v3.19.3

Revenue from Contract with Customers (Performance Obligations in Next 12 Months) (Details) $ in Thousands | Sep. 30, 2019 USD ($)
--- | ---
Segment Reporting Information [Line Items] |
Revenue, Remaining Performance Obligation, Amount | $ 3,463,744
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-10-01 |
Segment Reporting Information [Line Items] |
Revenue, Remaining Performance Obligation, Amount | $ 749,453
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period | 12 months
Refined Products Segment [Member] |
Segment Reporting Information [Line Items] |
Revenue, Remaining Performance Obligation, Amount | $ 2,034,378
Refined Products Segment [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-10-01 |
Segment Reporting Information [Line Items] |
Revenue, Remaining Performance Obligation, Amount | 289,478
Crude Oil Pipeline and Terminals Segment [Member] |
Segment Reporting Information [Line Items] |
Revenue, Remaining Performance Obligation, Amount | 1,206,147
Crude Oil Pipeline and Terminals Segment [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-10-01 |
Segment Reporting Information [Line Items] |
Revenue, Remaining Performance Obligation, Amount | 337,928
Marine Storage Segment [Member] |
Segment Reporting Information [Line Items] |
Revenue, Remaining Performance Obligation, Amount | 223,219
Marine Storage Segment [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-10-01 |
Segment Reporting Information [Line Items] |
Revenue, Remaining Performance Obligation, Amount | $ 122,047
Minimum [Member] | Refined Products Segment [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-10-01 |
Segment Reporting Information [Line Items] |
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period | 1 year
Minimum [Member] | Crude Oil Pipeline and Terminals Segment [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-10-01 |
Segment Reporting Information [Line Items] |
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period | 1 year
Minimum [Member] | Marine Storage Segment [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-10-01 |
Segment Reporting Information [Line Items] |
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period | 1 year
Maximum [Member] | Refined Products Segment [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-10-01 |
Segment Reporting Information [Line Items] |
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period | 19 years
Maximum [Member] | Crude Oil Pipeline and Terminals Segment [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-10-01 |
Segment Reporting Information [Line Items] |
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period | 10 years
Maximum [Member] | Marine Storage Segment [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-10-01 |
Segment Reporting Information [Line Items] |
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period | 5 years

X
- Definition Amount of transaction price allocated to performance obligation that has not been recognized as revenue. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 13 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130556-203045 + Details
Name: | us-gaap_RevenueRemainingPerformanceObligation
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Period in which remaining performance obligation is expected to be recognized as revenue, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 13 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130556-203045 + Details
Name: | us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | instant

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_SegmentReportingInformationLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis=2019-10-01
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_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |