Commitments And Contingencies (Narrative) (Details) (USD $)	3 Months Ended		9 Months Ended							0 Months Ended			9 Months Ended	12 Months Ended				84 Months Ended		2 Months Ended	3 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Aug. 31, 2009 Cus	Sep. 30, 2012 State Street Global Advisors [Member] trusts Cus	Feb. 03, 2012 State Street Global Advisors [Member]	Sep. 15, 2008 State Street Global Advisors [Member] Cus	Aug. 31, 2009 Securities Finance [Member]	Sep. 30, 2012 Securities Finance [Member]	Sep. 30, 2010 Securities Finance [Member]	Sep. 30, 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, 2007 Foreign Exchange [Member]	Sep. 30, 2012 Shareholder Litigation [Member] Cus	Dec. 31, 2012 Lehman Entities [Member]	Sep. 30, 2012 Lehman Entities [Member]	Sep. 30, 2011 Lehman Entities [Member]	Sep. 30, 2012 Maximum [Member] State Street Global Advisors [Member]	Sep. 30, 2012 Minimum [Member] State Street Global Advisors [Member]
Loss Contingencies [Line Items]
Percent of fair market value that must be maintained in collateral			100.00%
Cash collateral provided for securities lending	$ 8,700,000,000		$ 8,700,000,000		$ 5,210,000,000
Cash Collateral Received For Securities Lending	7,050,000,000		7,050,000,000		4,590,000,000
Number of Clients Entered Into Settlement Relating to Prudential Retirement Insurance Annuity Company Suit							1
Compensation Received By Prudential								28,000,000
Litigation reserve							60,000,000				10,000,000												80,000,000	0
Number of Common Trusts Managed Through SSgA							4
Number of Clients With Exposure to Lehman Brothers Entities							7
Number of Clients With Suits Pending Related to Lehman Brothers							1
Number of Clients Entered Into Settlement Relating to Lehman Brothers Suit							5
Number of customer not entered into settlement agreements									2
Investments In Funds By Customers Not Settled									48,000,000
Estimated indirect foreign exchange revenue													196,000,000	331,000,000	336,000,000	369,000,000	462,000,000
Number of Suits From Related Paricipants 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											13,000,000	49,000,000
Actual damages asserted by attorney general																		56,000,000
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
Litigation Settlement																						400,000,000
Gain (Loss) Related to Litigation Settlement	362,000,000	0	362,000,000	0																10,000,000	362,000,000
Settlement, amount															12,000,000
Unrecognized Tax Benefits	94,000,000		94,000,000		125,000,000
Notional amount of contingencies accounted for as derivative financial instruments	$ 35,830,000,000		$ 35,830,000,000		$ 40,960,000,000