Consolidated Statements of Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement [Abstract]
Revenues	$ 20,869	$ 23,515	$ 23,855
Operating expenses:
Compensation and benefits	4,609	5,347	5,394
Purchased services	2,554	2,700	2,870
Depreciation and amortization	2,476	2,403	2,317
Fuel	1,789	2,944	3,346
Equipment rents	664	758	732
Materials and other	1,037	1,292	1,396
Total operating expenses	13,129	15,444	16,055
Operating income	7,740	8,071	7,800
Interest expense	1,037	1,070	1,041
Other (income) expense, net	(89)	(249)	(104)
Income before income taxes	6,792	7,250	6,863
Income tax expense	1,631	1,769	1,644
Net income	$ 5,161	$ 5,481	$ 5,219