Fair Value (Schedule of Fair Value Measurements on a Recurring Basis) (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended		12 Months Ended
	Jun. 30, 2013		Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account assets	$ 653		$ 637
Reduction in assets from netting and the result of cash collateral deposited with derivative counterparties	861		1,450
Reduction in liabilities from netting and the result of cash collateral received from derivative counterparties	904		478
Pricing Methods with Significant Unobservable Market Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	6,894		6,980
Liabilities, fair value disclosure	117		115
Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	100,180		109,682
Derivative assets	6,135		4,556
Other assets	95		68
Assets, fair value disclosure	107,063		114,943
Derivative instruments, liabilities	5,996		5,367
Other liabilities	95		66
Liabilities, fair value disclosure	6,091		5,433
Recurring | U.S. government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account assets	20		20
Recurring | Non-U.S. government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account assets	370		391
Recurring | US Treasury and federal agencies, direct obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	777		841
Recurring | US Treasury and federal agencies, mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	26,462		32,212
Recurring | Total asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	29,993		32,483
Recurring | Asset-backed securities, student loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	15,140		16,421
Recurring | Asset-backed securities, credit cards
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	9,134		9,986
Recurring | Asset-backed securities, sub-prime
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	1,325		1,399
Recurring | Asset-backed securities, other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	4,394		4,677
Recurring | Total non-U.S. debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	23,596		25,128
Recurring | Non-U.S. debt securities, mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	10,391		11,405
Recurring | Non-U.S. debt securities, asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	5,467		6,218
Recurring | Non-US debt securities, government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	3,430		3,199
Recurring | Non-U.S. debt securities, other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	4,308		4,306
Recurring | State and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	8,119		7,551
Recurring | Collateralized mortgage obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	4,976		4,954
Recurring | Other U.S.debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account assets	263		226
Available-for-sale securities	5,065		5,298
Recurring | U.S. equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	43		31
Recurring | Non-U.S. equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	1		1
Recurring | Money-market mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	1,148		1,183
Recurring | Quoted Market Prices in Active Markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	3		3
Derivative assets	0		0
Other assets	95		66
Assets, fair value disclosure	546		551
Derivative instruments, liabilities
Other liabilities	95		66
Liabilities, fair value disclosure	95		66
Recurring | Quoted Market Prices in Active Markets (Level 1) | Foreign exchange contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	0		0
Recurring | Quoted Market Prices in Active Markets (Level 1) | Interest-rate contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	0		0
Recurring | Quoted Market Prices in Active Markets (Level 1) | U.S. government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account assets	20		20
Recurring | Quoted Market Prices in Active Markets (Level 1) | Non-U.S. government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account assets	370		391
Recurring | Quoted Market Prices in Active Markets (Level 1) | US Treasury and federal agencies, direct obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	3		3
Recurring | Quoted Market Prices in Active Markets (Level 1) | US Treasury and federal agencies, mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0		0
Recurring | Quoted Market Prices in Active Markets (Level 1) | Total asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0		0
Recurring | Quoted Market Prices in Active Markets (Level 1) | Asset-backed securities, student loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0		0
Recurring | Quoted Market Prices in Active Markets (Level 1) | Asset-backed securities, credit cards
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0		0
Recurring | Quoted Market Prices in Active Markets (Level 1) | Asset-backed securities, sub-prime
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0		0
Recurring | Quoted Market Prices in Active Markets (Level 1) | Asset-backed securities, other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0		0
Recurring | Quoted Market Prices in Active Markets (Level 1) | Total non-U.S. debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0		0
Recurring | Quoted Market Prices in Active Markets (Level 1) | Non-U.S. debt securities, mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0		0
Recurring | Quoted Market Prices in Active Markets (Level 1) | Non-U.S. debt securities, asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0		0
Recurring | Quoted Market Prices in Active Markets (Level 1) | Non-US debt securities, government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0		0
Recurring | Quoted Market Prices in Active Markets (Level 1) | Non-U.S. debt securities, other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0		0
Recurring | Quoted Market Prices in Active Markets (Level 1) | State and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0		0
Recurring | Quoted Market Prices in Active Markets (Level 1) | Collateralized mortgage obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0		0
Recurring | Quoted Market Prices in Active Markets (Level 1) | Other U.S.debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account assets	58		71
Available-for-sale securities	0		0
Recurring | Quoted Market Prices in Active Markets (Level 1) | U.S. equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0		0
Recurring | Quoted Market Prices in Active Markets (Level 1) | Non-U.S. equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0		0
Recurring | Quoted Market Prices in Active Markets (Level 1) | Money-market mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0		0
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	93,404		102,812
Derivative assets	11,509		9,488
Other assets	0		2
Assets, fair value disclosure	105,118		112,457
Derivative instruments, liabilities	11,417		9,323
Other liabilities	0		0
Liabilities, fair value disclosure	11,417		9,323
