XML 115 R58.htm IDEA: XBRL DOCUMENT v2.4.0.8
Investments (Narrative) (Detail) (USD $)
In Millions, unless otherwise specified
 6 Months Ended 12 Months Ended
Jun. 30, 2013
security
Dec. 31, 2012
security
Schedule Of Investments [Line Items]    
Fair value of securities on deposit with various regulatory authorities $ 11 $ 10
Fair value of securities pledged as collateral 762 820
Cash pledged as collateral under investment agreements $ 33 $ 144
Weighted average contractual maturity period in years for securities in an unrealized loss position 20 years 23 years
Number of Securities in unrealized loss position 70 153
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 40 89