v3.4.0.3
Equity (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2016
Mar. 31, 2015
Increase (decrease) in shareholders' equity    
Balance at the beginning of the period $ 435.2 $ 816.5
Net income (loss) (12.9) 12.3
Realized and unrealized gain on hedging activities, net of tax (0.3) (0.3)
Foreign currency translation adjustments 18.5 (35.1)
Common share repurchases (0.9)  
Stock-based compensation 0.6 0.4
Dividends paid to noncontrolling interests   (2.7)
Dividends declared on common shares   (2.9)
Dividends declared on preferred shares of a subsidiary company (2.0) (2.3)
Balance at the end of the period 438.2 785.9
Total Atlantic Power Corporation Shareholder's Equity    
Increase (decrease) in shareholders' equity    
Balance at the beginning of the period 213.9 356.2
Net income (loss) (14.9) 17.5
Realized and unrealized gain on hedging activities, net of tax (0.3) (0.3)
Foreign currency translation adjustments 18.5 (35.1)
Common share repurchases (0.9)  
Stock-based compensation 0.6 0.4
Dividends declared on common shares   (2.9)
Balance at the end of the period 216.9 335.8
Preferred Shares of A Subsidiary Company    
Increase (decrease) in shareholders' equity    
Balance at the beginning of the period 221.3 221.3
Net income (loss) 2.0 2.3
Dividends declared on preferred shares of a subsidiary company (2.0) (2.3)
Balance at the end of the period $ 221.3 221.3
Noncontrolling Interests    
Increase (decrease) in shareholders' equity    
Balance at the beginning of the period   239.0
Net income (loss)   (7.5)
Dividends paid to noncontrolling interests   (2.7)
Balance at the end of the period   $ 228.8