Regulatory Capital (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Retained earnings	$ 22,794	$ 21,918
Capital ratio: required common equity tier 1 capital	8.00%	8.50%
Capital ratio: required tier 1 capital	0.095	0.100
Capital ratio: required total capital	0.115	0.120
Basel III Advanced Approaches
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 10,683	$ 10,636
Retained earnings	22,794	21,918
Accumulated other comprehensive income (loss)	(430)	(870)
Treasury stock, at cost	(10,645)	(10,209)
Total	22,402	21,475
Goodwill and other intangible assets, net of associated deferred tax liabilities	(8,973)	(9,112)
Other adjustments	(261)	(150)
Common equity tier 1 capital	13,168	12,213
Preferred stock	2,471	2,962
Tier 1 capital	15,639	15,175
Qualifying subordinated long-term debt	964	1,095
Allowance for credit losses	47	5
Total capital	16,650	16,275
Credit risk	57,975	54,763
Operational risk	44,225	47,963
Securitizations	1,563	1,638
Equity	103,763	104,364
All other	$ 256,418	$ 219,624
Common equity tier 1 capital	12.70%	11.70%
Tier 1 capital	0.151	0.145
Total capital	0.160	0.156
Basel III Standardized Approach
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 10,683	$ 10,636
Retained earnings	22,794	21,918
Accumulated other comprehensive income (loss)	(430)	(870)
Treasury stock, at cost	(10,645)	(10,209)
Total	22,402	21,475
Goodwill and other intangible assets, net of associated deferred tax liabilities	(8,973)	(9,112)
Other adjustments	(261)	(150)
Common equity tier 1 capital	13,168	12,213
Preferred stock	2,471
Tier 1 capital	15,639	15,175
Qualifying subordinated long-term debt	964	1,095
Allowance for credit losses	163	90
Total capital	16,766	16,360
Credit risk	105,276	102,367
Securitizations	1,563	1,638
Equity	106,839	104,005
All other	$ 256,418	$ 219,624
Common equity tier 1 capital	12.30%	11.70%
Tier 1 capital	0.146	0.146
Total capital	0.157	0.157
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	13,103	13,218
Accumulated other comprehensive income (loss)	(174)	(654)
Treasury stock, at cost	0	0
Total	25,822	25,457
Goodwill and other intangible assets, net of associated deferred tax liabilities	(8,705)	(8,839)
Other adjustments	(119)	(1)
Common equity tier 1 capital	16,998	16,617
Preferred stock	0	0
Tier 1 capital	16,998	16,617
Qualifying subordinated long-term debt	969	1,099
Allowance for credit losses	55	3
Total capital	18,022	17,719
Credit risk	54,016	51,610
Operational risk	43,738	44,138
Securitizations	1,563	1,638
Equity	99,317	97,386
All other	$ 252,725	$ 216,397
Common equity tier 1 capital	17.10%	17.10%
Tier 1 capital	0.171	0.171
Total capital	0.181	0.182
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	13,103	13,218
Accumulated other comprehensive income (loss)	(174)	(654)
Treasury stock, at cost	0	0
Total	25,822	25,457
Goodwill and other intangible assets, net of associated deferred tax liabilities	(8,705)	(8,839)
Other adjustments	(119)	(1)
Common equity tier 1 capital	16,998	16,617
Preferred stock	0	0
Tier 1 capital	16,998	16,617
Qualifying subordinated long-term debt	969	1,099
Allowance for credit losses	163	90
Total capital	18,130	17,806
Credit risk	101,462	98,979
Securitizations	1,563	1,638
Equity	103,025	100,617
All other	$ 252,725	$ 216,397
Common equity tier 1 capital	16.50%	16.50%
Tier 1 capital	0.165	0.165
Total capital	0.176	0.177