MPLX (MPLX) 10-K 24 Feb 17 2016 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Feb. 13, 2017	Jun. 30, 2016
Entity Information [Line Items]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	FY
Trading Symbol	MPLX
Entity Registrant Name	MPLX LP
Entity Central Index Key	1,552,000
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$ 8,400
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	FY
Trading Symbol	MPLX
Entity Registrant Name	MPLX LP
Entity Central Index Key	1,552,000
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$ 8,400
Common Units [Member]
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		357,257,661
Entity Common Stock, Shares Outstanding		357,257,661
Class B Units [Member]
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		3,990,878
Entity Common Stock, Shares Outstanding		3,990,878
General Partner Units [Member]
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		7,372,419
Entity Common Stock, Shares Outstanding		7,372,419

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) shares in Millions, $ in Millions		12 Months Ended
		Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Revenues and other income:
Service revenue		$ 958		$ 130		$ 70
Service revenue - related parties		603		593		662
Operating Leases, Income Statement, Lease Revenue		298		20		0
Operating Lease, Income Statement, Lease Revenue, Related Parties		114		101		15
Product sales		572		36		0
Product sales - related parties		11		1		0
Gain (Loss) on Disposition of Assets for Financial Service Operations		1		0		0
Income (Loss) from Equity Method Investments		(74)	[1]	3		0
Other income		6		6		6
Other income - related parties		101		71		40
Total revenues and other income		2,590		961		793
Costs and expenses:
Cost of revenues (excludes items below)		354		225		228
Purchased product costs		448		20		0
Cost of Rental Sales and Occupancy Costs		53		5		1
Purchases - related parties		316		166		153
Depreciation and amortization		546		116		75
Goodwill and Intangible Asset Impairment		130		0		0
General and administrative expenses		193		118		81
Other taxes		43		13		10
Total costs and expenses		2,083		663		548
Income from operations		507		298		245
Interest And Other Financial Costs From Related Parties		1		0		0
Interest expense, net		210		35		4
Other Nonoperating Income (Expense)		50		13		1
Income before income taxes		246		250		240
(Benefit) provision for income taxes		(12)		1		1
Net income		258		249		239
Less: Net income attributable to noncontrolling interests		2		1		57
Income (Loss) Attributable to Predecessor		23		92		61
Net income attributable to MPLX LP	[2]	233		156		121
Dividends, Preferred Stock		41		0		0
Less: General partner’s interest in net income attributable to MPLX LP		191		57		6
Limited partners’ interest in net income attributable to MPLX LP		$ 1		$ 99		$ 115
Weighted average limited partner units outstanding:
Weighted Average Limited Partnership Units Outstanding, Basic		338		99		76
Weighted Average Limited Partnership Units Outstanding, Diluted		345		100		76
MPC [Member]
Revenues and other income:
Service revenue - related parties		$ 603		$ 593		$ 662
Operating Lease, Income Statement, Lease Revenue, Related Parties		114		101		15
Product sales - related parties		11	[3]	1	[3]	0
Other income - related parties		60		68		39
Limited Partners Common Units [Member]
Costs and expenses:
Net income attributable to MPLX LP	[2]	$ 1		$ 97		$ 58
Per Unit Data (See Note 7)
Basic (in USD per unit)		$ 0		$ 1.23		$ 1.55
Diluted (in USD per unit)		$ 0		$ 1.22		$ 1.55
Weighted average limited partner units outstanding:
Weighted Average Limited Partnership Units Outstanding, Basic		331		79		37
Weighted Average Limited Partnership Units Outstanding, Diluted		338		80		37
Cash distributions declared per limited partner common unit		$ 2.0500		$ 1.8200		$ 1.4100
Limited Partners Subordinated Units [Member] | MPC [Member]
Costs and expenses:
Net income attributable to MPLX LP	[2]			$ 2		$ 55
Per Unit Data (See Note 7)
Basic (in USD per unit)				$ 0.11		$ 1.50
Diluted (in USD per unit)				0.11		1.50
Basic and Diluted (in USD per unit)		$ 0		$ 0.11		$ 1.50
Weighted average limited partner units outstanding:
Weighted Average Limited Partnership Units Outstanding, Basic				18		37
Weighted Average Limited Partnership Units Outstanding, Diluted				18		37
Basic and Diluted Units (in units)		0		18		37
[1]	(2)Income (loss) from equity method investments includes the impact of any basis differential amortization or accretion.
[2]	(1)Allocation of net income (loss) attributable to MPLX LP assumes all earnings for the period had been distributed based on the current period distribution priorities.
[3]	(1)For 2016 and 2015, there were $46 million and $1 million, respectively, of 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. There were no such transactions in 2014.

Consolidated Statements of Inc3

Consolidated Statements of Income Consolidated Statements of Income (Parenthetical) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Interest Costs Capitalized	$ 1	$ 28	$ 5

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 234	$ 43
Receivables, net	297	245
Receivables - related parties	122	187
Inventories	54	51
Other current assets	33	50
Total current assets	740	576
Equity method investments	2,467	2,458
Property, plant and equipment, net	10,730	9,997
Intangibles, net	492	466
Goodwill	2,199	2,570
Long-term receivables - related parties	4	25
Other noncurrent assets	14	12
Total assets	16,646	16,104
Current liabilities:
Accounts payable	123	91
Accrued liabilities	228	187
Payables - related parties	75	54
Deferred Revenue, Current	2	0
Deferred revenue - related parties	34	32
Accrued property, plant and equipment	132	168
Accrued taxes	33	27
Accrued interest payable	53	54
Other current liabilities	24	12
Total current liabilities	704	625
Long-term deferred revenue	12	4
Long-term deferred revenue - related parties	15	9
Long-term debt	4,422	5,255
Deferred income taxes	5	378
Deferred credits and other liabilities	169	166
Total liabilities	5,327	6,437
Temporary Equity, Carrying Amount, Including Portion Attributable to Noncontrolling Interests	1,000	0
Equity
Total MPLX LP partners' capital	10,301	9,654
Noncontrolling interest	18	13
Total equity	10,319	9,667
Liabilities and Equity	16,646	16,104
MPC [Member]
Current assets:
Receivables - related parties	117	175
Long-term receivables - related parties	4	25
Current liabilities:
Payables - related parties	51	33
Limited Partners Common Units [Member] | MPC [Member]
Equity
Total MPLX LP partners' capital	1,069	465
Limited Partners Class B Units [Member]
Equity
Total MPLX LP partners' capital	133	266
General Partner [Member] | MPC [Member]
Equity
Total MPLX LP partners' capital	1,013	819
Public [Member] | Limited Partners Common Units [Member]
Equity
Total MPLX LP partners' capital	8,086	7,691
Predecessor [Member] | MPC [Member]
Equity
Total MPLX LP partners' capital	$ 0	413
Total equity		$ 413

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - shares	Dec. 31, 2016	Dec. 31, 2015
Units outstanding	7,371,105
Limited Partners Common Units [Member] | Public [Member]
Units issued	271,000,000	240,000,000
Units outstanding	271,000,000	240,000,000
Limited Partners Class B Units [Member]
Units issued	4,000,000	8,000,000
Units outstanding	4,000,000	8,000,000
MPC [Member] | Limited Partners Common Units [Member]
Units issued	86,000,000	57,000,000
Units outstanding	86,000,000	57,000,000
MPC [Member] | Limited Partners Subordinated Units [Member]
Units issued	0	0
Units outstanding	0	0
MPC [Member] | General Partner [Member]
Units issued	7,000,000	7,000,000
Units outstanding	7,000,000	7,000,000

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016		Dec. 31, 2015	Dec. 31, 2014
Operating activities:
Net income	$ 258		$ 249	$ 239
Adjustments to reconcile net income to net cash provided by operating activities:
Amortization of Debt Issuance Costs	46		5	1
Depreciation and amortization	546		116	75
Goodwill and Intangible Asset Impairment	130		0	0
Deferred income taxes	(17)		1	0
Asset retirement expenditures	(5)		(1)	(2)
Gain on disposal of assets	(1)		0	0
Loss (income) from equity method investments	74	[1]	(3)	0
Distributions from unconsolidated affiliates	148		15	0
Changes in:
Current receivables	(52)		(29)	2
Increase (Decrease) in Inventories	(8)		1	1
Change in fair value of derivatives	43		(6)	0
Current accounts payable and accrued liabilities	100		2	1
Receivables from / liabilities to related parties	6		(22)	15
All other, net	20		12	2
Net cash provided by operating activities	1,288		340	334
Investing activities:
Additions to property, plant and equipment	(1,206)		(288)	(141)
Acquisitions, net of cash acquired	0		(1,218)	0
Payments for (Proceeds from) Investments	77		(77)	0
Proceeds from Sales of Assets, Investing Activities	1		0	0
Investments in unconsolidated affiliates	(87)		(14)	0
All other, net	3		(2)	4
Net cash used in investing activities	(1,212)		(1,599)	(137)
Financing activities:
Long-term debt - borrowings	434		1,490	1,160
Long-term debt - repayments	(1,312)		(1,441)	(526)
Related party debt - borrowings	2,532		301	0
Related party debt - repayments	(2,540)		(293)	0
Debt issuance costs	0		(11)	(3)
Net proceeds from equity offerings	792		1	230
Proceeds from Issuance of Preferred Limited Partners Units	984		0	0
Issuance of units in MarkWest Merger	0			0
Partners' Capital Account, Sale of Units	792		1
Contributions from MPC - MarkWest Merger	0		1,230	0
Payments of Distributions on Preferred Units	(25)		0	0
Distributions to unitholders and general partner	(845)		(158)	(103)
Distributions to noncontrolling interests	(3)		(1)	(47)
Proceeds from Noncontrolling Interests	6		0	0
Payments to Class B Unitholders	25		0	0
Proceeds from (Payments for) Other Financing Activities	(4)		0	0
Proceeds from Contributions from Parent	225		0	0
Distributions related to purchase of additional interest in Pipe Line Holdings	0		(12)	(910)
Payments of Distributions to Affiliates	(104)			(25)
Net cash provided by (used in) financing activities	115		1,275	(224)
Cash and cash equivalents at end of period	234		43	27
Cash and cash equivalents at beginning of period	43		27	54
Net increase (decrease) in cash and cash equivalents	191		16	(27)
MPC [Member] | Predecessor [Member]
Operating activities:
Net income			92	61
Financing activities:
Payments of Distributions to Affiliates	$ (104)		$ 0	$ (25)
[1]	(2)Income (loss) from equity method investments includes the impact of any basis differential amortization or accretion.

Consolidated Statements of Equi

Consolidated Statements of Equity - USD ($) $ in Millions	Total	MPC [Member]	Limited Partners Common Units [Member]	Limited Partners Common Units [Member]Public [Member]	Limited Partners Common Units [Member]MPC [Member]	Limited Partners Class B Units [Member]Public [Member]	Limited Partners Subordinated Units [Member]MPC [Member]	General Partner [Member]MPC [Member]	Noncontrolling Interest [Member]	Noncontrolling Interest [Member]MPC [Member]	General Partner Units [Member]	General Partner Units [Member]General Partner [Member]MPC [Member]
Partners' Capital, Including Portion Attributable to Noncontrolling Interest | Predecessor [Member]		$ 285
Partners' Capital, Including Portion Attributable to Noncontrolling Interest	$ 1,399			$ 412	$ 57		$ 209	$ (32)		$ 468
Purchase of additional interest in Pipe Line Holdings	(910)				200			(638)		(472)
Payments of Distributions to Affiliates | Predecessor [Member]		(25)
Payments of Distributions to Affiliates	(25)
Partners' Capital Account, Public Sale of Units Net of Offering Costs	230			221								$ 9
Net income | Predecessor [Member]		61
Net income	239			31	27		58	5		57
Distributions to unitholders and general partner	(103)			(26)	(23)		(50)	(4)
Distributions to noncontrolling interest	(47)									(47)
Equity-based compensation	1			1
Proceeds from Noncontrolling Interests	0
Partners' Capital, Including Portion Attributable to Noncontrolling Interest | Predecessor [Member]		321
Partners' Capital, Including Portion Attributable to Noncontrolling Interest	784			639	261		217	(660)		6
Purchase of additional interest in Pipe Line Holdings	(12)							(6)		$ (6)
Payments of Distributions to Affiliates | Predecessor [Member]		0
Contribution from MPC	1,280							1,280
Issuance of units	1			1
Net income | Predecessor [Member]		92
Net income	249			15	36		48	57	$ 1
Distributions to unitholders and general partner	(158)			(40)	(52)		(45)	(21)
Distributions to noncontrolling interest	(1)								(1)
Subordinated unit conversion					220		(220)
Equity-based compensation	17			17
Deferred income tax impact from changes in equity	1			(1)
Issuance of units in MarkWest Merger	7,495			7,060		$ 266		169
Noncontrolling interest assumed in MarkWest Merger	13								13
Proceeds from Noncontrolling Interests	0
Partners' Capital, Including Portion Attributable to Noncontrolling Interest | Predecessor [Member]		413
Partners' Capital, Including Portion Attributable to Noncontrolling Interest	9,667			7,691	465	266	0	819	13
Payments of Distributions to Affiliates | Predecessor [Member]		(104)
Payments of Distributions to Affiliates	(104)
Contribution from MPC	225	15	$ 15		84			141
Partners' Capital Account, Contributions	(188)							(188)
Noncash Partner Capital Account Distributions	563							563
Issuance of units	792			776				16			$ 1
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Excluding Portion Attributable to Temporary Equity | Predecessor [Member]		23
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest, Excluding Portion Attributable to Temporary Equity	217			(5)	6			191	2
Net income	258
Stockholders' Equity, Change in Reporting Entity | Predecessor [Member]		$ (332)
Stockholders' Equity, Change in Reporting Entity					669			(337)
Distributions to unitholders and general partner	(845)			(513)	(142)			(190)
Distributions to noncontrolling interest	(3)								(3)
Subordinated unit conversion				133		133
Equity-based compensation	6			6
Deferred income tax impact from changes in equity	(17)			(2)	(13)			(2)
Proceeds from Noncontrolling Interests	6								6
Partners' Capital, Including Portion Attributable to Noncontrolling Interest	$ 10,319			$ 8,086	$ 1,069	$ 133	$ 0	$ 1,013	$ 18

Description of the Business and

Description of the Business and Basis of Presentation	12 Months Ended
	Dec. 31, 2016
Text Block [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, growth-oriented master limited partnership formed by Marathon Petroleum Corporation. MPLX LP and its subsidiaries (collectively, the “Partnership”) are engaged in the gathering, processing and transportation of natural gas; the gathering, transportation, fractionation, storage and marketing of NGLs; and the gathering, transportation and storage of crude oil and refined petroleum products. The Partnership’s principal executive office is located in Findlay, Ohio. The Partnership was formed on March 27, 2012 as a Delaware limited partnership and completed its initial public offering (the “Initial Offering”) on October 31, 2012 . On December 4, 2015 , a wholly-owned subsidiary of the Partnership merged with MarkWest Energy Partners L.P. (the “MarkWest Merger”), which is one of the largest processors of natural gas in the United States and the largest processor and fractionator in the Marcellus and Utica shale plays. This acquisition is discussed further in Note 4 . Effective March 31, 2016 , the Partnership acquired MPC’s inland marine business, Hardin Street Marine LLC. The acquisition is also described further in Note 4 . Unless the context otherwise requires, references in this report to “MPLX LP,” the “Partnership,” or like terms refer to MPLX LP and its subsidiaries, including MPLX Operations LLC (“MPLX Operations”), MPLX Terminal and Storage LLC (“MPLX Terminal and Storage”), MarkWest Energy Partners, L.P. (“MarkWest”), MarkWest Hydrocarbon, L.L.C. (“MarkWest Hydrocarbon”), MPLX Pipe Line Holdings LLC (“Pipe Line Holdings”), Marathon Pipe LLC (“MPL”), Ohio River Pipe Line LLC (“ORPL”) and Hardin Street Marine LLC (“HSM”). References to “MPC” refer collectively to Marathon Petroleum Corporation and its subsidiaries, other than the Partnership. References to “Predecessor” refer collectively to HSM’s related assets, liabilities and results of the operations. The Partnership’s business consists of two segments: Logistics and Storage (“L&S”) and Gathering and Processing (“G&P”). See Note 10 for additional information regarding operations. Basis of Presentation – The Partnership’s consolidated financial statements include all majority-owned and controlled subsidiaries. For non-wholly-owned consolidated subsidiaries, the interests owned by third parties, including MPC, have been recorded as Noncontrolling interest in the accompanying Consolidated Balance Sheets. Intercompany investments, accounts and transactions have been eliminated. The Partnership’s investments in which the Partnership exercises significant influence but does not control and does not have a controlling financial interest are accounted for using the equity method. The Partnership’s investments in a VIE in which the Partnership exercises significant influence but does not control and is not the primary beneficiary are also accounted for using the equity method. The accompanying consolidated financial statements of the Partnership have been prepared in accordance with GAAP.

Summary of Principal Accounting

Summary of Principal Accounting Policies	12 Months Ended
	Dec. 31, 2016
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; valuing inventory; 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 – The Partnership’s assessment of each of the revenue recognition criteria as they relate to its revenue producing activities are as follows: persuasive evidence of an arrangement exists, delivery, the fee is fixed or determinable and collectability is reasonably assured. It is upon delivery or title transfer to the customer that the Partnership meets all four revenue recognition criteria and it is at such time that the Partnership recognizes Product sales . Additionally, it is upon completion of services provided that the Partnership meets all four revenue recognition criteria and it is at such time that the Partnership recognizes Service revenue . L&S Segment Revenues are recognized in the L&S segment for crude oil and product pipeline transportation based on the delivery of actual volumes transported at regulated tariff rates. When MPC ships volumes on our pipeline systems under a joint tariff with a third party, those revenues are recorded as sales and other operating revenues, and not as sales to related parties, because we receive payment from the third party. Revenues are recognized for crude oil and refined product storage as performed based on contractual rates. Operating fees received for operating pipeline systems are recognized as a component of other income in the period the service is performed. All such amounts are reported as Service revenue on the Consolidated Statements of Income. Under our MPC transportation services agreements, if MPC fails to transport its minimum throughput volumes during any quarter, then MPC will pay us a deficiency payment equal to the volume of the deficiency multiplied by the tariff rate then in effect. MPC may then apply the amount of any such deficiency payments as a credit for volumes transported on the applicable pipeline system in excess of its minimum volume commitment during the following four or eight quarters under the terms of the applicable transportation services agreement. The deficiency payments are initially recorded as Deferred revenue - related parties in the Consolidated Balance Sheets. The Partnership recognizes revenues for the deficiency payments at the earlier of when credits are used for volumes transported in excess of minimum volume commitments, when it becomes impossible to physically transport volumes necessary to utilize the credits or upon the expiration of the applicable four or eight quarter period. The use or expiration of the credits is a decrease in Deferred revenue - related parties . In addition, capital projects the Partnership undertakes at the request of MPC are reimbursed in cash and recognized in income over the remaining term of the applicable transportation services agreements. HSM is a provider of marine transportation services for its customers and does not assume ownership of the products it transports. The Partnership transports cargo from a designated origin to a designated destination at a pre-established fixed rate. Costs incurred as part of moving the products are paid by the customer subsequent to April 1, 2016. G&P Segment The Partnership generates the majority of its G&P segment revenues from natural gas gathering, transportation and processing; NGL gathering, transportation, fractionation, marketing and storage; and crude oil gathering and transportation. The Partnership disaggregates revenue as Product sales , Service revenue and Rental income on the Consolidated Statements of Income. Revenue is reported as follows: • Product sales – Product sales represent the sale of NGLs, condensate and natural gas. The product is primarily obtained as consideration for or related to providing midstream services. • Service revenue – Service revenue represents all other revenue generated as the result of performing the services listed above. • Rental income – Rental income represents revenue generated as the result of implicit operating lease arrangements. The Partnership enters into a variety of contract types in order to generate Product sales and Service revenue. The Partnership provides services under the following different types of arrangements: • Fee-based arrangements – Under fee-based arrangements, the Partnership 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 gathering and transportation of crude oil. The revenue the Partnership earns from these arrangements is generally directly related to the volume of natural gas, NGLs or crude oil that flows through the Partnership’s systems and facilities and is not normally directly dependent on commodity prices. In certain cases, the Partnership’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. In certain instances when specifically stated in the contract terms, the Partnership 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 the Partnership is the principal in the transaction. • Percent-of-proceeds arrangements – Under percent-of-proceeds arrangements, the Partnership 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, the Partnership delivers an agreed-upon percentage of the residue gas and NGLs to the producer (take-in-kind arrangements) and sells the volumes the Partnership retains to third parties. Revenue from these arrangements is reported on a gross basis where the Partnership acts as the principal, as the Partnership has physical inventory risk and does not earn a fixed dollar amount. The agreed-upon percentage paid to the producer is reported as Purchased product costs on the Consolidated Statements of Income. Revenue is recognized on a net basis when the Partnership acts as an agent and earns a fixed dollar amount of physical product and does not have risk of loss of the gross amount of gas and/or NGLs. Percent-of-proceeds revenue is reported as Product sales on the Consolidated Statements of Income. • Keep-whole arrangements – Under keep-whole arrangements, the Partnership 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, the Partnership must either purchase natural gas at market prices for return to producers or make cash payment to the producers equal to the energy content of this natural gas. Certain keep-whole arrangements also have provisions that require the Partnership 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. 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 the Partnership is the principal in the arrangement. Natural gas purchased to return to the producer and shared NGL profits are recorded as Purchased product costs in the Consolidated Statements of Income. • Percent-of-index arrangements – Under percent-of-index arrangements, the Partnership purchases natural gas at either (1) a percentage discount to a specified index price, (2) a specified index price less a fixed amount or (3) a percentage discount to a specified index price less an additional fixed amount. The Partnership then gathers and delivers the natural gas to pipelines where the Partnership resells the natural gas at the index price or at a different percentage discount to the index price. Revenue generated from percent-of-index arrangements are reported as Product sales on the Consolidated Statements of Income and are recognized on a gross basis as the Partnership purchases and takes title to the product prior to sale and is the principal in the transaction. In many cases, the Partnership 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 keep-whole arrangements, percent-of-proceeds arrangements or percent-of-index arrangements, the Partnership records such fees as Service revenue on the Consolidated Statements of Income. The terms of the Partnership’s contracts vary based on gas quality conditions, the competitive environment when the contracts are signed and customer requirements. Amounts billed to customers for shipping and handling, including fuel costs, are included in Product sales on the Consolidated Statements of Income, except under contracts where we are acting as an agent. Shipping and handling costs associated with product sales are included in Purchased product costs on the Consolidated Statements of Income. Taxes collected from customers and remitted to the appropriate taxing authority are excluded from revenue. Facility expenses and depreciation represent those expenses related to operating our various facilities and are necessary to provide both Product sales and Service revenue . Based on the terms of certain natural gas gathering, transportation and processing agreements, the Partnership is considered to be the lessor under several implicit operating lease arrangements in accordance with GAAP. The Partnership’s primary implicit 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 customer 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. Other significant 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 the Partnership earns minimum monthly fees for providing processing services to a single producer using a dedicated processing plant. Revenues 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. Similarly, the Partnership is considered to be the lessor under implicit operating lease arrangements with MPC in accordance with GAAP. The Partnership’s primary implicit lease operations with MPC relate to the transportation services agreement between HSM and MPC. Revenue related to this agreement is recorded as Rental income-related parties on the Consolidated Statements of Income. The rental cost of sales related to the HSM implicit lease is depreciation of the HSM assets. All other services are provided to MPC on an as-needed basis and recorded as Service revenue-related parties on the Consolidated Statements of Income. Revenue and Expense Accruals – The Partnership 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 the Partnership’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. The Partnership 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 the Partnership’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. At December 31, 2016 and 2015 , the amount of restricted cash included in Other current assets on the Consolidated Balance Sheets was $5 million and $9 million , respectively. Receivables – Receivables primarily consist of customer accounts receivable, which are recorded at the invoiced amount and generally do not bear interest. Management reviews the allowance quarterly. Past-due balances over 90 days and other higher risk amounts are 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 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 weighted-average cost or net realizable value. Materials and supplies are stated at the lower of cost or net realizable value. Cost for materials and supplies is determined primarily using the weighted-average cost method. Processed natural gas and NGL inventories include material, labor and overhead. Shipping and handling costs related to purchases of natural gas and NGLs are included in inventory. 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. Expenditures that extend the useful lives of assets are capitalized. Repairs, maintenance and renewals that do not extend the useful lives of the assets are expensed as incurred. Interest costs for the construction or development of long-lived assets are capitalized and amortized over the related asset’s estimated useful life. Leasehold improvements are amortized over the shorter of the useful life or lease term. When items of property, plant and equipment are sold or otherwise disposed of, any gains or losses are reported in 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. The Partnership evaluates transactions involving the sale of property, plant and equipment to determine if they are, in-substance, the sale of real estate. Tangible assets may be considered real estate if the costs to relocate them for use in a different location exceed 10 percent of the asset’s fair value. Financial assets, primarily in the form of ownership interests in an entity, may be in-substance real estate based on the significance of the real estate in the entity. Sales of real estate are not considered consummated if the Partnership maintains an interest in the asset after it is sold or has certain other forms of continuing involvement. Significant judgment is required to determine if a transaction is a sale of real estate and if a transaction has been consummated. If a sale of real estate is not considered consummated, the Partnership cannot record the transaction as a sale and must account for the transaction under an alternative method of accounting such as a financing or leasing arrangement. The Partnership’s policy is to evaluate whether there has been an impairment in the value of long-lived assets when certain events indicate that the remaining balance may not be recoverable. Qualitative and quantitative information is reviewed in order to determine if a triggering event has occurred or if an impairment indicator exists. If we determine that a triggering event has occurred we would complete a full impairment analysis. If we determine that the carrying value of a reporting unit is not recoverable, a loss is recorded for the difference between the fair value and the carrying value. The Partnership evaluates the carrying value of its property, plant and equipment on at least a segment level and at lower levels where the cash flows for specific assets can be identified, which generally is the component level for our G&P and L&S segments. Management considers the dedicated volume of producer customers’ reserves and future NGL product and natural gas prices to estimate cash flows. The amount of additional producer customers’ reserves developed by future drilling activity depends, in part, on expected commodity prices. Projections of producer customers’ reserves, drilling activity and future commodity prices are inherently subjective and contingent upon a number of variable factors, many of which are difficult to forecast. Any significant variance in any of these assumptions or factors could materially affect future cash flows, which could result in the impairment of an asset group. For assets identified to be disposed of in the future, the carrying value of these assets is compared to the estimated fair value, less the cost to sell, to determine if impairment is required. Until the assets are disposed of, an estimate of the fair value is redetermined when related events or circumstances change. Intangibles – The Partnership’s intangibles are mainly comprised of customer contracts and related relationships acquired in business combinations and recorded under the acquisition method of accounting at their estimated fair values at the date of acquisition. Using relevant information and assumptions, management determines the fair value of acquired identifiable intangible assets. Fair value was calculated using the multi-period excess earnings method under the income approach for each reporting unit. This valuation method is based on first forecasting gross profit for the existing customer base and then applying expected attrition rates. The operating cash flows are calculated by determining the costs required to generate gross profit from the existing customer base. The key assumptions include overall gross profit growth, attrition rate of existing customers over time and the discount rate. Amortization of intangibles with definite lives is calculated using the straight-line method which is reflective of benefit pattern in which the estimated economic benefit is expected to be received over the estimated useful life of the intangible asset. The estimated economic life is determined by assessing the life of the assets related to the contracts and relationships, likelihood of renewals, the projected reserves, competitive factors, regulatory or legal provisions and maintenance and renewal costs. Intangibles with indefinite lives 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. The Partnership has no intangibles with indefinite lives. Goodwill – Goodwill is the cost of an acquisition less the fair value of the net identifiable assets and noncontrolling interest, if any, of the acquired business. The Partnership evaluates goodwill for impairment annually as of November 30, and whenever events or changes in circumstances indicate it is more likely than not that the fair value of a reporting unit is less than its carrying amount. The Partnership determined its reporting units based on the criteria included in ASC 280 which requires a component to be a business with discrete financial information that management reviews on a regular basis. Management reviews its determination of reporting units on an annual basis. The Partnership may first assess qualitative factors to evaluate whether it is more likely than not that the fair value of a reporting unit is less than its carrying amount as the basis for determining whether it is necessary to perform the two-step goodwill impairment test. The Partnership may elect to perform the two-step goodwill impairment test without completing a qualitative assessment. If a two-step process goodwill impairment test is elected or required, the first step involves comparing the fair value of the reporting unit to which goodwill has been allocated, with its carrying amount. If the carrying amount of a reporting unit exceeds its fair value, the second step of the process involves comparing the implied fair value to the carrying value of the goodwill for that reporting unit. If the carrying value of the goodwill of a reporting unit exceeds the implied fair value of that goodwill, the excess of the carrying value over the implied fair value is recognized as an impairment loss. During 2016 , impairment charges of approximately $130 million were recorded. There were no impairments as a result of the Partnership’s November 30, 2015 and November 30, 2016 goodwill impairment analyses. 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. The Partnership 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. A receivable is recorded for environmental costs indemnified by MPC. 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. The Partnership 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 the Partnership 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 in 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. The Partnership 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. The Partnership uses evidence of a loss in value to identify if an investment has an other than a temporary decline. 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 (including derivative instruments embedded in other contracts) are recorded at fair value and are reflected in the Consolidated Balance Sheets on a net basis, as either an asset or liability, as they are governed by the master netting agreements. The Partnership discloses the fair value of all of its derivative instruments under the captions Other noncurrent assets , Other current liabilities and Deferred credits and other liabilities on the Consolidated Balance Sheets, inclusive of option premiums, if any. Changes in the fair value of derivative instruments are reported in the Consolidated Statements of Income in accounts related to the item whose value or cash flows are being managed. All derivative instruments were 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. 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, 2016 , 2015 and 2014 , the Partnership did not designate any hedges or designate any contracts as normal purchases and normal sales, with the exception of electricity contracts, for which the normal purchases and normal sales designation was elected during the year ended December 31, 2016 . 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 a fair value hierarchy established by GAAP, which classifies the inputs used to measure fair value into the following levels: • Level 1 inputs to the valuation methodology are quoted prices (unadjusted) for identical assets or liabilities in active markets. • Level 2 inputs to the valuation methodology include quoted prices for similar assets and liabilities in active markets and inputs that are observable for the asset or liability, either directly or indirectly, for substantially the full term of the financial instrument. • Level 3 inputs to the valuation methodology are unobservable and significant to the fair value measurement. 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 determination to classify a financial instrument within Level 3 of the valuation hierarchy is based upon the significance of the unobservable inputs to the overall fair value measurement. However, Level 3 financial instruments typically include, in addition to the unobservable or Level 3 inputs, observable inputs (that is, inputs that are actively quoted and can be validated to external sources); accordingly, the gains and losses for Level 3 financial instruments include changes in fair value due in part to observable inputs that are part of the valuation methodology. Level 3 financial instruments include crude oil options, all NGL derivatives and the embedded derivatives in commodity contracts discussed in Note 15 as they have significant unobservable inputs. The methods and assumptions described above may produce a fair value that may not be realized in future periods upon settlement. Furthermore, while the Partnership 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 – The Partnership issues phantom units under its share-based compensation plan as described further in Note 20 . 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, the Partnership 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 – The Partnership elected to adopt the simplified method to establish the beginning balance of the additional paid-in capital pool (“APIC P

Accounting Standards

Accounting Standards	12 Months Ended
	Dec. 31, 2016
Accounting Standards [Abstract]
New Accounting Pronouncements and Changes in Accounting Principles [Text Block]	Accounting Standards Recently Adopted In September 2015, the FASB issued an accounting standard update that eliminates the requirement to restate prior period financial statements for measurement period adjustments related to business combinations. This accounting standard update requires that the cumulative impact of a measurement period adjustment be recognized in the reporting period in which the adjustment is identified. The change was effective for interim and annual periods beginning after December 15, 2015. The Partnership recognized measurement period adjustments during the first and second quarters of 2016 on a cumulative prospective basis as additional analysis was completed on the preliminary purchase price allocation for the acquisition of MarkWest. See Notes 4 and 18 for further discussion and detail related to these measurement period adjustments. In April 2015, the FASB issued an accounting standard update requiring that the earnings of transferred net assets prior to the dropdown date of the net assets to a master limited partnership be allocated entirely to the general partner when calculating earnings per unit under the two class method. Under this guidance, previously reported earnings per unit of the limited partners will not change as a result of a dropdown transaction. The change was effective for fiscal years and interim periods within those fiscal years beginning after December 15, 2015. Retrospective application is required. The Partnership adopted this accounting standard update in the first quarter of 2016 and it did not have a material impact on the consolidated financial statements. In April 2015, the FASB issued an accounting standard update clarifying whether a customer should account for a cloud computing arrangement as an acquisition of a software license or as a service arrangement by providing characteristics that a cloud computing arrangement must have in order to be accounted for as a software license acquisition. The change was effective for fiscal years and interim periods within those fiscal years beginning after December 15, 2015. Retrospective or prospective application is allowed. The Partnership adopted this accounting standard update prospectively in the first quarter of 2016 and it did not have a material impact on the consolidated financial statements. In February 2015, the FASB issued an accounting standard update making targeted changes to the current consolidation guidance. The accounting standard update changes the considerations related to substantive rights, related parties, and decision making fees when applying the VIE consolidation model and eliminates certain guidance for limited partnerships and similar entities under the voting interest consolidation model. The change was effective for fiscal years and interim periods within those fiscal years beginning after December 15, 2015. The Partnership adopted this accounting standard update in the first quarter of 2016 and it did not have a material impact on the consolidated financial statements. In August 2014, the FASB issued an accounting standard update requiring management to assess an entity’s ability to continue as a going concern and to provide related footnote disclosures in certain circumstances. Management is required to assess if there is substantial doubt about an entity’s ability to continue as a going concern within one year after the issuance of the financial statements. Disclosures are required if conditions give rise to substantial doubt and the type of disclosure is determined based on whether management’s plans will be able to alleviate the substantial doubt. The change was effective for the first fiscal period ending after December 15, 2016, and for fiscal periods and interim periods thereafter. The adoption of this accounting standard update in the fourth quarter of 2016 did not have a material impact on the Partnership’s disclosures. Not Yet Adopted In January 2017, the FASB issued an accounting standard update which simplifies the subsequent measurement of goodwill by eliminating Step 2 from the goodwill impairment test. Under the new guidance, the recognition of an impairment charge is calculated based on the amount by which the carrying amount exceeds the reporting unit’s fair value; however, the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. The guidance should be applied on a prospective basis, and is effective for annual or any interim goodwill impairment tests in fiscal years beginning after December 15, 2019. Early adoption is permitted for interim or annual goodwill impairment tests performed on testing dates after January 1, 2017. The Partnership is in the process of determining the impact of the accounting standard update on the consolidated financial statements. In January 2017, the FASB issued an accounting standard update to clarify the definition of a business with the objective of adding guidance to assist entities with evaluating whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. The standard is intended to narrow the definition of a business by specifying the minimum inputs and processes and by narrowing the definition of outputs. The change is effective for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years. The guidance will be applied prospectively and early adoption is permitted for certain transactions. The Partnership is in the process of determining the impact of the accounting standard update on the consolidated financial statements. In November 2016, the FASB issued an accounting standard update requiring that the statement of cash flows explain the change during the period in the total of cash, cash equivalents, and amounts generally described as restricted cash or restricted cash equivalents. The change is effective for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years, with early adoption permitted. Retrospective application is required. The application of this accounting standard update will not have a material impact on the Consolidated Statements of Cash Flows. In October 2016, the FASB issued an accounting standard update to amend the consolidation guidance issued in February 2015 to require that a decision maker consider, in the determination of the primary beneficiary, its indirect interest in a VIE held by a related party that is under common control on a proportionate basis only. The change is effective for the financial statements for fiscal years beginning after December 15, 2016, and interim periods within those fiscal years, with early adoption permitted. The Partnership is required to apply the standard retrospectively to January 1, 2016. The Partnership has analyzed the accounting standard update and does not expect an impact on the consolidated financial statements. In August 2016, the FASB issued an accounting standard update related to the classification of certain cash flows. The accounting standard update provides specific guidance on eight cash flow classification issues, including debt prepayment or debt extinguishment costs and distributions received from equity method investees. The change is effective for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years, with early adoption permitted. The Partnership does not expect application of this accounting standard update to have a material impact on the Consolidated Statements of Cash Flows. In June 2016, the FASB issued an accounting standard update related to the accounting for credit losses on certain financial instruments. The guidance requires that for most financial assets, losses are 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 Partnership does not expect application of this accounting standard update to have a material impact on the consolidated financial statements. In March 2016, the FASB issued an accounting standard update on the accounting for employee share-based payments. This accounting standard update requires the recognition of income tax effects of awards through the income statement when awards vest or are settled. It will also increase the amount an employer can withhold for tax purposes without triggering liability accounting. Lastly, it allows employers to make a policy election to account for forfeitures as they occur. The changes are effective for fiscal years beginning after December 15, 2016, and interim periods within those fiscal years, and early adoption is permitted. Under the new guidance, the Partnership intends to continue estimating forfeiture rates to calculate compensation cost. The application of this accounting standard update will not have a material impact on the Partnership’s consolidated financial statements. In February 2016, the FASB issued an accounting standard update requiring lessees to record virtually all leases on their balance sheets. The accounting standard update also requires expanded disclosures to help financial statement users better understand the amount, timing and uncertainty of cash flows arising from leases. For lessors, this amended guidance modifies the classification criteria and the accounting for sales-type and direct financing leases. The change will be effective on a modified retrospective basis for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years, with early adoption permitted. The Partnership is currently evaluating the impact of this standard on our financial statements and disclosures, internal controls, and accounting policies. This evaluation process includes reviewing all forms of leases, performing a completeness assessment over the lease population and analyzing the practical expedients in order to determine the best path to implementation. The Partnership does not plan to early adopt the standard. In January 2016, the FASB issued an accounting standard update requiring unconsolidated equity investments, not accounted for under the equity method, to be measured at fair value with changes in fair value recognized in net income. The accounting standard update also requires the use of the exit price notion when measuring the fair value of financial instruments for disclosure purposes and the separate presentation of financial assets and liabilities by measurement category and form on the balance sheet and accompanying notes. The accounting standard update eliminates the requirement to disclose the methods and assumptions used in estimating the fair value of financial instruments measured at amortized cost. Lastly, the accounting standard update requires separate presentation in other comprehensive income of the portion of the total change in the fair value of a liability resulting from a change in the instrument-specific credit risk when electing to measure the liability at fair value in accordance with the fair value option for financial instruments. The changes are effective for fiscal years and interim periods within those fiscal years beginning after December 15, 2017. Early adoption is permitted only for guidance regarding presentation of the liability’s credit risk. The application of this accounting standard update will not have a material impact on the Partnership’s consolidated financial statements. In May 2014, the FASB issued an initial accounting standard update for revenue recognition for contracts with customers. The guidance in the accounting standard update states that revenue is recognized when a customer obtains control of a good or service. Recognition of the revenue will involve a multiple step approach including identifying the contract, identifying the separate performance obligations, determining the transaction price, allocating the price to the performance obligations and then recognizing the revenue as the obligations are satisfied. Additional disclosures will be required to provide adequate information to understand the nature, amount, timing and uncertainty of reported revenues and revenues expected to be recognized. The change will be effective on a retrospective or modified retrospective basis for fiscal years beginning after December 15, 2017, and interim periods within those years, with early adoption permitted no earlier than January 1, 2017. The Partnership is currently evaluating the impact of the revenue recognition standard on the Partnership’s financial statements and disclosures, internal controls, and accounting policies. This evaluation process includes a phased approach, the first phase of which includes reviewing a sample of our contracts and transaction types across our segments. The Partnership is currently in the process of completing this first phase and evaluating the methods of adoption. Based on the results of the first phase assessment to date, the Partnership has reached tentative conclusions for some contract types and does not believe revenue recognition patterns for fee-based or percent-of-proceeds contracts will change materially. The Partnership is currently working to understand the accounting impact on keep-whole and percent-of-liquids agreements under the new standard, specifically related to the accounting for noncash consideration received in the form of a commodity product. The Partnership does expect certain amounts to be grossed up in revenue as a result of implementation. The Partnership continues to work through implementation efforts and will provide updates as qualitative and quantitative conclusions are reached throughout 2017.

