Loans and Allowance for Credit Losses - Narrative (Details) $ in Millions	3 Months Ended
Mar. 31, 2022 USD ($) loanSegment loan	Mar. 31, 2021 USD ($)	Dec. 31, 2021 USD ($) loan
Financing Receivable, Credit Quality Indicator [Line Items]
Number of loans and leases segments \| loanSegment	2
Loans and leases pledged as collateral	$ 11,010.0		$ 10,080.0
Number of loans on non-accrual status \| loan	0		0
Financing receivable, held-for-sale	$ 57.0		$ 8.0
Loans modified in troubled debt restructurings \| loan	0
Loans no longer meeting similar risk of collective pool \| loan	5
Loans no longer meeting similar risk of collective pool, amount	$ 135.0
Allowance for credit losses on loans	$ 86.0		$ 87.0
Investment grade loans	83.00%
Speculative grade loans	15.00%
Speculative senior secured loans with BB or B rating	95.00%
Allowance for credit loss, period increase (decrease)	$ 0.0	$ (13.0)
Financing Receivable, Credit Loss, Expense (Reversal)		$ 9.0
Leveraged Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Financing receivable, sale	89.0
Financing receivable, held-for-sale	51.0
Commercial and Financial Segment
Financing Receivable, Credit Quality Indicator [Line Items]
Allowance for credit losses on loans	$ 7.5

Financing Receivable, Recorded Investment, Nonaccrual Status, Number of Loans

No definition available.

Name:	stt_FinancingReceivableRecordedInvestmentNonaccrualStatusNumberofLoans
Namespace Prefix:	stt_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Investment Grade Loans

+ References

No definition available.

+ Details

Name:	stt_InvestmentGradeLoans
Namespace Prefix:	stt_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Loans And Leases Receivable, Number Of Loans And Leases Segments

+ References

No definition available.

+ Details

Name:	stt_LoansAndLeasesReceivableNumberOfLoansAndLeasesSegments
Namespace Prefix:	stt_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Loans No Longer Meeting Similar Risk of Collective Pool

+ References

No definition available.

+ Details

Name:	stt_LoansNoLongerMeetingSimilarRiskofCollectivePool
Namespace Prefix:	stt_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Number of Loans, No Longer Met Similar Risk

+ References

No definition available.

+ Details

Name:	stt_NumberofLoansNoLongerMetSimilarRisk
Namespace Prefix:	stt_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Speculative Grade Loans

+ References

No definition available.

+ Details

Name:	stt_SpeculativeGradeLoans
Namespace Prefix:	stt_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Speculative Senior Secured Loans, with BB or B Rating

+ References

No definition available.

+ Details

Name:	stt_SpeculativeSeniorSecuredLoanswithBBorBRating
Namespace Prefix:	stt_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount excluding accrued interest, of allowance for credit loss on financing receivable.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=124255206&loc=SL82895884-210446

+ Details

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

- Definition

Amount of increase (decrease) in allowance for credit loss on financing receivable.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=123577603&loc=SL6953423-111524

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesPeriodIncreaseDecrease
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=123577603&loc=SL6953676-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsNumberOfContracts2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

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

- Definition

Amount of decrease from sale and reclassification to held-for-sale of financing receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 11
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919244-210447

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=123577603&loc=SL6953423-111524

+ Details

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

- Definition

Carrying amount as of the balance sheet date of loans that have been pledged as collateral for borrowings. If the secured party has the right by contract or custom to sell or re-pledge the collateral, then the debtor reclassifies that asset and report that asset in its statement of financial position separately from other assets not so encumbered.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=66007379&loc=d3e113888-111728

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=123577603&loc=d3e5086-111524

+ Details

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

- Definition

Amount, before valuation allowance, of financing receivable classified as held-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=124259787&loc=d3e4428-111522

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 310
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=124265262&loc=d3e48678-111004

+ Details

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

- Definition

Amount of credit loss expense (reversal of expense) for financing receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(11))
-URI http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260

+ Details

Name:	us-gaap_ProvisionForLoanLossesExpensed
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=stt_LeveragedLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=stt_CommercialandFinancialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: