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, 2015	Mar. 31, 2014
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Incurred loss and loss expenses	$ 749	$ 732
Consolidated Property and Casualty Insurance Entity
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct incurred loss and loss expenses	691	677
Assumed incurred loss and loss expenses	(1)	2
Ceded incurred loss and loss expenses	(1)	(3)
Incurred loss and loss expenses	$ 689	$ 676