Fair Value Disclosures (Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis) (Details) - Nonrecurring - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Assets at Fair Value
Loans	$ 3,687	$ 2,318
Other assets-Other investments	114	144
Other assets-Premises, equipment and software	0	0
Total assets, fair value	3,801	2,462
Liabilities at Fair Value
Other liabilities and accrued expenses-Lending commitments	357	196
Total liabilities at fair value	357	196
Assets
Fair Value Adjustment Disclosure
Gains (losses) from fair value remeasurements	(170)	(73)	$ (90)
Loans
Fair Value Adjustment Disclosure
Gains (losses) from fair value remeasurements	(68)	18	40
Other Assets-Other Investments
Fair Value Adjustment Disclosure
Gains (losses) from fair value remeasurements	(56)	(66)	(52)
Other Assets-Premises, Equipment and Software
Fair Value Adjustment Disclosure
Gains (losses) from fair value remeasurements	(46)	(25)	(76)
Intangible Assets
Fair Value Adjustment Disclosure
Gains (losses) from fair value remeasurements	0	0	(2)
Liabilities
Fair Value Adjustment Disclosure
Gains (losses) from fair value remeasurements	(48)	75	121
Other Liabilities and Accrued Expenses-Lending Commitments
Fair Value Adjustment Disclosure
Gains (losses) from fair value remeasurements	(48)	75	$ 121
Level 2
Assets at Fair Value
Loans	2,307	1,394
Other assets-Other investments	14	0
Other assets-Premises, equipment and software	0	0
Total assets, fair value	2,321	1,394
Liabilities at Fair Value
Other liabilities and accrued expenses-Lending commitments	292	158
Total liabilities at fair value	292	158
Level 3
Assets at Fair Value
Loans	1,380	924
Other assets-Other investments	100	144
Other assets-Premises, equipment and software	0	0
Total assets, fair value	1,480	1,068
Liabilities at Fair Value
Other liabilities and accrued expenses-Lending commitments	65	38
Total liabilities at fair value	$ 65	$ 38

Fair value portion of investments classified as other.

No definition available.

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

- Definition

Fair value portion of other liabilities and accrued expenses

+ References

No definition available.

+ Details

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

- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

+ Details

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

- References

No definition available.

+ Details

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

- References

No definition available.

+ Details

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

- Definition

For each line item in the statement of financial position, the amounts of gains and losses from fair value changes included in earnings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 30
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14172-108612

+ Details

Name:	us-gaap_FairValueOptionChangesInFairValueGainLoss1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Fair value of financial and nonfinancial obligations.

+ References

+ Details

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

- References

No definition available.

+ Details

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

- Definition

Fair value portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables.

+ References

No definition available.

+ Details

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

- Definition

Fair value portion of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19190-110258

+ Details

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

- Details

Name:	us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsNonrecurringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: