Segment Reporting and Significant Expenses- Schedule of Reconciliation of Segment Operating Income (Details) - USD ($) $ 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
Segment Reporting Information [Line Items]
Segment 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]
Trucking Revenue and Eliminations	[1]								14,540		14,657		14,853
Trucking Expenses and Eliminations		(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	[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]
Operating Segments
Segment Reporting Information [Line Items]
Segment Operating Income									5,346		5,467		5,902
Operating Income									5,346		5,467		5,902
Operating Segments | Rail Operations
Segment Reporting Information [Line Items]
Segment Operating Income									5,346		5,467		5,902
Trucking Revenue and Eliminations									13,696		13,775		13,887
Operating Income									5,346		5,467		5,902
Operating Segments | Trucking Operating Segment
Segment Reporting Information [Line Items]
Trucking Revenue and Eliminations									851		887		968
Trucking Expenses and Eliminations									(952)		(855)		(916)
Eliminations
Segment Reporting Information [Line Items]
Trucking Revenue and Eliminations									(7)		(5)		(2)
Trucking Expenses and Eliminations									7		5		2
Eliminations | Trucking Operating Segment
Segment Reporting Information [Line Items]
Trucking Revenue and Eliminations									844		882		966
Trucking Expenses and Eliminations									$ (945)		$ (850)		$ (914)

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