Income taxes (Details 3) (USD $) In Millions	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Deferred tax assets
Deferred taxes reported on line Deferred and refundable income taxes in the Statement of Financial Position	$ 824	$ 802	$ 785
Deferred taxes reported on line Noncurrent deferred and refundable income taxes in the Statement of Financial Position	2,493	2,704	3,298
Total deferred tax assets reported as Total assets in the Statement of Financial Position	3,317	3,506	4,083
Deferred tax liabilities
Deferred taxes reported on line Other current liabilities in the Statement of Financial Position	7	11	9
Deferred taxes reported on line Other liabilities in the Statement of Financial Position	141	138	130
Deferred income taxes-net	$ 3,169	$ 3,357	$ 3,944

The current portion of the aggregate tax effects as of the balance sheet date of all future tax deductions arising from temporary differences between tax basis and generally accepted accounting principles basis recognition of assets, liabilities, revenues and expenses, which can only be deducted for tax purposes when permitted under enacted tax laws; after deducting the allocated valuation allowance, if any, to reduce such amount to net realizable value. Deferred tax liabilities and assets shall be classified as current or noncurrent based on the classification of the related asset or liability for financial reporting. A deferred tax liability or asset that is not related to an asset or liability for financial reporting, including deferred tax assets related to carryforwards, shall be classified according to the expected reversal date of the temporary difference. An unrecognized tax benefit that is directly related to a position taken in a tax year that results in a net operating loss carryforward should be presented as a reduction of the related deferred tax asset.

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Represents the noncurrent portion of deferred tax liabilities, which result from applying the applicable tax rate to net taxable temporary differences pertaining to each jurisdiction to which the entity is obligated to pay income tax. A noncurrent taxable temporary difference is a difference between the tax basis and the carrying amount of a noncurrent asset or liability in the financial statements prepared in accordance with generally accepted accounting principles. In a classified statement of financial position, an enterprise shall separate deferred tax liabilities and assets into a current amount and a noncurrent amount. Deferred tax liabilities and assets shall be classified as current or noncurrent based on the classification of the related asset or liability for financial reporting. A deferred tax liability or asset that is not related to an asset or liability for financial reporting, including deferred tax assets related to carryforwards, shall be classified according to the expected reversal date of the temporary difference.

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