Expenses - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Acquisition related costs	$ 12	$ 7
Restructuring charges	16	$ 97
Severance and Benefit Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 14
State Street Beacon
Restructuring Cost and Reserve [Line Items]
Restructuring charges			$ 142
State Street Beacon | Severance and Benefit Costs
Restructuring Cost and Reserve [Line Items]
Restructuring charges			$ 94