Equity Method Investments Equit

Equity Method Investments Equity Method Investments	12 Months Ended
	Dec. 31, 2016
Equity Method Investments	Equity Method Investments MarkWest Utica EMG Effective January 1, 2012, MarkWest Utica Operating Company, LLC (“Utica Operating”), a wholly-owned and consolidated subsidiary of MarkWest, and EMG Utica (together the “Members”) executed agreements to form a joint venture, MarkWest Utica EMG, to develop significant natural gas gathering, processing and NGL fractionation, transportation and marketing infrastructure in eastern Ohio. The related limited liability company agreement has been amended from time to time (the limited liability company agreement as currently in effect is referred to as the “Amended LLC Agreement”). The aggregate funding commitment of EMG Utica was $950 million (the “Minimum EMG Investment”). Thereafter, Utica Operating was required to fund, as needed, 100 percent of future capital for MarkWest Utica EMG until such time as the aggregate capital that had been contributed by the Members reached $2 billion , which occurred prior to the MarkWest Merger. Until such time as the investment balances of Utica Operating and EMG Utica are in the ratio of 70 percent and 30 percent , respectively (such time being referred to as the “Second Equalization Date”), EMG Utica will have the right, but not the obligation, to fund up to 10 percent of each capital call for MarkWest Utica EMG, and Utica Operating will be required to fund all remaining capital not elected to be funded by EMG Utica. After the Second Equalization Date, Utica Operating and EMG Utica will have the right, but not the obligation, to fund their pro rata portion (based on their respective investment balances) of any additional required capital and may also fund additional capital that the other party elects not to fund. As of December 31, 2016 , EMG Utica has contributed $1 billion and Utica Operating has contributed approximately $ 1.5 billion to MarkWest Utica EMG. Under the Amended LLC Agreement, after EMG Utica has contributed more than $500 million to MarkWest Utica EMG and prior to December 31, 2016, EMG Utica’s investment balance will also be increased by a quarterly special non-cash allocation of income (“Preference Amount”) that is based upon the amount of capital contributed by EMG Utica in excess of $500 million . No Preference Amount will accrue to EMG Utica’s investment balance after December 31, 2016. EMG Utica received a special non-cash allocation of income of approximately $16 million and approximately $4 million for the year ended December 31, 2016 and for the 28 days ended December 31, 2015 , respectively. Under the Amended LLC Agreement, Utica Operating continued to receive 60 percent of cash generated by MarkWest Utica EMG that was available for distribution until the earlier of December 31, 2016 or the date on which Utica Operating’s investment balance equaled 60 percent of the aggregate investment balances of the Members. After December 31, 2016, cash generated by MarkWest Utica EMG that is available for distribution will be allocated to the Members in proportion to their respective investment balances. As of December 31, 2016, Utica Operating’s investment balance in MarkWest Utica EMG was approximately 56 percent. MarkWest Utica EMG is deemed to be a VIE. As of the date of the MarkWest Merger, Utica Operating is not deemed to be the primary beneficiary due to EMG Utica’s voting rights on significant matters. The Partnership’s portion of MarkWest Utica EMG’s net assets, which was $2.2 billion at December 31, 2016 and 2015 , respectively, is reported under the caption Equity Method Investments on the Consolidated Balance Sheets. The Partnership’s maximum exposure to loss as a result of its involvement with MarkWest Utica EMG 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. The Partnership did not provide any financial support to MarkWest Utica EMG that it was not contractually obligated to provide during the year ended December 31, 2016 and the 28 days ended December 31, 2015. The Partnership receives management fee revenue for engineering and construction and administrative services for operating MarkWest Utica EMG, and is also reimbursed for personnel services (“Operational Service” revenue). The amount of Operational Service revenue related to MarkWest Utica EMG for the year ended December 31, 2016 and for the 28 days ended December 31, 2015 was $16 million and less than $1 million , respectively, and is reported as Other income - related parties in the Consolidated Statements of Income. Ohio Gathering Ohio Gathering is a subsidiary of MarkWest Utica EMG and is engaged in providing natural gas gathering services in the Utica Shale in eastern Ohio. Ohio Gathering is a joint venture between MarkWest Utica EMG and Summit Midstream Partners, LLC (“Summit”). As of December 31, 2016, we have a 34 percent indirect ownership interest in Ohio Gathering. As Ohio Gathering is a subsidiary of MarkWest Utica EMG, which is accounted for as an equity method investment, the Partnership reports its portion of Ohio Gathering’s net assets as a component of its investment in MarkWest Utica EMG. The Partnership receives Operational Service revenue for operating Ohio Gathering. The amount of Operational Service revenue related to Ohio Gathering for the year ended December 31, 2016 and the 28 days ended December 31, 2015 was approximately $15 million and $2 million , respectively, and is reported as Other income - related parties in the Consolidated Statements of Income. Ohio Condensate Ohio Condensate is a joint venture between MarkWest Utica EMG Condensate, L.L.C., a wholly-owned and consolidated subsidiary of MarkWest, and Summit formed for the purpose of gathering (by pipeline), stabilization, terminalling, transportation and storage of well-head condensate within certain defined areas in the state of Ohio. The Partnership accounts for Ohio Condensate, which is a VIE, as an equity method investment as MPLX LP exercises significant influence, but does not control Ohio Condensate and is not its primary beneficiary due to Summit’s voting rights on significant matters. The Partnership’s portion of Ohio Condensate’s net assets, which was $10 million and $100 million at December 31, 2016 and 2015, respectively, are reported under the caption Equity method investments on the Consolidated Balance Sheets. The Partnership receives Operational Service revenue for operating Ohio Condensate. The amount of Operational Service revenue related to Ohio Condensate for the year ended December 31, 2016 and the 28 days ended December 31, 2015 was $4 million and less than $1 million , respectively, and is reported as Other income - related parties in the Consolidated Statements of Income. Summarized financial information for the year ended December 31, 2016 and from the date of the MarkWest Merger through December 31, 2015 for equity method investments is as follows: Year Ended December 31, 2016 (In millions) MarkWest Utica EMG Ohio Condensate Other VIEs Non-VIEs Total Revenue and other income $ 216 $ 15 $ 3 $ 148 $ 382 Cost and expenses 100 110 1 117 328 Income (loss) from operations 116 (95 ) 2 31 54 Net income (loss) 114 (95 ) 2 31 52 Income (loss) from equity method investments (2) 8 (89 ) — 7 (74 ) Year Ended December 31, 2015 (In millions) MarkWest Utica EMG Ohio Condensate Other VIEs Non-VIEs Total Revenue and other income $ 18 $ 2 $ — $ 9 $ 29 Cost and expenses 9 2 — 8 19 Income from operations 9 — — 1 10 Net income 10 — — 1 11 Income from equity method investments (2) 2 1 — — 3 Summarized balance sheet information as of December 31, 2016 and 2015 for equity method investments is as follows: December 31, 2016 (In millions) MarkWest Utica EMG (1) Ohio Condensate Other VIEs Non-VIEs Total Current assets $ 45 $ 2 $ — $ 40 $ 87 Noncurrent assets 2,173 30 102 375 2,680 Current liabilities 30 3 1 26 60 Noncurrent liabilities 2 13 — — 15 December 31, 2015 (In millions) MarkWest Utica EMG (1) Ohio Condensate Other VIEs Non-VIEs Total Current assets $ 113 $ 7 $ — $ 30 $ 150 Noncurrent assets 2,207 127 42 243 2,619 Current liabilities 77 6 1 18 102 Noncurrent liabilities 1 12 — — 13 (1) MarkWest Utica EMG’s noncurrent assets includes its investment in its subsidiary Ohio Gathering, which does not appear elsewhere in this table. The investment was $794 million and $781 million as of December 31, 2016 and 2015 , respectively. (2) Income (loss) from equity method investments includes the impact of any basis differential amortization or accretion. As of December 31, 2016 and 2015 , the carrying value of our equity method investments was $ 1.1 billion and $961 million , respectively, higher than the underlying net assets of investees. This basis difference is being amortized or accreted into net income over the remaining estimated useful lives of the underlying net assets, except for $ 459 million of excess related to goodwill as of December 31, 2016 . During the second quarter of 2016, forecasts for Ohio Condensate were reduced to align with updated forecasts for customer requirements. As the operator of that entity responsible for maintaining its financial records, the Partnership completed a fixed asset impairment analysis as of June 30, 2016, in accordance with ASC Topic 360, to determine the potential fixed asset impairment charge. The resulting fixed asset impairment charge recorded within Ohio Condensate’s financial statements was $96 million . Based on the Partnership’s 60 percent ownership of Ohio Condensate, approximately $58 million was recorded in the second quarter of 2016 in (Loss) income from equity method investments on the accompanying Consolidated Statements of Income. The Partnership’s investment in Ohio Condensate, which was established at fair value in connection with the MarkWest Merger, exceeded its proportionate share of the underlying net assets. Therefore, in conjunction with the ASC Topic 360 impairment analysis, the Partnership completed an equity method impairment analysis in accordance with ASC Topic 323 to determine the potential additional equity method impairment charge to be recorded on the Partnership’s consolidated financial statements resulting from an other-than-temporary impairment. As a result, an additional impairment charge of approximately $31 million was recorded in the second quarter of 2016 in (Loss) income from equity method investments on the accompanying Consolidated Statements of Income, which eliminated the basis differential established in connection with the MarkWest Merger. The fair value of Ohio Condensate and its underlying fixed assets was determined based upon applying the discounted cash flow method, which is an income approach, and the guideline public company method, which is a market 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 a discount rate of 11.2 percent . An increase to the discount rate of 50 basis points would have resulted in an additional charge of $1 million on the Consolidated Statements of Income. Fair value determinations require considerable judgment and are sensitive to changes in underlying assumptions and factors. As such, the fair value of the Ohio Condensate equity method investment and its underlying fixed assets represents a Level 3 measurement. As a result, there can be no assurance that the estimates and assumptions made for purposes of the interim impairment test will prove to be an accurate prediction of the future.

Related Party Agreements and Tr

Related Party Agreements and Transactions	12 Months Ended
	Dec. 31, 2016
Related Party Transactions [Abstract]
Related Party Agreements and Transactions	Related Party Agreements and Transactions The Partnership’s material related parties include: • MPC, which refines, markets and transports crude oil and petroleum products, primarily in the Midwest, Gulf Coast, East Coast and Southeast regions of the United States. • Centennial Pipeline LLC (“Centennial”), in which MPC has a 50 percent interest. Centennial owns a products pipeline and storage facility. • Muskegon Pipeline LLC (“Muskegon”), in which MPC has a 60 percent interest. Muskegon owns a common carrier products pipeline. • MarkWest Utica EMG, in which MPLX LP has a 56 percent interest as of December 31, 2016 . MarkWest Utica EMG is engaged in significant natural gas processing and NGL fractionation, transportation and marketing in the state of Ohio. • Ohio Gathering, in which MPLX LP has a 34 percent indirect interest as of December 31, 2016 . Ohio Gathering is a subsidiary of MarkWest Utica EMG providing natural gas gathering service in the Utica Shale region of eastern Ohio. • Ohio Condensate, in which MPLX LP has a 60 percent interest. Ohio Condensate is engaged in wellhead condensate gathering, stabilization, terminalling, transportation and storage within certain defined areas of Ohio. Commercial Agreements The Partnership has various long-term, fee-based transportation services and storage services agreements with MPC. Under these long term, fee based agreements, the Partnership provides transportation and storage services to MPC, and MPC has committed to provide the Partnership with minimum quarterly throughput volumes on crude oil and products systems and minimum storage volumes of crude oil, products and butane. The Partnership believes the terms and conditions under these agreements, as well as the initial agreements with MPC described below, are generally no less favorable to either party than those that could have been negotiated with unaffiliated parties with respect to similar services. The commercial agreements with MPC include: • three separate 10 -year transportation services agreements and one five -year transportation services agreement under which MPC pays the Partnership fees for transporting crude oil on various of our crude oil pipeline systems; • four separate 10 -year transportation services agreements under which MPC pays the Partnership fees for transporting products on each of our refined product pipeline systems; • a five -year transportation services agreement under which MPC pays the Partnership fees for handling crude oil and products at our Wood River, Illinois barge dock; • a 10 -year storage services agreement under which MPC pays the Partnership fees for providing storage services at our Neal, West Virginia butane cavern; • five separate three -year storage services agreements under which MPC pays the Partnership fees for providing storage services at our tank farms; and • a six -year transportation services agreement under which MPC pays the Partnership fees for providing marine transportation of crude oil, feedstocks and refined petroleum products, and related services. All of the transportation services agreements with MPC for the Partnership’s crude oil and product pipeline systems include automatic renewal terms ranging from two to five years, unless terminated by either party. The Partnership’s butane cavern storage services agreement with MPC does not automatically renew. The storage services agreements with MPC for the Partnership’s tank farms automatically renew for additional one -year terms unless terminated by either party. Under all of our transportation services agreements, except for our marine agreement, if MPC fails to transport its minimum throughput volumes during any quarter, then MPC will pay us a deficiency payment equal to the volume of the deficiency multiplied by the tariff rate then in effect (the “Quarterly Deficiency Payment”). Under these transportation services agreements, the amount of any Quarterly Deficiency Payment paid by MPC may be applied as a credit for any volumes transported on the applicable pipeline system in excess of MPC’s minimum volume commitment during any of the succeeding four quarters, or eight quarters in the case of the transportation services agreements covering our Wood River to Patoka crude system and our Wood River barge dock, after which time any unused credits will expire. Upon the expiration or termination of a transportation services agreement, MPC will have the opportunity to apply any such remaining credit amounts until the completion of any such four-quarter or eight-quarter period, as applicable. Any such remaining credits may be used against any volumes shipped by MPC on the applicable pipeline system, without regard to any minimum volume commitment that may have been in place during the term of the agreement. Under the storage services agreements, as amended, the Partnership is obligated to make available to MPC on a firm basis the available storage capacity at our tank farms and butane cavern, and MPC pays the Partnership a per-barrel fee for such storage capacity, regardless of whether MPC fully utilizes the available capacity. On January 1, 2015, HSM entered into a long-term, fee-based transportation services agreement with MPC for a period of six years. Under the agreement, the Partnership provides marine transportation of crude oil, feedstocks and refined petroleum products, as well as related services. Under the agreement MPC pays HSM monthly for the following: the specified day rate for equipment and charges for services related to transportation, tankerman services and cleaning and repair charges. Fleeting services are billed monthly. On the anniversary of the contract, pursuant to the amended and restated fee-based transportation services agreement effective July 1, 2015, the day rates and charges for services related to transportation are adjusted for inflation. Prior to January 1, 2015, this agreement did not exist. On January 1, 2015, MPC conveyed various operating leases to HSM for third-party barges and fleeting property within the states of Indiana, Kentucky, Louisiana, Ohio and West Virginia in which MPC was either the lessor or lessee. Operating Agreements The Partnership operates various pipeline systems owned by MPC under operating services agreements. Under these operating services agreements, the Partnership 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. Management Services Agreements The Partnership has two management services agreements with MPC under which it provides management services to MPC with respect to certain of MPC’s retained pipeline assets. The Partnership may adjust annually for inflation and based on changes in the scope of management services provided. The Partnership also receives engineering and construction and administrative management fee revenue and other direct personnel costs for operating some joint venture entities. The Partnership, 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 expires on June 30, 2020. Omnibus Agreement The Partnership has an omnibus agreement with MPC that addresses its payment of a fixed annual fee to MPC for the provision of executive management services by certain executive officers of the general partner and the Partnership’s reimbursement of MPC for the provision of certain general and administrative services to it. It also provides for MPC’s indemnification of the Partnership for certain matters, including environmental, title and tax matters; as well as our indemnification of MPC for certain matters under this agreement. Employee Services Agreements The Partnership has four employee services agreements with MPC. Two of the employee services agreements with MPC were entered into effective October 1, 2012, under which the Partnership reimburses MPC for the provision of certain operational and management services in support of our pipelines, barge dock, butane cavern and tank farms within the L&S segment. Effective December 28, 2015, the Partnership entered into an additional employee services agreement with MPC, which requires that we reimburse MPC for certain operational and management services to us in support of our G&P segment and certain of our other operations. Lastly, we are party to an employee services agreement with MPC dated January 1, 2015, pursuant to which HSM reimburses MPC for employee benefit expenses along with certain operation and management services provided in support of HSM’s areas of operation. The agreement is effective until December 31, 2019. Prior to January 1, 2015, this agreement did not exist. Loan Agreements On December 4, 2015 , the Partnership entered into a loan agreement with MPC Investment LLC (“MPC Investment”), a wholly-owned subsidiary of MPC. Under the terms of the agreement, MPC Investment will make a loan or loans to the Partnership on a revolving basis as requested by the Partnership and as agreed to by MPC Investment, in an amount or amounts that do not result in the aggregate principal amount of all loans outstanding exceeding $500 million 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 December 4, 2020 . 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 December 4, 2020 . Borrowings under the loan will bear interest at LIBOR plus 1.50 percent . Borrowings were at an average interest rate of 1.939 percent and 1.744 percent , per annum for 2016 and 2015, respectively. In connection with this loan agreement, the Partnership terminated the previous revolving credit agreement of $50 million with MPC, effective December 31, 2015 . During 2016 , the Partnership borrowed $2.5 billion and repaid $2.5 billion , resulting in no outstanding balance at December 31, 2016 . During 2015 , the Partnership borrowed $301 million and repaid $293 million , for an outstanding balance at December 31, 2015 of $8 million , which is included in Payables to related parties on the Consolidated Balance Sheets. Related Party Transactions The Partnership believes that transactions with related parties were conducted on terms comparable to those with unrelated parties. Related party sales to MPC consisted of crude oil and refined products pipeline transportation services based on regulated tariff rates and storage services based on contracted rates. Related party sales to MPC also consist of revenue related to volume deficiency credits. Revenue received from related parties related to service and product sales were as follows: (In millions) 2016 2015 2014 Service revenue MPC $ 603 $ 593 $ 662 Rental income MPC $ 114 $ 101 $ 15 Product sales (1) MPC $ 11 $ 1 $ — (1) For 2016 and 2015, there were $46 million and $1 million , respectively, of 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. There were no such transactions in 2014. Related party sales to MPC consist of crude oil and refined products pipeline transportation services based on regulated tariff rates, storage services based on contracted rates and transportation services provided by HSM. Under the Partnership’s pipeline transportation services agreements, if MPC fails to transport its minimum throughput volumes during any quarter, then MPC will pay the Partnership a deficiency payment equal to the volume of the deficiency multiplied by the tariff rate then in effect. The deficiency amounts are recorded as Deferred revenue-related parties on the Consolidated Balance Sheets. MPC may then apply the amount of any such deficiency payments as a credit for volumes transported on the applicable pipeline system in excess of its minimum volume commitment during the following four or eight quarters under the terms of the applicable transportation services agreement. The Partnership recognizes revenues for the deficiency payments when credits are used for volumes transported in excess of minimum quarterly volume commitments, when it becomes impossible to physically transport volumes necessary to utilize the credits or upon the expiration of the credits. The use or expiration of the credits is a decrease in Deferred revenue-related parties . The revenue received from related parties included in Other income - related parties on the Consolidated Statements of Income was as follows: (In millions) 2016 2015 2014 MPC $ 60 $ 68 $ 39 MarkWest Utica EMG 16 — — Centennial 1 1 1 Ohio Gathering 15 2 — Ohio Condensate 4 — — Other 5 — — Total $ 101 $ 71 $ 40 MPC provides executive management services and certain general and administrative services to the Partnership under the terms of the omnibus agreement. Expenses incurred under these agreements are shown in the table below by the income statement line where they were recorded. These expenses also include similar charges incurred by HSM for the time period prior to the acquisition and therefore not covered by the omnibus agreement. Charges for services included in Purchases from related parties primarily relate to services that support the Partnership’s operations and maintenance activities, as well as compensation expenses. Charges for services included in General and administrative expenses primarily relate to services that support the Partnership’s executive management, accounting and human resources activities. These charges were as follows: (In millions) 2016 2015 2014 Purchases from related parties $ 29 $ 30 $ 30 General and administrative expenses 39 46 46 Total $ 68 $ 76 $ 76 Also under terms of the omnibus agreement, some service costs related to engineering services are associated with assets under construction. These costs added to Property, plant and equipment were as follows: (In millions) 2016 2015 2014 MPC $ 38 $ 13 $ 8 MPLX LP obtains employee services from MPC under employee services agreements. Expenses incurred under these agreements are shown in the table below by the income statement line where they were recorded. The costs of personnel directly involved in or supporting operations and maintenance activities are classified as Purchases from related parties on the Consolidated Balance Sheets. The costs of personnel involved in executive management, accounting and human resources activities are classified as General and administrative expenses in the Consolidated Statements of Income. Employee services expenses from related parties were as follows: (In millions) 2016 2015 2014 Purchases - related parties $ 287 $ 136 $ 123 General and administrative expenses 72 22 24 Total $ 359 $ 158 $ 147 Receivables from related parties which include reimbursements from the MarkWest Merger to be provided by MPC for the conversion of Class B units were as follows: December 31, (In millions) 2016 2015 MPC $ 117 $ 175 MarkWest Utica EMG 2 4 Ohio Gathering 2 5 Other 1 3 Total $ 122 $ 187 Long-term receivables with related parties, including straight-line rental income for both periods presented, as well as reimbursements from the MarkWest Merger to be provided by MPC for the conversion of Class B units for the period ended December 31, 2015, were as follows: December 31, (In millions) 2016 2015 MPC $ 4 $ 25 Payables to related parties were as follows: December 31, (In millions) 2016 2015 MPC $ 51 $ 33 MarkWest Utica EMG 24 21 Total $ 75 $ 54 In recent years, MPC did not ship its minimum committed volumes on certain pipeline systems. In addition, capital projects the Partnership is undertaking at the request of MPC are reimbursed in cash and recognized in income over the remaining term of the applicable transportation services agreements. The Deferred revenue-related parties balance associated with the minimum volume deficiencies and project reimbursements were as follows: December 31, (In millions) 2016 2015 Minimum volume deficiencies - MPC $ 44 $ 36 Project reimbursements - MPC 5 5 Total $ 49 $ 41

Net Income Per Limited Partner

Net Income Per Limited Partner Unit	12 Months Ended
	Dec. 31, 2016
Earnings Per Share [Abstract]
Net Income Per Limited Partner Unit	Net Income (Loss) Per Limited Partner Unit Net income (loss) per unit applicable to common limited partner units and to subordinated limited partner units is computed by dividing the respective limited partners’ interest in net income attributable to MPLX LP by the weighted average number of common units and subordinated units outstanding. Because the Partnership has more than one class of participating securities, it uses the two-class method when calculating the net income per unit applicable to limited partners. The classes of participating securities include common units, subordinated units, general partner units, Preferred units, certain equity-based compensation awards and incentive distribution rights. The HSM acquisition was a transfer between entities under common control. As an entity 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 HSM will be included in the net income (loss) per unit calculation prospectively as described above. As discussed further in Note 8 , the subordinated units, all of which were owned by MPC, were converted into common units during the third quarter of 2015. For purposes of calculating net income (loss) per unit, the subordinated units were treated as if they converted to common units on July 1, 2015. In 2016 and 2015, the Partnership had dilutive potential common units consisting of certain equity-based compensation awards and Class B units. Diluted net income per limited partner unit for the 2014 reporting period is the same as basic net income per limited partner unit as there were no potentially dilutive common or subordinated units outstanding as of December 31, 2014. (In millions) 2016 2015 2014 Net income attributable to MPLX LP $ 233 $ 156 $ 121 Less: Distributions declared on Preferred units (1) 41 — — General partner’s distributions declared (including IDRs) (1) 205 60 6 Limited partners’ distributions declared on common units (1) 692 224 54 Limited partner’s distributions declared on subordinated units (1) — 31 52 Undistributed net (loss) income attributable to MPLX LP $ (705 ) $ (159 ) $ 9 (1) See Note 8 for information regarding the distribution. 2016 (In millions, except per-unit data) General Partner Limited Partners’ Common Units Redeemable Preferred Units Total Basic and diluted net income attributable to MPLX LP per unit: Net income attributable to MPLX LP: Distributions declared (including IDRs) $ 205 $ 692 $ 41 $ 938 Undistributed net loss attributable to MPLX LP (14 ) (691 ) — (705 ) Net income attributable to MPLX LP (1) $ 191 $ 1 $ 41 $ 233 Weighted average units outstanding: Basic 7 331 338 Diluted 7 338 345 Net income attributable to MPLX LP per limited partner unit: Basic $ — Diluted $ — 2015 (In millions, except per-unit data) General Partner Limited Partners’ Common Units Limited Partner’s Subordinated Units Total Basic and diluted net income attributable to MPLX LP per unit: Net income attributable to MPLX LP: Distributions declared (including IDRs) $ 60 $ 224 $ 31 $ 315 Undistributed net loss attributable to MPLX LP (3 ) (127 ) (29 ) (159 ) Net income attributable to MPLX LP (1) $ 57 $ 97 $ 2 $ 156 Weighted average units outstanding: Basic 2 79 18 99 Diluted 2 80 18 100 Net income attributable to MPLX LP per limited partner unit: Basic $ 1.23 $ 0.11 Diluted $ 1.22 $ 0.11 2014 (In millions, except per-unit data) General Partner Limited Partners’ Common Units Limited Partner’s Subordinated Units Total Basic and diluted net income attributable to MPLX LP per unit: Net income attributable to MPLX LP: Distribution declared $ 6 $ 54 $ 52 $ 112 Undistributed net income attributable to MPLX LP 2 4 3 9 Net income attributable to MPLX LP (1) $ 8 $ 58 $ 55 $ 121 Weighted average units outstanding: Basic 2 37 37 76 Diluted 2 37 37 76 Net income attributable to MPLX LP per limited partner unit: Basic $ 1.55 $ 1.50 Diluted $ 1.55 $ 1.50 (1) Allocation of net income (loss) attributable to MPLX LP assumes all earnings for the period had been distributed based on the current period distribution priorities.

Equity

Equity	12 Months Ended
	Dec. 31, 2016
Equity [Abstract]
Equity	Equity Units Outstanding – The Partnership had 357,193,288 common units outstanding as of December 31, 2016 . Of that number, 86,619,313 were owned by MPC, which also owned the two percent general partner interest, represented by 7,371,105 general partner units. Subordinated Unit Conversion – Following payment of the cash distribution for the second quarter of 2015, the requirements for the conversion of all subordinated units were satisfied under the partnership agreement. As a result, effective August 17, 2015 , the 36,951,515 subordinated units owned by MPC were converted into common units on a one-for-one basis and thereafter participate on terms equal with all other common units in distributions of available cash. The conversion did not impact the amount of the cash distributions paid by the Partnership or the total units outstanding. Reorganization Transactions – On September 1, 2016, the Partnership and various affiliates initiated a series of reorganization transactions in order to simplify the Partnership’s ownership structure and its financial and tax reporting requirements (the "Class A Reorganization"). In connection with these transactions, all of the issued and outstanding MPLX LP Class A units, all of which were held by MarkWest Hydrocarbon, were either distributed to or purchased by MPC in exchange for $84 million in cash, 21,401,137 MPLX LP common units and 436,758 MPLX LP general partner units. Following these initial transactions, all of the MPLX LP Class A units were exchanged on a one-for-one basis for newly issued common units representing limited partner interests in MPLX LP. MPC also contributed $141 million to facilitate the repayment of intercompany debt between MarkWest Hydrocarbon and MarkWest. As a result of these transactions, the MPLX LP Class A units were eliminated, are no longer outstanding and no longer participate in distributions of cash from the Partnership. Cash that is derived from or attributable to MarkWest Hydrocarbon’s operations is now treated in the same manner as cash derived from or attributable to other operations of the Partnership and its subsidiaries. MarkWest Merger – On December 4, 2015, the Partnership completed the MarkWest Merger. As defined in the merger agreement, each common unit of MarkWest issued and outstanding at the effective time of the MarkWest Merger was converted into the right to receive 1.09 common units of MPLX LP. This resulted in the issuance of 216,350,465 common units. The Class A units of MarkWest outstanding immediately prior to the MarkWest Merger were converted into 28,554,313 Class A units of MPLX LP having substantially similar rights and obligations that the Class A units of MarkWest had immediately prior to the combination. Each Class B unit of MarkWest outstanding had immediately prior to the merger converted into the right to receive one Class B unit of MPLX LP having substantially similar rights, including conversion and registration rights, and obligations that the Class B units of MarkWest had immediately prior to the merger. This resulted in the issuance of 7,981,756 MPLX LP Class B units. Each Class B unit of MPLX LP will automatically convert into 1.09 MPLX LP common units and the right to receive $6.20 in cash in equal installments, the first of which occurred on July 1, 2016 and the second of which will occur on July 1, 2017. ATM Program – On August 4, 2016, the Partnership entered into a second amended and restated distribution agreement (the “Distribution Agreement”) providing for the continuous issuance of common units, in amounts, at prices and on terms to be determined by market conditions and other factors at the time of our offerings (such continuous offering program, or at-the-market program is referred to as our “ATM Program”). The Partnership expects the net proceeds from sales under the ATM Program will be used for general partnership purposes, including repayment or refinancing of debt, and funding for acquisitions, working capital requirements and capital expenditures. During the year ended December 31, 2015 , the Partnership issued an aggregate of 25,166 common units under our ATM Program, generating net proceeds of approximately $1 million . During the year ended December 31, 2016 , the Partnership issued an aggregate of 26,347,887 common units under the ATM Program generating net proceeds of approximately $776 million . As of December 31, 2016 , $717 million of common units remains available for issuance through the ATM program under the Distribution Agreement. The table below summarizes the changes in the number of units outstanding for the years ended December 31, 2014 , 2015 , and 2016 : (In units) Common Class B Subordinated General Partner Total Balance at December 31, 2013 36,951,515 — 36,951,515 1,508,225 75,411,255 Unit-based compensation awards 15,479 — — 316 15,795 Contribution of interest in Pipe Line Holdings 2,924,104 — — 59,676 2,983,780 December 2014 equity offering 3,450,000 — — 70,408 3,520,408 Balance at December 31, 2014 43,341,098 — 36,951,515 1,638,625 81,931,238 Unit-based compensation awards 18,932 — — 386 19,318 Issuance of units under the ATM program 25,166 — — 514 25,680 Subordinated unit conversion 36,951,515 — (36,951,515 ) — — MarkWest Merger 216,350,465 7,981,756 — 5,160,950 229,493,171 Balance at December 31, 2015 296,687,176 7,981,756 — 6,800,475 311,469,407 Unit-based compensation awards 120,989 — — 2,470 123,459 Issuance of units under the ATM Program 26,347,887 — — 537,710 26,885,597 Contribution of HSM (See Note 4) 22,534,002 — — 459,878 22,993,880 Class B conversion 4,350,057 (3,990,878 ) — 7,330 366,509 Class A Reorganization 7,153,177 — — (436,758 ) 6,716,419 Balance at December 31, 2016 357,193,288 3,990,878 — 7,371,105 368,555,271 2016 Activity On July 1, 2016, 3,990,878 Class B units converted to 4,350,057 common units and received the second quarter distribution. As a result of the Class B units converted to common units during the period, MPLX GP contributed less than $1 million in exchange for 7,330 general partner units to maintain its two percent general partner interest. As a result of the unit-based compensation awards issued during the period, MPLX GP contributed less than $1 million in exchange for 2,470 general partner units to maintain its two percent general partner interest. As a result of common units issued under the ATM Program during the period, MPLX GP contributed $16 million in exchange for 537,710 general partner units to maintain its two percent general partner interest. In connection with the Class A Reorganization, 7 million common units were acquired by MPC that represents the common units received by MPC on the exchange of the MPLX LP Class A units less the units redeemed in the distribution of MPLX Holdings Inc., including the MPLX LP Class A units. Additionally, MPLX LP transferred common units representing a two percent ownership interest of MPLX Holdings Inc. to MPLX GP in exchange for 436,758 MPLX LP general partner units held by MPLX GP, as discussed above. 2015 Activity As a result of common units issued under the ATM Program during 2015 , MPLX GP contributed less than $1 million in exchange for 514 general partner units to maintain its two percent general partner interest. In connection with the MarkWest Merger discussed in Note 4 , MPLX GP contributed $169 million in exchange for 5,160,950 general partner units to maintain its two percent general partner interest. 2014 Activity Effective December 1, 2014 , as discussed in Note 4 , the Partnership accepted a contribution of 7.625 percent of outstanding partnership interests of Pipe Line Holdings from subsidiaries of MPC in exchange for the issuance of equity valued at $200 million . The equity consideration consisted of 2,924,104 MPLX LP common units and was calculated by dividing $200 million by the average closing price for MPLX LP common units for the ten trading days preceding December 1, 2014, which was $68.397 . On December 8, 2014, the Partnership closed an equity offering of 3,450,000 common units at a public offering price of $66.68 per unit. The Partnership used the net proceeds of $221 million to repay borrowings under its revolving credit facility and for general partnership purposes. As a result of the contribution mentioned above and the December 2014 equity offering, MPLX GP contributed $9 million in exchange for 130,084 general partner units to maintain its two percent general partnership interest. Issuance of Additional Securities – The partnership agreement authorizes the Partnership to issue an unlimited number of additional partnership securities for the consideration and on the terms and conditions determined by the general partner without the approval of the unitholders. Incentive Distribution Rights – The following table illustrates the percentage allocations of available cash from operating surplus between the common and subordinated unitholders and the general partner based on the specified target distribution levels. The amounts set forth under “Marginal percentage interest in distributions” are the percentage interests of the general partner and common and subordinated unitholders in any available cash from operating surplus the Partnership distributes up to and including the corresponding amount in the column “Total quarterly distribution per unit target amount.” The percentage interests shown for its common and subordinated unitholders and the general partner for the minimum quarterly distribution are also applicable to quarterly distribution amounts that are less than the minimum quarterly distribution. The percentage interests set forth below for the general partner include its two percent general partner interest and assume that the general partner has contributed any additional capital necessary to maintain its two percent general partner interest, the general partner has not transferred its incentive distribution rights and that there are no arrearages on common units. Net Income Allocation – In preparing the Consolidated Statements of Equity, net income (loss) attributable to MPLX LP is allocated to Preferred unitholders based on a fixed distribution schedule, as discussed in Note 9 , and subsequently allocated to the general partner and limited partner unitholders. However, when distributions related to the incentive distribution rights are made, earnings equal to the amount of those distributions are first allocated to the general partner before the remaining earnings are allocated to the limited partner unitholders based on their respective ownership percentages. The following table presents the allocation of the general partner’s interest in net income attributable to MPLX LP: (In millions) 2016 2015 2014 Net income attributable to MPLX LP $ 233 $ 156 $ 121 Less: Preferred unit distributions 41 — — General partner's incentive distribution rights and other 191 55 4 Net income attributable to MPLX LP available to general and limited partners $ 1 $ 101 $ 117 General partner's two percent interest in net income attributable to MPLX LP $ — $ 2 $ 2 General partner's incentive distribution rights and other 191 55 4 General partner's interest in net income attributable to MPLX LP $ 191 $ 57 $ 6 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 general partner will receive. In accordance with the partnership agreement, on January 25, 2017 , the Partnership declared a quarterly cash distribution, based on the results of the fourth quarter of 2016 , totaling $242 million , or $0.5200 per unit. This distribution was paid on February 14, 2017 to unitholders of record on February 6, 2017 . See the table below for the IDR impact for 2016 . The allocation of total quarterly cash distributions to general, limited, and Preferred unitholders is as follows for the years ended December 31, 2016 , 2015 and 2014 . The 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) 2016 2015 2014 General partner's distributions: General partner's distributions $ 18 $ 6 $ 2 General partner's incentive distribution rights distributions 187 54 4 Total general partner's distributions 205 60 6 Limited partners' distributions: Common unitholders 692 224 54 Subordinated unitholders — 31 52 Total limited partners' distributions 692 255 106 Preferred unit distributions 41 — — Total cash distributions declared $ 938 $ 315 $ 112

Redeemable Preferred Units (Not

Redeemable Preferred Units (Notes)	12 Months Ended
	Dec. 31, 2016
Temporary Equity Disclosure [Text Block]	Redeemable Preferred Units Private Placement of Preferred Units – On May 13, 2016, MPLX LP completed the private placement of approximately 30.8 million 6.5 percent Series A Convertible Preferred units (the "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 Preferred units were used for capital expenditures, repayment of debt and general partnership purposes. The Preferred units rank senior to all common units with respect to distributions and rights upon liquidation. The holders of the Preferred units are entitled to receive cumulative quarterly distributions equal to $0.528125 per unit commencing for the quarter ended June 30, 2016, with a prorated amount from the date of issuance. Following the second anniversary of the issuance of the Preferred units, the holders of the Preferred units will receive as a distribution the greater of $0.528125 per unit or the amount of per unit distributions paid to common units. Since the Preferred unit distribution was declared subsequent to the end of the second quarter of 2016, the distribution was not accrued to the Preferred unitholders’ capital account. For the quarter ended June 30, 2016, the Preferred units received an earned aggregate cash distribution of $9 million , based on the quarterly per unit distribution prorated for the 49-day period the Preferred units were outstanding during the second quarter of 2016. The changes in the redeemable preferred balance for 2016 were as follows: (In millions) Redeemable Preferred Units Issuance of MPLX LP redeemable Preferred units on May 13, 2016 $ 984 Net income allocated for May 13, 2016 through December 31, 2016 41 Distributions received by Preferred unitholders (25 ) Balance at December 31, 2016 $ 1,000 The purchasers may convert their Preferred units into common units, at any time after the third anniversary of the issuance date or prior to liquidation, dissolution or winding up of the Partnership, in full or in part, subject to minimum conversion amounts and conditions. After the fourth anniversary of the issuance date, the Partnership may convert the 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 LP common units is greater than $48.75 for the 20 day trading period immediately preceding the conversion notice date. The conversion rate for the 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. The holders of the Preferred units are entitled to vote on an as-converted basis with the common unitholders and will have certain other class voting rights with respect to any amendment to the partnership agreement that would adversely affect any rights, preferences or privileges of the Preferred units. In addition, upon certain events involving a change in control the holders of Preferred units may elect, among other potential elections, to convert their Preferred units to common units at the then change of control conversion rate. The Preferred units are considered redeemable securities under GAAP due to the existence of redemption provisions upon a deemed liquidation event which is outside the Partnership’s control. Therefore they are presented as temporary equity in the mezzanine section of the Consolidated Balance Sheets. The Preferred units have been recorded at their issuance date fair value, net of issuance costs. Income allocations increase the carrying value, and declared distributions decreased the carrying value of the Preferred units. Because the 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 Preferred units would become redeemable.

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2016
Segment Reporting [Abstract]
Segment Information	egment Information The Partnership’s chief operating decision maker is the chief executive officer (“CEO”) of its general partner. The CEO reviews the Partnership’s discrete financial information, makes operating decisions, assesses financial performance and allocates resources on a type of service basis. The Partnership 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 and stores crude oil and refined petroleum products. Segment information for prior periods includes HSM as it is an entity under common control. • G&P - gathers, processes and transports natural gas; gathers, transports, fractionates, stores and markets NGLs. This segment is the result of the MarkWest Merger on December 4, 2015 discussed in more detail in Note 4 . Segment information for periods prior to the MarkWest Merger does not include amounts for these operations. The Partnership has investments in entities that are accounted for using the equity method of accounting (see Note 5 ). However, the CEO views the Partnership-operated equity method investments’ financial information as if those investments were consolidated. Segment operating income represents income from operations attributable to the reportable segments. Corporate general and administrative expenses, unrealized derivative (losses) gains, property, plant and equipment, goodwill impairment and depreciation and amortization are not allocated to the reportable segments. Management does not consider these items allocable to or controllable by any individual segment and, therefore, excludes these items when evaluating segment performance. Segment results are also adjusted to exclude the portion of income from operations attributable to the noncontrolling interests related to partially-owned entities that are either consolidated or accounted for as equity method investments. Segment operating income attributable to MPLX LP excludes the operating income related to the Predecessor of the inland marine business prior to the March 31, 2016 acquisition. The tables below present information about income from operations and capital expenditures for the reported segments: 2016 (In millions) L&S G&P Total Revenues and other income: Segment revenues $ 787 $ 2,185 $ 2,972 Segment other income 68 1 69 Total segment revenues and other income 855 2,186 3,041 Costs and expenses: Segment cost of revenues 368 907 1,275 Segment operating income before portion attributable to noncontrolling interest and Predecessor 487 1,279 1,766 Segment portion attributable to noncontrolling interest and Predecessor 34 147 181 Segment operating income attributable to MPLX LP $ 453 $ 1,132 $ 1,585 2015 (In millions) L&S G&P Total Revenues and other income: Segment revenues $ 760 $ 150 $ 910 Segment other income 75 — 75 Total segment revenues and other income 835 150 985 Costs and expenses: Segment cost of revenues 379 62 441 Segment operating income before portion attributable to noncontrolling interest and Predecessor 456 88 544 Segment portion attributable to noncontrolling interest and Predecessor 134 12 146 Segment operating income attributable to MPLX LP $ 322 $ 76 $ 398 2014 (In millions) L&S Revenues and other income: Segment revenues $ 747 Segment other income 46 Total segment revenues and other income 793 Costs and expenses: Segment cost of revenues 392 Segment operating income before portion attributable to noncontrolling interest and Predecessor 401 Segment portion attributable to noncontrolling interest and Predecessor 188 Segment operating income attributable to MPLX LP $ 213 (in millions) 2016 2015 2014 Reconciliation to Income from operations: L&S segment operating income attributable to MPLX LP $ 453 $ 322 $ 213 G&P segment operating income attributable to MPLX LP 1,132 76 — Segment operating income attributable to MPLX LP 1,585 398 213 Segment portion attributable to unconsolidated affiliates (173 ) (8 ) 85 Segment portion attributable to Predecessor 34 133 103 (Loss) income from equity method investments (74 ) 3 — Other income - related parties 40 2 — Unrealized derivative (losses) gains (1) (36 ) 4 — Depreciation and amortization (546 ) (116 ) (75 ) Impairment expense (130 ) — — General and administrative expenses (193 ) (118 ) (81 ) Income from operations $ 507 $ 298 $ 245 (in millions) 2016 2015 2014 Reconciliation to Total revenues and other income: Total segment revenues and other income $ 3,041 $ 985 $ 793 Revenue adjustment from unconsolidated affiliates (402 ) (28 ) — (Loss) income from equity method investments (74 ) 3 — Other income - related parties 40 2 — Unrealized derivative losses (1) (15 ) (1 ) — Total revenues and other income $ 2,590 $ 961 $ 793 (in millions) 2016 2015 2014 Reconciliation to Net income attributable to noncontrolling interests and Predecessor: Segment portion attributable to noncontrolling interest and Predecessor $ 181 $ 146 $ 188 Portion of noncontrolling interests and Predecessor related to items below segment income from operations (124 ) (48 ) (70 ) Portion of operating income attributable to noncontrolling interests of unconsolidated affiliates (32 ) (5 ) — Net income attributable to noncontrolling interests and Predecessor $ 25 $ 93 $ 118 (1) The Partnership makes a distinction between realized or unrealized gains and losses on derivatives. During the period when a derivative contract is outstanding, we record changes in the fair value of the derivative as an unrealized gain or loss. When a derivative contract matures or is settled, we reverse the previously recorded unrealized gain or loss and record the realized gain or loss of the contract. The following reconciles segment capital expenditures to total capital expenditures: (In millions) 2016 2015 2014 L&S segment capital expenditures $ 443 $ 212 $ 141 G&P segment capital expenditures 894 100 — Total segment capital expenditures 1,337 312 141 Less: Capital expenditures for Partnership-operated, non-wholly-owned subsidiaries in G&P segment 131 24 — Total capital expenditures $ 1,206 $ 288 $ 141 Total assets by reportable segment were: December 31, (In millions) 2016 2015 Cash and cash equivalents $ 234 $ 43 L&S 2,115 1,842 G&P 14,297 14,219 Total assets $ 16,646 $ 16,104

Major Customer and Concentratio

Major Customer and Concentration of Credit Risk	12 Months Ended
	Dec. 31, 2016
Risks and Uncertainties [Abstract]
Major Customer and Concentration of Credit Risk	Major Customers and Concentration of Credit Risk MPC accounted for 30 percent, 79 percent and 90 percent of the Partnership’s total revenues and other income for 2016 , 2015 and 2014 , respectively, excluding revenues attributable to volumes shipped by MPC under joint tariffs with third parties, which are treated as third-party revenue for accounting purposes. A second customer accounted for 12 percent of the Partnership’s total revenues and other income for 2016 . Revenues from this customer are from product sales, gathering, processing and fractionation services in the G&P segment. As of December 31, 2016 , the Partnership had $59 million of accounts receivable from this customer. A third customer accounted for 10 percent of the Partnership’s total revenues and other income for 2016 . Revenues from this customer are from product sales, processing and fractionation services in the G&P segment. As of December 31, 2016 , the Partnership had $13 million of accounts receivable from this customer. The Partnership 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 the Partnership’s overall exposure to credit risk as they may be similarly affected by changes in economic, regulatory and other factors. The Partnership 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.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income Taxes	Income Tax The Partnership is not a taxable entity for United States federal income tax purposes or for the majority of states that impose an income tax. Taxes on the Partnership’s net income generally are borne by its partners through the allocation of taxable income. The Partnership’s income tax (benefit) provision results from partnership activity in the states of Texas, Ohio and Tennessee. As a result of the Class A Reorganization discussed in Note 8 , MarkWest Hydrocarbon (MarkWest Hydrocarbon, Inc. prior to the Class A Reorganization) is no longer a tax paying entity for federal income tax purposes or for the majority of states that impose an income tax effective September 1, 2016. After MarkWest Hydrocarbon files its 2016 income tax returns in 2017, the Partnership anticipates a residual tax provision to be recorded. In connection with the Class A Reorganization, MPC assumed $377 million of MPLX LP’s deferred tax liabilities. The Partnership and MarkWest Hydrocarbon recorded income tax expense of $12 million , $1 million and $1 million for the years ended December 31, 2016 , 2015 and 2014 , respectively. The effective tax rate was five percent for 2016 , and less than one percent for 2015 and 2014 , respectively. The components of the provision for income tax expense (benefit) are as follows: December 31, (In millions) 2016 2015 Current income tax expense: Federal $ 4 $ — State 1 — Total current 5 — Deferred income tax (benefit) expense: Federal (16 ) 3 State (1 ) (2 ) Total deferred (17 ) 1 (Benefit) provision for income tax $ (12 ) $ 1 A reconciliation of the (benefit) provision for income tax and the amount computed by applying the federal statutory rate of 35 percent to the income before income taxes for each of the years ended December 31, 2016 and 2015 is as follows: December 31, 2016 (In millions) MarkWest Hydrocarbon (1) Partnership Eliminations Consolidated (Loss) income before (benefit) provision for income tax $ (41 ) $ 285 $ 2 $ 246 Federal statutory rate 35 % — % — % Federal income tax at statutory rate (14 ) — — (14 ) State income taxes net of federal benefit (2 ) 1 — (1 ) Provision on income from MPLX LP Class A units 3 — — 3 Change in state statutory rate (1 ) — — (1 ) Other 1 — — 1 (Benefit) provision for income tax $ (13 ) $ 1 $ — $ (12 ) December 31, 2015 (In millions) MarkWest Hydrocarbon (1) Partnership Eliminations Consolidated Income before provision (benefit) for income tax $ 9 $ 240 $ 1 $ 250 Federal statutory rate 35 % — % — % Federal income tax at statutory rate 3 — — 3 State income taxes net of federal benefit — (2 ) — (2 ) Provision on income from MPLX LP Class A units 1 — — 1 Other (1 ) — — (1 ) Provision (benefit) for income tax $ 3 $ (2 ) $ — $ 1 (1) MarkWest Hydrocarbon paid tax on its share of the Partnership’s income or loss as a result of its ownership of MPLX LP Class A units through September 1, 2016. Deferred tax assets and liabilities consist of the following: December 31, (In millions) 2016 2015 Deferred tax assets: Derivatives $ — $ 9 Net operating loss carryforwards — 62 Total deferred tax assets — 71 Deferred tax liabilities: Property, plant and equipment 5 7 Investments in subsidiaries and affiliates — 442 Total deferred tax liabilities 5 449 Net deferred tax liabilities $ 5 $ 378 At December 31, 2016 , MarkWest Hydrocarbon had no tax-effected federal or state operating loss carryforwards. These were assumed by MPC on September 1, 2016 in connection with the Class A Reorganization discussed in Note 8 . Significant judgment is required in evaluating tax positions and determining the Partnership and MarkWest Hydrocarbon’s provision for income taxes. During the ordinary course of business, there may be transactions and calculations for which the ultimate tax determination is uncertain. However, the Partnership and MarkWest Hydrocarbon did not have any material uncertain tax positions for the years ended December 31, 2016 , 2015 or 2014 . Any interest and penalties related to income taxes were recorded as a part of the provision for income taxes. Such interest and penalties were a net expense of less than $1 million in 2016 and 2015 , respectively, and a net benefit of less than $1 million in 2014 . As of December 31, 2016 and 2015 , less than $1 million , respectively, of interest and penalties were accrued related to income taxes. In addition, the Partnership and MarkWest Hydrocarbon’s former corporate entity have federal tax years 2013 through 2015 and state tax years 2012 through 2015 open to examination.

