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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, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Investments [Abstract]        
Balance as of beginning-of-period $ 378 $ 393 $ 378 $ 430
Increases attributable to:        
Credit losses on securities for which an OTTI was not previously recognized 1 4 2 5
Credit losses on securities for which an OTTI was previously recognized     1 3
Decreases attributable to:        
Securities sold, paid down or matured (4) (7) (6) (48)
Balance as of end-of-period $ 375 $ 390 $ 375 $ 390