Investment Securities - Realized Gains and Losses and OTTI Losses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Securities gains and losses
Realized gains	$ 58	$ 122	$ 137	$ 664
Realized losses	(103)	(123)	(507)	(696)
OTTI losses	(1)	0	(1)	(6)
Net investment securities losses	(46)	(1)	(371)	(38)
Excluded realized losses on securities sold previously reported as OTTI loss due to intention to sell			21	6
Credit-related losses recognized in income
Securities gains and losses
OTTI losses	0	0	0	0
Investment securities the Firm intends to sell
Securities gains and losses
OTTI losses	$ (1)	$ 0	$ (1)	$ (6)