v2.4.0.8

Product Sales Revenues (Components Of Product Sales Revenues) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Product Information [Line Items]
Physical sale of petroleum products	$ 108,320		$ 146,887		$ 555,870		$ 500,347
NYMEX Adjustments Included in Product Sales	47,545		(2,035)		33,715		4,138
Total product sales revenue	155,865		144,852		589,585		504,485
Butane Blending and Fractionation Activities [Member]
Product Information [Line Items]
NYMEX Adjustments Included in Product Sales	47,546	[1]	(2,035)	[1]	33,703	[1]	4,149	[1]
Other Commodity Activities [Member]
Product Information [Line Items]
NYMEX Adjustments Included in Product Sales	$ (1)		$ 0		$ 12		$ (11)
[1] The associated petroleum products for these activities are, to the extent still owned as of the statement date, or were, to the extent no longer owned as of the statement date, classified as inventory in current assets on our consolidated balance sheets.

X

- Definition

NYMEX Adjustments Included in Product Sales

+ References

No definition available.

+ Details

Name:	mmp_NYMEXAdjustmentsIncludedinProductSales
Namespace Prefix:	mmp_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Details

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

X

- Definition

Revenue derived from energy-related services such as supplying various forms of energy from the operation of on-site facilities or cogeneration plants and procurement services provided to energy purchasers.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Article 5

+ Details

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

X

- Definition

Revenue derived from energy-related services such supplying various forms of energy (such as steam, electricity and chilled water from the operation of on-site facilities or cogeneration plants), procurement services provided to energy purchasers, and the marketing and trading of energy commodities and derivatives.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Article 5

+ Details

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