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
	Mar. 31, 2014	Mar. 31, 2013
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Net incurred loss and loss expenses	$ 732	$ 568
Property, Liability And Casualty Insurance Segment
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct incurred loss and loss expenses	677	535
Assumed incurred loss and loss expenses	2	2
Ceded incurred loss and loss expenses	(3)	(13)
Net incurred loss and loss expenses	$ 676	$ 524