Income Taxes Components (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Current tax expense (benefit)	$ 43.1	$ 6.8	$ 0.4
Deferred tax expense	(5.3)	14.0	23.0
Total tax provision	$ 37.8	$ 20.8	$ 23.4