Asset Acquisition, Capital Distribution To General Partner

No definition available.

Name:	shlx_AssetAcquisitionCapitalDistributionToGeneralPartner
Namespace Prefix:	shlx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Asset Acquisition, Consideration Transferred

+ References

No definition available.

+ Details

Name:	shlx_AssetAcquisitionConsiderationTransferred
Namespace Prefix:	shlx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Asset Acquisition, Consideration Transferred, Common Units, Weighted Average Sales Price

+ References

No definition available.

+ Details

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

- Definition

Asset Acquisition, Consideration Transferred, Equity Interests Issued and Issuable

+ References

No definition available.

+ Details

Name:	shlx_AssetAcquisitionConsiderationTransferredEquityInterestsIssuedAndIssuable
Namespace Prefix:	shlx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Asset Acquisition

+ References

No definition available.

+ Details

Name:	shlx_AssetAcquisitionLineItems
Namespace Prefix:	shlx_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Equity Method Investment, Ownership Percentage Acquired

+ References

No definition available.

+ Details

Name:	shlx_EquityMethodInvestmentOwnershipPercentageAcquired
Namespace Prefix:	shlx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Payments To Acquire Asset, Gross

+ References

No definition available.

+ Details

Name:	shlx_PaymentsToAcquireAssetGross
Namespace Prefix:	shlx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Number of common units issued of limited liability company (LLC).

+ 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

Reference 2: 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

Reference 3: 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

+ Details

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

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

This element represents the aggregate cost of investments accounted for under the equity method of accounting.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.12)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_EquityMethodInvestmentAggregateCost
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571

+ Details

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

- Definition

The number of general partner units issued.

+ References

Reference 1: 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_GeneralPartnersCapitalAccountUnitsIssued
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity.

+ References

No definition available.

+ Details

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

- Definition

Amount, after tax, of reclassification adjustment from accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 17A
-URI http://asc.fasb.org/extlink&oid=118930883&loc=SL34724391-108580

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=118930883&loc=d3e637-108580

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=118930883&loc=d3e689-108580

+ Details

Name:	us-gaap_OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIPensionAndOtherPostretirementBenefitPlansForNetGainLossNetOfTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	shlx_AssetAcquisitionAxis=shlx_June2019AcquisitionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	srt_ConsolidatedEntitiesAxis=srt_SubsidiariesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=shlx_TenYearFixedFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=shlx_ShellTreasuryCenterWestIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=shlx_ExplorerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=shlx_ColonialMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Acquisitions - June 2019 Acquisitions (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended		6 Months Ended
	Jun. 06, 2019	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Asset Acquisition [Line Items]
Remeasurements of pension and other postretirement benefits related to equity method investments, net of tax		$ 0	$ 0	$ 0	$ 0
June 2019 Acquisition
Asset Acquisition [Line Items]
Consideration transferred	$ 800
Historical carrying value of net assets under common control	90
Remeasurements of pension and other postretirement benefits related to equity method investments, net of tax	6
Capital distribution to general partner	510
Non-cash equity consideration	$ 200
Common units, weighted average sales price (in dollars per unit)	$ 20.68
General partners' capital account, units issued (in shares)	193,424
General Partner \| June 2019 Acquisition
Asset Acquisition [Line Items]
Noncontrolling interest	2.00%
Subsidiary \| Shell Midstream LP Holdings LLC \| June 2019 Acquisition
Asset Acquisition [Line Items]
Common units issued (in shares)	9,477,756
Revolving Credit Facility \| Ten Year Fixed Facility
Asset Acquisition [Line Items]
Debt instrument term				10 years
Revolving Credit Facility \| Shell Treasury Center West Inc \| Ten Year Fixed Facility
Asset Acquisition [Line Items]
Debt instrument term				10 years
Revolving Credit Facility \| Shell Treasury Center West Inc \| Ten Year Fixed Facility \| June 2019 Acquisition
Asset Acquisition [Line Items]
Consideration, cash on hand	$ 600
Debt instrument term	10 years
Explorer
Asset Acquisition [Line Items]
Ownership		38.59%		38.59%		12.62%
Explorer \| June 2019 Acquisition
Asset Acquisition [Line Items]
Equity method investment, ownership interest acquired	25.97%
Ownership		38.59%		38.59%
Colonial Pipeline Company (“Colonial”)
Asset Acquisition [Line Items]
Ownership		16.125%		16.125%		6.00%
Colonial Pipeline Company (“Colonial”) \| June 2019 Acquisition
Asset Acquisition [Line Items]
Equity method investment, ownership interest acquired	10.125%
Ownership		16.125%		16.125%