Fair value measurements - Financial assets and liabilities (Detail) - USD ($)
$ in Millions
Dec. 31, 2018
Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments in fixed maturity securities $ 19,898 $ 21,353
Investments in equity securities 172,757 [1] 170,540 [2]
Loans and finance receivables - carrying value 16,280 13,748
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 62,515 62,178
Insurance and Other [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments in fixed maturity securities 19,898 21,353
Investments in equity securities 172,757 170,540
Equity method investments - carrying value 17,325 21,024
Loans and finance receivables - carrying value 16,280 13,748
Derivative contract liabilities 2,452 2,172
Notes payable and other borrowings - carrying value 34,975 40,409
The Kraft Heinz Company [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Equity method investments - carrying value 13,813 17,635
Equity method investments - fair value 14,007 25,306
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 4,223 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 189 854
Foreign governments [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments in fixed maturity securities 7,502 8,822
Corporate bonds [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments in fixed maturity securities 7,440 6,862
Mortgage-backed securities [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments in fixed maturity securities 544 862
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 172,253 170,494
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 203 46
Loans and finance receivables - fair value 1,531 17
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  
Loans and finance receivables - fair value 14,846 14,119
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 66,422 70,538
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 35,335 41,757
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 5
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 2,452 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 [3] 2 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 [3] 52 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 [3] 118 113
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 3
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] 101 69
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] 9 10
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 14,007 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 2,933 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 1,290 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 189 854
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 5,417 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 2,085 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 7,434 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 544 862
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 172,757 170,540
Loans and finance receivables - carrying value 16,280 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 62,515 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 34,975 40,409
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 2,452 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 [3] 172 142
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 [3] 111 82
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 13,813 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 4,223 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 189 854
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 7,502 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 7,440 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 544 862
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 172,757 170,540
Loans and finance receivables - fair value 16,377 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 66,422 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 35,361 41,762
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 2,452 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 [3] 172 142
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 [3] 111 82
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 14,007 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 4,223 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 189 854
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 7,502 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 7,440 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 $ 544 $ 862
[1] 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).
[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] Assets are included in other assets and liabilities are included in accounts payable, accruals and other liabilities.