Regulatory Capital (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Retained earnings	$ 15,795	$ 14,882
Tier One Common Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets	4.50%	4.00%
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets	6.00%	5.50%
Capital Required for Capital Adequacy to Risk Weighted Assets	8.00%	8.00%
Tier One Leverage Capital Required for Capital Adequacy to Average Assets	4.00%	4.00%
Basel III Advanced Approaches
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 10,246	$ 10,295
Retained earnings	15,795	14,882
Accumulated other comprehensive income (loss)	(1,177)	(641)
Treasury Stock Value, Excluding Preferred Shares	(6,143)	(5,158)
Total shareholders’ equity	18,721	19,378
Goodwill and other intangible assets, net of associated deferred tax liabilities	(5,987)	(5,869)
Other adjustments, common tier calculation	(62)	(36)
Tier one common risk-based capital	12,672	13,473
Preferred stock	2,703	1,961
Trust preferred capital securities subject to phase-out from tier 1 capital	237	475
Other adjustments, tier 1 risk based calculation	(94)	(145)
Tier One Risk Based Capital	15,518	15,764
Total Capital Qualifying Subordinated Long-Term Debt	1,438	1,618
Trust preferred capital securities phased out of tier 1 capital	713	475
Total Capital ALLL & Other	12	0
Other adjustments, total capital calculation	2	4
Capital	17,683	17,861
Risk-weighted assets - credit risk	55,914	66,874
Risk-weighted assets - operational risk	44,014	35,866
Risk-weighted assets - market risk	4,437	5,087
Total risk-weighted assets	104,365	107,827
Adjusted Quarterly Average Assets	$ 244,553	$ 247,740
Value-at-risk	12.10%	12.50%
Stressed value-at-risk	14.90%	14.60%
Correlation valuation adjustment	16.90%	16.60%
Tier One Leverage Capital to Average Assets	6.30%	6.40%
Basel III Standardized Approach
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 10,246
Retained earnings	15,795
Accumulated other comprehensive income (loss)	(1,177)
Treasury Stock Value, Excluding Preferred Shares	(6,143)
Total shareholders’ equity	18,721
Goodwill and other intangible assets, net of associated deferred tax liabilities	(5,987)
Other adjustments, common tier calculation	(62)
Tier one common risk-based capital	12,672
Preferred stock	2,703
Trust preferred capital securities subject to phase-out from tier 1 capital	237
Other adjustments, tier 1 risk based calculation	(94)
Tier One Risk Based Capital	15,518
Total Capital Qualifying Subordinated Long-Term Debt	1,438
Trust preferred capital securities phased out of tier 1 capital	713
Total Capital ALLL & Other	69	$ 0
Other adjustments, total capital calculation	2
Capital	17,740
Risk-weighted assets - credit risk	103,004
Risk-weighted assets - market risk	2,761
Total risk-weighted assets	105,765
Adjusted Quarterly Average Assets	$ 244,553
Value-at-risk	12.00%
Stressed value-at-risk	14.70%
Correlation valuation adjustment	16.80%
Tier One Leverage Capital to Average Assets	6.30%
Basel III Transitional Approach
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus		10,295
Retained earnings		14,882
Accumulated other comprehensive income (loss)		(641)
Treasury Stock Value, Excluding Preferred Shares		(5,158)
Total shareholders’ equity		19,378
Goodwill and other intangible assets, net of associated deferred tax liabilities		(5,869)
Other adjustments, common tier calculation		(36)
Tier one common risk-based capital		13,473
Preferred stock		1,961
Trust preferred capital securities subject to phase-out from tier 1 capital		475
Other adjustments, tier 1 risk based calculation		(145)
Tier One Risk Based Capital		15,764
Total Capital Qualifying Subordinated Long-Term Debt		1,618
Trust preferred capital securities phased out of tier 1 capital		475
Other adjustments, total capital calculation		4
Capital		17,861
Risk-weighted assets - credit risk		87,502
Risk-weighted assets - market risk		2,910
