Fair value measurements - Financial assets and liabilities (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in equity securities	$ 103,274		$ 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	37,861		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	749		842
Other investments carried at cost	5,235		4,952
Loans and finance receivables - carrying value	12,855		12,809
Derivative contract liabilities	6,241		7,933
Notes payable and other borrowings - carrying value	12,831		13,045
Insurance and Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities	28,756		31,449
Investments in equity securities	101,933		86,467
Other investments carried at cost	29,484		16,057
Notes payable and other borrowings - carrying value	13,261		13,535
Fixed Maturities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities	29,505		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	2,811		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	2,748		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	10,238		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	11,464		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	2,244		2,587
Other Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments carried at fair value	35,459		21,884
Other investments carried at cost	34,719		21,009
Other Investments [Member] | Finance and Financial Products [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments carried at fair value	5,235		4,952
Other investments carried at cost	5,235		4,952
Other Investments [Member] | Insurance and Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments carried at fair value	17,974		16,932
Other investments carried at cost	17,234		16,057
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	103,205		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]	1	[1]
Fair Value, Measurements, Recurring [Member] | Quoted Prices (Level 1) [Member] | Railroad, Utilities and Energy [Member] | Accounts Payable, Accruals and Other Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract liabilities	5	[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	62		64
Loans and finance receivables - fair value	481		304
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	15	[1]	128	[1]
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	41,194		42,074
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Railroad, Utilities and Energy [Member] | Accounts Payable, Accruals and Other Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract liabilities	164	[1]	217	[1]
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	12,509		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	19		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	13,612		14,284
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	7		35
Loans and finance receivables - fair value	11,551		11,687
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	51	[1]	91	[1]
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Railroad, Utilities and Energy [Member] | Accounts Payable, Accruals and Other Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract liabilities	9	[1]	7	[1]
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	725		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	5,874		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	348		429
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	1,128		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	4,079		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	1,682		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	2,748		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	6,159		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	10,833		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	2,244		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	631		650
Fair Value, Measurements, Recurring [Member] | Other Investments [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments carried at fair value	1,703
Fair Value, Measurements, Recurring [Member] | Other Investments [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments carried at fair value	15,497		15,750
Other investments carried at cost	18,259		6,134
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	103,274		87,662
Loans and finance receivables - carrying value	12,855		12,809
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	67	[1]	220	[1]
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	37,861		36,156
Carrying Value [Member] | Fair Value, Measurements, Recurring [Member] | Railroad, Utilities and Energy [Member] | Accounts Payable, Accruals and Other Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract liabilities	178	[1]	234	[1]
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	12,831		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	5,874		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	348		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	19		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	13,261		13,535
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	2,811		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	2,748		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	10,238		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	11,464		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	2,244		2,587
Carrying Value [Member] | Fair Value, Measurements, Recurring [Member] | Other Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments carried at fair value	17,200		15,750
Other investments carried at cost	17,519		5,259
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	103,274		87,662
Loans and finance receivables - fair value	12,032		11,991
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	67	[1]	220	[1]
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	41,194		42,074
Fair Value [Member] | Fair Value, Measurements, Recurring [Member] | Railroad, Utilities and Energy [Member] | Accounts Payable, Accruals and Other Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract liabilities	178	[1]	234	[1]
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	13,234		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	5,874		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	348		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	19		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	13,612		14,284
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	2,811		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	2,748		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	10,238		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	11,464		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	2,244		2,587
Fair Value [Member] | Fair Value, Measurements, Recurring [Member] | Other Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments carried at fair value	17,200		15,750
Other investments carried at cost	$ 18,259		$ 6,134

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