Supplemental financial information - Amounts Reclassified out of AOCI (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other income (expense), net (OI&E)		$ 27	$ 34	$ 151	$ 122
Provision for income taxes		(234)	(155)	(183)	(524)
Net income		1,353	1,425	3,907	3,947
Reclassification out of Accumulated Other Comprehensive Income | Net actuarial losses of defined benefit plans
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other income (expense), net (OI&E)	[1]	9	12	28	40
Provision for income taxes		(2)	(3)	(7)	(10)
Net income		7	9	21	30
Reclassification out of Accumulated Other Comprehensive Income | Prior service credit of defined benefit plans
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other income (expense), net (OI&E)	[1]	(1)	0	(1)	0
Provision for income taxes		0	0	0	0
Net income		$ (1)	$ 0	$ (1)	$ 0

[1] Detailed in Note 6.