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Commitments And Contingencies (Commitments And Contingencies Activity) (Details) - USD ($)
$ in Millions
9 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Liability Activity [Abstract]    
Current portion, ending balance at September 30 $ 182  
Environmental [Abstract]    
Beginning balance. 233 $ 227
Accruals 56 55
Payments (41) (47)
Ending balance at September 30. 248 235
Current portion, ending balance at September 30. 60 65
Personal Injury [Member]    
Liability Activity [Abstract]    
Beginning balance 270 265
Current year accruals 69 52
Changes in estimates for prior years 19 (4)
Payments (55) (47)
Ending balance at September 30 303 266
Current portion, ending balance at September 30 $ 62 $ 62