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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
Mar. 31, 2018
Mar. 31, 2017
Investments [Abstract]    
Balance as of beginning-of-period $ 378 $ 430
Increases attributable to:    
Credit losses on securities for which an OTTI was not previously recognized 2 1
Credit losses on securities for which an OTTI was previously recognized   3
Decreases attributable to:    
Securities sold, paid down or matured (2) (41)
Balance as of end-of-period $ 378 $ 393