Regulatory Capital (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Retained earnings	$ 15,135	$ 14,882
Tier One Common Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets	4.50%	4.00%
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets	6.00%	5.50%
Capital Required for Capital Adequacy to Risk Weighted Assets	8.00%	8.00%
Tier One Leverage Capital Required for Capital Adequacy to Average Assets	4.00%	4.00%
Basel III Advanced Approaches
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	10,248	10,295
Retained earnings	15,135	14,882
Accumulated other comprehensive income (loss)	(1,226)	(641)
Treasury Stock Value, Excluding Preferred Shares	(5,519)	(5,158)
Total shareholders’ equity	18,638	19,378
Goodwill and other intangible assets, net of associated deferred tax liabilities	(5,932)	(5,869)
Other adjustments, common tier calculation	(62)	(36)
Tier one common risk-based capital	12,644	13,473
Preferred stock	1,961	1,961
Trust preferred capital securities subject to phase-out from tier 1 capital	237	475
Other adjustments, tier 1 risk based calculation	(94)	(145)
Tier One Risk Based Capital	14,748	15,764
Total Capital Qualifying Subordinated Long-Term Debt	1,439	1,618
Trust preferred capital securities phased out of tier 1 capital	713	475
Other adjustments, total capital calculation	2	4
Capital	16,902	17,861
Risk-weighted assets - credit risk	63,820	66,874
Risk-weighted assets - operational risk	35,765	35,866
Risk-weighted assets - market risk	4,413	5,087
Total risk-weighted assets	103,998	107,827
Adjusted Quarterly Average Assets	252,406	247,740
Value-at-risk	12.20%	12.50%
Stressed value-at-risk	14.20%	14.60%
Correlation valuation adjustment	16.30%	16.60%
Tier One Leverage Capital to Average Assets	5.80%	6.40%
Basel III Standardized Approach
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	10,248
Retained earnings	15,135
Accumulated other comprehensive income (loss)	(1,226)
Treasury Stock Value, Excluding Preferred Shares	(5,519)
Total shareholders’ equity	18,638
Goodwill and other intangible assets, net of associated deferred tax liabilities	(5,932)
Other adjustments, common tier calculation	(62)
Tier one common risk-based capital	12,644
Preferred stock	1,961
Trust preferred capital securities subject to phase-out from tier 1 capital	237
Other adjustments, tier 1 risk based calculation	(94)
Tier One Risk Based Capital	14,748
Total Capital Qualifying Subordinated Long-Term Debt	1,439
Trust preferred capital securities phased out of tier 1 capital	713
Other adjustments, total capital calculation	2
Capital	16,902
Risk-weighted assets - credit risk	119,582
Risk-weighted assets - market risk	2,364
Total risk-weighted assets	121,946
Adjusted Quarterly Average Assets	252,406
Value-at-risk	10.40%
Stressed value-at-risk	12.10%
Correlation valuation adjustment	13.90%
Tier One Leverage Capital to Average Assets	5.80%
Basel III Transitional Approach
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus		10,295
Retained earnings		14,882
Accumulated other comprehensive income (loss)		(641)
Treasury Stock Value, Excluding Preferred Shares		(5,158)
Total shareholders’ equity		19,378
Goodwill and other intangible assets, net of associated deferred tax liabilities		(5,869)
Other adjustments, common tier calculation		(36)
Tier one common risk-based capital		13,473
Preferred stock		1,961
Trust preferred capital securities subject to phase-out from tier 1 capital		475
Other adjustments, tier 1 risk based calculation		(145)
Tier One Risk Based Capital		15,764
Total Capital Qualifying Subordinated Long-Term Debt		1,618
Trust preferred capital securities phased out of tier 1 capital		475
Other adjustments, total capital calculation		4
Capital		17,861
Risk-weighted assets - credit risk		87,502
Risk-weighted assets - market risk		2,910
