Reinsurance - Incurred Consolidated Property Casualty Insurance Loss and Loss Expenses on Assumed and Ceded Business (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Net incurred loss and loss expenses	$ 686	$ 642	$ 2,181	$ 1,841
Consolidated Property and Casualty Insurance Entity
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct incurred loss and loss expenses	633	597	2,026	1,725
Assumed incurred loss and loss expenses	1	1	5	8
Ceded incurred loss and loss expenses	(12)	(5)	(26)	(33)
Net incurred loss and loss expenses	$ 622	$ 593	$ 2,005	$ 1,700