Rollforward of Credit Losses Recognized in Earnings Related to Securities (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Schedule of Available-for-sale Securities [Line Items]
Beginning balance	$ 25	$ 32	$ 25	$ 31
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Additions, Additional Credit Losses	0	0	1	1
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Reductions, Cash Flows	0	(1)	(1)	(1)
Ending balance	$ 25	$ 31	$ 25	$ 31