Income taxes - Reconciliation of unrecognized tax benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Reconciliation of the beginning and ending amount of gross unrecognized tax benefits
Beginning balance	$ 1,140	$ 1,886	$ 1,759
Additions for tax positions related to current year	94	72	141
Additions for tax positions related to prior years	42	91	43
Reductions for tax positions related to prior years	(19)	(66)	(30)
Reductions for settlements	(27)	(840)	(24)
Reductions for expiration of statute of limitations	(7)	(3)	(3)
Ending balance	1,223	1,140	1,886
Amount that, if recognized, would impact the effective tax rate	$ 997	$ 874	$ 1,688