Fair value measurements - Financial Instruments (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011		Dec. 31, 2010
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments in equity securities	$ 76,991		$ 61,513
Railroad, Utilities and Energy [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes payable and other borrowings - carrying value	32,580		31,626
Finance and Financial Products [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments in fixed maturity securities	966		1,080
Loans and finance receivables	13,934		15,226
Derivative contract liabilities	10,139		8,371
Notes payable and other borrowings - carrying value	14,036		14,477
Other investments - carrying value	3,810		3,676
Insurance and Other [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments in fixed maturity securities	31,222		33,803
Investments in equity securities	76,063		59,819
Notes payable and other borrowings - carrying value	13,768		12,471
Other investments - carrying value	13,111		19,333
Carrying Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments in fixed maturity securities	32,188		34,883
Investments in equity securities	76,991		61,513
Loans and finance receivables	13,934		15,226
Other investments - carrying value	16,921		23,009
Carrying Value [Member] | Railroad, Utilities and Energy [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes payable and other borrowings - carrying value	32,580		31,626
Carrying Value [Member] | Finance and Financial Products [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative contract liabilities	10,139		8,371
Notes payable and other borrowings - carrying value	14,036		14,477
Carrying Value [Member] | Insurance and Other [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes payable and other borrowings - carrying value	13,768		12,471
Carrying Value [Member] | Other Assets [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative contract assets	327	[1]	574	[1]
Carrying Value [Member] | Accounts Payable, Accruals and Other Liabilities [Member] | Railroad, Utilities and Energy [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative contract liabilities	336	[2]	621	[2]
Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments in fixed maturity securities	32,188		34,883
Investments in equity securities	76,991		61,513
Loans and finance receivables	13,126		14,453
Other investments - fair value	17,927		24,147
Fair Value [Member] | Railroad, Utilities and Energy [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes payable and other borrowings - fair value	38,257		33,932
Fair Value [Member] | Finance and Financial Products [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative contract liabilities	10,139		8,371
Notes payable and other borrowings - fair value	14,959		15,191
Fair Value [Member] | Insurance and Other [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes payable and other borrowings - fair value	14,334		12,705
Fair Value [Member] | Other Assets [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative contract assets	327	[1]	574	[1]
Fair Value [Member] | Accounts Payable, Accruals and Other Liabilities [Member] | Railroad, Utilities and Energy [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative contract liabilities	$ 336	[2]	$ 621	[2]

[1] Included in other assets

[2] Included in accounts payable, accruals and other liabilities