Summary of significant accounting policies - Investments (Details) - Vricon - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Equity method investments
Ownership interest	50.00%
Summarized Consolidated Balance Sheets
Current assets	$ 49	$ 12
Non-current assets	5	6
Total assets	54	18
Total liabilities	10	5
Summarized Consolidated Statements of Operations
Revenues	54	21	$ 14
Gross profit	51	19	14
Income from operations	32	2	1
Net income	$ 24	$ 1	$ 1