Consolidated Statements of Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Statement [Abstract]
Revenues	$ 23,282	$ 20,869	$ 23,515
Operating expenses:
Compensation and benefits	4,767	4,609	5,347
Fuel	2,766	1,789	2,944
Purchased services	2,715	2,554	2,700
Depreciation and amortization	2,456	2,476	2,403
Equipment rents	677	664	758
Materials and other	1,103	1,037	1,292
Total operating expenses	14,484	13,129	15,444
Operating income	8,798	7,740	8,071
Interest expense	1,032	1,037	1,070
Other (income) expense, net	(95)	(89)	(249)
Income before income taxes	7,861	6,792	7,250
Income tax expense	1,871	1,631	1,769
Net income	$ 5,990	$ 5,161	$ 5,481