Investment Securities - Schedule of Marketable Securities (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Dec. 31, 2014
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	95,524	$ 94,108
Available for sale, gross unrealized gains	1,429	1,229
Available for sale, gross unrealized losses	341	424
Investment securities available for sale	96,612us-gaap_AvailableForSaleSecurities	94,913us-gaap_AvailableForSaleSecurities
Held to maturity, amortized cost	16,245us-gaap_HeldToMaturitySecurities	17,723us-gaap_HeldToMaturitySecurities
Held to maturity, gross unrealized gains	273	309
Held to maturity, gross unrealized losses	101	190
Held to maturity, fair value	16,417	17,842
Total asset-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	19,922	20,615
Available for sale, gross unrealized gains	209	218
Available for sale, gross unrealized losses	211	224
Investment securities available for sale	19,920	20,609
Held to maturity, amortized cost	3,197	3,288
Held to maturity, gross unrealized gains	8	7
Held to maturity, gross unrealized losses	5	5
Held to maturity, fair value	3,200	3,290
US Treasury and federal agencies, direct obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	12,803	10,573
Available for sale, gross unrealized gains	194	83
Available for sale, gross unrealized losses	1	1
Investment securities available for sale	12,996	10,655
Held to maturity, amortized cost	5,112	5,114
Held to maturity, gross unrealized gains	0	0
Held to maturity, gross unrealized losses	69	147
Held to maturity, fair value	5,043	4,967
US Treasury and federal agencies, mortgage-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	20,861	20,648
Available for sale, gross unrealized gains	251	193
Available for sale, gross unrealized losses	66	127
Investment securities available for sale	21,046	20,714
Held to maturity, amortized cost	57	62
Held to maturity, gross unrealized gains	4	4
Held to maturity, gross unrealized losses	0	0
Held to maturity, fair value	61	66
Asset-backed securities, student loans
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	12,070	12,478
Available for sale, gross unrealized gains	107	106
Available for sale, gross unrealized losses	113	124
Investment securities available for sale	12,064	12,460
Held to maturity, amortized cost	1,755	1,814
Held to maturity, gross unrealized gains	3	2
Held to maturity, gross unrealized losses	5	4
Held to maturity, fair value	1,753	1,812
Asset-backed securities, credit cards
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	2,941	3,077
Available for sale, gross unrealized gains	10	10
Available for sale, gross unrealized losses	34	34
Investment securities available for sale	2,917	3,053
Held to maturity, amortized cost	897	897
Held to maturity, gross unrealized gains	2	2
Held to maturity, gross unrealized losses	0	0
Held to maturity, fair value	899	899
Asset-backed securities, sub-prime
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	961	1,005
Available for sale, gross unrealized gains	2	2
Available for sale, gross unrealized losses	52	56
Investment securities available for sale	911	951
Asset-backed securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	3,950	4,055
Available for sale, gross unrealized gains	90	100
Available for sale, gross unrealized losses	12	10
Investment securities available for sale	4,028	4,145
Held to maturity, amortized cost	545	577
Held to maturity, gross unrealized gains	3	3
Held to maturity, gross unrealized losses	0	1
Held to maturity, fair value	548	579
Total non-U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	20,861	21,939
Available for sale, gross unrealized gains	216	241
Available for sale, gross unrealized losses	10	11
Investment securities available for sale	21,067	22,169
Held to maturity, amortized cost	5,786	6,881
Held to maturity, gross unrealized gains	165	191
Held to maturity, gross unrealized losses	19	23
Held to maturity, fair value	5,932	7,049
Non-U.S. debt securities, mortgage-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	8,522	9,442
Available for sale, gross unrealized gains	146	168
Available for sale, gross unrealized losses	4	4
Investment securities available for sale	8,664	9,606
Held to maturity, amortized cost	3,275	3,787
Held to maturity, gross unrealized gains	154	177
Held to maturity, gross unrealized losses	19	22
Held to maturity, fair value	3,410	3,942
Non-U.S. debt securities, asset-backed securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	3,353	3,215
Available for sale, gross unrealized gains	9	11
Available for sale, gross unrealized losses	1	0
Investment securities available for sale	3,361	3,226
Held to maturity, amortized cost	2,298	2,868
Held to maturity, gross unrealized gains	11	14
Held to maturity, gross unrealized losses	0	1
Held to maturity, fair value	2,309	2,881
Government securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	3,800	3,899
Available for sale, gross unrealized gains	11	10
Available for sale, gross unrealized losses	0	0
Investment securities available for sale	3,811	3,909
Held to maturity, amortized cost	148	154
Held to maturity, gross unrealized gains	0	0
Held to maturity, gross unrealized losses	0	0
