Distribution To General Partner, Amount, Waived

No definition available.

Name:	shlx_DistributionToGeneralPartnerAmountWaived
Namespace Prefix:	shlx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Distribution To General Partner, Quarterly Distribution

+ References

No definition available.

+ Details

Name:	shlx_DistributionToGeneralPartnerQuarterlyDistribution
Namespace Prefix:	shlx_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Distribution To General Partner, Unit Distribution

+ References

No definition available.

+ Details

Name:	shlx_DistributionToGeneralPartnerUnitDistribution
Namespace Prefix:	shlx_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Transportation, Terminaling, and Storage Services Revenue To Be Received

+ References

No definition available.

+ Details

Name:	shlx_TransportationTerminalingAndStorageServicesRevenueToBeReceived
Namespace Prefix:	shlx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Percentage of voting equity interests acquired at the acquisition date in the business combination.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463

+ Details

Name:	us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Per unit of ownership amount of cash distributions paid to unit-holder of a limited partnership (LP).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 272
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70434-108055

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 272
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70478-108055

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

+ Details

Name:	us-gaap_DistributionMadeToLimitedPartnerDistributionsPaidPerUnit
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage investment held by the managing member or general partner of the limited liability company (LLC) or limited partnership (LP).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 272
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70478-108055

+ Details

Name:	us-gaap_LimitedLiabilityCompanyLLCOrLimitedPartnershipLPManagingMemberOrGeneralPartnerOwnershipInterest
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of each class of partnership units outstanding at the balance sheet date. Units represent shares of ownership of the general, limited, and preferred partners.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-04.16(a))
-URI http://asc.fasb.org/extlink&oid=6488278&loc=d3e603758-122996

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-04.16(b))
-URI http://asc.fasb.org/extlink&oid=6488278&loc=d3e603758-122996

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 5
-Subparagraph (SAB TOPIC 4.F)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187171-122770

+ Details

Name:	us-gaap_PartnersCapitalAccountUnits
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_PartnerTypeOfPartnersCapitalAccountAxis=us-gaap_GeneralPartnerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	shlx_AgreementAxis=shlx_PurchaseAndSaleAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	shlx_AgreementAxis=shlx_PartnershipInterestsRestructuringAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementClassOfStockAxis=shlx_CommonUnitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=shlx_ShellMidstreamLPHoldingsLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementClassOfStockAxis=shlx_SeriesAPerpetualConvertiblePreferredUnitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_OwnershipAxis=shlx_MattoxPipelineCompanyLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_OwnershipAxis=shlx_ShellMidstreamLPHoldingsLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Subsequent Events (Details) - USD ($) $ / shares in Units, $ in Millions			3 Months Ended
	Apr. 22, 2020	Apr. 01, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Subsequent Event [Line Items]
Distributions paid per limited partner unit (in dollars per share)			$ 0.460	$ 0.4600	$ 0.4450	$ 0.4300	$ 0.4150	$ 0.4000
General Partner
Subsequent Event [Line Items]
Capital units, publicly owned (in shares)			4,761,012
Subsequent Event
Subsequent Event [Line Items]
Distributions paid per limited partner unit (in dollars per share)	$ 0.4600
Subsequent Event \| Purchase And Sale Agreement
Subsequent Event [Line Items]
Transportation, terminaling, and storage services revenue to be received		$ 151
Subsequent Event \| Partnership Interests Restructuring Agreement \| Common Units
Subsequent Event [Line Items]
Capital units, publicly owned (in shares)		393,289,537
Subsequent Event \| Partnership Interests Restructuring Agreement \| Common Units \| Shell Midstream LP Holdings LLC
Subsequent Event [Line Items]
Capital units, publicly owned (in shares)		269,457,304
Subsequent Event \| Partnership Interests Restructuring Agreement \| Series A Perpetual Convertible Preferred Units
Subsequent Event [Line Items]
Distribution to general partner (in units)		50,782,904
Distribution to general partner, quarterly distribution (in dollars per unit)		$ 0.2363
Subsequent Event \| Partnership Interests Restructuring Agreement \| General Partner
Subsequent Event [Line Items]
Distribution to general partner, waived		$ 20
Subsequent Event \| Partnership Interests Restructuring Agreement \| General Partner \| Common Units
Subsequent Event [Line Items]
Distribution to general partner (in units)		160,000,000
Subsequent Event \| Mattox Pipeline Company LLC \| Purchase And Sale Agreement
Subsequent Event [Line Items]
Percentage of voting interests acquired		79.00%
Subsequent Event \| Shell Midstream LP Holdings LLC \| Partnership Interests Restructuring Agreement \| Shell Midstream LP Holdings LLC
Subsequent Event [Line Items]
Aggregate percentage of general partner interest		68.50%