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Retirement Plans (Schedule Of Changes In Projected Benefit Obligation And Plan Assets) (Details) - USD ($)
$ in Millions
 12 Months Ended
Jun. 30, 2019
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Projected Benefit Obligation [Abstract]        
OPEB Plan amendment (Note 5) $ (92)   $ (92)  
Pension [Member]        
Projected Benefit Obligation [Abstract]        
Projected benefit obligation at beginning of year   $ 4,847 4,181  
Service cost   91 80 $ 105
Interest cost   137 160 145
Actuarial loss/(gain)   812 656  
Gross benefits paid   (229) (230)  
Projected benefit obligation at end of year   5,658 4,847 4,181
Plan Assets [Abstract]        
Fair value of plan assets at beginning of year   4,528 3,887  
Actual return/(loss) on plan assets   686 841  
Non-qualified plan benefit contributions   31 30  
Gross benefits paid   (229) (230)  
Fair value of plan assets at end of year   5,016 4,528 3,887
Defined Benefit Plan, Funded Status of Plan [Abstract]        
Funded status at end of year   (642) (319)  
OPEB [Member]        
Projected Benefit Obligation [Abstract]        
Projected benefit obligation at beginning of year   205 298  
Service cost   1 1 2
Interest cost   5 9 10
OPEB Plan amendment (Note 5)   (2) (92)  
Actuarial loss/(gain)     11  
Gross benefits paid   (19) (22)  
Projected benefit obligation at end of year   190 205 298
Plan Assets [Abstract]        
Fair value of plan assets at beginning of year    
Actual return/(loss) on plan assets    
Non-qualified plan benefit contributions - OPEB   19 22  
Gross benefits paid   (19) (22)  
Fair value of plan assets at end of year  
Defined Benefit Plan, Funded Status of Plan [Abstract]        
Funded status at end of year   $ (190) $ (205)