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Commitments And Contingencies (Commitments And Contingencies Activity) (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Liability Activity [Abstract]    
Current portion, ending balance at March 31 $ 177  
Environmental [Abstract]    
Beginning balance. 233 $ 227
Accruals 12 15
Payments (11) (16)
Ending balance at March 31. 234 226
Current portion, ending balance at March 31. 63 64
Personal Injury [Member]    
Liability Activity [Abstract]    
Beginning balance 270 265
Current year accruals 18 18
Changes in estimates for prior years 21 2
Payments (16) (15)
Ending balance at March 31 293 270
Current portion, ending balance at March 31 $ 60 $ 62