Reinsurance - Incurred Consolidated Property Casualty Insurance Loss and Loss Expenses on Assumed and Ceded Business (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Incurred loss and loss expenses	$ 712	$ 763	$ 1,461	$ 1,495
Consolidated Property and Casualty Insurance Entity
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct incurred loss and loss expenses	675	716	1,366	1,393
Assumed incurred loss and loss expenses	1	2	0	4
Ceded incurred loss and loss expenses	(22)	(11)	(23)	(14)
Incurred loss and loss expenses	$ 654	$ 707	$ 1,343	$ 1,383