Regulatory Capital (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Retained earnings	$ 20,911	$ 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	$ 10,586	$ 10,565
Retained earnings	20,911	20,606
Accumulated other comprehensive income (loss)	(1,168)	(1,332)
Treasury stock, at cost	(8,969)	(8,715)
Total	21,360	21,124
Goodwill and other intangible assets, net of associated deferred tax liabilities	(9,294)	(9,350)
Other adjustments	(167)	(194)
Common equity tier 1 capital	11,899	11,580
Preferred stock	3,690	3,690
Tier 1 capital	15,589	15,270
Qualifying subordinated long-term debt	787	778
Allowance for loan and lease losses and other	10	14
Total capital	16,386	16,062
Credit risk	49,451	47,738
Operational risk	47,213	46,060
Market risk	1,359	1,517
Total risk-weighted assets	98,023	95,315
Adjusted quarterly average assets	$ 210,099	$ 211,924
Common equity tier 1 capital	12.10%	12.10%
Tier 1 capital	15.90%	16.00%
Total capital	16.70%	16.90%
Basel III Standardized Approach
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 10,586	$ 10,565
Retained earnings	20,911	20,606
Accumulated other comprehensive income (loss)	(1,168)	(1,332)
Treasury stock, at cost	(8,969)	(8,715)
Total	21,360	21,124
Goodwill and other intangible assets, net of associated deferred tax liabilities	(9,294)	(9,350)
Other adjustments	(167)	(194)
Common equity tier 1 capital	11,899	11,580
Preferred stock	3,690	3,690
Tier 1 capital	15,589	15,270
Qualifying subordinated long-term debt	787	778
Allowance for loan and lease losses and other	84	83
Total capital	16,460	16,131
Credit risk	102,284	97,303
Market risk	1,359	1,517
Total risk-weighted assets	103,643	98,820
Adjusted quarterly average assets	$ 210,099	$ 211,924
Common equity tier 1 capital	11.50%	11.70%
Tier 1 capital	15.00%	15.50%
Total capital	15.90%	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	14,273	14,261
Accumulated other comprehensive income (loss)	(954)	(1,112)
Treasury stock, at cost	0	0
Total	26,213	26,043
Goodwill and other intangible assets, net of associated deferred tax liabilities	(9,016)	(9,073)
Other adjustments	(1)	(29)
Common equity tier 1 capital	17,196	16,941
Preferred stock	0	0
Tier 1 capital	17,196	16,941
Qualifying subordinated long-term debt	785	776
Allowance for loan and lease losses and other	6	11
Total capital	17,987	17,728
Credit risk	47,106	45,565
Operational risk	44,416	44,494
Market risk	1,359	1,517
Total risk-weighted assets	92,881	91,576
Adjusted quarterly average assets	$ 207,417	$ 209,413
Common equity tier 1 capital	18.50%	18.50%
Tier 1 capital	18.50%	18.50%
Total capital	19.40%	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	14,273	14,261
Accumulated other comprehensive income (loss)	(954)	(1,112)
Treasury stock, at cost	0	0
Total	26,213	26,043
Goodwill and other intangible assets, net of associated deferred tax liabilities	(9,016)	(9,073)
Other adjustments	(1)	(29)
Common equity tier 1 capital	17,196	16,941
Preferred stock	0	0
Tier 1 capital	17,196	16,941
Qualifying subordinated long-term debt	785	776
Allowance for loan and lease losses and other	83	83
Total capital	18,064	17,800
Credit risk	99,673	94,776
Market risk	1,359	1,517
Total risk-weighted assets	101,032	96,293
Adjusted quarterly average assets	$ 207,417	$ 209,413
Common equity tier 1 capital	17.00%	17.60%
Tier 1 capital	17.00%	17.60%
Total capital	17.90%	18.50%