Expenses - Activity Related To Restructuring-Related Accruals (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015
Restructuring Reserve [Roll Forward]
Balance as of December 31, 2014	$ 71us-gaap_RestructuringReserve
Additional accruals for Business Operations and Information Technology Transformation program	(3)stt_RestructuringAccrualsOther
Payments and adjustments	(18)us-gaap_PaymentsForRestructuring
Balance as of March 31, 2015	54us-gaap_RestructuringReserve
2012 Expense Control Measures
Restructuring Reserve [Roll Forward]
Additional accruals for 2012 expense control measures	4
Employee- Related Costs
Restructuring Reserve [Roll Forward]
Balance as of December 31, 2014	40
Additional accruals for Business Operations and Information Technology Transformation program	(3)
Payments and adjustments	(10)
Balance as of March 31, 2015	27
Employee- Related Costs \| 2012 Expense Control Measures
Restructuring Reserve [Roll Forward]
Additional accruals for 2012 expense control measures	0
Real Estate Consolidation
Restructuring Reserve [Roll Forward]
Balance as of December 31, 2014	24
Additional accruals for Business Operations and Information Technology Transformation program	0
Payments and adjustments	(3)
Balance as of March 31, 2015	21
Real Estate Consolidation \| 2012 Expense Control Measures
Restructuring Reserve [Roll Forward]
Additional accruals for 2012 expense control measures	0
Asset and Other Write-Offs
Restructuring Reserve [Roll Forward]
Balance as of December 31, 2014	7
Additional accruals for Business Operations and Information Technology Transformation program	0
Payments and adjustments	(5)
Balance as of March 31, 2015	6
Asset and Other Write-Offs \| 2012 Expense Control Measures
Restructuring Reserve [Roll Forward]
Additional accruals for 2012 expense control measures	$ 4

Restructuring Accruals Other

No definition available.

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- Definition

Amount of cash payments made as the result of exit or disposal activities. Excludes payments associated with a discontinued operation or an asset retirement obligation.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

+ Details

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- Definition

Carrying amount (including both current and noncurrent portions of the accrual) as of the balance sheet date pertaining to a specified type of cost associated with exit from or disposal of business activities or restructuring pursuant to a duly authorized plan.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 420

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SAB TOPIC 5.P.4(b))

-URI http://asc.fasb.org/extlink&oid=27011515&loc=d3e140904-122747

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

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 5

-Section P

-Subsection 3, 4

+ Details

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Period Type:	instant

- Definition

Amount of any reversal and other adjustment made during the period to the amount of a previously accrued liability for a specified type of restructuring cost, excluding adjustments for costs incurred during the period, costs settled during the period, and foreign currency translation adjustments.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 420

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6394359&loc=d3e17939-110869

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 420

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SAB TOPIC 5.P.4(b))

-URI http://asc.fasb.org/extlink&oid=27011515&loc=d3e140904-122747

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

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 5

-Section P

-Subsection 3, 4

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 420

-SubTopic 10

-Section 40

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6394291&loc=d3e17658-110867

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