Summary of significant accounting policies - Investments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jul. 01, 2020
Summarized Consolidated Balance Sheets
Current assets	$ 468	$ 1,261
Total assets	4,483	5,157
Total liabilities	663	996
Total liabilities	3,547	4,395
Summarized Consolidated Statement of Operations
Net income (loss)	$ 303	109	$ (1,250)
Vricon
Equity method investments
Remaining ownership interest acquired				50.00%
Vricon
Summarized Consolidated Balance Sheets
Current assets		49
Non-current assets		5
Total assets		54
Total liabilities		10
Summarized Consolidated Statement of Operations
Revenues		54	21
Gross profit		51	19
Income from operations		32	2
Net income (loss)		$ 24	$ 1