Securities-Debt Securities Credit Losses Roll Forward Recorded in Earnings (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Other than Temporary Impairment [Roll Forward]
Beginning balance	$ 288	$ 253
Add: Initial OTTI credit losses	0	9
Subsequent OTTI credit losses	4	12
Less: Realized losses for securities sold	118	8
Ending balance	$ 174	$ 266