Employee benefit plans - Components of net periodic benefit cost (Details) - Pension - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Employee benefit plans
Interest cost	$ 3	$ 4	$ 10	$ 13
Expected return on plan assets	(7)	(7)	(21)	(20)
Amortization of net loss	1		4	1
Expenses paid	1	1	2	2
Net periodic benefit income	$ (2)	$ (2)	$ (5)	$ (4)