Significant accounting policies and practices - Narrative (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Voting interests of investee	20.00%
Percentage of LIFO Inventory	37.00%
Excess of current or replacement costs over costs determined under LIFO	$ 950		$ 1,000
Operating lease liabilities	5,882
Assets	817,729		707,794		$ 702,095
Liabilities	389,166		355,294
Equipment held for lease	15,065		14,298
Difference Between Lease Guidance in Effect Before and After Topic 842 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating leases, right of use assets		$ 6,200
Operating lease liabilities		5,900
ASC 842 [Member] | Difference Between Lease Guidance in Effect Before and After Topic 842 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other assets		(300)
Assets		5,900
Liabilities		$ 5,900
ASC 606 [Member] | Difference Between Lease Guidance in Effect Before and After Topic 842 [Member] | Aircraft Sold Under Fractional Aircraft Ownership Programs [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Equipment held for lease				$ 3,500
Aircraft repurchase liabilities and unearned lease revenues				$ 3,500
Other Assets [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Unamortized balances of deferred policy acquisition costs	2,937		$ 2,658
Operating leases, right of use assets	$ 5,941
Minimum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Insurance interest rate assumption	3.00%
Maximum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Insurance interest rate assumption	7.50%
Buildings and improvements [Member] | Minimum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful life (in years)	5 years
Buildings and improvements [Member] | Maximum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful life (in years)	50 years
Machinery and equipment [Member] | Minimum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful life (in years)	3 years
Machinery and equipment [Member] | Maximum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful life (in years)	25 years
Furniture, fixtures and other [Member] | Minimum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful life (in years)	3 years
Furniture, fixtures and other [Member] | Maximum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful life (in years)	15 years
Track structure and other roadway [Member] | Minimum [Member] | Railroad [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful life (in years)	10 years
Track structure and other roadway [Member] | Maximum [Member] | Railroad [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful life (in years)	100 years
Locomotives, freight cars and other equipment [Member] | Minimum [Member] | Railroad [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful life (in years)	6 years
Locomotives, freight cars and other equipment [Member] | Maximum [Member] | Railroad [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful life (in years)	41 years
Utility generation, transmission and distribution systems [Member] | Minimum [Member] | Utilities and Energy [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful life (in years)	5 years
Utility generation, transmission and distribution systems [Member] | Maximum [Member] | Utilities and Energy [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful life (in years)	80 years
Interstate natural gas pipeline assets [Member] | Minimum [Member] | Utilities and Energy [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful life (in years)	3 years
Interstate natural gas pipeline assets [Member] | Maximum [Member] | Utilities and Energy [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful life (in years)	80 years
Independent power plants and other assets [Member] | Minimum [Member] | Utilities and Energy [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful life (in years)	3 years
Independent power plants and other assets [Member] | Maximum [Member] | Utilities and Energy [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful life (in years)	30 years
Equipment held for lease [Member] | Minimum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful life (in years)	5 years
Equipment held for lease [Member] | Maximum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Estimated useful life (in years)	35 years