Benefit Expenses Excluded From Activity in Benefits Payable (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Expense Detail of Military Benefits Payable and Future Policy Benefit Liabilities [Line Items]
Military services	$ 908	$ 3,247	$ 3,059
Future policy benefits	136	114	266
Total	$ 1,044	$ 3,361	$ 3,325