Long-Term Debt - Schedule of Long Term Debt (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Long-term finance leases	$ 78	$ 102
Total long-term debt	12,509	11,093
Fair Value Hedges
Debt Instrument [Line Items]
Decrease in carrying value of long-term debt	$ 157	157
Senior notes \| 3.55% notes due 2025
Debt Instrument [Line Items]
Interest rate on debt	3.55%
Senior notes \| 2.55% notes due 2020
Debt Instrument [Line Items]
Interest rate on debt	2.55%
Senior notes \| 3.7% notes due in 2023
Debt Instrument [Line Items]
Interest rate on debt	3.70%
Senior notes \| 3.3% notes due 2024
Debt Instrument [Line Items]
Interest rate on debt	3.30%
Senior notes \| 2.354% Notes Due 2025
Debt Instrument [Line Items]
Interest rate on debt	2.354%
Senior notes \| 2.653% notes due 2023
Debt Instrument [Line Items]
Interest rate on debt	2.653%
Senior notes \| 4.375% notes due 2021
Debt Instrument [Line Items]
Interest rate on debt	4.375%
Senior notes \| 1.95% Notes Due 2021
Debt Instrument [Line Items]
Interest rate on debt	1.95%
Senior notes \| 2.65% notes due 2026
Debt Instrument [Line Items]
Interest rate on debt	2.65%
Senior notes \| 4.141% Notes Due 2029
Debt Instrument [Line Items]
Interest rate on debt	4.141%
Senior notes \| 3.776% Notes Due 2024
Debt Instrument [Line Items]
Interest rate on debt	3.776%
Senior notes \| 7.35% notes due 2026
Debt Instrument [Line Items]
Interest rate on debt	7.35%
Subordinated notes \| 3.1% subordinated notes due 2023
Debt Instrument [Line Items]
Interest rate on debt	3.10%
Subordinated notes \| 3.031% Notes Due 2034
Debt Instrument [Line Items]
Interest rate on debt	3.031%
Parent Company and Non-banking Subsidiaries \| Senior notes \| 3.55% notes due 2025
Debt Instrument [Line Items]
Long-term debt	$ 1,331	1,268
Parent Company and Non-banking Subsidiaries \| Senior notes \| 2.55% notes due 2020
Debt Instrument [Line Items]
Long-term debt	1,191	1,177
Parent Company and Non-banking Subsidiaries \| Senior notes \| 3.7% notes due in 2023
Debt Instrument [Line Items]
Long-term debt	1,037	1,006
Parent Company and Non-banking Subsidiaries \| Senior notes \| 3.3% notes due 2024
Debt Instrument [Line Items]
Long-term debt	1,022	979
Parent Company and Non-banking Subsidiaries \| Senior notes \| 2.354% Notes Due 2025
Debt Instrument [Line Items]
Long-term debt	991	0
Parent Company and Non-banking Subsidiaries \| Senior notes \| 2.653% notes due 2023
Debt Instrument [Line Items]
Long-term debt	753	734
Parent Company and Non-banking Subsidiaries \| Senior notes \| 4.375% notes due 2021
Debt Instrument [Line Items]
Long-term debt	748	731
Parent Company and Non-banking Subsidiaries \| Senior notes \| 1.95% Notes Due 2021
Debt Instrument [Line Items]
Long-term debt	744	725
Parent Company and Non-banking Subsidiaries \| Senior notes \| 2.65% notes due 2026
Debt Instrument [Line Items]
Long-term debt	741	698
Parent Company and Non-banking Subsidiaries \| Senior notes \| 4.141% Notes Due 2029
Debt Instrument [Line Items]
Long-term debt	546	513
Parent Company and Non-banking Subsidiaries \| Senior notes \| 3.776% Notes Due 2024
Debt Instrument [Line Items]
Long-term debt	522	507
Parent Company and Non-banking Subsidiaries \| Senior notes \| Floating-rate notes due 2020
Debt Instrument [Line Items]
Long-term debt	500	499
Parent Company and Non-banking Subsidiaries \| Senior notes \| 7.35% notes due 2026
Debt Instrument [Line Items]
Long-term debt	150	150
Parent Company and Non-banking Subsidiaries \| Subordinated notes \| 3.1% subordinated notes due 2023
Debt Instrument [Line Items]
Long-term debt	1,006	972
Parent Company and Non-banking Subsidiaries \| Subordinated notes \| 3.031% Notes Due 2034
Debt Instrument [Line Items]
Long-term debt	492	0
Parent Company and Non-banking Subsidiaries \| Junior subordinated debentures \| Floating Rate Subordinated Debentures Due 2047
Debt Instrument [Line Items]
Long-term debt	499	794
Parent Company and Non-banking Subsidiaries \| Junior subordinated debentures \| Floating-rate subordinated notes due to State Street Capital Trust I in 2028
Debt Instrument [Line Items]
Long-term debt	100	150
State Street Bank
Debt Instrument [Line Items]
Long-term finance leases	$ 136	$ 190

Increase (Decrease) In Carrying Value Of Long Term Debt

No definition available.

Name:	stt_IncreaseDecreaseInCarryingValueOfLongTermDebt
Namespace Prefix:	stt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Contractual interest rate for funds borrowed, under the debt 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(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
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_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of lessee's right to use underlying asset under finance lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77888419&loc=SL77918627-209977

+ Details

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

- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=109500613&loc=SL6031897-161870

Reference 2: 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(a)(16))
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

Reference 3: 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 4: 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

+ Details

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

- Definition

Amount of long-term debt and lease obligation, including portion classified as current.

+ References

No definition available.

+ Details

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