Investments (Narrative) (Detail) (USD $)	3 Months Ended
	Mar. 31, 2014 Security	Mar. 31, 2013	Dec. 31, 2013
Investments, Debt and Equity Securities [Abstract]
Net unrealized appreciation (depreciation) included in OCI	$ 4,000,000	$ 24,000,000
Net unrealized depreciation included in AOCI	2,000,000		4,000,000
Percentage of mortgage-backed securities represented by investments in US government agency bonds	82.00%		83.00%
Credit losses recognized in net income for corporate securities	4,000,000	1,000,000
Credit losses recognized in net income for mortgage-backed securities	0	0
Number of fixed maturities in an unrealized loss position	4,540
Total number of fixed maturities	24,991
Largest single unrealized loss in the fixed maturities	5,000,000
Number of equity securities in an unrealized loss position	58
Total number of equity securities	186
Largest single unrealized loss in the equity securities	54,000,000
Restricted assets in fixed maturities and short-term investments	16,500,000,000		16,300,000,000
Restricted assets in cash	$ 98,000,000		$ 162,000,000