Equity (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		7 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016
Increase (decrease) in shareholders' equity
Balance at the beginning of the period			$ 435.2	$ 816.5
Net (loss) income			(29.3)	25.8
Realized and unrealized gain on hedging activities, net of tax		$ 0.3	(0.3)
Foreign currency translation adjustments	$ 1.0	4.5	19.4	(30.6)
Common share repurchases			(4.7)
Stock-based compensation			0.8	1.0
Dividends paid to noncontrolling interests				(3.7)
Dividends declared on common shares				(5.8)
Dividends declared on preferred shares of a subsidiary company			(4.2)	(4.6)
Derecognition of noncontrolling interests upon sale of subsidiaries				(224.3)
Balance at the end of the period	416.9	574.3	416.9	574.3	$ 416.9
Stock Repurchase Program
Total Number of Shares Purchased					2,025,080
Common stock repurchased, value					$ 4.7
Total Atlantic Power Corporation Shareholder's Equity
Increase (decrease) in shareholders' equity
Balance at the beginning of the period			213.9	356.2
Net (loss) income			(33.5)	32.2
Realized and unrealized gain on hedging activities, net of tax			(0.3)
Foreign currency translation adjustments			19.4	(30.6)
Common share repurchases			(4.7)
Stock-based compensation			0.8	1.0
Dividends declared on common shares				(5.8)
Balance at the end of the period	195.6	353.0	195.6	353.0	195.6
Preferred Shares of A Subsidiary Company
Increase (decrease) in shareholders' equity
Balance at the beginning of the period			221.3	221.3
Net (loss) income			4.2	4.6
Dividends declared on preferred shares of a subsidiary company			(4.2)	(4.6)
Balance at the end of the period	$ 221.3	$ 221.3	$ 221.3	221.3	$ 221.3
Noncontrolling Interests
Increase (decrease) in shareholders' equity
Balance at the beginning of the period				239.0
Net (loss) income				(11.0)
Dividends paid to noncontrolling interests				(3.7)
Derecognition of noncontrolling interests upon sale of subsidiaries				$ (224.3)