Operations and Segmentation (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Commodity Group Information [Line Items]
Freight revenues	$ 5,132	$ 3,972	$ 9,781	$ 8,852
Subsidiary revenue	180	150	357	364
Accessorial revenues	176	103	337	220
Other revenues	16	19	30	37
Total operating revenues	5,504	4,244	10,505	9,473
Cargo and Freight [Member]
Commodity Group Information [Line Items]
Freight revenues	5,132	3,972	9,781	8,852
Bulk [Member]
Commodity Group Information [Line Items]
Freight revenues	1,648	1,386	3,160	2,920
Industrial [Member]
Commodity Group Information [Line Items]
Freight revenues	1,859	1,500	3,515	3,394
Premium [Member]
Commodity Group Information [Line Items]
Freight revenues	1,625	1,086	3,106	2,538
Mexico [Member]
Commodity Group Information [Line Items]
Freight revenues	$ 618	$ 389	$ 1,200	$ 972