Long-Term Debt - Schedule of Long Term Debt (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Long-term finance leases	$ 55	$ 78
Total long-term debt	13,805	12,509
Fair Value Hedges
Debt Instrument [Line Items]
Decrease in carrying value of long-term debt	$ 691	157
Senior notes | 3.55% notes due 2025
Debt Instrument [Line Items]
Interest rate on debt	3.55%
Senior notes | 2.55% notes due 2020
Debt Instrument [Line Items]
Interest rate on debt	2.55%
Senior notes | 3.7% notes due in 2023
Debt Instrument [Line Items]
Interest rate on debt	3.70%
Senior notes | 3.3% notes due 2024
Debt Instrument [Line Items]
Interest rate on debt	3.30%
Senior notes | 2.354% notes due 2025
Debt Instrument [Line Items]
Interest rate on debt	2.354%
Senior notes | 2.400% notes due 2030
Debt Instrument [Line Items]
Interest rate on debt	2.40%
Senior notes | 2.825% notes due 2023
Debt Instrument [Line Items]
Interest rate on debt	2.825%
Senior notes | 2.901% notes due 2026
Debt Instrument [Line Items]
Interest rate on debt	2.901%
Senior notes | 3.152% notes due 2031
Debt Instrument [Line Items]
Interest rate on debt	3.152%
Senior notes | 2.653% notes due 2023
Debt Instrument [Line Items]
Interest rate on debt	2.653%
Senior notes | 4.375% notes due 2021
Debt Instrument [Line Items]
Interest rate on debt	4.375%
Senior notes | 1.95% notes due 2021
Debt Instrument [Line Items]
Interest rate on debt	1.95%
Senior notes | 2.65% notes due 2026
Debt Instrument [Line Items]
Interest rate on debt	2.65%
Senior notes | 4.141% notes due 2029
Debt Instrument [Line Items]
Interest rate on debt	4.141%
Senior notes | 3.776% notes due 2024
Debt Instrument [Line Items]
Interest rate on debt	3.776%
Senior notes | 7.35% notes due 2026
Debt Instrument [Line Items]
Interest rate on debt	7.35%
Subordinated notes | 3.1% subordinated notes due 2023
Debt Instrument [Line Items]
Interest rate on debt	3.10%
Subordinated notes | 3.031% notes due 2034
Debt Instrument [Line Items]
Interest rate on debt	3.031%
Parent Company and Non-banking Subsidiaries | Senior notes | 3.55% notes due 2025
Debt Instrument [Line Items]
Long-term debt	$ 1,413	1,331
Parent Company and Non-banking Subsidiaries | Senior notes | 2.55% notes due 2020
Debt Instrument [Line Items]
Long-term debt	0	1,191
Parent Company and Non-banking Subsidiaries | Senior notes | 3.7% notes due in 2023
Debt Instrument [Line Items]
Long-term debt	1,070	1,037
Parent Company and Non-banking Subsidiaries | Senior notes | 3.3% notes due 2024
Debt Instrument [Line Items]
Long-term debt	1,075	1,022
Parent Company and Non-banking Subsidiaries | Senior notes | 2.354% notes due 2025
Debt Instrument [Line Items]
Long-term debt	1,047	991
Parent Company and Non-banking Subsidiaries | Senior notes | 2.400% notes due 2030
Debt Instrument [Line Items]
Long-term debt	821	0
Parent Company and Non-banking Subsidiaries | Senior notes | 2.825% notes due 2023
Debt Instrument [Line Items]
Long-term debt	748	0
Parent Company and Non-banking Subsidiaries | Senior notes | 2.901% notes due 2026
Debt Instrument [Line Items]
Long-term debt	498	0
Parent Company and Non-banking Subsidiaries | Senior notes | 3.152% notes due 2031
Debt Instrument [Line Items]
Long-term debt	497	0
Parent Company and Non-banking Subsidiaries | Senior notes | 2.653% notes due 2023
Debt Instrument [Line Items]
Long-term debt	766	753
Parent Company and Non-banking Subsidiaries | Senior notes | 4.375% notes due 2021
Debt Instrument [Line Items]
Long-term debt	752	748
Parent Company and Non-banking Subsidiaries | Senior notes | 1.95% notes due 2021
Debt Instrument [Line Items]
Long-term debt	753	744
Parent Company and Non-banking Subsidiaries | Senior notes | 2.65% notes due 2026
Debt Instrument [Line Items]
Long-term debt	796	741
Parent Company and Non-banking Subsidiaries | Senior notes | 4.141% notes due 2029
Debt Instrument [Line Items]
Long-term debt	594	546
Parent Company and Non-banking Subsidiaries | Senior notes | 3.776% notes due 2024
Debt Instrument [Line Items]
Long-term debt	538	522
Parent Company and Non-banking Subsidiaries | Senior notes | Floating-rate notes due 2020
Debt Instrument [Line Items]
Long-term debt	0	500
Parent Company and Non-banking Subsidiaries | Senior notes | 7.35% notes due 2026
Debt Instrument [Line Items]
Long-term debt	150	150
Parent Company and Non-banking Subsidiaries | Subordinated notes | 3.1% subordinated notes due 2023
Debt Instrument [Line Items]
Long-term debt	1,039	1,006
Parent Company and Non-banking Subsidiaries | Subordinated notes | 3.031% notes due 2034
Debt Instrument [Line Items]
Long-term debt	546	492
Parent Company and Non-banking Subsidiaries | Junior subordinated debentures | Floating Rate Subordinated Debentures Due 2047
Debt Instrument [Line Items]
Long-term debt	499	499
Parent Company and Non-banking Subsidiaries | Junior subordinated debentures | Floating-rate subordinated notes due to State Street Capital Trust I in 2028
Debt Instrument [Line Items]
Long-term debt	100	100
State Street Bank
Debt Instrument [Line Items]
Long-term finance leases	$ 103	$ 136