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Commitments And Contingencies (Commitments And Contingencies Activity) (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2020
Mar. 31, 2019
Liability Activity [Abstract]    
Current portion, ending balance at March 31 $ 177  
Environmental [Abstract]    
Beginning balance. 227 $ 223
Accruals 15 10
Payments (16) (17)
Ending balance at March 31. 226 216
Current portion, ending balance at March 31. 64 63
Personal Injury [Member]    
Liability Activity [Abstract]    
Beginning balance 265 271
Current year accruals 18 18
Changes in estimates for prior years 2 (2)
Payments (15) (21)
Ending balance at March 31 270 266
Current portion, ending balance at March 31 $ 62 $ 67