XML 52 R34.htm IDEA: XBRL DOCUMENT v2.4.0.6
Investments - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended 12 Months Ended
Mar. 31, 2013
Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]    
Proceeds from sale of available-for-sale securities $ 399 $ 380
Number of securities with unrealized gross losses 130 89