Supplemental financial information - Restructuring charges and other (Details) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure Text Block Supplement [Abstract]
Restructuring charges	[1]									$ (15)	$ 6	$ 11
Gains on sales of assets										(21)	(3)	0
Restructuring charges/other		$ 0	$ 0	$ (36)	$ 0	$ (2)	$ 1	$ 3	$ 1	$ (36)	$ 3	$ 11

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