Commitments And Contingencies (Narrative) (Details)	3 Months Ended			12 Months Ended				84 Months Ended
	Mar. 31, 2012 USD ($) Cus trusts	Sep. 30, 2011 USD ($)	Sep. 30, 2007	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 ($)	Aug. 31, 2009 USD ($)	Sep. 15, 2008 USD ($) Cus	Jun. 30, 2007 USD ($)	Mar. 31, 2012 Maximum [Member] USD ($)	Mar. 31, 2012 Minimum [Member] USD ($)
Commitments and Contingencies Disclosure [Abstract]
Percent of fair market value that must be maintained in collateral	100.00%
Cash collateral provided for securities lending	$ 7,020,000,000			$ 5,210,000,000
Cash Collateral Received For Securities Lending	6,410,000,000			4,590,000,000
Net Assets Of Registered Sub Prime Funds														300,000,000
Average Decline In Net Asset Value Per Share			7.23%
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
Asserted damages by two participants in the agency securities lending program												120,000,000
The difference between the amortized cost and market value of the in-kind distribution	23,600,000										49,000,000
Estimated indirect foreign exchange revenue	75,000,000			331,000,000	336,000,000	369,000,000	462,000,000
Actual damages asserted by attorney general								56,000,000
Settlement, amount		400,000,000			12,000,000
Number of Putative Class Action Suits Related to TAG	2
Loss Contingency, Damages Sought, Value	100,000,000
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
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
Number of Suits From Related Paricipants of Agency Securities Lending Program	2
Unrecognized Tax Benefits	87,000,000			125,000,000
Notional amount of contingencies accounted for as derivative financial instruments	$ 38,730,000,000			$ 40,960,000,000