v3.10.0.1

Revenue from Contract with Customers (Disaggregated Revenue) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Revenues	$ 2,826,573	$ 2,507,661	$ 2,205,410
Operating Leases, Income Statement, Lease Revenue	(88,304)
Unrealized Gain (Loss) on Derivatives	(85,011)
Revenue from Related Parties	(20,365)
Revenue from Contract with Customer, Excluding Assessed Tax	2,632,893
Service [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,878,988	1,731,775	1,591,119
Product [Member]
Disaggregation of Revenue [Line Items]
Revenues	927,220	758,206	599,602
Product and Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenues	20,365	17,680	14,689
Transferred over Time [Member] | Transportation [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,086,956
Transferred over Time [Member] | Terminalling [Member]
Disaggregation of Revenue [Line Items]
Revenues	189,013
Transferred over Time [Member] | Storage [Member]
Disaggregation of Revenue [Line Items]
Revenues	352,442
Transferred over Time [Member] | Ancillary Services [Member]
Disaggregation of Revenue [Line Items]
Revenues	162,273
Transferred over Time [Member] | Lease Revenue [Member]
Disaggregation of Revenue [Line Items]
Revenues	88,304
Transferred over Time [Member] | Service [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,878,988
Transferred at Point in Time [Member] | Product [Member]
Disaggregation of Revenue [Line Items]
Revenues	927,220
Operating Segments [Member] | Refined Products Segment [Member]
Disaggregation of Revenue [Line Items]
Revenues	2,025,636	1,814,568	1,564,892
Operating Leases, Income Statement, Lease Revenue	(11,142)
Unrealized Gain (Loss) on Derivatives	(85,643)
Revenue from Related Parties	(1,512)
Revenue from Contract with Customer, Excluding Assessed Tax	1,927,339
Operating Segments [Member] | Refined Products Segment [Member] | Service [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,151,980	1,096,040	1,002,368
Operating Segments [Member] | Refined Products Segment [Member] | Product [Member]
Disaggregation of Revenue [Line Items]
Revenues	872,144	717,140	561,759
Operating Segments [Member] | Refined Products Segment [Member] | Product and Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,512	1,388	765
Operating Segments [Member] | Refined Products Segment [Member] | Transferred over Time [Member] | Transportation [Member]
Disaggregation of Revenue [Line Items]
Revenues	749,266
Operating Segments [Member] | Refined Products Segment [Member] | Transferred over Time [Member] | Terminalling [Member]
Disaggregation of Revenue [Line Items]
Revenues	179,999
Operating Segments [Member] | Refined Products Segment [Member] | Transferred over Time [Member] | Storage [Member]
Disaggregation of Revenue [Line Items]
Revenues	100,564
Operating Segments [Member] | Refined Products Segment [Member] | Transferred over Time [Member] | Ancillary Services [Member]
Disaggregation of Revenue [Line Items]
Revenues	111,009
Operating Segments [Member] | Refined Products Segment [Member] | Transferred over Time [Member] | Lease Revenue [Member]
Disaggregation of Revenue [Line Items]
Revenues	11,142
Operating Segments [Member] | Refined Products Segment [Member] | Transferred over Time [Member] | Service [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,151,980
Operating Segments [Member] | Refined Products Segment [Member] | Transferred at Point in Time [Member] | Product [Member]
Disaggregation of Revenue [Line Items]
Revenues	872,144
Operating Segments [Member] | Crude Oil Pipeline and Terminals Segment [Member]
Disaggregation of Revenue [Line Items]
Revenues	611,448	507,458	451,540
Operating Leases, Income Statement, Lease Revenue	(60,598)
Unrealized Gain (Loss) on Derivatives	632
Revenue from Related Parties	(14,832)
Revenue from Contract with Customer, Excluding Assessed Tax	536,650
Operating Segments [Member] | Crude Oil Pipeline and Terminals Segment [Member] | Service [Member]
Disaggregation of Revenue [Line Items]
Revenues	549,849	458,455	407,837
Operating Segments [Member] | Crude Oil Pipeline and Terminals Segment [Member] | Product [Member]
Disaggregation of Revenue [Line Items]
Revenues	46,767	35,053	31,170
Operating Segments [Member] | Crude Oil Pipeline and Terminals Segment [Member] | Product and Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenues	14,832	13,950	12,533
Operating Segments [Member] | Crude Oil Pipeline and Terminals Segment [Member] | Transferred over Time [Member] | Transportation [Member]
Disaggregation of Revenue [Line Items]
Revenues	337,690
Operating Segments [Member] | Crude Oil Pipeline and Terminals Segment [Member] | Transferred over Time [Member] | Terminalling [Member]
