Reinsurance - Life Insurance Contract Holders' Benefits Incurred on Ceded Business (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Assumed earned premiums	$ 3	$ 3	$ 5	$ 6
Net incurred loss and loss expenses	631	687	1,199	1,269
Life Insurance Segment
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Direct policyholders' benefits incurred	62	57	126	110
Assumed policyholders' benefits incurred	0	0	0
Assumed earned premiums	0	0	0	0
Ceded policyholders' benefits incurred	(14)	(10)	(34)	(20)
Net incurred loss and loss expenses	$ 48	$ 47	$ 92	$ 90