Deferred Policy Acquisition Costs - Policy Acquisition Costs Deferred and Related Amortization Reflected In Operating Results (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Balance, beginning of year	$ 1,210	[1]	$ 1,142		$ 1,113
Costs deferred during year
Commissions and brokerage	1,919		1,910		1,734
Premium taxes and assessments	247		235		232
Underwriting and policy issuance costs	248		248		247
Total costs deferred during year	2,414		2,393		2,213
Foreign currency translation effect	(7)		5		(1)
Amortization during year	(2,411)		(2,330)	[1]	(2,183)	[1]
Balance, end of year	$ 1,206		$ 1,210	[1]	$ 1,142

[1] As Adjusted