Contingencies (Narrative) (Details) In Millions, unless otherwise specified				1 Months Ended			1 Months Ended		0 Months Ended			1 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2014 USD ($)	Dec. 31, 2013 USD ($)	Aug. 31, 2009 customer	Jan. 31, 2014 Transition Management claim	Sep. 30, 2014 Transition Management USD ($)	Sep. 30, 2014 Transition Management Legal Reserve USD ($)	Jan. 31, 2014 Transition Management Regulatory Matter USD ($)	Jan. 31, 2014 Transition Management Regulatory Matter GBP (£)	Aug. 31, 2009 Securities Finance USD ($)	Sep. 30, 2014 Securities Finance USD ($)	Jun. 30, 2013 Securities Finance USD ($)	Oct. 31, 2009 Foreign Exchange USD ($)	Sep. 30, 2014 Foreign Exchange USD ($)	Dec. 31, 2013 Foreign Exchange USD ($)	Dec. 31, 2012 Foreign Exchange USD ($)	Dec. 31, 2011 Foreign Exchange USD ($)	Dec. 31, 2010 Foreign Exchange USD ($)	Dec. 31, 2009 Foreign Exchange USD ($)	Dec. 31, 2008 Foreign Exchange USD ($)	Sep. 30, 2014 Putative Class Action claim	Sep. 30, 2014 Shareholder Litigation USD ($) complaint shareholder	Sep. 30, 2014 Salary Savings Program USD ($)	Sep. 30, 2014 Investment Servicing USD ($) claim
Loss Contingencies [Line Items]
Loss Contingency, Estimate of Possible Loss													$ 70
Loss Contingency, Estimate Of Possible Loss, net of tax													53
Legal reserves						111
Number of pending claims																				2			1
Settlement, amount							37.8	22.9
Litigation reserve					4.3					10.0													4.3
Number of suits from related participants of agency securities lending program			2
Loss contingency, damages sought, value									125
Realized loss on sales of securities											11
Actual damages asserted by attorney general												100
Estimated indirect foreign exchange revenue													186	285	248	331	336	369	462
Shareholder related class action complaints pending in Boston Federal Court																					3
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 beneficiaries of State Street Salary Savings Program																					2
Settlement Liabilities, Current																					60	10
Claims settled				6
Unrecognized tax benefits	$ 155	$ 164