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Commitments And Contingencies (Commitments And Contingencies Activity) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Commitments and Contingencies [Line Items]      
Current portion, ending balance at December 31 $ 190 $ 211  
Environmental [Abstract]      
Beginning balance. 223 196 $ 212
Accruals 67 84 45
Payments (63) (57) (61)
Ending balance at December 31 227 223 196
Current portion, ending balance at December 31 62 59 57
Personal Injury [Member]      
Commitments and Contingencies [Line Items]      
Beginning balance 271 285 290
Current year accruals 78 74 77
Changes in estimates for prior years (11) (16) (7)
Payments (73) (72) (75)
Ending balance at December 31 265 271 285
Current portion, ending balance at December 31 $ 63 $ 72 $ 66