Operations and Segmentation (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Commodity Group Information [Line Items]
Freight revenues	$ 5,166	$ 4,596	$ 14,947	$ 13,448
Subsidiary revenue	182	193	539	557
Accessorial revenues	198	114	535	334
Other revenues	20	16	50	53
Total operating revenues	5,566	4,919	16,071	14,392
Cargo and Freight [Member]
Commodity Group Information [Line Items]
Freight revenues	5,166	4,596	14,947	13,448
Bulk [Member]
Commodity Group Information [Line Items]
Freight revenues	1,687	1,478	4,847	4,398
Industrial [Member]
Commodity Group Information [Line Items]
Freight revenues	1,911	1,567	5,426	4,961
Premium [Member]
Commodity Group Information [Line Items]
Freight revenues	1,568	1,551	4,674	4,089
Mexico [Member]
Commodity Group Information [Line Items]
Freight revenues	$ 592	$ 556	$ 1,800	$ 1,500