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Investments (Net Realized Gains (Losses) From Sales Of Available-For-Sale Securities) (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended 6 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Jun. 30, 2013
Jun. 30, 2012
Investments [Abstract]        
Proceeds from sales $ 1,436 $ 2,482 $ 2,314 $ 4,534
Available For Sale Securities Realized Gain Loss [Abstract]        
Gains 11 27 47 58
Losses $ (7) $ (16) $ (10) $ (96)