Variable interest entities - Schedule of results of variable interest entities (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Variable Interest Entity [Line Items]
Gross profit	$ 4,309	$ 4,059	$ 10,172	$ 9,541
Net loss	1,503	1,376	2,728	2,789
Net cash used in operating activities			2,710	2,259
Variable interest entity, primary beneficiary
Variable Interest Entity [Line Items]
Total revenues	77	88	243	282
Total cost of revenues	(75)	(86)	(240)	(262)
Gross profit	2	2	3	20
Net loss	$ (13)	$ (10)	(43)	(22)
Net cash used in operating activities			$ (12)	$ (11)