	0
Total compensation expense													(22)	(23)	(15)
Goodwill and Intangible Asset Impairment													(1,197)	0	0
Interest and Other Financial Costs													873	613	301
Income (Loss) from Equity Method Investments	[2],[3]												290	247	78
Distributions from unconsolidated affiliates													525	412	241
Unrealized gains	[4]														(6)
Acquisition Costs, Period Cost													(14)	(4)	(11)
Other Cost and Expense, Operating													(1)	0	0
Net income		$ (573)	$ 689	$ 657		$ 689		$ 611		$ 516	$ 456	$ 423	1,462	2,006	836
Logistics and Storage [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization													(503)	(308)	(163)
Gathering and Processing [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization													(751)	(559)	(520)
Operating Segments
Segment Reporting Information [Line Items]
Adjusted EBITDA													4,334	3,475	2,004
Amortization of deferred financing costs													42	55	53
Operating Segments | Logistics and Storage [Member]
Segment Reporting Information [Line Items]
Adjusted EBITDA	[6]												2,748	2,057	775
Income (Loss) from Equity Method Investments													200	171	36
Operating Segments | Gathering and Processing [Member]
Segment Reporting Information [Line Items]
Adjusted EBITDA	[6]												1,586	1,418	1,229
Income (Loss) from Equity Method Investments													90	76	42
Segment Reconciling Items
Segment Reporting Information [Line Items]
Distributions from unconsolidated affiliates													562	458	231
Adjusted EBITDA attributable to noncontrolling interests													32	18	8
Adjusted EBITDA attributable to Predecessor	[7]												770	335	$ 47
Not Designated as Hedging Instrument
Segment Reporting Information [Line Items]
Unrealized Gain (Loss) on Derivatives and Commodity Contracts	[4]												$ 1	$ 5
[1]	Depreciation and amortization attributable to L&S was $503 million , $308 million and $163 million for the years ended 2019 , 2018 and 2017 , respectively. Depreciation and amortization attributable to G&P was $751 million , $559 million and $520 million for 2019 , 2018 and 2017 , respectively.
[2]	“Income from equity method investments” includes the impact of any basis differential amortization or accretion.
[3]	The financial information for equity method investments for 2019 includes financial information of equity method investments acquired as part of the Merger. The financial information for equity method investments for 2018 includes financial information of equity method investments acquired as part of the Merger for the last three months of 2018. The financial information for equity method investments for 2017 does not include financial information of equity method investments acquired as part of the Merger. See Note 1
[4]	MPLX makes a distinction between realized or unrealized gains and losses on derivatives. During the period when a derivative contract is outstanding, changes in the fair value of the derivative are recorded as an unrealized gain or loss. When a derivative contract matures or is settled, the previously recorded unrealized gain or loss is reversed and the realized gain or loss of the contract is recorded.
[5]	As discussed in Note 1, MPLX’s acquisition of ANDX is considered a transfer between entities under common control due to MPC’s prior relationship with ANDX. Transfers of businesses between entities under common control require prior periods to be retrospectively adjusted for those dates that the entity was under common control. Accordingly, the tables above include the historical results of ANDX beginning October 1, 2018. Amounts shown for the fourth quarter of 2018 as well as the first and second quarters of 2019 are different than amounts previously reported for Total revenues and other income, Income from operations and Net income as a results of this retrospective adjustment for ANDX. Total revenues and other income originally reported for the fourth quarter of 2018 and the first and second quarters of 2019 was $1,715 million , $1,646 million and $1,629 million , respectively. Income from operations originally reported for the fourth quarter of 2018 and the first and second quarters of 2019 was $666 million , $678 million and $659 million , respectively. Net income originally reported for the fourth quarter of 2018 and the first and second quarters of 2019 was $439 million , $509 million and $488 million , respectively.
[6]	See below for the reconciliation from Segment Adjusted EBITDA to “Net income.”
[7]	The Adjusted EBITDA adjustments related to Predecessor are excluded from Adjusted EBITDA attributable to MPLX LP prior to the acquisition date.

Major Customers and Concentra_2

Major Customers and Concentration of Credit Risk (Details) - First Major Customer - MPC		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues And Other Income]
Concentration Risk [Line Items]
Concentration risk, percentage	[1]	54.00%	48.00%	36.00%
Revenue Benchmark [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	[1],[2]	56.00%	50.00%	37.00%
Logistics and Storage [Member] | Revenues And Other Income]
Concentration Risk [Line Items]
Concentration risk, percentage	[1]	88.00%	90.00%	90.00%
Logistics and Storage [Member] | Revenue Benchmark [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	[1],[2]	91.00%	94.00%	92.00%
Gathering and Processing [Member] | Revenues And Other Income]
Concentration Risk [Line Items]
Concentration risk, percentage	[1]	4.00%	2.00%	0.00%
Gathering and Processing [Member] | Revenue Benchmark [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	[1],[2]	4.00%	3.00%	0.00%
[1]	The percent calculations exclude revenues attributable to volumes shipped by MPC under joint tariffs with third parties, which are treated as third-party revenue for accounting purposes.
[2]	Operating revenues consist of service revenue, service revenue - product related, rental income and product sales.

Inventories (Summary of Invento

Inventories (Summary of Inventories) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Inventory Disclosure [Abstract]
NGLs	$ 5	$ 9
Line fill	10	9
Spare parts, materials and supplies	95	80
Total inventories	$ 110	$ 98

Property, Plant and Equipment_2

Property, Plant and Equipment (Summary of Property, Plant and Equipment) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 26,867	$ 25,213
Less accumulated depreciation	4,722	3,688
Property, plant and equipment, net	22,145	21,525
Natural gas gathering and NGL transportation pipelines and facilities
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	7,037	6,349
Processing, fractionation and storage facilities
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	6,410	6,045
Pipelines and related assets
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	5,117	5,111
Barges and towing vessels
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	739	621
Terminals and related assets
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,222	2,757
Refineries and related assets [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,383	1,447
Land, building, office equipment and other
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	2,554	1,562
Construction-in-progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 1,405	$ 1,321
Minimum | Natural gas gathering and NGL transportation pipelines and facilities
Property, Plant and Equipment [Line Items]
Estimated useful lives	5 years
Minimum | Processing, fractionation and storage facilities
Property, Plant and Equipment [Line Items]
Estimated useful lives	5 years
Minimum | Pipelines and related assets
Property, Plant and Equipment [Line Items]
Estimated useful lives	2 years
Minimum | Barges and towing vessels
Property, Plant and Equipment [Line Items]
Estimated useful lives	15 years
Minimum | Terminals and related assets
Property, Plant and Equipment [Line Items]
Estimated useful lives	4 years
Minimum | Refineries and related assets [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives	13 years
Minimum | Land, building, office equipment and other
Property, Plant and Equipment [Line Items]
Estimated useful lives	2 years
Maximum | Natural gas gathering and NGL transportation pipelines and facilities
Property, Plant and Equipment [Line Items]
Estimated useful lives	40 years
Maximum | Processing, fractionation and storage facilities
Property, Plant and Equipment [Line Items]
Estimated useful lives	46 years
Maximum | Pipelines and related assets
Property, Plant and Equipment [Line Items]
Estimated useful lives	51 years
Maximum | Barges and towing vessels
Property, Plant and Equipment [Line Items]
Estimated useful lives	20 years
Maximum | Terminals and related assets
Property, Plant and Equipment [Line Items]
Estimated useful lives	45 years
Maximum | Refineries and related assets [Member]
Property, Plant and Equipment [Line Items]
Estimated useful lives	38 years
Maximum | Land, building, office equipment and other
Property, Plant and Equipment [Line Items]
Estimated useful lives	45 years

Property Plant and Equipment (N

Property Plant and Equipment (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Accumulated depreciation	$ 4,722	$ 3,688

Goodwill and Intangibles (Goodw

Goodwill and Intangibles (Goodwill) (Narrative) (Details)	Nov. 30, 2019USD ($)	Nov. 29, 2019USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2018USD ($)
Goodwill [Line Items]
Goodwill, Impairment Loss	$ 41,000,000	$ 1,156,000,000	$ 1,197,000,000
Number of reporting units	6	12
Goodwill			9,536,000,000	$ 2,245,000,000	$ 10,016,000,000
Reporting Unit, Zero or Negative Carrying Amount, Amount of Allocated Goodwill			$ 1
Measurement Input, Discount Rate [Member] | Goodwill | Income Approach Valuation Technique | Minimum
Goodwill [Line Items]
Fair Value Inputs				9.00%
Measurement Input, Discount Rate [Member] | Goodwill | Income Approach Valuation Technique | Maximum
Goodwill [Line Items]
Fair Value Inputs				10.00%

Goodwill and Intangibles (Recon

Goodwill and Intangibles (Reconciliation of Goodwill) (Details) - USD ($) $ in Millions		Nov. 30, 2019	Nov. 29, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Goodwill [Line Items]
Gross goodwill				$ 10,863		$ 2,375
Accumulated impairment losses				(1,327)		(130)
Goodwill, beginning balance				10,016	$ 2,245
Impairment losses		$ (41)	$ (1,156)	(1,197)
Acquisitions	[1]			717	7,771
Goodwill, ending balance				9,536	10,016
Logistics and Storage [Member]
Goodwill [Line Items]
Gross goodwill				7,722		162
Accumulated impairment losses				0		0
Goodwill, beginning balance				7,234	162
Impairment losses				0
Acquisitions	[1]			488	7,072
Goodwill, ending balance				7,722	7,234
Gathering and Processing [Member]
Goodwill [Line Items]
Gross goodwill				3,141		2,213
Accumulated impairment losses				(1,327)		$ (130)
Goodwill, beginning balance				2,782	2,083
Impairment losses				1,197
Acquisitions	[1]			229	699
Goodwill, ending balance				$ 1,814	$ 2,782
[1]	Acquisitions in 2018 are inclusive of the Mt. Airy Terminal acquisition as well as the Merger while acquisitions in 2019 are inclusive of measurement period adjustments related to the previously mentioned transactions.

