Expenses - Narrative (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Restructuring Cost and Reserve [Line Items]
Acquisition related costs	$ 33			$ 7	$ 47	$ 15
State Street Beacon
Restructuring Cost and Reserve [Line Items]
Accruals for State Street Beacon	10	$ 13	$ 97		120
State Street Beacon | Employee Related Costs
Restructuring Cost and Reserve [Line Items]
Accruals for State Street Beacon	8	$ (1)	$ 86
State Street Beacon | Minimum
Restructuring Cost and Reserve [Line Items]
Expected restructuring cost	300				300
State Street Beacon | Minimum | Employee Related Costs
Restructuring Cost and Reserve [Line Items]
Expected restructuring cost	250				250
State Street Beacon | Minimum | Information Technology and Real Estate
Restructuring Cost and Reserve [Line Items]
Expected restructuring cost	50				50
State Street Beacon | Maximum
Restructuring Cost and Reserve [Line Items]
Expected restructuring cost	400				400
State Street Beacon | Maximum | Employee Related Costs
Restructuring Cost and Reserve [Line Items]
Expected restructuring cost	300				300
State Street Beacon | Maximum | Information Technology and Real Estate
Restructuring Cost and Reserve [Line Items]
Expected restructuring cost	100				$ 100
GEAM
Restructuring Cost and Reserve [Line Items]
Acquisition related costs	$ 29