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Commitments And Contingencies (Commitments And Contingencies Activity) (Details) - USD ($)
$ in Millions
6 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Liability Activity [Abstract]    
Current portion, ending balance at June 30 $ 186  
Environmental [Abstract]    
Beginning balance. 233 $ 227
Accruals 43 28
Payments (26) (27)
Ending balance at June 30. 250 228
Current portion, ending balance at June 30. 63 63
Personal Injury [Member]    
Liability Activity [Abstract]    
Beginning balance 270 265
Current year accruals 45 34
Changes in estimates for prior years 17 (4)
Payments (31) (36)
Ending balance at June 30 301 259
Current portion, ending balance at June 30 $ 62 $ 65