Goodwill and Intangibles (Intan

Goodwill and Intangibles (Intangible Assets) (Details) - USD ($) $ in Millions		Oct. 01, 2018	Dec. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Gross			$ 1,571	$ 1,502
Accumulated amortization	[1]		(301)	(143)
Intangibles, net			1,270	1,359
Logistics and Storage [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization of Intangible Assets			31	14
Gross			283	249
Accumulated amortization	[1]		(45)	(14)
Intangibles, net			$ 238	235
Logistics and Storage [Member] | Minimum
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life			6 years
Logistics and Storage [Member] | Maximum
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life			8 years
Gathering and Processing [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization of Intangible Assets			$ 127	49
Gross			1,288	1,253
Accumulated amortization	[1]		(256)	(129)
Intangibles, net			$ 1,032	$ 1,124
Gathering and Processing [Member] | Minimum
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life			6 years
Gathering and Processing [Member] | Maximum
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life			25 years
Andeavor Logistics [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life			9 years
Andeavor Logistics [Member] | Minimum
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life		2 years
Andeavor Logistics [Member] | Maximum
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life		10 years
[1]	Amortization expense attributable to the G&P segment for the years ended December 31, 2019 and 2018 was $127 million and $49 million , respectively. Amortization expense attributable to the L&S segment for the year ended December 31, 2019 and 2018 was $31 million and $14 million , respectively.

Goodwill and Intangibles (Futur

Goodwill and Intangibles (Future Amortization Expense) (Details) $ in Millions	Dec. 31, 2019USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
2018	$ 155
2019	155
2020	155
2021	155
2022	150
Thereafter	500
Total future intangibles amortization expenses	$ 1,270

Fair Value Measurements - Recur

Fair Value Measurements - Recurring (Financial Instruments by Valuation Hierarchy) (Details) - Fair Value, Recurring [Member] - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	$ 0	$ 0
Liabilities	(60)	(61)
Embedded derivatives in commodity contracts | Significant unobservable inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0	0
Liabilities	$ (60)	$ (61)

Fair Value Measurements - Rec_2

Fair Value Measurements - Recurring (Significant Unobservable Inputs in Level 3 Valuation) (Details)	12 Months Ended
	Dec. 31, 2019USD ($)
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Embedded Derivative Renewal Term	5 years
Embedded Derivative Second Renewal Term	5 years
Significant unobservable inputs (Level 3) | Commodity contracts | Minimum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs commodity price	$ 0.43
Significant unobservable inputs (Level 3) | Commodity contracts | Maximum
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair value inputs commodity price	$ 1.23
Significant unobservable inputs (Level 3) | Embedded derivatives in commodity contracts
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs Probability of Renewal	94.00%
Fair Value Inputs Probability of Renewal Second Term	83.00%

Fair Value Measurements - Rec_3

Fair Value Measurements - Recurring (Changes in Level 3 Measurements) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018
Commodity Derivative Contracts (net)
Derivative assets and liabilities classified by the Partnership within Level 3 of the valuation hierarchy [Roll Forward]
Fair value at beginning of period		$ 0	$ (2)
Total gains/(losses) (realized and unrealized) included in earnings(1)	[1]	0	6
Settlements		0	(4)
Fair value at end of period		0	0
The amount of total losses for the period included in earnings attributable to the change in unrealized gains or losses relating to liabilities still held at end of period		0	0
Embedded Derivatives in Commodity Contracts (net)
Derivative assets and liabilities classified by the Partnership within Level 3 of the valuation hierarchy [Roll Forward]
Fair value at beginning of period		(61)	(64)
Total gains/(losses) (realized and unrealized) included in earnings(1)	[1]	(5)	(9)
Settlements		6	12
Fair value at end of period		(60)	(61)
The amount of total losses for the period included in earnings attributable to the change in unrealized gains or losses relating to liabilities still held at end of period		$ (5)	$ (8)
[1]	Gains and losses on commodity derivatives classified as Level 3 are recorded in “Product sales” on the Consolidated Statements of Income. Gains and losses on derivatives embedded in commodity contracts are recorded in “Purchased product costs” and “Cost of revenues” on the Consolidated Statements of Income.

Fair Value Measurements - Repor

Fair Value Measurements - Reported (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	$ 21,054	$ 18,070
SMR liability	90	92
Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	19,800	18,511
SMR liability	$ 80	$ 86

Derivative Financial Instrume_3

Derivative Financial Instruments (Embedded Derivatives in Commodity Contracts) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Derivative [Line Items]
Term of counterparty option to renew gas purchase agreement	5 years
Embedded derivative in natural gas processing and purchase contract [Member] | Embedded derivatives in commodity contracts
Derivative [Line Items]
Number of renewals	2
Term of counterparty option to renew gas purchase agreement	5 years
Embedded derivative fair value of embedded derivative liability including inception value allocable to host contract	$ 60	$ 61

Derivative Financial Instrume_4

Derivative Financial Instruments (Derivatives Balance Sheet Location) (Details) - Commodity contracts - USD ($) $ in Millions		Dec. 31, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset	[1]	$ 0	$ 0
Derivative liability, fair value, gross liability	[1]	(60)	(61)
Not Designated as Hedging Instrument | Other current assets
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset	[1]	0	0
Not Designated as Hedging Instrument | Other current liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, fair value, gross liability	[1]	(5)	(7)
Not Designated as Hedging Instrument | Other noncurrent assets
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset	[1]	0	0
Not Designated as Hedging Instrument | Other Noncurrent Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liability, fair value, gross liability	[1]	$ (55)	$ (54)
[1]	Includes embedded derivatives in commodity contracts as discussed above.

Derivative Financial Instrume_5

Derivative Financial Instruments (Derivatives Income Statement Location) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized gains	[1]			$ (6)
Total derivative loss		$ (5)	$ (3)	(24)
Product sales
Derivative Instruments, Gain (Loss) [Line Items]
Realized gains/(losses)		0	4	(9)
Unrealized gains				4
Total derivative loss		0	6	(5)
Purchased product costs
Derivative Instruments, Gain (Loss) [Line Items]
Realized gains/(losses)		(6)	(12)	(9)
Unrealized gains				(10)
Total derivative loss		(5)	(9)	(19)
Cost of revenues
Derivative Instruments, Gain (Loss) [Line Items]
Realized gains/(losses)		0	0	0
Unrealized gains				0
Total derivative loss		0	0	$ 0
Not Designated as Hedging Instrument
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized Gain (Loss) on Derivatives and Commodity Contracts	[1]	1	5
Not Designated as Hedging Instrument | Product sales
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized Gain (Loss) on Derivatives and Commodity Contracts		0	2
Not Designated as Hedging Instrument | Purchased product costs
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized Gain (Loss) on Derivatives and Commodity Contracts		1	3
Not Designated as Hedging Instrument | Cost of revenues
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized Gain (Loss) on Derivatives and Commodity Contracts		$ 0	$ 0
[1]	MPLX makes a distinction between realized or unrealized gains and losses on derivatives. During the period when a derivative contract is outstanding, changes in the fair value of the derivative are recorded as an unrealized gain or loss. When a derivative contract matures or is settled, the previously recorded unrealized gain or loss is reversed and the realized gain or loss of the contract is recorded.

