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		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Net incurred loss and loss expenses	$ 763	$ 631	$ 1,495	$ 1,199
Property, Liability And Casualty Insurance Segment
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct incurred loss and loss expenses	716	593	1,393	1,128
Assumed incurred loss and loss expenses	2	5	4	7
Ceded incurred loss and loss expenses	(11)	(15)	(14)	(28)
Net incurred loss and loss expenses	$ 707	$ 583	$ 1,383	$ 1,107