Regulatory Capital (Details) - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Retained earnings	$ 31,864	$ 31,392
Capital ratio: required common equity tier 1 capital	8.00%	8.00%
Capital ratio: required tier 1 capital	0.095	0.095
Capital ratio: required total capital	0.115	0.115
Tier 1 leverage capital ratio, minimum	0.040	0.040
Leverage ratio minimum	0.05
Basel III Advanced Approaches
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 11,205	$ 11,209
Retained earnings	31,864	31,392
Accumulated other comprehensive income (loss)	(1,282)	(1,043)
Treasury stock, at cost	(17,604)	(17,276)
Total	24,183	24,282
Goodwill and other intangible assets, net of associated deferred tax liabilities	(8,845)	(8,921)
Other adjustments	(540)	(549)
Common equity tier 1 capital	14,798	14,812
Preferred stock	3,559	3,559
Tier 1 capital	18,357	18,371
Qualifying subordinated long-term debt	1,698	1,872
Allowance for credit losses	30	18
Total capital	20,085	20,261
Credit risk	65,126	60,594
Operational risk	51,000	51,638
Market risk	2,185	2,125
Total risk-weighted assets	118,311	114,357
Adjusted quarterly average assets	$ 342,329	$ 332,978
Common equity tier 1 capital	12.50%	13.00%
Tier 1 capital	0.155	0.161
Total capital	0.170	0.177
Tier 1 leverage capital ratio, actual	0.054	0.055
Basel III Standardized Approach
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 11,205	$ 11,209
Retained earnings	31,864	31,392
Accumulated other comprehensive income (loss)	(1,282)	(1,043)
Treasury stock, at cost	(17,604)	(17,276)
Total	24,183	24,282
Goodwill and other intangible assets, net of associated deferred tax liabilities	(8,845)	(8,921)
Other adjustments	(540)	(549)
Common equity tier 1 capital	14,798	14,812
Preferred stock	3,559	3,559
Tier 1 capital	18,357	18,371
Qualifying subordinated long-term debt	1,698	1,872
Allowance for credit losses	179	203
Total capital	20,234	20,446
Credit risk	137,626	125,138
Market risk	2,185	2,125
Total risk-weighted assets	139,811	127,263
Adjusted quarterly average assets	$ 342,329	$ 332,978
Common equity tier 1 capital	10.60%	11.60%
Tier 1 capital	0.131	0.144
Total capital	0.145	0.161
Tier 1 leverage capital ratio, actual	0.054	0.055
State Street Bank | Basel III Advanced Approaches
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 13,333	$ 13,333
Retained earnings	16,418	16,401
Accumulated other comprehensive income (loss)	(1,040)	(815)
Treasury stock, at cost	0	0
Total	28,711	28,919
Goodwill and other intangible assets, net of associated deferred tax liabilities	(8,242)	(8,342)
Other adjustments	(404)	(419)
Common equity tier 1 capital	20,065	20,158
Preferred stock	0	0
Tier 1 capital	20,065	20,158
Qualifying subordinated long-term debt	523	524
Allowance for credit losses	30	18
Total capital	20,618	20,700
Credit risk	60,963	56,438
Operational risk	49,988	50,025
Market risk	2,185	2,125
Total risk-weighted assets	113,136	108,588
Adjusted quarterly average assets	$ 337,440	$ 328,034
Common equity tier 1 capital	17.70%	18.60%
Tier 1 capital	0.177	0.186
Total capital	0.182	0.191
Tier 1 leverage capital ratio, actual	0.059	0.061
State Street Bank | Basel III Standardized Approach
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 13,333	$ 13,333
Retained earnings	16,418	16,401
Accumulated other comprehensive income (loss)	(1,040)	(815)
Treasury stock, at cost	0	0
Total	28,711	28,919
Goodwill and other intangible assets, net of associated deferred tax liabilities	(8,242)	(8,342)
Other adjustments	(404)	(419)
Common equity tier 1 capital	20,065	20,158
Preferred stock	0	0
Tier 1 capital	20,065	20,158
Qualifying subordinated long-term debt	523	524
Allowance for credit losses	179	203
Total capital	20,767	20,885
Credit risk	134,313	121,747
Market risk	2,185	2,125
Total risk-weighted assets	136,498	123,872
Adjusted quarterly average assets	$ 337,440	$ 328,034
Common equity tier 1 capital	14.70%	16.30%
Tier 1 capital	0.147	0.163
Total capital	0.152	0.169
Tier 1 leverage capital ratio, actual	0.059	0.061