Debt (Summary of Outstanding Bo

Debt (Summary of Outstanding Borrowings) (Details) - USD ($) $ in Millions		Dec. 31, 2019	Sep. 30, 2019	Sep. 23, 2019	Sep. 09, 2019	Jul. 30, 2019	Dec. 31, 2018	Nov. 15, 2018	Oct. 01, 2018	Feb. 08, 2018
Debt Instrument [Line Items]
Finance Lease, Liability		$ 19
Debt and capital lease obligations		20,119					$ 18,866
Unamortized debt issuance costs		106					97
Unamortized discount		300					334
Amounts due within one year		9					513
Total long-term debt due after one year		19,704					17,922
MPLX Revolving Credit Facility due July 2024 [Member]
Debt Instrument [Line Items]
Outstanding balance		0					0
Term loan facility due 2019
Debt Instrument [Line Items]
Outstanding balance		1,000					0
Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross					$ 2,000
Senior Notes | Floating Rate Senior Notes Due September 2021 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		1,000			1,000		0
Senior Notes | Floating Rate Senior Notes Due September 2022 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		1,000			$ 1,000		0
MPLX LP | Line of Credit | MPLX Revolving Credit Facility due July 2024 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		0
MPLX LP | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross				$ 3,060				$ 2,250		$ 5,500
MPLX LP | Senior Notes | Senior Notes Due October 2022 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		266		266			0
MPLX LP | Senior Notes | Senior Notes Due December 2022 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		486		486			0
MPLX LP | Senior Notes | Senior Notes Due March 2023 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		500					500
MPLX LP | Senior Notes | 4.500% senior notes due July 2023
Debt Instrument [Line Items]
Long-term debt, gross		989					989
MPLX LP | Senior Notes | Senior Notes Due May 2024 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		381		381			0
MPLX LP | Senior Notes | 4.875% senior notes due December 2024
Debt Instrument [Line Items]
Long-term debt, gross		1,149					1,149
MPLX LP | Senior Notes | Senior Notes Due January 2025 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		708		708			0
MPLX LP | Senior Notes | 4.000% senior notes due February 2025
Debt Instrument [Line Items]
Long-term debt, gross		500					500
MPLX LP | Senior Notes | 4.875% senior notes due June 2025
Debt Instrument [Line Items]
Long-term debt, gross		1,189					1,189
MPLX LP | Senior Notes | 4.125% senior notes due March 2027
Debt Instrument [Line Items]
Long-term debt, gross		1,250					1,250
MPLX LP | Senior Notes | Senior Notes Due December 2027 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		732		732			0
MPLX LP | Senior Notes | Senior Notes Due March 2028 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		1,250					1,250
MPLX LP | Senior Notes | Senior Notes Due February 2029 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		750					750
MPLX LP | Senior Notes | Senior Notes Due April 2038 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		1,750					1,750
MPLX LP | Senior Notes | 5.200% senior notes due March 2047
Debt Instrument [Line Items]
Long-term debt, gross		1,000					1,000
MPLX LP | Senior Notes | Senior Notes Due December 2047 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		487		487			0
MPLX LP | Senior Notes | Senior Notes Due April 2048 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		1,500					1,500
MPLX LP | Senior Notes | Senior Notes Due February 2049 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		1,500					1,500
MPLX LP | Senior Notes | Senior Notes Due April 2058 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		500					500
MarkWest | Senior Notes | MarkWest senior notes
Debt Instrument [Line Items]
Long-term debt, gross		23					23
ANDX LP [Member] | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross		190	$ 690	$ 3,060		$ 3,750	3,750
Andeavor Logistics [Member] | ANDX Bank Revolving Credit Facilities [Member]
Debt Instrument [Line Items]
Long-term debt, gross							1,200		$ 1,100
Outstanding balance		0					1,245
Marathon Pipe Line LLC | Finance Lease [Member]
Debt Instrument [Line Items]
Finance Lease, Liability	[1]	$ 19					$ 21
[1]	See Note 22 for lease information.

Debt (Summary of Outstanding _2

Debt (Summary of Outstanding Borrowings Interest Rates and Table Due Dates) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Sep. 23, 2019	Dec. 10, 2018
MPLX LP | MPLX Revolving Credit Facility due July 2024 [Member]
Debt Instrument [Line Items]
Proceeds from long-term lines of credit	$ 5,310
MPLX LP | Line of Credit | MPLX Revolving Credit Facility due July 2024 [Member]
Debt Instrument [Line Items]
Expiration date	Jul. 30, 2024
MPLX LP | Senior Notes | 5.500% senior notes due February 2023
Debt Instrument [Line Items]
Interest rate, stated percentage			5.50%
MPLX LP | Senior Notes | Senior Notes Due March 2023 [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date	Sep. 9, 2021
MPLX LP | Senior Notes | Floating Rate Senior Notes Due September 2022 [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date	Sep. 9, 2022
MPLX LP | Senior Notes | 4.875% senior notes due December 2024
Debt Instrument [Line Items]
Interest rate, stated percentage	6.25%
Debt Instrument, Maturity Date	Oct. 15, 2022
MPLX LP | Senior Notes | 4.000% senior notes due February 2025
Debt Instrument [Line Items]
Interest rate, stated percentage	3.50%
Debt Instrument, Maturity Date	Dec. 1, 2022
MPLX LP | Senior Notes | 4.875% senior notes due June 2025
Debt Instrument [Line Items]
Interest rate, stated percentage	3.375%
Debt Instrument, Maturity Date	Mar. 15, 2023
MPLX LP | Senior Notes | 4.500% senior notes due July 2023
Debt Instrument [Line Items]
Interest rate, stated percentage	4.50%
Debt Instrument, Maturity Date	Jul. 15, 2023
MPLX LP | Senior Notes | Senior Notes Due March 2028 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage	4.00%
Debt Instrument, Maturity Date	Mar. 15, 2028
MPLX LP | Senior Notes | Senior Notes Due February 2029 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage	4.80%
Debt Instrument, Maturity Date	Feb. 15, 2029
MPLX LP | Senior Notes | Senior Notes Due April 2038 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage	4.50%
Debt Instrument, Maturity Date	Apr. 15, 2038
MPLX LP | Senior Notes | 5.200% senior notes due March 2047
Debt Instrument [Line Items]
Interest rate, stated percentage	5.20%
Debt Instrument, Maturity Date	Mar. 1, 2047
MPLX LP | Senior Notes | Senior Notes Due April 2048 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage	4.70%
Debt Instrument, Maturity Date	Apr. 15, 2048
MPLX LP | Senior Notes | Senior Notes Due November 2049 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage	5.50%
Debt Instrument, Maturity Date	Feb. 15, 2049
MPLX LP | Senior Notes | Senior Notes Due April 2058 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage	4.90%
Debt Instrument, Maturity Date	Apr. 15, 2058
MPLX LP | Senior Notes | Senior Notes Due May 2024 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage	6.375%
Debt Instrument, Maturity Date	May 1, 2024
MPLX LP | Senior Notes | 4.875% senior notes due December 2024
Debt Instrument [Line Items]
Interest rate, stated percentage	4.875%
Debt Instrument, Maturity Date	Dec. 1, 2024
MPLX LP | Senior Notes | Senior Notes Due January 2025 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage	5.25%
Debt Instrument, Maturity Date	Jan. 15, 2025
MPLX LP | Senior Notes | 4.000% senior notes due February 2025
Debt Instrument [Line Items]
Interest rate, stated percentage	4.00%
Debt Instrument, Maturity Date	Feb. 15, 2025
MPLX LP | Senior Notes | 4.875% senior notes due June 2025
Debt Instrument [Line Items]
Interest rate, stated percentage	4.875%
Debt Instrument, Maturity Date	Jun. 1, 2025
MPLX LP | Senior Notes | Senior Notes Due March 2027 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage	4.125%
Debt Instrument, Maturity Date	Mar. 1, 2027
MPLX LP | Senior Notes | Senior Notes Due December 2027 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage	4.25%
Debt Instrument, Maturity Date	Dec. 1, 2027
MPLX LP | Senior Notes | Senior Notes Due December 2047 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage	5.20%
Debt Instrument, Maturity Date	Dec. 1, 2047
MarkWest | Senior Notes | 4.500% senior notes due July 2023
Debt Instrument [Line Items]
Interest rate, stated percentage	4.50%
Debt Instrument, Maturity Date	Jul. 15, 2023
MarkWest | Senior Notes | 4.875% senior notes due December 2024
Debt Instrument [Line Items]
Interest rate, stated percentage	4.875%
Debt Instrument, Maturity Date	Dec. 1, 2024
MarkWest | Senior Notes | 4.875% senior notes due June 2025
Debt Instrument [Line Items]
Interest rate, stated percentage	4.875%
Debt Instrument, Maturity Date	Jun. 1, 2025
MarkWest | Senior Notes | Senior Notes Due October 2019 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage	5.50%
Debt Instrument, Maturity Date	Oct. 15, 2019
Marathon Pipe Line LLC | Finance Lease [Member]
Debt Instrument [Line Items]
Finance Lease Due Date Year	2020
ANDX LP [Member] | Senior Notes | 4.875% senior notes due December 2024
Debt Instrument [Line Items]
Interest rate, stated percentage		6.25%
ANDX LP [Member] | Senior Notes | 4.000% senior notes due February 2025
Debt Instrument [Line Items]
Interest rate, stated percentage		3.50%
ANDX LP [Member] | Senior Notes | Senior Notes Due May 2024 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage		6.375%
ANDX LP [Member] | Senior Notes | Senior Notes Due January 2025 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage		5.25%
ANDX LP [Member] | Senior Notes | Senior Notes Due December 2027 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage		4.25%
ANDX LP [Member] | Senior Notes | Senior Notes Due December 2047 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage		5.20%
ANDX LP [Member] | Senior Notes | Senior Notes Due October 2019 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage		5.50%
ANDX LP [Member] | Finance Lease [Member]
Debt Instrument [Line Items]
Finance Lease Due Date Year	2029

