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Retirement Plans (Amounts Recognized As A Component Of AOCI) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Pension Benefits [Member]    
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax [Abstract]    
Accumulated other comprehensive (gain) loss at beginning of year $ 754 $ 556
Net actuarial (gain) loss recognized during year (58) (24)
Net actuarial (gain) loss occurring during year 260 263
Settlement loss recognized (57) (41)
Net amount recognized in comprehensive (loss) for the year 145 198
Accumulated other comprehensive (gain) loss at end of year 899 754
Postretirement Benefits Other Than Pensions (OPEB) [Member]    
Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), before Tax [Abstract]    
Accumulated other comprehensive (gain) loss at beginning of year (41) 33
Net actuarial (gain) loss recognized during year 4 (3)
Prior service credit recognized during year 11 9
Prior service credit occurring during year (149)  
Net actuarial (gain) loss occurring during year 130 (80)
Net amount recognized in comprehensive (loss) for the year (4) (74)
Accumulated other comprehensive (gain) loss at end of year $ (45) $ (41)