Income taxes - Reconciliation of unrecognized tax benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Reconciliation of the beginning and ending amount of gross unrecognized tax benefits
Beginning balance	$ 1,223	$ 1,140	$ 1,886
Additions for tax positions related to current year	118	94	72
Additions for tax positions related to prior years	49	42	91
Reductions for tax positions related to prior years	(30)	(19)	(66)
Reductions for settlements	(60)	(27)	(840)
Reductions for expiration of statute of limitations	(11)	(7)	(3)
Ending balance	1,289	1,223	1,140
Amount that, if recognized, would impact the effective tax rate	$ 1,137	$ 997	$ 874