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.