Inventories

Inventories	12 Months Ended
	Dec. 31, 2016
Inventory Disclosure [Abstract]
Inventories [Text Block]	Inventories Inventories consist of the following: December 31, (In millions) 2016 2015 NGLs $ 2 $ 3 Line fill 9 5 Spare parts, materials and supplies 43 43 Total inventories $ 54 $ 51

Property, Plant and Equipment

Property, Plant and Equipment	12 Months Ended
	Dec. 31, 2016
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) 2016 2015 Natural gas gathering and NGL transportation pipelines and facilities 5 - 30 years $ 4,748 $ 4,307 Processing, fractionation and storage facilities 25 - 30 years 3,467 3,185 Pipelines and related assets 19 - 42 years 1,492 1,128 Barges and towing vessels 20 years 479 475 Land, building, office equipment and other 3 - 30 years 701 606 Construction-in-progress 958 946 Total 11,845 10,647 Less accumulated depreciation 1,115 650 Property, plant and equipment, net $ 10,730 $ 9,997 Property, plant and equipment includes gross assets acquired under capital leases of approximately $25 million at December 31, 2016 and 2015 , respectively, with related amounts in accumulated depreciation of approximately $8 million and $7 million at December 31, 2016 and 2015 , respectively.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements Fair Values – Recurring Fair value measurements and disclosures relate primarily to the Partnership’s derivative positions as discussed in Note 16 . As part of the MarkWest Merger, the MarkWest opening balance sheet was valued at fair value (see Note 4 ). Money market funds, which are included in Cash and cash equivalents on the Consolidated Balance Sheets, are measured at fair value and are included in Level 1 measurements of the valuation hierarchy. The derivative contracts are measured at fair value on a recurring basis and classified within Level 2 and Level 3 of the valuation hierarchy. The Level 2 and Level 3 measurements are obtained using a market approach. LIBOR rates are an observable input for the measurement of all derivative contracts. The measurements for all commodity contracts contain observable inputs in the form of forward prices based on WTI crude oil prices; and Columbia Appalachia, Henry Hub, PEPL and Houston Ship Channel natural gas prices. Level 2 instruments include crude oil and natural gas swap contracts. The valuations are based on the appropriate commodity prices and contain no significant unobservable inputs. Level 3 instruments include all NGL transactions and embedded derivatives in commodity contracts. The significant unobservable inputs for NGL transactions and embedded derivatives in commodity contracts include NGL prices interpolated and extrapolated due to inactive markets, electricity price curves, and probability of renewal. The following table presents the financial instruments carried at fair value classified by the valuation hierarchy: December 31, 2016 December 31, 2015 (In millions) Assets Liabilities Assets Liabilities Significant other observable inputs (Level 2) Commodity contracts $ — $ — $ 2 $ — Significant unobservable inputs (Level 3) Commodity contracts — (6 ) 7 — Embedded derivatives in commodity contracts — (54 ) — (32 ) Total carrying value in Consolidated Balance Sheets $ — $ (60 ) $ 9 $ (32 ) The following table provides additional information about the significant unobservable inputs used in the valuation of Level 3 instruments as of December 31, 2016 . The market approach is used for valuation of all instruments. Level 3 Instrument Balance Sheet Classification Unobservable Inputs Value Range Time Period Commodity contracts Liabilities Forward ethane prices (per gallon) (1) $0.28 - $0.31 Jan. 17 - Dec. 17 Forward propane prices (per gallon) (1) $0.66 - $0.72 Jan. 17 - Dec. 17 Forward isobutane prices (per gallon) (1) $0.85 - $0.97 Jan. 17 - Dec. 17 Forward normal butane prices (per gallon) (1) $0.79 - $0.93 Jan. 17 - Dec. 17 Forward natural gasoline prices (per gallon) (1) $1.16 - $1.24 Jan. 17 - Dec. 17 Embedded derivatives in commodity contracts Liabilities Forward propane prices (per gallon) (1) $0.62 - $0.72 Jan. 17 - Dec. 22 Forward isobutane prices (per gallon) (1) $0.82 - $0.97 Jan. 17 - Dec. 22 Forward normal butane prices (per gallon) (1) $0.78 - $0.93 Jan. 17 - Dec. 22 Forward natural gasoline prices (per gallon) (1) $1.16 - $1.27 Jan. 17 - Dec. 22 Forward natural gas prices (per mmbtu) (2) $2.37 - $3.72 Jan. 17 - Dec. 22 Probability of renewal (3) 50.0% Probability of renewal for second 5-yr term (3) 75.0% (1) NGL prices used in the valuations decrease in the early years and increase over time. (2) Natural gas prices used in the valuations are higher in the early years and decrease over time. (3) The producer counterparty to the embedded derivative has the option to renew the gas purchase agreement and the related keep-whole processing agreement for two successive five -year terms after 2022. The embedded gas purchase agreement cannot be renewed without the renewal of the related keep-whole processing agreement. Due to the significant number of years until the renewal options are exercisable and the high level of uncertainty regarding the counterparty’s future business strategy, the future commodity price environment, and the future competitive environment for midstream services in the Southern Appalachian region, management determined that a 50 percent probability of renewal for the first five-year term and 75 percent for the second five-year term are appropriate assumptions. Included in this assumption is a further extension of management’s estimates of future frac spreads through 2032. Fair Value Sensitivity Related to Unobservable Inputs Commodity contracts (assets and liabilities) – For the Partnership’s commodity contracts, increases in forward NGL prices result in a decrease in the fair value of the derivative assets and an increase in the fair value of the derivative liabilities. The forward prices for the individual NGL products generally increase or decrease in a positive correlation with one another. Embedded derivatives in commodity contracts – The Partnership has a single embedded derivative liability comprised of both the purchase of natural gas at prices impacted by the frac spread and the probability of contract renewal (the “Natural Gas Embedded Derivative”), as discussed further in Note 16 . Increases (decreases) in the frac spread result in an increase (decrease) in the fair value of the embedded derivative liability. An increase in the probability of renewal would result in an increase in the fair value of the related embedded derivative liability. Embedded derivatives in utility contracts – The Partnership had an embedded derivative contract that fixed a component of the utilities costs at a plant in the Southwest operations to an index price of electricity which expired as of December 31, 2016. Increases (decreases) in the index price for electricity resulted in a decrease (increase) in the realized losses presented in Cost of Revenues on the Income Statement. Level 3 Valuation Process The Partnership’s Risk Management Department (the “Risk Department”) is responsible for the valuation of the Partnership’s commodity derivative contracts and embedded derivatives in commodity contracts, except for the Natural Gas Embedded Derivative. The Risk Department reports to the Chief Financial Officer and is responsible for the oversight of the Partnership’s commodity risk management program. The members of the Risk Department have the requisite experience, knowledge and day-to-day involvement in the energy commodity markets to ensure appropriate valuations and understand the changes in the valuations from period to period. The valuations of the Level 3 commodity derivative contracts are performed by a third-party pricing service and reviewed and validated on a quarterly basis by the Risk Department by comparing the pricing and option volatilities to actual market data and/or data provided by at least one other independent third-party pricing service. Management is responsible for the valuation of the Natural Gas Embedded Derivative discussed in Note 16 . Included in the valuation of the Natural Gas Embedded Derivative are assumptions about the forward price curves for NGLs and natural gas for periods in which price curves are not available from third-party pricing services due to insufficient market data. The Risk Department must develop forward price curves for NGLs and natural gas through the initial contract term (January 2017 through December 2022) for management’s use in determining the fair value of the Natural Gas Embedded Derivative. In developing the pricing curves for these periods, the Risk Department maximizes its use of the latest known market data and trends as well as its understanding of the historical relationships between forward NGL and natural gas prices and the forward market data that is available for the required period, such as crude oil pricing and natural gas pricing from other markets. However, there is very limited actual market data available to validate the Risk Department’s estimated price curves. Management also assesses the probability of the producer customer’s renewal of the contracts, which includes consideration of: • The estimated favorability of the contracts to the producer customer as compared to other options that would be available to them at the time and in the relative geographic area of their producing assets. • Extrapolated pricing curves, using a weighted average probability method that is based on historical frac spreads, which impact the calculation of favorability. • The producer customer’s potential business strategy decision points that may exist at the time the counterparty would elect whether to renew the contracts. Changes in Level 3 Fair Value Measurements The tables below include a roll forward of the balance sheet amounts for the years ended December 31, 2016 and 2015 (including the change in fair value) for assets and liabilities classified by the Partnership within Level 3 of the valuation hierarchy, except for the changes in goodwill. See Note 5 for detail of the Ohio Condensate equity method impairment charge, which included a Level 3 valuation adjustment for the year ended December 31, 2016. See Note 18 for a rollforward of goodwill, which included a Level 3 valuation adjustment for the year ended December 31, 2016. 2016 2015 (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 $ 7 $ (32 ) $ — $ — Net positions assumed in conjunction with the MarkWest Merger — — 7 (38 ) Total (loss) gain (realized and unrealized) included in earnings (1) (13 ) (29 ) 3 5 Settlements — 7 (3 ) 1 Fair value at end of period $ (6 ) $ (54 ) $ 7 $ (32 ) The amount of total (losses) gains for the period included in earnings attributable to the change in unrealized gains or losses relating to liabilities still held at end of period $ (6 ) $ (26 ) $ 2 $ 5 (1) Gains and losses on Commodity Derivative Contracts classified as Level 3 are recorded in Product sales in the accompanying Consolidated Statements of Income. Gains and losses on Embedded Derivatives in Commodity Contracts are recorded in Cost of revenues and Purchased product costs . Fair Values – Reported The Partnership’s primary financial instruments are cash and cash equivalents, receivables, receivables from related parties, accounts payable, payables to related parties and long-term debt. The Partnership’s fair value assessment incorporates a variety of considerations, including (1) the short-term 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. The Partnership 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 SMR liability and $4.1 billion aggregate principal of the Partnership’s long-term debt were recorded at fair value in connection with the MarkWest Merger as of December 4, 2015, which established a new cost basis for each of those liabilities. The fair value of the 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 the Partnership’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 Partnership’s long-term debt, excluding capital leases, and SMR liability. December 31, 2016 2015 (In millions) Fair Value Carrying Value Fair Value Carrying Value Long-term debt $ 4,953 $ 4,422 $ 5,212 $ 5,255 SMR liability $ 108 $ 96 $ 99 $ 100

Derivative Financial Instrument

Derivative Financial Instruments	12 Months Ended
	Dec. 31, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments and Hedging Activities Disclosure [Text Block]	Derivative Financial Instruments Commodity Derivatives NGL and natural gas prices are volatile and are impacted by changes in fundamental supply and demand, as well as market uncertainty, availability of NGL transportation and fractionation capacity and a variety of additional factors that are beyond the Partnership’s control. The Partnership’s profitability is directly affected by prevailing commodity prices primarily as a result of processing or conditioning at its own or third-party processing plants, purchasing and selling or gathering and transporting volumes of natural gas at index-related prices and the cost of third-party transportation and fractionation services. To the extent that commodity prices influence the level of natural gas drilling by the Partnership’s producer customers, such prices also affect profitability. To protect itself financially against adverse price movements and to maintain more stable and predictable cash flows so that the Partnership can meet its cash distribution objectives, debt service and capital plans, the Partnership executes a strategy governed by its risk management policy. The Partnership has a committee comprised of senior management that oversees risk management activities, continually monitors the risk management program and adjusts its strategy as conditions warrant. The Partnership enters into certain derivative contracts to reduce the risks associated with unfavorable changes in the prices of natural gas and NGLs. Derivative contracts utilized are swaps traded on the OTC market and fixed price forward contracts. The risk management policy does not allow the Partnership to take speculative positions with its derivative contracts. To mitigate its cash flow exposure to fluctuations in the price of NGLs, the Partnership has entered into derivative financial instruments relating to the future price of NGLs and crude oil. The Partnership currently manages the majority of its NGL price risk using direct product NGL derivative contracts. The Partnership enters into NGL derivative contracts when adequate market liquidity exists and future prices are satisfactory. A portion of the Partnership’s NGL price exposure is managed by using crude oil contracts. In periods where NGL prices and crude oil prices are not consistent with the historical relationship, the crude oil contracts create increased risk and additional gains or losses. The Partnership may settle its crude oil contracts prior to the contractual settlement date in order to take advantage of favorable terms and reduce the future exposure resulting from the less effective crude oil contracts. Based on its current volume forecasts, the majority of its derivative positions used to manage the future commodity price exposure are expected to be direct product NGL derivative contracts. To mitigate its cash flow exposure to fluctuations in the price of natural gas, the Partnership primarily utilizes derivative financial instruments relating to the future price of natural gas and takes into account the partial offset of its long and short gas positions resulting from normal operating activities. As a result of its current derivative positions, the Partnership has mitigated a portion of its expected commodity price risk through the fourth quarter of 2017. The Partnership would be exposed to additional commodity risk in certain situations such as if producers under deliver or over deliver product or when processing facilities are operated in different recovery modes. In the event the Partnership has derivative positions in excess of the product delivered or expected to be delivered, the excess derivative positions may be terminated. Management conducts a standard credit review on counterparties to derivative contracts, and has provided the counterparties with a guaranty as credit support for its obligations. A separate agreement with certain counterparties allows MarkWest Liberty Midstream to enter into derivative positions without posting cash collateral. The Partnership uses standardized agreements that allow for offset of certain positive and negative exposures (“master netting arrangements”) in the event of default or other terminating events, including bankruptcy. The Partnership records derivative contracts at fair value in the Consolidated Balance Sheets and has not elected hedge accounting or the normal purchases and normal sales designation (except for electricity and certain other qualifying contracts, for which the normal purchases and normal sales designation has been elected). The Partnership’s accounting may cause volatility in the Consolidated Statements of Income as the Partnership recognizes in current earnings all unrealized gains and losses from the changes in fair value of derivatives. The Partnership makes a distinction between realized or unrealized gains and losses on derivatives. During the period when a derivative contract is outstanding, we record changes in the fair value of the derivative as an unrealized gain or loss. When a derivative contract matures or is settled, we reverse the previously recorded unrealized gain or loss and record the realized gain or loss of the contract. Volume of Commodity Derivative Activity As of December 31, 2016 , the Partnership had the following outstanding commodity contracts that were executed to manage the cash flow risk associated with future sales of NGLs: Derivative contracts not designated as hedging instruments Financial Position Notional Quantity (net) Crude Oil (bbl) Short 36,500 Natural Gas (MMBtu) Long 297,017 NGLs (gal) Short 64,211,702 Embedded Derivatives in Commodity Contracts The Partnership has a commodity contract with a producer customer in the Southern Appalachian region that creates a floor on the frac spread for gas purchases of 9,000 Dth/d. The commodity contract is a component of a broader regional arrangement that also includes a keep-whole processing agreement. For accounting purposes, these contracts have been aggregated into a single contract and are evaluated together. In February 2011, the Partnership executed agreements with the producer customer to extend the commodity contract and the related processing agreement from March 31, 2015 to December 31, 2022, with the producer customer’s option to extend the agreement for two successive five year terms through December 31, 2032. The purchase of gas at prices based on the frac spread and the option to extend the agreements have been identified as a single embedded derivative, which is recorded at fair value. The probability of renewal is determined based on extrapolated pricing curves, a review of the overall expected favorability of the contracts based on such pricing curves, and assumptions about the counterparty’s potential business strategy decision points that may exist at the time the counterparty would elect whether to renew the contract. The changes in fair value of this 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 in the Consolidated Statements of Income. As of December 31, 2016 and 2015 , the estimated fair value of this contract was a liability of $54 million and $31 million , respectively. During the years ended December 31, 2016 and 2015, the Partnership had a commodity contract that allowed for the Partnership to fix a component of the utilities cost to an index price on electricity at a plant location in the Southwest Operations which expired as of December 31, 2016. Changes in the fair value of the derivative component of this contract were recognized as Cost of revenues in the Consolidated Statements of Income. As of December 31, 2015 , the estimated fair value of this contract was a liability of $1 million . Financial Statement Impact of Derivative Contracts Certain derivative positions are subject to master netting agreements, therefore the Partnership has elected to offset derivative assets and liabilities that are legally permissible to be offset. As of December 31, 2016 and 2015, there were no derivative assets or liabilities that were offset in the Consolidated Balance Sheets. The impact of the Partnership’s derivative instruments on its Consolidated Balance Sheets is summarized below: (In millions) December 31, 2016 December 31, 2015 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 $ — $ (13 ) $ 9 $ (5 ) Other noncurrent assets / deferred credits and other liabilities — (47 ) — (27 ) Total $ — $ (60 ) $ 9 $ (32 ) (1) Includes embedded derivatives in commodity contracts as discussed above. In the table above, the Partnership does not offset a counterparty’s current derivative contracts with the counterparty’s non-current derivative contracts, although the Partnership’s master netting arrangements would allow current and non-current positions to be offset in the event of default. Additionally, in the event of a default, the Partnership’s master netting arrangements would allow for the offsetting of all transactions executed under the master netting arrangement. These types of transactions may include non-derivative instruments, derivatives qualifying for scope exceptions, receivables and payables arising from settled positions and other forms of non-cash collateral (such as letters of credit). The impact of the Partnership’s derivative contracts not designated as hedging instruments and the location of gain or (loss) recognized in the Consolidated Statements of Income is summarized below: December 31, (In millions) 2016 2015 Product sales Realized gain $ 2 $ 4 Unrealized loss (15 ) (1 ) Total revenue: derivative (loss) gain from product sales (13 ) 3 Purchased product costs Realized loss (5 ) — Unrealized (loss) gain (22 ) 5 Total purchased product costs: derivative (loss) gain from product purchases (27 ) 5 Cost of revenues Realized loss (3 ) — Unrealized gain 1 — Total cost of revenues: derivative loss from cost of revenues (2 ) — Total derivative (losses) gains $ (42 ) $ 8

Debt

Debt	12 Months Ended
	Dec. 31, 2016
Debt Disclosure [Abstract]
Debt	Debt The Partnership’s outstanding borrowings at December 31, 2016 and 2015 consisted of the following: December 31, (In millions) 2016 2015 MPLX LP: Bank revolving credit facility due 2020 $ — $ 877 Term loan facility due 2019 250 250 5.500% senior notes due 2023 710 710 4.500% senior notes due 2023 989 989 4.875% senior notes due 2024 1,149 1,149 4.000% senior notes due 2025 500 500 4.875% senior notes due 2025 1,189 1,189 Consolidated subsidiaries: MarkWest - 4.500% - 5.500% senior notes, due 2023 - 2025 63 63 MPL - capital lease obligations due 2020 8 9 Total 4,858 5,736 Unamortized debt issuance costs (7 ) (8 ) Unamortized discount (1) (428 ) (472 ) Amounts due within one year (1 ) (1 ) Total long-term debt due after one year $ 4,422 $ 5,255 (1) Includes $420 million and $464 million discount as of December 31, 2016 and 2015, respectively, related to the difference between the fair value and the principal amount of the assumed MarkWest debt. The following table shows five years of scheduled debt payments. (In millions) 2017 $ 1 2018 1 2019 251 2020 5 2021 — Credit Agreements On November 20, 2014 , MPLX LP entered into a credit agreement with a syndicate of lenders (“MPLX Credit Agreement”) which provided for a five -year, $1 billion bank revolving credit facility and a $250 million term loan facility. In connection with the closing of the MarkWest Merger, the Partnership amended the MPLX Credit Agreement to, among other things, increase the aggregate amount of revolving credit capacity under the credit agreement by $1 billion , for total aggregate commitments of $2 billion , and to extend the maturity for the bank revolving credit facility to December 4, 2020 . The term loan facility was not amended and matures on November 20, 2019 . Also in connection with the closing of the MarkWest Merger, MarkWest’s bank revolving credit facility was terminated and the approximately $943 million outstanding under MarkWest’s bank revolving credit facility was repaid with $850 million of borrowings under MPLX LP’s bank revolving credit facility and $93 million of cash. The bank revolving credit facility includes a letter of credit issuing capacity of up to $250 million and swingline capacity of up to $100 million . The borrowing capacity under the MPLX Credit Agreement may be increased by up to an additional $500 million , subject to certain conditions, including the consent of lenders whose commitments would increase. In addition, the maturity date may be extended from time-to-time during its term to a date that is one year after the then-effective maturity subject to the approval of lenders holding the majority of the commitments then outstanding, provided that the commitments of any non-consenting lenders will be terminated on the then-effective maturity date. The term loan facility was drawn in full on November 20, 2014. The maturity date for the term loan facility may be extended for up to two additional one -year periods subject to the consent of the lenders holding a majority of the outstanding term loan borrowings, provided that the portion of the term loan borrowings held by any non-consenting lenders will continue to be due and payable on the then-effective maturity date. The borrowings under this facility during 2016 were at an average interest rate of 1.954 percent . 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 . The Partnership is charged various fees and expenses in connection with the agreement, including administrative agent fees, commitment fees on the unused portion of the bank revolving credit 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 the Partnership’s long-term debt. The MPLX Credit Agreement includes certain representations and warranties, affirmative and restrictive covenants and events of default that the Partnership considers to be usual and customary for an agreement of this type. This agreement includes a financial covenant that requires the Partnership 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 completed and capital projects undertaken during the relevant period. Other covenants restrict the Partnership and certain of its subsidiaries from incurring debt, creating liens on its assets and entering into transactions with affiliates. As of December 31, 2016 , the Partnership was in compliance with the covenants contained in the MPLX Credit Agreement. During 2016 , the Partnership borrowed $434 million under the bank revolving credit facility, at an average interest rate of 1.899 percent , per annum, and repaid $1.3 billion under the bank revolving credit facility. At December 31, 2016 , the Partnership had no borrowings against the facility and $3 million letters of credit outstanding under this facility, resulting in total availability of $2 billion , or 99.9 percent of the borrowing capacity. During 2015 , the Partnership borrowed $992 million under the bank revolving credit facility, at an average interest rate of 1.617 percent , per annum, and repaid $500 million of these borrowings. At December 31, 2015 , the Partnership had $877 million of borrowings and $8 million letters of credit outstanding under this facility, resulting in total unused loan availability of $1.12 billion , or 55.8 percent of the borrowing capacity. During 2014 , in connection with entering into the above mentioned MPLX Credit Agreement, the Partnership terminated its previously existing $500 million five -year MPLX Operations bank revolving credit agreement, dated as of September 14, 2012 . However, during 2014, we borrowed $280 million under the previously existing agreement, at an average interest rate of 1.535 percent , per annum, and repaid all of these borrowings. Senior Notes In connection with the MarkWest Merger, MPLX LP assumed MarkWest’s outstanding debt, which included $4.1 billion aggregate principal amount of senior notes. On December 22, 2015, approximately $4.04 billion aggregate principal amount of MarkWest’s outstanding senior notes were exchanged for an aggregate principal amount of approximately $4.04 billion of new unsecured senior notes issued by MPLX LP in an exchange offer and consent solicitation undertaken by MPLX LP and MarkWest, leaving approximately $63 million aggregate principal of outstanding senior notes held by MarkWest. The MPLX LP senior notes consist of (i) approximately $710 million aggregate principal amount of 5.500 percent senior notes due February 15, 2023 , (ii) approximately $989 million aggregate principal amount of 4.500 percent senior notes due July 15, 2023 , (iii) approximately $1.15 billion aggregate principal amount of 4.875 percent senior notes due December 1, 2024 , (iv) approximately $500 million aggregate principal amount of four percent unsecured senior notes due February 15, 2025 , and (v) approximately $1.19 billion aggregate principal amount of 4.875 percent senior notes due June 1, 2025 . Interest on each series of MPLX LP senior notes is payable semi-annually in arrears according to the table below. Senior Notes Interest payable semi-annually in arrears 5.500% senior notes due 2023 February 15 th and August 15 th 4.500% senior notes due 2023 January 15 th and July 15 th 4.875% senior notes due 2024 June 1 st and December 1 st 4.000% senior notes due 2025 February 15 th and August 15 th 4.875% senior notes due 2025 June 1 st and December 1 st After giving effect to the exchange offer and consent solicitation referred to above, as of December 31, 2016, MarkWest had outstanding (i) approximately $40 million aggregate principal amount of 5.500 percent senior notes due February 15, 2023 , (ii) approximately $11 million aggregate principal amount of 4.500 percent senior notes due July 15, 2023 , (iii) approximately $1 million aggregate principal amount of 4.875 percent senior notes due December 1, 2024 and (iv) approximately $11 million aggregate principal amount of 4.875 percent senior notes due June 1, 2025 . Interest on each series of the MarkWest senior notes is payable semi-annually in arrears consistent with the table above. On February 12, 2015, the Partnership completed a public offering of $500 million aggregate principal amount of four percent unsecured senior notes due February 15, 2025 (the “Feb 2025 Notes”). The net proceeds from the offering of the Feb 2025 Notes were approximately $495 million , after deducting underwriting discounts. The net proceeds were used to repay the amounts outstanding under its bank revolving credit facility, as well as for general partnership purposes. Interest is payable semi-annually in arrears, commencing on August 15, 2015. 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 the Partnership 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. The Partnership 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, 2016 and 2015 , the following amounts related to the SMR are included in the accompanying Consolidated Balance Sheets: (In millions) December 31, 2016 December 31, 2015 Assets Property, plant and equipment, net of accumulated depreciation $ 61 $ 69 Liabilities Accrued liabilities 5 4 Deferred credits and other liabilities 91 96

Goodwill and Intangibles

Goodwill and Intangibles	12 Months Ended
	Dec. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets Disclosure [Text Block]	Goodwill and Intangibles Goodwill The Partnership 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. The Partnership has performed its annual impairment tests, and no additional impairments in the carrying value of goodwill were identified in the periods presented. During the first quarter of 2016, the Partnership determined that an interim impairment analysis of the goodwill recorded in connection with the MarkWest Merger was necessary based on consideration of a number of first quarter events and circumstances, including i) continued deterioration of near term commodity prices as well as longer term pricing trends, ii) recent guidance on reductions to forecasted capital spending, the slowing of drilling activity and the resulting reduced production growth forecasts released or communicated by the Partnership’s producer customers and iii) increases in cost of capital. The combination of these factors was considered to be a triggering event requiring an interim impairment test. Based on the first step of the interim goodwill impairment analysis, the fair value for the three reporting units to which goodwill was assigned in connection with the MarkWest Merger was less than the respective carrying value. In step two of the impairment analysis, the implied fair values of the goodwill were compared to the carrying values within those reporting units. Based on this assessment, it was determined that goodwill was impaired in two of the three reporting units. Accordingly, the Partnership recorded an impairment charge of approximately $129 million in the first quarter of 2016. In the second quarter of 2016, the Partnership completed its purchase price allocation, which resulted in an additional $1 million of impairment expense that would have been recorded in the first quarter of 2016 had the purchase price allocation been completed as of that date. This adjustment to the impairment expense was the result of completing an evaluation of the deferred tax liabilities associated with the MarkWest Merger and their impact on the resulting goodwill that was recognized. The fair value of the reporting units for the interim goodwill impairment analysis was determined based on applying the discounted cash flow method, which is an income approach, and the guideline public company method, which is a market 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 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 10.5 percent to 11.5 percent . The fair value of the intangibles was determined based on applying the multi-period excess earnings method, which is an income approach. Key assumptions included attrition rates by reporting unit ranging from 5.0 percent to 10.0 percent and discount rates by reporting unit ranging from 11.5 percent to 12.8 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, 2014 $ 116 $ — $ 116 Accumulated impairment losses — — — Balance as of December 31, 2014 116 — 116 Acquisitions — 2,454 2,454 Gross goodwill as of December 31, 2015 116 2,454 2,570 Accumulated impairment losses — — — Balance as of December 31, 2015 116 2,454 2,570 Purchase price allocation adjustments (1) — (241 ) (241 ) Impairment losses — (130 ) (130 ) Balance as of December 31, 2016 $ 116 $ 2,083 $ 2,199 Gross goodwill as of December 31, 2016 $ 116 $ 2,213 $ 2,329 Accumulated impairment losses — (130 ) (130 ) Balance as of December 31, 2016 $ 116 $ 2,083 $ 2,199 (1) See Note 4 for further discussion on purchase price allocation adjustments. Intangible Assets The Partnership’s intangible assets as of December 31, 2016 and 2015 are comprised of customer contracts and relationships, as follows: December 31, 2016 December 31, 2015 (In millions) Gross Accumulated Amortization Net Gross Accumulated Amortization Net Useful Life L&S $ — $ — $ — $ — $ — $ — N/A G&P 533 (41 ) 492 468 (2 ) 466 11-25 years $ 533 $ (41 ) $ 492 $ 468 $ (2 ) $ 466 Estimated future amortization expense related to the intangible assets at December 31, 2016 is as follows: (In millions) 2017 $ 38 2018 38 2019 38 2020 38 2021 38 Thereafter 302 Total $ 492

Supplemental Cash Flow Informat

Supplemental Cash Flow Information	12 Months Ended
	Dec. 31, 2016
Supplemental Cash Flow Elements [Abstract]
Supplemental Cash Flow Information	Supplemental Cash Flow Information (In millions) 2016 2015 2014 Net cash provided by operating activities included: Interest paid (net of amounts capitalized) $ 212 $ 13 $ 3 Income taxes paid 3 — — Non-cash investing and financing activities: Net transfers of property, plant and equipment from materials and supplies inventories $ 4 $ 5 $ 1 Contribution - common units issued (1) 669 — 200 Acquisition: Fair value of MPLX LP units issued (1) — 7,326 — Payable to seller — 50 — (1) See Note 4 . 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) 2016 2015 2014 (Decrease) increase in capital accruals $ (25 ) $ 26 $ 11 In connection with the acquisition of HSM described in Note 4 , MPC agreed to waive first quarter 2016 distributions on the MPLX LP common units issued in connection with the transaction. MPC did not receive general partner distributions or incentive distribution rights that would have otherwise accrued on such MPLX LP common units with respect to the first quarter distributions. The value of these waived distributions was $15 million .

Equity-Based Compensation Plan

Equity-Based Compensation Plan	12 Months Ended
	Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Equity-Based Compensation Plan	Equity-based Compensation Plan Description of the Plan The MPLX LP 2012 Incentive Compensation Plan (“MPLX 2012 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 Partnership’s or any of its affiliates’ employees, officers and directors, including directors and officers of MPC. No more than 2.75 million MPLX LP common limited partner units may be delivered under the MPLX 2012 Plan. Units delivered pursuant to an award granted under the MPLX 2012 Plan may be funded through acquisition on the open market, from the Partnership or from an affiliate of the Partnership, as determined by the Board. Unit-based awards under the Plan The Partnership 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 – The Partnership grants phantom units under 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. The Partnership grants phantom units under the MPLX 2012 Plan to certain officers and non-officers of MPLX LP, MPLX LP’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, 2016 and 2015 were $2 million and less than $1 million , respectively. The fair values of phantom units are based on the fair value of MPLX LP common limited partner units on the grant date. Performance Units – The Partnership grants performance units under the MPLX 2012 Plan to certain officers of MPLX LP’s general partner and certain eligible MPC officers who make significant contributions to its business. These awards are intended to have a per unit payout determined by the total unitholder return of MPLX LP common units as compared to the total unitholder return of a selected group of peer partnerships. The final per-unit payout will be the average of the results of four measurement periods during the 36 month requisite service period. These performance units will pay out 75 percent in cash and 25 percent in MPLX LP 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 and have a weighted average grant date fair value of $0.63 per unit for 2016 and $1.03 per unit for 2015 , as calculated using a Monte Carlo valuation model. Outstanding Phantom Unit Awards The following is a summary of phantom unit award activity of MPLX LP common limited partner units in 2016 : Phantom Units Number of Units Weighted Average Fair Value Aggregate Intrinsic Value (In millions) Outstanding at December 31, 2015 1,031,219 $ 35.49 Granted 458,727 29.42 Settled (166,576 ) 38.12 Forfeited (149,959 ) 32.72 Outstanding at December 31, 2016 1,173,411 33.09 Vested and expected to vest at December 31, 2016 1,157,676 33.12 $ 40 Convertible at December 31, 2016 494,189 34.11 $ 17 The 494,189 convertible units are held by our non-employee directors and certain officers. These units are non-forfeitable and issuable upon the holder’s departure from service to the company. The following is a summary of the values related to phantom units held by officers and non-employee directors: Phantom Units Intrinsic Value of Units Issued During the Period (in millions) Weighted Average Grant Date Fair Value of Units Granted During the Period 2016 $ 5 $ 29.42 2015 3 35.00 2014 1 49.56 As of December 31, 2016 , unrecognized compensation cost related to phantom unit awards was $17 million , which is expected to be recognized over a weighted average period of 2.0 years . Outstanding Performance Unit Awards The following is a summary of activity of performance unit awards paying out in MPLX LP common limited partner units in 2016 : Performance Units Number of Units Weighted Outstanding at December 31, 2015 1,521,392 $ 1.00 Granted 789,375 0.63 Settled (458,011 ) 0.79 Forfeited (53,507 ) 1.06 Outstanding at December 31, 2016 1,799,249 0.89 As of December 31, 2016 , 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 1.6 years . Performance units paying out in 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: 2016 2015 2014 Risk-free interest rate 0.96 % 0.95 % 0.63 % Look-back period 2.83 years 2.84 years 2.84 years Expected volatility 47.59 % 30.12 % 17.17 % Grant date fair value of performance units granted $ 0.63 $ 1.03 $ 1.16 The assumption for expected volatility of our unit price reflects the historical volatility of MPLX LP 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. Total Unit-Based Compensation Expense Total unit-based compensation expense for awards settling in MPLX LP common units was $10 million in 2016 , $4 million in 2015 and $3 million in 2014 . Approximately $15 million was charged to the MarkWest purchase price in 2015 for MPLX LP unit-based compensation awards granted in connection with the MarkWest Merger. MPC’s Stock-based Compensation Stock-based compensation expenses charged to MPLX LP under our employee services agreement with MPC were $5 million for 2016 and $1 million for 2015 and 2014 , respectively.

