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Benefit Plans (Summary Of Performance Shares and Performance Units Vested Awards) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Performance Shares Liability Awards [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vested (in shares/awards) 63,565 66,322 90,806
Performance Units Liability Awards [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vested (in shares/awards) 16,661 20,131 31,910
2017 Grant [Member] | Performance Shares Liability Awards [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vested (in shares/awards) 63,565    
Vested percentage of the target 155.00%    
Cash and stock payout value $ 6    
Cash payout value $ 5    
Common stock shares from vested performance shares (in shares) 9,543    
2017 Grant [Member] | Performance Units Liability Awards [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vested (in shares/awards) 16,661    
Vested percentage of the target 155.00%    
Cash and stock payout value $ 2    
Cash payout value $ 2    
2016 Grant [Member] | Performance Shares Liability Awards [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vested (in shares/awards)   66,322  
Vested percentage of the target   142.50%  
Cash and stock payout value   $ 4  
Cash payout value   $ 4  
Common stock shares from vested performance shares (in shares)   6,447  
2016 Grant [Member] | Performance Units Liability Awards [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vested (in shares/awards)   20,131  
Vested percentage of the target   142.50%  
Cash and stock payout value   $ 1  
Cash payout value   $ 1  
2015 Grant [Member] | Performance Shares Liability Awards [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vested (in shares/awards)     90,806
Vested percentage of the target     137.50%
Cash and stock payout value     $ 5
Cash payout value     $ 5
Common stock shares from vested performance shares (in shares)     5,078
2015 Grant [Member] | Performance Units Liability Awards [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vested (in shares/awards)     31,910
Vested percentage of the target     137.50%
Cash and stock payout value     $ 1
Cash payout value     $ 1