Disaggregation of Revenue [Line Items]
Revenues	6,365
Operating Segments [Member] | Crude Oil Pipeline and Terminals Segment [Member] | Transferred over Time [Member] | Storage [Member]
Disaggregation of Revenue [Line Items]
Revenues	119,606
Operating Segments [Member] | Crude Oil Pipeline and Terminals Segment [Member] | Transferred over Time [Member] | Ancillary Services [Member]
Disaggregation of Revenue [Line Items]
Revenues	25,590
Operating Segments [Member] | Crude Oil Pipeline and Terminals Segment [Member] | Transferred over Time [Member] | Lease Revenue [Member]
Disaggregation of Revenue [Line Items]
Revenues	60,598
Operating Segments [Member] | Crude Oil Pipeline and Terminals Segment [Member] | Transferred over Time [Member] | Service [Member]
Disaggregation of Revenue [Line Items]
Revenues	549,849
Operating Segments [Member] | Crude Oil Pipeline and Terminals Segment [Member] | Transferred at Point in Time [Member] | Product [Member]
Disaggregation of Revenue [Line Items]
Revenues	46,767
Operating Segments [Member] | Marine Storage Segment [Member]
Disaggregation of Revenue [Line Items]
Revenues	193,180	189,038	189,785
Operating Leases, Income Statement, Lease Revenue	(16,564)
Unrealized Gain (Loss) on Derivatives	0
Revenue from Related Parties	(4,021)
Revenue from Contract with Customer, Excluding Assessed Tax	172,595
Operating Segments [Member] | Marine Storage Segment [Member] | Service [Member]
Disaggregation of Revenue [Line Items]
Revenues	180,850	180,683	181,721
Operating Segments [Member] | Marine Storage Segment [Member] | Product [Member]
Disaggregation of Revenue [Line Items]
Revenues	8,309	6,013	6,673
Operating Segments [Member] | Marine Storage Segment [Member] | Product and Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenues	4,021	2,342	1,391
Operating Segments [Member] | Marine Storage Segment [Member] | Transferred over Time [Member] | Transportation [Member]
Disaggregation of Revenue [Line Items]
Revenues	0
Operating Segments [Member] | Marine Storage Segment [Member] | Transferred over Time [Member] | Terminalling [Member]
Disaggregation of Revenue [Line Items]
Revenues	2,649
Operating Segments [Member] | Marine Storage Segment [Member] | Transferred over Time [Member] | Storage [Member]
Disaggregation of Revenue [Line Items]
Revenues	135,963
Operating Segments [Member] | Marine Storage Segment [Member] | Transferred over Time [Member] | Ancillary Services [Member]
Disaggregation of Revenue [Line Items]
Revenues	25,674
Operating Segments [Member] | Marine Storage Segment [Member] | Transferred over Time [Member] | Lease Revenue [Member]
Disaggregation of Revenue [Line Items]
Revenues	16,564
Operating Segments [Member] | Marine Storage Segment [Member] | Transferred over Time [Member] | Service [Member]
Disaggregation of Revenue [Line Items]
Revenues	180,850
Operating Segments [Member] | Marine Storage Segment [Member] | Transferred at Point in Time [Member] | Product [Member]
Disaggregation of Revenue [Line Items]
Revenues	8,309
Intersegment Eliminations [Member]
Disaggregation of Revenue [Line Items]
Revenues	(3,691)	(3,403)	(807)
Operating Leases, Income Statement, Lease Revenue	0
Unrealized Gain (Loss) on Derivatives	0
Revenue from Related Parties	0
Revenue from Contract with Customer, Excluding Assessed Tax	(3,691)
Intersegment Eliminations [Member] | Service [Member]
Disaggregation of Revenue [Line Items]
Revenues	(3,691)	(3,403)	(807)
Intersegment Eliminations [Member] | Product [Member]
Disaggregation of Revenue [Line Items]
Revenues	0	0	0
Intersegment Eliminations [Member] | Product and Service, Other [Member]
Disaggregation of Revenue [Line Items]
Revenues	0	$ 0	$ 0
Intersegment Eliminations [Member] | Transferred over Time [Member] | Transportation [Member]
Disaggregation of Revenue [Line Items]
Revenues	0
Intersegment Eliminations [Member] | Transferred over Time [Member] | Terminalling [Member]
Disaggregation of Revenue [Line Items]
Revenues	0
Intersegment Eliminations [Member] | Transferred over Time [Member] | Storage [Member]
Disaggregation of Revenue [Line Items]
Revenues	(3,691)
Intersegment Eliminations [Member] | Transferred over Time [Member] | Ancillary Services [Member]
Disaggregation of Revenue [Line Items]
Revenues	0
Intersegment Eliminations [Member] | Transferred over Time [Member] | Lease Revenue [Member]
Disaggregation of Revenue [Line Items]
Revenues	0
Intersegment Eliminations [Member] | Transferred over Time [Member] | Service [Member]
Disaggregation of Revenue [Line Items]
Revenues	(3,691)
Intersegment Eliminations [Member] | Transferred at Point in Time [Member] | Product [Member]
Disaggregation of Revenue [Line Items]
Revenues	$ 0

