Derivative contracts - Narrative (Detail) (Not Designated as Hedging Instrument [Member], USD $)							6 Months Ended				6 Months Ended				6 Months Ended
	Jun. 30, 2012 Finance and Financial Products [Member]	Dec. 31, 2011 Finance and Financial Products [Member]	Jun. 30, 2012 Finance and Financial Products [Member] Other Assets [Member]		Dec. 31, 2011 Finance and Financial Products [Member] Other Assets [Member]		Jun. 30, 2012 Finance and Financial Products [Member] Equity Index Put Options [Member]		Dec. 31, 2011 Finance and Financial Products [Member] Equity Index Put Options [Member]		Jun. 30, 2012 Finance and Financial Products [Member] Credit Default Contracts - High Yield Indexes [Member]		Dec. 31, 2011 Finance and Financial Products [Member] Credit Default Contracts - High Yield Indexes [Member]		Jun. 30, 2012 Finance and Financial Products [Member] Credit Default Contracts - States and Municipalities [Member]		Dec. 31, 2011 Finance and Financial Products [Member] Credit Default Contracts - States and Municipalities [Member]		Jul. 31, 2012 Finance and Financial Products [Member] Credit Default Contracts - States and Municipalities [Member] Agreement to Terminate Derivative Contracts [Member]	Jun. 30, 2012 Railroad, Utilities and Energy [Member] Other Assets [Member]	Dec. 31, 2011 Railroad, Utilities and Energy [Member] Other Assets [Member]	Jun. 30, 2012 Railroad, Utilities and Energy [Member] Accounts Payable, Accruals and Other Liabilities [Member]	Dec. 31, 2011 Railroad, Utilities and Energy [Member] Accounts Payable, Accruals and Other Liabilities [Member]
Derivative [Line Items]
Aggregate intrinsic value of equity index put option contracts							$ 5,700,000,000
Maturity date, range, start							June 2018				December 2012				2019
Maturity date, range, end							January 2026				2013				2054
Weighted average remaining life of derivative contract							8 years 6 months								8 years 9 months 18 days
Notional Value							33,463,000,000	[1]	34,014,000,000	[1]	3,258,000,000	[2]	4,568,000,000	[2]	16,042,000,000	[2]	16,042,000,000	[2]	8,250,000,000
Percent of the notional value of derivative contracts where the potential obligations cannot be settled before the maturity dates of the underlying obligations, percentage															50.00%
Collateral posting requirements under contracts with collateral provisions	271,000,000	238,000,000
Additional collateral posting requirements	1,100,000,000
Assets			219,000,000	[3]	256,000,000	[3]														39,000,000	71,000,000
Liabilities	$ 10,137,000,000	$ 10,139,000,000					$ 8,983,000,000		$ 8,499,000,000		$ 15,000,000		$ 198,000,000		$ 953,000,000		$ 1,297,000,000					$ 312,000,000	$ 336,000,000

[1] Represents the aggregate undiscounted amount payable at the contract expiration dates assuming that the value of each index is zero at the contract expiration date.

[2] Represents the maximum undiscounted future value of losses payable under the contracts. The number of losses required to exhaust contract limits under substantially all of the contracts is dependent on the loss recovery rate related to the specific obligor at the time of a default.

[3] Included in other assets of finance and financial products businesses.