Equity Earnings Per Share (Details) - CAD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net Income Available to Restricted Voting Stockholders		$ 416.2	$ 27.9	$ 0.0
Restricted Stock
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	0.2
Participating Securities
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Unvested Restricted Stock Awards, Issued and Non Issued		0.2	0.3
Restricted Voting Shares
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Weighted Average Number of Shares Outstanding, Basic		34.7	27.6
Restricted Voting Shares | Restricted Stock
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements		0.2	0.2
Discontinued Operations [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net Income Available to Restricted Voting Stockholders		$ 394.4	$ 19.0
Discontinued Operations [Member] | Participating Securities
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net Income Available to Restricted Voting Stockholders		0.4	0.2
Discontinued Operations [Member] | Restricted Voting Shares
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net Income Available to Restricted Voting Stockholders		$ 394.0	$ 18.8
Earnings Per Share, Basic		$ 11.37	$ 0.69
Continuing Operations [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net Income Available to Restricted Voting Stockholders		$ 21.8	$ 8.9
Continuing Operations [Member] | Participating Securities
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net Income Available to Restricted Voting Stockholders		0.4	0.2
Continuing Operations [Member] | Restricted Voting Shares
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net Income Available to Restricted Voting Stockholders		$ 21.4	$ 8.7
Earnings Per Share, Basic		$ 0.62	$ 0.31