Commitments (Narrative) (Details) (Scenario, Forecast [Member], Natural Gas [Member])	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
2015 Deliveries [Member]
Commitments and Contingencies Disclosure [Line Items]
Notional amount, per day		65
2016 Deliveries [Member]
Commitments and Contingencies Disclosure [Line Items]
Notional amount, per day	9
2015 and 2016 Deliveries [Member]
Commitments and Contingencies Disclosure [Line Items]
Underlying derivative (Cdn $ per barrel)	4.13	4.13