Revenue from Contracts with Customers - Disaggregation of Revenues (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Disaggregation of Revenue [Line Items]
Servicing fees	$ 1,421	$ 1,296
Management fees	472	382
Trading services	304	275
Securities finance	141	133
Processing fees and other	25	112
Total fee revenue	2,363	2,198
Net interest income	658	510
Gains (losses) related to investment securities, net	(2)	(40)
Total revenue	3,019	$ 2,668
Investment Servicing
Disaggregation of Revenue [Line Items]
Topic 606 revenue	1,612
All other revenue	910
Total revenue	2,522
Investment Servicing \| Servicing fees
Disaggregation of Revenue [Line Items]
Topic 606 revenue	1,421
All other revenue	0
Servicing fees	1,421
Investment Servicing \| Management fees
Disaggregation of Revenue [Line Items]
Topic 606 revenue	0
All other revenue	0
Management fees	0
Investment Servicing \| Trading services
Disaggregation of Revenue [Line Items]
Topic 606 revenue	95
All other revenue	179
Trading services	274
Investment Servicing \| Securities finance
Disaggregation of Revenue [Line Items]
Topic 606 revenue	77
All other revenue	64
Securities finance	141
Investment Servicing \| Processing fees and other
Disaggregation of Revenue [Line Items]
Topic 606 revenue	19
All other revenue	6
Processing fees and other	25
Investment Servicing \| Total fee revenue
Disaggregation of Revenue [Line Items]
Topic 606 revenue	1,612
All other revenue	249
Total fee revenue	1,861
Investment Servicing \| Net interest income
Disaggregation of Revenue [Line Items]
Topic 606 revenue	0
All other revenue	663
Net interest income	663
Investment Servicing \| Securities gains/ (losses)
Disaggregation of Revenue [Line Items]
Topic 606 revenue	0
All other revenue	(2)
Gains (losses) related to investment securities, net	(2)
Investment Management
Disaggregation of Revenue [Line Items]
Topic 606 revenue	502
All other revenue	(5)
Total revenue	497
Investment Management \| Servicing fees
Disaggregation of Revenue [Line Items]
Topic 606 revenue	0
All other revenue	0
Servicing fees	0
Investment Management \| Management fees
Disaggregation of Revenue [Line Items]
Topic 606 revenue	472
All other revenue	0
Management fees	472
Investment Management \| Trading services
Disaggregation of Revenue [Line Items]
Topic 606 revenue	30
All other revenue	0
Trading services	30
Investment Management \| Securities finance
Disaggregation of Revenue [Line Items]
Topic 606 revenue	0
All other revenue	0
Securities finance	0
Investment Management \| Processing fees and other
Disaggregation of Revenue [Line Items]
Topic 606 revenue	0
All other revenue	0
Processing fees and other	0
Investment Management \| Total fee revenue
Disaggregation of Revenue [Line Items]
Topic 606 revenue	502
All other revenue	0
Total fee revenue	502
Investment Management \| Net interest income
Disaggregation of Revenue [Line Items]
Topic 606 revenue	0
All other revenue	(5)
Net interest income	(5)
Investment Management \| Securities gains/ (losses)
Disaggregation of Revenue [Line Items]
Topic 606 revenue	0
All other revenue	0
Gains (losses) related to investment securities, net	$ 0

Revenue from Other Than Contract with Customer

No definition available.

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

- Definition

Trading Services Revenue

+ References

No definition available.

+ Details

Name:	stt_TradingServicesRevenue
Namespace Prefix:	stt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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_DisaggregationOfRevenueLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Income from services rendered by trust departments or by any consolidated subsidiaries acting in a fiduciary capacity, including fees earned for (1) acting as an agent for fiduciary placement and loans and (2) custody or investment advisory services when such fees are not separately billed to the customer. This item excludes commissions and fees received for the accumulation or disbursement of funds deposited to Individual Retirement or Keogh plan accounts when such are not handled by the reporting entity's trust department.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.13 (a))
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

+ Details

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

- Definition

Amount of fee and commission revenue classified as other.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.13)
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

+ Details

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

- Definition

The net amount of operating interest income (expense).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.10)
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

+ Details

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

- Definition

Amount of revenue from providing investment advisory, asset management and administrative services, including, but not limited to, distribution and shareholder services, accounting, tax, legal, regulatory filing, share registration, and shareholder correspondence activities.

+ References

No definition available.

+ Details

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

- Definition

Amount of fees and commissions from banking, advisory, brokerage, and securities underwriting activities. Activities include, but are not limited to, underwriting securities, private placements of securities, investment advisory and management services, merger and acquisition services, sale and servicing of mutual funds, and other related consulting fees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.13(b))
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

+ Details

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

- Definition

This item represents the net total realized and unrealized gain (loss) included in earnings for the period as a result of selling or holding marketable securities categorized as trading, available-for-sale, or held-to-maturity, including the unrealized holding gain (loss) of held-to-maturity securities transferred to the trading security category and the cumulative unrealized gain (loss) which was included in other comprehensive income (a separate component of shareholders' equity) for available-for-sale securities transferred to trading securities during the period. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (a),(c)-(e)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27357-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.7(c))
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 10
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27405-111563

+ Details

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

- Definition

The total amount of noninterest income which may be derived from: (1) fees and commissions; (2) premiums earned; (3) insurance policy charges; (4) the sale or disposal of assets; and (5) other sources not otherwise specified.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.13)
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

+ Details

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

- Definition

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 32
-Paragraph 2A
-URI http://asc.fasb.org/extlink&oid=82859839&loc=SL82860478-203043

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82913847&loc=SL49130543-203045

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82913847&loc=SL49130539-203045

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=82913847&loc=SL49130545-203045

+ Details

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

- Definition

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.1)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

+ Details

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

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=stt_InvestmentServicingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ProductOrServiceAxis=stt_AccountServicingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ProductOrServiceAxis=stt_ManagementServicesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ProductOrServiceAxis=stt_TradingServicesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ProductOrServiceAxis=stt_SecuritiesFinancingServicesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ProductOrServiceAxis=stt_ProcessingServicesandOtherMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ProductOrServiceAxis=stt_RevenueFromFeesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ProductOrServiceAxis=stt_InterestIncomeNetMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ProductOrServiceAxis=stt_GainsLossesRelatedtoInvestmentSecuritiesNetMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=stt_InvestmentManagementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: