Fair Value (Schedule Of Fair Value Measurements On A Recurring Basis) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011		Dec. 31, 2010
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account assets	$ 707		$ 479
Quoted Market Prices In Active Markets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Direct obligations	1,727		6,529
Non-U.S. equity securities	1		7
Total investment securities available for sale	1,728		6,536
Other assets	110		168
Total assets carried at fair value	2,407		7,061
Other liabilities	110		168
Total liabilities carried at fair value	110		724
Pricing Methods With Significant Observable Market Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Direct obligations	1,109		1,048
Mortgage-backed securities	28,832		22,967
Student loans	15,685		13,181
Credit cards	10,396		7,560
Sub-prime	1,404		1,818
Other	667		569
Total asset-backed securities	28,152		23,128
Non-U.S. debt securities	16,378		10,872
State and political subdivisions	6,997		6,554
Collateralized mortgage obligations	3,753		1,502
Other U.S. debt securities	3,613		2,533
U.S. equity securities	640		1,115
Non-U.S. equity securities	117		119
Total investment securities available for sale	89,591		69,838
Total assets carried at fair value	103,570		77,931
Other liabilities			3
Total liabilities carried at fair value	14,162		8,557
Pricing Methods With Significant Unobservable Market Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage-backed securities	1,189		673
Student loans	860		1,234
Credit cards	91		43
Other	2,798		2,000
Total asset-backed securities	3,749		3,277
Non-U.S. debt securities	3,296		1,145
State and political subdivisions	50		50
Collateralized mortgage obligations	227		359
Other U.S. debt securities	2		3
Total investment securities available for sale	8,513		5,507
Total assets carried at fair value	8,691		5,761
Other liabilities	20
Total liabilities carried at fair value	201		269
Impact Of Netting [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets carried at fair value	(7,653)	[1]	(2,970)	[1]
Total liabilities carried at fair value	(7,653)	[1]	(2,970)	[1]
Total Net Carrying Value In Consolidated Statement Of Condition [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Direct obligations	2,836		7,577
Mortgage-backed securities	30,021		23,640
Student loans	16,545		14,415
Credit cards	10,487		7,603
Sub-prime	1,404		1,818
Other	3,465		2,569
Total asset-backed securities	31,901		26,405
Non-U.S. debt securities	19,674		12,017
State and political subdivisions	7,047		6,604
Collateralized mortgage obligations	3,980		1,861
Other U.S. debt securities	3,615		2,536
U.S. equity securities	640		1,115
Non-U.S. equity securities	118		126
Total investment securities available for sale	99,832		81,881
Other assets	110		168
Total assets carried at fair value	107,015		87,783
Other liabilities	130		171
Total liabilities carried at fair value	6,820		6,580
Parent Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account assets	138		122
U.S. Government Securities [Member] | Quoted Market Prices In Active Markets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account assets	20		20
Accrued expenses and other liabilities			210
U.S. Government Securities [Member] | Total Net Carrying Value In Consolidated Statement Of Condition [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account assets	20		20
Accrued expenses and other liabilities			210
Non-U.S. Government Securities [Member] | Quoted Market Prices In Active Markets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account assets	498		297
Accrued expenses and other liabilities			345
Non-U.S. Government Securities [Member] | Total Net Carrying Value In Consolidated Statement Of Condition [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account assets	498		297
Accrued expenses and other liabilities			345
Asset-Backed Securities [Member] | Pricing Methods With Significant Observable Market Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-U.S. debt securities	2,535		1,046
Asset-Backed Securities [Member] | Pricing Methods With Significant Unobservable Market Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-U.S. debt securities	1,768		740
Asset-Backed Securities [Member] | Total Net Carrying Value In Consolidated Statement Of Condition [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-U.S. debt securities	4,303		1,786
Mortgage-Backed Securities [Member] | Pricing Methods With Significant Observable Market Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-U.S. debt securities	9,418		5,898
Mortgage-Backed Securities [Member] | Pricing Methods With Significant Unobservable Market Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-U.S. debt securities	1,457		396
Mortgage-Backed Securities [Member] | Total Net Carrying Value In Consolidated Statement Of Condition [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-U.S. debt securities	10,875		6,294
Government Securities [Member] | Pricing Methods With Significant Observable Market Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-U.S. debt securities	1,671		2,004
Government Securities [Member] | Pricing Methods With Significant Unobservable Market Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-U.S. debt securities			1
Government Securities [Member] | Total Net Carrying Value In Consolidated Statement Of Condition [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-U.S. debt securities	1,671		2,005
Other Trading Account Assets [Member] | Quoted Market Prices In Active Markets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account assets	51		40
Other Trading Account Assets [Member] | Pricing Methods With Significant Observable Market Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account assets	138		122
Other Trading Account Assets [Member] | Total Net Carrying Value In Consolidated Statement Of Condition [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account assets	189		162
Foreign Exchange Contracts [Member] | Pricing Methods With Significant Observable Market Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments, assets	12,045		7,804
Derivative instruments liabilities	12,191		8,195
Foreign Exchange Contracts [Member] | Pricing Methods With Significant Unobservable Market Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments, assets	168		254
Derivative instruments liabilities	161		260
Interest-Rate Contracts [Member] | Quoted Market Prices In Active Markets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments liabilities			1
Interest-Rate Contracts [Member] | Pricing Methods With Significant Observable Market Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments, assets	1,795		165
Derivative instruments liabilities	1,970		358
Interest-Rate Contracts [Member] | Pricing Methods With Significant Unobservable Market Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments, assets	10
Derivative instruments liabilities	11
Other [Member] | Pricing Methods With Significant Observable Market Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-U.S. debt securities	2,754		1,924
Derivative instruments, assets	1		2
Derivative instruments liabilities	1		1
Other [Member] | Pricing Methods With Significant Unobservable Market Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-U.S. debt securities	71		8
Derivative instruments liabilities	9		9
Other [Member] | Total Net Carrying Value In Consolidated Statement Of Condition [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-U.S. debt securities	2,825		1,932
Derivative Instruments [Member] | Quoted Market Prices In Active Markets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments liabilities			1
Derivative Instruments [Member] | Pricing Methods With Significant Observable Market Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments, assets	13,841		7,971
Derivative instruments liabilities	14,162		8,554
Derivative Instruments [Member] | Pricing Methods With Significant Unobservable Market Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments, assets	178		254
Derivative instruments liabilities	181		269
Derivative Instruments [Member] | Impact Of Netting [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments, assets	(7,653)	[1]	(2,970)	[1]
Derivative instruments liabilities	(7,653)	[1]	(2,970)	[1]
Derivative Instruments [Member] | Total Net Carrying Value In Consolidated Statement Of Condition [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments, assets	6,366		5,255
Derivative instruments liabilities	$ 6,690		$ 5,854

[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. This netting cannot be disaggregated by type of derivative instrument.