Regulatory Capital (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Retained earnings	$ 18,675	$ 17,459
Capital ratio: required common equity tier 1 capital	6.50%	5.50%
Capital ratio: required tier 1 capital	8.00%	7.00%
Capital ratio: required total capital	10.00%	9.00%
Capital ratio: required tier 1 leverage	4.00%	4.00%
Percentage of goodwill and other intangible assets net of associated deferred tax liabilities allocated to other intangible assets	80.00%	60.00%
Basel III Advanced Approaches
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 10,307	$ 10,286
Retained earnings	18,675	17,459
Accumulated other comprehensive income (loss)	(985)	(1,936)
Treasury stock, at cost	(8,697)	(7,682)
Total	19,300	18,127
Goodwill and other intangible assets, net of associated deferred tax liabilities	(6,739)	(6,348)
Other adjustments	(122)	(155)
Common equity tier 1 capital	12,439	11,624
Preferred stock	3,196	3,196
Trust preferred capital securities subject to phase-out from tier 1 capital	0	0
Other adjustments	(29)	(103)
Tier 1 capital	15,606	14,717
Qualifying subordinated long-term debt	1,072	1,172
Trust preferred capital securities phased out of tier 1 capital	0	0
ALLL and other	5	19
Other adjustments	1	1
Total capital	16,684	15,909
Credit risk	50,197	50,900
Operational risk(4)	45,795	44,579
Market risk	3,005	3,822
Total risk-weighted assets	98,997	99,301
Adjusted quarterly average assets	$ 211,396	$ 226,310
Common equity tier 1 capital	12.60%	11.70%
Tier 1 capital	15.80%	14.80%
Total capital	16.90%	16.00%
Tier 1 leveraged	7.40%	6.50%
Basel III Standardized Approach
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 10,307	$ 10,286
Retained earnings	18,675	17,459
Accumulated other comprehensive income (loss)	(985)	(1,936)
Treasury stock, at cost	(8,697)	(7,682)
Total	19,300	18,127
Goodwill and other intangible assets, net of associated deferred tax liabilities	(6,739)	(6,348)
Other adjustments	(122)	(155)
Common equity tier 1 capital	12,439	11,624
Preferred stock	3,196	3,196
Trust preferred capital securities subject to phase-out from tier 1 capital	0	0
Other adjustments	(29)	(103)
Tier 1 capital	15,606	14,717
Qualifying subordinated long-term debt	1,072	1,172
Trust preferred capital securities phased out of tier 1 capital	0	0
ALLL and other	79	77
Other adjustments	1	1
Total capital	16,758	15,967
Credit risk	106,377	98,125
Market risk	1,203	1,751
Total risk-weighted assets	107,580	99,876
Adjusted quarterly average assets	$ 211,396	$ 226,310
Common equity tier 1 capital	11.60%	11.60%
Tier 1 capital	14.50%	14.70%
Total capital	15.60%	16.00%
Tier 1 leveraged	7.40%	6.50%
State Street Bank | Basel III Advanced Approaches
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 11,382	$ 11,376
Retained earnings	12,286	12,285
Accumulated other comprehensive income (loss)	(808)	(1,648)
Treasury stock, at cost	0	0
Total	22,860	22,013
Goodwill and other intangible assets, net of associated deferred tax liabilities	(6,447)	(6,060)
Other adjustments	(90)	(148)
Common equity tier 1 capital	16,323	15,805
Preferred stock	0	0
Trust preferred capital securities subject to phase-out from tier 1 capital	0	0
Other adjustments	0	0
Tier 1 capital	16,323	15,805
Qualifying subordinated long-term debt	1,076	1,179
Trust preferred capital securities phased out of tier 1 capital	0	0
ALLL and other	0	15
Other adjustments	0	0
Total capital	17,399	16,999
Credit risk	47,282	47,383
Operational risk(4)	45,270	44,043
Market risk	3,005	3,822
Total risk-weighted assets	95,557	95,248
Adjusted quarterly average assets	$ 208,308	$ 222,584
Common equity tier 1 capital	17.10%	16.60%
Tier 1 capital	17.10%	16.60%
Total capital	18.20%	17.80%
Tier 1 leveraged	7.80%	7.10%
State Street Bank | Basel III Standardized Approach
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 11,382	$ 11,376
Retained earnings	12,286	12,285
Accumulated other comprehensive income (loss)	(808)	(1,648)
Treasury stock, at cost	0	0
Total	22,860	22,013
Goodwill and other intangible assets, net of associated deferred tax liabilities	(6,447)	(6,060)
Other adjustments	(90)	(148)
Common equity tier 1 capital	16,323	15,805
Preferred stock	0	0
Trust preferred capital securities subject to phase-out from tier 1 capital	0	0
Other adjustments	0	0
Tier 1 capital	16,323	15,805
Qualifying subordinated long-term debt	1,076	1,179
Trust preferred capital securities phased out of tier 1 capital	0	0
ALLL and other	79	77
Other adjustments	0	0
Total capital	17,478	17,061
Credit risk	103,024	94,413
Market risk	1,203	1,751
Total risk-weighted assets	104,227	96,164
Adjusted quarterly average assets	$ 208,308	$ 222,584
Common equity tier 1 capital	15.70%	16.40%
Tier 1 capital	15.70%	16.40%
Total capital	16.80%	17.70%
Tier 1 leveraged	7.80%	7.10%