Commitments And Contingencies (Narrative) (Details) (USD $)	12 Months Ended				0 Months Ended			12 Months Ended					108 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Aug. 31, 2009 customer	Dec. 31, 2012 Legal Reserve [Member]	Aug. 31, 2009 Securities Finance [Member]	Dec. 31, 2012 Securities Finance [Member]	Sep. 30, 2010 Securities Finance [Member]	Dec. 31, 2012 Foreign Exchange [Member]	Dec. 31, 2011 Foreign Exchange [Member]	Dec. 31, 2010 Foreign Exchange [Member]	Dec. 31, 2009 Foreign Exchange [Member]	Dec. 31, 2008 Foreign Exchange [Member]	Dec. 31, 2009 Foreign Exchange [Member]	Dec. 31, 2012 Shareholder Litigation [Member] shareholder customer
Loss Contingencies [Line Items]
Unfunded Commitments To Extend Credit	$ 17,860,000,000	$ 17,300,000,000
Unfunded commitments to extend credit, short term	76.00%
Percent of fair market value that must be maintained in collateral	100.00%
Cash collateral provided for securities lending	7,570,000,000	5,210,000,000
Cash collateral received for securities lending	5,720,000,000	4,590,000,000
Number of suits from related participants of agency securities lending program			2
Loss contingency, damages sought, value					120,000,000
The difference between the amortized cost and market value of the in-kind distribution						11,000,000	49,000,000
Litigation reserve						10,000,000
Actual damages asserted by attorney general													100,000,000
Settlement, amount										12,000,000
Estimated indirect foreign exchange revenue								248,000,000	331,000,000	336,000,000	369,000,000	462,000,000
Shareholder related class action complaints pending in Boston Federal Court														4
Number of class action complaints pending in Boston Federal Court brought on behalf of State Street shareholders														1
Number of class action complaints pending in Boston Federal Court brought on behalf of State Street participants and benficiaries of State Street Salary Savings Program														2
Legal reserves				$ 10,000,000