Lease Operations

Lease Operations	12 Months Ended
	Dec. 31, 2016
Leases [Abstract]
Leases	Lease Operations Based on the terms of certain natural gas gathering, transportation and processing agreements, the Partnership is considered to be the lessor under several implicit operating lease arrangements in accordance with GAAP. The Partnership’s primary implicit 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 2023 and will continue thereafter on a year to year basis until terminated by either party. Other significant 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 the Partnership 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 expire during 2023 and 2030. Based on the terms of the Partnership’s fee-based transportation services agreement with MPC, HSM is also considered to be a lessor of its marine equipment in accordance with GAAP. The Partnership’s revenue from its implicit lease arrangements, excluding executory costs, totaled approximately $464 million in 2016 , $89 million in 2015 and $14 million in 2014 . The Partnership’s implicit lease arrangements related to the processing facilities contain contingent rental provisions whereby the Partnership receives additional fees if the producer customer exceeds the monthly minimum processed volumes. During the years ended December 31, 2016 and 2015 , the Partnership received $7 million and less than $1 million , respectively, in contingent lease payments. The following is a schedule of minimum future rentals on the non-cancellable operating leases as of December 31, 2016 : (In millions) Intercompany Third Party Total 2017 $ 101 $ 197 $ 298 2018 101 200 301 2019 101 202 303 2020 101 201 302 2021 — 185 185 2022 and thereafter — 460 460 Total minimum future rentals $ 404 $ 1,445 $ 1,849 The following schedule summarizes the Partnership’s investment in assets held for operating lease by major classes as of December 31, 2016 and 2015 : December 31, (In millions) 2016 2015 Natural gas gathering and NGL transportation pipelines and facilities $ 650 $ 619 Natural gas processing facilities 844 753 Barges 388 360 Towing vessels 91 91 Construction in progress 219 110 Property, plant and equipment 2,192 1,933 Less: accumulated depreciation (266 ) (170 ) Total property, plant and equipment $ 1,926 $ 1,763

Asset Retirement Obligations

Asset Retirement Obligations	12 Months Ended
	Dec. 31, 2016
Asset Retirement Obligation Disclosure [Abstract]
Asset Retirement Obligation Disclosure [Text Block]	Asset Retirement Obligations The Partnership’s assets subject to AROs are primarily certain gas-gathering pipelines and processing facilities, a crude oil pipeline and other related pipeline assets. The Partnership also has land leases that require the Partnership to return the land to its original condition upon termination of the lease. The Partnership reviews current laws and regulations governing obligations for asset retirements and leases, as well as the Partnership’s leases and other agreements. The following is a reconciliation of the changes in the ARO from January 1, 2015 to December 31, 2016: (In millions) 2016 2015 ARO at beginning of period $ 17 $ — Liabilities assumed in conjunction with the MarkWest Merger — 15 Liabilities incurred 8 2 Adjustments to AROs (1 ) — Accretion expense 1 — ARO at end of period $ 25 $ 17 At December 31, 2016 and 2015 , there were no assets legally restricted for purposes of settling AROs. The AROs have been recorded as part of Deferred credits and other liabilities in the accompanying Consolidated Balance Sheets. In addition to recorded AROs, the Partnership has other AROs related to certain gathering, processing and other assets as a result of environmental and other legal requirements. The Partnership is not required to perform such work until it permanently ceases operations of the respective assets. Because the Partnership considers the operational life of these assets to be indeterminable, an associated ARO cannot be estimated and is not recorded.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies The Partnership 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 the Partnership has not recorded an accrued liability, the Partnership 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 – The Partnership 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, 2016 and 2015 , accrued liabilities for remediation totaled $1 million and $1 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, 2016 and 2015 , there was less than $1 million , respectively, in receivables from MPC for indemnification of environmental costs related to incidents occurring prior to the Initial Offering. In July 2015, representatives from the EPA and the United States Department of Justice conducted a raid on a MarkWest Liberty Midstream pipeline launcher/receiver site utilized for pipeline maintenance operations in Washington County, Pennsylvania pursuant to a search warrant issued by a magistrate of the United States District Court for the Western District of Pennsylvania. As part of this initiative, the U.S. Attorney’s Office for the Western District of Pennsylvania, proceeded with an investigation of MarkWest Liberty Midstream’s launcher/receiver, pipeline and compressor station operations. In response to the investigation, MarkWest initiated independent studies which demonstrated that there was no risk to worker safety and no threat of public harm associated with MarkWest Liberty Midstream’s launcher/receiver operations. These findings were supported by a subsequent inspection and review by the Occupational Safety and Health Administration. After providing these studies, and other substantial documentation related to MarkWest Liberty Midstream's pipeline and compressor stations, and arranging site visits and conducting several meetings with the government’s representatives, on September 13, 2016, the U.S. Attorney’s Office for the Western District of Pennsylvania rendered a declination decision, dropping its criminal investigation and declining to pursue charges in this matter. MarkWest Liberty Midstream continues to discuss with the EPA and the State of Pennsylvania civil enforcement allegations associated with permitting or other related regulatory obligations for its launcher/receiver and compressor station facilities in the region. In connection with these discussions, MarkWest Liberty Midstream received an initial proposal from the EPA to settle all civil claims associated with this matter for the combination of a proposed cash penalty of approximately $2.4 million and proposed supplemental environmental projects with an estimated cost of approximately $3.6 million . MarkWest Liberty Midstream will be submitting a response asserting that this action involves novel issues surrounding primarily minor source emissions from facilities that the agencies themselves considered de minimis were not the subject of regulation and consequently that the settlement proposal is excessive. MarkWest will continue to negotiate with EPA regarding the amount and scope of the proposed settlement. The Partnership is involved in a number of other environmental enforcement matters arising in the ordinary course of business. While the outcome and impact on MPLX LP 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 – In 2003, the State of Illinois brought an action against the Premcor Refining Group, Inc. (“Premcor”) and Apex Refining Company (“Apex”) asserting claims for environmental cleanup related to the refinery owned by these entities in the Hartford/Wood River, Illinois area. In 2006, Premcor and Apex filed third-party complaints against numerous owners and operators of petroleum products facilities in the Hartford/Wood River, Illinois area, including MPL. These complaints, which have been amended since filing, assert claims of common law nuisance and contribution under the Illinois Contribution Act and other laws for environmental cleanup costs that may be imposed on Premcor and Apex by the State of Illinois. On September 6, 2016, the trial court approved a settlement between Apex and the State of Illinois whereby Apex agreed to settle all claims against it for a $10 million payment. Premcor has objected to this ruling and is seeking an appeal. There are several third-party defendants in the litigation and MPL has asserted cross-claims in contribution against the various third-party defendants. This litigation is currently pending in the Third Judicial Circuit Court, Madison County, Illinois. While the ultimate outcome of these litigated matters remains uncertain, neither the likelihood of an unfavorable outcome nor the ultimate liability, if any, with respect to this matter can be determined at this time and the Partnership is unable to estimate a reasonably possible loss (or range of loss) for this litigation. Under the omnibus agreement, MPC will indemnify the Partnership for the full cost of any losses should MPL be deemed responsible for any damages in this lawsuit. The Partnership is also a party to a number of other lawsuits and other proceedings arising in the ordinary course of business. While the ultimate outcome and impact to the Partnership cannot be predicted with certainty, the Partnership believes the resolution of these other lawsuits and proceedings will not have a material adverse effect on its consolidated financial position, results of operations or cash flows. Guarantees – Over the years, the Partnership 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 the Partnership to perform upon the occurrence of a triggering event or condition. These guarantees and indemnifications are part of the normal course of selling assets. The Partnership 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. Contractual Commitments and Contingencies – At December 31, 2016 the Partnership’s contractual commitments to acquire property, plant and equipment totaled $588 million . In addition, from time to time and in the ordinary course of business, the Partnership and its affiliates provide guarantees of the Partnership’s subsidiaries payment and performance obligations in the G&P segment. Our contractual commitments at December 31, 2016 were primarily related to plant expansion projects for the Marcellus and Southwest Operations and the Cornerstone Pipeline project. Certain natural gas processing and gathering arrangements require the Partnership 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, 2016 , management does not believe there are any indications that the Partnership 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. Lease and Other Contractual Obligations – The Partnership executed transportation and terminalling agreements that obligate us to minimum volume, throughput or payment commitments over the terms of the agreements, which range from three to ten years. After the minimum volume commitments are met in the transportation and terminalling agreements, the Partnership pays additional amounts based on throughput. There are escalation clauses in the transportation and terminalling agreements, which are based on CPI adjustments. The minimum future payments under these agreements as of December 31, 2016 are as follows: (In millions) 2017 $ 46 2018 62 2019 61 2020 61 2021 61 2022 and thereafter 317 Total $ 608 The Partnership has various non-cancellable operating lease agreements and a long-term propane storage agreement expiring at various times through fiscal year 2040. Most of these leases include renewal options. The Partnership also leases certain pipelines under a capital lease that has a fixed price purchase option in 2020. Future minimum commitments as of December 31, 2016 , 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) Capital Obligations Operating Obligations 2017 $ 1 $ 61 2018 1 51 2019 2 42 2020 5 37 2021 — 36 Later years — 76 Total minimum lease payments 9 $ 303 Less: imputed interest costs 1 Present value of net minimum lease payments $ 8 Operating lease rental expense was: (In millions) 2016 2015 2014 Minimum rental expense $ 57 $ 21 $ 17 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) 2017 $ 17 2018 17 2019 17 2020 17 2021 17 2022 and thereafter 143 Total minimum payments 228 Less: Services element 87 Less: Interest 45 Total SMR liability 96 Less: Current portion of SMR liability 5 Long-term portion of SMR liability $ 91

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2016
Subsequent Events [Abstract]
Subsequent Events [Text Block]	Subsequent Event On February 6, 2017, MarkWest Liberty Midstream executed definitive agreements with Antero Midstream LLC, and affiliate of Antero Midstream LP (“Antero Midstream”) for the formation of a joint venture, Sherwood Midstream LLC (“Sherwood Midstream”), to process natural gas at the Sherwood Complex and fractionate natural gas liquids at the Hopedale Complex. Sherwood Midstream is owned 50 percent by Antero Midstream and 50 percent by MarkWest Liberty Midstream. These transactions were effective as of January 1, 2017. In connection with these transactions, MarkWest Liberty Midstream contributed approximately $134 million of assets to Sherwood Midstream, comprised of the three 200 mmcf/d gas processing plants under construction at the Sherwood Complex. MarkWest Liberty Midstream will operate Sherwood Midstream’s gas processing facilities and will also retain sole and exclusive ownership and operation of the existing six 200 mmcf/d gas processing plants at the Sherwood Complex. In addition, MarkWest Liberty Midstream and Sherwood Midstream entered into a joint venture, Sherwood Midstream Holdings LLC (“Sherwood Midstream Holdings”), to own certain infrastructure at the Sherwood Complex that is shared by and supports the operation of both the Sherwood Midstream and MarkWest Liberty Midstream gas processing plants. MarkWest Liberty Midstream contributed approximately $207 million of assets to Sherwood Midstream Holdings, and as of February 6, 2017, MarkWest Liberty Midstream owned a 79 percent ownership interest in Sherwood Midstream Holdings, and the remaining 21 percent ownership interest was owned by Sherwood Midstream. Sherwood Midstream also purchased an interest in 20 mbpd of existing propane and heavier NGL fractionation capacity owned by MarkWest Ohio Fractionation Company, L.L.C. (“Ohio Fractionation”), a subsidiary of MarkWest Liberty Midstream, at the Hopedale Complex for $125 million . Sherwood Midstream will also have the option to purchase an interest in future fractionation train expansions at the Hopedale Complex, subject to the production of incremental NGLs from Sherwood Midstream’s processing facilities. Ohio Fractionation and MarkWest Utica EMG will continue to own and operate the remaining portion of the Hopedale Complex, including all rail and marketing infrastructure, as well as the NGL pipelines connecting MarkWest Liberty Midstream’s and MarkWest Utica EMG’s gas processing plants to the Hopedale Complex. In connection with the foregoing transactions, Antero Midstream made an initial capital contribution to Sherwood Midstream of approximately $154 million , and it is expected that MarkWest Liberty Midstream and Antero Midstream will each contribute 50 percent of capital needed to fund Sherwood Midstream’s operations. On February 10, 2017, the Partnership completed a public offering of $1.25 billion aggregate principal amount of 4.125 percent unsecured senior notes due March 2027 (the “2027 Senior Notes”) and $1.0 billion aggregate principal amount of 5.200 percent unsecured senior notes due March 2047 (the “2047 Senior Notes” and, collectively with the 2027 Senior Notes, the “New Senior Notes”). The 2027 Senior Notes and the 2047 Senior Notes were offered at a price to the public of 99.834 percent and 99.304 percent of par, respectively, at an interest rate of 4.125 percent and 5.200 percent , respectively. The Partnership intends to use the net proceeds from this offering for general partnership purposes, which may include, from time to time, acquisitions (including the previously announced planned dropdown of assets from MPC, the acquisition of the Ozark pipeline, and the acquisition of a partial, indirect equity interest in the Bakken Pipeline system) and capital expenditures. On February 13, 2017, the Partnership announced that it has entered into an asset purchase agreement with Enbridge Pipelines (Ozark) LLC (“Enbridge Ozark”), under which an affiliate of Pipe Line Holdings has agreed to purchase Ozark pipeline for approximately $220 million from Enbridge Ozark. The Ozark pipeline is a 433-mile , 22-inch crude oil pipeline originating in Cushing, Oklahoma, and terminating in Wood River, Illinois, and capable of transporting approximately 230,000 barrels per day. This purchase transaction is expected to close in the first quarter of 2017. On February 15, 2017, MPLX LP closed on its previously announced intent to participate in a joint venture with Enbridge Energy Partners L.P. (“Enbridge Energy Partners”) to acquire a 9.1875 percent indirect interest in the Dakota Access Pipeline (“DAPL”) and Energy Transfer Crude Oil Company Pipeline (“ETCOP”) projects, collectively referred to as the Bakken Pipeline system, from Energy Transfer Partners, L.P. (“ETP”) and Sunoco Logistics Partners, L.P. (“SXL”) for $500 million . The Bakken Pipeline system is currently expected to deliver in excess of 470,000 barrels per day 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. ETP and SXL collectively own a 75 percent interest in each of the two joint ventures that are developing the Bakken Pipeline system. MPLX LP and Enbridge Energy Partners intend to form a new joint venture to acquire 49 percent of ETP and SXL’s 75 percent indirect interest in the Bakken Pipeline system. MPLX LP will own 25 percent of this new joint venture with Enbridge, which results in its 9.1875 percent indirect ownership interest in the Bakken Pipeline system. MPLX LP expects to account for its investment using the equity method of accounting.

Select Quarterly Financial Data

Select Quarterly Financial Data	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Select Quarterly Financial Data	Select Quarterly Financial Data (Unaudited) 2016 (3) 2015 (In millions, except per unit data) 1st Qtr. (1) 2nd Qtr. (2) 3rd Qtr. 4th Qtr. 1st Qtr. 2nd Qtr. 3rd Qtr. 4th Qtr. (3) Total revenues and other income $ 609 $ 564 $ 703 $ 714 $ 201 $ 213 $ 214 $ 333 Income from operations 27 76 207 197 74 82 68 74 Net (loss) income (37 ) 20 143 132 68 76 63 42 Net (loss) income attributable to MPLX LP (60 ) 19 141 133 46 51 41 18 Net (loss) income attributable to MPLX LP per limited partner unit: Common - basic $ (0.33 ) $ (0.11 ) $ 0.22 $ 0.17 $ 0.46 $ 0.50 $ 0.41 $ (0.14 ) Common - diluted (0.33 ) (0.11 ) 0.21 0.17 0.46 0.50 0.41 (0.14 ) Subordinated - basic and diluted — — — — 0.46 0.50 — — Cash distributions declared per limited partner common unit $ 0.5050 $ 0.5100 $ 0.5150 $ 0.5200 $ 0.4100 $ 0.4400 $ 0.4700 $ 0.5000 Distributions declared: Limited partner units - Public $ 127 $ 131 $ 135 $ 140 $ 10 $ 10 $ 11 $ 120 Limited partner units - MPC 29 41 44 45 23 25 27 29 General partner units - MPC 4 4 5 5 1 1 1 3 Incentive distribution rights - MPC 40 46 49 52 3 6 8 37 Redeemable preferred units — 9 16 16 — — — — Total distributions declared $ 200 $ 231 $ 249 $ 258 $ 37 $ 42 $ 47 $ 189 (1) First quarter 2016 results included goodwill impairment expense of $129 million . See Note 18 for more information. (2) Second quarter 2016 results included impairment expense related to equity method investments of $89 million . See Note 5 for more information. (3) These amounts include results from the MarkWest Merger which closed on December 4, 2015. See Note 4 for more information on the MarkWest Merger.

Description of the Business a32

Description of the Business and Basis of Presentation Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Consolidation, Policy [Policy Text Block]	Basis of Presentation – The Partnership’s consolidated financial statements include all majority-owned and controlled subsidiaries. For non-wholly-owned consolidated subsidiaries, the interests owned by third parties, including MPC, have been recorded as Noncontrolling interest in the accompanying Consolidated Balance Sheets. Intercompany investments, accounts and transactions have been eliminated. The Partnership’s investments in which the Partnership exercises significant influence but does not control and does not have a controlling financial interest are accounted for using the equity method. The Partnership’s investments in a VIE in which the Partnership exercises significant influence but does not control and is not the primary beneficiary are also accounted for using the equity method. The accompanying consolidated financial statements of the Partnership have been prepared in accordance with GAAP.

Summary of Principal Accounti33

Summary of Principal Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2016
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, growth-oriented master limited partnership formed by Marathon Petroleum Corporation. MPLX LP and its subsidiaries (collectively, the “Partnership”) are engaged in the gathering, processing and transportation of natural gas; the gathering, transportation, fractionation, storage and marketing of NGLs; and the gathering, transportation and storage of crude oil and refined petroleum products. The Partnership’s principal executive office is located in Findlay, Ohio. The Partnership was formed on March 27, 2012 as a Delaware limited partnership and completed its initial public offering (the “Initial Offering”) on October 31, 2012 . On December 4, 2015 , a wholly-owned subsidiary of the Partnership merged with MarkWest Energy Partners L.P. (the “MarkWest Merger”), which is one of the largest processors of natural gas in the United States and the largest processor and fractionator in the Marcellus and Utica shale plays. This acquisition is discussed further in Note 4 . Effective March 31, 2016 , the Partnership acquired MPC’s inland marine business, Hardin Street Marine LLC. The acquisition is also described further in Note 4 . Unless the context otherwise requires, references in this report to “MPLX LP,” the “Partnership,” or like terms refer to MPLX LP and its subsidiaries, including MPLX Operations LLC (“MPLX Operations”), MPLX Terminal and Storage LLC (“MPLX Terminal and Storage”), MarkWest Energy Partners, L.P. (“MarkWest”), MarkWest Hydrocarbon, L.L.C. (“MarkWest Hydrocarbon”), MPLX Pipe Line Holdings LLC (“Pipe Line Holdings”), Marathon Pipe LLC (“MPL”), Ohio River Pipe Line LLC (“ORPL”) and Hardin Street Marine LLC (“HSM”). References to “MPC” refer collectively to Marathon Petroleum Corporation and its subsidiaries, other than the Partnership. References to “Predecessor” refer collectively to HSM’s related assets, liabilities and results of the operations. The Partnership’s business consists of two segments: Logistics and Storage (“L&S”) and Gathering and Processing (“G&P”). See Note 10 for additional information regarding operations. Basis of Presentation – The Partnership’s consolidated financial statements include all majority-owned and controlled subsidiaries. For non-wholly-owned consolidated subsidiaries, the interests owned by third parties, including MPC, have been recorded as Noncontrolling interest in the accompanying Consolidated Balance Sheets. Intercompany investments, accounts and transactions have been eliminated. The Partnership’s investments in which the Partnership exercises significant influence but does not control and does not have a controlling financial interest are accounted for using the equity method. The Partnership’s investments in a VIE in which the Partnership exercises significant influence but does not control and is not the primary beneficiary are also accounted for using the equity method. The accompanying consolidated financial statements of the Partnership have been prepared in accordance with GAAP.
Consolidation, Policy [Policy Text Block]	Basis of Presentation – The Partnership’s consolidated financial statements include all majority-owned and controlled subsidiaries. For non-wholly-owned consolidated subsidiaries, the interests owned by third parties, including MPC, have been recorded as Noncontrolling interest in the accompanying Consolidated Balance Sheets. Intercompany investments, accounts and transactions have been eliminated. The Partnership’s investments in which the Partnership exercises significant influence but does not control and does not have a controlling financial interest are accounted for using the equity method. The Partnership’s investments in a VIE in which the Partnership exercises significant influence but does not control and is not the primary beneficiary are also accounted for using the equity method. The accompanying consolidated financial statements of the Partnership have been prepared in accordance with GAAP.
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; valuing inventory; 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 – The Partnership’s assessment of each of the revenue recognition criteria as they relate to its revenue producing activities are as follows: persuasive evidence of an arrangement exists, delivery, the fee is fixed or determinable and collectability is reasonably assured. It is upon delivery or title transfer to the customer that the Partnership meets all four revenue recognition criteria and it is at such time that the Partnership recognizes Product sales . Additionally, it is upon completion of services provided that the Partnership meets all four revenue recognition criteria and it is at such time that the Partnership recognizes Service revenue . L&S Segment Revenues are recognized in the L&S segment for crude oil and product pipeline transportation based on the delivery of actual volumes transported at regulated tariff rates. When MPC ships volumes on our pipeline systems under a joint tariff with a third party, those revenues are recorded as sales and other operating revenues, and not as sales to related parties, because we receive payment from the third party. Revenues are recognized for crude oil and refined product storage as performed based on contractual rates. Operating fees received for operating pipeline systems are recognized as a component of other income in the period the service is performed. All such amounts are reported as Service revenue on the Consolidated Statements of Income. Under our MPC transportation services agreements, if MPC fails to transport its minimum throughput volumes during any quarter, then MPC will pay us a deficiency payment equal to the volume of the deficiency multiplied by the tariff rate then in effect. MPC may then apply the amount of any such deficiency payments as a credit for volumes transported on the applicable pipeline system in excess of its minimum volume commitment during the following four or eight quarters under the terms of the applicable transportation services agreement. The deficiency payments are initially recorded as Deferred revenue - related parties in the Consolidated Balance Sheets. The Partnership recognizes revenues for the deficiency payments at the earlier of when credits are used for volumes transported in excess of minimum volume commitments, when it becomes impossible to physically transport volumes necessary to utilize the credits or upon the expiration of the applicable four or eight quarter period. The use or expiration of the credits is a decrease in Deferred revenue - related parties . In addition, capital projects the Partnership undertakes at the request of MPC are reimbursed in cash and recognized in income over the remaining term of the applicable transportation services agreements. HSM is a provider of marine transportation services for its customers and does not assume ownership of the products it transports. The Partnership transports cargo from a designated origin to a designated destination at a pre-established fixed rate. Costs incurred as part of moving the products are paid by the customer subsequent to April 1, 2016. G&P Segment The Partnership generates the majority of its G&P segment revenues from natural gas gathering, transportation and processing; NGL gathering, transportation, fractionation, marketing and storage; and crude oil gathering and transportation. The Partnership disaggregates revenue as Product sales , Service revenue and Rental income on the Consolidated Statements of Income. Revenue is reported as follows: • Product sales – Product sales represent the sale of NGLs, condensate and natural gas. The product is primarily obtained as consideration for or related to providing midstream services. • Service revenue – Service revenue represents all other revenue generated as the result of performing the services listed above. • Rental income – Rental income represents revenue generated as the result of implicit operating lease arrangements. The Partnership enters into a variety of contract types in order to generate Product sales and Service revenue. The Partnership provides services under the following different types of arrangements: • Fee-based arrangements – Under fee-based arrangements, the Partnership 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 gathering and transportation of crude oil. The revenue the Partnership earns from these arrangements is generally directly related to the volume of natural gas, NGLs or crude oil that flows through the Partnership’s systems and facilities and is not normally directly dependent on commodity prices. In certain cases, the Partnership’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. In certain instances when specifically stated in the contract terms, the Partnership 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 the Partnership is the principal in the transaction. • Percent-of-proceeds arrangements – Under percent-of-proceeds arrangements, the Partnership 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, the Partnership delivers an agreed-upon percentage of the residue gas and NGLs to the producer (take-in-kind arrangements) and sells the volumes the Partnership retains to third parties. Revenue from these arrangements is reported on a gross basis where the Partnership acts as the principal, as the Partnership has physical inventory risk and does not earn a fixed dollar amount. The agreed-upon percentage paid to the producer is reported as Purchased product costs on the Consolidated Statements of Income. Revenue is recognized on a net basis when the Partnership acts as an agent and earns a fixed dollar amount of physical product and does not have risk of loss of the gross amount of gas and/or NGLs. Percent-of-proceeds revenue is reported as Product sales on the Consolidated Statements of Income. • Keep-whole arrangements – Under keep-whole arrangements, the Partnership 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, the Partnership must either purchase natural gas at market prices for return to producers or make cash payment to the producers equal to the energy content of this natural gas. Certain keep-whole arrangements also have provisions that require the Partnership 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. 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 the Partnership is the principal in the arrangement. Natural gas purchased to return to the producer and shared NGL profits are recorded as Purchased product costs in the Consolidated Statements of Income. • Percent-of-index arrangements – Under percent-of-index arrangements, the Partnership purchases natural gas at either (1) a percentage discount to a specified index price, (2) a specified index price less a fixed amount or (3) a percentage discount to a specified index price less an additional fixed amount. The Partnership then gathers and delivers the natural gas to pipelines where the Partnership resells the natural gas at the index price or at a different percentage discount to the index price. Revenue generated from percent-of-index arrangements are reported as Product sales on the Consolidated Statements of Income and are recognized on a gross basis as the Partnership purchases and takes title to the product prior to sale and is the principal in the transaction. In many cases, the Partnership 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 keep-whole arrangements, percent-of-proceeds arrangements or percent-of-index arrangements, the Partnership records such fees as Service revenue on the Consolidated Statements of Income. The terms of the Partnership’s contracts vary based on gas quality conditions, the competitive environment when the contracts are signed and customer requirements. Amounts billed to customers for shipping and handling, including fuel costs, are included in Product sales on the Consolidated Statements of Income, except under contracts where we are acting as an agent. Shipping and handling costs associated with product sales are included in Purchased product costs on the Consolidated Statements of Income. Taxes collected from customers and remitted to the appropriate taxing authority are excluded from revenue. Facility expenses and depreciation represent those expenses related to operating our various facilities and are necessary to provide both Product sales and Service revenue . Based on the terms of certain natural gas gathering, transportation and processing agreements, the Partnership is considered to be the lessor under several implicit operating lease arrangements in accordance with GAAP. The Partnership’s primary implicit 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 customer 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. Other significant 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 the Partnership earns minimum monthly fees for providing processing services to a single producer using a dedicated processing plant. Revenues 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. Similarly, the Partnership is considered to be the lessor under implicit operating lease arrangements with MPC in accordance with GAAP. The Partnership’s primary implicit lease operations with MPC relate to the transportation services agreement between HSM and MPC. Revenue related to this agreement is recorded as Rental income-related parties on the Consolidated Statements of Income. The rental cost of sales related to the HSM implicit lease is depreciation of the HSM assets. All other services are provided to MPC on an as-needed basis and recorded as Service revenue-related parties on the Consolidated Statements of Income.
Revenue and Expense Accruals	Revenue and Expense Accruals – The Partnership 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 the Partnership’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. The Partnership 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 the Partnership’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. At December 31, 2016 and 2015 , the amount of restricted cash included in Other current assets on the Consolidated Balance Sheets was $5 million and $9 million , respectively.
Receivables	Receivables – Receivables primarily consist of customer accounts receivable, which are recorded at the invoiced amount and generally do not bear interest. Management reviews the allowance quarterly. Past-due balances over 90 days and other higher risk amounts are 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.
Inventory	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 weighted-average cost or net realizable value. Materials and supplies are stated at the lower of cost or net realizable value. Cost for materials and supplies is determined primarily using the weighted-average cost method. Processed natural gas and NGL inventories include material, labor and overhead. Shipping and handling costs related to purchases of natural gas and NGLs are included in inventory.
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. Expenditures that extend the useful lives of assets are capitalized. Repairs, maintenance and renewals that do not extend the useful lives of the assets are expensed as incurred. Interest costs for the construction or development of long-lived assets are capitalized and amortized over the related asset’s estimated useful life. Leasehold improvements are amortized over the shorter of the useful life or lease term. When items of property, plant and equipment are sold or otherwise disposed of, any gains or losses are reported in 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. The Partnership evaluates transactions involving the sale of property, plant and equipment to determine if they are, in-substance, the sale of real estate. Tangible assets may be considered real estate if the costs to relocate them for use in a different location exceed 10 percent of the asset’s fair value. Financial assets, primarily in the form of ownership interests in an entity, may be in-substance real estate based on the significance of the real estate in the entity. Sales of real estate are not considered consummated if the Partnership maintains an interest in the asset after it is sold or has certain other forms of continuing involvement. Significant judgment is required to determine if a transaction is a sale of real estate and if a transaction has been consummated. If a sale of real estate is not considered consummated, the Partnership cannot record the transaction as a sale and must account for the transaction under an alternative method of accounting such as a financing or leasing arrangement. The Partnership’s policy is to evaluate whether there has been an impairment in the value of long-lived assets when certain events indicate that the remaining balance may not be recoverable. Qualitative and quantitative information is reviewed in order to determine if a triggering event has occurred or if an impairment indicator exists. If we determine that a triggering event has occurred we would complete a full impairment analysis. If we determine that the carrying value of a reporting unit is not recoverable, a loss is recorded for the difference between the fair value and the carrying value. The Partnership evaluates the carrying value of its property, plant and equipment on at least a segment level and at lower levels where the cash flows for specific assets can be identified, which generally is the component level for our G&P and L&S segments. Management considers the dedicated volume of producer customers’ reserves and future NGL product and natural gas prices to estimate cash flows. The amount of additional producer customers’ reserves developed by future drilling activity depends, in part, on expected commodity prices. Projections of producer customers’ reserves, drilling activity and future commodity prices are inherently subjective and contingent upon a number of variable factors, many of which are difficult to forecast. Any significant variance in any of these assumptions or factors could materially affect future cash flows, which could result in the impairment of an asset group. For assets identified to be disposed of in the future, the carrying value of these assets is compared to the estimated fair value, less the cost to sell, to determine if impairment is required. Until the assets are disposed of, an estimate of the fair value is redetermined when related events or circumstances change.
Intangibles	Intangibles – The Partnership’s intangibles are mainly comprised of customer contracts and related relationships acquired in business combinations and recorded under the acquisition method of accounting at their estimated fair values at the date of acquisition. Using relevant information and assumptions, management determines the fair value of acquired identifiable intangible assets. Fair value was calculated using the multi-period excess earnings method under the income approach for each reporting unit. This valuation method is based on first forecasting gross profit for the existing customer base and then applying expected attrition rates. The operating cash flows are calculated by determining the costs required to generate gross profit from the existing customer base. The key assumptions include overall gross profit growth, attrition rate of existing customers over time and the discount rate. Amortization of intangibles with definite lives is calculated using the straight-line method which is reflective of benefit pattern in which the estimated economic benefit is expected to be received over the estimated useful life of the intangible asset. The estimated economic life is determined by assessing the life of the assets related to the contracts and relationships, likelihood of renewals, the projected reserves, competitive factors, regulatory or legal provisions and maintenance and renewal costs. Intangibles with indefinite lives 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. The Partnership has no intangibles with indefinite lives.
Goodwill	Goodwill – Goodwill is the cost of an acquisition less the fair value of the net identifiable assets and noncontrolling interest, if any, of the acquired business. The Partnership evaluates goodwill for impairment annually as of November 30, and whenever events or changes in circumstances indicate it is more likely than not that the fair value of a reporting unit is less than its carrying amount. The Partnership determined its reporting units based on the criteria included in ASC 280 which requires a component to be a business with discrete financial information that management reviews on a regular basis. Management reviews its determination of reporting units on an annual basis. The Partnership may first assess qualitative factors to evaluate whether it is more likely than not that the fair value of a reporting unit is less than its carrying amount as the basis for determining whether it is necessary to perform the two-step goodwill impairment test. The Partnership may elect to perform the two-step goodwill impairment test without completing a qualitative assessment. If a two-step process goodwill impairment test is elected or required, the first step involves comparing the fair value of the reporting unit to which goodwill has been allocated, with its carrying amount. If the carrying amount of a reporting unit exceeds its fair value, the second step of the process involves comparing the implied fair value to the carrying value of the goodwill for that reporting unit. If the carrying value of the goodwill of a reporting unit exceeds the implied fair value of that goodwill, the excess of the carrying value over the implied fair value is recognized as an impairment loss. During 2016 , impairment charges of approximately $130 million were recorded. There were no impairments as a result of the Partnership’s November 30, 2015 and November 30, 2016 goodwill impairment analyses.
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. The Partnership 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. A receivable is recorded for environmental costs indemnified by MPC.
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. The Partnership 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 the Partnership 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 in 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. The Partnership 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. The Partnership uses evidence of a loss in value to identify if an investment has an other than a temporary decline.
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 – Derivative instruments (including derivative instruments embedded in other contracts) are recorded at fair value and are reflected in the Consolidated Balance Sheets on a net basis, as either an asset or liability, as they are governed by the master netting agreements. The Partnership discloses the fair value of all of its derivative instruments under the captions Other noncurrent assets , Other current liabilities and Deferred credits and other liabilities on the Consolidated Balance Sheets, inclusive of option premiums, if any. Changes in the fair value of derivative instruments are reported in the Consolidated Statements of Income in accounts related to the item whose value or cash flows are being managed. All derivative instruments were 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. 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, 2016 , 2015 and 2014 , the Partnership did not designate any hedges or designate any contracts as normal purchases and normal sales, with the exception of electricity contracts, for which the normal purchases and normal sales designation was elected during the year ended December 31, 2016 .
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 a fair value hierarchy established by GAAP, which classifies the inputs used to measure fair value into the following levels: • Level 1 inputs to the valuation methodology are quoted prices (unadjusted) for identical assets or liabilities in active markets. • Level 2 inputs to the valuation methodology include quoted prices for similar assets and liabilities in active markets and inputs that are observable for the asset or liability, either directly or indirectly, for substantially the full term of the financial instrument. • Level 3 inputs to the valuation methodology are unobservable and significant to the fair value measurement. 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 determination to classify a financial instrument within Level 3 of the valuation hierarchy is based upon the significance of the unobservable inputs to the overall fair value measurement. However, Level 3 financial instruments typically include, in addition to the unobservable or Level 3 inputs, observable inputs (that is, inputs that are actively quoted and can be validated to external sources); accordingly, the gains and losses for Level 3 financial instruments include changes in fair value due in part to observable inputs that are part of the valuation methodology. Level 3 financial instruments include crude oil options, all NGL derivatives and the embedded derivatives in commodity contracts discussed in Note 15 as they have significant unobservable inputs. The methods and assumptions described above may produce a fair value that may not be realized in future periods upon settlement. Furthermore, while the Partnership 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 – The Partnership issues phantom units under its share-based compensation plan as described further in Note 20 . 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, the Partnership may issue new common units, acquire common units in the open market or use common units already owned by the general partner.
Tax Effect of Share based Compensation	Tax Effects of Share-Based Compensation – The Partnership 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 in the accompanying Consolidated Balance Sheets.
Income taxes	Income Taxes – The Partnership is not a taxable entity for federal income tax purposes. As a result of the MarkWest Merger, discussed further in Note 4 , MarkWest was the surviving entity for tax purposes. MarkWest is not a taxable entity for federal income tax purposes. As such, the Partnership does not directly pay federal income tax. Taxes on the Partnership’s net income generally are borne by its partners through the allocation of taxable income. The Partnership’s taxable income or loss, which may vary substantially from the net income or loss reported in the Consolidated Statements of Income, is includable in the federal income tax returns of each partner. The Partnership and certain legal entities are, however, taxable entities under certain state jurisdictions. As a result of the Class A Reorganization discussed in Note 8 , MarkWest Hydrocarbon (MarkWest Hydrocarbon, Inc. prior to the Class A Reorganization) is no longer a tax paying entity for federal income tax purposes or for the majority of states that impose an income tax effective September 1, 2016. Prior to the Class A Reorganization, in addition to paying tax on its own earnings, MarkWest Hydrocarbon recognized a tax expense or a tax benefit on its proportionate share of Partnership income or loss resulting from MarkWest Hydrocarbon’s ownership of Class A units of the Partnership, even though for financial reporting purposes such income or loss was eliminated in consolidation. The Class A units represented limited partner interests with the same rights as common units except that the Class A units did not have voting rights, except as required by law. Class A units were not treated as outstanding common units in the Consolidated Balance Sheets as they were eliminated in the consolidation of MarkWest Hydrocarbon. The deferred income tax component prior to the reorganization related to the change in the temporary book to tax basis difference in the carrying amount of the investment in the Partnership which resulted primarily from timing differences in MarkWest Hydrocarbon’s proportionate share of the book income or loss as compared with the MarkWest Hydrocarbon’s proportionate share of the taxable income or loss of the Partnership. The Partnership 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.
Net income per limited partner unit	Distributions – In preparing the Consolidated Statements of Equity, net income attributable to MPLX LP is allocated to Preferred unitholders based on a fixed distribution schedule, as discussed in Note 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 incentive distribution rights are made, earnings equal to the amount of those distributions are 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 – The Partnership 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, subordinated units, general partner units, Preferred units, certain equity-based compensation awards and incentive distribution rights. Class B units are considered to be a separate class of common units that do 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 Preferred unitholders based on a fixed distribution schedule and subsequently allocated to remaining unitholders in accordance with their respective ownership percentages. However, when distributions related to the incentive distribution rights are 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. In preparing net income per limited partner units, during periods in which a net loss attributable to the Partnership is reported or periods in which the total distributions exceed the reported net income attributable to the Partnership’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 the Partnership’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 the Partnership’s unitholders, after deducting amounts that are allocable to the outstanding equity-based compensation awards, Preferred units, and incentive distribution rights, is a loss as the impact would be anti-dilutive.
Business Combinations	Business Combinations – The Partnership 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. For all material acquisitions, management engages an independent valuation specialist to assist with the determination of fair value of the assets acquired, liabilities assumed, noncontrolling interest, 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, the Partnership will record any material adjustments to the initial estimate based on new information obtained about facts and circumstances that existed as of the acquisition date. An income, market or cost valuation method may be utilized to estimate the fair value of the assets acquired, liabilities assumed, and noncontrolling interest, 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. See Note 4 for more information about the MarkWest Merger.
Accounting for Changes in Ownership Interests in Subsidiaries	Accounting for Changes in Ownership Interests in Subsidiaries – The Partnership’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 in 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 which 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.

Acquisition (Tables)

