Employee benefit plans - Components of net periodic benefit (credits) cost (Details) - Pensions Plans - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Employee benefit plans
Service cost	$ 1	$ 2
Interest cost	6
Expected return on plan assets	(6)
Net periodic benefit (credit) cost	$ 1	$ 2