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Commitments And Contingencies (Commitments And Contingencies Activity) (Details) - USD ($)
$ in Millions
9 Months Ended
Sep. 30, 2020
Sep. 30, 2019
Liability Activity [Abstract]    
Current portion, ending balance at September 30 $ 180  
Environmental [Abstract]    
Beginning balance. 227 $ 223
Accruals 55 52
Payments (47) (49)
Ending balance at September 30. 235 226
Current portion, ending balance at September 30. 65 62
Personal Injury [Member]    
Liability Activity [Abstract]    
Beginning balance 265 271
Current year accruals 52 59
Changes in estimates for prior years (4) (17)
Payments (47) (41)
Ending balance at September 30 266 272
Current portion, ending balance at September 30 $ 62 $ 61