Debt (Schedule of Debt Payments

Debt (Schedule of Debt Payments) (Detail) $ in Millions	Dec. 31, 2019USD ($)
Debt Disclosure [Abstract]
2020	$ 10
2021	2,002
2022	1,802
2023	1,502
2024	$ 1,601

Debt (Credit Agreements) (Detai

Debt (Credit Agreements) (Detail) $ in Millions	Sep. 26, 2019USD ($)	Jul. 30, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Jul. 29, 2019USD ($)	Oct. 01, 2018USD ($)
Debt Instrument [Line Items]
Long-term debt - repayments				$ 7,924	$ 6,946	$ 416
MPLX Revolving Credit Facility due July 2024 [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity		$ 3,500
Long-term Line of Credit			$ 0	0	0
MPLX Revolving Credit Facility due July 2024 [Member] | Letter of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity		300
MPLX Revolving Credit Facility due July 2024 [Member] | Swingline Loan
Debt Instrument [Line Items]
Maximum borrowing capacity		$ 150
MPLX Revolving Credit Facility due July 2024 [Member] | MPLX LP
Debt Instrument [Line Items]
Proceeds from long-term lines of credit				$ 5,310
Interest rate, effective percentage				3.547%
Debt Instrument, Description of Variable Rate Basis		Adjusted LIBOR or the Alternate Base Rate (as defined in the MPLX Credit Agreement), at our election, plus a specified margin
Number of prior quarterly reporting periods used in determining compliance with covenant of ratio of consolidated net debt to consolidated EBITDA		4
Repayments of long-term lines of credit				$ 5,310
Letters of credit outstanding, amount				1
Remaining borrowing capacity				$ 3,500
Remaining borrowing capacity, percentage				100.00%
MPLX Revolving Credit Facility due July 2024 [Member] | MPLX LP | Maximum
Debt Instrument [Line Items]
Additional borrowing capacity		$ 1,000
Covenant of ratio of consolidated net debt to consolidated EBITDA (in ratio)		5
Covenant of ratio of consolidated net debt to consolidated EBITDA following certain acquisitions (in ratio)		5.5
MPLX Revolving Credit Facility due July 2024 [Member] | MPLX LP | Minimum
Debt Instrument [Line Items]
Covenant of ratio of consolidated net debt to consolidated EBITDA (in ratio)		1
Covenant of ratio of consolidated net debt to consolidated EBITDA following certain acquisitions (in ratio)		1
MPLX Revolving Credit Facility due July 2024 [Member] | MPLX LP | Letter of Credit
Debt Instrument [Line Items]
Number of renewals		2
Debt Instrument, Renewal Term		1 year
Term loan facility due 2019
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 1,000
Debt Instrument, Description of Variable Rate Basis	(i) the Adjusted LIBO Rate (as defined in the Term Loan Agreement) plus a margin ranging from 75.0 basis points to 100.0 basis points per annum, depending on MPLX’s credit ratings, or (ii) the Alternate Base Rate (as defined in the Term Loan Agreement)
Number of prior quarterly reporting periods used in determining compliance with covenant of ratio of consolidated net debt to consolidated EBITDA	4
Long-term Debt, Maturity Date				Sep. 26, 2021
Long-term Line of Credit			$ 0	$ 1,000	0
Term loan facility due 2019 | Maximum
Debt Instrument [Line Items]
Covenant of ratio of consolidated net debt to consolidated EBITDA (in ratio)	5
Covenant of ratio of consolidated net debt to consolidated EBITDA following certain acquisitions (in ratio)	5.5
Term loan facility due 2019 | Minimum
Debt Instrument [Line Items]
Covenant of ratio of consolidated net debt to consolidated EBITDA (in ratio)	1
Covenant of ratio of consolidated net debt to consolidated EBITDA following certain acquisitions (in ratio)	1
Term loan facility due 2019 | MPLX LP
Debt Instrument [Line Items]
Interest rate, effective percentage	2.561%
MPLX Revolver due July 2022 | MPLX LP
Debt Instrument [Line Items]
Proceeds from long-term lines of credit					$ 1,410
Interest rate, effective percentage			3.464%		3.464%
Repayments of long-term lines of credit					$ 1,915
Letters of credit outstanding, amount			$ 3		3
Remaining borrowing capacity			$ 2,200		$ 2,200
Remaining borrowing capacity, percentage			99.90%		99.90%
ANDX Bank Revolving Credit Facilities [Member] | Andeavor Logistics [Member]
Debt Instrument [Line Items]
Proceeds from long-term lines of credit			$ 760	$ 864
Interest rate, effective percentage			4.061%	4.129%	4.061%
Long-term debt, outstanding			$ 1,200		$ 1,200			$ 1,100
Repayments of long-term lines of credit			635	$ 2,100
Line of Credit Facility, Current Borrowing Capacity							$ 2,100
Long-term Line of Credit			$ 1,245	$ 0	1,245
Line of Credit | MPLX Revolver | MPLX LP
Debt Instrument [Line Items]
Proceeds from long-term lines of credit					$ 0
Line of Credit | MPLX Revolving Credit Facility due July 2024 [Member] | MPLX LP
Debt Instrument [Line Items]
Expiration date				Jul. 30, 2024
Long-term debt, outstanding				$ 0

Debt (Senior Notes) (Details)

Debt (Senior Notes) (Details) - USD ($) $ in Thousands	Oct. 15, 2019	Sep. 09, 2019	Jul. 30, 2019	Feb. 08, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2019	Sep. 23, 2019	Dec. 10, 2018	Nov. 15, 2018
Debt Instrument [Line Items]
Extinguishment of Debt, Gain (Loss), Net of Tax					$ 0	$ 46,000	$ 0
Long-term debt - repayments					7,924,000	6,946,000	$ 416,000
Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross		$ 2,000,000
Percent of par		100.00%
Senior Notes | Floating Rate Senior Notes Due September 2021 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 1,000,000			1,000,000	0
Debt Instrument, Description of Variable Rate Basis		LIBOR plus 0.9 percent per annum
Senior Notes | Floating Rate Senior Notes Due September 2022 [Member]
Debt Instrument [Line Items]
Long-term debt, gross		$ 1,000,000			$ 1,000,000	0
Debt Instrument, Description of Variable Rate Basis		LIBOR plus 1.1 percent per annum
MPLX LP | MPLX Revolving Credit Facility due July 2024 [Member]
Debt Instrument [Line Items]
Debt Instrument, Description of Variable Rate Basis			Adjusted LIBOR or the Alternate Base Rate (as defined in the MPLX Credit Agreement), at our election, plus a specified margin
MPLX LP | MPLX 364-Day Term Loan [Member]
Debt Instrument [Line Items]
Repayments of Short-term Debt				$ 4,100,000
MPLX LP | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross				$ 5,500,000					$ 3,060,000		$ 2,250,000
MPLX LP | Senior Notes | Floating Rate Senior Notes Due September 2021 [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date					Sep. 9, 2021
MPLX LP | Senior Notes | Floating Rate Senior Notes Due September 2022 [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date					Sep. 9, 2022
MPLX LP | Senior Notes | Senior Notes Due February 2029 [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date					Feb. 15, 2029
Long-term debt, gross					$ 750,000	750,000
Interest rate, stated percentage					4.80%
Percent of par											99.432%
MPLX LP | Senior Notes | Senior Notes Due February 2049 [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date					Feb. 15, 2049
Long-term debt, gross					$ 1,500,000	1,500,000
Interest rate, stated percentage					5.50%
Percent of par											98.031%
MPLX LP | Senior Notes | 5.500% senior notes due February 2023
Debt Instrument [Line Items]
Long-term debt, gross										$ 750,000
Interest rate, stated percentage										5.50%
Percent of par										101.833%
MPLX LP | Senior Notes | Senior Notes Due March 2023 [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date					Mar. 15, 2023
Long-term debt, gross					$ 500,000	500,000
Interest rate, stated percentage					3.375%
Percent of par				99.931%
MPLX LP | Senior Notes | 4.125% senior notes due March 2027
Debt Instrument [Line Items]
Debt Instrument, Maturity Date					Mar. 1, 2027
Long-term debt, gross					$ 1,250,000	1,250,000
Interest rate, stated percentage					4.125%
MPLX LP | Senior Notes | 5.200% senior notes due March 2047
Debt Instrument [Line Items]
Debt Instrument, Maturity Date					Mar. 1, 2047
Long-term debt, gross					$ 1,000,000	1,000,000
Interest rate, stated percentage					5.20%
MPLX LP | Senior Notes | Senior Notes Due March 2028 [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date					Mar. 15, 2028
Long-term debt, gross					$ 1,250,000	1,250,000
Interest rate, stated percentage					4.00%
Percent of par				99.551%
MPLX LP | Senior Notes | Senior Notes Due April 2038 [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date					Apr. 15, 2038
Long-term debt, gross					$ 1,750,000	1,750,000
Interest rate, stated percentage					4.50%
Percent of par				98.811%
MPLX LP | Senior Notes | Senior Notes Due April 2048 [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date					Apr. 15, 2048
Long-term debt, gross					$ 1,500,000	1,500,000
Interest rate, stated percentage					4.70%
Percent of par				99.348%
MPLX LP | Senior Notes | Senior Notes Due April 2058 [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date					Apr. 15, 2058
Long-term debt, gross					$ 500,000	500,000
Interest rate, stated percentage					4.90%
Percent of par				99.289%
MPLX LP | Senior Notes | Senior Notes Due October 2022 [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date					Oct. 15, 2022
Long-term debt, gross					$ 266,000	0			266,000
Interest rate, stated percentage					6.25%
MPLX LP | Senior Notes | Senior Notes Due December 2022 [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date					Dec. 1, 2022
Long-term debt, gross					$ 486,000	0			486,000
Interest rate, stated percentage					3.50%
MPLX LP | Senior Notes | Senior Notes Due May 2024 [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date					May 1, 2024
Long-term debt, gross					$ 381,000	0			381,000
Interest rate, stated percentage					6.375%
MPLX LP | Senior Notes | Senior Notes Due January 2025 [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date					Jan. 15, 2025
Long-term debt, gross					$ 708,000	0			708,000
Interest rate, stated percentage					5.25%
MPLX LP | Senior Notes | Senior Notes Due December 2027 [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date					Dec. 1, 2027
Long-term debt, gross					$ 732,000	0			732,000
Interest rate, stated percentage					4.25%
MPLX LP | Senior Notes | Senior Notes Due December 2047 [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date					Dec. 1, 2047
Long-term debt, gross					$ 487,000	0			487,000
Interest rate, stated percentage					5.20%
ANDX LP [Member] | Senior Notes
Debt Instrument [Line Items]
Long-term debt, gross			$ 3,750,000		$ 190,000	$ 3,750,000		$ 690,000	3,060,000
ANDX LP [Member] | Senior Notes | Senior Notes Due October 2019 [Member]
Debt Instrument [Line Items]
Long-term debt, gross									$ 500,000
Interest rate, stated percentage									5.50%
Long-term debt - repayments	$ 500,000
Interest Costs Incurred	$ 13,750
ANDX LP [Member] | Senior Notes | Senior Notes Due October 2022 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage									6.25%
ANDX LP [Member] | Senior Notes | Senior Notes Due December 2022 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage									3.50%
ANDX LP [Member] | Senior Notes | Senior Notes Due May 2024 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage									6.375%
ANDX LP [Member] | Senior Notes | Senior Notes Due January 2025 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage									5.25%
ANDX LP [Member] | Senior Notes | Senior Notes Due December 2027 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage									4.25%
ANDX LP [Member] | Senior Notes | Senior Notes Due December 2047 [Member]
Debt Instrument [Line Items]
Interest rate, stated percentage									5.20%
MarkWest | Senior Notes | Senior Notes Due October 2019 [Member]
Debt Instrument [Line Items]
Debt Instrument, Maturity Date					Oct. 15, 2019
Interest rate, stated percentage					5.50%
MarkWest | Senior Notes | 5.500% senior notes due February 2023
Debt Instrument [Line Items]
Long-term debt, gross										$ 40,000
Debt Premium [Member]
Debt Instrument [Line Items]
Extinguishment of Debt, Gain (Loss), Net of Tax					$ 14,000
Minimum | ANDX LP [Member] | Senior Notes
Debt Instrument [Line Items]
Interest rate, stated percentage			3.50%
Maximum | ANDX LP [Member] | Senior Notes
Debt Instrument [Line Items]
Interest rate, stated percentage			6.375%
Letter of Credit | MPLX LP | MPLX Revolving Credit Facility due July 2024 [Member]
Debt Instrument [Line Items]
Debt Instrument, Renewal Term			1 year

