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Investments (Schedule Of Changes in Amount Of Credit Losses Of OTTI Recognized In Net Income (Loss)) (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Investments [Abstract]        
Balance as of beginning-of-period $ 390 $ 431 $ 430 $ 382
Increases attributable to:        
Credit losses on securities for which an OTTI was not previously recognized 8 6 13 67
Credit losses on securities for which an OTTI was previously recognized 1 5 4 12
Decreases attributable to:        
Securities sold, paid down or matured (21) (6) (69) (25)
Balance as of end-of-period $ 378 $ 436 $ 378 $ 436