Derivative financial instruments and risk management (Details 6) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Offsetting Liabilities
Gross Amount of Recognized Liabilities	$ (214)	$ (50)	$ (144)
Gross Amounts Offset in the Statement of Financial Position	0	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	(214)	(50)	(144)
Financial Instruments	35	41	71
Cash Collateral Pledged	0	0	0
Net Amount of Liabilities	(179)us-gaap_DerivativeLiabilities	(9)us-gaap_DerivativeLiabilities	(73)us-gaap_DerivativeLiabilities
Machinery, Energy & Transportation
Offsetting Liabilities
Gross Amount of Recognized Liabilities	(191)	(40)	(129)
Gross Amounts Offset in the Statement of Financial Position	0	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	(191)	(40)	(129)
Financial Instruments	27	32	59
Cash Collateral Pledged	0	0	0
Net Amount of Liabilities	(164)	(8)	(70)
Financial Products
Offsetting Liabilities
Gross Amount of Recognized Liabilities	(23)	(10)	(15)
Gross Amounts Offset in the Statement of Financial Position	0	0	0
Net Amounts of Liabilities Presented in the Statement of Financial Position	(23)	(10)	(15)
Financial Instruments	8	9	12
Cash Collateral Pledged	0	0	0
Net Amount of Liabilities	$ (15)	$ (1)	$ (3)

Fair value, after offset of derivative asset, of financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, elected not to be and before offset against a right to receive collateral under a master netting arrangement. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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