Supplemental cash flow - (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Supplemental cash flow information:
Cash paid for interest	$ (79)	$ (54)
Income tax payments	(1)	(1)
Supplemental non-cash investing and financing activities:
Accrued capital expenditures	13	5
Amount of interest payments made on Revolving Credit Facility	$ 42	$ 21