Variable Interest Entities and Securitization Activities (Transfers of Assets with Continuing Involvement 1) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Variable Interest Entity
Derivative assets (fair value)	$ 33,148	$ 30,813
Derivative liabilities (fair value)	25,986	26,695
SPE
Variable Interest Entity
Retained interests	1,252	988
Interests purchased in the secondary market (fair value)	271	619
Derivative assets (fair value)	191	227
Derivative liabilities (fair value)	119	85
SPE \| Investment Grade
Variable Interest Entity
Retained interests	836	411
Interests purchased in the secondary market (fair value)	183	533
SPE \| Non-investment Grade
Variable Interest Entity
Retained interests	416	577
Interests purchased in the secondary market (fair value)	88	86
SPE \| RML
Variable Interest Entity
SPE assets (UPB)	14,978	15,555
Retained interests	1	1
Interests purchased in the secondary market (fair value)	16	16
Derivative assets (fair value)	0	1
Derivative liabilities (fair value)	0	0
SPE \| RML \| Investment Grade
Variable Interest Entity
Retained interests	0	0
Interests purchased in the secondary market (fair value)	0	0
SPE \| RML \| Non-investment Grade
Variable Interest Entity
Retained interests	1	1
Interests purchased in the secondary market (fair value)	16	16
SPE \| CML
Variable Interest Entity
SPE assets (UPB)	59,607	62,744
Retained interests	431	391
Interests purchased in the secondary market (fair value)	169	160
Derivative assets (fair value)	0	0
Derivative liabilities (fair value)	0	0
SPE \| CML \| Investment Grade
Variable Interest Entity
Retained interests	324	293
Interests purchased in the secondary market (fair value)	112	94
SPE \| CML \| Non-investment Grade
Variable Interest Entity
Retained interests	107	98
Interests purchased in the secondary market (fair value)	57	66
SPE \| U.S. Agency CMO
Variable Interest Entity
SPE assets (UPB)	14,751	11,612
Retained interests	825	407
Interests purchased in the secondary market (fair value)	71	439
Derivative assets (fair value)	0	0
Derivative liabilities (fair value)	0	0
SPE \| U.S. Agency CMO \| Investment Grade
Variable Interest Entity
Retained interests	825	407
Interests purchased in the secondary market (fair value)	71	439
SPE \| U.S. Agency CMO \| Non-investment Grade
Variable Interest Entity
Retained interests	0	0
Interests purchased in the secondary market (fair value)	0	0
SPE \| CLN and Other
Variable Interest Entity
SPE assets (UPB)	16,823	17,060
Retained interests	313	482
Interests purchased in the secondary market (fair value)	15	4
Derivative assets (fair value)	191	226
Derivative liabilities (fair value)	119	85
SPE \| CLN and Other \| Investment Grade
Variable Interest Entity
Retained interests	5	4
Interests purchased in the secondary market (fair value)	0	0
SPE \| CLN and Other \| Non-investment Grade
Variable Interest Entity
Retained interests	308	478
Interests purchased in the secondary market (fair value)	$ 15	$ 4

Fair value of interests purchased in the secondary market

No definition available.

Name:	ms_InterestsPurchasedInSecondaryMarketFairValue
Namespace Prefix:	ms_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Special Purpose Entity Carrying Amount Of Collateralized Assets

+ References

No definition available.

+ Details

Name:	ms_SpecialPurposeEntityCarryingAmountOfCollateralizedAssets
Namespace Prefix:	ms_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13433-108611

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13495-108611

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=82849420&loc=SL20226008-175313

+ Details

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

- Definition

Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=82849420&loc=SL20226008-175313

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13495-108611

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77997519&loc=d3e13433-108611

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

+ Details

Name:	us-gaap_DerivativeLiabilities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair value portion of interest continued to be held by a transferor after transferring financial assets to a third party.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 10
-Section 15
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=77996609&loc=d3e94415-111705

+ Details

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

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

- Details

Name:	ms_QualifyingSpecialPurposeEntityClassificationAxis=ms_SpecialPurposeEntitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConcentrationRiskByTypeAxis=ms_InvestmentGradeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConcentrationRiskByTypeAxis=ms_NoninvestmentGradeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_ResidentialMortgageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CommercialMortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=ms_CreditLinkedNotesAndOtherMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: