Expenses - Narrative (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 Cost and Reserve [Line Items]
Acquisition related costs	$ 9		$ 7
Restructuring charges	62		13		$ 79	$ 110
State Street Beacon
Restructuring Cost and Reserve [Line Items]
Restructuring charges	62	$ 16	13	$ 97
State Street Beacon | Severance and Benefit Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 60	$ 14	$ (1)	$ 86