Income taxes (Income Before Income Taxes) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Examination [Line Items]
Income before income taxes	$ 9,545	$ 9,597	$ 9,163
Domestic [Member]
Income Tax Examination [Line Items]
Income before income taxes	4,856	4,436	4,478
Foreign [Member]
Income Tax Examination [Line Items]
Income before income taxes	$ 4,689	$ 5,161	$ 4,685

Amount of income (loss) from continuing operations before deduction of income tax expense (benefit) and income (loss) attributable to noncontrolling interest, and addition of income (loss) from equity method investments.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(h)(1)(i))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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Period Type:	duration