Total risk-weighted assets		90,412
Adjusted Quarterly Average Assets		247,740
Value-at-risk		14.90%
Stressed value-at-risk		17.40%
Correlation valuation adjustment		19.80%
Tier One Leverage Capital to Average Assets		6.40%
State Street Bank | Basel III Advanced Approaches
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	10,901	10,867
Retained earnings	9,801	9,416
Accumulated other comprehensive income (loss)	(1,048)	(535)
Treasury Stock Value, Excluding Preferred Shares	0	0
Total shareholders’ equity	19,654	19,748
Goodwill and other intangible assets, net of associated deferred tax liabilities	(5,632)	(5,577)
Other adjustments, common tier calculation	(102)	(128)
Tier one common risk-based capital	13,920	14,043
Preferred stock	0	0
Trust preferred capital securities subject to phase-out from tier 1 capital	0	0
Other adjustments, tier 1 risk based calculation	0	0
Tier One Risk Based Capital	13,920	14,043
Total Capital Qualifying Subordinated Long-Term Debt	1,453	1,634
Trust preferred capital securities phased out of tier 1 capital	0	0
Other adjustments, total capital calculation	0	0
Capital	15,373	15,677
Risk-weighted assets - credit risk	56,527	59,836
Risk-weighted assets - operational risk	35,348	35,449
Risk-weighted assets - market risk	4,407	5,048
Total risk-weighted assets	96,282	100,333
Adjusted Quarterly Average Assets	248,022	243,549
Value-at-risk	14.50%	14.00%
Stressed value-at-risk	14.50%	14.00%
Correlation valuation adjustment	16.00%	15.60%
Tier One Leverage Capital to Average Assets	5.60%	5.80%
State Street Bank | Basel III Standardized Approach
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	10,901
Retained earnings	9,801
Accumulated other comprehensive income (loss)	(1,048)
Treasury Stock Value, Excluding Preferred Shares	0
Total shareholders’ equity	19,654
Goodwill and other intangible assets, net of associated deferred tax liabilities	(5,632)
Other adjustments, common tier calculation	(102)
Tier one common risk-based capital	13,920
Preferred stock	0
Trust preferred capital securities subject to phase-out from tier 1 capital	0
Other adjustments, tier 1 risk based calculation	0
Tier One Risk Based Capital	13,920
Total Capital Qualifying Subordinated Long-Term Debt	1,453
Trust preferred capital securities phased out of tier 1 capital	0
Other adjustments, total capital calculation	0
Capital	15,373
Risk-weighted assets - credit risk	112,454
Risk-weighted assets - market risk	2,363
Total risk-weighted assets	114,817
Adjusted Quarterly Average Assets	248,022
Value-at-risk	12.10%
Stressed value-at-risk	12.10%
Correlation valuation adjustment	13.40%
Tier One Leverage Capital to Average Assets	5.60%
State Street Bank | Basel III Transitional Approach
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus		10,867
Retained earnings		9,416
Accumulated other comprehensive income (loss)		(535)
Treasury Stock Value, Excluding Preferred Shares		0
Total shareholders’ equity		19,748
Goodwill and other intangible assets, net of associated deferred tax liabilities		(5,577)
Other adjustments, common tier calculation		(128)
Tier one common risk-based capital		14,043
Preferred stock		0
Trust preferred capital securities subject to phase-out from tier 1 capital		0
Other adjustments, tier 1 risk based calculation		0
Tier One Risk Based Capital		14,043
Total Capital Qualifying Subordinated Long-Term Debt		1,634
Trust preferred capital securities phased out of tier 1 capital		0
Other adjustments, total capital calculation		0
Capital		15,677
Risk-weighted assets - credit risk		84,433
Risk-weighted assets - market risk		2,909
Total risk-weighted assets		87,342
Adjusted Quarterly Average Assets		$ 243,549
Value-at-risk		16.10%
Stressed value-at-risk		16.10%
Correlation valuation adjustment		17.90%
Tier One Leverage Capital to Average Assets		5.80%