Significant accounting policies and practices - Summary of Reclassifications to Amounts Previously Reported (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2024		Dec. 31, 2023		Dec. 31, 2022
Assets:
Inventories		$ 24,008		$ 25,856
Goodwill	[1]	83,880		84,626		$ 78,119
Costs and expenses:
Interest expense		5,200		5,003		4,352
Insurance and Other [Member]
Assets:
Cash and cash equivalents		44,333	[2]	34,268	[2]	32,260
Other receivables		43,887		46,261
Inventories		24,008		25,856
Property, plant and equipment		30,071		30,199
Goodwill		56,860		57,473
Other intangible assets		34,638		35,884
Other		24,994		21,866
Liabilities:
Accounts payable, accruals and other liabilities		37,489		36,559
Notes payable and other borrowings		44,885		48,468
Revenues:
Sales and service revenues		202,334		207,148		157,518
Interest, dividend and other investment income		21,825		15,764		10,263
Costs and expenses:
Cost of sales and services		163,642		169,281		124,319
Selling, general and administrative expenses		25,642		25,458		19,506
Interest expense		1,594		1,671		1,187
Railroad, Utilities and Energy [Member]
Assets:
Cash and cash equivalents		3,396	[2]	3,754	[2]	3,551
Receivables		4,503		4,999
Property, plant and equipment		175,030		169,447
Goodwill		27,020		27,153
Other		20,811		19,845
Liabilities:
Accounts payable, accruals and other liabilities		18,226		18,304
Notes payable and other borrowings		79,877		79,803
Revenues:
Utility and energy operating revenues		21,518		21,232		21,023
Service revenues and other income		4,917		4,728		5,324
Costs and expenses:
Utilities and energy cost of sales and other expenses		16,984		18,399		15,896
Interest expense		$ 3,606		3,332		$ 3,165
Previously Reported [Member] | Insurance and Other [Member]
Assets:
Cash and cash equivalents				33,672
Other receivables				44,174
Inventories				24,159
Property, plant and equipment				22,030
Goodwill				50,868
Other intangible assets				29,327
Other				19,568
Liabilities:
Accounts payable, accruals and other liabilities				32,402
Notes payable and other borrowings				42,692
Revenues:
Sales and service revenues				155,687
Interest, dividend and other investment income				15,561
Costs and expenses:
Cost of sales and services				122,569
Selling, general and administrative expenses				22,605
Interest expense				1,258
Previously Reported [Member] | Railroad, Utilities and Energy [Member]
Assets:
Cash and cash equivalents				4,350
Receivables				7,086
Property, plant and equipment				177,616
Goodwill				33,758
Other				30,397
Liabilities:
Accounts payable, accruals and other liabilities				22,461
Notes payable and other borrowings				85,579
Revenues:
Utility and energy operating revenues				72,693
Service revenues and other income				4,931
Costs and expenses:
Utilities and energy cost of sales and other expenses				67,964
Interest expense				3,745
Reclassification [Member] | Insurance and Other [Member]
Assets:
Cash and cash equivalents				596
Other receivables				2,087
Inventories				1,697
Property, plant and equipment				8,169
Goodwill				6,605
Other intangible assets				6,557
Other				2,298
Liabilities:
Accounts payable, accruals and other liabilities				4,157
Notes payable and other borrowings				5,776
Revenues:
Sales and service revenues				51,461
Interest, dividend and other investment income				203
Costs and expenses:
Cost of sales and services				46,712
Selling, general and administrative expenses				2,853
Interest expense				413
Reclassification [Member] | Railroad, Utilities and Energy [Member]
Assets:
Cash and cash equivalents				(596)
Receivables				(2,087)
Property, plant and equipment				(8,169)
Goodwill				(6,605)
Other				(10,552)
Liabilities:
Accounts payable, accruals and other liabilities				(4,157)
Notes payable and other borrowings				(5,776)
Revenues:
Utility and energy operating revenues				(51,461)
Service revenues and other income				(203)
Costs and expenses:
Utilities and energy cost of sales and other expenses				(49,565)
Interest expense				$ (413)

[1] Net of accumulated goodwill impairments of $11.5 billion as of December 31, 2024, $11.1 billion as of December 31, 2023 and $11.0 billion as of December 31, 2022.

[2] Includes U.S. Treasury Bills with maturities of three months or less when purchased of $14.4 billion at December 31, 2024 and $4.8 billion at December 31, 2023.