Property Casualty Loss and Loss Expenses - Consolidated Property Casualty Loss and Loss Expense Reserves (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Summary of Consolidated Property Casualty Loss and Loss Expense Reserves [Roll Forward]
Gross loss and loss expense reserves, beginning of period	$ 4,577	$ 4,323	$ 4,438	$ 4,241
Less reinsurance recoverable	278	289	282	299
Net loss and loss expense reserves, beginning of period	4,299	4,034	4,156	3,942
Current accident year	724	773	1,435	1,478
Prior accident years	(70)	(66)	(92)	(95)
Total incurred	654	707	1,343	1,383
Current accident year	304	309	451	506
Prior accident years	294	306	693	693
Total paid	598	615	1,144	1,199
Net loss and loss expense reserves, end of period	4,355	4,126	4,355	4,126
Plus reinsurance recoverable	292	282	292	282
Gross loss and loss expense reserves, end of period	$ 4,647	$ 4,408	$ 4,647	$ 4,408