v2.4.0.6
Equity (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Increase (decrease) in shareholders' equity    
Balance $ 1,186.4 $ 1,115.8
Net income (loss) 7.8 (39.3)
Net income (loss) 7.8 (39.2)
Realized and unrealized loss on hedging activities, net of tax 0.3 0.2
Realized and unrealized loss on hedging activities, net of tax 0.3 0.3
Foreign currency translation adjustment, net of tax (12.1) 17.2
Common shares issued for LTIP 0.3 0.2
Contribution by noncontrolling interest 2.0  
Costs associated with tax equity raise (0.7)  
Dividends paid to noncontrolling interest (1.0)  
Dividends declared on common shares (24.6) (32.4)
Dividends declared on preferred shares of a subsidiary company (3.2) (3.2)
Balance 1,155.2 1,058.5
Total Atlantic Power Corporation Shareholders' Equity
    
Increase (decrease) in shareholders' equity    
Balance 729.7 891.5
Net income (loss) 6.5 (42.3)
Realized and unrealized loss on hedging activities, net of tax 0.3 0.2
Foreign currency translation adjustment, net of tax (12.1) 17.2
Common shares issued for LTIP 0.3 0.2
Costs associated with tax equity raise (0.7)  
Dividends declared on common shares (24.6) (32.4)
Balance 699.4 834.4
Preferred shares issued by a subsidiary company
    
Increase (decrease) in shareholders' equity    
Balance 221.3 221.3
Net income (loss) 3.2 3.2
Dividends declared on preferred shares of a subsidiary company (3.2) (3.2)
Balance 221.3 221.3
Noncontrolling Interests
    
Increase (decrease) in shareholders' equity    
Balance 235.4 3.0
Net income (loss) (1.9) (0.2)
Contribution by noncontrolling interest 2.0  
Dividends paid to noncontrolling interest (1.0)  
Balance $ 234.5 $ 2.8