Deferred revenues (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Revenue from Contract with Customer [Abstract]
Deferred revenues	$ 1,100		$ 1,100		$ 1,400
Revenue recognized included in beginning deferred revenue	$ 54	$ 100	$ 1,300	$ 1,400