Expenses - Restructuring Reserve (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Restructuring Reserve [Roll Forward]
Beginning balance	$ 198	$ 341	$ 201
Accruals	133	110	300
Payments and Other Adjustments	(131)	(251)	(153)
Ending balance	196	198	341
Employee Related Costs
Restructuring Reserve [Roll Forward]
Beginning balance	190	303	166
Accruals	82	98	259
Payments and Other Adjustments	(78)	(209)	(115)
Ending balance	190	190	303
Real Estate Actions
Restructuring Reserve [Roll Forward]
Beginning balance	7	37	32
Accruals	51	12	41
Payments and Other Adjustments	(52)	(42)	(36)
Ending balance	6	7	37
Asset and Other Write-offs
Restructuring Reserve [Roll Forward]
Beginning balance	1	1	3
Accruals	0	0	0
Payments and Other Adjustments	(1)	0	(2)
Ending balance	0	1	1
State Street Beacon
Restructuring Reserve [Roll Forward]
Accruals	(4)	(2)	(7)
State Street Beacon | Employee Related Costs
Restructuring Reserve [Roll Forward]
Accruals	(4)	(2)	(7)
State Street Beacon | Real Estate Actions
Restructuring Reserve [Roll Forward]
Accruals	0	0	0
State Street Beacon | Asset and Other Write-offs
Restructuring Reserve [Roll Forward]
Accruals	$ 0	$ 0	$ 0