Significant accounting policies and practices - Narrative (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Jan. 01, 2019	Jan. 01, 2018	Dec. 31, 2017
Significant Accounting Policies [Line Items]
Percentage of LIFO inventory	39.00%
Excess of current or replacement costs over costs determined under LIFO	$ 1,000
Minimum [Member]
Significant Accounting Policies [Line Items]
Insurance interest rate assumption	1.00%
Maximum [Member]
Significant Accounting Policies [Line Items]
Insurance interest rate assumption	7.00%
Insurance and Other [Member]
Significant Accounting Policies [Line Items]
Equipment held for lease	$ 14,298			$ 10,167
Aircraft repurchase liabilities and unearned lease revenues	$ 4,593
Buildings and improvements [Member] | Minimum [Member]
Significant Accounting Policies [Line Items]
Estimated useful life (in years)	5 years
Buildings and improvements [Member] | Maximum [Member]
Significant Accounting Policies [Line Items]
Estimated useful life (in years)	50 years
Machinery and equipment [Member] | Minimum [Member]
Significant Accounting Policies [Line Items]
Estimated useful life (in years)	3 years
Machinery and equipment [Member] | Maximum [Member]
Significant Accounting Policies [Line Items]
Estimated useful life (in years)	25 years
Furniture, fixtures and other [Member] | Minimum [Member]
Significant Accounting Policies [Line Items]
Estimated useful life (in years)	3 years
Furniture, fixtures and other [Member] | Maximum [Member]
Significant Accounting Policies [Line Items]
Estimated useful life (in years)	15 years
Track structure and other roadway [Member] | Railroad [Member] | Minimum [Member]
Significant Accounting Policies [Line Items]
Estimated useful life (in years)	9 years
Track structure and other roadway [Member] | Railroad [Member] | Maximum [Member]
Significant Accounting Policies [Line Items]
Estimated useful life (in years)	100 years
Locomotives, freight cars and other equipment [Member] | Railroad [Member] | Minimum [Member]
Significant Accounting Policies [Line Items]
Estimated useful life (in years)	6 years
Locomotives, freight cars and other equipment [Member] | Railroad [Member] | Maximum [Member]
Significant Accounting Policies [Line Items]
Estimated useful life (in years)	41 years
Utility generation, transmission and distribution systems [Member] | Utilities and Energy [Member] | Minimum [Member]
Significant Accounting Policies [Line Items]
Estimated useful life (in years)	5 years
Utility generation, transmission and distribution systems [Member] | Utilities and Energy [Member] | Maximum [Member]
Significant Accounting Policies [Line Items]
Estimated useful life (in years)	80 years
Interstate natural gas pipeline assets [Member] | Utilities and Energy [Member] | Minimum [Member]
Significant Accounting Policies [Line Items]
Estimated useful life (in years)	3 years
Interstate natural gas pipeline assets [Member] | Utilities and Energy [Member] | Maximum [Member]
Significant Accounting Policies [Line Items]
Estimated useful life (in years)	80 years
Independent power plants and other assets [Member] | Utilities and Energy [Member] | Minimum [Member]
Significant Accounting Policies [Line Items]
Estimated useful life (in years)	3 years
Independent power plants and other assets [Member] | Utilities and Energy [Member] | Maximum [Member]
Significant Accounting Policies [Line Items]
Estimated useful life (in years)	30 years
Equipment held for lease [Member] | Minimum [Member]
Significant Accounting Policies [Line Items]
Estimated useful life (in years)	6 years
Equipment held for lease [Member] | Maximum [Member]
Significant Accounting Policies [Line Items]
Estimated useful life (in years)	35 years
Other Assets [Member]
Significant Accounting Policies [Line Items]
Unamortized balances of deferred policy acquisition costs	$ 2,658			$ 2,529
Aircraft Sold Under Fractional Aircraft Ownership Programs [Member] | ASC 606 [Member] | Insurance and Other [Member]
Significant Accounting Policies [Line Items]
Equipment held for lease			$ 3,500
Aircraft repurchase liabilities and unearned lease revenues			$ 3,500
Subsequent Event [Member] | ASU 2016-02 [Member]
Significant Accounting Policies [Line Items]
Operating leases, right of use assets		$ 6,000
Operating lease liabilities		$ 6,000