Supplemental financial information - Restructuring balances (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Restructuring Reserve [Roll Forward]
Balance, January 1		$ 28	$ 29	$ 40
Restructuring charges	[1]	(15)	6	11
Non-cash items	[2]	0	(3)	(1)
Payments		(13)	(4)	(21)
Balance, December 31		$ 0	$ 28	$ 29

[1] Includes severance and benefits, accelerated depreciation, changes in estimates or other exit costs.

[2] Reflects charges for impacts of accelerated depreciation and changes in exchange rates.