CONSOLIDATED INCOME STATEMENTS - USD ($) shares in Millions, $ in Millions		3 Months Ended					6 Months Ended	9 Months Ended	12 Months Ended
		Mar. 31, 2024	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2023	Sep. 30, 2023	Dec. 31, 2024		Dec. 31, 2023		Dec. 31, 2022
Income Statement [Abstract]
Revenue	[1]								$ 14,540		$ 14,657		$ 14,853
Expense
Labor and Fringe		$ 805	$ 814	$ 761	$ 748	$ 729	$ 1,477	$ 2,238	3,165	[1]	3,052	[1]	2,885	[1]
Purchased Services and Other		721	714	700	691	697	1,388	2,088	2,852	[1]	2,802	[1]	2,728	[1]
Depreciation and Amortization			405	403	404	395	799	1,202	1,658	[1],[2]	1,607	[1],[2]	1,502	[1],[2]
Fuel	[1]								1,168		1,377		1,626
Equipment and Other Rents	[1]								355		354		396
Goodwill Impairment (Note 19)	[1],[2]								108		0		0
Gains on Property Dispositions	[1],[2]								(11)		(34)		(238)
Total Expense		2,344	2,365	2,301	2,233	2,259	4,492	6,793	9,295	[1]	9,158	[1]	8,899	[1]
Operating Income		1,337	1,315	1,271	1,466	1,447	2,913	4,184	5,245	[1]	5,499	[1]	5,954	[1]
Interest Expense	[1]								(832)		(809)		(742)
Other Income - Net (Note 14)	[1]								142		139		133
Earnings Before Income Taxes		1,168	1,144	1,102	1,296	1,287	2,583	3,685	4,555	[1]	4,829	[1]	5,345	[1]
Income Tax Expense		(288)	(262)	(274)	(312)	(313)	(625)	(899)	(1,085)	[1]	(1,161)	[1]	(1,231)	[1]
Net Earnings		$ 880	$ 882	$ 828	$ 984	$ 974	$ 1,958	$ 2,786	$ 3,470	[1],[3]	$ 3,668	[1],[3]	$ 4,114	[1],[4]
Net Earnings Per Share
Basic (in dollars per share)		$ 0.45	$ 0.45	$ 0.42	$ 0.49	$ 0.47	$ 0.96	$ 1.38	$ 1.79	[1]	$ 1.83	[1]	$ 1.93	[1]
Assuming Dilution (in dollars per share)		$ 0.45	$ 0.45	$ 0.41	$ 0.49	$ 0.47	$ 0.96	$ 1.37	$ 1.79	[1]	$ 1.82	[1]	$ 1.92	[1]
Average Common Shares Outstanding (Millions)
Basic (in shares)	[1]								1,939		2,008		2,136
Assuming Dilution (in shares)	[1]								1,943		2,013		2,141

[1] See Note 20, Revision of Prior Period Financial Statements

[2] See Note 20, Revision of Prior Period Financial Statements.

[3] See Note 20, Revision of Prior Period Financial Statements.

[4] See Note 20, Revision of Prior Period Financial Statements.