Expenses - Restructuring Reserve (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2017	Jun. 30, 2016
Restructuring Reserve [Roll Forward]
Accruals for State Street Beacon	$ 62		$ 13		$ 79	$ 110
State Street Beacon
Restructuring Reserve [Roll Forward]
Beginning balance	54	$ 56	108	$ 23	56	23
Accruals for State Street Beacon	62	16	13	97
Payments and Other Adjustments	(16)	(18)	(39)	(12)
Ending balance	100	54	82	108	100	82
State Street Beacon | Employee Related Costs
Restructuring Reserve [Roll Forward]
Beginning balance	38	37	91	9	37	9
Accruals for State Street Beacon	60	14	(1)	86
Payments and Other Adjustments	(11)	(13)	(35)	(4)
Ending balance	87	38	55	91	87	55
State Street Beacon | Real Estate Consolidation
Restructuring Reserve [Roll Forward]
Beginning balance	14	17	10	11	17	11
Accruals for State Street Beacon	0	0	15	0
Payments and Other Adjustments	(3)	(3)	(3)	(1)
Ending balance	11	14	22	10	11	22
State Street Beacon | Asset and Other Write-offs
Restructuring Reserve [Roll Forward]
Beginning balance	2	2	7	3	2	3
Accruals for State Street Beacon	2	2	(1)	11
Payments and Other Adjustments	(2)	(2)	(1)	(7)
Ending balance	$ 2	$ 2	$ 5	$ 7	$ 2	$ 5