Fair value measurements - Financial assets and liabilities (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in equity securities	$ 97,163		$ 87,662
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	36,890		36,156
Finance and Financial Products [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities	782		842
Other investments carried at cost	5,152		4,952
Loans and finance receivables - carrying value	12,751		12,809
Derivative contract liabilities	6,721		7,933
Notes payable and other borrowings - carrying value	12,960		13,045
Insurance and Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities	30,601		31,449
Investments in equity securities	95,878		86,467
Other investments carried at cost	16,779		16,057
Notes payable and other borrowings - carrying value	13,399		13,535
Fixed Maturities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities	31,383		32,291
Fixed Maturities [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	2,916		2,775
Fixed Maturities [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	2,822		2,913
Fixed Maturities [Member] | Foreign governments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities	11,037		11,355
Fixed Maturities [Member] | Corporate bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities	12,180		12,661
Fixed Maturities [Member] | Mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities	2,428		2,587
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	97,064		87,563
Fair Value, Measurements, Recurring [Member] | Quoted Prices (Level 1) [Member] | Other Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract assets			1	[1]
Fair Value, Measurements, Recurring [Member] | Quoted Prices (Level 1) [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	2	[1]	10	[1]
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	64		64
Loans and finance receivables - fair value	389		304
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	42,422		42,074
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	13,007		13,194
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Finance and Financial Products [Member] | Other, principally interest rate and foreign currency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract liabilities	12		2
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	14,118		14,284
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Other Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract assets	52	[1]	128	[1]
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [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	149	[1]	217	[1]
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	35		35
Loans and finance receivables - fair value	11,550		11,687
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	773		811
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Finance and Financial Products [Member] | Equity Index Put Options [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract liabilities	6,264		7,502
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Finance and Financial Products [Member] | Credit Default Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract liabilities	445		429
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Other Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract assets	74	[1]	91	[1]
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [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	6	[1]	7	[1]
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Other Fixed Maturities and Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments carried at fair value	16,669		15,750
Other investments carried at cost	6,092		6,134
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Quoted Prices (Level 1) [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	1,067		1,225
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Quoted Prices (Level 1) [Member] | Foreign governments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities	4,417		4,571
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Significant Other Observable Inputs (Level 2) [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	1,848		1,549
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Significant Other Observable Inputs (Level 2) [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	2,822		2,912
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Significant Other Observable Inputs (Level 2) [Member] | Foreign governments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities	6,620		6,784
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Significant Other Observable Inputs (Level 2) [Member] | Corporate bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities	11,532		12,011
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Significant Other Observable Inputs (Level 2) [Member] | Mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities	2,428		2,587
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Significant Unobservable Inputs (Level 3) [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	1		1
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Significant Unobservable Inputs (Level 3) [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			1
Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Corporate bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities	648		650
Carrying Value [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in equity securities	97,163		87,662
Loans and finance receivables - carrying value	12,751		12,809
Carrying Value [Member] | Fair Value, Measurements, Recurring [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	36,890		36,156
Carrying Value [Member] | Fair Value, Measurements, Recurring [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	12,960		13,045
Carrying Value [Member] | Fair Value, Measurements, Recurring [Member] | Finance and Financial Products [Member] | Equity Index Put Options [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract liabilities	6,264		7,502
Carrying Value [Member] | Fair Value, Measurements, Recurring [Member] | Finance and Financial Products [Member] | Credit Default Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract liabilities	445		429
Carrying Value [Member] | Fair Value, Measurements, Recurring [Member] | Finance and Financial Products [Member] | Other, principally interest rate and foreign currency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract liabilities	12		2
Carrying Value [Member] | Fair Value, Measurements, Recurring [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	13,399		13,535
Carrying Value [Member] | Fair Value, Measurements, Recurring [Member] | Other Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract assets	126	[1]	220	[1]
Carrying Value [Member] | Fair Value, Measurements, Recurring [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	157	[1]	234	[1]
Carrying Value [Member] | Fair Value, Measurements, Recurring [Member] | Other Fixed Maturities and Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments carried at fair value	16,669		15,750
Other investments carried at cost	5,262		5,259
Carrying Value [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Maturities [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	2,916		2,775
Carrying Value [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Maturities [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	2,822		2,913
Carrying Value [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Foreign governments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities	11,037		11,355
Carrying Value [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Corporate bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities	12,180		12,661
Carrying Value [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities	2,428		2,587
Fair Value [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in equity securities	97,163		87,662
Loans and finance receivables - fair value	11,939		11,991
Fair Value [Member] | Fair Value, Measurements, Recurring [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	42,422		42,074
Fair Value [Member] | Fair Value, Measurements, Recurring [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	13,780		14,005
Fair Value [Member] | Fair Value, Measurements, Recurring [Member] | Finance and Financial Products [Member] | Equity Index Put Options [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract liabilities	6,264		7,502
Fair Value [Member] | Fair Value, Measurements, Recurring [Member] | Finance and Financial Products [Member] | Credit Default Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract liabilities	445		429
Fair Value [Member] | Fair Value, Measurements, Recurring [Member] | Finance and Financial Products [Member] | Other, principally interest rate and foreign currency [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract liabilities	12		2
Fair Value [Member] | Fair Value, Measurements, Recurring [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	14,118		14,284
Fair Value [Member] | Fair Value, Measurements, Recurring [Member] | Other Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract assets	126	[1]	220	[1]
Fair Value [Member] | Fair Value, Measurements, Recurring [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	157	[1]	234	[1]
Fair Value [Member] | Fair Value, Measurements, Recurring [Member] | Other Fixed Maturities and Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments carried at fair value	16,669		15,750
Other investments carried at cost	6,092		6,134
Fair Value [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Maturities [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	2,916		2,775
Fair Value [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Maturities [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	2,822		2,913
Fair Value [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Foreign governments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities	11,037		11,355
Fair Value [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Corporate bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities	12,180		12,661
Fair Value [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities	$ 2,428		$ 2,587

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