Employee benefit plans - Components of net periodic benefit cost (Details) - Pension - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Employee benefit plans
Interest cost	$ 3	$ 4
Expected return on plan assets	(7)	(6)
Amortization of net loss	1
Expenses paid	1	1
Net periodic benefit cost	$ (2)	$ (1)