Regulatory Capital (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Retained earnings	$ 21,612	$ 20,553
Capital ratio: required common equity tier 1 capital	8.50%	7.50%
Capital ratio: required tier 1 capital	10.00%	9.00%
Capital ratio: required total capital	12.00%	11.00%
Basel III Advanced Approaches
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 10,621	$ 10,565
Retained earnings	21,612	20,606
Accumulated other comprehensive income (loss)	(1,000)	(1,332)
Treasury stock, at cost	(9,729)	(8,715)
Total	21,504	21,124
Goodwill and other intangible assets, net of associated deferred tax liabilities	(9,117)	(9,350)
Other adjustments	(158)	(194)
Common equity tier 1 capital	12,229	11,580
Preferred stock	3,690	3,690
Tier 1 capital	15,919	15,270
Qualifying subordinated long-term debt	607	778
Allowance for loan and lease losses and other	4	14
Total capital	16,530	16,062
Credit risk	51,726	47,738
Operational risk	46,913	46,060
Market risk	1,688	1,517
Total risk-weighted assets	100,327	95,315
Adjusted quarterly average assets	$ 213,997	$ 211,924
Common equity tier 1 capital	12.20%	12.10%
Tier 1 capital	15.90%	16.00%
Total capital	16.50%	16.90%
Basel III Standardized Approach
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 10,621	$ 10,565
Retained earnings	21,612	20,606
Accumulated other comprehensive income (loss)	(1,000)	(1,332)
Treasury stock, at cost	(9,729)	(8,715)
Total	21,504	21,124
Goodwill and other intangible assets, net of associated deferred tax liabilities	(9,117)	(9,350)
Other adjustments	(158)	(194)
Common equity tier 1 capital	12,229	11,580
Preferred stock	3,690	3,690
Tier 1 capital	15,919	15,270
Qualifying subordinated long-term debt	607	778
Allowance for loan and lease losses and other	86	83
Total capital	16,612	16,131
Credit risk	107,013	97,303
Market risk	1,688	1,517
Total risk-weighted assets	108,701	98,820
Adjusted quarterly average assets	$ 213,997	$ 211,924
Common equity tier 1 capital	11.30%	11.70%
Tier 1 capital	14.60%	15.50%
Total capital	15.30%	16.30%
State Street Bank | Basel III Advanced Approaches
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 12,878	$ 12,894
Retained earnings	14,194	14,261
Accumulated other comprehensive income (loss)	(761)	(1,112)
Treasury stock, at cost	0	0
Total	26,311	26,043
Goodwill and other intangible assets, net of associated deferred tax liabilities	(8,845)	(9,073)
Other adjustments	0	(29)
Common equity tier 1 capital	17,466	16,941
Preferred stock	0	0
Tier 1 capital	17,466	16,941
Qualifying subordinated long-term debt	604	776
Allowance for loan and lease losses and other	3	11
Total capital	18,073	17,728
Credit risk	49,183	45,565
Operational risk	44,125	44,494
Market risk	1,688	1,517
Total risk-weighted assets	94,996	91,576
Adjusted quarterly average assets	$ 210,625	$ 209,413
Common equity tier 1 capital	18.40%	18.50%
Tier 1 capital	18.40%	18.50%
Total capital	19.00%	19.40%
State Street Bank | Basel III Standardized Approach
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 12,878	$ 12,894
Retained earnings	14,194	14,261
Accumulated other comprehensive income (loss)	(761)	(1,112)
Treasury stock, at cost	0	0
Total	26,311	26,043
Goodwill and other intangible assets, net of associated deferred tax liabilities	(8,845)	(9,073)
Other adjustments	0	(29)
Common equity tier 1 capital	17,466	16,941
Preferred stock	0	0
Tier 1 capital	17,466	16,941
Qualifying subordinated long-term debt	604	776
Allowance for loan and lease losses and other	86	83
Total capital	18,156	17,800
Credit risk	104,242	94,776
Market risk	1,688	1,517
Total risk-weighted assets	105,930	96,293
Adjusted quarterly average assets	$ 210,625	$ 209,413
Common equity tier 1 capital	16.50%	17.60%
Tier 1 capital	16.50%	17.60%
Total capital	17.10%	18.50%