Commitments, Guarantees and Contingencies (Obligations under Guarantee Arrangements) (Details) $ in Millions	Mar. 31, 2018 USD ($)
Credit Derivatives
Guarantees
Maximum potential payout/notional	$ 249,070
Carrying amount: (asset)	(1,587)
Collateral/recourse	0
Credit Derivatives \| Less than 1 (Year)
Guarantees
Maximum potential payout/notional	81,715
Credit Derivatives \| 1 - 3 (Years)
Guarantees
Maximum potential payout/notional	69,986
Credit Derivatives \| 3 - 5 (Years)
Guarantees
Maximum potential payout/notional	58,118
Credit Derivatives \| Over 5 (Years)
Guarantees
Maximum potential payout/notional	39,251
Other Credit Contracts
Guarantees
Maximum potential payout/notional	129
Carrying amount: liability	20
Collateral/recourse	0
Other Credit Contracts \| Less than 1 (Year)
Guarantees
Maximum potential payout/notional	0
Other Credit Contracts \| 1 - 3 (Years)
Guarantees
Maximum potential payout/notional	2
Other Credit Contracts \| 3 - 5 (Years)
Guarantees
Maximum potential payout/notional	0
Other Credit Contracts \| Over 5 (Years)
Guarantees
Maximum potential payout/notional	127
Non-credit Derivatives
Guarantees
Maximum potential payout/notional	4,119,239
Carrying amount: liability	45,314
Collateral/recourse	0
Non-credit Derivatives \| Less than 1 (Year)
Guarantees
Maximum potential payout/notional	1,903,988
Non-credit Derivatives \| 1 - 3 (Years)
Guarantees
Maximum potential payout/notional	1,196,331
Non-credit Derivatives \| 3 - 5 (Years)
Guarantees
Maximum potential payout/notional	379,171
Non-credit Derivatives \| Over 5 (Years)
Guarantees
Maximum potential payout/notional	639,749
Standby Letters of Credit and Other Financial Guarantees Issued
Guarantees
Maximum potential payout/notional	8,095
Carrying amount: (asset)	(182)
Collateral/recourse	6,588
Standby letters of credit	700
Standby Letters of Credit and Other Financial Guarantees Issued \| Less than 1 (Year)
Guarantees
Maximum potential payout/notional	806
Standby Letters of Credit and Other Financial Guarantees Issued \| 1 - 3 (Years)
Guarantees
Maximum potential payout/notional	1,114
Standby Letters of Credit and Other Financial Guarantees Issued \| 3 - 5 (Years)
Guarantees
Maximum potential payout/notional	1,272
Standby Letters of Credit and Other Financial Guarantees Issued \| Over 5 (Years)
Guarantees
Maximum potential payout/notional	4,903
Market Value Guarantees
Guarantees
Maximum potential payout/notional	160
Carrying amount: liability	0
Collateral/recourse	0
Market Value Guarantees \| Less than 1 (Year)
Guarantees
Maximum potential payout/notional	40
Market Value Guarantees \| 1 - 3 (Years)
Guarantees
Maximum potential payout/notional	62
Market Value Guarantees \| 3 - 5 (Years)
Guarantees
Maximum potential payout/notional	58
Market Value Guarantees \| Over 5 (Years)
Guarantees
Maximum potential payout/notional	0
Liquidity Facilities
Guarantees
Maximum potential payout/notional	3,367
Carrying amount: (asset)	(5)
Collateral/recourse	5,475
Liquidity Facilities \| Less than 1 (Year)
Guarantees
Maximum potential payout/notional	3,367
Liquidity Facilities \| 1 - 3 (Years)
Guarantees
Maximum potential payout/notional	0
Liquidity Facilities \| 3 - 5 (Years)
Guarantees
Maximum potential payout/notional	0
Liquidity Facilities \| Over 5 (Years)
Guarantees
Maximum potential payout/notional	0
Whole Loan Sales Guarantees
Guarantees
Maximum potential payout/notional	23,225
Carrying amount: liability	8
Collateral/recourse	0
Whole Loan Sales Guarantees \| Less than 1 (Year)
Guarantees
Maximum potential payout/notional	0
Whole Loan Sales Guarantees \| 1 - 3 (Years)
Guarantees
Maximum potential payout/notional	1
Whole Loan Sales Guarantees \| 3 - 5 (Years)
Guarantees
Maximum potential payout/notional	1
Whole Loan Sales Guarantees \| Over 5 (Years)
Guarantees
Maximum potential payout/notional	23,223
Securitizations Representations and Warranties
Guarantees
Maximum potential payout/notional	60,861
Carrying amount: liability	91
Collateral/recourse	0
Securitizations Representations and Warranties \| Less than 1 (Year)
Guarantees
Maximum potential payout/notional	0
Securitizations Representations and Warranties \| 1 - 3 (Years)
Guarantees
Maximum potential payout/notional	0
Securitizations Representations and Warranties \| 3 - 5 (Years)
Guarantees
Maximum potential payout/notional	0
Securitizations Representations and Warranties \| Over 5 (Years)
Guarantees
Maximum potential payout/notional	60,861
General Partner Guarantees
Guarantees
Maximum potential payout/notional	436
Carrying amount: liability	59
Collateral/recourse	0
General Partner Guarantees \| Less than 1 (Year)
Guarantees
Maximum potential payout/notional	33
General Partner Guarantees \| 1 - 3 (Years)
Guarantees
Maximum potential payout/notional	52
General Partner Guarantees \| 3 - 5 (Years)
Guarantees
Maximum potential payout/notional	324
General Partner Guarantees \| Over 5 (Years)
Guarantees
Maximum potential payout/notional	$ 27

Guarantor Obligations, Collateral and Recourse

No definition available.

Name:	ms_GuarantorObligationsCollateralAndRecourse
Namespace Prefix:	ms_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The current carrying amount of the liability for the freestanding or embedded guarantor's obligations under the guarantee or each group of similar guarantees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=82913245&loc=d3e12069-110248

+ Details

Name:	us-gaap_GuaranteeObligationsCurrentCarryingValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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_GuaranteeObligationsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=82913245&loc=d3e12069-110248

+ Details

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

- Definition

The carrying amount of the contractual right to receive fees, as compensation in exchange for providing a guarantee to a third party, over life of the guarantee.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.10)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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

- Details

Name:	us-gaap_UnderlyingAssetClassAxis=us-gaap_CreditRiskContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ms_CreditDerivativesByMaturityAxis=ms_LessThanTwelveMonthsFromBalanceSheetDateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ms_CreditDerivativesByMaturityAxis=ms_MoreThanOneAndWithinThreeYearsFromBalanceSheetDateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ms_CreditDerivativesByMaturityAxis=ms_MoreThanThreeAndWithinFiveYearsFromBalanceSheetDateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ms_CreditDerivativesByMaturityAxis=ms_MoreThanFiveYearsFromBalanceSheetDateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_UnderlyingAssetClassAxis=us-gaap_OtherCreditDerivativesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_UnderlyingAssetClassAxis=us-gaap_DerivativeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_UnderlyingAssetClassAxis=us-gaap_StandbyLettersOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_UnderlyingAssetClassAxis=us-gaap_MarketValueGuaranteeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_UnderlyingAssetClassAxis=ms_LiquidityFacilitiesGuaranteeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_UnderlyingAssetClassAxis=ms_WholeLoanSalesRepresentationsAndWarrantiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_UnderlyingAssetClassAxis=ms_SecuritizationsRepresentationsAndGuaranteesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_UnderlyingAssetClassAxis=ms_GeneralPartnerGuaranteeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: