Expenses - Restructuring Reserve (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Restructuring Reserve [Roll Forward]
Beginning balance	$ 56	$ 23	$ 23
Accruals for State Street Beacon	16	97
Payments and Other Adjustments	(18)		(107)
Ending balance	54		56
Employee Related Costs
Restructuring Reserve [Roll Forward]
Beginning balance	37	9	9
Accruals for State Street Beacon	14
Payments and Other Adjustments	(13)		(64)
Ending balance	38		37
Real Estate Consolidation
Restructuring Reserve [Roll Forward]
Beginning balance	17	11	11
Accruals for State Street Beacon	0
Payments and Other Adjustments	(3)		(12)
Ending balance	14		17
Asset and Other Write-offs
Restructuring Reserve [Roll Forward]
Beginning balance	2	$ 3	3
Accruals for State Street Beacon	2
Payments and Other Adjustments	(2)		(31)
Ending balance	$ 2		2
Business Operations and IT
Restructuring Reserve [Roll Forward]
Accruals for State Street Beacon			(2)
Business Operations and IT | Employee Related Costs
Restructuring Reserve [Roll Forward]
Accruals for State Street Beacon			(2)
Business Operations and IT | Real Estate Consolidation
Restructuring Reserve [Roll Forward]
Accruals for State Street Beacon			0
Business Operations and IT | Asset and Other Write-offs
Restructuring Reserve [Roll Forward]
Accruals for State Street Beacon			0
State Street Beacon
Restructuring Reserve [Roll Forward]
Accruals for State Street Beacon			142
State Street Beacon | Employee Related Costs
Restructuring Reserve [Roll Forward]
Accruals for State Street Beacon			94
State Street Beacon | Real Estate Consolidation
Restructuring Reserve [Roll Forward]
Accruals for State Street Beacon			18
State Street Beacon | Asset and Other Write-offs
Restructuring Reserve [Roll Forward]
Accruals for State Street Beacon			$ 30