Supplemental financial information - Amounts Reclassified out of AOCI (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other income (expense), net (OI&E)		$ 34	$ 23	$ 122	$ 75
Provision for income taxes		(155)	(354)	(524)	(842)
Net income		1,425	1,570	3,947	4,341
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]	12	20	40	43
Provision for income taxes		(3)	(5)	(10)	(10)
Net income		9	15	30	33
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]	0	(1)	0	(3)
Provision for income taxes		0	0	0	0
Net income		$ 0	$ (1)	$ 0	$ (3)

[1] Detailed in Note 6.