Held to maturity, fair value	148	154
Non-U.S. debt securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	5,186	5,383
Available for sale, gross unrealized gains	50	52
Available for sale, gross unrealized losses	5	7
Investment securities available for sale	5,231	5,428
Held to maturity, amortized cost	65	72
Held to maturity, gross unrealized gains	0	0
Held to maturity, gross unrealized losses	0	0
Held to maturity, fair value	65	72
State and political subdivisions
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	10,729	10,532
Available for sale, gross unrealized gains	357	325
Available for sale, gross unrealized losses	37	37
Investment securities available for sale	11,049	10,820
Held to maturity, amortized cost	3	9
Held to maturity, gross unrealized gains	0	0
Held to maturity, gross unrealized losses	0	0
Held to maturity, fair value	3	9
Collateralized mortgage obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	5,738	5,280
Available for sale, gross unrealized gains	99	71
Available for sale, gross unrealized losses	7	12
Investment securities available for sale	5,830	5,339
Held to maturity, amortized cost	2,090	2,369
Held to maturity, gross unrealized gains	96	107
Held to maturity, gross unrealized losses	8	15
Held to maturity, fair value	2,178	2,461
Other U.S. debt securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	3,987	4,033
Available for sale, gross unrealized gains	94	88
Available for sale, gross unrealized losses	8	12
Investment securities available for sale	4,073	4,109
U.S. equity securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	31	29
Available for sale, gross unrealized gains	9	10
Available for sale, gross unrealized losses	1	0
Investment securities available for sale	39	39
Non-U.S. equity securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	2	2
Available for sale, gross unrealized gains	0	0
Available for sale, gross unrealized losses	0	0
Investment securities available for sale	2	2
U.S. money-market mutual funds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	582	449
Available for sale, gross unrealized gains	0	0
Available for sale, gross unrealized losses	0	0
Investment securities available for sale	582	449
Non-U.S. money-market mutual funds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Available for sale, amortized cost	8	8
Available for sale, gross unrealized gains	0	0
Available for sale, gross unrealized losses	0	0
Investment securities available for sale	8	8
Federal Family Education Loan Program
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Federal government credit support guarantee, percentage minimum	97.00%
Collateralized Loan Obligations
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Investment securities available for sale	3,600	3,800
Automobile Loan Securities
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Investment securities available for sale	348	315
Non-US Debt Securities, Covered Bonds
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Investment securities available for sale	3,300
Non-U.S. debt securities, other
Available-For-Sale and Held-To-Maturity-Securities [Line Items]
Investment securities available for sale	1,100	$ 1,200

Name:	stt_AvailableForSaleAndHeldToMaturitySecuritiesLineItems
Namespace Prefix:	stt_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax

+ References

No definition available.

+ Details

Name:	stt_AvailableforsaleSecuritiesAccumulatedGrossUnrealizedGainbeforeTax
Namespace Prefix:	stt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax

+ References

No definition available.

+ Details

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

- Definition

Federal Government Credit Support Guarantee Percentage Minimum

+ References

No definition available.

+ Details

Name:	stt_FederalGovernmentCreditSupportGuaranteePercentageMinimum
Namespace Prefix:	stt_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Held-to-maturity Securities, Accumulated Unrecognized Holding Gain

+ References

No definition available.

+ Details

Name:	stt_HeldtomaturitySecuritiesAccumulatedUnrecognizedHoldingGain
Namespace Prefix:	stt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Held-to-maturity Securities, Accumulated Unrecognized Holding Loss

+ References

No definition available.

+ Details

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

- Definition

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 5

-Subparagraph (aa)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562

+ Details

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

- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.2)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 5

-Subparagraph (f)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 5

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.1)

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.6)

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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

- Definition

Fair value of investments in debt securities classified as held-to-maturity.

+ References

+ Details

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