Debt (SMR Transaction) (Details

Debt (SMR Transaction) (Details) - USD ($) $ in Millions	Sep. 01, 2009	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property, plant and equipment, net		$ 22,145	$ 21,525
Accrued liabilities		187	272
Deferred credits and other liabilities		192	208
Steam Methane Reformer Held Under Financing Arrangement [Member]
Property, Plant and Equipment [Line Items]
Proceeds from liability	$ 73
Imputed interest rate on liability	6.39%
Property, plant and equipment, net		46	51
Accrued liabilities		5	5
Deferred credits and other liabilities		$ 75	$ 81

Revenue Disaggregation of Reven

Revenue Disaggregation of Revenue (Details) - USD ($) $ in Millions		3 Months Ended											12 Months Ended
		Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	[1]	Mar. 31, 2019	[1]	Dec. 31, 2018	[1]	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													$ 7,041	$ 5,449
Other Operating Income													(5)	(3)	$ (24)
Total revenues and other income		$ 2,316	$ 2,280	$ 2,210		$ 2,235		$ 2,295		$ 1,712	$ 1,578	$ 1,420	9,041	7,005	3,867
Other income													12	7	6
Service [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													2,498	1,856	1,156
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties													3,455	2,404	1,082
Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													140	220	0
Product [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													806	887	889
Revenue from Contract with Customer, excluding Assessed Tax and Non-ASC 606 Revenue													806	882
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties	[2]												142	87	$ 8
Logistics and Storage [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													3,856	2,598
Logistics and Storage [Member] | Service [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													346	174
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties													3,419	2,401
Logistics and Storage [Member] | Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													0	0
Logistics and Storage [Member] | Product [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, excluding Assessed Tax and Non-ASC 606 Revenue													65	12
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties													26	11
Gathering and Processing [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													3,185	2,851
Gathering and Processing [Member] | Service [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													2,152	1,682
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties													36	3
Gathering and Processing [Member] | Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax													140	220
Gathering and Processing [Member] | Product [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, excluding Assessed Tax and Non-ASC 606 Revenue													741	870
Revenue from Contract with Customer, Excluding Assessed Tax, Related Parties													116	76
Other Income [Member]
Disaggregation of Revenue [Line Items]
Other Operating Income													0	5
Other income	[3]												$ 2,000	$ 1,556
[1]	As discussed in Note 1, MPLX’s acquisition of ANDX is considered a transfer between entities under common control due to MPC’s prior relationship with ANDX. Transfers of businesses between entities under common control require prior periods to be retrospectively adjusted for those dates that the entity was under common control. Accordingly, the tables above include the historical results of ANDX beginning October 1, 2018. Amounts shown for the fourth quarter of 2018 as well as the first and second quarters of 2019 are different than amounts previously reported for Total revenues and other income, Income from operations and Net income as a results of this retrospective adjustment for ANDX. Total revenues and other income originally reported for the fourth quarter of 2018 and the first and second quarters of 2019 was $1,715 million , $1,646 million and $1,629 million , respectively. Income from operations originally reported for the fourth quarter of 2018 and the first and second quarters of 2019 was $666 million , $678 million and $659 million , respectively. Net income originally reported for the fourth quarter of 2018 and the first and second quarters of 2019 was $439 million , $509 million and $488 million , respectively.
[2]	There were additional product sales to MPC that net to zero within the consolidated financial statements as the transactions are recorded net due to the terms of the agreements under which such product was sold. For 2019 , 2018 and 2017 , these sales totaled $1,120 million , $607 million and $254 million , respectively.
[3]	Non-ASC 606 Revenue includes rental income, income from equity method investments, derivative gains and losses, mark-to-market adjustments, and other income.

Revenue Contract Balance Rollfo

Revenue Contract Balance Rollforward (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018
Beginning Balance Deferred Revenue, Noncurrent		$ 132
Ending Balance Deferred Revenue, Noncurrent		217	$ 132
Contract with Customer, Liability, Change in Timeframe, Performance Obligation Satisfied, Revenue Recognized		0	0
Accounting Standards Update 2014-09 [Member]
Beginning Balance Contract with Customer, Asset, Gross	[1]	36	4
Contract with Customer, Asset Increase (Decrease)		5	32	[2]
Contract with Customer, Asset, Reclassified to Receivable	[3]	(2)	0
Ending Balance Contract with Customer, Asset, Gross		39	36	[1]
Beginning Balance Deferred Revenue, Current	[1]	13	5
Deferred Revenue, Period Increase (Decrease)		17	19	[2]
Deferred Revenue, Revenue Recognized	[3]	(7)	(11)
Ending Balance Deferred Revenue, Current		23	13	[1]
Beginning Balance Deferred revenue - related parties	[1]	65	42
Deferred Revenue - Related Party, Period Increase (Decrease)		55	60	[2]
Deferred Revenue - Related Parties, Revenue Recognized	[3]	(67)	(37)
Ending Balance Deferred Revenue, Current, Related Parties		53	65	[1]
Beginning Balance Deferred Revenue, Noncurrent	[1]	56	5
Deferred Revenue, Noncurrent, Period Increase (Decrease)		34	51	[2]
Deferred Revenue, Noncurrent, Revenue Recognized	[3]	0	0
Ending Balance Deferred Revenue, Noncurrent		90	56	[1]
Beginning Balance Deferred Revenue, Noncurrent, Related Parties	[1]	52	43
Deferred Revenue, Noncurrent, Related Party, Period Increase (Decrease)		3	9	[2]
Deferred Revenue, Noncurrent, Related Parties, Revenue Recognized	[3]	0	0
Ending Balance Deferred Revenue, Noncurrent, Related Parties		$ 55	$ 52	[1]
[1]	Balance represents ASC 606 portion of each respective line item.
[2]	Includes opening balances related to the Merger.
[3]	No significant revenue was recognized related to past performance obligations for the years ended December 31, 2019 and 2018 .

