Reinsurance - Incurred Consolidated Property Casualty Insurance Loss and Loss Expenses on Assumed and Ceded Business (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Incurred loss and loss expenses	$ 670	$ 686	$ 2,131	$ 2,181
Consolidated Property and Casualty Insurance Entity
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct incurred loss and loss expenses	618	633	1,984	2,026
Assumed incurred loss and loss expenses	2	1	2	5
Ceded incurred loss and loss expenses	(7)	(12)	(30)	(26)
Incurred loss and loss expenses	$ 613	$ 622	$ 1,956	$ 2,005