Regulatory Capital (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Retained earnings	$ 16,049	$ 14,737
Capital ratio: required common equity tier 1 capital	4.50%	4.00%
Capital ratio: required tier 1 capital	6.00%	5.50%
Capital ratio: required total capital	8.00%	8.00%
Capital ratio: required tier 1 leverage	4.00%	4.00%
Basel III Advanced Approaches
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 10,250	$ 10,295
Retained earnings	16,049	14,737
Accumulated other comprehensive income (loss)	(1,422)	(642)
Treasury stock, at cost	(6,457)	(5,158)
Total	18,420	19,232
Goodwill and other intangible assets, net of associated deferred tax liabilities	(5,927)	(5,869)
Other adjustments	(60)	(36)
Common equity tier 1 capital	12,433	13,327
Preferred stock	2,703	1,961
Trust preferred capital securities subject to phase-out from tier 1 capital	237	475
Other adjustments	(109)	(145)
Tier 1 capital	15,264	15,618
Qualifying subordinated long-term debt	1,358	1,618
Trust preferred capital securities phased out of tier 1 capital	713	475
ALLL and other	12	0
Other adjustments	2	4
Total capital	17,349	17,715
Credit risk	51,733	66,874
Operational risk	43,882	35,866
Market risk	3,937	5,087
Total risk-weighted assets	99,552	107,827
Adjusted quarterly average assets	$ 221,880	$ 247,740
Common equity tier 1 capital	12.50%	12.40%
Tier 1 capital	15.30%	14.50%
Total capital	17.40%	16.40%
Tier 1 leveraged	6.90%	6.30%
Basel III Standardized Approach
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 10,250
Retained earnings	16,049
Accumulated other comprehensive income (loss)	(1,422)
Treasury stock, at cost	(6,457)
Total	18,420
Goodwill and other intangible assets, net of associated deferred tax liabilities	(5,927)
Other adjustments	(60)
Common equity tier 1 capital	12,433
Preferred stock	2,703
Trust preferred capital securities subject to phase-out from tier 1 capital	237
Other adjustments	(109)
Tier 1 capital	15,264
Qualifying subordinated long-term debt	1,358
Trust preferred capital securities phased out of tier 1 capital	713
ALLL and other	66
Other adjustments	2
Total capital	17,403
Credit risk	93,515
Market risk	2,378
Total risk-weighted assets	95,893
Adjusted quarterly average assets	$ 221,880
Common equity tier 1 capital	13.00%
Tier 1 capital	15.90%
Total capital	18.10%
Tier 1 leveraged	6.90%
Basel III Transitional Approach
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus		$ 10,295
Retained earnings		14,737
Accumulated other comprehensive income (loss)		(642)
Treasury stock, at cost		(5,158)
Total		19,232
Goodwill and other intangible assets, net of associated deferred tax liabilities		(5,869)
Other adjustments		(36)
Common equity tier 1 capital		13,327
Preferred stock		1,961
Trust preferred capital securities subject to phase-out from tier 1 capital		475
Other adjustments		(145)
Tier 1 capital		15,618
Qualifying subordinated long-term debt		1,618
Trust preferred capital securities phased out of tier 1 capital		475
ALLL and other		0
Other adjustments		4
Total capital		17,715
Credit risk		87,502
Market risk		2,910
Total risk-weighted assets		90,412
Adjusted quarterly average assets		$ 247,740
Common equity tier 1 capital		14.70%
Tier 1 capital		17.30%
Total capital		19.60%
Tier 1 leveraged		6.30%
State Street Bank | Basel III Advanced Approaches
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 10,938	$ 10,867
Retained earnings	10,655	9,270
Accumulated other comprehensive income (loss)	(1,230)	(536)
Treasury stock, at cost	0	0
Total	20,363	19,601
Goodwill and other intangible assets, net of associated deferred tax liabilities	(5,631)	(5,577)
Other adjustments	(85)	(128)
Common equity tier 1 capital	14,647	13,896
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	14,647	13,896
Qualifying subordinated long-term debt	1,371	1,634
Trust preferred capital securities phased out of tier 1 capital	0	0
ALLL and other	8	0
Other adjustments	0	0
Total capital	16,026	15,530
Credit risk	47,677	59,836
Operational risk	43,324	35,449
Market risk	3,939	5,048
Total risk-weighted assets	94,940	100,333
Adjusted quarterly average assets	$ 217,358	$ 243,549
Common equity tier 1 capital	15.40%	13.80%
Tier 1 capital	15.40%	13.80%
Total capital	16.90%	15.50%
Tier 1 leveraged	6.70%	5.70%
State Street Bank | Basel III Standardized Approach
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 10,938
Retained earnings	10,655
Accumulated other comprehensive income (loss)	(1,230)
Treasury stock, at cost	0
Total	20,363
Goodwill and other intangible assets, net of associated deferred tax liabilities	(5,631)
Other adjustments	(85)
Common equity tier 1 capital	14,647
Preferred stock	0
Trust preferred capital securities subject to phase-out from tier 1 capital	0
Other adjustments	0
Tier 1 capital	14,647
Qualifying subordinated long-term debt	1,371
Trust preferred capital securities phased out of tier 1 capital	0
ALLL and other	66
Other adjustments	0
Total capital	16,084
Credit risk	89,164
Market risk	2,378
Total risk-weighted assets	91,542
Adjusted quarterly average assets	$ 217,358
Common equity tier 1 capital	16.00%
Tier 1 capital	16.00%
Total capital	17.60%
Tier 1 leveraged	6.70%
State Street Bank | Basel III Transitional Approach
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus		$ 10,867
Retained earnings		9,270
Accumulated other comprehensive income (loss)		(536)
Treasury stock, at cost		0
Total		19,601
Goodwill and other intangible assets, net of associated deferred tax liabilities		(5,577)
Other adjustments		(128)
Common equity tier 1 capital		13,896
Preferred stock		0
Trust preferred capital securities subject to phase-out from tier 1 capital		0
Other adjustments		0
Tier 1 capital		13,896
Qualifying subordinated long-term debt		1,634
Trust preferred capital securities phased out of tier 1 capital		0
ALLL and other		0
Other adjustments		0
Total capital		15,530
Credit risk		84,433
Market risk		2,909
Total risk-weighted assets		87,342
Adjusted quarterly average assets		$ 243,549
Common equity tier 1 capital		15.90%
Tier 1 capital		15.90%
Total capital		17.80%
Tier 1 leveraged		5.70%