Regulatory Matters (Regulatory Capital Ratios And Related Amounts) (Details) (USD $) In Millions, unless otherwise specified									12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2012 Statutory Minimum Requirement [Member]		Dec. 31, 2012 Standard Requirement Well Capitalized [Member]		Dec. 31, 2012 State Street [Member]	Dec. 31, 2011 State Street [Member]	Dec. 31, 2012 State Street Bank [Member]	Dec. 31, 2011 State Street Bank [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 capital, ratio					4.00%	[1]	6.00%	[1]	19.10%	18.80%	17.30%	17.60%
Total capital, ratio					8.00%	[1]	10.00%	[1]	20.60%	20.50%	19.10%	19.60%
Tier 1 leverage ratio					4.00%	[1]	5.00%	[1]	7.10%	7.30%	6.30%	6.70%
Total shareholders’ equity	$ 20,869	$ 19,398	$ 17,787	$ 14,491					$ 20,869	$ 19,398	$ 19,681	$ 18,494
Trust preferred capital securities									950	950	0	0
Net unrealized loss on available-for-sale securities and cash flow hedges									(525)	395	(523)	398
Deferred tax liability, associated with acquisitions									699	757	680	737
Recognition of pension plan funded status									283	248	277	245
Goodwill	5,977	5,645	5,597						(5,977)	(5,645)	(5,679)	(5,353)
Other intangible assets	2,539	2,459	2,593						(2,539)	(2,459)	(2,392)	(2,297)
Tier 1 capital									13,760	13,644	12,044	12,224
Qualifying subordinated debt									1,219	1,339	1,223	1,343
Allowances for on- and off-balance sheet credit exposures									39	40	39	40
Unrealized gain on available-for-sale equity securities	(2,001)	(1,471)							2	0	0	0
Tier 2 capital									1,260	1,379	1,262	1,383
Deductions for investments in finance subsidiaries									(191)	(181)	0	0
Total capital									14,829	14,842	13,306	13,607
On-balance sheet									58,238	52,642	55,949	49,659
Off-balance sheet									13,155	19,115	13,144	19,109
Market-risk equivalents									519	661	445	611
Total									71,912	72,418	69,538	69,379
Adjusted quarterly average assets									$ 192,817	$ 186,336	$ 189,780	$ 183,086

[1] State Street Bank must comply with the regulatory guideline for “well capitalized” in order for the parent company to maintain its status as a financial holding company, including maintaining a minimum tier 1 risk-based capital ratio of 6%, a minimum total risk-based capital ratio of 10%, and a minimum tier 1 leverage ratio of 5%. The “well capitalized” guideline requires us to maintain a minimum tier 1 risk-based capital ratio of 6% and a minimum total risk-based capital ratio of 10%.