Deferred Policy Acquisition Costs and Asset Reconciliation, Including Amortized Deferred Policy Acquisition Costs (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Deferred Policy Acquisition Costs And Insurance Expenses [Line Items]
Deferred policy acquisition costs asset, beginning of year	$ 477	$ 458
Capitalized deferred policy acquisition costs	170	164
Amortized deferred policy acquisition costs	(156)	(150)
Amortized shadow deferred policy acquisition costs	(8)
Deferred policy acquisition costs asset, end of year	$ 483	$ 472