X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DisaggregationOfRevenueLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

The total amount of revenue recognized for the period from operating leases, including minimum lease revenue, contingent revenue, percentage revenue and sublease revenue.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 20
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=77902458&loc=d3e39896-112707

+ Details

Name:	us-gaap_OperatingLeasesIncomeStatementLeaseRevenue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130543-203045

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130539-203045

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130545-203045

+ Details

Name:	us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Amount of revenue, fees and commissions earned from transactions between (a) a parent company and its subsidiaries; (b) subsidiaries of a common parent; (c) an entity and trusts for the benefit of employees, for example, but not limited to, pension and profit-sharing trusts that are managed by or under the trusteeship of the entity's management; (d) an entity and its principal, owners, management, or members of their immediate families; and (e) affiliates.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07.1(c))
-URI http://asc.fasb.org/extlink&oid=114873854&loc=SL114874292-224272

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1(e))
-URI http://asc.fasb.org/extlink&oid=115205541&loc=SL114868664-224227

+ Details

Name:	us-gaap_RevenueFromRelatedParties
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=115929826&loc=d3e8736-108599

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1)
-URI http://asc.fasb.org/extlink&oid=115205541&loc=SL114868664-224227

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=115929826&loc=d3e8933-108599

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=115929826&loc=d3e8736-108599

+ Details

Name:	us-gaap_Revenues
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of derivative instruments, including options, swaps, futures, and forward contracts, held at each balance sheet date, that was included in earnings for the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

+ Details

Name:	us-gaap_UnrealizedGainLossOnDerivatives
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Details

Name:	srt_ProductOrServiceAxis=us-gaap_ServiceMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_ProductOrServiceAxis=us-gaap_ProductMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_ProductOrServiceAxis=us-gaap_ProductAndServiceOtherMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_TimingOfTransferOfGoodOrServiceAxis=us-gaap_TransferredOverTimeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_ProductOrServiceAxis=mmp_TransportationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_ProductOrServiceAxis=mmp_TerminallingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_ProductOrServiceAxis=mmp_StorageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_ProductOrServiceAxis=mmp_AncillaryServicesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_ProductOrServiceAxis=mmp_LeaseRevenueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_TimingOfTransferOfGoodOrServiceAxis=us-gaap_TransferredAtPointInTimeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_ConsolidationItemsAxis=us-gaap_OperatingSegmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=mmp_RefinedProductsSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=mmp_CrudeOilPipelineandTerminalsSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=mmp_MarineStorageSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_ConsolidationItemsAxis=us-gaap_IntersegmentEliminationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: