Property Casualty Loss and Loss Expenses - Consolidated Property Casualty Loss and Loss Expense Reserves (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Summary of Consolidated Property Casualty Loss and Loss Expense Reserves [Roll Forward]
Gross loss and loss expense reserves, beginning of period	$ 4,323	$ 4,173	$ 4,241	$ 4,169
Less reinsurance receivable	289	349	299	356
Net loss and loss expense reserves, beginning of period	4,034	3,824	3,942	3,813
Current accident year	773	675	1,478	1,209
Prior accident years	(66)	(92)	(95)	(102)
Total incurred	707	583	1,383	1,107
Current accident year	309	249	506	370
Prior accident years	306	272	693	664
Total paid	615	521	1,199	1,034
Net loss and loss expense reserves, end of period	4,126	3,886	4,126	3,886
Plus reinsurance receivable	282	333	282	333
Gross loss and loss expense reserves, end of period	$ 4,408	$ 4,219	$ 4,408	$ 4,219