Expenses - Restructuring Reserve (Details) - USD ($)	3 Months Ended				6 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2018	Jun. 30, 2017
Restructuring Reserve [Roll Forward]
Beginning balance	$ 175,000,000	$ 201,000,000		$ 56,000,000	$ 201,000,000	$ 56,000,000
Ending balance	141,000,000	175,000,000			141,000,000
Employee Related Costs
Restructuring Reserve [Roll Forward]
Beginning balance	144,000,000	166,000,000		37,000,000	166,000,000	37,000,000
Ending balance	113,000,000	144,000,000			113,000,000
Real Estate Actions
Restructuring Reserve [Roll Forward]
Beginning balance	28,000,000	32,000,000		17,000,000	32,000,000	17,000,000
Ending balance	25,000,000	28,000,000			25,000,000
Asset and Other Write-offs
Restructuring Reserve [Roll Forward]
Beginning balance	3,000,000	3,000,000		2,000,000	3,000,000	2,000,000
Ending balance	3,000,000	3,000,000			3,000,000
State Street Beacon
Restructuring Reserve [Roll Forward]
Beginning balance			$ 54,000,000
Accruals	0	0	62,000,000	16,000,000	$ 0	79,000,000
Payments and Other Adjustments	(34,000,000)	(26,000,000)	(16,000,000)	(18,000,000)
Ending balance			100,000,000	54,000,000		100,000,000
State Street Beacon | Employee Related Costs
Restructuring Reserve [Roll Forward]
Beginning balance			38,000,000
Accruals	0	0	60,000,000	14,000,000
Payments and Other Adjustments	(31,000,000)	(22,000,000)	(11,000,000)	(13,000,000)
Ending balance			87,000,000	38,000,000		87,000,000
State Street Beacon | Real Estate Actions
Restructuring Reserve [Roll Forward]
Beginning balance			14,000,000
Accruals	0	0	0	0
Payments and Other Adjustments	(3,000,000)	(4,000,000)	(3,000,000)	(3,000,000)
Ending balance			11,000,000	14,000,000		11,000,000
State Street Beacon | Asset and Other Write-offs
Restructuring Reserve [Roll Forward]
Beginning balance			2,000,000
Accruals	0	0	2,000,000	2,000,000
Payments and Other Adjustments	$ 0	$ 0	(2,000,000)	(2,000,000)
Ending balance			$ 2,000,000	$ 2,000,000		$ 2,000,000