Regulatory Capital (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Retained earnings	$ 17,047	$ 16,049
Capital ratio: required common equity tier 1 capital	5.50%	4.50%
Capital ratio: required tier 1 capital	7.00%	6.00%
Capital ratio: required total capital	9.00%	8.00%
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	60.00%	40.00%
Basel III Advanced Approaches
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 10,282	$ 10,250
Retained earnings	17,047	16,049
Accumulated other comprehensive income (loss)	(1,107)	(1,422)
Treasury stock, at cost	(7,382)	(6,457)
Total	18,840	18,420
Goodwill and other intangible assets, net of associated deferred tax liabilities	(6,483)	(5,927)
Other adjustments	(88)	(60)
Common equity tier 1 capital	12,269	12,433
Preferred stock	3,196	2,703
Trust preferred capital securities subject to phase-out from tier 1 capital	0	237
Other adjustments	(58)	(109)
Tier 1 capital	15,407	15,264
Qualifying subordinated long-term debt	1,259	1,358
Trust preferred capital securities phased out of tier 1 capital	890	713
ALLL and other	3	12
Other adjustments	1	2
Total capital	17,560	17,349
Credit risk	51,916	51,733
Operational risk	44,643	43,882
Market risk	3,177	3,937
Total risk-weighted assets	99,736	99,552
Adjusted quarterly average assets	$ 226,093	$ 221,880
Common equity tier 1 capital	12.30%	12.50%
Tier 1 capital	15.40%	15.30%
Total capital	17.60%	17.40%
Tier 1 leveraged	6.80%	6.90%
Basel III Standardized Approach
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 10,282	$ 10,250
Retained earnings	17,047	16,049
Accumulated other comprehensive income (loss)	(1,107)	(1,422)
Treasury stock, at cost	(7,382)	(6,457)
Total	18,840	18,420
Goodwill and other intangible assets, net of associated deferred tax liabilities	(6,483)	(5,927)
Other adjustments	(88)	(60)
Common equity tier 1 capital	12,269	12,433
Preferred stock	3,196	2,703
Trust preferred capital securities subject to phase-out from tier 1 capital	0	237
Other adjustments	(58)	(109)
Tier 1 capital	15,407	15,264
Qualifying subordinated long-term debt	1,259	1,358
Trust preferred capital securities phased out of tier 1 capital	890	713
ALLL and other	75	66
Other adjustments	1	2
Total capital	17,632	17,403
Credit risk	96,668	93,515
Market risk	1,706	2,378
Total risk-weighted assets	98,374	95,893
Adjusted quarterly average assets	$ 226,093	$ 221,880
Common equity tier 1 capital	12.50%	13.00%
Tier 1 capital	15.70%	15.90%
Total capital	17.90%	18.10%
Tier 1 leveraged	6.80%	6.90%
State Street Bank | Basel III Advanced Approaches
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 11,339	$ 10,938
Retained earnings	11,593	10,655
Accumulated other comprehensive income (loss)	(880)	(1,230)
Treasury stock, at cost	0	0
Total	22,052	20,363
Goodwill and other intangible assets, net of associated deferred tax liabilities	(6,152)	(5,631)
Other adjustments	(83)	(85)
Common equity tier 1 capital	15,817	14,647
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	15,817	14,647
Qualifying subordinated long-term debt	1,270	1,371
Trust preferred capital securities phased out of tier 1 capital	0	0
ALLL and other	4	8
Other adjustments	0	0
Total capital	17,091	16,026
Credit risk	47,609	47,677
Operational risk	44,115	43,324
Market risk	3,177	3,939
Total risk-weighted assets	94,901	94,940
Adjusted quarterly average assets	$ 221,508	$ 217,358
Common equity tier 1 capital	16.70%	15.40%
Tier 1 capital	16.70%	15.40%
Total capital	18.00%	16.90%
Tier 1 leveraged	7.10%	6.70%
State Street Bank | Basel III Standardized Approach
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 11,339	$ 10,938
Retained earnings	11,593	10,655
Accumulated other comprehensive income (loss)	(880)	(1,230)
Treasury stock, at cost	0	0
Total	22,052	20,363
Goodwill and other intangible assets, net of associated deferred tax liabilities	(6,152)	(5,631)
Other adjustments	(83)	(85)
Common equity tier 1 capital	15,817	14,647
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	15,817	14,647
Qualifying subordinated long-term debt	1,270	1,371
Trust preferred capital securities phased out of tier 1 capital	0	0
ALLL and other	75	66
Other adjustments	0	0
Total capital	17,162	16,084
Credit risk	92,165	89,164
Market risk	1,706	2,378
Total risk-weighted assets	93,871	91,542
Adjusted quarterly average assets	$ 221,508	$ 217,358
Common equity tier 1 capital	16.80%	16.00%
Tier 1 capital	16.80%	16.00%
Total capital	18.30%	17.60%
Tier 1 leveraged	7.10%	6.70%