Income Taxes (Summary of Income Tax Expense (Recovery)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Canadian:
Current tax expense	$ 43.4	$ 60.9	$ 21.7
Deferred tax expense	(2.7)	2.7	5.6
Foreign:
Current tax expense before application of operating loss carryforwards	100.2	29.6	30.1
Tax benefit of operating loss carryforwards	(1.4)	(4.0)	(2.2)
Total current tax expense	98.8	25.6	27.9
Deferred tax expense	(63.1)	(3.0)	(1.8)
Total deferred tax (recovery) expense	(63.1)	(3.0)	(1.8)
Income tax expense	$ 76.4	$ 86.2	$ 53.4