Acquisition (Tables)	12 Months Ended
	Dec. 31, 2016
Business Acquisition [Line Items]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Table Text Block]	Changes in MPLX LP’s equity resulting from changes in its ownership interest in Pipe Line Holdings were as follows: (In millions) 2015 2014 Net income attributable to MPLX LP $ 156 $ 121 Transfer to noncontrolling interest: Decrease in general partner-MPC equity for purchases of additional interest in Pipe Line Holdings (6 ) (638 ) Change from net income attributable to MPLX LP and transfer to noncontrolling interest $ 150 $ (517 )
Business Combination Disclosure [Text Block]	Acquisitions Acquisition of Hardin Street Marine LLC On March 14, 2016, the Partnership entered into a Membership Interests Contribution Agreement (the “Contribution Agreement”) with MPLX GP LLC (“MPLX GP”), MPLX Logistics Holdings LLC and MPC Investment LLC (“MPC Investment”), each a wholly-owned subsidiary of MPC, related to the acquisition of HSM, MPC’s inland marine business, from MPC. Pursuant to the Contribution Agreement, the transaction was valued at $600 million , consisting of a fixed number of common units and general partner units of 22,534,002 and 459,878 , respectively. The general partner units maintain MPC’s two percent general partner interest in the Partnership. The acquisition closed on March 31, 2016 and the fair value of the common units and general partner units issued was $669 million and $14 million , respectively, as recorded on the Consolidated Statements of Equity. MPC agreed to waive distributions in the first quarter of 2016 on MPLX LP common units issued in connection with this transaction. MPC did not receive general partner distributions or incentive distribution rights that would have otherwise accrued on such MPLX LP common units with respect to the first quarter distributions. The value of these waived distributions was $15 million . The inland marine business, comprised of 18 tow boats and 205 barges which transport light products, heavy oils, crude oil, renewable fuels, chemicals and feedstocks in the Midwest and U.S. Gulf Coast regions, accounted for nearly 60 percent of the total volumes MPC shipped by inland marine vessels as of March 31, 2016. The Partnership accounts for HSM as a reporting unit of the L&S segment. The acquisition from MPC was a transfer between entities under common control. As an entity under common control with MPC, the Partnership recorded the assets acquired from MPC on its consolidated Balance Sheets at MPC’s historical basis instead of fair value. Transfers of businesses between entities under common control require prior periods to be retrospectively adjusted to furnish comparative information. Accordingly, the Partnership has retrospectively adjusted the historical financial results for all periods to include HSM. Purchase of MarkWest Energy Partners, L.P. On December 4, 2015 , a wholly-owned subsidiary of the Partnership merged with MarkWest. Each common unit of MarkWest issued and outstanding immediately prior to the effective time of the MarkWest Merger was converted into a right to receive 1.09 common units representing limited partner interests in MPLX LP, plus a one-time cash payment of $6.20 per unit. Each Class B unit of MarkWest issued and outstanding immediately prior to the effective time of the MarkWest Merger was converted into the right to receive one Class B unit of MPLX LP. Each Class B unit of MPLX LP will convert into 1.09 common units of MPLX LP and the right to receive $6.20 in cash, and the conversion of the Class B units will occur in equal installments, the first of which occurred on July 1, 2016 and the second of which will occur on July 1, 2017. MPC contributed approximately $1.3 billion of cash to the Partnership to pay the aggregate cash consideration to MarkWest unitholders, without receiving any new equity in exchange. At closing, MPC made a payment of $1.2 billion to MarkWest common unitholders and the remaining $50 million is payable in equal amounts, the first of which was paid in July 2016 and the second of which will be paid in July 2017, in connection with the conversion of the remaining outstanding Class B units to MPLX LP common units. The Partnership’s financial results reflect the results MarkWest from the date of the acquisition. The components of the fair value of consideration transferred are as follows: (In millions) Fair value of units issued $ 7,326 Cash 1,230 Paid/payable to MarkWest Class B unitholders 50 Total fair value of consideration transferred $ 8,606 The following table summarizes the final purchase price allocation. Subsequent to December 31, 2015, additional analysis was completed and adjustments were made to the preliminary purchase price allocation as noted in the table below. The fair value of assets acquired and liabilities and noncontrolling interests assumed at the acquisition date as of December 31, 2016, are as follows: (In millions) As Originally Reported Adjustments As Adjusted Cash and cash equivalents $ 12 $ — $ 12 Receivables 164 — 164 Inventories 33 (1 ) 32 Other current assets 44 — 44 Equity method investments 2,457 143 2,600 Property, plant and equipment 8,474 43 8,517 Intangibles 468 65 533 Other noncurrent assets 5 — 5 Total assets acquired 11,657 250 11,907 Accounts payable 322 — 322 Accrued liabilities 13 6 19 Accrued taxes 21 — 21 Other current liabilities 44 — 44 Long-term debt 4,567 — 4,567 Deferred income taxes 374 3 377 Deferred credits and other liabilities 151 — 151 Noncontrolling interest 13 — 13 Total liabilities and noncontrolling interest assumed 5,505 9 5,514 Net assets acquired excluding goodwill 6,152 241 6,393 Goodwill 2,454 (241 ) 2,213 Net assets acquired $ 8,606 $ — $ 8,606 Adjustments to the preliminary purchase price stem mainly from additional information obtained by management in the first and second quarters of 2016 about facts and circumstances that existed at the acquisition date, including updates to forecasted employee benefit costs, maintenance capital expenditures and completion of certain valuations to determine the underlying fair value of certain acquired assets. The adjustment to intangibles mainly relates to a misstatement in the original preliminary purchase price allocation. The correction of the error resulted in a $68 million reduction to the carrying value of goodwill and an offsetting increase of $64 million in intangibles and $2 million in each of equity method investments and property, plant and equipment. Management concluded that the correction of the error is immaterial to the consolidated financial statements of all periods presented. As further discussed in Note 18 , in the first quarter of 2016 the Partnership recorded a goodwill impairment charge based on the implied fair value of goodwill as of the interim impairment analysis date. During the second quarter of 2016, the Partnership finalized its analysis of the final purchase price allocation. The completion of the purchase price allocation resulted in a refinement of the impairment expense recorded, as more fully discussed in Note 18 . The increase to the fair value of intangibles and property, plant and equipment noted above resulted in additional amortization and depreciation expense of approximately $1 million recognized for the year ended December 31, 2016 , in Depreciation and amortization in the Consolidated Statements of Income, that would have been recorded for the year ended December 31, 2015, had the fair value adjustments been recorded as of December 4, 2015. The increase in the fair value of equity investments above would not have had a material effect on the income from equity method investments had the fair value adjustment been recorded as of December 4, 2015. The purchase price allocation resulted in the recognition of $2.2 billion of goodwill in three reporting units within the Partnership’s G&P segment, substantially all of which is not deductible for tax purposes. Goodwill represents the complimentary aspects of the highly diverse asset base of MarkWest and MPLX LP that will provide significant additional opportunities across multiple segments of the hydrocarbon value chain. The Partnership recognized $36 million of acquisition-related costs associated with the MarkWest Merger. These costs were expensed, with $30 million included in General and administrative expenses and $6 million included in Other financial costs . The fair value of the common units issued was determined on the basis of the closing market price of the Partnership’s units as of the effective time of the transaction and is considered a Level 1 measurement. The fair value of the Class B units issued was determined based on reference to the value of the common units, adjusted for a lack of distributions prior to their stated conversion dates, and is considered a Level 2 measurement. The fair values of the long-term debt and SMR liabilities were determined as of the acquisition date using the methods discussed in Note 15 . The fair value of the equity method investments was determined based on applying the discounted cash flow method, which is an income approach, to the Partnership’s equity method investments on an individual basis. Key assumptions include discount rates of 9.4 percent to 11.1 percent and terminal values based on the Gordon growth method to capitalize the cash flows, using a 2.5 percent long term growth rate. Intangibles represent customer contracts and related relationships. The fair value of the intangibles was determined based on applying the multi-period excess earnings method, which is an income approach. Key assumptions include attrition rates by reporting unit ranging from 5.0 percent to 10.0 percent and discount rates by reporting unit ranging from 11.5 percent to 12.8 percent . The fair value of property, plant and equipment was determined primarily based on the cost approach. Key assumptions include inputs to the valuation methodology such as recent purchases of similar items and published data for similar items. Components were adjusted for economic and functional obsolescence, location, normal useful lives, and capacity (if applicable). The fair value measurements for equity method investments, intangibles, and property, plant and equipment are based on significant inputs that are not observable in the market and, therefore, represent Level 3 measurements. The amounts of revenue and income from operations associated with MarkWest in the Consolidated Statements of Income for 2015 are as follows: (In millions) 2015 Revenues and other income $ 126 Income from operations 32 Unaudited Pro Forma Financial Information The following unaudited pro forma financial information presents consolidated results assuming the MarkWest Merger occurred on January 1, 2014. (In millions, except per unit data) 2015 2014 Revenues and other income $ 2,677 $ 2,972 Net income attributable to MPLX LP 247 330 Net income attributable to MPLX LP per unit - basic 0.47 1.09 Net income attributable to MPLX LP per unit - diluted 0.45 1.03 The unaudited pro forma financial information includes adjustments primarily to align accounting policies, adjust depreciation expense to reflect the fair value of property, plant and equipment, increase amortization expense related to identifiable intangible assets and adjust interest expense related to the fair value of MarkWest’s long-term debt, as well as the related income tax effects. The pro forma financial information does not give effect to potential synergies that could result from the acquisition and is not necessarily indicative of the results of future operations. MarkWest has a 60 percent legal ownership interest in MarkWest Utica EMG for the years ended December 31, 2015 and 2014, respectively. MarkWest Utica EMG’s inability to fund its planned activities without subordinated financial support qualify it as a VIE. The financing structure for MarkWest Utica EMG at its inception resulted in a de-facto agent relationship under which MarkWest was deemed to be the primary beneficiary of MarkWest Utica EMG. Therefore, MarkWest consolidated MarkWest Utica EMG in its historical financial statements. In the fourth quarter of 2015, based on economic conditions and other pertinent factors, the accounting for its investment in MarkWest Utica EMG was re-assessed. As of December 4, 2015 , the entity has been deconsolidated. For purposes of this pro forma financial information, MarkWest Utica EMG has been consolidated for the period prior to the acquisition consistent with its treatment in the historical periods presented. A summary of the amounts included in the historical financial statements of MarkWest for the year ended December 31, 2014 and the period from January 1, 2015 through December 3, 2015 related to MarkWest Utica EMG are as follows: (in millions) 2015 2014 Revenue and other income $ 152 $ 85 Cost of revenue excluding depreciation and amortization 27 48 Depreciation and amortization 61 50 Net income attributable to noncontrolling interest 64 31 Net loss (5 ) (46 ) EMG Utica, LLC (“EMG Utica”), a joint venture partner in MarkWest Utica EMG, received a special non-cash allocation of income of approximately $41 million and $37 million for the period from January 1, 2015 through December 3, 2015 and the year ended December 31, 2014, respectively. See Note 5 for a description of the transaction and its impact on the financial statements. Net income of MarkWest would not have changed had MarkWest Utica EMG been deconsolidated for the year ended December 31, 2014 and the period from January 1, 2015 through December 3, 2015. Purchases of Pipe Line Holdings Effective December 4, 2015 , the Partnership purchased the remaining 0.5 percent interest in Pipe Line Holdings from subsidiaries of MPC for consideration of $12 million . This resulted in Pipe Line Holdings becoming a wholly-owned subsidiary of the Partnership. The Partnership recorded the 0.5 percent interest at its historical carrying value of $6 million and the excess cash paid and equity contributed over historical carrying value of $6 million as a decrease to general partner equity. Prior to this transaction, the 0.5 percent interest was held by MPC and was reflected as the noncontrolling interest retained by MPC in the consolidated financial statements. Effective December 1, 2014 , the Partnership purchased a 22.875 percent interest in Pipe Line Holdings from subsidiaries of MPC for consideration of $600 million , which was financed through borrowings under our bank revolving credit facility, as discussed in Note 17 . In addition, the Partnership accepted a contribution of 7.625 percent of outstanding partnership interests of Pipe Line Holdings from subsidiaries of MPC in exchange for the issuance of equity valued at $200 million , as discussed in Note 8 . The Partnership recorded the combined 30.5 percent interest at its historical carrying value of $335 million and the excess cash paid and equity contributed over historical carrying value of $465 million as a decrease to general partner equity. Prior to this transaction, the 30.5 percent interest was held by MPC and was reflected as part of the noncontrolling interest retained by MPC in the consolidated financial statements. Beginning December 1, 2014, the consolidated financial statements reflect the 99.5 percent general partner interest in Pipe Line Holdings owned by MPLX LP, while the 0.5 percent limited partner interest held by MPC is reflected as a noncontrolling interest. On March 1, 2014 , the Partnership acquired a 13 percent interest in Pipe Line Holdings from MPC for consideration of $310 million , which was funded with $40 million of cash on hand and $270 million of borrowings on the bank revolving credit facility. The Partnership recorded the 13 percent interest in Pipe Line Holdings at its historical carrying value of $138 million and the excess cash paid over historical carrying value of $172 million as a decrease to general partner equity. In addition, on May 1, 2013 , the Partnership acquired a five percent interest in Pipe Line Holdings from MPC for consideration of $100 million , which was funded with cash on hand. The Partnership recorded the five percent interest in Pipe Line Holdings at its historical carrying value of $54 million and the excess cash paid over historical carrying value of $46 million as a decrease to general partner equity. These acquisitions were accounted for on a prospective basis and the terms of the acquisitions were approved by the conflicts committee of the board of directors of the general partner, which is comprised entirely of independent directors. Changes in MPLX LP’s equity resulting from changes in its ownership interest in Pipe Line Holdings were as follows: (In millions) 2015 2014 Net income attributable to MPLX LP $ 156 $ 121 Transfer to noncontrolling interest: Decrease in general partner-MPC equity for purchases of additional interest in Pipe Line Holdings (6 ) (638 ) Change from net income attributable to MPLX LP and transfer to noncontrolling interest $ 150 $ (517 )
Business Acquisition, Pro Forma Information [Table Text Block]	The following unaudited pro forma financial information presents consolidated results assuming the MarkWest Merger occurred on January 1, 2014. (In millions, except per unit data) 2015 2014 Revenues and other income $ 2,677 $ 2,972 Net income attributable to MPLX LP 247 330 Net income attributable to MPLX LP per unit - basic 0.47 1.09 Net income attributable to MPLX LP per unit - diluted 0.45 1.03
MarkWest [Member]
Business Acquisition [Line Items]
Components Of The Fair Value Of Consideration Transferred [Table Text Block]	The components of the fair value of consideration transferred are as follows: (In millions) Fair value of units issued $ 7,326 Cash 1,230 Paid/payable to MarkWest Class B unitholders 50 Total fair value of consideration transferred $ 8,606
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed [Table Text Block]	The following table summarizes the final purchase price allocation. Subsequent to December 31, 2015, additional analysis was completed and adjustments were made to the preliminary purchase price allocation as noted in the table below. The fair value of assets acquired and liabilities and noncontrolling interests assumed at the acquisition date as of December 31, 2016, are as follows: (In millions) As Originally Reported Adjustments As Adjusted Cash and cash equivalents $ 12 $ — $ 12 Receivables 164 — 164 Inventories 33 (1 ) 32 Other current assets 44 — 44 Equity method investments 2,457 143 2,600 Property, plant and equipment 8,474 43 8,517 Intangibles 468 65 533 Other noncurrent assets 5 — 5 Total assets acquired 11,657 250 11,907 Accounts payable 322 — 322 Accrued liabilities 13 6 19 Accrued taxes 21 — 21 Other current liabilities 44 — 44 Long-term debt 4,567 — 4,567 Deferred income taxes 374 3 377 Deferred credits and other liabilities 151 — 151 Noncontrolling interest 13 — 13 Total liabilities and noncontrolling interest assumed 5,505 9 5,514 Net assets acquired excluding goodwill 6,152 241 6,393 Goodwill 2,454 (241 ) 2,213 Net assets acquired $ 8,606 $ — $ 8,606
Business Acquisition, Pro Forma Information [Table Text Block]	The amounts of revenue and income from operations associated with MarkWest in the Consolidated Statements of Income for 2015 are as follows: (In millions) 2015 Revenues and other income $ 126 Income from operations 32
MarkWest Utica EMG [Member]
Business Acquisition [Line Items]
Historical Information for Deconsolidated Entity [Table Text Block]	A summary of the amounts included in the historical financial statements of MarkWest for the year ended December 31, 2014 and the period from January 1, 2015 through December 3, 2015 related to MarkWest Utica EMG are as follows: (in millions) 2015 2014 Revenue and other income $ 152 $ 85 Cost of revenue excluding depreciation and amortization 27 48 Depreciation and amortization 61 50 Net income attributable to noncontrolling interest 64 31 Net loss (5 ) (46 )

Equity Method Investments Equ35

Equity Method Investments Equity Method Investments (Tables)	12 Months Ended
	Dec. 31, 2016
Schedule of Equity Method Investments [Line Items]
Summarized Financial Information For Equity Method Investees Table [Text Block]	Summarized financial information for the year ended December 31, 2016 and from the date of the MarkWest Merger through December 31, 2015 for equity method investments is as follows: Year Ended December 31, 2016 (In millions) MarkWest Utica EMG Ohio Condensate Other VIEs Non-VIEs Total Revenue and other income $ 216 $ 15 $ 3 $ 148 $ 382 Cost and expenses 100 110 1 117 328 Income (loss) from operations 116 (95 ) 2 31 54 Net income (loss) 114 (95 ) 2 31 52 Income (loss) from equity method investments (2) 8 (89 ) — 7 (74 ) Year Ended December 31, 2015 (In millions) MarkWest Utica EMG Ohio Condensate Other VIEs Non-VIEs Total Revenue and other income $ 18 $ 2 $ — $ 9 $ 29 Cost and expenses 9 2 — 8 19 Income from operations 9 — — 1 10 Net income 10 — — 1 11 Income from equity method investments (2) 2 1 — — 3 Summarized balance sheet information as of December 31, 2016 and 2015 for equity method investments is as follows: December 31, 2016 (In millions) MarkWest Utica EMG (1) Ohio Condensate Other VIEs Non-VIEs Total Current assets $ 45 $ 2 $ — $ 40 $ 87 Noncurrent assets 2,173 30 102 375 2,680 Current liabilities 30 3 1 26 60 Noncurrent liabilities 2 13 — — 15 December 31, 2015 (In millions) MarkWest Utica EMG (1) Ohio Condensate Other VIEs Non-VIEs Total Current assets $ 113 $ 7 $ — $ 30 $ 150 Noncurrent assets 2,207 127 42 243 2,619 Current liabilities 77 6 1 18 102 Noncurrent liabilities 1 12 — — 13 (1) MarkWest Utica EMG’s noncurrent assets includes its investment in its subsidiary Ohio Gathering, which does not appear elsewhere in this table. The investment was $794 million and $781 million as of December 31, 2016 and 2015 , respectively. (2) Income (loss) from equity method investments includes the impact of any basis differential amortization or accretion.

Related Party Agreements and 36

Related Party Agreements and Transactions (Tables)	12 Months Ended
	Dec. 31, 2016
Related Party Transactions [Abstract]
Revenue from Related Parties	Revenue received from related parties related to service and product sales were as follows: (In millions) 2016 2015 2014 Service revenue MPC $ 603 $ 593 $ 662 Rental income MPC $ 114 $ 101 $ 15 Product sales (1) MPC $ 11 $ 1 $ —
Summary of Fees Received for Operating Pipelines for Related Parties Included in Other Income - Related Parties	The revenue received from related parties included in Other income - related parties on the Consolidated Statements of Income was as follows: (In millions) 2016 2015 2014 MPC $ 60 $ 68 $ 39 MarkWest Utica EMG 16 — — Centennial 1 1 1 Ohio Gathering 15 2 — Ohio Condensate 4 — — Other 5 — — Total $ 101 $ 71 $ 40
Schedule of Entity Wide Information Allocated Related Party Omnibus Agreement Costs by Income Stmt Line	MPC provides executive management services and certain general and administrative services to the Partnership under the terms of the omnibus agreement. Expenses incurred under these agreements are shown in the table below by the income statement line where they were recorded. These expenses also include similar charges incurred by HSM for the time period prior to the acquisition and therefore not covered by the omnibus agreement. Charges for services included in Purchases from related parties primarily relate to services that support the Partnership’s operations and maintenance activities, as well as compensation expenses. Charges for services included in General and administrative expenses primarily relate to services that support the Partnership’s executive management, accounting and human resources activities. These charges were as follows: (In millions) 2016 2015 2014 Purchases from related parties $ 29 $ 30 $ 30 General and administrative expenses 39 46 46 Total $ 68 $ 76 $ 76
Summary of Related Party Costs Added to Property, Plant and Equipment	Also under terms of the omnibus agreement, some service costs related to engineering services are associated with assets under construction. These costs added to Property, plant and equipment were as follows: (In millions) 2016 2015 2014 MPC $ 38 $ 13 $ 8
Summary of Allocated Related Party Employee Benefit Costs by Income Statement Line Item	Employee services expenses from related parties were as follows: (In millions) 2016 2015 2014 Purchases - related parties $ 287 $ 136 $ 123 General and administrative expenses 72 22 24 Total $ 359 $ 158 $ 147
Receivables from Related Parties	Receivables from related parties which include reimbursements from the MarkWest Merger to be provided by MPC for the conversion of Class B units were as follows: December 31, (In millions) 2016 2015 MPC $ 117 $ 175 MarkWest Utica EMG 2 4 Ohio Gathering 2 5 Other 1 3 Total $ 122 $ 187
Schedule of Long Term Receivables with Related Parties	Long-term receivables with related parties, including straight-line rental income for both periods presented, as well as reimbursements from the MarkWest Merger to be provided by MPC for the conversion of Class B units for the period ended December 31, 2015, were as follows: December 31, (In millions) 2016 2015 MPC $ 4 $ 25
Payables to Related Parties	Payables to related parties were as follows: December 31, (In millions) 2016 2015 MPC $ 51 $ 33 MarkWest Utica EMG 24 21 Total $ 75 $ 54
Schedule Of Related Party Deferred Revenue Table	The Deferred revenue-related parties balance associated with the minimum volume deficiencies and project reimbursements were as follows: December 31, (In millions) 2016 2015 Minimum volume deficiencies - MPC $ 44 $ 36 Project reimbursements - MPC 5 5 Total $ 49 $ 41

Net Income Per Limited Partne37

Net Income Per Limited Partner Unit (Tables)	12 Months Ended
	Dec. 31, 2016
Earnings Per Share [Abstract]
Schedule of Net Income Per Limited Partner Unit	Diluted net income per limited partner unit for the 2014 reporting period is the same as basic net income per limited partner unit as there were no potentially dilutive common or subordinated units outstanding as of December 31, 2014. (In millions) 2016 2015 2014 Net income attributable to MPLX LP $ 233 $ 156 $ 121 Less: Distributions declared on Preferred units (1) 41 — — General partner’s distributions declared (including IDRs) (1) 205 60 6 Limited partners’ distributions declared on common units (1) 692 224 54 Limited partner’s distributions declared on subordinated units (1) — 31 52 Undistributed net (loss) income attributable to MPLX LP $ (705 ) $ (159 ) $ 9 (1) See Note 8 for information regarding the distribution.
Schedule of Basic and Diluted Earnings Per Unit	(1) See Note 8 for information regarding the distribution. 2016 (In millions, except per-unit data) General Partner Limited Partners’ Common Units Redeemable Preferred Units Total Basic and diluted net income attributable to MPLX LP per unit: Net income attributable to MPLX LP: Distributions declared (including IDRs) $ 205 $ 692 $ 41 $ 938 Undistributed net loss attributable to MPLX LP (14 ) (691 ) — (705 ) Net income attributable to MPLX LP (1) $ 191 $ 1 $ 41 $ 233 Weighted average units outstanding: Basic 7 331 338 Diluted 7 338 345 Net income attributable to MPLX LP per limited partner unit: Basic $ — Diluted $ — 2015 (In millions, except per-unit data) General Partner Limited Partners’ Common Units Limited Partner’s Subordinated Units Total Basic and diluted net income attributable to MPLX LP per unit: Net income attributable to MPLX LP: Distributions declared (including IDRs) $ 60 $ 224 $ 31 $ 315 Undistributed net loss attributable to MPLX LP (3 ) (127 ) (29 ) (159 ) Net income attributable to MPLX LP (1) $ 57 $ 97 $ 2 $ 156 Weighted average units outstanding: Basic 2 79 18 99 Diluted 2 80 18 100 Net income attributable to MPLX LP per limited partner unit: Basic $ 1.23 $ 0.11 Diluted $ 1.22 $ 0.11 2014 (In millions, except per-unit data) General Partner Limited Partners’ Common Units Limited Partner’s Subordinated Units Total Basic and diluted net income attributable to MPLX LP per unit: Net income attributable to MPLX LP: Distribution declared $ 6 $ 54 $ 52 $ 112 Undistributed net income attributable to MPLX LP 2 4 3 9 Net income attributable to MPLX LP (1) $ 8 $ 58 $ 55 $ 121 Weighted average units outstanding: Basic 2 37 37 76 Diluted 2 37 37 76 Net income attributable to MPLX LP per limited partner unit: Basic $ 1.55 $ 1.50 Diluted $ 1.55 $ 1.50 (1) Allocation of net income (loss) attributable to MPLX LP assumes all earnings for the period had been distributed based on the current period distribution priorities.

Equity (Tables)

Equity (Tables)	12 Months Ended
	Dec. 31, 2016
Equity [Abstract]
Schedule of Stockholders Equity	The table below summarizes the changes in the number of units outstanding for the years ended December 31, 2014 , 2015 , and 2016 : (In units) Common Class B Subordinated General Partner Total Balance at December 31, 2013 36,951,515 — 36,951,515 1,508,225 75,411,255 Unit-based compensation awards 15,479 — — 316 15,795 Contribution of interest in Pipe Line Holdings 2,924,104 — — 59,676 2,983,780 December 2014 equity offering 3,450,000 — — 70,408 3,520,408 Balance at December 31, 2014 43,341,098 — 36,951,515 1,638,625 81,931,238 Unit-based compensation awards 18,932 — — 386 19,318 Issuance of units under the ATM program 25,166 — — 514 25,680 Subordinated unit conversion 36,951,515 — (36,951,515 ) — — MarkWest Merger 216,350,465 7,981,756 — 5,160,950 229,493,171 Balance at December 31, 2015 296,687,176 7,981,756 — 6,800,475 311,469,407 Unit-based compensation awards 120,989 — — 2,470 123,459 Issuance of units under the ATM Program 26,347,887 — — 537,710 26,885,597 Contribution of HSM (See Note 4) 22,534,002 — — 459,878 22,993,880 Class B conversion 4,350,057 (3,990,878 ) — 7,330 366,509 Class A Reorganization 7,153,177 — — (436,758 ) 6,716,419 Balance at December 31, 2016 357,193,288 3,990,878 — 7,371,105 368,555,271
Schedule Of Calculation Of Net Income Applicable to Partners	Net Income Allocation – In preparing the Consolidated Statements of Equity, net income (loss) attributable to MPLX LP is allocated to Preferred unitholders based on a fixed distribution schedule, as discussed in Note 9 , and subsequently allocated to the general partner and limited partner unitholders. However, when distributions related to the incentive distribution rights are made, earnings equal to the amount of those distributions are first allocated to the general partner before the remaining earnings are allocated to the limited partner unitholders based on their respective ownership percentages. The following table presents the allocation of the general partner’s interest in net income attributable to MPLX LP: (In millions) 2016 2015 2014 Net income attributable to MPLX LP $ 233 $ 156 $ 121 Less: Preferred unit distributions 41 — — General partner's incentive distribution rights and other 191 55 4 Net income attributable to MPLX LP available to general and limited partners $ 1 $ 101 $ 117 General partner's two percent interest in net income attributable to MPLX LP $ — $ 2 $ 2 General partner's incentive distribution rights and other 191 55 4 General partner's interest in net income attributable to MPLX LP $ 191 $ 57 $ 6
Distributions Made to Limited Partner, by Distribution	The allocation of total quarterly cash distributions to general, limited, and Preferred unitholders is as follows for the years ended December 31, 2016 , 2015 and 2014 . The 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) 2016 2015 2014 General partner's distributions: General partner's distributions $ 18 $ 6 $ 2 General partner's incentive distribution rights distributions 187 54 4 Total general partner's distributions 205 60 6 Limited partners' distributions: Common unitholders 692 224 54 Subordinated unitholders — 31 52 Total limited partners' distributions 692 255 106 Preferred unit distributions 41 — — Total cash distributions declared $ 938 $ 315 $ 112

Redeemable Preferred Units (Tab

Redeemable Preferred Units (Tables)	12 Months Ended
	Dec. 31, 2016
Temporary Equity [Table Text Block]	The changes in the redeemable preferred balance for 2016 were as follows: (In millions) Redeemable Preferred Units Issuance of MPLX LP redeemable Preferred units on May 13, 2016 $ 984 Net income allocated for May 13, 2016 through December 31, 2016 41 Distributions received by Preferred unitholders (25 ) Balance at December 31, 2016 $ 1,000

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2016
Segment Reporting [Abstract]
Income from operations and capital expenditures by segment [Table Text Block]	2016 (In millions) L&S G&P Total Revenues and other income: Segment revenues $ 787 $ 2,185 $ 2,972 Segment other income 68 1 69 Total segment revenues and other income 855 2,186 3,041 Costs and expenses: Segment cost of revenues 368 907 1,275 Segment operating income before portion attributable to noncontrolling interest and Predecessor 487 1,279 1,766 Segment portion attributable to noncontrolling interest and Predecessor 34 147 181 Segment operating income attributable to MPLX LP $ 453 $ 1,132 $ 1,585 2015 (In millions) L&S G&P Total Revenues and other income: Segment revenues $ 760 $ 150 $ 910 Segment other income 75 — 75 Total segment revenues and other income 835 150 985 Costs and expenses: Segment cost of revenues 379 62 441 Segment operating income before portion attributable to noncontrolling interest and Predecessor 456 88 544 Segment portion attributable to noncontrolling interest and Predecessor 134 12 146 Segment operating income attributable to MPLX LP $ 322 $ 76 $ 398 2014 (In millions) L&S Revenues and other income: Segment revenues $ 747 Segment other income 46 Total segment revenues and other income 793 Costs and expenses: Segment cost of revenues 392 Segment operating income before portion attributable to noncontrolling interest and Predecessor 401 Segment portion attributable to noncontrolling interest and Predecessor 188 Segment operating income attributable to MPLX LP $ 213
Reconciliation to Income from Operations [Table Text Block]	(in millions) 2016 2015 2014 Reconciliation to Income from operations: L&S segment operating income attributable to MPLX LP $ 453 $ 322 $ 213 G&P segment operating income attributable to MPLX LP 1,132 76 — Segment operating income attributable to MPLX LP 1,585 398 213 Segment portion attributable to unconsolidated affiliates (173 ) (8 ) 85 Segment portion attributable to Predecessor 34 133 103 (Loss) income from equity method investments (74 ) 3 — Other income - related parties 40 2 — Unrealized derivative (losses) gains (1) (36 ) 4 — Depreciation and amortization (546 ) (116 ) (75 ) Impairment expense (130 ) — — General and administrative expenses (193 ) (118 ) (81 ) Income from operations $ 507 $ 298 $ 245
Reconciliation to Total Revenues and other income [Table Text Block]	(in millions) 2016 2015 2014 Reconciliation to Total revenues and other income: Total segment revenues and other income $ 3,041 $ 985 $ 793 Revenue adjustment from unconsolidated affiliates (402 ) (28 ) — (Loss) income from equity method investments (74 ) 3 — Other income - related parties 40 2 — Unrealized derivative losses (1) (15 ) (1 ) — Total revenues and other income $ 2,590 $ 961 $ 793
Reconciliation of Net Income Attributable to Noncontrolling Interests [Table Text Block]	(in millions) 2016 2015 2014 Reconciliation to Net income attributable to noncontrolling interests and Predecessor: Segment portion attributable to noncontrolling interest and Predecessor $ 181 $ 146 $ 188 Portion of noncontrolling interests and Predecessor related to items below segment income from operations (124 ) (48 ) (70 ) Portion of operating income attributable to noncontrolling interests of unconsolidated affiliates (32 ) (5 ) — Net income attributable to noncontrolling interests and Predecessor $ 25 $ 93 $ 118
Reconciliation of Other Significant Reconciling Items from Segments to Consolidated [Table Text Block]	The following reconciles segment capital expenditures to total capital expenditures: (In millions) 2016 2015 2014 L&S segment capital expenditures $ 443 $ 212 $ 141 G&P segment capital expenditures 894 100 — Total segment capital expenditures 1,337 312 141 Less: Capital expenditures for Partnership-operated, non-wholly-owned subsidiaries in G&P segment 131 24 — Total capital expenditures $ 1,206 $ 288 $ 141
Reconciliation of Assets from Segment to Consolidated [Table Text Block]	Total assets by reportable segment were: December 31, (In millions) 2016 2015 Cash and cash equivalents $ 234 $ 43 L&S 2,115 1,842 G&P 14,297 14,219 Total assets $ 16,646 $ 16,104

Income Taxes (Tables)

Income Taxes (Tables) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Federal income tax at statutory rate	$ (14)	$ 3
Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]	The components of the provision for income tax expense (benefit) are as follows: December 31, (In millions) 2016 2015 Current income tax expense: Federal $ 4 $ — State 1 — Total current 5 — Deferred income tax (benefit) expense: Federal (16 ) 3 State (1 ) (2 ) Total deferred (17 ) 1 (Benefit) provision for income tax $ (12 ) $ 1
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]	A reconciliation of the (benefit) provision for income tax and the amount computed by applying the federal statutory rate of 35 percent to the income before income taxes for each of the years ended December 31, 2016 and 2015 is as follows: December 31, 2016 (In millions) MarkWest Hydrocarbon (1) Partnership Eliminations Consolidated (Loss) income before (benefit) provision for income tax $ (41 ) $ 285 $ 2 $ 246 Federal statutory rate 35 % — % — % Federal income tax at statutory rate (14 ) — — (14 ) State income taxes net of federal benefit (2 ) 1 — (1 ) Provision on income from MPLX LP Class A units 3 — — 3 Change in state statutory rate (1 ) — — (1 ) Other 1 — — 1 (Benefit) provision for income tax $ (13 ) $ 1 $ — $ (12 ) December 31, 2015 (In millions) MarkWest Hydrocarbon (1) Partnership Eliminations Consolidated Income before provision (benefit) for income tax $ 9 $ 240 $ 1 $ 250 Federal statutory rate 35 % — % — % Federal income tax at statutory rate 3 — — 3 State income taxes net of federal benefit — (2 ) — (2 ) Provision on income from MPLX LP Class A units 1 — — 1 Other (1 ) — — (1 ) Provision (benefit) for income tax $ 3 $ (2 ) $ — $ 1 (1) MarkWest Hydrocarbon paid tax on its share of the Partnership’s income or loss as a result of its ownership of MPLX LP Class A units through September 1, 2016.
Schedule of Deferred Tax Assets and Liabilities [Table Text Block]	Deferred tax assets and liabilities consist of the following: December 31, (In millions) 2016 2015 Deferred tax assets: Derivatives $ — $ 9 Net operating loss carryforwards — 62 Total deferred tax assets — 71 Deferred tax liabilities: Property, plant and equipment 5 7 Investments in subsidiaries and affiliates — 442 Total deferred tax liabilities 5 449 Net deferred tax liabilities $ 5 $ 378

Inventories (Tables)

Inventories (Tables)	12 Months Ended
	Dec. 31, 2016
Inventory Disclosure [Abstract]
Schedule of Components of Inventory [Table Text Block]	Inventories consist of the following: December 31, (In millions) 2016 2015 NGLs $ 2 $ 3 Line fill 9 5 Spare parts, materials and supplies 43 43 Total inventories $ 54 $ 51

Property, Plant and Equipment (

Property, Plant and Equipment (Tables)	12 Months Ended
	Dec. 31, 2016
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) 2016 2015 Natural gas gathering and NGL transportation pipelines and facilities 5 - 30 years $ 4,748 $ 4,307 Processing, fractionation and storage facilities 25 - 30 years 3,467 3,185 Pipelines and related assets 19 - 42 years 1,492 1,128 Barges and towing vessels 20 years 479 475 Land, building, office equipment and other 3 - 30 years 701 606 Construction-in-progress 958 946 Total 11,845 10,647 Less accumulated depreciation 1,115 650 Property, plant and equipment, net $ 10,730 $ 9,997

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2016
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 classified by the valuation hierarchy: December 31, 2016 December 31, 2015 (In millions) Assets Liabilities Assets Liabilities Significant other observable inputs (Level 2) Commodity contracts $ — $ — $ 2 $ — Significant unobservable inputs (Level 3) Commodity contracts — (6 ) 7 — Embedded derivatives in commodity contracts — (54 ) — (32 ) Total carrying value in Consolidated Balance Sheets $ — $ (60 ) $ 9 $ (32 )
Fair Value Inputs Assets and Liabilities Quantitative Information [Table Text Block]	The following table provides additional information about the significant unobservable inputs used in the valuation of Level 3 instruments as of December 31, 2016 . The market approach is used for valuation of all instruments. Level 3 Instrument Balance Sheet Classification Unobservable Inputs Value Range Time Period Commodity contracts Liabilities Forward ethane prices (per gallon) (1) $0.28 - $0.31 Jan. 17 - Dec. 17 Forward propane prices (per gallon) (1) $0.66 - $0.72 Jan. 17 - Dec. 17 Forward isobutane prices (per gallon) (1) $0.85 - $0.97 Jan. 17 - Dec. 17 Forward normal butane prices (per gallon) (1) $0.79 - $0.93 Jan. 17 - Dec. 17 Forward natural gasoline prices (per gallon) (1) $1.16 - $1.24 Jan. 17 - Dec. 17 Embedded derivatives in commodity contracts Liabilities Forward propane prices (per gallon) (1) $0.62 - $0.72 Jan. 17 - Dec. 22 Forward isobutane prices (per gallon) (1) $0.82 - $0.97 Jan. 17 - Dec. 22 Forward normal butane prices (per gallon) (1) $0.78 - $0.93 Jan. 17 - Dec. 22 Forward natural gasoline prices (per gallon) (1) $1.16 - $1.27 Jan. 17 - Dec. 22 Forward natural gas prices (per mmbtu) (2) $2.37 - $3.72 Jan. 17 - Dec. 22 Probability of renewal (3) 50.0% Probability of renewal for second 5-yr term (3) 75.0% (1) NGL prices used in the valuations decrease in the early years and increase over time. (2) Natural gas prices used in the valuations are higher in the early years and decrease over time. (3) The producer counterparty to the embedded derivative has the option to renew the gas purchase agreement and the related keep-whole processing agreement for two successive five -year terms after 2022. The embedded gas purchase agreement cannot be renewed without the renewal of the related keep-whole processing agreement. Due to the significant number of years until the renewal options are exercisable and the high level of uncertainty regarding the counterparty’s future business strategy, the future commodity price environment, and the future competitive environment for midstream services in the Southern Appalachian region, management determined that a 50 percent probability of renewal for the first five-year term and 75 percent for the second five-year term are appropriate assumptions. Included in this assumption is a further extension of management’s estimates of future frac spreads through 2032.
Schedule of changes in Level 3 fair value measurements [Table Text Block]	The tables below include a roll forward of the balance sheet amounts for the years ended December 31, 2016 and 2015 (including the change in fair value) for assets and liabilities classified by the Partnership within Level 3 of the valuation hierarchy, except for the changes in goodwill. See Note 5 for detail of the Ohio Condensate equity method impairment charge, which included a Level 3 valuation adjustment for the year ended December 31, 2016. See Note 18 for a rollforward of goodwill, which included a Level 3 valuation adjustment for the year ended December 31, 2016. 2016 2015 (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 $ 7 $ (32 ) $ — $ — Net positions assumed in conjunction with the MarkWest Merger — — 7 (38 ) Total (loss) gain (realized and unrealized) included in earnings (1) (13 ) (29 ) 3 5 Settlements — 7 (3 ) 1 Fair value at end of period $ (6 ) $ (54 ) $ 7 $ (32 ) The amount of total (losses) gains for the period included in earnings attributable to the change in unrealized gains or losses relating to liabilities still held at end of period $ (6 ) $ (26 ) $ 2 $ 5 (1) Gains and losses on Commodity Derivative Contracts classified as Level 3 are recorded in Product sales in the accompanying Consolidated Statements of Income. Gains and losses on Embedded Derivatives in Commodity Contracts are recorded in Cost of revenues and Purchased product costs .
Fair Value, by Balance Sheet Grouping [Table Text Block]	The following table summarizes the fair value and carrying value of the Partnership’s long-term debt, excluding capital leases, and SMR liability. December 31, 2016 2015 (In millions) Fair Value Carrying Value Fair Value Carrying Value Long-term debt $ 4,953 $ 4,422 $ 5,212 $ 5,255 SMR liability $ 108 $ 96 $ 99 $ 100

Derivative Financial Instrume45

Derivative Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2016
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block]	Volume of Commodity Derivative Activity As of December 31, 2016 , the Partnership had the following outstanding commodity contracts that were executed to manage the cash flow risk associated with future sales of NGLs: Derivative contracts not designated as hedging instruments Financial Position Notional Quantity (net) Crude Oil (bbl) Short 36,500 Natural Gas (MMBtu) Long 297,017 NGLs (gal) Short 64,211,702
Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block]	The impact of the Partnership’s derivative instruments on its Consolidated Balance Sheets is summarized below: (In millions) December 31, 2016 December 31, 2015 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 $ — $ (13 ) $ 9 $ (5 ) Other noncurrent assets / deferred credits and other liabilities — (47 ) — (27 ) Total $ — $ (60 ) $ 9 $ (32 ) (1) Includes embedded derivatives in commodity contracts as discussed above.
Derivative Instruments, Gain (Loss) [Table Text Block]	The impact of the Partnership’s derivative contracts not designated as hedging instruments and the location of gain or (loss) recognized in the Consolidated Statements of Income is summarized below: December 31, (In millions) 2016 2015 Product sales Realized gain $ 2 $ 4 Unrealized loss (15 ) (1 ) Total revenue: derivative (loss) gain from product sales (13 ) 3 Purchased product costs Realized loss (5 ) — Unrealized (loss) gain (22 ) 5 Total purchased product costs: derivative (loss) gain from product purchases (27 ) 5 Cost of revenues Realized loss (3 ) — Unrealized gain 1 — Total cost of revenues: derivative loss from cost of revenues (2 ) — Total derivative (losses) gains $ (42 ) $ 8

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2016
Debt Disclosure [Abstract]
Summary of Outstanding Borrowings	The Partnership’s outstanding borrowings at December 31, 2016 and 2015 consisted of the following: December 31, (In millions) 2016 2015 MPLX LP: Bank revolving credit facility due 2020 $ — $ 877 Term loan facility due 2019 250 250 5.500% senior notes due 2023 710 710 4.500% senior notes due 2023 989 989 4.875% senior notes due 2024 1,149 1,149 4.000% senior notes due 2025 500 500 4.875% senior notes due 2025 1,189 1,189 Consolidated subsidiaries: MarkWest - 4.500% - 5.500% senior notes, due 2023 - 2025 63 63 MPL - capital lease obligations due 2020 8 9 Total 4,858 5,736 Unamortized debt issuance costs (7 ) (8 ) Unamortized discount (1) (428 ) (472 ) Amounts due within one year (1 ) (1 ) Total long-term debt due after one year $ 4,422 $ 5,255 (1) Includes $420 million and $464 million discount as of December 31, 2016 and 2015, respectively, related to the difference between the fair value and the principal amount of the assumed MarkWest debt.
Schedule of Debt Payments	The following table shows five years of scheduled debt payments. (In millions) 2017 $ 1 2018 1 2019 251 2020 5 2021 —
Schedule of interest payable dates	Interest on each series of MPLX LP senior notes is payable semi-annually in arrears according to the table below. Senior Notes Interest payable semi-annually in arrears 5.500% senior notes due 2023 February 15 th and August 15 th 4.500% senior notes due 2023 January 15 th and July 15 th 4.875% senior notes due 2024 June 1 st and December 1 st 4.000% senior notes due 2025 February 15 th and August 15 th 4.875% senior notes due 2025 June 1 st and December 1 st
Schedule of amounts related to the SMR included in the Balance Sheet	As of December 31, 2016 and 2015 , the following amounts related to the SMR are included in the accompanying Consolidated Balance Sheets: (In millions) December 31, 2016 December 31, 2015 Assets Property, plant and equipment, net of accumulated depreciation $ 61 $ 69 Liabilities Accrued liabilities 5 4 Deferred credits and other liabilities 91 96

Goodwill and Intangibles (Table

Goodwill and Intangibles (Tables)	12 Months Ended
	Dec. 31, 2016
Goodwill [Line Items]
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, 2014 $ 116 $ — $ 116 Accumulated impairment losses — — — Balance as of December 31, 2014 116 — 116 Acquisitions — 2,454 2,454 Gross goodwill as of December 31, 2015 116 2,454 2,570 Accumulated impairment losses — — — Balance as of December 31, 2015 116 2,454 2,570 Purchase price allocation adjustments (1) — (241 ) (241 ) Impairment losses — (130 ) (130 ) Balance as of December 31, 2016 $ 116 $ 2,083 $ 2,199 Gross goodwill as of December 31, 2016 $ 116 $ 2,213 $ 2,329 Accumulated impairment losses — (130 ) (130 ) Balance as of December 31, 2016 $ 116 $ 2,083 $ 2,199 (1) See Note 4 for further discussion on purchase price allocation adjustments.
Schedule of Acquired Finite-Lived Intangible Assets by Major Class	The Partnership’s intangible assets as of December 31, 2016 and 2015 are comprised of customer contracts and relationships, as follows: December 31, 2016 December 31, 2015 (In millions) Gross Accumulated Amortization Net Gross Accumulated Amortization Net Useful Life L&S $ — $ — $ — $ — $ — $ — N/A G&P 533 (41 ) 492 468 (2 ) 466 11-25 years $ 533 $ (41 ) $ 492 $ 468 $ (2 ) $ 466
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense	Estimated future amortization expense related to the intangible assets at December 31, 2016 is as follows: (In millions) 2017 $ 38 2018 38 2019 38 2020 38 2021 38 Thereafter 302 Total $ 492

Supplemental Cash Flow Inform48

Supplemental Cash Flow Information (Tables)	12 Months Ended
	Dec. 31, 2016
Supplemental Cash Flow Elements [Abstract]
Summary of Supplemental Cash Flow Information	(In millions) 2016 2015 2014 Net cash provided by operating activities included: Interest paid (net of amounts capitalized) $ 212 $ 13 $ 3 Income taxes paid 3 — — Non-cash investing and financing activities: Net transfers of property, plant and equipment from materials and supplies inventories $ 4 $ 5 $ 1 Contribution - common units issued (1) 669 — 200 Acquisition: Fair value of MPLX LP units issued (1) — 7,326 — Payable to seller — 50 — (1) 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) 2016 2015 2014 (Decrease) increase in capital accruals $ (25 ) $ 26 $ 11

Equity-Based Compensation Plan

Equity-Based Compensation Plan (Tables)	12 Months Ended
	Dec. 31, 2016
Phantom Units [Member]
Equity Transactions And Share Based Compensation [Line Items]
Summary of Unit Award Activity	The following is a summary of phantom unit award activity of MPLX LP common limited partner units in 2016 : Phantom Units Number of Units Weighted Average Fair Value Aggregate Intrinsic Value (In millions) Outstanding at December 31, 2015 1,031,219 $ 35.49 Granted 458,727 29.42 Settled (166,576 ) 38.12 Forfeited (149,959 ) 32.72 Outstanding at December 31, 2016 1,173,411 33.09 Vested and expected to vest at December 31, 2016 1,157,676 33.12 $ 40 Convertible at December 31, 2016 494,189 34.11 $ 17
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 held by officers and non-employee directors: Phantom Units Intrinsic Value of Units Issued During the Period (in millions) Weighted Average Grant Date Fair Value of Units Granted During the Period 2016 $ 5 $ 29.42 2015 3 35.00 2014 1 49.56
Performance Shares [Member]
Equity Transactions And Share Based Compensation [Line Items]
Summary of Unit Award Activity	The following is a summary of activity of performance unit awards paying out in MPLX LP common limited partner units in 2016 : Performance Units Number of Units Weighted Outstanding at December 31, 2015 1,521,392 $ 1.00 Granted 789,375 0.63 Settled (458,011 ) 0.79 Forfeited (53,507 ) 1.06 Outstanding at December 31, 2016 1,799,249 0.89
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: 2016 2015 2014 Risk-free interest rate 0.96 % 0.95 % 0.63 % Look-back period 2.83 years 2.84 years 2.84 years Expected volatility 47.59 % 30.12 % 17.17 % Grant date fair value of performance units granted $ 0.63 $ 1.03 $ 1.16

Lease Operations (Tables)

Lease Operations (Tables)	12 Months Ended
	Dec. 31, 2016
Leases [Abstract]
Schedule of Future Minimum Rental Payments Receivable for Operating Leases [Table Text Block]	The following is a schedule of minimum future rentals on the non-cancellable operating leases as of December 31, 2016 : (In millions) Intercompany Third Party Total 2017 $ 101 $ 197 $ 298 2018 101 200 301 2019 101 202 303 2020 101 201 302 2021 — 185 185 2022 and thereafter — 460 460 Total minimum future rentals $ 404 $ 1,445 $ 1,849
Schedule of Property Subject to or Available for Operating Lease [Table Text Block]	The following schedule summarizes the Partnership’s investment in assets held for operating lease by major classes as of December 31, 2016 and 2015 : December 31, (In millions) 2016 2015 Natural gas gathering and NGL transportation pipelines and facilities $ 650 $ 619 Natural gas processing facilities 844 753 Barges 388 360 Towing vessels 91 91 Construction in progress 219 110 Property, plant and equipment 2,192 1,933 Less: accumulated depreciation (266 ) (170 ) Total property, plant and equipment $ 1,926 $ 1,763

Asset Retirement Obligations (T

Asset Retirement Obligations (Tables)	12 Months Ended
	Dec. 31, 2016
Asset Retirement Obligation Disclosure [Abstract]
Schedule of Change in Asset Retirement Obligation [Table Text Block]	The following is a reconciliation of the changes in the ARO from January 1, 2015 to December 31, 2016: (In millions) 2016 2015 ARO at beginning of period $ 17 $ — Liabilities assumed in conjunction with the MarkWest Merger — 15 Liabilities incurred 8 2 Adjustments to AROs (1 ) — Accretion expense 1 — ARO at end of period $ 25 $ 17

Commitments and Contingencies C

Commitments and Contingencies Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2016
Commitments and Contingencies (Minimum Future Payments) [Abstract]
Contractual Obligation, Fiscal Year Maturity Schedule	The Partnership executed transportation and terminalling agreements that obligate us to minimum volume, throughput or payment commitments over the terms of the agreements, which range from three to ten years. After the minimum volume commitments are met in the transportation and terminalling agreements, the Partnership pays additional amounts based on throughput. There are escalation clauses in the transportation and terminalling agreements, which are based on CPI adjustments. The minimum future payments under these agreements as of December 31, 2016 are as follows: (In millions) 2017 $ 46 2018 62 2019 61 2020 61 2021 61 2022 and thereafter 317 Total $ 608
Schedule Of Future Minimum Lease Payments For Operating And Capital Leases Table	The Partnership has various non-cancellable operating lease agreements and a long-term propane storage agreement expiring at various times through fiscal year 2040. Most of these leases include renewal options. The Partnership also leases certain pipelines under a capital lease that has a fixed price purchase option in 2020. Future minimum commitments as of December 31, 2016 , 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) Capital Obligations Operating Obligations 2017 $ 1 $ 61 2018 1 51 2019 2 42 2020 5 37 2021 — 36 Later years — 76 Total minimum lease payments 9 $ 303 Less: imputed interest costs 1 Present value of net minimum lease payments $ 8
Schedule of Rent Expense	Operating lease rental expense was: (In millions) 2016 2015 2014 Minimum rental expense $ 57 $ 21 $ 17
Schedule of minimum amounts payable annually under the product supply agreement	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) 2017 $ 17 2018 17 2019 17 2020 17 2021 17 2022 and thereafter 143 Total minimum payments 228 Less: Services element 87 Less: Interest 45 Total SMR liability 96 Less: Current portion of SMR liability 5 Long-term portion of SMR liability $ 91

Select Quarterly Financial Da53

Select Quarterly Financial Data (Tables)	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Summary of Quarterly Financial Data	2016 (3) 2015 (In millions, except per unit data) 1st Qtr. (1) 2nd Qtr. (2) 3rd Qtr. 4th Qtr. 1st Qtr. 2nd Qtr. 3rd Qtr. 4th Qtr. (3) Total revenues and other income $ 609 $ 564 $ 703 $ 714 $ 201 $ 213 $ 214 $ 333 Income from operations 27 76 207 197 74 82 68 74 Net (loss) income (37 ) 20 143 132 68 76 63 42 Net (loss) income attributable to MPLX LP (60 ) 19 141 133 46 51 41 18 Net (loss) income attributable to MPLX LP per limited partner unit: Common - basic $ (0.33 ) $ (0.11 ) $ 0.22 $ 0.17 $ 0.46 $ 0.50 $ 0.41 $ (0.14 ) Common - diluted (0.33 ) (0.11 ) 0.21 0.17 0.46 0.50 0.41 (0.14 ) Subordinated - basic and diluted — — — — 0.46 0.50 — — Cash distributions declared per limited partner common unit $ 0.5050 $ 0.5100 $ 0.5150 $ 0.5200 $ 0.4100 $ 0.4400 $ 0.4700 $ 0.5000 Distributions declared: Limited partner units - Public $ 127 $ 131 $ 135 $ 140 $ 10 $ 10 $ 11 $ 120 Limited partner units - MPC 29 41 44 45 23 25 27 29 General partner units - MPC 4 4 5 5 1 1 1 3 Incentive distribution rights - MPC 40 46 49 52 3 6 8 37 Redeemable preferred units — 9 16 16 — — — — Total distributions declared $ 200 $ 231 $ 249 $ 258 $ 37 $ 42 $ 47 $ 189 (1) First quarter 2016 results included goodwill impairment expense of $129 million . See Note 18 for more information. (2) Second quarter 2016 results included impairment expense related to equity method investments of $89 million . See Note 5 for more information. (3) These amounts include results from the MarkWest Merger which closed on December 4, 2015. See Note 4 for more information on the MarkWest Merger.