Revenue Remaining Performance O

Revenue Remaining Performance Obligations (Details) $ in Millions	Dec. 31, 2019USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Contract with Customer, Liability	$ 220
Revenue, Remaining Performance Obligation, Expected to be Recognized in Current Fiscal Year	1,717
Revenue, Remaining Performance Obligation, Expected to be Recognized in Next Fiscal Year	1,693
Revenue, Remaining Performance Obligation, Expected to be Recognized in Third Fiscal Year	1,640
Revenue, Remaining Performance Obligation, Expected to be Recognized in Fourth Fiscal Year	1,555
Revenue, Remaining Performance Obligation, Expected to be Recognized in Fifth Fiscal Year and Thereafter	5,317
Revenue, Remaining Performance Obligation, Amount	$ 11,922	[1],[2],[3]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	24 years
[1]	All fixed consideration from contracts with customers is included in the amounts presented above. Variable consideration that is constrained or not required to be estimated as it reflects our efforts to perform is excluded.
[2]	Arrangements deemed implicit leases are included in “Rental income” and are excluded from this table.
[3]	Only minimum volume commitments that are deemed fixed are included in the table above. MPLX has various minimum volume commitments in processing arrangements that vary based on the actual Btu content of the gas received. These amounts are deemed variable consideration and are excluded from the table above.

Supplemental Cash Flow Inform_3

Supplemental Cash Flow Information (Summary of Supplemental Cash Flow Information) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Supplemental Cash Flow Elements [Abstract]
Cash and cash equivalents		$ 15	$ 77
Net cash provided by operating activities included:
Interest paid (net of amounts capitalized)		835	568	$ 263
Income taxes paid		1	1	3
Operating Lease, Payments		85	0	0
Finance Lease, Interest Expense		1	0	0
Finance Lease, Principal Payments		5	0	0
Non-cash investing and financing activities:
Net transfers of property, plant and equipment from materials and supplies inventories		2	2	6
Sales-type Lease, Selling Profit (Loss)		21	0	0
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability		26	0	0
Right-of-Use Asset Obtained in Exchange for Finance Lease Liability		4	0	0
Contribution - fixed assets to joint venture	[1]	0	0	337
Contribution - common units issued	[2]	7,722	4,236	1,133
Acquisitions [Abstract]
Restricted Cash	[3]	0	8
Cash, cash equivalents and restricted cash at end of period		$ 15	$ 85	$ 9	$ 239
[1]	Contribution of assets to Sherwood Midstream and Sherwood Midstream Holdings.
[2]	For 2017, includes limited and general partner units issued to MPC as consideration in the acquisitions of the joint-interests, HST, WHC and MPLXT. For 2018, includes limited and general partner units issued to MPC as consideration in the acquisition of Refining Logistics and Fuels Distribution. For 2019, includes limited partner units issued to MPC and public unitholders as consideration in the Merger. See Note 4 .
[3]	The restricted cash balance is included within “Other current assets” on the Consolidated Balance Sheets.

Supplemental Cash Flow Inform_4

Supplemental Cash Flow Information Supplemental Cash Flow Information (Details) $ in Millions	Dec. 31, 2017USD ($)
LOOP LOCAP SAX and Explorer
Suppplemental Cash Flow [Line Items]
Accounts payable, related parties	$ 11

Supplemental Cash Flow Inform_5

Supplemental Cash Flow Information (Summary of Reconciliation of Additions to Property, Plant and Equipment to Total Capital Expenditures) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Supplemental Cash Flow Elements [Abstract]
Increase/(decrease) in capital accruals	$ (146)	$ 135	$ 71

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Income Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	[1]	$ (15)	$ (16)	$ (14)
Other Comprehensive Income (Loss), Net of Tax	[2]	1	(2)
Pension Plan [Member] | Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	[1]	(14)	(14)	(13)
Other Comprehensive Income (Loss), Net of Tax	[2]	0	(1)
Other Postretirement Benefits Plan [Member] | Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	[1]	(1)	(2)	$ (1)
Other Comprehensive Income (Loss), Net of Tax	[2]	$ 1	$ (1)
[1]	These components of “Accumulated other comprehensive loss” are included in the computation of net periodic benefit cost by LOOP and Explorer and are therefore included on the Consolidated Statements of Income under the caption “Income/(loss) from equity method investments.”
[2]	Components of other comprehensive loss - remeasurements relate to actuarial gains and losses as well as amortization of prior service costs. MPLX records an adjustment to “Comprehensive income” in accordance with its ownership interest in LOOP and Explorer.

Equity-Based Compensation (Narr

Equity-Based Compensation (Narrative) (Detail) - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Compensation Expense
Total compensation expense		$ (22)	$ (23)	$ (15)
Phantom Units
Unit-based awards under the Plan
Grant date fair value of performance units granted		$ 32.62	$ 33.84	$ 36.26
Outstanding Phantom and Performance Unit Awards
Non-forfeitable at December 31, 2019(1)	[1]	507,471
Unrecognized compensation cost		$ 9
Cost not yet recognized, period for recognition		1 year 3 months 18 days
Vested and expected to vest at December 31, 2019		1,104,552
Performance Shares
Unit-based awards under the Plan
Grant date fair value of performance units granted		$ 0.76		$ 0.90
Outstanding Phantom and Performance Unit Awards
Unrecognized compensation cost		$ 1
Cost not yet recognized, period for recognition		2 years
Vested and expected to vest at December 31, 2019		84,735
Mplx 2012 Incentive Compensation Plan [Member]
Compensation Expense
Total compensation expense		$ 22	$ 24	$ 18
Maximum | Mplx Two Thousand Eighteen Incentive Compensation Plan [Member]
Equity-Based Compensation [Line Items]
Stock or Units Available for Distributions		16,000,000
Maximum | Mplx 2012 Incentive Compensation Plan [Member]
Equity-Based Compensation [Line Items]
Stock or Units Available for Distributions		2,750,000
Officer | Mplx 2012 Incentive Compensation Plan [Member] | Phantom Units
Unit-based awards under the Plan
Award requisite service period		3 years
Accrued distributions		$ 6	4
Officer | Mplx 2012 Incentive Compensation Plan [Member] | Performance Shares
Unit-based awards under the Plan
Award percentage paid out in cash		75.00%
Award percentage paid out in stock		25.00%
General and administrative expenses
Compensation Expense
Stock-based compensation plans expenses		$ 10	$ 8	$ 2
[1]	Represents a subset of phantom units held by our non-employee directors and certain of our officers and non-officer employees that are generally non-forfeitable and that would be paid out as common units upon the holder’s separation from service.

Equity-Based Compensation (Summ

Equity-Based Compensation (Summary of Phantom Unit Award Activity) (Detail) - Phantom Units - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Number of Units
Outstanding at December 31, 2018		1,154,335
Granted		219,488
Settled		(426,451)
Forfeited		(46,337)
Outstanding at December 31, 2019		1,109,568	1,154,335
Vested and expected to vest at December 31, 2019		1,104,552
Non-forfeitable at December 31, 2019(1)	[1]	507,471
Weighted Average Fair Value
Outstanding at December 31, 2016 (usd per share)		$ 34.34
Grant date fair value of performance units granted		32.62	$ 33.84	$ 36.26
Settled (usd per share)		33.84
Forfeited (usd per share)		33.63
Outstanding at December 31, 2017 (usd per share)		35.97	$ 34.34
Vested and expected to vest at December 31, 2017 (usd per share)		35.98
Convertible at December 31, 2017 (usd per share)	[1]	$ 37.32
Aggregate Intrinsic Value
Vested and expected to vest at December 31, 2019		$ 28
Non-forfeitable at December 31, 2019(1)	[1]	$ 13
[1]	Represents a subset of phantom units held by our non-employee directors and certain of our officers and non-officer employees that are generally non-forfeitable and that would be paid out as common units upon the holder’s separation from service.

