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, 2014	Dec. 31, 2013	Dec. 31, 2012
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Balance, beginning of year	$ 1,255	$ 1,206	$ 1,210
Costs deferred during year
Commissions and brokerage	2,073	1,979	1,919
Premium taxes and assessments	258	263	247
Underwriting and policy issuance costs	262	271	248
Total costs deferred during year	2,593	2,513	2,414
Foreign currency translation effect	(16)	(10)	(7)
Amortization during year	(2,548)	(2,454)	(2,411)
Balance, end of year	$ 1,284	$ 1,255	$ 1,206