Property Casualty Loss and Loss Expenses - Consolidated Property Casualty Loss and Loss Expense Reserves (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Summary of Consolidated Property Casualty Loss and Loss Expense Reserves [Roll Forward]
Gross loss and loss expense reserves, beginning of period	$ 4,660	$ 4,438
Less reinsurance recoverable	281	282
Net loss and loss expense reserves, beginning of period	4,379	4,156
Current accident year	723	711
Prior accident years	(62)	(22)
Total incurred	661	689
Current accident year	146	147
Prior accident years	416	399
Total paid	562	546
Net loss and loss expense reserves, end of period	4,478	4,299
Plus reinsurance recoverable	272	278
Gross loss and loss expense reserves, end of period	$ 4,750	$ 4,577