Equity (Additional Details) (Details) - CAD ($) $ / shares in Units, shares in Millions, $ in Millions		12 Months Ended
	Nov. 29, 2018	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017
Stockholders Equity, Return Of Capital		$ 3,977.4
Percentage approval needed by shareholders			66.66%
Stated Capital Reduction(Note 3)		$ 0.0
Voting Shares
Voting Shares, Outstanding		116.3
Restricted Voting Shares | Voting Shares
Voting Shares, Outstanding		34.9
Special Voting Shares | Voting Shares
Voting Shares, Outstanding		81.4
Cumulative Redeemable Minimum Rate Reset Preferred Shares, Series 1 [Member] | Preferred Stock [Member]
Preferred Stock, Shares Outstanding		12.0
Cumulative Redeemable Minimum Rate Reset Preferred Shares, Series 3 [Member] | Preferred Stock [Member]
Preferred Stock, Shares Outstanding		10.0
Participating Securities
RSUs outstanding		0.2		0.3
Voting Shares
Stockholders Equity, Return Of Capital	$ 1,200.0
Return of capital, per share	$ 11.40
Retained earnings (deficit)
Stockholders Equity, Return Of Capital		$ 1,195.1
Stated Capital Reduction(Note 3)		(1,450.0)
Kinder Morgan interest
Stockholders Equity, Return Of Capital	$ 2,800.0	$ 2,782.3