Financial and Other Derivative Instruments (Cumulative Gross Volume of Derivative Contracts Outstanding) (Details)	3 Months Ended
	Mar. 31, 2019 CAD ($) MMBTU MWh
Natural gas (MMBtu)
Derivative [Line Items]
Commodity | MMBTU	2,537,411,045
Electricity (MWh)
Derivative [Line Items]
Commodity | MWh	33,565,053
Foreign currency exchange (Canadian dollars)
Derivative [Line Items]
Foreign currency exchange (Canadian dollars) | $	$ 97,013,854