Employee benefit plans - Components of net periodic benefit cost (Details) - Pension - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Employee benefit plans
Interest cost	$ 4	$ 5
Expected return on plan assets	(6)	(6)
Expenses paid	1	$ 1
Net periodic benefit cost	$ (1)