Commitments, Leases, Guarantees and Contingencies - Obligations under Guarantee Arrangements (Details) $ in Millions	Sep. 30, 2019 USD ($)
Credit derivatives
Guarantees
Maximum potential payout/notional	$ 229,412
Carrying amount: asset	789
Collateral/recourse	0
Credit derivatives \| Less Than 1 (Year)
Guarantees
Maximum potential payout/notional	33,594
Credit derivatives \| 1 - 3 (Years)
Guarantees
Maximum potential payout/notional	40,198
Credit derivatives \| 3 - 5 (Years)
Guarantees
Maximum potential payout/notional	96,188
Credit derivatives \| Over 5 (Years)
Guarantees
Maximum potential payout/notional	59,432
Other credit contracts
Guarantees
Maximum potential payout/notional	116
Carrying amount: liability	(18)
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	0
Other credit contracts \| 3 - 5 (Years)
Guarantees
Maximum potential payout/notional	0
Other credit contracts \| Over 5 (Years)
Guarantees
Maximum potential payout/notional	116
Non-credit derivatives
Guarantees
Maximum potential payout/notional	4,290,521
Carrying amount: liability	(76,165)
Collateral/recourse	0
Non-credit derivatives \| Less Than 1 (Year)
Guarantees
Maximum potential payout/notional	1,715,003
Non-credit derivatives \| 1 - 3 (Years)
Guarantees
Maximum potential payout/notional	1,467,985
Non-credit derivatives \| 3 - 5 (Years)
Guarantees
Maximum potential payout/notional	434,155
Non-credit derivatives \| Over 5 (Years)
Guarantees
Maximum potential payout/notional	673,378
Standby letters of credit and other financial guarantees issued1
Guarantees
Maximum potential payout/notional	7,531
Carrying amount: asset	224
Collateral/recourse	6,488
Standby letters of credit	600
Standby letters of credit and other financial guarantees issued1 \| Less Than 1 (Year)
Guarantees
Maximum potential payout/notional	1,018
Standby letters of credit and other financial guarantees issued1 \| 1 - 3 (Years)
Guarantees
Maximum potential payout/notional	886
Standby letters of credit and other financial guarantees issued1 \| 3 - 5 (Years)
Guarantees
Maximum potential payout/notional	1,410
Standby letters of credit and other financial guarantees issued1 \| Over 5 (Years)
Guarantees
Maximum potential payout/notional	4,217
Market value guarantees
Guarantees
Maximum potential payout/notional	175
Carrying amount: asset	0
Collateral/recourse	72
Market value guarantees \| Less Than 1 (Year)
Guarantees
Maximum potential payout/notional	85
Market value guarantees \| 1 - 3 (Years)
Guarantees
Maximum potential payout/notional	89
Market value guarantees \| 3 - 5 (Years)
Guarantees
Maximum potential payout/notional	1
Market value guarantees \| Over 5 (Years)
Guarantees
Maximum potential payout/notional	0
Liquidity facilities
Guarantees
Maximum potential payout/notional	4,545
Carrying amount: asset	6
Collateral/recourse	7,925
Liquidity facilities \| Less Than 1 (Year)
Guarantees
Maximum potential payout/notional	4,545
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	23,196
Carrying amount: liability	0
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	0
Whole loan sales guarantees \| 3 - 5 (Years)
Guarantees
Maximum potential payout/notional	0
Whole loan sales guarantees \| Over 5 (Years)
Guarantees
Maximum potential payout/notional	23,196
Securitization representations and warranties
Guarantees
Maximum potential payout/notional	66,530
Carrying amount: liability	(42)
Collateral/recourse	0
Securitization representations and warranties \| Less Than 1 (Year)
Guarantees
Maximum potential payout/notional	0
Securitization representations and warranties \| 1 - 3 (Years)
Guarantees
Maximum potential payout/notional	0
Securitization representations and warranties \| 3 - 5 (Years)
Guarantees
Maximum potential payout/notional	0
Securitization representations and warranties \| Over 5 (Years)
Guarantees
Maximum potential payout/notional	66,530
General partner guarantees
Guarantees
Maximum potential payout/notional	275
Carrying amount: liability	(44)
Collateral/recourse	0
General partner guarantees \| Less Than 1 (Year)
Guarantees
Maximum potential payout/notional	65
General partner guarantees \| 1 - 3 (Years)
Guarantees
Maximum potential payout/notional	127
General partner guarantees \| 3 - 5 (Years)
Guarantees
Maximum potential payout/notional	12
General partner guarantees \| Over 5 (Years)
Guarantees
Maximum potential payout/notional	71
Client clearing guarantees
Guarantees
Maximum potential payout/notional	9,746
Carrying amount: liability	0
Collateral/recourse	9,745
Client clearing guarantees \| Less Than 1 (Year)
Guarantees
Maximum potential payout/notional	9,746
Client clearing guarantees \| 1 - 3 (Years)
Guarantees
Maximum potential payout/notional	0
Client clearing guarantees \| 3 - 5 (Years)
Guarantees
Maximum potential payout/notional	0
Client clearing guarantees \| Over 5 (Years)
Guarantees
Maximum potential payout/notional	$ 0

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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=118943654&loc=d3e12069-110248

+ Details

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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

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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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=118943654&loc=d3e12069-110248

+ Details

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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://fasb.org/us-gaap/role/ref/legacyRef
-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://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(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-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

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-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=119400593&loc=d3e572229-122910

+ Details

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

- Details

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- Details

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- Details

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- Details

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- Details

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- Details

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Namespace Prefix:
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- Details

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Namespace Prefix:
Data Type:	na
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- Details

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

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

Name:	us-gaap_UnderlyingAssetClassAxis=ms_SecuritizationsRepresentationsAndGuaranteesMember
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Data Type:	na
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- Details

Name:	us-gaap_UnderlyingAssetClassAxis=ms_GeneralPartnerGuaranteeMember
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- Details

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