Equity-Based Compensation (Su_2

Equity-Based Compensation (Summary of Values Related To Vested and Unvested Restricted Stock Awards) (Details) - Phantom Units - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Equity-Based Compensation [Line Items]
Intrinsic value of units issued during the period	$ 14	$ 18	$ 15
Grant date fair value of performance units granted	$ 32.62	$ 33.84	$ 36.26

Equity-Based Compensation (Su_3

Equity-Based Compensation (Summary of Performance Unit Award Activity) (Details) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Phantom Units
Equity-Based Compensation [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 32.62	$ 33.84	$ 36.26
Granted	219,488
Weighted Average Fair Value
Outstanding at December 31, 2016 (usd per share)	$ 34.34
Settled (usd per share)	33.84
Forfeited (usd per share)	33.63
Outstanding at December 31, 2017 (usd per share)	35.97	$ 34.34
Performance Shares
Equity-Based Compensation [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 0.76		$ 0.90
Number of Units
Outstanding at December 31, 2018	1,941,750
Granted	987,994
Settled	(772,397)
Forfeited	0
Outstanding at December 31, 2019	2,157,347	1,941,750
Weighted Average Fair Value
Outstanding at December 31, 2016 (usd per share)	$ 0.80
Granted (usd per share)	0.76
Settled (usd per share)	0.63
Forfeited (usd per share)	0
Outstanding at December 31, 2017 (usd per share)	0.84	$ 0.80
Performance Units Market Condition [Member]
Equity-Based Compensation [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	0.68
Maximum | Performance Unit Performance Condition [Member]
Equity-Based Compensation [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	2
ANDX LP [Member] | Phantom Units
Equity-Based Compensation [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 43.64
Granted	208,533

Equity-Based Compensation (Assu

Equity-Based Compensation (Assumptions) (Details) - Performance Shares - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2017
Equity-Based Compensation [Line Items]
Risk-free interest rate	2.51%	1.52%
Look-back period	2 years 10 months 2 days	2 years 9 months 29 days
Expected volatility	25.01%	49.34%
Grant date fair value of performance units granted	$ 0.76	$ 0.90

Leases Lessee Disclosures (Deta

Leases Lessee Disclosures (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Lessee, Lease, Description [Line Items]
Operating Leases, Rent Expense, Net		$ 89	$ 64
Lessee, Operating Lease, Liability, Payments, Due Next Twelve Months	$ 78
Finance Lease, Liability, Payments, Due Next Twelve Months	10
Lessee, Operating Lease, Liability, Payments, Due Year Two	73
Finance Lease, Liability, Payments, Due Year Two	2
Lessee, Operating Lease, Liability, Payments, Due Year Three	63
Finance Lease, Liability, Payments, Due Year Three	2
Lessee, Operating Lease, Liability, Payments, Due Year Four	56
Finance Lease, Liability, Payments, Due Year Four	2
Lessee, Operating Lease, Liability, Payments, Due Year Five	36
Finance Lease, Liability, Payments, Due Year Five	1
Lessee, Operating Lease, Liability, Payments, Due after Year Five	139
Finance Lease, Liability, Payments, Due after Year Five	10
Lessee, Operating Lease, Liability, Payments, Due	445
Finance Lease, Liability, Payment, Due	27
Operating Lease, Right-of-Use Asset	365	0
Operating Lease, Liability, Current	66	0
Operating Lease, Cost	75
Finance Lease, Right-of-Use Asset, Amortization	5
Finance Lease, Interest Expense	1	0	$ 0
Finance Lease Cost	6
Variable Lease, Cost	11
Operating Leases, Future Minimum Payments Due, Next Twelve Months		90
Capital Leases, Future Minimum Payments Due, Next Twelve Months		5
Operating Leases, Future Minimum Payments, Due in Two Years		88
Capital Leases, Future Minimum Payments Due in Two Years		8
Operating Leases, Future Minimum Payments, Due in Three Years		83
Capital Leases, Future Minimum Payments Due in Three Years		3
Operating Leases, Future Minimum Payments, Due in Four Years		76
Capital Leases, Future Minimum Payments Due in Four Years		2
Operating Leases, Future Minimum Payments, Due in Five Years		70
Capital Leases, Future Minimum Payments Due in Five Years		2
Operating Leases, Future Minimum Payments, Due Thereafter		825
Capital Leases, Future Minimum Payments Due Thereafter		4
Operating Leases, Future Minimum Payments Due		1,232
Capital Leases, Future Minimum Payments Due		24
Less: imputed interest costs		3
Capital Leases, Future Minimum Payments, Present Value of Net Minimum Payments		21
Short-term Lease, Cost	80
Lease, Cost	172
Operating Lease, Liability, Noncurrent	$ 302	0
Operating Lease, Weighted Average Remaining Lease Term	8 years 7 months 2 days
Operating Lease, Weighted Average Discount Rate, Percent	4.38%
Property, plant and equipment, gross	$ 26,867	25,213
Accumulated depreciation	4,722	3,688
Property, plant and equipment, net	22,145	21,525
Other current liabilities	136	645
Long-term debt	$ 19,704	17,922
Finance Lease, Weighted Average Remaining Lease Term	10 years 1 month 28 days
Finance Lease, Weighted Average Discount Rate, Percent	5.87%
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	$ 77
Finance Lease, Interest Payment on Liability	8
Operating Lease, Liability	368
Finance Lease, Liability	19
Marathon Petroleum Corporation [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Liability, Payments, Due Next Twelve Months	14
Lessee, Operating Lease, Liability, Payments, Due Year Two	14
Lessee, Operating Lease, Liability, Payments, Due Year Three	14
Lessee, Operating Lease, Liability, Payments, Due Year Four	14
Lessee, Operating Lease, Liability, Payments, Due Year Five	14
Lessee, Operating Lease, Liability, Payments, Due after Year Five	605
Lessee, Operating Lease, Liability, Payments, Due	675
Operating Lease, Right-of-Use Asset	232	0
Operating Lease, Liability, Current	1	0
Operating Lease, Cost	14
Finance Lease, Right-of-Use Asset, Amortization	0
Finance Lease, Interest Expense	0
Finance Lease Cost	0
Variable Lease, Cost	1
Short-term Lease, Cost	0
Lease, Cost	15
Operating Lease, Liability, Noncurrent	$ 230	$ 0
Operating Lease, Weighted Average Remaining Lease Term	47 years 2 months 12 days
Operating Lease, Weighted Average Discount Rate, Percent	5.80%
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	$ 444
Operating Lease, Liability	231
Finance Lease [Member]
Lessee, Lease, Description [Line Items]
Property, plant and equipment, gross	46
Accumulated depreciation	19
Property, plant and equipment, net	27
Other current liabilities	9
Long-term debt	10
Other Liabilities	$ 19
Lease Agreements, Lessee [Member] | Maximum
Lessee, Lease, Description [Line Items]
Term Of Agreements	59 years
Renewal Term Agreement	50 years
Lease Agreements, Lessee [Member] | Minimum
Lessee, Lease, Description [Line Items]
Term Of Agreements	1 year
Renewal Term Agreement	1 year

Leases Lessor Disclosures (Deta

Leases Lessor Disclosures (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2019
Lessor, Lease, Description [Line Items]
Lessor, Sales-type Lease, Assumptions and Judgments, Value of Underlying Asset, Amount		$ 29
Deferred Rent Receivables, Net		3
Property Subject to or Available for Operating Lease, Gross		6,947	$ 6,212
Sales-type and Direct Financing Leases, Lease Receivable, Payments to be Received, Current Year		14
Sales-type and Direct Financing Leases, Lease Receivable, Payments to be Received, Next Twelve Months		14
Sales-type and Direct Financing Leases, Lease Receivable, Payments to be Received, Two Years		14
Sales-type and Direct Financing Leases, Lease Receivable, Payments to be Received, Three Years		15
Sales-type and Direct Financing Leases, Lease Receivable, Payments to be Received, Four Years		15
Sales-type and Direct Financing Leases, Lease Receivable, Payments to be Received, Thereafter		20
Sales-type and Direct Financing Leases, Lease Receivable, Payments to be Received		92
Operating Leases, Future Minimum Payments Receivable, Current		1,320	1,448
Operating Lease, Lease Income	[1]	257
Sales-type Lease, Selling Profit (Loss)		21	0	$ 0
Operating Leases, Future Minimum Payments Receivable, in Two Years		1,309	1,438
Operating Leases, Future Minimum Payments Receivable, in Three Years		1,304	1,300
Operating Leases, Future Minimum Payments Receivable, in Four Years		1,244	1,294
Operating Leases, Future Minimum Payments Receivable, in Five Years		1,182	1,239
Operating Leases, Future Minimum Payments Receivable, Thereafter		3,771	4,900
Operating Leases, Future Minimum Payments Receivable		10,130	11,619
Sales-type and Direct Financing Leases, Lease Receivable, Undiscounted Excess Amount		45
Sales-type Lease, Lease Receivable		47
Property Subject to or Available for Operating Lease, Accumulated Depreciation		2,355	2,074
Property Subject to or Available for Operating Lease, Net		4,592	4,138
Operating Leases, Income Statement, Minimum Lease Revenue			1,032	$ 601
Marathon Petroleum Corporation [Member]
Lessor, Lease, Description [Line Items]
Operating Lease, Lease Income	[1]	1,020
Sales-type Lease, Interest Income		6
Sales-type Lease, Variable Lease Income		1
Sales-type Lease, Unguaranteed Residual Asset		7	0		$ 6
Related Party [Member]
Lessor, Lease, Description [Line Items]
Lessor, Operating Lease, Payments to be Received, Remainder of Fiscal Year		1,134
Operating Leases, Future Minimum Payments Receivable, Current			1,277
Lessor, Operating Lease, Payments to be Received, Next Twelve Months		1,130
Operating Leases, Future Minimum Payments Receivable, in Two Years			1,275
Lessor, Operating Lease, Payments to be Received, Two Years		1,127
Operating Leases, Future Minimum Payments Receivable, in Three Years			1,146
Lessor, Operating Lease, Payments to be Received, Three Years		1,074
Operating Leases, Future Minimum Payments Receivable, in Four Years			1,143
Lessor, Operating Lease, Payments to be Received, Four Years		1,015
Operating Leases, Future Minimum Payments Receivable, in Five Years			1,094
Lessor, Operating Lease, Payments to be Received, Thereafter		2,699
Operating Leases, Future Minimum Payments Receivable, Thereafter			3,786
Operating Leases, Future Minimum Payments Receivable		8,179	9,721
Third Party
Lessor, Lease, Description [Line Items]
Lessor, Operating Lease, Payments to be Received, Remainder of Fiscal Year		186
Operating Leases, Future Minimum Payments Receivable, Current			171
Lessor, Operating Lease, Payments to be Received, Next Twelve Months		179
Operating Leases, Future Minimum Payments Receivable, in Two Years			163
Lessor, Operating Lease, Payments to be Received, Two Years		177
Operating Leases, Future Minimum Payments Receivable, in Three Years			154
Lessor, Operating Lease, Payments to be Received, Three Years		170
Operating Leases, Future Minimum Payments Receivable, in Four Years			151
Lessor, Operating Lease, Payments to be Received, Four Years		167
Operating Leases, Future Minimum Payments Receivable, in Five Years			145
Lessor, Operating Lease, Payments to be Received, Thereafter		1,072
Operating Leases, Future Minimum Payments Receivable, Thereafter			1,114
Operating Leases, Future Minimum Payments Receivable		1,951	1,898
Natural gas gathering and NGL transportation pipelines and facilities
Lessor, Lease, Description [Line Items]
Property Subject to or Available for Operating Lease, Gross		1,120	964
Processing, fractionation and storage facilities
Lessor, Lease, Description [Line Items]
Property Subject to or Available for Operating Lease, Gross		2,176	1,670
Pipelines and related assets
Lessor, Lease, Description [Line Items]
Property Subject to or Available for Operating Lease, Gross		362	376
Barges and towing vessels
Lessor, Lease, Description [Line Items]
Property Subject to or Available for Operating Lease, Gross		738	619
Terminals and related assets
Lessor, Lease, Description [Line Items]
Property Subject to or Available for Operating Lease, Gross		1,232	1,415
Refineries and related assets [Member]
Lessor, Lease, Description [Line Items]
Property Subject to or Available for Operating Lease, Gross		1,083	981
Land, building, office equipment and other
Lessor, Lease, Description [Line Items]
Property Subject to or Available for Operating Lease, Gross		$ 236	$ 187
Maximum | Lease Agreements, Lessor [Member]
Lessor, Lease, Description [Line Items]
Term Of Agreements		11 years
Renewal Term Agreement		5 years
Minimum | Lease Agreements, Lessor [Member]
Lessor, Lease, Description [Line Items]
Term Of Agreements		1 year
Renewal Term Agreement		1 year
[1]	These amounts are presented net of executory costs.

