XML 120 R92.htm IDEA: XBRL DOCUMENT v3.8.0.1
Asset Impairment Charges and Reversals (Details) - CAD
 3 Months Ended 12 Months Ended
Jan. 26, 2017
Nov. 24, 2016
Jun. 30, 2017
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Canadian Coal            
Disclosure of impairment loss recognised or reversed [line items]            
Annual cash payments   CAD 37,400,000        
Wintering Hills            
Disclosure of impairment loss recognised or reversed [line items]            
Equity participation percentage 51.00%          
Cash transferred CAD 61,000,000          
Sundance Unit 1            
Disclosure of impairment loss recognised or reversed [line items]            
Impairment loss     CAD 20,000,000      
Centralia Gas            
Disclosure of impairment loss recognised or reversed [line items]            
Reversal of impairment loss           CAD 2,000,000
Investments accounted for using equity method | Alberta Merchant CGU            
Disclosure of impairment loss recognised or reversed [line items]            
Levy on carbon emissions in excess of defined limits       CAD 20 CAD 30  
Minimum | Investments accounted for using equity method | Alberta Merchant CGU            
Disclosure of impairment loss recognised or reversed [line items]            
Price on geenhouse gas emissions           10
Maximum | Investments accounted for using equity method | Alberta Merchant CGU            
Disclosure of impairment loss recognised or reversed [line items]            
Price on geenhouse gas emissions           CAD 50