Regulatory Matters Regulatory Matters (Details) - Alberta Utilities Commission [Member] - AltaLink [Member] CAD in Millions, $ in Millions	1 Months Ended				3 Months Ended		6 Months Ended
	Jul. 31, 2016 USD ($)	Jul. 31, 2016 CAD	Oct. 31, 2015 CAD	Nov. 30, 2014 CAD	Jun. 30, 2016 USD ($)	Jun. 30, 2016 CAD	Jun. 30, 2016 USD ($)
Schedule Of Regulatory Assets and Liabilities [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount						CAD 225	$ 225
2015-2016 GTA [Member] | GTA 2015 [Member]
Schedule Of Regulatory Assets and Liabilities [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount				CAD 811
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount			CAD 672
2015-2016 GTA [Member] | GTA 2016 [Member]
Schedule Of Regulatory Assets and Liabilities [Line Items]
Public Utilities, Requested Rate Increase (Decrease), Amount				CAD 1,000
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount			CAD 704
Subsequent Event [Member]
Schedule Of Regulatory Assets and Liabilities [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount		CAD 415
Subsequent Event [Member] | 2015-2016 GTA [Member]
Schedule Of Regulatory Assets and Liabilities [Line Items]
Public Utilities, approved rate increase (decrease) per month		61
Public Utilities, requested rate increase (decrease) per month | $	$ 12
Subsequent Event [Member] | 2015-2016 GTA [Member] | GTA 2015 [Member]
Schedule Of Regulatory Assets and Liabilities [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount		599
Subsequent Event [Member] | 2015-2016 GTA [Member] | GTA 2016 [Member]
Schedule Of Regulatory Assets and Liabilities [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount		685
Amount for discontinuance of CWIP in rate base [Member] | Subsequent Event [Member]
Schedule Of Regulatory Assets and Liabilities [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount		82
Amount previously collected as CWIP given as refund [Member]
Schedule Of Regulatory Assets and Liabilities [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount | $					$ 200		200
Amount previously collected as CWIP given as refund [Member] | Subsequent Event [Member]
Schedule Of Regulatory Assets and Liabilities [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount		277
Amount previously collected as CWIP given as returns [Member] | Subsequent Event [Member]
Schedule Of Regulatory Assets and Liabilities [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount		12
Amount for change to flow through method for income taxes [Member]
Schedule Of Regulatory Assets and Liabilities [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount						CAD 25	$ 25
Amount for change to flow through method for income taxes [Member] | Subsequent Event [Member]
Schedule Of Regulatory Assets and Liabilities [Line Items]
Public Utilities, Approved Rate Increase (Decrease), Amount		CAD 68