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | Foreign exchange contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	11,438		9,265
Derivative instruments, liabilities	11,085		8,978
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | Interest-rate contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	71		223
Derivative instruments, liabilities	332		345
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments, liabilities	0		0
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | US Treasury and federal agencies, direct obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	774		838
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | US Treasury and federal agencies, mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	25,598		31,387
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | Total asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	25,741		27,834
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | Asset-backed securities, student loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	14,760		15,833
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | Asset-backed securities, credit cards
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	9,110		9,919
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | Asset-backed securities, sub-prime
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	1,325		1,399
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | Asset-backed securities, other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	546		683
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | Total non-U.S. debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	22,231		23,909
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | Non-U.S. debt securities, mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	10,063		10,850
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | Non-U.S. debt securities, asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	4,711		5,694
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | Non-US debt securities, government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	3,430		3,199
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | Non-U.S. debt securities, other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	4,027		4,166
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | State and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	8,074		7,503
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | Collateralized mortgage obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	4,738		4,837
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | Other U.S.debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading account assets	205		155
Available-for-sale securities	5,056		5,289
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | U.S. equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	43		31
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | Non-U.S. equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	1		1
Recurring | Pricing Methods with Significant Observable Market Inputs (Level 2) | Money-market mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	1,148		1,183
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	6,773		6,867
Derivative assets	121		113
Other assets	0		0
Assets, fair value disclosure	6,894		6,980
Derivative instruments, liabilities	117		115
Other liabilities	0		0
Liabilities, fair value disclosure	117		115
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Foreign exchange contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	121		113
Derivative instruments, liabilities	108		106
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Interest-rate contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	0		0
Derivative instruments, liabilities	0		0
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative instruments, liabilities	9		9
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | US Treasury and federal agencies, mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	864		825
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Total asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	4,252		4,649
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Asset-backed securities, student loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	380		588
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Asset-backed securities, credit cards
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	24		67
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Asset-backed securities, sub-prime
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0		0
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Asset-backed securities, other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	3,848		3,994
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Total non-U.S. debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	1,365		1,219
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Non-U.S. debt securities, mortgage-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	328		555
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Non-U.S. debt securities, asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	756		524
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Non-US debt securities, government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0		0
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Non-U.S. debt securities, other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	281		140
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | State and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	45		48
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Collateralized mortgage obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	238		117
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Other U.S.debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	9		9
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | U.S. equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0		0
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Non-U.S. equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0		0
Recurring | Pricing Methods with Significant Unobservable Market Inputs (Level 3) | Money-market mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0		0
Recurring | Impact of Netting
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	(5,495)	[1]	(5,045)	[2]
Other assets	0	[1]	0	[2]
Assets, fair value disclosure	(5,495)	[1]	(5,045)	[2]
Derivative instruments, liabilities	(5,538)	[1]	(4,071)	[2]
Other liabilities	0	[1]	0	[2]
Liabilities, fair value disclosure	$ (5,538)	[1]	$ (4,071)	[2]

[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 $861 million and $904 million, respectively, for cash collateral received from and provided to derivative counterparties. Netting cannot be disaggregated by type of derivative instrument

[2] 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 $1.45 billion and $478 million, respectively, for cash collateral received from and provided to derivative counterparties.