Nature Of Operations (Details) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020 USD ($) mi	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2020 USD ($) segment mi	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Commodity Group Information [Line Items]
Other subsidiary revenues									$ 743	$ 880	$ 881
Accessorial revenues									473	514	502
Other revenues									66	71	65
Total operating revenues	$ 5,141	$ 4,919	$ 4,244	$ 5,229	$ 5,212	$ 5,516	$ 5,596	$ 5,384	$ 19,533	21,708	22,832
Network route miles | mi	32,313								32,313
Route miles owned | mi	26,069								26,069
Reportable segments | segment									1
Cargo and Freight [Member]
Commodity Group Information [Line Items]
Freight revenues									$ 18,251	20,243	21,384
Bulk [Member]
Commodity Group Information [Line Items]
Freight revenues									5,960	6,529	7,069
Industrial [Member]
Commodity Group Information [Line Items]
Freight revenues									6,622	7,472	7,689
Premium [Member]
Commodity Group Information [Line Items]
Freight revenues									5,669	6,242	6,626
Mexico [Member]
Commodity Group Information [Line Items]
Freight revenues									$ 2,100	$ 2,300	$ 2,500