Description of the Business a54

Description of the Business and Basis of Presentation (Detail)	Mar. 31, 2016	Dec. 04, 2015	Oct. 31, 2012	Mar. 27, 2012	Dec. 31, 2016
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
MarkWest [Member]
Description Of Business And Basis Of Presentation [Line Items]
Effective date of acquisition		Dec. 4, 2015
Hardin Street Marine [Member]
Description Of Business And Basis Of Presentation [Line Items]
Effective date of acquisition	Mar. 31, 2016

Summary of Principal Accounti55

Summary of Principal Accounting Policies (Detail) - USD ($) $ in Millions	Mar. 27, 2012	Dec. 31, 2016	Dec. 31, 2015
Summary of Principal Accounting Policies [Line Items]
Date of partnership formation	Mar. 27, 2012
Number of reportable segments		2
Restricted cash		$ 5	$ 9
Threshold Relocation Cost of Assets as Percentage of Fair Value to be Classified as Real Estate		10.00%
Goodwill, Impairment Loss		$ 130	$ 0

Acquisitions (Purchase of MarkW

Acquisitions (Purchase of MarkWest Energy Partners L.P.) (Details) $ / shares in Units, $ in Millions		Dec. 04, 2015USD ($)$ / shares	Dec. 01, 2014USD ($)	Mar. 01, 2014USD ($)	May 02, 2013USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2016USD ($)		Sep. 30, 2016USD ($)	[2]	Jun. 30, 2016USD ($)	[2],[3]	Mar. 31, 2016USD ($)		Dec. 31, 2015USD ($)		Sep. 30, 2015USD ($)	Jun. 30, 2015USD ($)	Mar. 31, 2015USD ($)	Jun. 30, 2016	Dec. 31, 2016USD ($)		Dec. 31, 2015USD ($)		Dec. 31, 2014USD ($)
Business Acquisition [Line Items]
Number of Tow Boats													18
Business Combination, Consideration Transferred, Equity Interests Issued and Issuable	[1]																				$ 0		$ 7,326		$ 0
Net income attributable to MPLX LP							$ 133	[2]	$ 141		$ 19		$ (60)	[2],[4]	$ 18	[2]	$ 41	$ 51	$ 46		233	[5]	156	[5]	121	[5]
Goodwill						$ 2,570	2,199								$ 2,570						2,199		2,570		116
Payments to Acquire Businesses, Gross				$ 310	$ 100																0		12		910
Depreciation and amortization																					546		116		75
Business Combination, Consideration Transferred, Liabilities Incurred																					0		50		0
MarkWest [Member]
Business Acquisition [Line Items]
Class B Units Conversion Ratio		1.09
Cash consideration to unitholders | $ / shares		$ 6.20
Business Combination, Consideration Transferred, Equity Interests Issued and Issuable		$ 7,326
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual																							126
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment		$ 8,517
Effective date of acquisition		Dec. 4, 2015
Common Units Conversion Ratio		1.09
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents		$ 12
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Other		44
Business Combination, Acquisition of Less than 100 Percent, Noncontrolling Interest, Fair Value		13
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities		5,514
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Other		44
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt		4,567
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities Noncurrent		377
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other		151
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net		6,393
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles		533
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual																							32
Goodwill		2,213
Business Combination, Recognized Identifiable Assets Acquired, Equity Method Investments		2,600
Payments to Acquire Businesses, Gross		1,230
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable		322
Business Combination, Consideration Transferred, Including Equity Interest in Acquiree Held Prior to Combination		8,606
Business Combination, Consideration Transferred, Liabilities Incurred		50
Business Acquisition, Transaction Costs							36														36
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest		8,606
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets		5
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets		11,907
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Receivables		164
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Inventory		32
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Current Liabilities Payroll And Benefits Payable		19
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Accrued Taxes		21
MPC [Member] | MarkWest [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Gross		1,200				$ 1,300
Business Combination, Consideration Transferred, Liabilities Incurred		$ 50
MarkWest Utica EMG [Member]
Business Acquisition [Line Items]
Net income attributable to MPLX LP																							(5)		(46)
Selling, General and Administrative Expenses [Member] | MarkWest [Member]
Business Acquisition [Line Items]
Business Acquisition, Transaction Costs							30														30
Nonoperating Income (Expense) [Member] | MarkWest [Member]
Business Acquisition [Line Items]
Business Acquisition, Transaction Costs							$ 6														6
Equity Method Investments [Member] | Income Approach Valuation Technique [Member]
Business Acquisition [Line Items]
Fair Value Inputs, Long-term Revenue Growth Rate		2.50%
Equity Method Investments [Member] | Minimum [Member] | Income Approach Valuation Technique [Member]
Business Acquisition [Line Items]
Fair Value Inputs, Discount Rate		9.40%																		10.50%
Equity Method Investments [Member] | Maximum [Member] | Income Approach Valuation Technique [Member]
Business Acquisition [Line Items]
Fair Value Inputs, Discount Rate		11.10%																		11.50%
Finite-Lived Intangible Assets [Member] | Minimum [Member] | Income Approach Valuation Technique [Member]
Business Acquisition [Line Items]
Fair Value Inputs, Discount Rate		11.50%
Fair Value Inputs, Attrition Rate		5.00%
Finite-Lived Intangible Assets [Member] | Maximum [Member] | Income Approach Valuation Technique [Member]
Business Acquisition [Line Items]
Fair Value Inputs, Discount Rate		12.80%
Fair Value Inputs, Attrition Rate		10.00%
Misstatement of Original Purchase Price Allocation [Member] | MarkWest [Member]
Business Acquisition [Line Items]
Goodwill		$ 68
Business Combination, Recognized Identifiable Assets Acquired, Equity Method Investments		2
Misstatement of Original Purchase Price Allocation [Member] | Customer Relationships [Member] | MarkWest [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill		64
Depreciation and amortization																					1
Scenario, Adjustment [Member] | MarkWest [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment		43
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents		0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Other		0
Business Combination, Acquisition of Less than 100 Percent, Noncontrolling Interest, Fair Value		0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities		9
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Other		0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt		0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities Noncurrent		3
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other		0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net		241
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles		65
Goodwill		(241)
Business Combination, Recognized Identifiable Assets Acquired, Equity Method Investments		143
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable		0
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest		0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets		0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets		250
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Receivables		0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Inventory		(1)
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Current Liabilities Payroll And Benefits Payable		6
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Accrued Taxes		0
Scenario, Previously Reported [Member] | MarkWest [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment		8,474
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents		12
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Other		44
Business Combination, Acquisition of Less than 100 Percent, Noncontrolling Interest, Fair Value		13
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities		5,505
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Other		44
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Long-term Debt		4,567
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities Noncurrent		374
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other		151
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net		6,152
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles		468
Goodwill		2,454
Business Combination, Recognized Identifiable Assets Acquired, Equity Method Investments		2,457
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable		322
Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest		8,606
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets		5
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets		11,657
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Receivables		164
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Inventory		33
Business Combination Recognized Identifiable Assets Acquired And Liabilities Assumed Current Liabilities Payroll And Benefits Payable		13
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Accrued Taxes		21
General Partner [Member]
Business Acquisition [Line Items]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Changes, Purchase of Interest by Parent		$ 6	$ 465	$ 172																			6		638
General Partner [Member] | MPC [Member]
Business Acquisition [Line Items]
Net income attributable to MPLX LP	[5]																				$ 191		$ 57		$ 8
[1]	(1)See Note 4.
[2]	(3)These amounts include results from the MarkWest Merger which closed on December 4, 2015. See Note 4 for more information on the MarkWest Merger.
[3]	(2)Second quarter 2016 results included impairment expense related to equity method investments of $89 million. See Note 5 for more information.
[4]	(1)First quarter 2016 results included goodwill impairment expense of $129 million. See Note 18 for more information.
[5]	(1)Allocation of net income (loss) attributable to MPLX LP assumes all earnings for the period had been distributed based on the current period distribution priorities.

Acquisitions (Pro Forma Financi

Acquisitions (Pro Forma Financial Information) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Business Acquisition, Pro Forma Revenue		$ 2,677	$ 2,972
Business Acquisition, Pro Forma Net Income (Loss)		$ 247	$ 330
Business Acquisition, Pro Forma Earnings Per Share, Basic		$ 0.47	$ 1.09
Business Acquisition, Pro Forma Information, Description	The unaudited pro forma financial information includes adjustments primarily to align accounting policies, adjust depreciation expense to reflect the fair value of property, plant and equipment, increase amortization expense related to identifiable intangible assets and adjust interest expense related to the fair value of MarkWest’s long-term debt, as well as the related income tax effects. The pro forma financial information does not give effect to potential synergies that could result from the acquisition and is not necessarily indicative of the results of future operations.
Business Acquisition, Pro Forma Earnings Per Share, Diluted		$ 0.45	$ 1.03

Acquisitions (Pro Forma Narrati

Acquisitions (Pro Forma Narrative) (Details)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Business Acquisition, Pro Forma Information, Description	The unaudited pro forma financial information includes adjustments primarily to align accounting policies, adjust depreciation expense to reflect the fair value of property, plant and equipment, increase amortization expense related to identifiable intangible assets and adjust interest expense related to the fair value of MarkWest’s long-term debt, as well as the related income tax effects. The pro forma financial information does not give effect to potential synergies that could result from the acquisition and is not necessarily indicative of the results of future operations.
MarkWest Utica EMG [Member]
Business Acquisition [Line Items]
Equity Method Investment, Ownership Percentage	56.00%	60.00%	60.00%

Acquisitions (Pro Forma Informa

Acquisitions (Pro Forma Information - Historical MarkWest Utica EMG Information) (Details) - USD ($) $ / shares in Units, $ in Millions	Dec. 04, 2015	Dec. 31, 2015	Dec. 31, 2016	[1]	Sep. 30, 2016	[1]	Jun. 30, 2016	[1],[2]	Mar. 31, 2016	[1]	Dec. 31, 2015	[1]	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Business Acquisition [Line Items]
Business Acquisition, Pro Forma Earnings Per Share, Basic																		$ 0.47		$ 1.09
Total revenues and other income			$ 714		$ 703		$ 564		$ 609		$ 333		$ 214	$ 213	$ 201	$ 2,590		$ 961		$ 793
Less: Net income attributable to noncontrolling interests																2		1		57
Net income attributable to MPLX LP			$ 133		$ 141		$ 19		$ (60)	[3]	$ 18		$ 41	$ 51	$ 46	233	[4]	156	[4]	121	[4]
MarkWest Utica EMG [Member]
Business Acquisition [Line Items]
Depreciation, Amortization and Accretion, Net																		61		50
Total revenues and other income																		152		85
Operating Expenses																		27		48
Less: Net income attributable to noncontrolling interests																		64		31
Net income attributable to MPLX LP																		(5)		(46)
MarkWest Utica EMG [Member]
Business Acquisition [Line Items]
Noncontrolling Owners Accrual of Preference Amount		$ 4														$ 16
Deconsolidation, Date	Dec. 4, 2015
EMG Utica, LLC [Member]
Business Acquisition [Line Items]
Noncontrolling Owners Accrual of Preference Amount																		$ 41		$ 37
[1]	(3)These amounts include results from the MarkWest Merger which closed on December 4, 2015. See Note 4 for more information on the MarkWest Merger.
[2]	(2)Second quarter 2016 results included impairment expense related to equity method investments of $89 million. See Note 5 for more information.
[3]	(1)First quarter 2016 results included goodwill impairment expense of $129 million. See Note 18 for more information.
[4]	(1)Allocation of net income (loss) attributable to MPLX LP assumes all earnings for the period had been distributed based on the current period distribution priorities.

Acquisition (Purchases of Pipe

Acquisition (Purchases of Pipe Line Holdings) (Details) - USD ($) $ in Millions

Dec. 04, 2015

Dec. 01, 2014

Mar. 01, 2014

May 02, 2013

Dec. 31, 2016

[1]

Sep. 30, 2016

[1]

Jun. 30, 2016

[1],[2]

Mar. 31, 2016

[1],[3]

Dec. 31, 2015

[1]

Sep. 30, 2015

Jun. 30, 2015

Mar. 31, 2015

Dec. 03, 2015

Dec. 31, 2016

Dec. 31, 2015

Dec. 31, 2014

Business Acquisition [Line Items]

Net income attributable to MPLX LP

$ 133

$ 141

$ 19

$ (60)

$ 18

$ 41

$ 51

$ 46

$ 233

[4]

$ 156

[4]

$ 121

[4]

Purchase of additional interest in Pipe Line Holdings

(12)

(910)

Payments to Acquire Businesses, Gross

$ 310

$ 100

0

12

910

Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Change Due to Net Income Attributable to Parent and Effects of Changes, Net

150

(517)

Noncontrolling Interest [Member]

Business Acquisition [Line Items]

Purchase of additional interest in Pipe Line Holdings

$ 6

$ 335

138

General Partner [Member]

Business Acquisition [Line Items]

Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Changes, Purchase of Interest by Parent

6

$ 465

$ 172

6

638

MPC [Member] | Noncontrolling Interest [Member]

Business Acquisition [Line Items]

Subsidiary of Limited Liability Company or Limited Partnership, Ownership Interest

0.50%

0.50%

Purchase of additional interest in Pipe Line Holdings

(6)

(472)

MPC [Member] | General Partner [Member]

Business Acquisition [Line Items]

Net income attributable to MPLX LP

[4]

$ 191

$ 57

$ 8

Mplx Pipe Line Holdings Lp [Member]

Business Acquisition [Line Items]

Subsidiary of Limited Liability Company or Limited Partnership, Ownership Interest

99.50%

Pipe Line Holding [Member]

Business Acquisition [Line Items]

Business Acquisition, Equity Interest Issued or Issuable, Value Assigned

$ 200

Percentage of Partners Interest Purchased and Contributed

30.50%

Payments to Acquire Businesses, Gross

$ 12

$ 600

Percentage Of Partners Interest Contributed

7.625%

Effective date of acquisition

Dec. 4, 2015

Dec. 1, 2014

Mar. 1, 2014

May 1, 2013

Percentage Of Partners Interest Acquired

0.50%

22.875%

13.00%

5.00%

Pipe Line Holding [Member] | Noncontrolling Interest [Member]

Business Acquisition [Line Items]

Purchase of additional interest in Pipe Line Holdings

$ 54

Pipe Line Holding [Member] | General Partner [Member]

Business Acquisition [Line Items]

Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Changes, Purchase of Interest by Parent

$ 46

Cash [Member] | Pipe Line Holding [Member]

Business Acquisition [Line Items]

Payments to Acquire Businesses, Gross

$ 40

Revolving Credit Facility [Member] | Pipe Line Holding [Member]

Business Acquisition [Line Items]

Payments to Acquire Businesses, Gross

$ 270

[1]

(3)These amounts include results from the MarkWest Merger which closed on December 4, 2015. See Note 4 for more information on the MarkWest Merger.

[2]

(2)Second quarter 2016 results included impairment expense related to equity method investments of $89 million. See Note 5 for more information.

[3]

(1)First quarter 2016 results included goodwill impairment expense of $129 million. See Note 18 for more information.

[4]

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

Acquisition Acquisition (Acquis

Acquisition Acquisition (Acquisition of Hardin Street Marine LLC) (Details) $ in Millions	Mar. 31, 2016USD ($)shares	Mar. 31, 2016USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Business Acquisition [Line Items]
Number of barges	205	205
Contribution from MPC			$ 225	$ 1,280
Hardin Street Marine [Member]
Business Acquisition [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned	$ 600	$ 600
Limited Partner [Member] | Hardin Street Marine [Member]
Business Acquisition [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares | shares	22,534,002
Business Acquisition, Equity Interest Issued or Issuable, Fair Value Assigned	$ 669	669
General Partner [Member] | Hardin Street Marine [Member]
Business Acquisition [Line Items]
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares | shares	459,878
Business Acquisition, Equity Interest Issued or Issuable, Fair Value Assigned	$ 14	$ 14
MPC [Member]
Business Acquisition [Line Items]
Percent of Volumes Shipped		60.00%
Contribution from MPC			$ 15

Equity Method Investments Equ62

Equity Method Investments Equity Method Investments (Narrative) (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Feb. 28, 2013
Schedule of Equity Method Investments [Line Items]
Equity method investments	$ 2,458	$ 2,467	$ 2,467	$ 2,458
Other income - related parties			101	71	$ 40
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity	961	$ 1,100	$ 1,100	$ 961
MarkWest Utica EMG [Member]
Schedule of Equity Method Investments [Line Items]
NCI owners total funding commitment						$ 950
Percentage of capital required by reporting entity after NCI minimum contribution						100.00%
Aggregate Contributions to VIE Threshold						$ 2,000
Maximum percentage ownership interest in joint ventures		70.00%	70.00%
Threshold percentage for noncontrolling owners to make pro rata contributions		30.00%	30.00%
Maximum noncontrolling percentage of capital contributions until pro rata ownership threshhold is reached			10.00%
Noncontrolling interest owners actual contribution		$ 1,000	$ 1,000
Contribution by the Partnership		$ 1,500	1,500
Noncontrolling interest owners capital contribution preference threshold						$ 500
Noncontrolling Owners Accrual of Preference Amount	4		$ 16
Percentage of available cash to be received by the Partnership		60.00%	60.00%
Percentage of aggregate investment balance for proportionate distribution of cash		60.00%	60.00%
Percentage of aggregate investment balance		56.00%	56.00%
Equity method investments		$ 2,200	$ 2,200
Other income - related parties	$ 1		$ 16
Equity Method Investment, Ownership Percentage	60.00%	56.00%	56.00%	60.00%	60.00%
Equity Method Investment Difference Between Carrying Amount And Underlying Equity Portion Related To Goodwill Not Amortized		$ 459	$ 459
Ohio Gathering
Schedule of Equity Method Investments [Line Items]
Other income - related parties	$ 2		$ 15
Equity Method Investment, Ownership Percentage		34.00%	34.00%
Ohio Condensate Company, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Income (Loss) from Equity Method Investments from Elimination of Basis Differential		$ (31)
Other income - related parties	1		$ 4
Partnership's portion of equity method investment net assets	100	$ 10	$ 10	$ 100
Equity Method Investment, Ownership Percentage		60.00%	60.00%
Income (Loss) from Equity Method Investments from Asset Impairment		$ (58)
Equity Method Investment, Other than Temporary Impairment			$ 96
Sensitivity Analysis of Fair Value, Impact to Income Statement			(1)
Utica Condensate
Schedule of Equity Method Investments [Line Items]
Investment in subsidiary	$ 781	$ 794	$ 794	$ 781
Equity Method Investments [Member] | Income Approach Valuation Technique [Member] | Ohio Condensate Company, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Fair Value Inputs, Discount Rate			11.20%

Equity Method Investments Equ63

Equity Method Investments Equity Method Investments (Summary of Equity Method Investment Financial Information) (Details) - USD ($)		1 Months Ended		12 Months Ended
		Dec. 31, 2015		Dec. 31, 2016		Dec. 31, 2015	Dec. 31, 2014
Schedule of Equity Method Investments [Line Items]
Revenue and other income		$ 29,000,000		$ 382,000,000
Equity Method Investment, Summarized Financial Information, Costs and Expenses		19,000,000		328,000,000
Income (loss) from operations		10,000,000		54,000,000
Net income (loss)		11,000,000		52,000,000
Income (Loss) from Equity Method Investments		3,000,000	[1]	(74,000,000)	[1]	$ 3,000,000	$ 0
Current assets		150,000,000		87,000,000		150,000,000
Noncurrent assets		2,619,000,000		2,680,000,000		2,619,000,000
Current liabilities		102,000,000		60,000,000		102,000,000
Noncurrent liabilities		13,000,000		15,000,000		13,000,000
MarkWest Utica EMG [Member]
Schedule of Equity Method Investments [Line Items]
Revenue and other income		18,000,000		216,000,000
Equity Method Investment, Summarized Financial Information, Costs and Expenses		9,000,000		100,000,000
Income (loss) from operations		9,000,000		116,000,000
Net income (loss)		10,000,000		114,000,000
Income (Loss) from Equity Method Investments	[1]	2,000,000		8,000,000
Current assets		113,000,000		45,000,000		113,000,000
Noncurrent assets	[2]	2,207,000,000		2,173,000,000		2,207,000,000
Current liabilities		77,000,000		30,000,000		77,000,000
Noncurrent liabilities		1,000,000		2,000,000		1,000,000
Ohio Condensate Company, LLC [Member]
Schedule of Equity Method Investments [Line Items]
Revenue and other income		2,000,000		15,000,000
Equity Method Investment, Summarized Financial Information, Costs and Expenses		2,000,000		110,000,000
Income (loss) from operations		0		(95,000,000)
Net income (loss)		0		(95,000,000)
Income (Loss) from Equity Method Investments	[1]	1,000,000		(89,000,000)
Current assets		7,000,000		2,000,000		7,000,000
Noncurrent assets		127,000,000		30,000,000		127,000,000
Current liabilities		6,000,000		3,000,000		6,000,000
Noncurrent liabilities		12,000,000		13,000,000		12,000,000
Other VIEs
Schedule of Equity Method Investments [Line Items]
Revenue and other income		0		3,000,000
Equity Method Investment, Summarized Financial Information, Costs and Expenses		0		1,000,000
Income (loss) from operations		0		2,000,000
Net income (loss)		0		2,000,000
Income (Loss) from Equity Method Investments	[1]	0		0
Current assets		0		0		0
Noncurrent assets		42,000,000		102,000,000		42,000,000
Current liabilities		1,000,000		1,000,000		1,000,000
Noncurrent liabilities		0		0		0
Non-VIEs
Schedule of Equity Method Investments [Line Items]
Revenue and other income		9,000,000		148,000,000
Equity Method Investment, Summarized Financial Information, Costs and Expenses		8,000,000		117,000,000
Income (loss) from operations		1,000,000		31,000,000
Net income (loss)		1,000,000		31,000,000
Income (Loss) from Equity Method Investments	[1]	0		7,000,000
Current assets		30,000,000		40,000,000		30,000,000
Noncurrent assets		243,000,000		375,000,000		243,000,000
Current liabilities		18,000,000		26,000,000		18,000,000
Noncurrent liabilities		$ 0		$ 0		$ 0
[1]	(2)Income (loss) from equity method investments includes the impact of any basis differential amortization or accretion.
[2]	(1)MarkWest Utica EMG’s noncurrent assets includes its investment in its subsidiary Ohio Gathering, which does not appear elsewhere in this table. The investment was $794 million and $781 million as of December 31, 2016 and 2015, respectively.

Related Party Agreements and 64

Related Party Agreements and Transactions (Narrative) (Detail) $ in Millions	Sep. 14, 2012	Dec. 31, 2015USD ($)	Dec. 31, 2016USD ($)Agreement	Dec. 31, 2015USD ($)	Dec. 31, 2014	Oct. 01, 2012
Loan Agreement [Abstract]
Line of Credit Facility, Initiation Date	Sep. 14, 2012
Five Year Transportation Services Agreement [Member] | Commercial Agreements [Member] | Handling Crude Oil And Products [Member]
Commercial Agreements
Number of agreements			1
Ten Year Storage Services Agreement [Member] | Commercial Agreements [Member] | Storage Services Butane Cavern [Member]
Commercial Agreements
Number of agreements			1
MPC [Member]
Related Party Transaction [Line Items]
Sales Revenue, Goods, Related Party, Net Zero			$ 46	$ 1
MPC [Member] | Operating Agreements [Member] | Minimum [Member]
Commercial Agreements
Duration of agreements (in years)			1 year
MPC [Member] | Operating Agreements [Member] | Maximum [Member]
Commercial Agreements
Duration of agreements (in years)			5 years
MPC [Member] | Management Services Agreements [Member]
Commercial Agreements
Number of agreements | Agreement			2
MPC [Member] | Employee Services Agreements [Member]
Commercial Agreements
Number of agreements			4			2
MPC [Member] | Ten Year Transportation Services Agreement [Member] | Commercial Agreements [Member] | Crude oil [Member]
Commercial Agreements
Number of agreements | Agreement			3
Duration of agreements (in years)			10 years
MPC [Member] | Ten Year Transportation Services Agreement [Member] | Commercial Agreements [Member] | Pipelines products [Member]
Commercial Agreements
Number of agreements | Agreement			4
Duration of agreements (in years)			10 years
MPC [Member] | Five Year Transportation Services Agreement [Member] | Commercial Agreements [Member] | Crude oil [Member]
Commercial Agreements
Number of agreements | Agreement			1
Duration of agreements (in years)			5 years
MPC [Member] | Five Year Transportation Services Agreement [Member] | Commercial Agreements [Member] | Handling Crude Oil And Products [Member]
Commercial Agreements
Duration of agreements (in years)			5 years
MPC [Member] | Ten Year Storage Services Agreement [Member] | Commercial Agreements [Member] | Storage Services Butane Cavern [Member]
Commercial Agreements
Duration of agreements (in years)			10 years
MPC [Member] | Three Year Storage Services Agreement [Member] | Commercial Agreements [Member] | Storage services tank farms [Member]
Commercial Agreements
Number of agreements | Agreement			5
Duration of agreements (in years)			3 years
MPC [Member] | Six Year Transportation Services Agreement [Member] | Commercial Agreements [Member] | Providing marine transportation of crude oil, feedstocks and refined petroleum products, and related services [Member]
Commercial Agreements
Duration of agreements (in years)			6 years
MPC [Member] | Transportation Services Agreements [Member] | Commercial Agreements [Member] | Crude oil and product pipeline [Member]
Commercial Agreements
Number of renewals			2
Renewal term agreement			5 years
MPC [Member] | Storage Services Agreements [Member] | Commercial Agreements [Member] | Storage services tank farms [Member]
Commercial Agreements
Renewal term agreement			1 year
Centennial Pipeline Llc [Member] | MPC [Member]
Related Party Transaction [Line Items]
Equity Method Investment, Ownership Percentage			50.00%
Muskegon [Member] | MPC [Member]
Related Party Transaction [Line Items]
Equity Method Investment, Ownership Percentage			60.00%
MarkWest Utica EMG [Member]
Related Party Transaction [Line Items]
Equity Method Investment, Ownership Percentage		60.00%	56.00%	60.00%	60.00%
Ohio Gathering
Related Party Transaction [Line Items]
Equity Method Investment, Ownership Percentage			34.00%
Ohio Condensate Company, LLC [Member]
Related Party Transaction [Line Items]
Equity Method Investment, Ownership Percentage			60.00%
Related Party Revolving Credit Agreement [Member] | MPC Investment [Member]
Loan Agreement [Abstract]
Line of Credit Facility, Initiation Date		Dec. 4, 2015
Line of Credit Facility, Current Borrowing Capacity			$ 500
Expiration date		Dec. 4, 2020
Description of variable rate basis		LIBOR plus 1.50 percent
Proceeds from Long-term Lines of Credit			2,500	$ 301
Repayments of Long-term Lines of Credit			2,500	293
Long-term Debt, Gross		$ 8	$ 0	$ 8
Debt Instrument, Interest Rate, Effective Percentage		1.744%	1.939%	1.744%
Related Party Revolving Credit Agreement [Member] | MPL Investment LLC [Member]
Loan Agreement [Abstract]
Line of Credit Facility, Current Borrowing Capacity			$ 50
Expiration date			Dec. 31, 2015

Related Party Agreements and 65

Related Party Agreements and Transactions (Revenue from Related Parties) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Related Party Transaction [Line Items]
Other income - related parties	$ 101		$ 71		$ 40
Service revenue - related parties	603		593		662
Operating Lease, Income Statement, Lease Revenue, Related Parties	114		101		15
Product sales - related parties	11		1		0
Other Affiliates [Member]
Related Party Transaction [Line Items]
Other income - related parties	5		0
Ohio Condensate Company, LLC [Member]
Related Party Transaction [Line Items]
Other income - related parties	4		0
MPC [Member]
Related Party Transaction [Line Items]
Other income - related parties	60		68		39
Service revenue - related parties	603		593		662
Operating Lease, Income Statement, Lease Revenue, Related Parties	114		101		15
Product sales - related parties	11	[1]	1	[1]	$ 0
MarkWest Utica EMG [Member]
Related Party Transaction [Line Items]
Other income - related parties	$ 16		$ 0
[1]	(1)For 2016 and 2015, there were $46 million and $1 million, respectively, of 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. There were no such transactions in 2014.

Related Party Agreements and 66

Related Party Agreements and Transactions (Summary of Fees Received for Operating Pipelines for Related Parties Included in Other Income - Related Parties) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Related Party Transaction [Line Items]
Other income - related parties	$ 101	$ 71	$ 40
MPC [Member]
Related Party Transaction [Line Items]
Other income - related parties	60	68	39
Centennial Pipeline Llc [Member]
Related Party Transaction [Line Items]
Other income - related parties	1	1	1
Ohio Gathering
Related Party Transaction [Line Items]
Other income - related parties	$ 15	$ 2	$ 0

Related Party Agreements and 67

Related Party Agreements and Transactions Related Party Agreements and Transactions (Charges related to Omnibus Agreement) (Details) - MPC [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	$ 68	$ 76	$ 76
Purchases From Related Parties [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	29	30	30
General and administrative expenses [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	$ 39	$ 46	$ 46

Related Party Agreements and 68

Related Party Agreements and Transactions (Summary of Related Party Costs Added to Property, Plant and Equipment) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
MPC [Member] | Asset under construction [Member]
Property, Plant and Equipment [Line Items]
Costs added to property, plant and equipment	$ 38	$ 13	$ 8

Related Party Agreements and 69

Related Party Agreements and Transactions (Summary of Allocated Related Party Employee Benefit Costs by Income Statement Line Item) (Detail) - MPC [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Related Party Transaction [Line Items]
Expenses incurred under employee services agreements	$ 359	$ 158	$ 147
Purchases From Related Parties [Member]
Related Party Transaction [Line Items]
Expenses incurred under employee services agreements	287	136	123
General and administrative expenses [Member]
Related Party Transaction [Line Items]
Expenses incurred under employee services agreements	$ 72	$ 22	$ 24

Related Party Agreements and 70

Related Party Agreements and Transactions (Receivables from Related Parties) (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Receivables - related parties	$ 122	$ 187
MPC [Member]
Related Party Transaction [Line Items]
Receivables - related parties	117	175
MarkWest Utica EMG [Member]
Related Party Transaction [Line Items]
Receivables - related parties	2	4
Ohio Gathering
Related Party Transaction [Line Items]
Receivables - related parties	2	5
Other Affiliates [Member]
Related Party Transaction [Line Items]
Receivables - related parties	$ 1	$ 3

Related Party Agreements and 71

Related Party Agreements and Transactions Related Party Agreements and Transactions (Long Term Receivables from Related Parties) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Long-term receivables - related parties	$ 4	$ 25
MPC [Member]
Related Party Transaction [Line Items]
Long-term receivables - related parties	$ 4	$ 25

Related Party Agreements and 72

Related Party Agreements and Transactions (Payables to Related Parties) (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Payables - related parties	$ 75	$ 54
MPC [Member]
Related Party Transaction [Line Items]
Payables - related parties	51	33
MarkWest Utica EMG [Member]
Related Party Transaction [Line Items]
Payables - related parties	$ 24	$ 21
Related Party Revolving Credit Agreement [Member] | MPC Investment [Member]
Related Party Transaction [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	1.939%	1.744%

Related Party Agreements and 73

Related Party Agreements and Transactions (Deferred Revenue from Related Parties) (Details) - MPC [Member] - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Deferred Revenue Related Parties	$ 49	$ 41
Minimum Committed Volume Contracts [Member]
Related Party Transaction [Line Items]
Deferred Revenue Related Parties	44	36
Reimbursable Projects [Member]
Related Party Transaction [Line Items]
Deferred Revenue Related Parties	$ 5	$ 5

Net Income Per Limited Partne74

Net Income Per Limited Partner Unit (Schedule of Distributions by Partner Class) (Detail) - USD ($) $ in Millions		3 Months Ended													12 Months Ended
		Dec. 31, 2016	[1]	Sep. 30, 2016	[1]	Jun. 30, 2016	[1]	Mar. 31, 2016	[1]	Dec. 31, 2015	[1]	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Net Income Per Share [Line Items]
Potentially dilutive securities															0		0
Net income attributable to MPLX LP		$ 133		$ 141		$ 19	[2]	$ (60)	[3]	$ 18		$ 41	$ 51	$ 46	$ 233	[4]	$ 156	[4]	$ 121	[4]
Less: distribution declared															(938)		(315)		(112)
Undistributed net (loss) income attributable to MPLX LP															(705)		(159)		9
Preferred Partner [Member]
Net Income Per Share [Line Items]
Net income attributable to MPLX LP	[4]														41
Less: distribution declared		(16)		(16)		(9)		0		0		0	0	0	(41)	[5]	0	[5]	0	[5]
Limited Partners Common Units [Member]
Net Income Per Share [Line Items]
Net income attributable to MPLX LP	[4]														1		97		58
Less: distribution declared	[5]														(692)		(224)		(54)
MPC [Member]
Net Income Per Share [Line Items]
Less: distribution declared		$ (45)		$ (44)		$ (41)		$ (29)		$ (29)		$ (27)	$ (25)	$ (23)
MPC [Member] | General Partner [Member]
Net Income Per Share [Line Items]
Net income attributable to MPLX LP	[4]														191		57		8
Less: distribution declared	[5]														(205)		(60)		(6)
MPC [Member] | Limited Partners Subordinated Units [Member]
Net Income Per Share [Line Items]
Net income attributable to MPLX LP	[4]																2		55
Less: distribution declared	[5]														$ 0		$ (31)		$ (52)
[1]	(3)These amounts include results from the MarkWest Merger which closed on December 4, 2015. See Note 4 for more information on the MarkWest Merger.
[2]	(2)Second quarter 2016 results included impairment expense related to equity method investments of $89 million. See Note 5 for more information.
[3]	(1)First quarter 2016 results included goodwill impairment expense of $129 million. See Note 18 for more information.
[4]	(1)Allocation of net income (loss) attributable to MPLX LP assumes all earnings for the period had been distributed based on the current period distribution priorities.
[5]	(1)See Note 8 for information regarding the distribution.

Net Income Per Limited Partne75

Net Income 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, 2016	[1]	Sep. 30, 2016	[1]	Jun. 30, 2016	[1]	Mar. 31, 2016	[1]	Dec. 31, 2015	[1]	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Net income attributable to MPLX LP:
Less: distribution declared															$ (938)		$ (315)		$ (112)
Undistributed net income loss attributable to MPLX LP															(705)		(159)		9
Net income attributable to MPLX LP		$ 133		$ 141		$ 19	[2]	$ (60)	[3]	$ 18		$ 41	$ 51	$ 46	$ 233	[4]	$ 156	[4]	$ 121	[4]
Weighted average units outstanding:
Basic (shares)															338		99		76
Diluted (shares)															345		100		76
Limited Partners Common Units [Member]
Net income attributable to MPLX LP:
Less: distribution declared	[5]														$ (692)		$ (224)		$ (54)
Undistributed net income loss attributable to MPLX LP															(691)		(127)		4
Net income attributable to MPLX LP	[4]														$ 1		$ 97		$ 58
Weighted average units outstanding:
Basic (shares)															331		79		37
Diluted (shares)															338		80		37
Net income attributable to MPLX LP subsequent to initial public offering per limited partner unit:
Basic (in USD per unit)		$ 0.17		$ 0.22		$ (0.11)	[2]	$ (0.33)	[3]	$ (0.14)		$ 0.41	$ 0.50	$ 0.46	$ 0		$ 1.23		$ 1.55
Diluted (in USD per unit)		$ 0.17		$ 0.21		$ (0.11)	[2]	$ (0.33)	[3]	$ (0.14)		$ 0.41	$ 0.50	$ 0.46	$ 0		$ 1.22		$ 1.55
Preferred Partner [Member]
Net income attributable to MPLX LP:
Less: distribution declared		$ (16)		$ (16)		$ (9)		$ 0		$ 0		$ 0	$ 0	$ 0	$ (41)	[5]	$ 0	[5]	$ 0	[5]
Undistributed net income loss attributable to MPLX LP															0
Net income attributable to MPLX LP	[4]														41
MPC [Member]
Net income attributable to MPLX LP:
Less: distribution declared		$ (45)		$ (44)		$ (41)		$ (29)		$ (29)		$ (27)	$ (25)	$ (23)
MPC [Member] | General Partner [Member]
Net income attributable to MPLX LP:
Less: distribution declared	[5]														(205)		(60)		(6)
Undistributed net income loss attributable to MPLX LP															(14)		(3)		2
Net income attributable to MPLX LP	[4]														$ 191		$ 57		$ 8
Weighted average units outstanding:
Basic (shares)															7		2		2
Diluted (shares)															7		2		2
MPC [Member] | Limited Partners Subordinated Units [Member]
Net income attributable to MPLX LP:
Less: distribution declared	[5]														$ 0		$ (31)		$ (52)
Undistributed net income loss attributable to MPLX LP																	(29)		3
Net income attributable to MPLX LP	[4]																$ 2		$ 55
Weighted average units outstanding:
Basic (shares)																	18		37
Diluted (shares)																	18		37
Net income attributable to MPLX LP subsequent to initial public offering per limited partner unit:
Basic (in USD per unit)																	$ 0.11		$ 1.50
Diluted (in USD per unit)																	$ 0.11		$ 1.50
[1]	(3)These amounts include results from the MarkWest Merger which closed on December 4, 2015. See Note 4 for more information on the MarkWest Merger.
[2]	(2)Second quarter 2016 results included impairment expense related to equity method investments of $89 million. See Note 5 for more information.
[3]	(1)First quarter 2016 results included goodwill impairment expense of $129 million. See Note 18 for more information.
[4]	(1)Allocation of net income (loss) attributable to MPLX LP assumes all earnings for the period had been distributed based on the current period distribution priorities.
[5]	(1)See Note 8 for information regarding the distribution.

