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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 6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Jun. 30, 2017
Jun. 30, 2016
Investments [Abstract]        
Balance as of beginning of period $ 393 $ 413 $ 430 $ 382
Increases attributable to:        
Credit losses on securities for which an OTTI was not previously recognized 4 26 5 61
Credit losses on securities for which an OTTI was previously recognized   2 3 7
Decreases attributable to:        
Securities sold, paid down or matured (7) (10) (48) (19)
Balance as of end of period $ 390 $ 431 $ 390 $ 431