Significant accounting policies and practices - Narrative (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Jan. 01, 2024	Dec. 31, 2023
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Percentage of LIFO Inventory	32.00%
Excess of current or replacement costs over costs determined under LIFO	$ 2,300		$ 2,300
Retained earnings	696,218		607,350
Property and Casualty Contracts [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Unamortized balances of deferred policy acquisition costs	3,900		3,900
Other Assets [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Unamortized balances of deferred policy acquisition costs	$ 4,600		$ 4,600
Maximum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Trade receivables, insurance premiums receivables and other receivables collection term	1 year
Maximum [Member] | Buildings and improvements [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful life (in years)	50 years
Maximum [Member] | Machinery and equipment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful life (in years)	30 years
Maximum [Member] | Furniture, fixtures and other [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful life (in years)	15 years
Maximum [Member] | Track structure and other roadway [Member] | Railroad [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful life (in years)	100 years
Maximum [Member] | Locomotives, freight cars and other equipment [Member] | Railroad [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful life (in years)	45 years
Maximum [Member] | Utility generation, transmission and distribution systems [Member] | Utilities and Energy [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful life (in years)	80 years
Maximum [Member] | Interstate natural gas pipeline assets [Member] | Utilities and Energy [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful life (in years)	80 years
Maximum [Member] | Independent power plants and other assets [Member] | Utilities and Energy [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful life (in years)	50 years
Maximum [Member] | Equipment held for lease [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful life (in years)	35 years
Minimum [Member] | Buildings and improvements [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful life (in years)	5 years
Minimum [Member] | Machinery and equipment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful life (in years)	3 years
Minimum [Member] | Furniture, fixtures and other [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful life (in years)	4 years
Minimum [Member] | Track structure and other roadway [Member] | Railroad [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful life (in years)	10 years
Minimum [Member] | Locomotives, freight cars and other equipment [Member] | Railroad [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful life (in years)	6 years
Minimum [Member] | Utility generation, transmission and distribution systems [Member] | Utilities and Energy [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful life (in years)	5 years
Minimum [Member] | Interstate natural gas pipeline assets [Member] | Utilities and Energy [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful life (in years)	3 years
Minimum [Member] | Independent power plants and other assets [Member] | Utilities and Energy [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful life (in years)	2 years
Minimum [Member] | Equipment held for lease [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful life (in years)	3 years
ASU 2023-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Change in accounting principle, accounting standards update, adopted	true
ASU 2023-02 [Member] | Cumulative effect, period of adoption, adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained earnings		$ 127
ASU 2023-07 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Change in accounting principle, accounting standards update, adopted	true
Change in accounting principle, accounting standards update, adoption date	Dec. 31, 2024