Investments (Narrative) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013 security	Dec. 31, 2012 security
Schedule Of Investments [Line Items]
Fair value of securities on deposit with various regulatory authorities	$ 10	$ 10
Fair value of securities pledged as collateral	735	820
Cash pledged as collateral under investment agreements	$ 22	$ 144
Weighted average contractual maturity period in years for securities in an unrealized loss position	18 years	23 years
Number of Securities in unrealized loss position	77	153
Rate that a security's fair value is below book value	5.00%
Greater Than Five Percent [Member]
Schedule Of Investments [Line Items]
Number of Securities in unrealized loss position	50	89