Property Casualty Loss and Loss Expenses - Consolidated Property Casualty Loss and Loss Expense Reserves (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Summary of Consolidated Property Casualty Loss and Loss Expense Reserves [Roll Forward]
Gross loss and loss expense reserves, beginning of period	$ 4,241	$ 4,169
Less reinsurance receivable	299	356
Net loss and loss expense reserves, beginning of period	3,942	3,813
Current accident year	705	534
Prior accident years	(29)	(10)
Total incurred	676	524
Current accident year	197	121
Prior accident years	387	392
Total paid	584	513
Net loss and loss expense reserves, end of period	4,034	3,824
Plus reinsurance receivable	289	349
Gross loss and loss expense reserves, end of period	$ 4,323	$ 4,173