Income taxes: Loss carry-forwards (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($)
Net operating loss carry-forwards
Net operating loss carry-forwards	$ 1,000.0
United States
Net operating loss carry-forwards
Net operating loss carry-forwards	39.5
Carry-forwards limited for use	25.6
Europe
Net operating loss carry-forwards
Net operating loss carry-forwards	967,900.0
Carry-forwards limited for use	141.2
Carry-forwards not limited for use	826.7
Mexico
Net operating loss carry-forwards
Net operating loss carry-forwards	7.3
Other than United States
Net operating loss carry-forwards
Carry-forwards not limited for use	$ 1,000.0