CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Project revenue:
Project revenue	$ 272.0	$ 281.6
Project expenses:
Fuel	70.9	72.3
Operations and maintenance	89.5	77.0
Depreciation and amortization	59.7	64.5
Total project expenses	220.1	213.8
Project other income (loss):
Change in fair value of derivative instruments (Notes 14 and 15)	6.8	(8.9)
Equity in earnings (loss) of unconsolidated affiliates (Note 6)	42.9	(3.0)
Interest, net	(1.2)	(1.1)
Impairment (Note 8)		(5.8)
Insurance gain (loss) (Note 23)	16.4	(1.0)
Other income (expense), net	2.1	(1.2)
Total project other income (loss)	67.0	(21.0)
Project income (loss)	118.9	46.8
Administrative and other expenses:
Administration	24.8	23.9
Interest expense, net	42.4	44.0
Foreign exchange loss	5.1	11.9
Other (income) expense, net (Note 14)	(2.7)	1.0
Total administrative and other expenses	69.6	80.8
Income (loss) from operations before income taxes	49.3	(34.0)
Income tax (benefit) expense (Note 16)	(24.2)	9.8
Net income (loss)	73.5	(43.8)
Net loss attributable to preferred shares of a subsidiary company (Note 20)	(0.7)	(1.2)
Net income (loss) attributable to Atlantic Power Corporation	$ 74.2	$ (42.6)
Net earnings (loss) per share attributable to Atlantic Power Corporation shareholders: (Note 21)
Basic (in dollars per share)	$ 0.77	$ (0.39)
Diluted (in dollars per share)	$ 0.62	$ (0.39)
Weighted average number of common shares outstanding: (Note 21)
Basic (in shares)	95.8	109.3
Diluted (in shares)	124.9	109.3
Energy sales
Project revenue:
Project revenue	$ 137.9	$ 138.0
Energy capacity revenue
Project revenue:
Project revenue	113.8	125.4
Other
Project revenue:
Project revenue	$ 20.3	$ 18.2