Supplemental financial information - Restructuring balances (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Restructuring Reserve [Roll Forward]
Balance, January 1		$ 0	$ 28	$ 29
Restructuring charges	[1]	25	(15)	6
Non-cash items	[2]	(1)
Non-cash items	[2]		0	(3)
Payments		(8)	(13)	(4)
Balance, December 31		$ 18	$ 0	$ 28

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

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