Income taxes (Details 7) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of the beginning and ending amount of gross unrecognized tax benefits
Unrecognized tax benefits, beginning	$ 1,796	$ 1,286	$ 1,032
Additions for tax positions related to current year	72	61	270
Additions for tax positions related to prior years	112	461	20
Reductions for tax positions related to prior years	(201)	(5)	(27)
Reductions for settlements	0	(6)	(9)
Reductions for expiration of statute of limitations	(1)	(1)	0
Unrecognized tax benefits, ending	1,778	1,796	1,286
Unrecognized tax benefits that, if recognized, would impact the effective tax rate	1,616	1,716	1,209
Net provision for interest and penalties	43	42	$ 38
Interest and penalties, accrued	233	$ 190
Income tax examination, proposed liability increase/(decrease)	$ 2,300

The amount of taxing authority proposed additional income tax and penalty for prior years.

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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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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount of unrecognized tax benefits.

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Amount of decrease in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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Amount of decrease in unrecognized tax benefits resulting from settlements with taxing authorities.

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Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return.

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Amount of increase in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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Amount of decrease in unrecognized tax benefits resulting from lapses of 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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