Expenses - Restructuring Reserve (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restructuring Reserve [Roll Forward]
Beginning balance	$ 56	$ 23	$ 69
Accruals	245	142
Payments and Other Adjustments	(100)	(107)	(51)
Ending balance	201	56	23
Employee Related Costs
Restructuring Reserve [Roll Forward]
Beginning balance	37	9	39
Payments and Other Adjustments	(57)	(64)	(25)
Ending balance	166	37	9
Real Estate Actions
Restructuring Reserve [Roll Forward]
Beginning balance	17	11	23
Payments and Other Adjustments	(17)	(12)	(9)
Ending balance	32	17	11
Asset and Other Write-offs
Restructuring Reserve [Roll Forward]
Beginning balance	2	3	7
Payments and Other Adjustments	(26)	(31)	(17)
Ending balance	3	2	3
Business Operations and IT
Restructuring Reserve [Roll Forward]
Accruals		(2)	5
Business Operations and IT | Employee Related Costs
Restructuring Reserve [Roll Forward]
Accruals		(2)	(5)
Business Operations and IT | Real Estate Actions
Restructuring Reserve [Roll Forward]
Accruals		0	(3)
Business Operations and IT | Asset and Other Write-offs
Restructuring Reserve [Roll Forward]
Accruals		0	$ 13
State Street Beacon
Restructuring Reserve [Roll Forward]
Accruals	245	142
State Street Beacon | Employee Related Costs
Restructuring Reserve [Roll Forward]
Accruals	186	94
State Street Beacon | Real Estate Actions
Restructuring Reserve [Roll Forward]
Accruals	32	18
State Street Beacon | Asset and Other Write-offs
Restructuring Reserve [Roll Forward]
Accruals	$ 27	$ 30