Regulatory Capital (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Retained earnings	$ 15,390	$ 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	15,390	14,882
Accumulated other comprehensive income (loss)	(1,055)	(641)
Treasury Stock Value, Excluding Preferred Shares	(5,830)	(5,158)
Total shareholders’ equity	18,753	19,378
Goodwill and other intangible assets, net of associated deferred tax liabilities	(5,974)	(5,869)
Other adjustments, common tier calculation	(66)	(36)
Tier one common risk-based capital	12,713	13,473
Preferred stock	2,703	1,961
Trust preferred capital securities subject to phase-out from tier 1 capital	237	475
Other adjustments, tier 1 risk based calculation	(98)	(145)
Tier One Risk Based Capital	15,555	15,764
Total Capital Qualifying Subordinated Long-Term Debt	1,438	1,618
Trust preferred capital securities phased out of tier 1 capital	713	475
Other adjustments, total capital calculation	2	4
Capital	17,708	17,861
Risk-weighted assets - credit risk	56,154	66,874
Risk-weighted assets - operational risk	43,885	35,866
Risk-weighted assets - market risk	4,494	5,087
Total risk-weighted assets	104,533	107,827
Adjusted Quarterly Average Assets	$ 257,227	$ 247,740
Value-at-risk	12.20%	12.50%
Stressed value-at-risk	14.90%	14.60%
Correlation valuation adjustment	16.90%	16.60%
Tier One Leverage Capital to Average Assets	6.00%	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	15,390
Accumulated other comprehensive income (loss)	(1,055)
Treasury Stock Value, Excluding Preferred Shares	(5,830)
Total shareholders’ equity	18,753
Goodwill and other intangible assets, net of associated deferred tax liabilities	(5,974)
Other adjustments, common tier calculation	(66)
Tier one common risk-based capital	12,713
Preferred stock	2,703
Trust preferred capital securities subject to phase-out from tier 1 capital	237
Other adjustments, tier 1 risk based calculation	(98)
Tier One Risk Based Capital	15,555
Total Capital Qualifying Subordinated Long-Term Debt	1,438
Trust preferred capital securities phased out of tier 1 capital	713
Other adjustments, total capital calculation	2
Capital	17,708
Risk-weighted assets - credit risk	107,003
Risk-weighted assets - market risk	2,785
Total risk-weighted assets	109,788
Adjusted Quarterly Average Assets	$ 257,227
Value-at-risk	11.60%
Stressed value-at-risk	14.20%
Correlation valuation adjustment	16.10%
Tier One Leverage Capital to Average Assets	6.00%
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	$ 10,912	$ 10,867
Retained earnings	10,299	9,416
Accumulated other comprehensive income (loss)	(929)	(535)
Treasury Stock Value, Excluding Preferred Shares	0	0
Total shareholders’ equity	20,282	19,748
Goodwill and other intangible assets, net of associated deferred tax liabilities	(5,667)	(5,577)
Other adjustments, common tier calculation	(109)	(128)
Tier one common risk-based capital	14,506	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	14,506	14,043
Total Capital Qualifying Subordinated Long-Term Debt	1,452	1,634
Trust preferred capital securities phased out of tier 1 capital	0	0
Other adjustments, total capital calculation	0	0
Capital	15,958	15,677
Risk-weighted assets - credit risk	51,190	59,836
Risk-weighted assets - operational risk	43,324	35,449
Risk-weighted assets - market risk	4,503	5,048
Total risk-weighted assets	99,017	100,333
Adjusted Quarterly Average Assets	$ 252,636	$ 243,549
Value-at-risk	14.70%	14.00%
Stressed value-at-risk	14.70%	14.00%
Correlation valuation adjustment	16.10%	15.60%
Tier One Leverage Capital to Average Assets	5.70%	5.80%
State Street Bank | Basel III Standardized Approach
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 10,912
Retained earnings	10,299
Accumulated other comprehensive income (loss)	(929)
Treasury Stock Value, Excluding Preferred Shares	0
Total shareholders’ equity	20,282
Goodwill and other intangible assets, net of associated deferred tax liabilities	(5,667)
Other adjustments, common tier calculation	(109)
Tier one common risk-based capital	14,506
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	14,506
Total Capital Qualifying Subordinated Long-Term Debt	1,452
Trust preferred capital securities phased out of tier 1 capital	0
Other adjustments, total capital calculation	0
Capital	15,958
Risk-weighted assets - credit risk	101,955
Risk-weighted assets - market risk	2,785
Total risk-weighted assets	104,740
Adjusted Quarterly Average Assets	$ 252,636
Value-at-risk	13.80%
Stressed value-at-risk	13.80%
Correlation valuation adjustment	15.20%
Tier One Leverage Capital to Average Assets	5.70%
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%