Trans Mountain Transaction (Details) $ / shares in Units, $ in Millions			8 Months Ended	12 Months Ended
	Nov. 29, 2018 CAD ($) $ / shares	Aug. 31, 2018 CAD ($)	Aug. 31, 2018 CAD ($)	Dec. 31, 2018 CAD ($)	Dec. 31, 2017 CAD ($)	Dec. 31, 2016 CAD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net Proceeds from Sale of the Trans Mountain Asset Group				$ 3,913.4	$ 0.0	$ 0.0
Stockholders Equity, Return Of Capital				3,977.4
Reduction of Capital				1,450.0
Benefit plan losses relates to he Trans Mountain Transactions				1,278.4	0.0	0.0
Increase (Decrease) in Accrued Taxes Payable				303.8	10.2	(0.5)
Major income and expense line items:
Income from Discontinued Operations, Net of Tax				1,318.2	110.2	131.4
Net cash provided by (used in)
Write off of deferred financing costs				60.5	0.0	0.0
Revolving Credit Facility [Member]
Net cash provided by (used in)
Line of Credit Facility, Maximum Borrowing Capacity				500.0
Voting Shares
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Stockholders Equity, Return Of Capital	$ 1,200.0
Return of capital, per share | $ / shares	$ 11.40
Kinder Morgan interest
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Stockholders Equity, Return Of Capital	$ 2,800.0			2,782.3
Trans Mountain Transaction [Member] | Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net Proceeds from Sale of the Trans Mountain Asset Group		$ 4,430.0
Contracted Purchase Price		4,500.0	$ 4,500.0
Working capital adjustments				37.0
Trans Mountain Asset Group, AOCL		26.2	26.2
Benefit plan losses relates to he Trans Mountain Transactions				1,278.4
Tax benefit included in Gain on sale of Trans Mountain Asset Group				81.4
Release of Deferred Income Taxes				389.0
Increase (Decrease) in Accrued Taxes Payable				$ 307.6
Major income and expense line items:
Revenues			214.3		324.9	328.3
Depreciation and amortization			(46.8)		(70.7)	(73.0)
Operating expenses, including general and administrative			(89.8)		(122.0)	(115.5)
Interest and other income (expense)			(22.4)		21.4	24.5
Income from operations of the Trans Mountain Asset Group before income taxes			55.3		153.6	164.3
Gain on sale of Trans Mountain Asset Group before income taxes			1,197.0		0.0	0.0
Income from Discontinued Operations before income taxes			1,252.3		153.6	164.3
Income tax benefit (expense)			65.9		(43.4)	(32.9)
Income from Discontinued Operations, Net of Tax			1,318.2		110.2	131.4
Carrying value of assets and liabilities:
Cash and cash equivalents		502.4	502.4		128.1
Accounts receivable					46.0
Other current assets					18.6
Property, Plant and Equipment, net					2,719.6
Goodwill					248.0
Non-current regulatory assets					29.1
Other non-current assets					53.7
Total assets of the Trans Mountain Asset Group					3,243.1
Credit Facility		$ 559.8	559.8		0.0
Accounts Payable					97.6
Current regulatory liabilities					103.1
Other current liabilities					6.6
Pension and postretirement benefits					75.4
Other non-current liabilities					38.1
Total liabilities of the Trans Mountain Asset Group					320.8
Net cash provided by (used in)
Operating activities			182.3		58.1	25.5
Investing activities			(507.3)		$ (462.6)	$ (190.3)
Write off of deferred financing costs			$ 60.5
Restricted Voting Shares
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Stockholders' Equity Note, Stock Split, Conversion Ratio				0.33
Special Voting Shares
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Stockholders' Equity Note, Stock Split, Conversion Ratio				0.33