Significant accounting policies (Details) shares in Millions	6 Months Ended
	Jun. 30, 2024 subsidiary shares	Jun. 30, 2023 shares
Accounting Policies [Abstract]
Number of wholly-owed subsidiaries | subsidiary	1
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Anti-dilutive common shares excluded from calculation of loss per common share (in shares)		20.2
Employee Stock Option
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Anti-dilutive common shares excluded from calculation of loss per common share (in shares)	20.5