Long-Term Debt (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010
Debt Instrument [Line Items]
Senior notes issued	$ 2,000,000,000
Non-cumulative perpetual preferred stock	500,000,000
Long-term debt	8,131,000,000		8,550,000,000
Capital lease included in long term debt	565,000,000		606,000,000
Office facility cost	272,000,000		279,000,000
One Lincoln Street Parking Garage [Member]
Debt Instrument [Line Items]
Capital lease included in long term debt	422,000,000		431,000,000
State Street Capital Trust III [Member]
Debt Instrument [Line Items]
Subordinated borrowing interest rate	6.001%
Debt Instrument maturity date	Dec. 31, 2042
State Street Capital Trusts I And IV [Member]
Debt Instrument [Line Items]
Number of statutory business trusts	2
Issued trust preferred capital securities	955,000,000,000
Number of years interest payments received on debentures deferral	5
Series A Preferred Stock [Member]
Debt Instrument [Line Items]
Non-cumulative perpetual preferred stock	500,000,000
Preferred stock liquidation preference per share	$ 100,000
8.25% Fixed-To-Floating-Rate Subordinated Notes Due To State Street Capital Trust III In 2042 [Member]
Debt Instrument [Line Items]
Subordinated borrowing interest rate	8.25%
Junior Subordinated Debentures Due 2042 [Member]
Debt Instrument [Line Items]
Original junior subordinated debentures interest rate	6.001%
Floating-Rate Subordinated Notes Due To State Street Capital Trust IV In 2037 [Member]
Debt Instrument [Line Items]
Subordinated borrowing, due date	Jan. 01, 2037
Long-term debt	800,000,000		800,000,000
4.956% Junior Subordinated Debenture Due 2018 [Member]
Debt Instrument [Line Items]
Subordinated borrowing interest rate	4.956%
Debt Instrument maturity date	Mar. 15, 2018
Issued junior subordinated debentures	500,000,000
Non-cumulative perpetual preferred stock	500,000,000
2.15% Notes Due 2012 [Member]
Debt Instrument [Line Items]
Subordinated borrowing interest rate	2.15%
Subordinated borrowing, due date	Apr. 30, 2012
Long-term debt	1,500,000,000	[1]	1,499,000,000	[1]
2.875% Notes Due 2016 [Member]
Debt Instrument [Line Items]
Subordinated borrowing interest rate	2.875%
Senior notes issued	1,000,000,000
Senior notes interest rate percentage	2.875%
Debt Instrument maturity date	Mar. 07, 2016
Subordinated borrowing, due date	Jan. 01, 2016
Long-term debt	999,000,000	[2]
4.30% Notes Due 2014 [Member]
Debt Instrument [Line Items]
Subordinated borrowing interest rate	4.30%
Subordinated borrowing, due date	May 30, 2014
Long-term debt	512,000,000		500,000,000
4.375% Notes Due 2021 [Member]
Debt Instrument [Line Items]
Subordinated borrowing interest rate	4.375%
Senior notes issued	750,000,000
Senior notes interest rate percentage	4.375%
Debt Instrument maturity date	Mar. 07, 2021
Subordinated borrowing, due date	Jan. 01, 2021
Long-term debt	757,000,000	[2]
5.375% Notes Due 2017 [Member]
Debt Instrument [Line Items]
Subordinated borrowing interest rate	5.375%
Subordinated borrowing, due date	Apr. 30, 2017
Long-term debt	450,000,000		450,000,000
Floating-Rate Notes Due 2011 [Member]
Debt Instrument [Line Items]
Subordinated borrowing, due date	Jan. 01, 2011
Long-term debt			1,450,000,000	[1]
Floating-Rate Notes Due 2014 [Member]
Debt Instrument [Line Items]
Senior notes issued	250,000,000
Debt Instrument maturity date	Mar. 07, 2014
Subordinated borrowing, due date	Jan. 01, 2014
Long-term debt	250,000,000
Floating-Rate Notes Due 2012 [Member]
Debt Instrument [Line Items]
Subordinated borrowing, due date	Apr. 30, 2012
Long-term debt	250,000,000		268,000,000
Floating-rate notes, interest rate term	three-month LIBOR rate plus 10 basis points
1.85% Notes Due 2011 [Member]
Debt Instrument [Line Items]
Subordinated borrowing interest rate	1.85%
Subordinated borrowing, due date	Jan. 01, 2011
Long-term debt			1,000,000,000	[1]
5.25% Subordinated Notes Due 2018 [Member]
Debt Instrument [Line Items]
Subordinated borrowing interest rate	5.25%
Subordinated borrowing, due date	Jan. 01, 2018
Long-term debt	453,000,000	[2]	439,000,000	[2]
5.30% Subordinated Notes Due 2016 [Member]
Debt Instrument [Line Items]
Subordinated borrowing interest rate	5.30%
Subordinated borrowing, due date	Jan. 01, 2016
Long-term debt	419,000,000		423,000,000
Floating Rate Subordinated Notes Due 2015 [Member]
Debt Instrument [Line Items]
Subordinated borrowing, due date	Jan. 01, 2015
Long-term debt	200,000,000		200,000,000
Floating-Rate Subordinated Notes Due To State Street Capital Trust I In 2028 [Member]
Debt Instrument [Line Items]
Subordinated borrowing, due date	Jan. 01, 2028
Long-term debt	$ 155,000,000		$ 155,000,000

[1] Notes are guaranteed by the FDIC under its Temporary Liquidity Guarantee Program, or TLGP.

[2] We have entered into interest-rate swap agreements, recorded as fair value hedges, to modify our interest expense on these subordinated notes from a fixed rate to a floating rate. As of December 31, 2011 and 2010, we recorded an increase of $140 million and $81 million, respectively, in the carrying value of long-term debt associated with fair value hedges. Refer to note 16 for additional information about derivatives.