Investments (Narrative) (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013 Security	Jun. 30, 2012	Jun. 30, 2013 Security	Jun. 30, 2012	Dec. 31, 2012
Investments, Debt and Equity Securities [Abstract]
Net unrealized appreciation (depreciation) included in OCI	$ 1,000,000	$ 16,000,000	$ 25,000,000	$ 84,000,000
Net unrealized depreciation included in AOCI	2,000,000		2,000,000		25,000,000
Percentage of mortgage-backed securities represented by investments in US government agency bonds	85.00%		85.00%		85.00%
Credit losses recognized in net income for corporate securities	6,000,000	1,000,000	7,000,000	4,000,000
Credit losses recognized in net income for mortgage-backed securities	0	0	0	3,000,000
Number of fixed maturities in an unrealized loss position	6,267		6,267
Total number of fixed maturities	23,938		23,938
Largest single unrealized loss in the fixed maturities	5,000,000		5,000,000
Number of equity securities in an unrealized loss position	74		74
Total number of equity securities	188		188
Largest single unrealized loss in the equity securities	40,000,000		40,000,000
Restricted assets in fixed maturities and short-term investments	16,000,000,000		16,000,000,000		16,600,000,000
Restricted assets in cash	$ 71,000,000		$ 71,000,000		$ 139,000,000