Fair value measurements - Financial assets and liabilities (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in equity securities	$ 88,027		$ 76,991
Insurance and Other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities	31,021		31,222
Investments in equity securities	87,088		76,063
Other investments - carrying value	14,980		13,111
Notes payable and other borrowings - carrying value	13,405		13,768
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	35,732		32,580
Finance and Financial Products [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities	868		966
Other investments - carrying value	4,719		3,810
Loans and finance receivables - carrying value	13,230		13,934
Derivative contract liabilities	10,090		10,139
Notes payable and other borrowings - carrying value	13,372		14,036
Fixed Maturities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities	31,889		32,188
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	2,583		2,935
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	2,829		3,070
Fixed Maturities [Member] | Foreign governments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities	11,530		10,843
Fixed Maturities [Member] | Corporate bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities	12,338		12,448
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	2,609		2,892
Assets and liabilities not carried at fair value [Member] | 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]
Loans and finance receivables - fair value	968
Assets and liabilities not carried at fair value [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans and finance receivables - fair value	11,745
Assets and liabilities not carried at fair value [Member] | 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	14,198
Assets and liabilities not carried at fair value [Member] | 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	42,084
Assets and liabilities not carried at fair value [Member] | Fair Value, Measurements, Recurring [Member] | Finance and Financial Products [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	13,529
Assets and liabilities not carried at fair value [Member] | Fair Value, Measurements, Recurring [Member] | Finance and Financial Products [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	843
Assets and liabilities not carried at fair value [Member] | Fair Value, Measurements, Recurring [Member] | Other Fixed Maturities and Equity Securities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments - fair value	6,189
Assets and liabilities carried at fair value [Member] | 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	87,928		76,906
Assets and liabilities carried at fair value [Member] | 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		63
Assets and liabilities carried at fair value [Member] | 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	245	[1]	205	[1]
Assets and liabilities carried at fair value [Member] | 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		22
Assets and liabilities carried at fair value [Member] | 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	98	[1]	122	[1]
Assets and liabilities carried at fair value [Member] | Fair Value, Measurements, Recurring [Member] | Railroad, Utilities and Energy [Member] | Quoted Prices (Level 1) [Member] | Accounts Payable, Accruals and Other Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract liabilities	11	[2]	12	[2]
Assets and liabilities carried at fair value [Member] | Fair Value, Measurements, Recurring [Member] | Railroad, Utilities and Energy [Member] | Significant Other Observable Inputs (Level 2) [Member] | Accounts Payable, Accruals and Other Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract liabilities	212	[2]	320	[2]
Assets and liabilities carried at fair value [Member] | Fair Value, Measurements, Recurring [Member] | Railroad, Utilities and Energy [Member] | Significant Unobservable Inputs (Level 3) [Member] | Accounts Payable, Accruals and Other Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract liabilities	7	[2]	4	[2]
Assets and liabilities carried at fair value [Member] | Fair Value, Measurements, Recurring [Member] | Finance and Financial Products [Member] | Significant Other Observable Inputs (Level 2) [Member] | Other Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract liabilities	81		113
Assets and liabilities carried at fair value [Member] | Fair Value, Measurements, Recurring [Member] | Finance and Financial Products [Member] | Significant Unobservable Inputs (Level 3) [Member] | Equity Index Put Options [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract liabilities	9,517		8,499
Assets and liabilities carried at fair value [Member] | Fair Value, Measurements, Recurring [Member] | Finance and Financial Products [Member] | Significant Unobservable Inputs (Level 3) [Member] | Credit Default Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract liabilities	492		1,527
Assets and liabilities carried at fair value [Member] | Fair Value, Measurements, Recurring [Member] | Other Fixed Maturities and Equity Securities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments - fair value	14,445		11,669
Assets and liabilities carried at fair value [Member] | 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	1,111		843
Assets and liabilities carried at fair value [Member] | 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	4,694		4,444
Assets and liabilities carried at fair value [Member] | 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	1,470		2,090
Assets and liabilities carried at fair value [Member] | 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	2,829		3,069
Assets and liabilities carried at fair value [Member] | 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	6,836		6,265
