Schedule V - Supplemental Information Concerning Property and Casualty Insurance Operations (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Supplemental Information for Property, Casualty Insurance Underwriters [Abstract]
Deferred acquisition costs	$ 598	$ 600
Reserves for unpaid claim and claim adjustment expenses	22,663	23,271
Discount deducted from claim and claim adjustment expense reserves above (based on interest rates ranging from 3.5% to 8.0%)	1,534	1,578
Unearned premiums	3,671	3,592
Net written premiums	6,962	7,088	$ 7,348
Net earned premiums	6,921	7,212	7,271
Net investment income	1,807	2,031	2,240
Incurred claim and claim adjustment expenses related to current year	4,934	5,043	5,113
Incurred claim and claim adjustment expenses related to prior years	(255)	(39)	(115)
Amortization of deferred acquisition costs	1,540	1,317	1,362
Paid claim and claim adjustment expenses	$ 4,945	$ 5,297	$ 5,566