Fair Value (Schedule of Fair Value Measurements on a Recurring Basis) (Details) (USD $) In Millions	Jun. 30, 2011		Dec. 31, 2010
Trading account assets	$ 2,427		$ 479
Quoted Market Prices in Active Markets (Level 1) [Member]
Trading account assets	2,282		357
Direct obligations	6,271		6,529
Mortgage-backed securities
Student loans
Credit cards
Sub-prime
Other
Total asset-backed securities
Non-U.S. debt securities
State and political subdivisions
Collateralized mortgage obligations
Other U.S. debt securities
U.S. equity securities
Non-U.S. equity securities	7		7
Total investment securities available for sale	6,278		6,536
Other assets	235		168
Total assets carried at fair value	8,795		7,061
Accrued expenses and other liabilities	2,169		723
Total liabilities carried at fair value	2,169		723
Pricing Methods with Significant Observable Market Inputs (Level 2) [Member]
Trading account assets	145		122
Direct obligations	1,110		1,048
Mortgage-backed securities	24,603		22,967
Student loans	14,674		12,764
Credit cards	9,789		7,560
Sub-prime	1,645		1,818
Other	613		563
Total asset-backed securities	26,721		22,705
Non-U.S. debt securities	16,157		11,295
State and political subdivisions	6,693		6,554
Collateralized mortgage obligations	2,481		1,502
Other U.S. debt securities	2,802		2,533
U.S. equity securities	563		1,115
Non-U.S. equity securities	183		119
Total investment securities available for sale	81,313		69,838
Other assets	8,529		7,971
Total assets carried at fair value	89,987		77,931
Accrued expenses and other liabilities	8,786		8,557
Total liabilities carried at fair value	8,786		8,557
Pricing Methods with Significant Unobservable Market Inputs (Level 3) [Member]
Direct obligations	17
Mortgage-backed securities	932		673
Student loans	1,246		1,165
Credit cards	79		43
Other	700		491
Total asset-backed securities	2,025		1,699
Non-U.S. debt securities	3,989		2,723
State and political subdivisions	54		50
Collateralized mortgage obligations	173		359
Other U.S. debt securities	2		3
Total investment securities available for sale	7,192		5,507
Other assets	209		254
Total assets carried at fair value	7,401		5,761
Accrued expenses and other liabilities	228		269
Total liabilities carried at fair value	228		269
Impact of Netting [Member]
Other assets	(4,067)	[1]	(2,970)	[1]
Total assets carried at fair value	(4,067)	[1]	(2,970)	[1]
Accrued expenses and other liabilities	(4,067)	[1]	(2,970)	[1]
Total liabilities carried at fair value	(4,067)	[1]	(2,970)	[1]
Total Net Carrying Value in Consolidated Statement of Condition [Member]
Trading account assets	2,427		479
Direct obligations	7,398		7,577
Mortgage-backed securities	25,535		23,640
Student loans	15,920		13,929
Credit cards	9,868		7,603
Sub-prime	1,645		1,818
Other	1,313		1,054
Total asset-backed securities	28,746		24,404
Non-U.S. debt securities	20,146		14,018
State and political subdivisions	6,747		6,604
Collateralized mortgage obligations	2,654		1,861
Other U.S. debt securities	2,804		2,536
U.S. equity securities	563		1,115
Non-U.S. equity securities	190		126
Total investment securities available for sale	94,783		81,881
Other assets	4,906		5,423
Total assets carried at fair value	102,116		87,783
Accrued expenses and other liabilities	7,116		6,579
Total liabilities carried at fair value	$ 7,116		$ 6,579

[1] Represents counterparty netting against level 2 financial assets and liabilities, where a legally enforceable master netting agreement exists between State Street and the counterparty.