v2.4.0.8
Equity (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended 9 Months Ended
Sep. 30, 2013
Sep. 30, 2012
Sep. 30, 2013
Sep. 30, 2012
Increase (decrease) in shareholders' equity        
Balance     $ 1,186.4 $ 1,115.8
Net income (loss) (40.6) (4.5) (31.7) (45.8)
Realized and unrealized loss on hedging activities, net of tax 0.1 (0.2) 1.1 (0.3)
Foreign currency translation adjustment, net of tax 10.7 19.3 (19.3) 22.6
Common shares issuance, net of costs       67.8
Common shares issued for LTIP     1.2 1.5
Contribution by and sale of noncontrolling interest     44.6  
Costs associated with tax equity raise     (0.9)  
Dividends paid to noncontrolling interest     (4.4)  
Dividends declared on common shares     (46.5) (99.0)
Dividends declared on preferred shares of a subsidiary company     (9.5) (9.8)
Balance 1,121.0 1,052.8 1,121.0 1,052.8
Total Atlantic Power Corporation Shareholders' Equity
        
Increase (decrease) in shareholders' equity        
Balance     729.7 891.5
Net income (loss)     (37.9) (54.9)
Realized and unrealized loss on hedging activities, net of tax     1.1 (0.3)
Foreign currency translation adjustment, net of tax     (19.3) 22.6
Common shares issuance, net of costs       67.8
Common shares issued for LTIP     1.2 1.5
Costs associated with tax equity raise     (0.9)  
Dividends declared on common shares     (46.5) (99.0)
Balance 627.4 829.2 627.4 829.2
Preferred shares issued by a subsidiary company
        
Increase (decrease) in shareholders' equity        
Balance     221.3 221.3
Net income (loss)     9.5 9.8
Dividends declared on preferred shares of a subsidiary company     (9.5) (9.8)
Balance 221.3 221.3 221.3 221.3
Noncontrolling Interests
        
Increase (decrease) in shareholders' equity        
Balance     235.4 3.0
Net income (loss)     (3.3) (0.7)
Contribution by and sale of noncontrolling interest     44.6  
Dividends paid to noncontrolling interest     (4.4)  
Balance $ 272.3 $ 2.3 $ 272.3 $ 2.3