Fair value measurements - Financial assets and liabilities (Detail) - USD ($) $ in Millions		Mar. 31, 2018		Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities		$ 19,920		$ 21,353
Investments in equity securities		172,976	[1]	170,540	[2]
Railroad, Utilities and Energy [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes payable and other borrowings - carrying value		62,667		62,178
Insurance and Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities		19,920		21,353
Investments in equity securities		166,658		164,026
Investment in Kraft Heinz common stock - carrying value		17,687		17,635
Investment in Kraft Heinz common stock - fair value		20,272		25,306
Notes payable and other borrowings - carrying value		25,663		27,324
Finance and Financial Products [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans and finance receivables - carrying value		13,845		13,748
Derivative contract liabilities		2,378		2,172
Notes payable and other borrowings - carrying value		10,755		13,085
Significant Unobservable Inputs (Level 3) [Member] | Equity Index Put Options [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract liabilities		2,378
Other Assets [Member] | Railroad, Utilities and Energy [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in equity securities	[3]	1,755		1,961
Other Assets [Member] | Finance and Financial Products [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in equity securities	[3]	4,563		4,553
U.S. Treasury, U.S. government corporations and agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities		3,608		3,953
States, municipalities and political subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities		759		854
Foreign governments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities		7,888		8,822
Corporate bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities		6,819		6,862
Mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities		846		862
Fair Value, Measurements, Recurring [Member] | Quoted Prices (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in equity securities		172,928		170,494
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in equity securities		48		46
Loans and finance receivables - fair value		18		17
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Railroad, Utilities and Energy [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes payable and other borrowings - fair value		68,603		70,538
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Insurance and Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes payable and other borrowings - fair value		26,046		28,180
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Finance and Financial Products [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes payable and other borrowings - fair value		11,035		13,577
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans and finance receivables - fair value		14,066		14,119
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Finance and Financial Products [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes payable and other borrowings - fair value		24		5
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Equity Index Put Options [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract liabilities		2,378		2,172
Fair Value, Measurements, Recurring [Member] | Other Assets [Member] | Quoted Prices (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract assets	[4]	1		1
Fair Value, Measurements, Recurring [Member] | Other Assets [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract assets	[4]	26		28
Fair Value, Measurements, Recurring [Member] | Other Assets [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract assets	[4]	114		113
Fair Value, Measurements, Recurring [Member] | Accounts Payable, Accruals and Other Liabilities [Member] | Quoted Prices (Level 1) [Member] | Railroad, Utilities and Energy [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract liabilities	[4]			3
Fair Value, Measurements, Recurring [Member] | Accounts Payable, Accruals and Other Liabilities [Member] | Significant Other Observable Inputs (Level 2) [Member] | Railroad, Utilities and Energy [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract liabilities	[4]	88		69
Fair Value, Measurements, Recurring [Member] | Accounts Payable, Accruals and Other Liabilities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Railroad, Utilities and Energy [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract liabilities	[4]	17		10
Fair Value, Measurements, Recurring [Member] | Kraft Heinz (previously Heinz Holding) [Member] | Quoted Prices (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment in Kraft Heinz common stock - fair value		20,272		25,306
Fair Value, Measurements, Recurring [Member] | U.S. Treasury, U.S. government corporations and agencies [Member] | Quoted Prices (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities		2,399		2,360
Fair Value, Measurements, Recurring [Member] | U.S. Treasury, U.S. government corporations and agencies [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities		1,209		1,593
Fair Value, Measurements, Recurring [Member] | States, municipalities and political subdivisions [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities		759		854
Fair Value, Measurements, Recurring [Member] | Foreign governments [Member] | Quoted Prices (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities		5,906		6,946
Fair Value, Measurements, Recurring [Member] | Foreign governments [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities		1,982		1,876
Fair Value, Measurements, Recurring [Member] | Corporate bonds [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities		6,813		6,856
Fair Value, Measurements, Recurring [Member] | Corporate bonds [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities		6		6
Fair Value, Measurements, Recurring [Member] | Mortgage-backed securities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities		846		862
Fair Value, Measurements, Recurring [Member] | Carrying Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in equity securities		172,976		170,540
Loans and finance receivables - carrying value		13,845		13,748
Fair Value, Measurements, Recurring [Member] | Carrying Value [Member] | Railroad, Utilities and Energy [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes payable and other borrowings - carrying value		62,667		62,178
Fair Value, Measurements, Recurring [Member] | Carrying Value [Member] | Insurance and Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes payable and other borrowings - carrying value		25,663		27,324
Fair Value, Measurements, Recurring [Member] | Carrying Value [Member] | Finance and Financial Products [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes payable and other borrowings - carrying value		10,755		13,085
Fair Value, Measurements, Recurring [Member] | Carrying Value [Member] | Equity Index Put Options [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract liabilities		2,378		2,172
Fair Value, Measurements, Recurring [Member] | Carrying Value [Member] | Other Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract assets	[4]	141		142
Fair Value, Measurements, Recurring [Member] | Carrying Value [Member] | Accounts Payable, Accruals and Other Liabilities [Member] | Railroad, Utilities and Energy [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract liabilities	[4]	105		82
Fair Value, Measurements, Recurring [Member] | Carrying Value [Member] | Kraft Heinz (previously Heinz Holding) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment in Kraft Heinz common stock - carrying value		17,687		17,635
Fair Value, Measurements, Recurring [Member] | Carrying Value [Member] | U.S. Treasury, U.S. government corporations and agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities		3,608		3,953
Fair Value, Measurements, Recurring [Member] | Carrying Value [Member] | States, municipalities and political subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities		759		854
Fair Value, Measurements, Recurring [Member] | Carrying Value [Member] | Foreign governments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities		7,888		8,822
Fair Value, Measurements, Recurring [Member] | Carrying Value [Member] | Corporate bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities		6,819		6,862
Fair Value, Measurements, Recurring [Member] | Carrying Value [Member] | Mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities		846		862
Fair Value, Measurements, Recurring [Member] | Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in equity securities		172,976		170,540
Loans and finance receivables - fair value		14,084		14,136
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Railroad, Utilities and Energy [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes payable and other borrowings - fair value		68,603		70,538
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Insurance and Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes payable and other borrowings - fair value		26,046		28,180
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Finance and Financial Products [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes payable and other borrowings - fair value		11,059		13,582
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Equity Index Put Options [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract liabilities		2,378		2,172
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Other Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract assets	[4]	141		142
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Accounts Payable, Accruals and Other Liabilities [Member] | Railroad, Utilities and Energy [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract liabilities	[4]	105		82
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Kraft Heinz (previously Heinz Holding) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment in Kraft Heinz common stock - fair value		20,272		25,306
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | U.S. Treasury, U.S. government corporations and agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities		3,608		3,953
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | States, municipalities and political subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities		759		854
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Foreign governments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities		7,888		8,822
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Corporate bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities		6,819		6,862
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | Mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities		$ 846		$ 862

[1] Approximately 68% of the aggregate fair value was concentrated in five companies (American Express Company - $14.1 billion; Apple Inc. - $40.7 billion; Bank of America Corporation - $21.0 billion; The Coca-Cola Company - $17.4 billion and Wells Fargo & Company - $25.2 billion).

[2] Approximately 65% of the aggregate fair value was concentrated in five companies (American Express Company - $15.1 billion; Apple Inc. - $28.2 billion; Bank of America Corporation - $20.7 billion; The Coca-Cola Company - $18.4 billion and Wells Fargo & Company - $29.3 billion).

[3] Included in other assets.

[4] Assets are included in other assets and liabilities are included in accounts payable, accruals and other liabilities.