Fair Value (Schedule Of Fair Value Measurements On A Recurring Basis) (Details) (USD $) In Millions	Sep. 30, 2011		Dec. 31, 2010
Trading account assets	$ 1,936		$ 479
U.S. Government Securities [Member] | Quoted Market Prices In Active Markets (Level 1) [Member]
Trading account assets	171		20
Accrued expenses and other liabilities			210
Trading account liabilities	35
U.S. Government Securities [Member] | Total Net Carrying Value In Consolidated Statement Of Condition [Member]
Trading account assets	171		20
Accrued expenses and other liabilities			210
Trading account liabilities	35
Non-U.S. Government Securities [Member] | Quoted Market Prices In Active Markets (Level 1) [Member]
Trading account assets	1,582		297
Accrued expenses and other liabilities			345
Trading account liabilities	1,661
Non-U.S. Government Securities [Member] | Total Net Carrying Value In Consolidated Statement Of Condition [Member]
Trading account assets	1,582		297
Accrued expenses and other liabilities			345
Trading account liabilities	1,661
Other Trading Account Assets [Member] | Quoted Market Prices In Active Markets (Level 1) [Member]
Trading account assets	45		40
Other Trading Account Assets [Member] | Pricing Methods With Significant Observable Market Inputs (Level 2) [Member]
Trading account assets	138		122
Other Trading Account Assets [Member] | Total Net Carrying Value In Consolidated Statement Of Condition [Member]
Trading account assets	183		162
Foreign Exchange Contracts [Member] | Pricing Methods With Significant Observable Market Inputs (Level 2) [Member]
Derivative instruments, assets	20,339		7,804
Derivative instruments liabilities	20,878		8,195
Foreign Exchange Contracts [Member] | Pricing Methods With Significant Unobservable Market Inputs (Level 3) [Member]
Derivative instruments, assets	311		254
Derivative instruments liabilities	298		260
Interest-Rate Contracts [Member] | Quoted Market Prices In Active Markets (Level 1) [Member]
Derivative instruments liabilities			1
Interest-Rate Contracts [Member] | Pricing Methods With Significant Observable Market Inputs (Level 2) [Member]
Derivative instruments, assets	1,443		165
Derivative instruments liabilities	1,692		358
Interest-Rate Contracts [Member] | Pricing Methods With Significant Unobservable Market Inputs (Level 3) [Member]
Derivative instruments, assets	11
Derivative instruments liabilities	23		9
Other [Member] | Pricing Methods With Significant Observable Market Inputs (Level 2) [Member]
Derivative instruments, assets	2		2
Derivative instruments liabilities	1		1
Total Derivative Instruments [Member] | Pricing Methods With Significant Observable Market Inputs (Level 2) [Member]
Derivative instruments, assets	21,784		7,971
Derivative instruments liabilities	22,571
Total Derivative Instruments [Member] | Pricing Methods With Significant Unobservable Market Inputs (Level 3) [Member]
Derivative instruments, assets	322		254
Derivative instruments liabilities	321
Total Derivative Instruments [Member] | Impact Of Netting [Member]
Derivative instruments, assets	(10,743)	[1]	(2,970)	[1]
Derivative instruments liabilities	(10,743)	[1]
Total Derivative Instruments [Member] | Total Net Carrying Value In Consolidated Statement Of Condition [Member]
Derivative instruments, assets	11,363		5,255
Derivative instruments liabilities	12,149
Quoted Market Prices In Active Markets (Level 1) [Member]
Direct obligations	4,141		6,529
Non-U.S. equity securities	8		7
Total investment securities available for sale	4,149		6,536
Other assets	148		168
Total assets carried at fair value	6,095		7,061
Other liabilities	148		168
Total liabilities carried at fair value	1,844		724
Pricing Methods With Significant Observable Market Inputs (Level 2) [Member]
Direct obligations	1,202		1,048
Mortgage-backed securities	26,527		22,967
Student loans	15,584		13,181
Credit cards	10,184		7,560
Sub-prime	1,486		1,818
Other	605		569
Total asset-backed securities	27,859		23,128
Non-U.S. debt securities	14,944		10,872
State and political subdivisions	6,845		6,554
Collateralized mortgage obligations	2,742		1,502
Other U.S. debt securities	3,259		2,533
U.S. equity securities	608		1,115
Non-U.S. equity securities	201		119
Total investment securities available for sale	84,187		69,838
Total assets carried at fair value	106,109		77,931
Other liabilities	1		3
Total liabilities carried at fair value	22,572		8,557
Pricing Methods With Significant Unobservable Market Inputs (Level 3) [Member]
Direct obligations	22
Mortgage-backed securities	1,499		673
Student loans	949		1,234
Credit cards	311		43
Other	2,733		2,000
Total asset-backed securities	3,993		3,277
Non-U.S. debt securities	2,342		1,145
State and political subdivisions	51		50
Collateralized mortgage obligations	350		359
Other U.S. debt securities	2		3
Total investment securities available for sale	8,259		5,507
Total assets carried at fair value	8,581		5,761
Other liabilities	11
Total liabilities carried at fair value	332		269
Impact Of Netting [Member]
Total assets carried at fair value	(10,743)	[1]	(2,970)	[1]
Total liabilities carried at fair value	(10,743)	[1]	(2,970)	[1]
Total Net Carrying Value In Consolidated Statement Of Condition [Member]
Direct obligations	5,365		7,577
Mortgage-backed securities	28,026		23,640
Student loans	16,533		14,415
Credit cards	10,495		7,603
Sub-prime	1,486		1,818
Other	3,338		2,569
Total asset-backed securities	31,852		26,405
Non-U.S. debt securities	17,286		12,017
State and political subdivisions	6,896		6,604
Collateralized mortgage obligations	3,092		1,861
Other U.S. debt securities	3,261		2,536
U.S. equity securities	608		1,115
Non-U.S. equity securities	209		126
Total investment securities available for sale	96,595		81,881
Other assets	148		168
Total assets carried at fair value	110,042		87,783
Other liabilities	160		171
Total liabilities carried at fair value	$ 14,005		$ 6,580

[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.