Commitments And Contingencies (Narrative) (Details)	0 Months Ended	3 Months Ended	6 Months Ended	12 Months Ended				84 Months Ended
	Aug. 31, 2009 USD ($) Cus	Sep. 30, 2011 USD ($)	Jun. 30, 2012 USD ($) cases trusts Cus	Dec. 31, 2011 USD ($)	Dec. 31, 2010 USD ($)	Dec. 31, 2009 USD ($)	Dec. 31, 2008 USD ($)	Dec. 31, 2007 USD ($)	Feb. 03, 2012 USD ($)	Dec. 31, 2011 EUR (€)	Sep. 30, 2010 USD ($)	Sep. 15, 2008 USD ($) Cus	Jun. 30, 2012 Maximum [Member] USD ($)	Jun. 30, 2012 Minimum [Member] USD ($)
Commitments and Contingencies Disclosure [Abstract]
Percent of fair market value that must be maintained in collateral			100.00%
Cash collateral provided for securities lending			$ 8,530,000,000	$ 5,210,000,000
Cash Collateral Received For Securities Lending			5,170,000,000	4,590,000,000
Number of Clients Entered Into Settlement Relating to Prudential Retirement Insurance Annuity Company Suit			1
Compensation Received By Prudential									28,100,000
Litigation reserve													85,000,000	0
Number of Common Trusts Managed Through SSgA			4
Number of Lehman Entities Entered Into Insolvency Proceedings												2
Net assets of a fund held by Lehman												312,000,000
Number of Clients With Exposure to Lehman Brothers Entities			7
Number of Clients With Suits Pending Related to Lehman Brothers			3
Number of Cases Related to Lehman Pending in Boston Federal Court			2
Number of Clients Entered Into Settlement Relating to Lehman Brothers Suit			3
Number of Clients Settlements Entered After Client Obtained Judgment From Dutch Court Relating to Lehman Suit			1
Settlements with Dutch customers										42,000,000
Number of customer not entered into settlement agreements												4
Investments In Funds By Customers Not Settled												143,000,000
Estimated indirect foreign exchange revenue			141,000,000	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			23,200,000								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
Settlement, amount		400,000,000			12,000,000
Unrecognized Tax Benefits			87,000,000	125,000,000
Notional amount of contingencies accounted for as derivative financial instruments			$ 37,230,000,000	$ 40,960,000,000