Commitments and Contingencies_2

Commitments and Contingencies (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Feb. 15, 2017
Commitments And Contingencies [Line Items]
Accrual for environmental loss contingencies	$ 19	$ 20
Contractual commitments to acquire property, plant and equipment	753
Environmental Loss Contingency [Member] | MPC
Commitments And Contingencies [Line Items]
Receivable from MPC for indemnification of environmental costs	0	$ 0
MarkWest, MarkWest Liberty Midstream, Ohio Fractionation, MarkWest Utica EMG [Member]
Commitments And Contingencies [Line Items]
EPA proposed penalty	0.9
Estimated cost of proposed supplemental environmental projects	$ 3.3
Bakken Pipeline System
Commitments And Contingencies [Line Items]
Equity method investment, ownership percentage			9.00%
Indirect Ownership Interest | Bakken Pipeline System
Commitments And Contingencies [Line Items]
Equity method investment, ownership percentage	9.00%
Guarantee Type, Other [Member]
Commitments And Contingencies [Line Items]
Guarantor Obligations, Maximum Exposure, Undiscounted	$ 230
Minimum | Minimum Committed Volume Contracts [Member]
Commitments And Contingencies [Line Items]
Term Of Agreements	4 years

Commitments and Contingencies_3

Commitments and Contingencies (Minimum Future Payments) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019USD ($)
Transportation And Terminalling Agreements
Other Commitments [Line Items]
2020	$ 2,246
2021	2,222
2022	2,199
2023	2,200
2024	1,753
2025 and thereafter	191
Total	$ 10,811
Minimum Committed Volume Contracts [Member] | Minimum
Other Commitments [Line Items]
Term Of Agreements	4 years
Minimum Committed Volume Contracts [Member] | Maximum
Other Commitments [Line Items]
Term Of Agreements	20 years

Commitments and Contingencies_4

Commitments and Contingencies (SMR Liability) (Details) - SMR Transaction $ in Millions	Dec. 31, 2019USD ($)
Recorded Unconditional Purchase Obligation [Line Items]
2018	$ 17
2019	17
2020	17
2021	17
2022	17
2023 and thereafter	92
Total minimum payments	177
Less: Services element	68
Less: Interest	29
Total SMR liability	80
Less: Current portion of SMR liability	5
Long-term portion of SMR liability	$ 75

Select Quarterly Financial Da_3

Select Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended											12 Months Ended
		Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019		Mar. 31, 2019		Dec. 31, 2018		Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Quarterly Financial Data [Line Items]
Total revenues and other income		$ 2,316	$ 2,280	$ 2,210	[1]	$ 2,235	[1]	$ 2,295	[1]	$ 1,712	$ 1,578	$ 1,420	$ 9,041		$ 7,005		$ 3,867
Income from operations		(346)	926	885	[1]	912	[1]	891	[1]	672	608	557	2,377		2,728		1,191
Net income		(573)	689	657	[1]	689	[1]	611	[1]	516	456	423	1,462		2,006		836
Net income (loss) attributable to MPLX LP		(581)	629	482	[1]	503	[1]	434	[1]	510	453	421	1,033	[2]	1,818	[2]	794	[2]
Distributions declared:
Total cash distributions declared													2,758		2,060		1,288
Total distributions declared		$ 747	$ 734	$ 734		$ 543		$ 534		$ 526	$ 517	$ 483
Limited Partners Common Units
Quarterly Financial Data [Line Items]
Net income (loss) attributable to MPLX LP	[2]												$ 910		$ 1,743		$ 411
Net income (loss) attributable to MPLX LP per limited partner unit:
Common - basic (in USD per unit)		$ (0.58)	$ 0.61	$ 0.56		$ 0.61		$ 0.52		$ 0.62	$ 0.55	$ 0.61	$ 1		$ 2.29		$ 1.07
Common - diluted (in USD per unit)		(0.58)	0.61	0.55		0.61		0.52		0.62	0.55	0.61	1		2.29		$ 1.06
Cash distributions declared per limited partner common unit		$ 0.6875	$ 0.6775	$ 0.6675		$ 0.6575		$ 0.6475		$ 0.6375	$ 0.6275	$ 0.6175	$ 2.6900		$ 2.5300
Distributions declared:
Total cash distributions declared	[3]												$ 2,635		$ 1,985		$ 895
Public | Limited Partners Common Units
Distributions declared:
Total cash distributions declared		$ 270	$ 266	$ 261		$ 191		$ 187		$ 185	$ 181	$ 179
MPC | Limited Partners Common Units
Distributions declared:
Total cash distributions declared		446	438	431		332		327		322	316	288
Preferred Class A [Member]
Distributions declared:
Limited partners' distributions		20	20	21		20		20		$ 19	$ 20	$ 16	81		75		65
Preferred Class B [Member]
Distributions declared:
Limited partners' distributions		$ 11	$ 10	21		0							$ 42		$ 0		$ 0
Previously Reported [Member]
Quarterly Financial Data [Line Items]
Total revenues and other income	[1]			1,629		1,646		1,715
Income from operations	[1]			659		678		666
Net income	[1]			$ 488		$ 509		$ 439
[1]	As discussed in Note 1, MPLX’s acquisition of ANDX is considered a transfer between entities under common control due to MPC’s prior relationship with ANDX. Transfers of businesses between entities under common control require prior periods to be retrospectively adjusted for those dates that the entity was under common control. Accordingly, the tables above include the historical results of ANDX beginning October 1, 2018. Amounts shown for the fourth quarter of 2018 as well as the first and second quarters of 2019 are different than amounts previously reported for Total revenues and other income, Income from operations and Net income as a results of this retrospective adjustment for ANDX. Total revenues and other income originally reported for the fourth quarter of 2018 and the first and second quarters of 2019 was $1,715 million , $1,646 million and $1,629 million , respectively. Income from operations originally reported for the fourth quarter of 2018 and the first and second quarters of 2019 was $666 million , $678 million and $659 million , respectively. Net income originally reported for the fourth quarter of 2018 and the first and second quarters of 2019 was $439 million , $509 million and $488 million , respectively.
[2]	Allocation of net income/(loss) attributable to MPLX LP assumes all earnings for the period had been distributed based on the distribution priorities applicable to the period.
[3]	See Note 8 for distribution information.