Long-Term Debt - Narrative (Details)	1 Months Ended	12 Months Ended
	Feb. 28, 2015 USD ($)	Dec. 31, 2015 USD ($) trust	Aug. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Debt Instrument [Line Items]
Bank notes authorized		$ 5,000,000,000
Senior debt authorized by BOD		5,000,000,000
Subordinated debt available for issuance		500,000,000
Capital lease obligation		231,000,000		$ 624,000,000
Building and Parking Garage
Debt Instrument [Line Items]
Capital lease obligation		$ 308,000,000		336,000,000
Office Building
Debt Instrument [Line Items]
Capital lease obligation				241,000,000
Construction in Progress
Debt Instrument [Line Items]
Capital lease obligation				$ 191,000,000
Floating-rate notes due 2020
Debt Instrument [Line Items]
Face amount on debt issued			$ 500,000,000
Senior notes | 2.875% notes due 2016
Debt Instrument [Line Items]
Interest rate on debt		2.875%
Senior notes | 4.375% notes due 2021
Debt Instrument [Line Items]
Interest rate on debt		4.375%
Senior notes | 2.55% notes due 2020
Debt Instrument [Line Items]
Interest rate on debt		2.55%	2.55%
Face amount on debt issued			$ 1,200,000,000.0
Senior notes | 3.55% notes due 2025
Debt Instrument [Line Items]
Interest rate on debt		3.55%	3.55%
Face amount on debt issued			$ 1,300,000,000.0
Senior notes | 3.30% notes due 2024
Debt Instrument [Line Items]
Interest rate on debt		3.30%
Senior notes | 3.70% notes due in 2023
Debt Instrument [Line Items]
Interest rate on debt		3.70%
Senior notes | 1.35% notes due 2018
Debt Instrument [Line Items]
Interest rate on debt		1.35%
Senior notes | 5.375% notes due 2017
Debt Instrument [Line Items]
Interest rate on debt		5.375%
Senior notes | 7.35% notes due 2026
Debt Instrument [Line Items]
Interest rate on debt		7.35%
Subordinated note | 3.10% subordinated notes due 2023
Debt Instrument [Line Items]
Interest rate on debt		3.10%
Subordinated note | Floating-rate extendible notes due 2016
Debt Instrument [Line Items]
Repayments of debt	$ 900,000,000
Subordinated note | 5.25% subordinated notes due 2018
Debt Instrument [Line Items]
Interest rate on debt		5.25%
Subordinated note | 5.30% subordinated notes due 2016
Debt Instrument [Line Items]
Interest rate on debt		5.30%
Junior Subordinated Debt | 4.956% junior subordinated debentures due 2018
Debt Instrument [Line Items]
Interest rate on debt		4.956%
State Street Capital Trusts I And I V
Debt Instrument [Line Items]
Number of statutory business trusts | trust		2
Junior subordinated debenture owed to unconsolidated subsidiary trust		$ 955,000,000