Employee benefit plans - Components of net periodic benefit cost (Details) - Pension - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Employee benefit plans
Interest cost	$ 5	$ 5	$ 9	$ 10
Expected return on plan assets	(7)	(6)	(13)	(12)
Amortization of net loss (gain)	1		1
Expenses paid			1	1
Net periodic benefit cost	$ (1)	$ (1)	$ (2)	$ (1)