Rollforward of Credit Losses Recognized in Earnings Related to Securities (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Schedule of Available-for-sale Securities [Line Items]
Beginning balance	$ 32	$ 27	$ 31	$ 25
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, Additional Credit Losses	0	2	1	4
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Reductions, Cash Flows	0	(1)	0	(1)
Ending balance	$ 32	$ 28	$ 32	$ 28