Securities-Net Securities Gains (Losses) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2014	Jun. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Securities [Abstract]
Realized gross gains	$ 23	$ 20	$ 29	$ 73	$ 137
Realized gross losses	(1)	0	(4)	(4)	(10)
Recognized gross impairments	(2)	(2)	(3)	(9)	(25)
Net securities gains	$ 20	$ 18	$ 22	$ 60	$ 102