Regulatory Capital (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Retained earnings	$ 21,274	$ 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	$ 10,613	$ 10,565
Retained earnings	21,274	20,606
Accumulated other comprehensive income (loss)	(885)	(1,332)
Treasury stock, at cost	(9,249)	(8,715)
Total	21,753	21,124
Goodwill and other intangible assets, net of associated deferred tax liabilities	(9,257)	(9,350)
Other adjustments	(129)	(194)
Common equity tier 1 capital	12,367	11,580
Preferred stock	3,690	3,690
Other adjustments	1	0
Tier 1 capital	16,058	15,270
Qualifying subordinated long-term debt	603	778
Allowance for loan and lease losses and other	11	14
Total capital	16,672	16,062
Credit risk	51,974	47,738
Operational risk	47,075	46,060
Market risk	1,650	1,517
Total risk-weighted assets	100,699	95,315
Adjusted quarterly average assets	$ 212,127	$ 211,924
Common equity tier 1 capital	12.30%	12.10%
Tier 1 capital	15.90%	16.00%
Total capital	16.60%	16.90%
Basel III Standardized Approach
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 10,613	$ 10,565
Retained earnings	21,274	20,606
Accumulated other comprehensive income (loss)	(885)	(1,332)
Treasury stock, at cost	(9,249)	(8,715)
Total	21,753	21,124
Goodwill and other intangible assets, net of associated deferred tax liabilities	(9,257)	(9,350)
Other adjustments	(129)	(194)
Common equity tier 1 capital	12,367	11,580
Preferred stock	3,690	3,690
Other adjustments	1	0
Tier 1 capital	16,058	15,270
Qualifying subordinated long-term debt	603	778
Allowance for loan and lease losses and other	87	83
Total capital	16,748	16,131
Credit risk	106,322	97,303
Market risk	1,650	1,517
Total risk-weighted assets	107,972	98,820
Adjusted quarterly average assets	$ 212,127	$ 211,924
Common equity tier 1 capital	11.50%	11.70%
Tier 1 capital	14.90%	15.50%
Total capital	15.50%	16.30%
State Street Bank | Basel III Advanced Approaches
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 12,894	$ 12,894
Retained earnings	14,367	14,261
Accumulated other comprehensive income (loss)	(670)	(1,112)
Treasury stock, at cost	0	0
Total	26,591	26,043
Goodwill and other intangible assets, net of associated deferred tax liabilities	(8,979)	(9,073)
Other adjustments	(1)	(29)
Common equity tier 1 capital	17,611	16,941
Preferred stock	0	0
Other adjustments	0	0
Tier 1 capital	17,611	16,941
Qualifying subordinated long-term debt	601	776
Allowance for loan and lease losses and other	8	11
Total capital	18,220	17,728
Credit risk	49,810	45,565
Operational risk	44,288	44,494
Market risk	1,650	1,517
Total risk-weighted assets	95,748	91,576
Adjusted quarterly average assets	$ 208,933	$ 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	$ 12,894	$ 12,894
Retained earnings	14,367	14,261
Accumulated other comprehensive income (loss)	(670)	(1,112)
Treasury stock, at cost	0	0
Total	26,591	26,043
Goodwill and other intangible assets, net of associated deferred tax liabilities	(8,979)	(9,073)
Other adjustments	(1)	(29)
Common equity tier 1 capital	17,611	16,941
Preferred stock	0	0
Other adjustments	0	0
Tier 1 capital	17,611	16,941
Qualifying subordinated long-term debt	601	776
Allowance for loan and lease losses and other	87	83
Total capital	18,299	17,800
Credit risk	103,544	94,776
Market risk	1,650	1,517
Total risk-weighted assets	105,194	96,293
Adjusted quarterly average assets	$ 208,933	$ 209,413
Common equity tier 1 capital	16.70%	17.60%
Tier 1 capital	16.70%	17.60%
Total capital	17.40%	18.50%