Equity (Units Outstanding) (Det

Equity (Units Outstanding) (Details) - shares	Jul. 01, 2016	Aug. 17, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Stockholders Equity [Line Items]
Aggregate percentage of general partner interest			2.00%
General partner units outstanding			7,371,105
Partners' Capital Account, Units, Converted			123,459	19,318	15,795
Limited Partners Common Units [Member]
Stockholders Equity [Line Items]
Common units outstanding			357,193,288
Subordinated Units [Member]
Stockholders Equity [Line Items]
Equity Instruments Conversion Date		Aug. 17, 2015
MPC [Member] | Limited Partners Common Units [Member]
Stockholders Equity [Line Items]
Common units outstanding			86,619,313
Limited Partners Common Units [Member]
Stockholders Equity [Line Items]
Partners' Capital Account, Units, Converted	4,350,057		120,989	18,932	15,479
Limited Partners Common Units [Member] | Subordinated Units [Member]
Stockholders Equity [Line Items]
Partners' Capital Account, Units, Converted		36,951,515		36,951,515
Limited Partners Common Units [Member] | MPC [Member]
Stockholders Equity [Line Items]
Common units outstanding			86,000,000	57,000,000

Equity (MarkWest Merger) (Detai

Equity (MarkWest Merger) (Details) $ / shares in Units, $ in Millions	Jul. 01, 2016shares	Dec. 04, 2015$ / sharesshares	Dec. 31, 2014shares	Dec. 31, 2016USD ($)shares	Dec. 31, 2015USD ($)shares	Dec. 31, 2014USD ($)shares
Stockholders Equity [Line Items]
Partners' Capital Account, Units, Sale of Units				26,885,597	25,680	3,520,408
Partners' Capital Account, Units, Contributed				6,716,419
Partners' Capital Account, Sale of Units | $				$ 792	$ 1
Partners' Capital Account, Units, Converted				123,459	19,318	15,795
Proceeds from Contributions from Parent | $				$ 225	$ 0	$ 0
Units Acquired					229,493,171
MarkWest [Member]
Stockholders Equity [Line Items]
Common Units Conversion Ratio		1.09
Class B Units Conversion Ratio		1.09
Cash consideration to unitholders | $ / shares		$ 6.20
General Partner Units [Member]
Stockholders Equity [Line Items]
Partners' Capital Account, Units, Sale of Units			130,084			70,408
Partners' Capital Account, Units, Contributed				436,758
Partners' Capital Account, Sale of Units | $				$ 1
Partners' Capital Account, Units, Converted				2,470	386	316
Limited Partners Common Units [Member]
Stockholders Equity [Line Items]
Partners' Capital Account, Units, Sale of Units						3,450,000
Partners' Capital Account, Units, Contributed				21,401,137
Partners' Capital Account, Units, Converted	4,350,057			120,989	18,932	15,479
Limited Partners Common Units [Member] | MarkWest [Member]
Stockholders Equity [Line Items]
Units Acquired		216,350,465			216,350,465
Class A Units [Member] | MarkWest [Member]
Stockholders Equity [Line Items]
Units Acquired				28,554,313
Class B Units [Member]
Stockholders Equity [Line Items]
Partners' Capital Account, Units, Converted	3,990,878
Class B Units [Member] | MarkWest [Member]
Stockholders Equity [Line Items]
Units Acquired				7,981,756	(7,981,756)
General Partner [Member] | MPC [Member]
Stockholders Equity [Line Items]
Partners' Capital Account, Sale of Units | $				$ 16
Proceeds from Contributions from Parent | $				141
Limited Partners Common Units [Member] | MPC [Member]
Stockholders Equity [Line Items]
Proceeds from Contributions from Parent | $				$ 84

Equity (ATM Program) (Details)

Equity (ATM Program) (Details) - USD ($) $ / shares in Units, $ in Millions	Jan. 25, 2017	Jul. 01, 2016	Dec. 04, 2015	Dec. 01, 2014	Mar. 01, 2014	May 02, 2013	Dec. 31, 2014	Dec. 31, 2016		Sep. 30, 2016	[1]	Jun. 30, 2016	[1]	Mar. 31, 2016	[1]	Dec. 31, 2015	[1]	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014		Dec. 08, 2014
Stockholders Equity [Line Items]
Distribution Made to Limited Partner, Cash Distributions Declared																					$ 938		$ 315		$ 112
Partners' Capital Account, Sale of Units																					$ 792		$ 1
Partners' Capital Account, Units, Acquisitions																							229,493,171
Partners' Capital Account, Units, Converted																					123,459		19,318		15,795
Limited Liability Company (LLC) or Limited Partnership (LP), Managing Member or General Partner, Ownership Interest																					2.00%
Units Offered																					26,885,597		25,680		3,520,408
Shares Issued, Price Per Share																											$ 66.68
Partners' Capital Account, Public Sale of Units Net of Offering Costs																									$ 230
ATM Program [Member]
Stockholders Equity [Line Items]
Partners' Capital Account, Public Sale of Units Net of Offering Costs																					$ 776		$ 1
Remaining Authorized Issuance Amount								$ 717													717
Preferred Partner [Member]
Stockholders Equity [Line Items]
Distribution Made to Limited Partner, Cash Distributions Declared								16	[1]	$ 16		$ 9		$ 0		$ 0		$ 0	$ 0	$ 0	41	[2]	$ 0	[2]	$ 0	[2]
General Partner Units [Member]
Stockholders Equity [Line Items]
Partners' Capital Account, Sale of Units																					$ 1
Partners' Capital Account, Units, Converted																					2,470		386		316
Units Offered							130,084																		70,408
General Partner Units [Member] | ATM Program [Member]
Stockholders Equity [Line Items]
Partners' Capital Account, Sale of Units																					$ 16		$ 1
Units Offered																					537,710		514
Class B Units [Member]
Stockholders Equity [Line Items]
Partners' Capital Account, Units, Converted		3,990,878
MarkWest [Member]
Stockholders Equity [Line Items]
Effective date of acquisition			Dec. 4, 2015
MarkWest [Member] | Class B Units [Member]
Stockholders Equity [Line Items]
Partners' Capital Account, Units, Acquisitions																					7,981,756		(7,981,756)
MarkWest Merger [Member] | General Partner Units [Member]
Stockholders Equity [Line Items]
Partners' Capital Account, Sale of Units																							$ 169
Partners' Capital Account, Units, Converted																							5,160,950
Pipe Line Holding [Member]
Stockholders Equity [Line Items]
Partners' Capital Account, Units, Acquisitions																									2,983,780
Effective date of acquisition			Dec. 4, 2015	Dec. 1, 2014	Mar. 1, 2014	May 1, 2013
Pipe Line Holding [Member] | General Partner Units [Member]
Stockholders Equity [Line Items]
Partners' Capital Account, Units, Acquisitions																									59,676
Public [Member]
Stockholders Equity [Line Items]
Distribution Made to Limited Partner, Cash Distributions Declared								140	[1]	135		131		127		120		11	10	10
Limited Partners Common Units [Member] | Public [Member]
Stockholders Equity [Line Items]
Partners' Capital Account, Sale of Units																					$ 776		$ 1
Partners' Capital Account, Public Sale of Units Net of Offering Costs																									$ 221
MPC [Member]
Stockholders Equity [Line Items]
Distribution Made to Limited Partner, Cash Distributions Declared								$ 45	[1]	$ 44		$ 41		$ 29		$ 29		$ 27	$ 25	$ 23
MPC [Member] | General Partner [Member]
Stockholders Equity [Line Items]
Partners' Capital Account, Sale of Units																					$ 16
MPC [Member] | General Partner [Member] | General Partner Units [Member]
Stockholders Equity [Line Items]
Partners' Capital Account, Public Sale of Units Net of Offering Costs																									$ 9
Subsequent Event [Member]
Stockholders Equity [Line Items]
Distribution Made to Limited Partner, Cash Distributions Declared	$ 242
[1]	(3)These amounts include results from the MarkWest Merger which closed on December 4, 2015. See Note 4 for more information on the MarkWest Merger.
[2]	(1)See Note 8 for information regarding the distribution.

Equity (Changes in Partners Cap

Equity (Changes in Partners Capital, Unit Rollforward) (Details) - USD ($) $ / shares in Units, $ in Millions	Jul. 01, 2016	Dec. 04, 2015	Aug. 17, 2015	Dec. 01, 2014	Dec. 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Mar. 31, 2016	Dec. 08, 2014
Stockholders Equity [Line Items]
Balance at December 31, 2014						311,469,407	81,931,238	75,411,255
Unit conversion						(123,459)	(19,318)	(15,795)
Units Acquired							229,493,171
Units Offered						26,885,597	25,680	3,520,408
Balance at December 31, 2014					81,931,238	311,469,407	81,931,238	75,411,255
Balance at December 31, 2015					81,931,238	368,555,271	311,469,407	81,931,238
2014 Activity [Abstract]
Shares Issued, Price Per Share										$ 66.68
Partners' Capital Account, Public Sale of Units Net of Offering Costs								$ 230
Partners' Capital Account, Units, Contributed						6,716,419
Limited Partners Common Units [Member]
Stockholders Equity [Line Items]
Balance at December 31, 2014						296,687,176	43,341,098	36,951,515
Unit conversion	(4,350,057)					(120,989)	(18,932)	(15,479)
Units Offered								3,450,000
Balance at December 31, 2014					43,341,098	296,687,176	43,341,098	36,951,515
Balance at December 31, 2015					43,341,098	357,193,288	296,687,176	43,341,098
2014 Activity [Abstract]
Partners' Capital Account, Units, Contributed						21,401,137
Class B Units [Member]
Stockholders Equity [Line Items]
Balance at December 31, 2014						7,981,756
Unit conversion	(3,990,878)
Balance at December 31, 2014						7,981,756	7,981,756
Balance at December 31, 2015						3,990,878	7,981,756
Limited Partners Subordinated Units [Member]
Stockholders Equity [Line Items]
Balance at December 31, 2014						0	36,951,515	36,951,515
Balance at December 31, 2014					36,951,515	0	36,951,515	36,951,515
Balance at December 31, 2015					36,951,515	0	0	36,951,515
General Partner Units [Member]
Stockholders Equity [Line Items]
Balance at December 31, 2014						6,800,475	1,638,625	1,508,225
Unit conversion						(2,470)	(386)	(316)
Units Offered					130,084			70,408
Balance at December 31, 2014					1,638,625	6,800,475	1,638,625	1,508,225
Balance at December 31, 2015					1,638,625	7,371,105	6,800,475	1,638,625
2014 Activity [Abstract]
Partners' Capital Account, Units, Contributed						436,758
Pipe Line Holding [Member]
Stockholders Equity [Line Items]
Units Acquired								2,983,780
2014 Activity [Abstract]
Percentage Of Partners Interest Contributed				7.625%
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned				$ 200
Pipe Line Holding [Member] | Limited Partners Common Units [Member]
Stockholders Equity [Line Items]
Units Acquired				2,924,104				2,924,104
2014 Activity [Abstract]
Shares Issued, Price Per Share				$ 68.397
Pipe Line Holding [Member] | General Partner Units [Member]
Stockholders Equity [Line Items]
Units Acquired								59,676
MarkWest [Member] | Limited Partners Common Units [Member]
Stockholders Equity [Line Items]
Units Acquired		216,350,465					216,350,465
MarkWest [Member] | Class B Units [Member]
Stockholders Equity [Line Items]
Units Acquired						7,981,756	(7,981,756)
Hardin Street Marine [Member]
Stockholders Equity [Line Items]
Units Acquired						22,993,880
2014 Activity [Abstract]
Business Acquisition, Equity Interest Issued or Issuable, Value Assigned									$ 600
Hardin Street Marine [Member] | Limited Partners Common Units [Member]
Stockholders Equity [Line Items]
Units Acquired						22,534,002
Hardin Street Marine [Member] | General Partner Units [Member]
Stockholders Equity [Line Items]
Units Acquired						459,878
Subordinated Units [Member] | Limited Partners Common Units [Member]
Stockholders Equity [Line Items]
Unit conversion			(36,951,515)				(36,951,515)
Subordinated Units [Member] | Limited Partners Subordinated Units [Member]
Stockholders Equity [Line Items]
Unit conversion							36,951,515
Class A Units [Member] | Limited Partners Common Units [Member]
2014 Activity [Abstract]
Partners' Capital Account, Units, Contributed						7,153,177
ATM Program [Member]
2014 Activity [Abstract]
Partners' Capital Account, Public Sale of Units Net of Offering Costs						$ 776	$ 1
ATM Program [Member] | Limited Partners Common Units [Member]
Stockholders Equity [Line Items]
Units Offered						26,347,887	25,166
ATM Program [Member] | General Partner Units [Member]
Stockholders Equity [Line Items]
Units Offered						537,710	514
Class B Units [Member]
Stockholders Equity [Line Items]
Unit conversion						(366,509)
Class B Units [Member] | General Partner Units [Member]
Stockholders Equity [Line Items]
Unit conversion						(7,330)

Equity (Incentive Distribution

Equity (Incentive Distribution Rights) (Details)	12 Months Ended
	Dec. 31, 2016$ / shares
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Aggregate percentage of general partner interest	2.00%
Minimum Quarterly Distribution [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Total quarterly distribution per unit target amount	$ 0.2625
Minimum [Member] | First Target Distribution [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Total quarterly distribution per unit target amount	0.2625
Minimum [Member] | Second Target Distribution [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Total quarterly distribution per unit target amount	0.301875
Minimum [Member] | Third Target Distribution [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Total quarterly distribution per unit target amount	0.328125
Minimum [Member] | Thereafter
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Total quarterly distribution per unit target amount	0.393750
Maximum [Member] | First Target Distribution [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Total quarterly distribution per unit target amount	0.301875
Maximum [Member] | Second Target Distribution [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Total quarterly distribution per unit target amount	0.328125
Maximum [Member] | Third Target Distribution [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Total quarterly distribution per unit target amount	$ 0.393750

Equity (Net Income Allocation)

Equity (Net Income Allocation) (Details) - USD ($) $ in Millions		3 Months Ended													12 Months Ended
		Dec. 31, 2016	[1]	Sep. 30, 2016	[1]	Jun. 30, 2016	[1]	Mar. 31, 2016	[1]	Dec. 31, 2015	[1]	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Class of Stock [Line Items]
Net income attributable to MPLX LP		$ 133		$ 141		$ 19	[2]	$ (60)	[3]	$ 18		$ 41	$ 51	$ 46	$ 233	[4]	$ 156	[4]	$ 121	[4]
Distribution Made to Limited Partner, Cash Distributions Declared															938		315		112
Incentive Distribution Rights And Other															191		55		4
Net income attributable to MPLX LP available to general and limited partners															1		101		117
General partner's two percent interest in net income attributable to MPLX LP															0		2		2
General partner’s interest in net income attributable to MPLX LP															191		57		6
Preferred Partner [Member]
Class of Stock [Line Items]
Net income attributable to MPLX LP	[4]														41
Distribution Made to Limited Partner, Cash Distributions Declared		$ 16		$ 16		$ 9		$ 0		$ 0		$ 0	$ 0	$ 0	$ 41	[5]	$ 0	[5]	$ 0	[5]
[1]	(3)These amounts include results from the MarkWest Merger which closed on December 4, 2015. See Note 4 for more information on the MarkWest Merger.
[2]	(2)Second quarter 2016 results included impairment expense related to equity method investments of $89 million. See Note 5 for more information.
[3]	(1)First quarter 2016 results included goodwill impairment expense of $129 million. See Note 18 for more information.
[4]	(1)Allocation of net income (loss) attributable to MPLX LP assumes all earnings for the period had been distributed based on the current period distribution priorities.
[5]	(1)See Note 8 for information regarding the distribution.

Equity (Cash Distributions) (De

Equity (Cash Distributions) (Details) - USD ($) $ / shares in Units, $ in Millions	Feb. 14, 2017	Feb. 06, 2017	Jan. 25, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Distribution Made to Limited Partner, Cash Distributions Declared				$ 938	$ 315	$ 112
General partner's distributions				18	6	2
General partner's incentive distribution rights distributions				187	54	4
Total general partner's distributions				205	60	6
Limited partners' distributions				692	255	106
Limited Partners Common Units [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Limited partners' distributions				692	224	54
Subordinated Units [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Limited partners' distributions				0	31	$ 52
Preferred Stock [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Limited partners' distributions				$ 41	$ 0
Subsequent Event [Member]
Incentive Distribution Made to Managing Member or General Partner [Line Items]
Distribution made to limited partner, declaration date			Jan. 25, 2017
Distribution Made to Limited Partner, Cash Distributions Declared			$ 242
Cash distributions declared per limited partner common unit			$ 0.5200
Distribution Made to Limited Partner, Distribution Date	Feb. 14, 2017
Distribution Made to Limited Partner, Date of Record		Feb. 6, 2017

Redeemable Preferred Units (Det

Redeemable Preferred Units (Details) - USD ($) $ / shares in Units, $ in Millions	May 13, 2016	Dec. 31, 2016		Sep. 30, 2016	[1]	Jun. 30, 2016	[1]	Mar. 31, 2016	[1]	Dec. 31, 2015		Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014		Dec. 08, 2014
Partners' Capital Account, Units, Sale of Units																26,885,597		25,680		3,520,408
Shares Issued, Price Per Share																						$ 66.68
Proceeds from Issuance of Preferred Limited Partners Units																$ 984		$ 0		$ 0
Distribution Made to Limited Partner, Cash Distributions Declared																938		315		112
Temporary Equity, Net Income															$ 41
Distribution Made to Limited Partner, Cash Distributions Paid																845		158		103
Temporary Equity, Carrying Amount, Including Portion Attributable to Noncontrolling Interests		$ 1,000								$ 0					1,000	1,000		0
Series A Convertible Preferred Units [Member]
Partners' Capital Account, Units, Sale of Units	30,800,000
Preferred Stock, Dividend Rate, Percentage	6.50%
Proceeds from Issuance of Preferred Limited Partners Units	$ 984
Preferred Stock, Dividend Rate, Per-Dollar-Amount	$ 0.528125
Preferred Units, Description	The purchasers may convert their Preferred units into common units, at any time after the third anniversary of the issuance date or prior to liquidation, dissolution or winding up of the Partnership, in full or in part, subject to minimum conversion amounts and conditions. After the fourth anniversary of the issuance date, the Partnership may convert the 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 LP common units is greater than $48.75 for the 20 day trading period immediately preceding the conversion notice date. The conversion rate for the 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. The holders of the Preferred units are entitled to vote on an as-converted basis with the common unitholders and will have certain other class voting rights with respect to any amendment to the partnership agreement that would adversely affect any rights, preferences or privileges of the Preferred units. In addition, upon certain events involving a change in control the holders of Preferred units may elect, among other potential elections, to convert their Preferred units to common units at the then change of control conversion rate.
Preferred Stock [Member] | Series A Convertible Preferred Units [Member]
Shares Issued, Price Per Share	$ 32.50
Preferred Partner [Member]
Distribution Made to Limited Partner, Cash Distributions Declared		$ 16	[1]	$ 16		$ 9		$ 0		$ 0	[1]	$ 0	$ 0	$ 0		$ 41	[2]	$ 0	[2]	$ 0	[2]
Distribution Made to Limited Partner, Cash Distributions Paid															$ (25)
[1]	(3)These amounts include results from the MarkWest Merger which closed on December 4, 2015. See Note 4 for more information on the MarkWest Merger.
[2]	(1)See Note 8 for information regarding the distribution.

Redeemable Preferred Units Poli

Redeemable Preferred Units Policy (Details) $ in Millions	8 Months Ended
	Dec. 31, 2016USD ($)
Temporary Equity Disclosure [Abstract]
Temporary Equity, Net Income	$ 41

Redeemable Preferred Units Narr

Redeemable Preferred Units Narrative (Details) - USD ($) $ in Millions

3 Months Ended

12 Months Ended

Dec. 31, 2016

[1]

Sep. 30, 2016

[1]

Jun. 30, 2016

[1]

Mar. 31, 2016

[1]

Dec. 31, 2015

[1]

Sep. 30, 2015

Jun. 30, 2015

Mar. 31, 2015

Dec. 31, 2016

Dec. 31, 2015

Dec. 31, 2014

Distribution Made to Limited Partner, Cash Distributions Declared

$ 938

$ 315

$ 112

Preferred Partner [Member]

Distribution Made to Limited Partner, Cash Distributions Declared

$ 16

$ 16

$ 9

$ 0

$ 0

$ 0

$ 0

$ 0

$ 41

[2]

$ 0

[2]

$ 0

[2]

[1]

(3)These amounts include results from the MarkWest Merger which closed on December 4, 2015. See Note 4 for more information on the MarkWest Merger.

[2]

(1)See Note 8 for information regarding the distribution.

Redeemable Preferred Units Tabl

Redeemable Preferred Units Table (Details) - USD ($) $ in Millions	8 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Temporary Equity, Net Income	$ 41
Distribution Made to Limited Partner, Cash Distributions Paid		$ 845	$ 158	$ 103
Temporary Equity, Carrying Amount, Including Portion Attributable to Noncontrolling Interests	1,000	$ 1,000	$ 0
Preferred Partner [Member]
Distribution Made to Limited Partner, Cash Distributions Paid	$ (25)

Segment Information (Details)

Segment Information (Details)	Dec. 04, 2015	Dec. 31, 2016
Segment Reporting Information [Line Items]
Number of reportable segments		2
MarkWest [Member]
Segment Reporting Information [Line Items]
Effective date of acquisition	Dec. 4, 2015

Segment Information (Income fro

Segment Information (Income from operations and capital expenditures) (Details) - USD ($) $ in Millions	3 Months Ended													12 Months Ended
	Dec. 31, 2016	[1]	Sep. 30, 2016	[1]	Jun. 30, 2016	[1],[2]	Mar. 31, 2016	[1]	Dec. 31, 2015	[1]	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Payments to Acquire Property, Plant, and Equipment														$ 1,206	$ 288	$ 141
Segment revenues														572	36	0
Segment other income														6	6	6
Total segment revenues and other income	$ 714		$ 703		$ 564		$ 609		$ 333		$ 214	$ 213	$ 201	2,590	961	793
Segment Reconciling Items [Member]
Segment Reporting Information [Line Items]
Payments to Acquire Property, Plant, and Equipment														(131)	(24)	0
Operating Segments [Member]
Segment Reporting Information [Line Items]
Payments to Acquire Property, Plant, and Equipment														1,337	312	141
Segment revenues														2,972	910
Segment other income														69	75
Total segment revenues and other income														3,041	985	793
Segment cost of revenues														1,275	441
Segment operating income before portion attributable to noncontrolling interest and Predecessor														1,766	544
Segment portion attributable to noncontrolling interest and Predecessor														181	146
Segment operating income attributable to MPLX LP														1,585	398	213
Operating Segments [Member] | L&S [Member]
Segment Reporting Information [Line Items]
Payments to Acquire Property, Plant, and Equipment														443	212	141
Segment revenues														787	760	747
Segment other income														68	75	46
Total segment revenues and other income														855	835	793
Segment cost of revenues														368	379	392
Segment operating income before portion attributable to noncontrolling interest and Predecessor														487	456	401
Segment portion attributable to noncontrolling interest and Predecessor														34	134	188
Segment operating income attributable to MPLX LP														453	322	213
Operating Segments [Member] | G&P [Member]
Segment Reporting Information [Line Items]
Payments to Acquire Property, Plant, and Equipment														894	100	$ 0
Segment revenues														2,185	150
Segment other income														1	0
Total segment revenues and other income														2,186	150
Segment cost of revenues														907	62
Segment operating income before portion attributable to noncontrolling interest and Predecessor														1,279	88
Segment portion attributable to noncontrolling interest and Predecessor														147	12
Segment operating income attributable to MPLX LP														$ 1,132	$ 76
[1]	(3)These amounts include results from the MarkWest Merger which closed on December 4, 2015. See Note 4 for more information on the MarkWest Merger.
[2]	(2)Second quarter 2016 results included impairment expense related to equity method investments of $89 million. See Note 5 for more information.

Segment Information (Reconcilia

Segment Information (Reconciliation to Income from operations) (Details) - USD ($) $ in Millions		1 Months Ended		3 Months Ended													12 Months Ended
		Dec. 31, 2015	[1]	Dec. 31, 2016	[2]	Sep. 30, 2016	[2]	Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2015	[2]	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016		Dec. 31, 2015	Dec. 31, 2014
Segment Reporting, Revenue Reconciling Item [Line Items]
Income (Loss) Attributable to Predecessor																	$ 23		$ 92	$ 61
(Loss) income from equity method investments		$ 3															(74)	[1]	3	0
Other income - related parties																	101		71	40
Goodwill and Intangible Asset Impairment								$ (1)		$ (129)							(130)		0	0
Depreciation and amortization																	(546)		(116)	(75)
General and administrative expenses																	(193)		(118)	(81)
Income from operations				$ 197		$ 207		$ 76	[2],[3]	$ 27	[2],[4]	$ 74		$ 68	$ 82	$ 74	507		298	245
Operating Segments [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Segment operating income attributable to MPLX LP																	1,585		398	213
Segment Reconciling Items [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Segment portion attributable to unconsolidated affiliates																	173		8	(85)
Income (Loss) Attributable to Predecessor																	34		133	103
(Loss) income from equity method investments																	(74)		3	0
Other income - related parties																	40		2	0
Unrealized derivative (losses) gains(1)	[5]																(36)		4	0
L&S [Member] | Operating Segments [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Segment operating income attributable to MPLX LP																	453		322	$ 213
G&P [Member] | Operating Segments [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Segment operating income attributable to MPLX LP																	$ 1,132		$ 76
[1]	(2)Income (loss) from equity method investments includes the impact of any basis differential amortization or accretion.
[2]	(3)These amounts include results from the MarkWest Merger which closed on December 4, 2015. See Note 4 for more information on the MarkWest Merger.
[3]	(2)Second quarter 2016 results included impairment expense related to equity method investments of $89 million. See Note 5 for more information.
[4]	(1)First quarter 2016 results included goodwill impairment expense of $129 million. See Note 18 for more information.
[5]	(1) The Partnership makes a distinction between realized or unrealized gains and losses on derivatives. During the period when a derivative contract is outstanding, we record changes in the fair value of the derivative as an unrealized gain or loss. When a derivative contract matures or is settled, we reverse the previously recorded unrealized gain or loss and record the realized gain or loss of the contract.

Segment Information (Reconcil90

Segment Information (Reconciliation to Total revenues and other income) (Details) - USD ($) $ in Millions		1 Months Ended		3 Months Ended													12 Months Ended
		Dec. 31, 2015	[3]	Dec. 31, 2016	[1]	Sep. 30, 2016	[1]	Jun. 30, 2016	[1],[2]	Mar. 31, 2016	[1]	Dec. 31, 2015	[1]	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016		Dec. 31, 2015	Dec. 31, 2014
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenues and other income				$ 714		$ 703		$ 564		$ 609		$ 333		$ 214	$ 213	$ 201	$ 2,590		$ 961	$ 793
Income (Loss) from Equity Method Investments		$ 3															(74)	[3]	3	0
Other income - related parties																	101		71	40
Operating Segments [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Total revenues and other income																	3,041		985	793
Segment Reconciling Items [Member]
Segment Reporting, Revenue Reconciling Item [Line Items]
Revenue adjustment for unconsolidated affiliates																	(402)		(28)	0
Income (Loss) from Equity Method Investments																	(74)		3	0
Other income - related parties																	40		2	0
Derivative, Loss on Derivative	[4]																$ (15)		$ (1)	$ 0
[1]	(3)These amounts include results from the MarkWest Merger which closed on December 4, 2015. See Note 4 for more information on the MarkWest Merger.
[2]	(2)Second quarter 2016 results included impairment expense related to equity method investments of $89 million. See Note 5 for more information.
[3]	(2)Income (loss) from equity method investments includes the impact of any basis differential amortization or accretion.
[4]	(1) The Partnership makes a distinction between realized or unrealized gains and losses on derivatives. During the period when a derivative contract is outstanding, we record changes in the fair value of the derivative as an unrealized gain or loss. When a derivative contract matures or is settled, we reverse the previously recorded unrealized gain or loss and record the realized gain or loss of the contract.

Segment Information (Reconcil91

Segment Information (Reconciliation to Net Income Attributable to Noncontrolling Interests (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reconciliation to Net Income Attributable to Noncontrolling Interests [Line Items]
Net Income Loss Attributable to Noncontrolling Interest and Predecessor	$ 25	$ 93	$ 118
Operating Segments [Member]
Reconciliation to Net Income Attributable to Noncontrolling Interests [Line Items]
Segment portion attributable to noncontrolling interest	181	146	188
Segment Reconciling Items [Member]
Reconciliation to Net Income Attributable to Noncontrolling Interests [Line Items]
Portion of noncontrolling interests and Predecessor related to items below segment income from operations	(124)	(48)	(70)
Portion of operating income attributable to noncontrolling interests of unconsolidated affiliates	$ (32)	$ (5)	$ 0

Segment Information (Reconcil92

Segment Information (Reconciliation of Segment Capital Expenditures) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting, Other Significant Reconciling Item [Line Items]
Additions to property, plant and equipment	$ (1,206)	$ (288)	$ (141)
Operating Segments [Member]
Segment Reporting, Other Significant Reconciling Item [Line Items]
Additions to property, plant and equipment	(1,337)	(312)	(141)
Operating Segments [Member] | L&S [Member]
Segment Reporting, Other Significant Reconciling Item [Line Items]
Additions to property, plant and equipment	(443)	(212)	(141)
Operating Segments [Member] | G&P [Member]
Segment Reporting, Other Significant Reconciling Item [Line Items]
Additions to property, plant and equipment	(894)	(100)	0
Segment Reconciling Items [Member]
Segment Reporting, Other Significant Reconciling Item [Line Items]
Additions to property, plant and equipment	$ 131	$ 24	$ 0

Segment Information (Assets by

Segment Information (Assets by Segment) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting, Asset Reconciling Item [Line Items]
Cash and cash equivalents	$ 234	$ 43	$ 27	$ 54
Assets	16,646	16,104
Operating Segments [Member] | L&S [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	2,115	1,842
Operating Segments [Member] | G&P [Member]
Segment Reporting, Asset Reconciling Item [Line Items]
Assets	$ 14,297	$ 14,219

Major Customer and Concentrat94

Major Customer and Concentration of Credit Risk (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Concentration Risk [Line Items]
Receivables, net	$ 297	$ 245
First Major Customer [Member] | MPC [Member] | Revenues And Other Income [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	30.00%	79.00%	90.00%
Second Major Customer [Member]
Concentration Risk [Line Items]
Receivables, net	$ 59
Second Major Customer [Member] | Revenues And Other Income [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	12.00%
Third Major Customer [Member]
Concentration Risk [Line Items]
Receivables, net	$ 13
Third Major Customer [Member] | Revenues And Other Income [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	10.00%

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016		Dec. 31, 2015	Dec. 31, 2014	Sep. 02, 2016
Income Taxes [Line Items]
(Benefit) provision for income tax	$ (12)		$ 1	$ 1
Income tax rate	5.00%		1.00%
Federal statutory rate	35.00%	[1]	35.00%
Interest and penalties, net expenses (benefits)	$ 1		$ 1
Income Tax Examination, Penalties and Interest Accrued	$ 1		1
Federal [Member] | Minimum [Member]
Income Taxes [Line Items]
Open Tax Year	2,013
Federal [Member] | Maximum [Member]
Income Taxes [Line Items]
Open Tax Year	2,015
State [Member] | Minimum [Member]
Income Taxes [Line Items]
Open Tax Year	2,012
State [Member] | Maximum [Member]
Income Taxes [Line Items]
Open Tax Year	2,015
MPC [Member]
Income Taxes [Line Items]
Deferred Tax Liabilities, Net					$ 377
MarkWest Hydrocarbon [Member]
Income Taxes [Line Items]
Operating Loss Carryforwards	$ 0
Reportable Legal Entities [Member] | MarkWest Hydrocarbon [Member]
Income Taxes [Line Items]
(Benefit) provision for income tax	$ (13)	[1]	$ 3
[1]	(1)MarkWest Hydrocarbon paid tax on its share of the Partnership’s income or loss as a result of its ownership of MPLX LP Class A units through September 1, 2016.

Income Taxes (Components of Tax

Income Taxes (Components of Tax Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current Federal Tax Expense (Benefit)	$ 4	$ 0
Current State and Local Tax Expense (Benefit)	1	0
Current Income Tax Expense (Benefit)	5	0
Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract]
Federal	(16)	3
State	(1)	(2)
Total deferred	(17)	1	$ 0
(Benefit) provision for income tax	$ (12)	$ 1	$ 1

Income Taxes (Reconciliation of

Income Taxes (Reconciliation of Federal Statutory Income Tax Rate) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016		Dec. 31, 2015	Dec. 31, 2014
Entity Information [Line Items]
(Loss) income before (benefit) provision for income tax		$ 246		$ 250	$ 240
Federal statutory rate		35.00%	[1]	35.00%
Federal income tax at statutory rate		$ (14)		$ 3
State income taxes net of federal benefit		(1)		(2)
Provision on income from MPLX LP Class A units		3		1
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount		(1)
Other		1		(1)
(Benefit) provision for income tax		(12)		1	$ 1
Reportable Legal Entities [Member] | MarkWest Hydrocarbon [Member]
Entity Information [Line Items]
(Loss) income before (benefit) provision for income tax		(41)	[1]	9
Federal income tax at statutory rate		(14)	[1]	3
State income taxes net of federal benefit		(2)	[1]	0
Provision on income from MPLX LP Class A units		3	[1]	1
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount	[1]	(1)
Other		1	[1]	(1)
(Benefit) provision for income tax		(13)	[1]	3
Reportable Legal Entities [Member] | Partnership [Member]
Entity Information [Line Items]
(Loss) income before (benefit) provision for income tax		285		240
Federal income tax at statutory rate		0		0
State income taxes net of federal benefit		1		(2)
Provision on income from MPLX LP Class A units		0		0
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount		0
Other		0		0
(Benefit) provision for income tax		1		(2)
Consolidation, Eliminations [Member]
Entity Information [Line Items]
(Loss) income before (benefit) provision for income tax		2		1
Federal income tax at statutory rate		0		0
State income taxes net of federal benefit		0		0
Provision on income from MPLX LP Class A units		0		0
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount		0
Other		0		0
(Benefit) provision for income tax		$ 0		$ 0
[1]	(1)MarkWest Hydrocarbon paid tax on its share of the Partnership’s income or loss as a result of its ownership of MPLX LP Class A units through September 1, 2016.

Income Taxes (Components of Def

Income Taxes (Components of Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Income Tax Examination, Penalties and Interest Accrued	$ 1	$ 1
Deferred Tax Assets, Net [Abstract]
Derivatives	0	9
Net operating loss carryforwards	0	62
Total deferred tax assets		71
Deferred Tax Liabilities, Net [Abstract]
Property, plant and equipment	5	7
Investments in subsidiaries and affiliates	0	442
Total deferred tax liabilities	5	449
Deferred Tax Liabilities, Net	$ 5	$ 378

Inventories (Details)

Inventories (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Inventory Disclosure [Abstract]
NGLs	$ 2	$ 3
Line fill	9	5
Spare parts, materials and supplies	43	43
Total inventories	$ 54	$ 51

Property, Plant and Equipmen100

Property, Plant and Equipment (Summary of Property, Plant and Equipment) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Property plant and equipment, gross	$ 11,845	$ 10,647
Less accumulated depreciation	1,115	650
Property, plant and equipment, net	10,730	9,997
Natural gas gathering and NGL transportation pipelines and facilities [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment, gross	4,748	4,307
Processing, fractionation and storage facilities [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment, gross	3,467	3,185
Pipelines and related assets [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment, gross	1,492	1,128
Barges and towing vessels [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment, gross	479	475
Land, building, office equipment and other [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment, gross	701	606
Asset under construction [Member]
Property, Plant and Equipment [Line Items]
Property plant and equipment, gross	$ 958	$ 946
Minimum [Member] | Natural gas gathering and NGL transportation pipelines and facilities [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	15 years
Minimum [Member] | Processing, fractionation and storage facilities [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	24 years
Minimum [Member] | Pipelines and related assets [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	19 years
Minimum [Member] | Land, building, office equipment and other [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	10 years
Maximum [Member] | Natural gas gathering and NGL transportation pipelines and facilities [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	30 years
Maximum [Member] | Processing, fractionation and storage facilities [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	37 years
Maximum [Member] | Pipelines and related assets [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	42 years
Maximum [Member] | Land, building, office equipment and other [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Lives	25 years

Property Plant and Equipment (N

Property Plant and Equipment (Narrative) (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Interest Cost Capitalized And Depreciation And Amortization Expenses For Property, Plant and Equipment [Line Items]
Accumulated depreciation	$ 1,115	$ 650
Assets Held under Capital Leases [Member]
Interest Cost Capitalized And Depreciation And Amortization Expenses For Property, Plant and Equipment [Line Items]
Capital leases	25	25
Accumulated depreciation	$ 8	$ 7

Fair Value Measurements - Recur

Fair Value Measurements - Recurring (Financial Instruments by Valuation Hierarchy) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets		$ 0	$ 9
Derivative Liability		(60)	(32)
Commodity contracts | Fair Value, Measurements, Recurring [Member] | Significant other observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets		0	2
Derivative Liability		0	0
Commodity contracts | Fair Value, Measurements, Recurring [Member] | Significant unobservable inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets		0	7
Derivative Liability		(6)	0
Embedded derivatives in commodity contracts | Fair Value, Measurements, Recurring [Member] | Significant unobservable inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets		0	0
Derivative Liability		$ (54)	$ (32)
Liability [Member] | Embedded derivatives in commodity contracts | Significant unobservable inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Inputs Probability of Renewal	[1]	50.00%
Fair Value Inputs Probability of Renewal Second Term	[1]	75.00%
[1]	(3)The producer counterparty to the embedded derivative has the option to renew the gas purchase agreement and the related keep-whole processing agreement for two successive five-year terms after 2022. The embedded gas purchase agreement cannot be renewed without the renewal of the related keep-whole processing agreement. Due to the significant number of years until the renewal options are exercisable and the high level of uncertainty regarding the counterparty’s future business strategy, the future commodity price environment, and the future competitive environment for midstream services in the Southern Appalachian region, management determined that a 50 percent probability of renewal for the first five-year term and 75 percent for the second five-year term are appropriate assumptions. Included in this assumption is a further extension of management’s estimates of future frac spreads through 2032.

Fair Value Measurements - Re103

Fair Value Measurements - Recurring (Significant Unobservable Inputs in Level 3 Valuation) (Details) - Significant unobservable inputs (Level 3)	12 Months Ended
	Dec. 31, 2016USD ($)
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Number Of Renewal Periods	2
Term of counterparty option to renew gas purchase agreement	5 years
Commodity contracts | Minimum [Member] | Assets [Member] | Ethanol prices [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs Forward Commodity Price	$ 0.0016
Commodity contracts | Minimum [Member] | Assets [Member] | Propane Contract [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs Forward Commodity Price	0.0039
Commodity contracts | Minimum [Member] | Assets [Member] | Isobutane Contract [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs Forward Commodity Price	0.0054
Commodity contracts | Minimum [Member] | Assets [Member] | Normal Butane Contract [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs Forward Commodity Price	0.0051
Commodity contracts | Minimum [Member] | Assets [Member] | Natural Gasoline Contract [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs Forward Commodity Price	0.0089
Commodity contracts | Maximum [Member] | Assets [Member] | Ethanol prices [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs Forward Commodity Price	0.0019
Commodity contracts | Maximum [Member] | Assets [Member] | Propane Contract [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs Forward Commodity Price	0.0044
Commodity contracts | Maximum [Member] | Assets [Member] | Isobutane Contract [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs Forward Commodity Price	0.0057
Commodity contracts | Maximum [Member] | Assets [Member] | Normal Butane Contract [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs Forward Commodity Price	0.0057
Commodity contracts | Maximum [Member] | Assets [Member] | Natural Gasoline Contract [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs Forward Commodity Price	$ 0.0093
Embedded derivatives in commodity contracts | Liability [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs Probability of Renewal	50.00%	[1]
Fair Value Inputs Probability of Renewal Second Term	75.00%	[1]
Embedded derivatives in commodity contracts | Minimum [Member] | Liability [Member] | Propane Contract [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs Forward Commodity Price	$ 0.0039
Embedded derivatives in commodity contracts | Minimum [Member] | Liability [Member] | Isobutane Contract [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs Forward Commodity Price	0.0053
Embedded derivatives in commodity contracts | Minimum [Member] | Liability [Member] | Normal Butane Contract [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs Forward Commodity Price	0.0048
Embedded derivatives in commodity contracts | Minimum [Member] | Liability [Member] | Natural Gasoline Contract [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs Forward Commodity Price	0.0089
Embedded derivatives in commodity contracts | Minimum [Member] | Liability [Member] | Natural Gas Contract [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs Forward Commodity Price	0.0218
Embedded derivatives in commodity contracts | Minimum [Member] | Liability [Member] | ERCOT Pricing [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs Commodity Price	0.2308
Embedded derivatives in commodity contracts | Maximum [Member] | Liability [Member] | Propane Contract [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs Forward Commodity Price	0.0049
Embedded derivatives in commodity contracts | Maximum [Member] | Liability [Member] | Isobutane Contract [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs Forward Commodity Price	0.0064
Embedded derivatives in commodity contracts | Maximum [Member] | Liability [Member] | Normal Butane Contract [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs Forward Commodity Price	0.0060
Embedded derivatives in commodity contracts | Maximum [Member] | Liability [Member] | Natural Gasoline Contract [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs Forward Commodity Price	0.0104
Embedded derivatives in commodity contracts | Maximum [Member] | Liability [Member] | Natural Gas Contract [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs Forward Commodity Price	0.0339
Embedded derivatives in commodity contracts | Maximum [Member] | Liability [Member] | ERCOT Pricing [Member]
Fair Value Inputs, Assets and Liabilities, Quantitative Information [Line Items]
Fair Value Inputs Commodity Price	$ 0.4458
[1]	(3)The producer counterparty to the embedded derivative has the option to renew the gas purchase agreement and the related keep-whole processing agreement for two successive five-year terms after 2022. The embedded gas purchase agreement cannot be renewed without the renewal of the related keep-whole processing agreement. Due to the significant number of years until the renewal options are exercisable and the high level of uncertainty regarding the counterparty’s future business strategy, the future commodity price environment, and the future competitive environment for midstream services in the Southern Appalachian region, management determined that a 50 percent probability of renewal for the first five-year term and 75 percent for the second five-year term are appropriate assumptions. Included in this assumption is a further extension of management’s estimates of future frac spreads through 2032.

