Securities-Pre-Tax Net Securities Gains (Losses) by Type (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Net securities gains	$ 24	$ 31	$ 22
U.S. Treasury
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Net securities gains	23	13	10
Non-agency RMBS
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Net securities gains	(1)	17	(2)
Other securities
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Net securities gains	$ 2	$ 1	$ 14