Expenses - Restructuring Reserve (Details) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017
Restructuring Reserve [Roll Forward]
Beginning balance	$ 141	$ 175	$ 201			$ 56	$ 201	$ 56
Ending balance	117	141	175				117
Employee Related Costs
Restructuring Reserve [Roll Forward]
Beginning balance	113	144	166			37	166	37
Ending balance	94	113	144				94
Real Estate Actions
Restructuring Reserve [Roll Forward]
Beginning balance	25	28	32			17	32	17
Ending balance	21	25	28				21
Asset and Other Write-offs
Restructuring Reserve [Roll Forward]
Beginning balance	3	3	3			2	3	2
Ending balance	2	3	3				2
State Street Beacon
Restructuring Reserve [Roll Forward]
Beginning balance				$ 100	$ 54
Accruals	(1)	0	0	33	62	16	$ (1)	112
Payments and Other Adjustments	(23)	(34)	(26)	(16)	(16)	(18)
Ending balance				117	100	54		117
State Street Beacon | Employee Related Costs
Restructuring Reserve [Roll Forward]
Beginning balance				87	38
Accruals	(1)	0	0	23	60	14
Payments and Other Adjustments	(18)	(31)	(22)	(10)	(11)	(13)
Ending balance				100	87	38		100
State Street Beacon | Real Estate Actions
Restructuring Reserve [Roll Forward]
Beginning balance				11	14
Accruals	0	0	0	9	0	0
Payments and Other Adjustments	(4)	(3)	(4)	(5)	(3)	(3)
Ending balance				15	11	14		15
State Street Beacon | Asset and Other Write-offs
Restructuring Reserve [Roll Forward]
Beginning balance				2	2
Accruals	0	0	0	1	2	2
Payments and Other Adjustments	$ (1)	$ 0	$ 0	(1)	(2)	(2)
Ending balance				$ 2	$ 2	$ 2		$ 2