Schedule V - Supplemental Information Concerning Property and Casualty Insurance Operations (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Supplemental Information for Property, Casualty Insurance Underwriters [Abstract]
Deferred acquisition costs	$ 599	$ 598
Reserves for unpaid claim and claim adjustment expenses	22,343	22,663
Discount deducted from claim and claim adjustment expense reserves above (based on interest rates ranging from 3.5% to 8.0%)	1,572	1,534
Unearned premiums	3,762	3,671
Net written premiums	6,988	6,962	$ 7,088
Net earned premiums	6,924	6,921	7,212
Net investment income	1,952	1,807	2,031
Incurred claim and claim adjustment expenses related to current year	5,025	4,934	5,043
Incurred claim and claim adjustment expenses related to prior years	(342)	(255)	(39)
Amortization of deferred acquisition costs	1,235	1,540	1,317
Paid claim and claim adjustment expenses	$ 5,134	$ 4,945	$ 5,297