Assets and liabilities carried at fair value [Member] | 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	11,687		11,801
Assets and liabilities carried at fair value [Member] | 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	2,609		2,892
Assets and liabilities carried at fair value [Member] | 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	2		2
Assets and liabilities carried at fair value [Member] | 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
Assets and liabilities carried at fair value [Member] | Fair Value, Measurements, Recurring [Member] | Fixed Maturities [Member] | Significant Unobservable Inputs (Level 3) [Member] | Foreign governments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in fixed maturity securities			134
Assets and liabilities carried at fair value [Member] | 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	651		647
Carrying Value [Member] | Assets and liabilities not carried at fair value [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans and finance receivables - carrying value	13,230		13,934
Carrying Value [Member] | Assets and liabilities not carried at 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 - carrying value	13,405		13,768
Carrying Value [Member] | Assets and liabilities not carried at 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 - carrying value	35,732		32,580
Carrying Value [Member] | Assets and liabilities not carried at 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 - carrying value	13,372		14,036
Carrying Value [Member] | Assets and liabilities not carried at 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 - carrying value	5,254		5,252
Carrying Value [Member] | Assets and liabilities carried at 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	88,027		76,991
Carrying Value [Member] | Assets and liabilities carried at 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	343	[1]	327	[1]
Carrying Value [Member] | Assets and liabilities carried at 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	230	[2]	336	[2]
Carrying Value [Member] | Assets and liabilities carried at 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	9,517		8,499
Carrying Value [Member] | Assets and liabilities carried at 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	492		1,527
Carrying Value [Member] | Assets and liabilities carried at fair value [Member] | Fair Value, Measurements, Recurring [Member] | Finance and Financial Products [Member] | Other Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract liabilities	81		113
Carrying Value [Member] | Assets and liabilities carried at 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 - carrying value	14,445		11,669
Carrying Value [Member] | Assets and liabilities carried at 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	2,583		2,935
Carrying Value [Member] | Assets and liabilities carried at 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	2,829		3,070
Carrying Value [Member] | Assets and liabilities carried at 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	11,530		10,843
Carrying Value [Member] | Assets and liabilities carried at 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	12,338		12,448
Carrying Value [Member] | Assets and liabilities carried at 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	2,609		2,892
Fair Value [Member] | Assets and liabilities not carried at fair value [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans and finance receivables - fair value	12,713		13,126
Fair Value [Member] | Assets and liabilities not carried at 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	14,198		14,334
Fair Value [Member] | Assets and liabilities not carried at 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	42,084		38,257
Fair Value [Member] | Assets and liabilities not carried at 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	14,372		14,959
Fair Value [Member] | Assets and liabilities not carried at 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 - fair value	6,189		6,258
Fair Value [Member] | Assets and liabilities carried at 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	88,027		76,991
Fair Value [Member] | Assets and liabilities carried at 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	343	[1]	327	[1]
Fair Value [Member] | Assets and liabilities carried at 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	230	[2]	336	[2]
Fair Value [Member] | Assets and liabilities carried at 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	9,517		8,499
Fair Value [Member] | Assets and liabilities carried at 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	492		1,527
Fair Value [Member] | Assets and liabilities carried at fair value [Member] | Fair Value, Measurements, Recurring [Member] | Finance and Financial Products [Member] | Other Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative contract liabilities	81		113
Fair Value [Member] | Assets and liabilities carried at 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 - fair value	14,445		11,669
Fair Value [Member] | Assets and liabilities carried at 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	2,583		2,935
Fair Value [Member] | Assets and liabilities carried at 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	2,829		3,070
Fair Value [Member] | Assets and liabilities carried at 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	11,530		10,843
Fair Value [Member] | Assets and liabilities carried at 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	12,338		12,448
Fair Value [Member] | Assets and liabilities carried at 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	$ 2,609		$ 2,892

[1] Included in other assets.

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