Fair Value (Schedule Of Fair Value Measurements On A Recurring Basis) (Details) (USD $)	3 Months Ended
	Mar. 31, 2012		Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account assets	$ 773,000,000		$ 707,000,000
Reduction in Assets From Netting and the Result of Cash Collateral Deposited with Derivative Counterparties	1,020,000,000
Reduction in Liabilities From Netting and the Result of Cash Collateral Received From Derivative Counterparties	357,000,000
Quoted Market Prices In Active Markets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Direct obligations	609,000,000		1,727,000,000
Mortgage-backed securities	0		0
Student loans	0		0
Credit cards	0		0
Sub-prime	0		0
Other	0		0
Total asset-backed securities	0		0
Non-U.S. debt securities	0		0
State and political subdivisions	0		0
Collateralized mortgage obligations	0		0
Other U.S. debt securities	0		0
U.S. equity securities	0		0
Non-U.S. equity securities	2,000,000		1,000,000
Total investment securities available for sale	611,000,000		1,728,000,000
Other assets	124,000,000		110,000,000
Total assets carried at fair value	1,357,000,000		2,407,000,000
Other Liabilities	124,000,000		110,000,000
Total liabilities carried at fair value	158,000,000		110,000,000
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	1,115,000,000		1,109,000,000
Mortgage-backed securities	31,805,000,000		28,832,000,000
Student loans	16,256,000,000		15,685,000,000
Credit cards	10,091,000,000		10,396,000,000
Sub-prime	1,379,000,000		1,404,000,000
Other	589,000,000		667,000,000
Total asset-backed securities	28,315,000,000		28,152,000,000
Non-U.S. debt securities	20,099,000,000		16,378,000,000
State and political subdivisions	7,138,000,000		6,997,000,000
Collateralized mortgage obligations	4,086,000,000		3,753,000,000
Other U.S. debt securities	4,051,000,000		3,613,000,000
U.S. equity securities	673,000,000		640,000,000
Non-U.S. equity securities	118,000,000		117,000,000
Total investment securities available for sale	97,400,000,000		89,591,000,000
Other assets	0		0
Total assets carried at fair value	104,694,000,000		103,570,000,000
Other Liabilities	0		0
Total liabilities carried at fair value	6,904,000,000		14,162,000,000
Pricing Methods With Significant Unobservable Market Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Direct obligations
Mortgage-backed securities	912,000,000		1,189,000,000
Student loans	511,000,000		860,000,000
Credit cards	119,000,000		91,000,000
Sub-prime	0		0
Other	3,090,000,000		2,798,000,000
Total asset-backed securities	3,720,000,000		3,749,000,000
Non-U.S. debt securities	1,818,000,000		3,296,000,000
State and political subdivisions	50,000,000		50,000,000
Collateralized mortgage obligations	193,000,000		227,000,000
Other U.S. debt securities	0		2,000,000
U.S. equity securities	0		0
Non-U.S. equity securities	0		0
Total investment securities available for sale	6,693,000,000		8,513,000,000
Other assets	0		0
Total assets carried at fair value	6,820,000,000		8,691,000,000
Other Liabilities	20,000,000		20,000,000
Total liabilities carried at fair value	155,000,000		201,000,000
Impact Of Netting [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets	0		0
Total assets carried at fair value	(3,598,000,000)	[1]	(7,653,000,000)	[1]
Other Liabilities	0		0
Total liabilities carried at fair value	(2,936,000,000)	[1]	(7,653,000,000)	[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	1,724,000,000		2,836,000,000
Mortgage-backed securities	32,717,000,000		30,021,000,000
Student loans	16,767,000,000		16,545,000,000
Credit cards	10,210,000,000		10,487,000,000
Sub-prime	1,379,000,000		1,404,000,000
Other	3,679,000,000		3,465,000,000
Total asset-backed securities	32,035,000,000		31,901,000,000
Non-U.S. debt securities	21,917,000,000		19,674,000,000
State and political subdivisions	7,188,000,000		7,047,000,000
Collateralized mortgage obligations	4,279,000,000		3,980,000,000
Other U.S. debt securities	4,051,000,000		3,615,000,000
U.S. equity securities	673,000,000		640,000,000
Non-U.S. equity securities	120,000,000		118,000,000
Total investment securities available for sale	104,704,000,000		99,832,000,000
Other assets	124,000,000		110,000,000
Total assets carried at fair value	109,273,000,000		107,015,000,000
Other Liabilities	144,000,000		130,000,000
Total liabilities carried at fair value	4,281,000,000		6,820,000,000
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	20,000,000		20,000,000
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	20,000,000		20,000,000
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	545,000,000		498,000,000
Trading Liabilities	34,000,000
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	545,000,000		498,000,000
Trading Liabilities	34,000,000
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	57,000,000		51,000,000
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	151,000,000		138,000,000
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	208,000,000		189,000,000
Mortgage-Backed Securities [Member] | Quoted Market Prices In Active Markets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-U.S. debt securities	0		0
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	11,102,000,000		9,418,000,000
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	469,000,000		1,457,000,000
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	11,571,000,000		10,875,000,000
Asset-Backed Securities [Member] | Quoted Market Prices In Active Markets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-U.S. debt securities	0		0
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	3,925,000,000		2,535,000,000
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	1,035,000,000		1,768,000,000
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	4,960,000,000		4,303,000,000
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]
Non-U.S. debt securities	0		0
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	1,703,000,000		1,671,000,000
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	0		0
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	1,703,000,000		1,671,000,000
Foreign Exchange 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, assets	0		0
Derivative instruments liabilities	0
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	6,942,000,000		12,045,000,000
Derivative instruments liabilities	6,515,000,000		12,191,000,000
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	127,000,000		168,000,000
Derivative instruments liabilities	126,000,000		161,000,000
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, assets	0		0
Derivative instruments liabilities	0
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	201,000,000		1,795,000,000
Derivative instruments liabilities	389,000,000		1,970,000,000
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	0		10,000,000
Derivative instruments liabilities	0		11,000,000
Other [Member] | Quoted Market Prices In Active Markets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Non-U.S. debt securities	0		0
Derivative instruments, assets			0
Derivative instruments liabilities	0
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	3,369,000,000		2,754,000,000
Derivative instruments, assets			1,000,000
Derivative instruments liabilities	0		1,000,000
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	314,000,000		71,000,000
Derivative instruments, assets			0
Derivative instruments liabilities	9,000,000		9,000,000
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	3,683,000,000		2,825,000,000
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, assets	0		0
Derivative instruments liabilities	0
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	7,143,000,000		13,841,000,000
Derivative instruments liabilities	6,904,000,000		14,162,000,000
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	127,000,000		178,000,000
Derivative instruments liabilities	135,000,000		181,000,000
Derivative Instruments [Member] | Impact Of Netting [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments, assets	(3,598,000,000)	[1]	(7,653,000,000)	[1]
Derivative instruments liabilities	(2,936,000,000)	[1]	(7,653,000,000)	[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	3,672,000,000		6,366,000,000
Derivative instruments liabilities	$ 4,103,000,000		$ 6,690,000,000

[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. Netting also reflects asset and liability reductions of $1.02 billion and $357 million, respectively, for cash collateral received from and deposited with derivative counterparties. This netting cannot be disaggregated by type of derivative instrument.