Total risk-weighted assets		90,412
Adjusted Quarterly Average Assets		$ 247,740
Value-at-risk		14.90%
Stressed value-at-risk		17.40%
Correlation valuation adjustment		19.80%
Tier One Leverage Capital to Average Assets		6.40%
State Street Bank | Basel III Advanced Approaches
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 10,924	$ 10,867
Retained earnings	10,886	9,416
Accumulated other comprehensive income (loss)	(1,011)	(535)
Treasury Stock Value, Excluding Preferred Shares	0	0
Total shareholders’ equity	20,799	19,748
Goodwill and other intangible assets, net of associated deferred tax liabilities	(5,687)	(5,577)
Other adjustments, common tier calculation	(92)	(128)
Tier one common risk-based capital	15,020	14,043
Preferred stock	0	0
Trust preferred capital securities subject to phase-out from tier 1 capital	0	0
Other adjustments, tier 1 risk based calculation	0	0
Tier One Risk Based Capital	15,020	14,043
Total Capital Qualifying Subordinated Long-Term Debt	1,452	1,634
Trust preferred capital securities phased out of tier 1 capital	0	0
Total Capital ALLL & Other	9	0
Other adjustments, total capital calculation	0	0
Capital	16,481	15,677
Risk-weighted assets - credit risk	50,936	59,836
Risk-weighted assets - operational risk	43,413	35,449
Risk-weighted assets - market risk	4,397	5,048
Total risk-weighted assets	98,746	100,333
Adjusted Quarterly Average Assets	$ 239,610	$ 243,549
Value-at-risk	15.20%	14.00%
Stressed value-at-risk	15.20%	14.00%
Correlation valuation adjustment	16.70%	15.60%
Tier One Leverage Capital to Average Assets	6.30%	5.80%
State Street Bank | Basel III Standardized Approach
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 10,924
Retained earnings	10,886
Accumulated other comprehensive income (loss)	(1,011)
Treasury Stock Value, Excluding Preferred Shares	0
Total shareholders’ equity	20,799
Goodwill and other intangible assets, net of associated deferred tax liabilities	(5,687)
Other adjustments, common tier calculation	(92)
Tier one common risk-based capital	15,020
Preferred stock	0
Trust preferred capital securities subject to phase-out from tier 1 capital	0
Other adjustments, tier 1 risk based calculation	0
Tier One Risk Based Capital	15,020
Total Capital Qualifying Subordinated Long-Term Debt	1,452
Trust preferred capital securities phased out of tier 1 capital	0
Total Capital ALLL & Other	69
Other adjustments, total capital calculation	0
Capital	16,541
Risk-weighted assets - credit risk	97,803
Risk-weighted assets - market risk	2,761
Total risk-weighted assets	100,564
Adjusted Quarterly Average Assets	$ 239,610
Value-at-risk	14.90%
Stressed value-at-risk	14.90%
Correlation valuation adjustment	16.40%
Tier One Leverage Capital to Average Assets	6.30%
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		9,416
Accumulated other comprehensive income (loss)		(535)
Treasury Stock Value, Excluding Preferred Shares		0
Total shareholders’ equity		19,748
Goodwill and other intangible assets, net of associated deferred tax liabilities		(5,577)
Other adjustments, common tier calculation		(128)
Tier one common risk-based capital		14,043
Preferred stock		0
Trust preferred capital securities subject to phase-out from tier 1 capital		0
Other adjustments, tier 1 risk based calculation		0
Tier One Risk Based Capital		14,043
Total Capital Qualifying Subordinated Long-Term Debt		1,634
Trust preferred capital securities phased out of tier 1 capital		0
Total Capital ALLL & Other		0
Other adjustments, total capital calculation		0
Capital		15,677
Risk-weighted assets - credit risk		84,433
Risk-weighted assets - market risk		2,909
Total risk-weighted assets		87,342
Adjusted Quarterly Average Assets		$ 243,549
Value-at-risk		16.10%
Stressed value-at-risk		16.10%
Correlation valuation adjustment		17.90%
Tier One Leverage Capital to Average Assets		5.80%