Financial and Other Derivative Instruments (Cumulative Gross Volume of Derivative Contracts Outstanding) (Details)	12 Months Ended
	Dec. 31, 2018 CAD ($) MWh MMBTU
Natural Gas (MMBtu)
Derivative [Line Items]
Commodity | MMBTU	2,171,541,994
Electricity (MWh)
Derivative [Line Items]
Commodity | MWh	36,163,761
Foreign Currency Exchange (Canadian dollars)
Derivative [Line Items]
Foreign Currency Exchange (Canadian dollars) | $	$ 101,975,644