v2.4.0.8

Business Combinations Business Combinations (Narrative) (Details) (Plains Pipeline Acquisition [Member], USD $) In Millions, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2013 mi
New Mexico System [Member] |
Business Acquisition [Line Items] |
Pipeline Length | 250
Payments to Acquire Businesses, Net of Cash Acquired | $ 57.0
Rocky Mountains [Member] |
Business Acquisition [Line Items] |
Pipeline Length | 550
Payments to Acquire Businesses, Net of Cash Acquired | $ 135.0
Number of Pipeline Terminals | 4
Storage Capacity | 1,700,000

X
- Definition Number of PipelineTerminals + References No definition available. + Details
Name: | mmp_NumberOfPipelineTerminals
Namespace Prefix: | mmp_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Pipeline, length + References No definition available. + Details
Name: | mmp_PipelineLength
Namespace Prefix: | mmp_
Data Type: | num:lengthItemType
Balance Type: | na
Period Type: | instant

X
- Definition Storage Capacity + References No definition available. + Details
Name: | mmp_StorageCapacity
Namespace Prefix: | mmp_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | us-gaap_BusinessAcquisitionLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The cash outflow associated with the acquisition of a business, net of the cash acquired from the purchase. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Investing Activities -URI http://asc.fasb.org/extlink&oid=6516133 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 13 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3213-108585 + Details
Name: | us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration