Income taxes (Details 6) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Reconciliation of the beginning and ending amount of gross unrecognized tax benefits
Unrecognized tax benefits, beginning	$ 958	$ 789	$ 761
Additions for tax positions related to current year	64	118	21
Additions for tax positions related to prior years	178	108	59
Reductions for tax positions related to prior years	(266)	(30)	(49)
Reductions for settlements	(191)	0	0
Reductions for expiration of statute of limitations	(28)	(27)	(3)
Unrecognized tax benefits, ending	715	958	789
Unrecognized tax benefits that, if recognized, would impact the effective tax rate	669	835	667
Interest and penalties, recognized	(114)	39	27
Interest and penalties, accrued	$ 134	$ 240	$ 201
Length of time tax year subject to examination, minimum	3 years
Length of time tax years subject to examination, maximum	8 years

Represents the maximum length of time tax years are typically subjec to examination in major non-U.S. juridictions.

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Represents the minimum length of time tax years are typically subject to examination in major non-U.S. jurisdictions.

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The amount of estimated penalties and interest accrued as of the balance sheet date arising from income tax examinations.

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The sum of the amounts of estimated penalties and interest recognized in the period arising from income tax examinations.

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The gross amount of unrecognized tax benefits pertaining to uncertain tax positions taken in tax returns as of the balance sheet date.

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The gross amount of decreases in unrecognized tax benefits resulting from tax positions taken in prior period tax returns, excluding amounts pertaining to examined tax returns.

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The gross amount of decreases in unrecognized tax benefits resulting from settlements with taxing authorities.

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The gross amount of increases in unrecognized tax benefits resulting from tax positions that have been or will be taken in the tax return for the current period, excluding amounts pertaining to examined tax returns.

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The gross amount of decreases in unrecognized tax benefits resulting from lapses of the applicable statutes of limitations.

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The total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate.

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