Regulatory Capital (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Retained earnings	$ 31,392	$ 29,582
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
Capital ratio: required total capital	0.040	0.040
Capital conservation buffer, capital conserved, minimum	0.025
Stress capital buffer, minimum	2.50%
Banking regulation, global systemically important bank (G-SIB) surcharge	0.010
Countercyclical capital buffer	0
Leverage ratio minimum	0.05
Basel III Advanced Approaches
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 11,209	$ 11,226
Retained earnings	31,392	29,582
Accumulated other comprehensive income (loss)	(1,043)	(2,100)
Treasury stock, at cost	(17,276)	(16,198)
Total	24,282	22,510
Goodwill and other intangible assets, net of associated deferred tax liabilities	(8,921)	(8,320)
Other adjustments	(549)	(391)
Common equity tier 1 capital	14,812	13,799
Preferred stock	3,559	2,816
Tier 1 capital	18,371	16,615
Qualifying subordinated long-term debt	1,872	1,861
Adjusted allowance for credit losses	18	0
Total capital	20,261	18,476
Credit risk	60,594	63,252
Operational risk	51,638	49,350
Market risk	2,125	2,000
Total risk-weighted assets	114,357	114,602
Adjusted quarterly average assets	$ 332,978	$ 318,470
Common equity tier 1 capital	13.00%	12.00%
Tier 1 capital	0.161	0.145
Total capital	0.177	0.161
Tier 1 leverage	0.055	0.052
Basel III Standardized Approach
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 11,209	$ 11,226
Retained earnings	31,392	29,582
Accumulated other comprehensive income (loss)	(1,043)	(2,100)
Treasury stock, at cost	(17,276)	(16,198)
Total	24,282	22,510
Goodwill and other intangible assets, net of associated deferred tax liabilities	(8,921)	(8,320)
Other adjustments	(549)	(391)
Common equity tier 1 capital	14,812	13,799
Preferred stock	3,559	2,816
Tier 1 capital	18,371	16,615
Qualifying subordinated long-term debt	1,872	1,861
Adjusted allowance for credit losses	203	183
Total capital	20,446	18,659
Credit risk	125,138	124,281
Market risk	2,125	2,000
Total risk-weighted assets	127,263	126,281
Adjusted quarterly average assets	$ 332,978	$ 318,470
Common equity tier 1 capital	11.60%	10.90%
Tier 1 capital	0.144	0.132
Total capital	0.161	0.148
Tier 1 leverage	0.055	0.052
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	16,401	15,977
Accumulated other comprehensive income (loss)	(815)	(1,805)
Treasury stock, at cost	0	0
Total	28,919	27,505
Goodwill and other intangible assets, net of associated deferred tax liabilities	(8,342)	(8,054)
Other adjustments	(419)	(278)
Common equity tier 1 capital	20,158	19,173
Preferred stock	0	0
Tier 1 capital	20,158	19,173
Qualifying subordinated long-term debt	524	530
Adjusted allowance for credit losses	18	0
Total capital	20,700	19,703
Credit risk	56,438	57,883
Operational risk	50,025	47,538
Market risk	2,125	2,000
Total risk-weighted assets	108,588	107,421
Adjusted quarterly average assets	$ 328,034	$ 314,754
Common equity tier 1 capital	18.60%	17.80%
Tier 1 capital	0.186	0.178
Total capital	0.191	0.183
Tier 1 leverage	0.061	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	16,401	15,977
Accumulated other comprehensive income (loss)	(815)	(1,805)
Treasury stock, at cost	0	0
Total	28,919	27,505
Goodwill and other intangible assets, net of associated deferred tax liabilities	(8,342)	(8,054)
Other adjustments	(419)	(278)
Common equity tier 1 capital	20,158	19,173
Preferred stock	0	0
Tier 1 capital	20,158	19,173
Qualifying subordinated long-term debt	524	530
Adjusted allowance for credit losses	203	183
Total capital	20,885	19,886
Credit risk	121,747	121,785
Market risk	2,125	2,000
Total risk-weighted assets	123,872	123,785
Adjusted quarterly average assets	$ 328,034	$ 314,754
Common equity tier 1 capital	16.30%	15.50%
Tier 1 capital	0.163	0.155
Total capital	0.169	0.161
Tier 1 leverage	0.061	0.061