Regulatory Capital (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Retained earnings	$ 22,315	$ 21,918
Capital ratio: required common equity tier 1 capital	8.00%	8.50%
Capital ratio: required tier 1 capital	9.50%	10.00%
Capital ratio: required total capital	11.50%	12.00%
Basel III Advanced Approaches
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 10,659	$ 10,636
Retained earnings	22,315	21,918
Accumulated other comprehensive income (loss)	(920)	(870)
Treasury stock, at cost	(10,664)	(10,209)
Total	21,390	21,475
Goodwill and other intangible assets, net of associated deferred tax liabilities	(8,994)	(9,112)
Other adjustments	(281)	(150)
Qualifying subordinated long-term debt	1,168	1,095
Allowance for credit losses	17	5
Total capital	15,771	16,275
Credit risk	60,468	54,763
Operational risk	46,738	47,963
Securitizations	1,850	1,638
Equity	109,056	104,364
All other	$ 239,861	$ 219,624
Common equity tier 1 capital	11.10%	11.70%
Tier 1 capital	13.40%	14.50%
Total capital	14.50%	15.60%
Basel III Standardized Approach
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 10,659	$ 10,636
Retained earnings	22,315	21,918
Accumulated other comprehensive income (loss)	(920)	(870)
Treasury stock, at cost	(10,664)	(10,209)
Total	21,390	21,475
Goodwill and other intangible assets, net of associated deferred tax liabilities	(8,994)	(9,112)
Other adjustments	(281)	(150)
Common equity tier 1 capital		12,213
Preferred stock	2,471	2,962
Tier 1 capital		15,175
Qualifying subordinated long-term debt	1,168	1,095
Allowance for credit losses	123	90
Total capital	15,877	16,360
Credit risk	110,913	102,367
Securitizations	1,850	1,638
Equity	112,763	104,005
All other	$ 239,861	$ 219,624
Common equity tier 1 capital	10.70%	11.70%
Tier 1 capital	12.90%	14.60%
Total capital	14.10%	15.70%
State Street Bank | Basel III Advanced Approaches
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 12,893	$ 12,893
Retained earnings	13,936	13,218
Accumulated other comprehensive income (loss)	(650)	(654)
Treasury stock, at cost	0	0
Total	26,179	25,457
Goodwill and other intangible assets, net of associated deferred tax liabilities	(8,726)	(8,839)
Other adjustments	(111)	(1)
Common equity tier 1 capital	17,342	16,617
Preferred stock	0	0
Tier 1 capital	17,342	16,617
Qualifying subordinated long-term debt	1,172	1,099
Allowance for credit losses	18	3
Total capital	18,532	17,719
Credit risk	57,169	51,610
Operational risk	43,925	44,138
Securitizations	1,850	1,638
Equity	102,944	97,386
All other	$ 236,431	$ 216,397
Common equity tier 1 capital	16.80%	17.10%
Tier 1 capital	16.80%	17.10%
Total capital	18.00%	18.20%
State Street Bank | Basel III Standardized Approach
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 12,893	$ 12,893
Retained earnings	13,936	13,218
Accumulated other comprehensive income (loss)	(650)	(654)
Treasury stock, at cost	0	0
Total	26,179	25,457
Goodwill and other intangible assets, net of associated deferred tax liabilities	(8,726)	(8,839)
Other adjustments	(111)	(1)
Common equity tier 1 capital	17,342	16,617
Preferred stock	0	0
Tier 1 capital	17,342	16,617
Qualifying subordinated long-term debt	1,172	1,099
Allowance for credit losses	123	90
Total capital	18,637	17,806
Credit risk	107,380	98,979
Securitizations	1,850	1,638
Equity	109,230	100,617
All other	$ 236,431	$ 216,397
Common equity tier 1 capital	15.90%	16.50%
Tier 1 capital	15.90%	16.50%
Total capital	17.10%	17.70%