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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, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Investments [Abstract]        
Balance as of beginning-of-period $ 375 $ 390 $ 378 $ 430
Increases attributable to:        
Credit losses on securities for which an OTTI was not previously recognized 2 8 4 13
Credit losses on securities for which an OTTI was previously recognized   1 1 4
Decreases attributable to:        
Securities sold, paid down or matured (5) (21) (11) (69)
Balance as of end-of-period $ 372 $ 378 $ 372 $ 378