Fair Value Measurements Fair Va

Fair Value Measurements Fair Value Measurements - Recurring (Changes in Level 3 Measurements) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015
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		$ 7	$ 0
Net positions assumed in conjunction with the MarkWest Merger		0	7
Total (loss) gain (realized and unrealized) included in earnings(1)	[1]	(13)	3
Settlements		0	(3)
Fair value at end of period		(6)	7
The amount of total (losses) gains for the period included in earnings attributable to the change in unrealized gains or losses relating to liabilities still held at end of period		(6)	2
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		(32)	0
Net positions assumed in conjunction with the MarkWest Merger		0	(38)
Total (loss) gain (realized and unrealized) included in earnings(1)	[1]	(29)	5
Settlements		7	1
Fair value at end of period		(54)	(32)
The amount of total (losses) gains for the period included in earnings attributable to the change in unrealized gains or losses relating to liabilities still held at end of period		$ (26)	$ 5
[1]	(1)Gains and losses on Commodity Derivative Contracts classified as Level 3 are recorded in Product sales in the accompanying Consolidated Statements of Income. Gains and losses on Embedded Derivatives in Commodity Contracts are recorded in Cost of revenues and Purchased product costs.

Fair Value Measurements Fair105

Fair Value Measurements Fair Value Measurements - Reported (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 04, 2015
Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	$ 4,422	$ 5,255
SMR liability	96	100
Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	4,953	5,212
SMR liability	108	99
MarkWest [Member] | Senior Notes [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt assumed in MarkWest Merger			$ 4,100
Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Asset	0	9
Derivative Liability	(60)	(32)
Commodity contracts | Significant other observable inputs (Level 2) | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Asset	0	2
Derivative Liability	0	0
Commodity contracts | Significant unobservable inputs (Level 3) | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Asset	0	7
Derivative Liability	(6)	0
Embedded derivatives in commodity contracts | Significant unobservable inputs (Level 3) | Fair Value, Measurements, Recurring [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative Asset	0	0
Derivative Liability	$ (54)	$ (32)

Derivative Financial Instrum106

Derivative Financial Instruments Derivative Financial Instruments (Volume of Derivative Activity) (Details) - Commodity contracts - Not Designated as Hedging Instrument [Member]	Dec. 31, 2016MMBTUbblgal
Short [Member]
Derivative [Line Items]
Crude Oil (bbl) | bbl	36,500
NGLs (gal) | gal	64,211,702
Long [Member]
Derivative [Line Items]
Nonmonetary Notional Amount Of Price Risk Derivatives Of Natural Gas | MMBTU	297,017

Derivative Financial Instrum107

Derivative Financial Instruments (Embedded Derivatives in Commodity Contracts) (Details) - Embedded derivatives in commodity contracts $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Embedded derivative in natural gas processing and purchase contract [Member]
Derivative [Line Items]
Notional amount for embedded derivative in commodity contract (in Dth per day)	9,000
Number of renewals	2
Embedded Derivative Renewal Term	5 years
Embedded Derivative Fair Value of Embedded Derivative Liability Including Inception Value Allocable to Host Contract	$ (54)	$ (31)
Embedded derivative in electricity purchase contract [Member]
Derivative [Line Items]
Embedded Derivative, Fair Value of Embedded Derivative Liability		$ 1

Derivative Financial Instrum108

Derivative Financial Instruments (Derivatives Balance Sheet Location) (Details) - Commodity contracts - USD ($) $ in Millions		Dec. 31, 2016	Dec. 31, 2015
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	[1]	$ 0	$ 9
Derivative Liability, Fair Value, Gross Liability	[1]	(60)	(32)
Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	[1]	0	9
Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	[1]	(13)	(5)
Other Noncurrent Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	[1]	0	0
Deferred credits and other liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	[1]	$ (47)	$ (27)
[1]	(1)Includes embedded derivatives in commodity contracts as discussed above.

Derivative Financial Instrum109

Derivative Financial Instruments (Derivatives Income Statement Location) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Product sales [Abstract]
Total revenue: derivative (loss) gain from product sales	$ (42)	$ 8
Purchased product costs [Abstract]
Total purchased product costs: derivative (loss) gain from product purchases	42	(8)
Product Sales [Member]
Product sales [Abstract]
Derivative Instruments Not Designated as Hedging Instruments, Realized Gain (Loss), Net	2	4
Derivative Instruments Not Designated as Hedging Instruments, Unrealized Gain (Loss), Net	(15)	(1)
Total revenue: derivative (loss) gain from product sales	(13)	3
Purchased product costs [Abstract]
Total purchased product costs: derivative (loss) gain from product purchases	13	(3)
Purchased product costs [Member]
Product sales [Abstract]
Derivative Instruments Not Designated as Hedging Instruments, Realized Gain (Loss), Net	(5)	0
Derivative Instruments Not Designated as Hedging Instruments, Unrealized Gain (Loss), Net	(22)	5
Total revenue: derivative (loss) gain from product sales	(27)	5
Purchased product costs [Abstract]
Total purchased product costs: derivative (loss) gain from product purchases	27	(5)
Cost of Sales [Member]
Product sales [Abstract]
Derivative Instruments Not Designated as Hedging Instruments, Realized Gain (Loss), Net	(3)	0
Derivative Instruments Not Designated as Hedging Instruments, Unrealized Gain (Loss), Net	1	0
Total revenue: derivative (loss) gain from product sales	(2)	0
Purchased product costs [Abstract]
Total purchased product costs: derivative (loss) gain from product purchases	$ 2	$ 0

Debt (Summary of Outstanding Bo

Debt (Summary of Outstanding Borrowings) (Details) - USD ($) $ in Millions		Dec. 31, 2016	Dec. 31, 2015	Dec. 22, 2015
Debt Instrument [Line Items]
Debt and Capital Lease Obligations		$ 4,858	$ 5,736
Unamortized Debt Issuance Expense		7	8
Debt Instrument, Unamortized Discount	[1]	428	472
Amounts due within one year		1	1
Total long-term debt due after one year		4,422	5,255
Mplx Lp [Member] | Line of Credit [Member] | MPLX Revolver [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		0	877
Mplx Lp [Member] | Unsecured Debt [Member] | MPLX Term Loan [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		250	250
Mplx Lp [Member] | Senior Notes [Member] | 5.500% senior notes due 2023
Debt Instrument [Line Items]
Long-term Debt, Gross		710	710
Mplx Lp [Member] | Senior Notes [Member] | 4.500% senior notes due 2023
Debt Instrument [Line Items]
Long-term Debt, Gross		989	989
Mplx Lp [Member] | Senior Notes [Member] | 4.875% senior notes due 2024
Debt Instrument [Line Items]
Long-term Debt, Gross		1,149	1,149
Mplx Lp [Member] | Senior Notes [Member] | 4.000% senior notes due 2025
Debt Instrument [Line Items]
Long-term Debt, Gross		500	500
Mplx Lp [Member] | Senior Notes [Member] | 4.875% senior notes due 2025
Debt Instrument [Line Items]
Long-term Debt, Gross		1,189	1,189
MarkWest [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 63
Debt Instrument, Unamortized Discount		420	464
MarkWest [Member] | Senior Notes [Member] | 5.500% senior notes due 2023
Debt Instrument [Line Items]
Long-term Debt, Gross		40
MarkWest [Member] | Senior Notes [Member] | 4.500% senior notes due 2023
Debt Instrument [Line Items]
Long-term Debt, Gross		11
MarkWest [Member] | Senior Notes [Member] | 4.875% senior notes due 2024
Debt Instrument [Line Items]
Long-term Debt, Gross		1
MarkWest [Member] | Senior Notes [Member] | 4.875% senior notes due 2025
Debt Instrument [Line Items]
Long-term Debt, Gross		11
MarkWest [Member] | Senior Notes [Member] | MarkWest Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		63	63
Marathon Pipe Line Llc [Member] | Capital Lease Obligations [Member]
Debt Instrument [Line Items]
MPL - capital lease obligations due 2020		$ 8	$ 9
[1]	(1)Includes $420 million and $464 million discount as of December 31, 2016 and 2015, respectively, related to the difference between the fair value and the principal amount of the assumed MarkWest debt.

Debt (Summary of Outstanding111

Debt (Summary of Outstanding Borrowings Interest Rates and Table Due Dates) (Details)	12 Months Ended
	Dec. 31, 2016	Feb. 12, 2015
Mplx Lp [Member] | MPLX Revolver [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Expiration Date	Dec. 4, 2020
Mplx Lp [Member] | MPLX Term Loan [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Expiration Date	Nov. 20, 2019
Mplx Lp [Member] | 4.000% senior notes due 2025
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.00%
Mplx Lp [Member] | Line of Credit [Member] | MPLX Revolver [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Expiration Date	Dec. 4, 2020
Mplx Lp [Member] | Unsecured Debt [Member] | MPLX Term Loan [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Expiration Date	Nov. 20, 2019
Mplx Lp [Member] | Senior Notes [Member] | 5.500% senior notes due 2023
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.50%
Debt Instrument, Maturity Date	Feb. 15, 2023
Mplx Lp [Member] | Senior Notes [Member] | 4.500% senior notes due 2023
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.50%
Debt Instrument, Maturity Date	Jul. 15, 2023
Mplx Lp [Member] | Senior Notes [Member] | 4.875% senior notes due 2024
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.875%
Debt Instrument, Maturity Date	Dec. 1, 2024
Mplx Lp [Member] | Senior Notes [Member] | 4.000% senior notes due 2025
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		4.00%
Debt Instrument, Maturity Date	Feb. 15, 2025
Mplx Lp [Member] | Senior Notes [Member] | 4.875% senior notes due 2025
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.875%
Debt Instrument, Maturity Date	Jun. 1, 2025
MarkWest [Member] | Senior Notes [Member] | 5.500% senior notes due 2023
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.50%
Debt Instrument, Maturity Date	Feb. 15, 2023
MarkWest [Member] | Senior Notes [Member] | 4.500% senior notes due 2023
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.50%
Debt Instrument, Maturity Date	Jul. 15, 2023
MarkWest [Member] | Senior Notes [Member] | 4.875% senior notes due 2024
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.875%
Debt Instrument, Maturity Date	Dec. 1, 2024
MarkWest [Member] | Senior Notes [Member] | 4.875% senior notes due 2025
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.875%
Debt Instrument, Maturity Date	Jun. 1, 2025
Marathon Pipe Line Llc [Member] | Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Capital Lease Due Date Year	2,020

Debt (Schedule of Debt Payments

Debt (Schedule of Debt Payments) (Detail) $ in Millions	Dec. 31, 2016USD ($)
Debt Disclosure [Abstract]
2,016	$ 1
2,017	1
2,018	251
2,018	5
2,019	$ 0

Debt (Credit Agreements) (Detai

Debt (Credit Agreements) (Detail) $ in Millions	Dec. 04, 2015USD ($)	Nov. 21, 2014	Sep. 14, 2012	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 22, 2015USD ($)	Nov. 20, 2014USD ($)
Debt Instrument [Line Items]
Term of senior unsecured revolving credit agreement (in years)						5 years
Line of Credit Facility, Initiation Date			Sep. 14, 2012
MPLX Revolver [Member] | Mplx Operations Llc [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage						1.535%
MPLX Revolver [Member] | Mplx Operations Llc [Member] | Maximum [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Borrowing Capacity, Description						500
MPLX Revolver [Member] | Mplx Lp [Member]
Debt Instrument [Line Items]
Debt Instrument, Issuance Date		Nov. 20, 2014
Debt Instrument, Term				5 years
Increase in borrowing capacity	$ 1,000
Line of Credit Facility, Expiration Date				Dec. 4, 2020
Debt Instrument, Interest Rate, Effective Percentage				1.899%	1.617%
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
Proceeds from Long-term Lines of Credit				$ 434	$ 992	$ 280
Repayments of Long-term Lines of Credit				1,300	500
Letters of Credit Outstanding, Amount				3	8
Line of Credit Facility, Remaining Borrowing Capacity				$ 2,000	$ 1,120
Line of Credit Facility, Remaining Borrowing Capacity, Percentage				99.90%	55.80%
MPLX Revolver [Member] | Mplx Lp [Member] | Maximum [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity				$ 2,000				$ 1,000
Line Of Credit Facility Additional Borrowing Capacity				$ 500
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 Revolver [Member] | Mplx Lp [Member] | Letter of credit [Member] | Maximum [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity				$ 250
MPLX Revolver [Member] | Mplx Lp [Member] | Swingline Loan [Member] | Maximum [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity				$ 100
MPLX Term Loan [Member] | Mplx Lp [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity								$ 250
Line of Credit Facility, Expiration Date				Nov. 20, 2019
Number Of Renewal Periods								2
Line Of Credit Facility Duration Of Renewal Period		1 year
Debt Instrument, Interest Rate, Effective Percentage				1.954%
Line of Credit [Member] | MPLX Revolver [Member] | Mplx Lp [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Expiration Date				Dec. 4, 2020
Long-term Debt, Gross				$ 0	$ 877
Senior Notes [Member] | MarkWest [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross							$ 63
Senior Notes [Member] | MarkWest Senior Notes [Member] | MarkWest [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 63	$ 63
MarkWest [Member]
Debt Instrument [Line Items]
Repayments of Long-term Lines of Credit	93
MarkWest [Member] | MPLX Revolver [Member]
Debt Instrument [Line Items]
Repayments of Long-term Lines of Credit	850
MarkWest [Member] | Line of Credit [Member]
Debt Instrument [Line Items]
Repayments of Long-term Lines of Credit	943
MarkWest [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 4,100

Debt (Senior Notes) (Details)

Debt (Senior Notes) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 22, 2015	Dec. 04, 2015	Feb. 12, 2015
MarkWest [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 4,100
Debt Instrument, Face Amount			$ 4,040
MarkWest [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 63
MarkWest [Member] | Senior Notes [Member] | 5.500% senior notes due 2023
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 40
Debt Instrument, Maturity Date	Feb. 15, 2023
Debt Instrument, Interest Rate, Stated Percentage	5.50%
MarkWest [Member] | Senior Notes [Member] | 4.500% senior notes due 2023
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 11
Debt Instrument, Maturity Date	Jul. 15, 2023
Debt Instrument, Interest Rate, Stated Percentage	4.50%
MarkWest [Member] | Senior Notes [Member] | 4.875% senior notes due 2024
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 1
Debt Instrument, Maturity Date	Dec. 1, 2024
Debt Instrument, Interest Rate, Stated Percentage	4.875%
MarkWest [Member] | Senior Notes [Member] | 4.875% senior notes due 2025
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 11
Debt Instrument, Maturity Date	Jun. 1, 2025
Debt Instrument, Interest Rate, Stated Percentage	4.875%
Mplx Lp [Member] | 4.000% senior notes due 2025
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.00%
Proceeds from (Repayments of) Debt	$ 495
Mplx Lp [Member] | Senior Notes [Member] | 5.500% senior notes due 2023
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 710	$ 710
Debt Instrument, Maturity Date	Feb. 15, 2023
Debt Instrument, Interest Rate, Stated Percentage	5.50%
Mplx Lp [Member] | Senior Notes [Member] | 4.500% senior notes due 2023
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 989	989
Debt Instrument, Maturity Date	Jul. 15, 2023
Debt Instrument, Interest Rate, Stated Percentage	4.50%
Mplx Lp [Member] | Senior Notes [Member] | 4.875% senior notes due 2024
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 1,149	1,149
Debt Instrument, Maturity Date	Dec. 1, 2024
Debt Instrument, Interest Rate, Stated Percentage	4.875%
Mplx Lp [Member] | Senior Notes [Member] | 4.875% senior notes due 2025
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 1,189	1,189
Debt Instrument, Maturity Date	Jun. 1, 2025
Debt Instrument, Interest Rate, Stated Percentage	4.875%
Mplx Lp [Member] | Senior Notes [Member] | 4.000% senior notes due 2025
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 500	$ 500
Debt Instrument, Maturity Date	Feb. 15, 2025
Debt Instrument, Interest Rate, Stated Percentage					4.00%

Debt (SMR Transaction) (Details

Debt (SMR Transaction) (Details) - USD ($) $ in Millions	Sep. 01, 2009	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Property, plant and equipment, net		$ 10,730	$ 9,997
Accrued liabilities		228	187
Deferred credits and other liabilities		$ 169	166
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		$ 61	69
Accrued liabilities		5	4
Deferred credits and other liabilities		$ 91	$ 96

Goodwill and Intangibles Goodwi

Goodwill and Intangibles Goodwill and Intangibles (Goodwill) (Details)		Dec. 04, 2015USD ($)	Jun. 30, 2016USD ($)	Mar. 31, 2016USD ($)	Jun. 30, 2016USD ($)	Sep. 30, 2016USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)
Goodwill [Line Items]
Goodwill, Purchase Accounting Adjustments	[1]						$ (241,000,000)
Goodwill, Gross							$ 2,329,000,000	$ 2,570,000,000	$ 116,000,000
Number of Reporting Units						3	3
Number of Reporting Units Impaired						2
Goodwill, Impairment Loss							$ 130,000,000	0
Beginning balance				$ 2,570,000,000	$ 2,570,000,000	$ 2,570,000,000	2,570,000,000	116,000,000
Acquisitions								2,454,000,000
Ending balance							2,199,000,000	2,570,000,000	116,000,000
Goodwill and Intangible Asset Impairment			$ 1,000,000	129,000,000			130,000,000	0	0
Goodwill, Impaired, Accumulated Impairment Loss							(130,000,000)	0	0
L&S [Member]
Goodwill [Line Items]
Goodwill, Purchase Accounting Adjustments							0
Goodwill, Gross							116,000,000	116,000,000	116,000,000
Goodwill, Impairment Loss							0
Beginning balance				116,000,000	116,000,000	116,000,000	116,000,000	116,000,000
Acquisitions								0
Ending balance							116,000,000	116,000,000	116,000,000
Goodwill, Impaired, Accumulated Impairment Loss							0	0	0
G&P [Member]
Goodwill [Line Items]
Goodwill, Purchase Accounting Adjustments	[1]						(241,000,000)
Goodwill, Gross							2,213,000,000	2,454,000,000	0
Goodwill, Impairment Loss							130,000,000
Beginning balance				$ 2,454,000,000	$ 2,454,000,000	$ 2,454,000,000	2,454,000,000	0
Acquisitions								2,454,000,000
Ending balance							2,083,000,000	2,454,000,000	0
Goodwill, Impaired, Accumulated Impairment Loss							$ (130,000,000)	$ 0	$ 0
MarkWest [Member]
Goodwill [Line Items]
Ending balance		$ 2,213,000,000
Effective date of acquisition		Dec. 4, 2015
Equity Method Investments [Member] | Income Approach Valuation Technique [Member] | Minimum [Member]
Goodwill [Line Items]
Fair Value Inputs, Discount Rate		9.40%			10.50%
Equity Method Investments [Member] | Income Approach Valuation Technique [Member] | Maximum [Member]
Goodwill [Line Items]
Fair Value Inputs, Discount Rate		11.10%			11.50%
Goodwill [Member] | Income Approach Valuation Technique [Member] | Minimum [Member]
Goodwill [Line Items]
Fair Value Inputs, Discount Rate					11.50%
Fair Value Inputs, Attrition Rate					5.00%
Goodwill [Member] | Income Approach Valuation Technique [Member] | Maximum [Member]
Goodwill [Line Items]
Fair Value Inputs, Discount Rate					12.80%
Fair Value Inputs, Attrition Rate					10.00%
[1]	(1)See Note 4 for further discussion on purchase price allocation adjustments.

Goodwill and Intangibles (Intan

Goodwill and Intangibles (Intangibles) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Accumulated Amortization	$ (41)	$ (2)
Intangibles, net	$ 492	466
Minimum [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	11 years
Maximum [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	25 years
L&S [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Accumulated Amortization	$ 0	0
Intangibles, net	0	0
G&P [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Accumulated Amortization	(41)	(2)
Intangibles, net	492	466
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	533	468
Customer Relationships [Member] | L&S [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	0	0
Customer Relationships [Member] | G&P [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	$ 533	$ 468

Goodwill and Intangibles (In118

Goodwill and Intangibles (Intangible Amortization) (Details) $ in Millions	Dec. 31, 2016USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
2,016	$ 38
2,017	38
2,018	38
2,019	38
2,020	38
Thereafter	302
Intangibles, net	$ 492

Supplemental Cash Flow Infor119

Supplemental Cash Flow Information (Summary of Supplemental Cash Flow Information) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Contribution from MPC		$ 225	$ 1,280
Net cash provided by operating activities included:
Interest paid (net of amounts capitalized)		212	13	$ 3
Income Taxes Paid		3
Non-cash investing and financing activities:
Net transfers of property, plant and equipment from materials and supplies inventories		4	5	1
Contribution - common units issued	[1]	669	0	200
Acquisitions [Abstract]
Fair value of MPLX LP units issued(1)	[1]	0	7,326	0
Payable to seller		0	$ 50	$ 0
MPC [Member]
Contribution from MPC		15
Limited Partners Common Units [Member]
Contribution from MPC		15
Limited Partners Common Units [Member] | MPC [Member]
Contribution from MPC		$ 84
[1]	(1)See Note 4.

Supplemental Cash Flow Infor120

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, 2016	Dec. 31, 2015	Dec. 31, 2014
Supplemental Cash Flow Elements [Abstract]
(Decrease) increase in capital accruals	$ (25)	$ 26	$ 11

Equity-Based Compensation Pl121

Equity-Based Compensation Plan (Narrative) (Detail) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)$ / sharesshares	Dec. 31, 2015USD ($)$ / shares	Dec. 31, 2014USD ($)$ / shares
Phantom Units [Member]
Unit-based awards under the Plan
Grant date fair value of performance units granted | $ / shares	$ 29.42	$ 35	$ 49.56
Outstanding Phantom Unit Awards
Convertible at December 31, 2016 | shares	494,189
Unrecognized compensation cost	$ 17
Cost not yet recognized, period for recognition	2 years
Performance Shares [Member]
Unit-based awards under the Plan
Grant date fair value of performance units granted | $ / shares	$ 0.63	$ 1.03	$ 1.16
Outstanding Phantom Unit Awards
Unrecognized compensation cost	$ 1
Cost not yet recognized, period for recognition	1 year 7 months
Mplx 2012 Incentive Compensation Plan [Member]
Compensation Expense
Total compensation expense	$ 10	$ 4	$ 3
Mplx 2012 Incentive Compensation Plan [Member] | Performance Shares [Member]
Unit-based awards under the Plan
Grant date fair value of performance units granted | $ / shares	$ 0.63	$ 1.03
Maximum [Member] | Mplx 2012 Incentive Compensation Plan [Member]
Description of the Plan
Common units available for delivery under the plan | shares	2,750,000
Officer [Member] | Mplx 2012 Incentive Compensation Plan [Member] | Phantom Units [Member]
Unit-based awards under the Plan
Award requisite service period	3 years
Accrued distributions	$ 2	$ 1
Officer [Member] | Mplx 2012 Incentive Compensation Plan [Member] | Performance Shares [Member]
Unit-based awards under the Plan
Award requisite service period	36 months
Measurement period	4
Award percentage paid out in cash	75.00%
Award percentage paid out in stock	25.00%
General and administrative expenses [Member]
Compensation Expense
Stock-based compensation plans expenses	$ 5	1	$ 1
MarkWest [Member] | Mplx 2012 Incentive Compensation Plan [Member]
Compensation Expense
Total compensation expense		$ 15

Equity-Based Compensation Pl122

Equity-Based Compensation Plan (Summary of Phantom Unit Award Activity) (Detail) - Phantom Units [Member] - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Number of Units
Outstanding at December 31, 2015	1,031,219
Granted	458,727
Settled	166,576
Forfeited	(149,959)
Outstanding at December 31, 2016	1,173,411	1,031,219
Vested and expected to vest at December 31, 2016	1,157,676
Convertible at December 31, 2016	494,189
Weighted Average Fair Value
Outstanding at December 31, 2014 (usd per share)	$ 35.49
Granted (usd per share)	29.42	$ 35	$ 49.56
Settled (usd per share)	38.12
Forfeited (usd per share)	32.72
Outstanding at December 31, 2015 (usd per share)	33.09	$ 35.49
Vested and expected to vest at December 31, 2014 (usd per share)	33.12
Convertible at December 31, 2014 (usd per share)	$ 34.11
Aggregate Intrinsic Value
Vested and expected to vest at December 31, 2016	$ 40
Convertible at December 31, 2016	$ 17

Equity-Based Compensation Pl123

Equity-Based Compensation Plan (Summary of Values Related To Vested and Unvested Restricted Stock Awards) (Details) - Phantom Units [Member] - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Equity-Based Compensation [Line Items]
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Vested In Period Total Intrinsic Value 1	$ 5	$ 3	$ 1
Grant date fair value of performance units granted	$ 29.42	$ 35	$ 49.56

Equity-Based Compensation Pl124

Equity-Based Compensation Plan (Summary of Performance Unit Award Activity) (Details) - Performance Shares [Member]	12 Months Ended
	Dec. 31, 2016$ / sharesshares
Number of Units
Outstanding at December 31, 2015 | shares	1,521,392
Granted | shares	789,375
Settled (usd per share) | $ / shares	$ 0.79
Forfeited | shares	(53,507)
Outstanding at December 31, 2016 | shares	1,799,249
Weighted Average Fair Value
Outstanding at December 31, 2014 (usd per share) | $ / shares	$ 1
Granted (usd per share) | $ / shares	0.63
Forfeited (usd per share) | $ / shares	1.06
Outstanding at December 31, 2015 (usd per share) | $ / shares	$ 0.89
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period | shares	(458,011)

Equity-Based Compensation Pl125

Equity-Based Compensation Plan (Assumptions) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Performance Shares [Member]
Equity-Based Compensation [Line Items]
Risk-free interest rate	0.96%	0.95%	0.63%
Look-back period	2 years 9 months 30 days	2 years 10 months 3 days	2 years 10 months 3 days
Expected volatility	47.59%	30.12%	17.17%
Grant date fair value of performance units granted	$ 0.63	$ 1.03	$ 1.16
General and administrative expenses [Member]
Equity-Based Compensation [Line Items]
Share-based Compensation	$ 5	$ 1	$ 1

Lease Operations Lease Operatio

Lease Operations Lease Operations (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Leases [Abstract]
Operating lease revenue, excluding executory costs	$ 464	$ 89	$ 14	$ 0
Operating Leases of Lessor Contingent Rentals Received	$ 7	$ 1

Lease Operations (Schedule of M

Lease Operations (Schedule of Minimum Future Rentals on Non-cancellable Leases) (Details) $ in Millions	Dec. 31, 2016USD ($)
Operating leases, Future Minimum Payments Receivable, Current Intercompany	$ 101
Operating Leases Future Minimum Payments Receivable Current, Third Party	197
Operating Leases, Future Minimum Payments Receivable, Current	298
Operating Leases Future Minimum Payments Receivable In Two Years, Intercompany	101
Operating Leases Future Minimum Payments Receivable In Two Years, Third Party	200
Operating Leases, Future Minimum Payments Receivable, in Two Years	301
Operating Leases Future Minimum Payments Receivable In Three Years, Intercompany	101
Operating Leases Future Minimum Payments Receivable In Three Years, Third Party	202
Operating Leases, Future Minimum Payments Receivable, in Three Years	303
Operating Leases Future Minimum Payments Receivable In Four Years, Intercompany	101
Operating Leases Future Minimum Payments Receivable In Four Years, Third Party	201
Operating Leases, Future Minimum Payments Receivable, in Four Years	302
Operating Leases Future Minimum Payments Receivable In Five Years, Intercompany	0
Operating Leases Future Minimum Payments Receivable In Five Years, Third Party	185
Operating Leases, Future Minimum Payments Receivable, in Five Years	185
Operating Leases Future Minimum Payments Receivable Thereafter, Intercompany	0
Operating Leases Future Minimum Payments Receivable Thereafter, Third Party	460
Operating Leases, Future Minimum Payments Receivable, Thereafter	460
Operating Leases Future Minimum Payments Receivable, Intercompany	404
Operating Leases Future Minimum Payments Receivable, Third Party	1,445
Operating Leases, Future Minimum Payments Receivable	$ 1,849

Lease Operations (Schedule of I

Lease Operations (Schedule of Investment in Assets Held for Operating Lease) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Property Subject to or Available for Operating Lease [Line Items]
Property, plant and equipment	$ 2,192	$ 1,933
Less: accumulated depreciation	(266)	(170)
Total property, plant and equipment	1,926	1,763
Natural gas gathering and NGL transportation pipelines and facilities [Member]
Property Subject to or Available for Operating Lease [Line Items]
Property, plant and equipment	650	619
Natural gas processing facilities [Member]
Property Subject to or Available for Operating Lease [Line Items]
Property, plant and equipment	844	753
Barges [Member]
Property Subject to or Available for Operating Lease [Line Items]
Property, plant and equipment	388	360
Barges and towing vessels [Member]
Property Subject to or Available for Operating Lease [Line Items]
Property, plant and equipment	91	91
Construction in Progress [Member]
Property Subject to or Available for Operating Lease [Line Items]
Property, plant and equipment	$ 219	$ 110

Asset Retirement Obligations (R

Asset Retirement Obligations (Reconciliation of Changes in the ARO) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Asset Retirement Obligations [Line Items]
ARO at beginning of period	$ 17	$ 0
Asset Retirement Obligation, Liabilities Incurred	8	2
Asset Retirement Obligation, Revision of Estimate	(1)	0
ARO at end of period	25	17
Asset Retirement Obligation, Accretion Expense	1	0
MarkWest [Member]
Asset Retirement Obligations [Line Items]
Asset Retirement Obligation, Liabilities Assumed	$ 0	$ 15

Asset Retirement Obligations As

Asset Retirement Obligations Asset Retirement Obligations (Narrative) (Details) - USD ($)	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Asset Retirement Obligation Disclosure [Abstract]
Asset Retirement Obligation	$ 25,000,000	$ 17,000,000	$ 0
Assets legally restricted for purposes of settling asset retirement obligations	$ 0	$ 0

Commitments and Contingencies (

Commitments and Contingencies (Detail) - USD ($) $ in Millions	Feb. 15, 2017	Sep. 06, 2016	Dec. 31, 2016	Dec. 31, 2015
Commitments And Contingencies [Line Items]
Accrual for Environmental Loss Contingencies			$ 1	$ 1
Estimated cost of proposed supplemental environmental projects			3.6
Contractual commitments to acquire property, plant and equipment			588
Environmental Loss Contingency [Member] | MPC [Member]
Commitments And Contingencies [Line Items]
Receivable from MPC for indemnification of environmental costs			1	$ 1
Apex [Member]
Commitments And Contingencies [Line Items]
Litigation Settlement, Amount		$ 10
Subsequent Event [Member]
Commitments And Contingencies [Line Items]
Equity Method Investment, Ownership Percentage	9.1875%
Payments to Acquire Interest in Joint Venture	$ 500
ETP and SXL ownership interest	75.00%
Percentage of ETP and SXL ownership to be acquired	49.00%
Percentage of Ownership Interest in Joint Venture Acquired	25.00%
Markwest Liberty Midstream [Member]
Commitments And Contingencies [Line Items]
EPA Proposed Penalty			$ 2.4

Commitments and Contingencie132

Commitments and Contingencies (Minimum Future Payments) (Details) - Operating Leases Propane Storage And Transporation And Terminalling Agreements [Member] $ in Millions	Dec. 31, 2016USD ($)
Other Commitments [Line Items]
2,016	$ 46
2,017	62
2,018	61
2,019	61
2,020	61
2021 and thereafter	317
Total	$ 608

Commitments and Contingencie133

Commitments and Contingencies (Future Minimum Commitments) (Details) $ in Millions	Dec. 31, 2016USD ($)
Capital Lease Obligations
2,016	$ 1
2,017	1
2,018	2
2,019	5
2,020	0
Later years	0
Total minimum lease payments	9
Less: imputed interest costs	1
Present value of net minimum lease payments	8
Operating Lease Obligations
2,016	61
2,017	51
2,018	42
2,019	37
2,020	36
Later years	76
Total minimum lease payments	$ 303

Commitments and Contingencie134

Commitments and Contingencies (Operating Lease Rental Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Operating Leases, Rent Expense	$ 57	$ 21	$ 17

Commitments and Contingencie135

Commitments and Contingencies (SMR Liability) (Details) - Steam Methane Reformer Held Under Financing Arrangement [Member] - SMR Liability [Member] $ in Millions	Dec. 31, 2016USD ($)
Recorded Unconditional Purchase Obligation [Line Items]
2,016	$ 17
2,017	17
2,018	17
2,019	17
2,020	17
2021 and thereafter	143
Total minimum payments	228
Less: Services element	87
Less: Interest	45
Total SMR liability	96
Less: Current portion of SMR liability	5
Long-term portion of SMR liability	$ 91

Commitments and Contingencie136

Commitments and Contingencies Commitments and Contingencies Investment in Pipeline Company (Details) - Subsequent Event [Member] $ in Millions	Feb. 15, 2017USD ($)BPD
Equity Method Investment, Ownership Percentage	9.1875%
Payments to Acquire Interest in Joint Venture | $	$ 500
Oil and Gas Delivery Commitments and Contracts, Daily Production | BPD	470,000
ETP and SXL ownership interest	75.00%
Percentage of Ownership Interest in Joint Venture Acquired	25.00%
Percentage of ETP and SXL ownership to be acquired	49.00%

Subsequents Event (Details)

Subsequents Event (Details) $ in Millions	Feb. 15, 2017USD ($)BPD	Feb. 13, 2017USD ($)	Jan. 01, 2017USD ($)	Mar. 01, 2014USD ($)	May 02, 2013USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Feb. 10, 2017USD ($)	Feb. 06, 2017
Subsequent Event [Line Items]
Payments to Acquire Businesses, Gross				$ 310	$ 100	$ 0	$ 12	$ 910
Subsequent Event [Member]
Subsequent Event [Line Items]
Equity Method Investment, Ownership Percentage	9.1875%
Payments to Acquire Interest in Joint Venture	$ 500
Oil and Gas Delivery Commitments and Contracts, Daily Production | BPD	470,000
ETP and SXL ownership interest	75.00%
Percentage of Ownership Interest in Joint Venture Acquired	25.00%
Percentage of ETP and SXL ownership to be acquired	49.00%
MarkWest Ohio Fractionation Company, L.L.C. [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Propane and heavier NGL fractionation capacity			20
Antero Midstream Partners L.P. [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Payments to Acquire Interest in Joint Venture			$ 154
Markwest Liberty Midstream [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Number of processing plants			6
Plant Capacity Volume			200
Sherwood Midstream LLC [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Payments to Acquire Interest in Joint Venture			$ 125
Pipe Line Holding [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Payments to Acquire Businesses, Gross		$ 220
Sherwood Midstream LLC [Member] | Antero Midstream Partners L.P. [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Equity Method Investment, Ownership Percentage			50.00%
Sherwood Midstream LLC [Member] | Markwest Liberty Midstream [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Equity Method Investment, Ownership Percentage			50.00%
Contribution of Property			$ 134
Contribute needed capital			50.00%
Number of gas processing plants [Line Items]			3
Plant Capacity Volume			200
Sherwood Midstream Holdings [Member] | Markwest Liberty Midstream [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Equity Method Investment, Ownership Percentage										79.00%
Contribution of Property			$ 207
Sherwood Midstream Holdings [Member] | Sherwood Midstream LLC [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Equity Method Investment, Ownership Percentage										21.00%
Senior Notes [Member] | Senior Notes Due March 2027 [Member] | Mplx Lp [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Long-term Debt, Gross									$ 1,250
Debt Instrument, Interest Rate, Stated Percentage									4.125%
Percent of Par									99.834%
Senior Notes [Member] | Senior Notes Due March 2047 [Member] | Mplx Lp [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Long-term Debt, Gross									$ 1,000
Debt Instrument, Interest Rate, Stated Percentage									5.20%
Percent of Par									99.304%
Ozark Pipeline [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Capable of transporting barrels per day		230,000

Select Quarterly Financial D138

Select Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended													12 Months Ended
		Dec. 31, 2016	[1]	Sep. 30, 2016	[1]	Jun. 30, 2016		Mar. 31, 2016		Dec. 31, 2015	[1]	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014
Quarterly Financial Data [Line Items]
Goodwill and Intangible Asset Impairment						$ 1		$ 129							$ 130		$ 0		$ 0
Total revenues and other income		$ 714		$ 703		564	[1],[2]	609	[1]	$ 333		$ 214	$ 213	$ 201	2,590		961		793
Income from operations		197		207		76	[1],[2]	27	[1],[3]	74		68	82	74	507		298		245
Net income		132		143		20	[1],[2]	(37)	[1],[3]	42		63	76	68	258		249		239
Net income attributable to MPLX LP		133		141		19	[1],[2]	(60)	[1],[3]	18		41	51	46	233	[4]	156	[4]	121	[4]
Distributions declared: [Abstract]
Limited partner units															938		315		112
Incentive distribution rights - MPC															187		54		4
Total distributions declared		$ 258		$ 249		$ 231	[1]	$ 200	[1]	$ 189		$ 47	$ 42	$ 37
Limited Partners Common Units [Member]
Quarterly Financial Data [Line Items]
Net income attributable to MPLX LP	[4]														$ 1		$ 97		$ 58
Net income attributable to MPLX LP subsequent to initial public offering per limited partner unit:
Common - basic		$ 0.17		$ 0.22		$ (0.11)	[1],[2]	$ (0.33)	[1],[3]	$ (0.14)		$ 0.41	$ 0.50	$ 0.46	$ 0		$ 1.23		$ 1.55
Common - diluted		0.17		0.21		(0.11)	[1],[2]	(0.33)	[1],[3]	(0.14)		0.41	0.50	0.46	0		1.22		1.55
Cash distributions declared per limited partner common unit		$ 0.5200		$ 0.5150		$ 0.5100	[1]	$ 0.5050	[1]	$ 0.5000		$ 0.4700	$ 0.4400	$ 0.4100	$ 2.0500		$ 1.8200		$ 1.4100
Distributions declared: [Abstract]
Limited partner units	[5]														$ 692		$ 224		$ 54
Preferred Partner [Member]
Quarterly Financial Data [Line Items]
Net income attributable to MPLX LP	[4]														41
Distributions declared: [Abstract]
Limited partner units		$ 16		$ 16		$ 9	[1]	$ 0	[1]	$ 0		$ 0	$ 0	$ 0	$ 41	[5]	0	[5]	0	[5]
Public [Member]
Distributions declared: [Abstract]
Limited partner units		140		135		131	[1]	127	[1]	120		11	10	10
MPC [Member]
Distributions declared: [Abstract]
Limited partner units		45		44		41	[1]	29	[1]	29		27	25	23
General partner units - MPC		5		5		4	[1]	4	[1]	3		1	1	1
Incentive distribution rights - MPC		$ 52		$ 49		$ 46	[1]	$ 40	[1]	$ 37		$ 8	$ 6	$ 3
MPC [Member] | Limited Partners Subordinated Units [Member]
Quarterly Financial Data [Line Items]
Net income attributable to MPLX LP	[4]																$ 2		$ 55
Net income attributable to MPLX LP subsequent to initial public offering per limited partner unit:
Common - basic																	$ 0.11		$ 1.50
Common - diluted																	0.11		1.50
Subordinated - basic and diluted		$ 0		$ 0		$ 0	[1]	$ 0	[1]	$ 0		$ 0	$ 0.50	$ 0.46	$ 0		$ 0.11		$ 1.50
Distributions declared: [Abstract]
Limited partner units	[5]														$ 0		$ 31		$ 52
Ohio Condensate Company, LLC [Member]
Quarterly Financial Data [Line Items]
Goodwill and Intangible Asset Impairment						$ 89
[1]	(3)These amounts include results from the MarkWest Merger which closed on December 4, 2015. See Note 4 for more information on the MarkWest Merger.
[2]	(2)Second quarter 2016 results included impairment expense related to equity method investments of $89 million. See Note 5 for more information.
[3]	(1)First quarter 2016 results included goodwill impairment expense of $129 million. See Note 18 for more information.
[4]	(1)Allocation of net income (loss) attributable to MPLX LP assumes all earnings for the period had been distributed based on the current period distribution priorities.
[5]	(1)See Note 8 for information regarding the distribution.