Discontinued operations - Financial information Operations (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
Revenues:
Total revenues									$ 367	$ 420	$ 425
Costs and expenses:
Selling, general and administrative									88	59	54
Depreciation and amortization									11	10	10
Impairment losses									12	477	0
Operating income (loss)									23	(389)	117
Interest expense, net									1	1	1
Other (income) expense, net									3		(6)
Income (loss) before taxes									19	(390)	122
Income tax expense (benefit)									(7)	(13)	6
Income (loss) from discontinued operations, net of tax	$ (10)	$ 16	$ 9	$ 11	$ (456)	$ 23	$ 15	$ 41	26	(377)	116
Product
Revenues:
Total revenues									206	238	275
Costs and expenses:
Costs, excluding depreciation and amortization									149	149	158
Service
Revenues:
Total revenues									161	182	150
Costs and expenses:
Costs, excluding depreciation and amortization									$ 84	$ 114	$ 86