Deferred Policy Acquisition Costs and Asset Reconciliation, Including Amortized Deferred Policy Acquisition Costs (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Deferred Policy Acquisition Costs And Insurance Expenses [Line Items]
Deferred policy acquisition costs asset, beginning of year	$ 484	$ 479	$ 477	$ 458
Capitalized deferred policy acquisition costs	192	168	554	500
Amortized deferred policy acquisition costs	(180)	(164)	(517)	(470)
Amortized shadow deferred policy acquisition costs	(5)	(4)	(23)	(9)
Deferred policy acquisition costs asset, end of year	$ 491	$ 479	$ 491	$ 479