Fair value measurements - Financial assets and liabilities (Detail) - USD ($) $ in Millions		Mar. 31, 2019		Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities		$ 19,415		$ 19,898
Investments in equity securities		191,771	[1]	172,757	[2]
Loans and finance receivables - carrying value		16,432		16,280
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		63,346		62,515
Insurance and Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities		19,415		19,898
Investments in equity securities		191,771		172,757
Equity method investments - carrying value		17,308		17,325
Loans and finance receivables - carrying value		16,432		16,280
Derivative contract liabilities		1,682		2,452
Notes payable and other borrowings - carrying value		33,847		34,975
The Kraft Heinz Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity method investments - carrying value		13,700		13,800
Equity method investments - fair value		10,600		14,000
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		3,918		4,223
States, municipalities and political subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities		151		189
Foreign governments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities		8,091		7,502
Corporate bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities		6,724		7,440
Mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities		531		544
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		191,420		172,253
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		50		203
Loans and finance receivables - fair value		1,641		1,531
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in equity securities		301		301
Loans and finance receivables - fair value		14,818		14,846
Fair Value, Measurements, Recurring [Member] | Railroad, Utilities and Energy [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes payable and other borrowings - fair value		69,937		66,422
Fair Value, Measurements, Recurring [Member] | Insurance and Other [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes payable and other borrowings - fair value		35,216		35,335
Fair Value, Measurements, Recurring [Member] | Insurance and Other [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notes payable and other borrowings - fair value		26		26
Fair Value, Measurements, Recurring [Member] | Equity Index Put Options [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract liabilities		1,682		2,452
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	[3]			2
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	[3]	52		52
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	[3]	119		118
Fair Value, Measurements, Recurring [Member] | Accounts Payable, Accruals and Other Liabilities [Member] | Railroad, Utilities and Energy [Member] | Quoted Prices (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract liabilities	[3]	1		1
Fair Value, Measurements, Recurring [Member] | Accounts Payable, Accruals and Other Liabilities [Member] | Railroad, Utilities and Energy [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract liabilities	[3]	83		101
Fair Value, Measurements, Recurring [Member] | Accounts Payable, Accruals and Other Liabilities [Member] | Railroad, Utilities and Energy [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract liabilities	[3]	15		9
Fair Value, Measurements, Recurring [Member] | The Kraft Heinz Company [Member] | Quoted Prices (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity method investments - fair value		10,626		14,007
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		2,846		2,933
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		1,072		1,290
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		151		189
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		5,840		5,417
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		2,251		2,085
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		6,720		7,434
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		4		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		531		544
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		191,771		172,757
Loans and finance receivables - carrying value		16,432		16,280
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		63,346		62,515
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		33,847		34,975
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		1,682		2,452
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	[3]	171		172
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	[3]	99		111
Fair Value, Measurements, Recurring [Member] | Carrying Value [Member] | The Kraft Heinz Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity method investments - carrying value		13,686		13,813
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		3,918		4,223
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		151		189
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		8,091		7,502
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		6,724		7,440
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		531		544
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		191,771		172,757
Loans and finance receivables - fair value		16,459		16,377
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		69,937		66,422
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		35,242		35,361
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		1,682		2,452
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	[3]	171		172
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	[3]	99		111
Fair Value, Measurements, Recurring [Member] | Fair Value [Member] | The Kraft Heinz Company [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity method investments - fair value		10,626		14,007
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		3,918		4,223
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		151		189
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		8,091		7,502
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		6,724		7,440
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		$ 531		$ 544

[1] Approximately 68% of the aggregate fair value was concentrated in five companies (American Express Company - $16.6 billion; Apple Inc. - $48.5 billion; Bank of America Corporation - $25.4 billion; The Coca-Cola Company - $18.7 billion and Wells Fargo & Company - $20.9 billion).

[2] Approximately 68% of the aggregate fair value was concentrated in five companies (American Express Company - $14.5 billion; Apple Inc. - $40.3 billion; Bank of America Corporation - $22.6 billion; The Coca-Cola Company - $18.9 billion and Wells Fargo & Company - $20.7 billion).

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