Supplemental financial information - Amounts reclassified out of accumulated other comprehensive income (loss), net of taxes, to net income (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other income (expense), net (OI&E)										$ 175	$ 98	$ 75
Interest and debt expense										170	125	78
Provision for income taxes										(711)	(1,106)	(2,398)
Net income		$ 1,070	$ 1,425	$ 1,305	$ 1,217	$ 1,239	$ 1,570	$ 1,405	$ 1,366	5,017	5,580	3,682
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]									51	65	83
Provision for income taxes										(13)	(15)	(27)
Net income										38	50	56
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	(4)	(6)
Provision for income taxes										0	1	1
Net income										0	(3)	(5)
Reclassification out of Accumulated Other Comprehensive Income | Derivative instruments - post adoption
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest and debt expense										0
Provision for income taxes										0
Net income										$ 0
Reclassification out of Accumulated Other Comprehensive Income | Derivative instruments - pre adoption
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest and debt expense											0	1
Provision for income taxes											0	0
Net income											$ 0	$ 1

[1] Detailed in Note 8.