v2.4.0.8
Guarantees and condensed consolidating financial information (Details 5) (USD $)
In Millions, unless otherwise specified
 6 Months Ended
Jun. 30, 2013
Jun. 30, 2012
Condensed consolidating statement of cash flows    
Net cash provided by operating activities $ 96.9  
Cash flows provided by (used in) investing activities:    
Grant proceeds from treasury 53.7  
Proceeds from sale of assets 148.3  
Cash (paid) received from equity investment   24.2
Change in restricted cash (19.4) 2.3
Biomass development costs (0.1) (0.2)
Construction in progress (26.2) (230.2)
Purchase of property, plant and equipment (5.0)  
Net cash provided by (used in) investing activities 151.3  
Cash flows provided by (used in) financing activities:    
Offering costs related to tax equity (1.0)  
Repayment of project-level debt (64.2) (9.3)
Proceeds from project-level debt 20.8 255.3
Payments for revolving credit facility borrowings (67.0) (60.8)
Equity investment from noncontrolling interest 44.6  
Dividends paid (52.5) (71.4)
Net cash provided by financing activities (119.3)  
Net increase (decrease) in cash and cash equivalents 128.9  
Cash and cash equivalents at beginning of period 60.2 60.7
Cash and cash equivalents at end of period 195.6 62.7
Guarantor Subsidiaries
    
Condensed consolidating statement of cash flows    
Net cash provided by operating activities 45.6  
Cash flows provided by (used in) investing activities:    
Grant proceeds from treasury 53.7  
Proceeds from sale of assets 148.3  
Cash (paid) received from equity investment 5.5  
Change in restricted cash (19.4)  
Biomass development costs (0.1)  
Construction in progress (26.2)  
Purchase of property, plant and equipment (3.6)  
Net cash provided by (used in) investing activities 158.2  
Cash flows provided by (used in) financing activities:    
Offering costs related to tax equity (1.0)  
Repayment of project-level debt (64.2)  
Proceeds from project-level debt 20.8  
Payments for revolving credit facility borrowings (47.0)  
Equity investment from noncontrolling interest 42.7  
Dividends paid (9.3)  
Net cash provided by financing activities (58.0)  
Net increase (decrease) in cash and cash equivalents 145.8  
Cash and cash equivalents at beginning of period 49.8  
Cash and cash equivalents at end of period 195.6  
Curtis Palmer
    
Condensed consolidating statement of cash flows    
Net cash provided by operating activities 1.4  
Cash flows provided by (used in) investing activities:    
Purchase of property, plant and equipment (1.4)  
Net cash provided by (used in) investing activities (1.4)  
Atlantic Power
    
Condensed consolidating statement of cash flows    
Net cash provided by operating activities 49.9  
Cash flows provided by (used in) investing activities:    
Cash (paid) received from equity investment (5.5)  
Net cash provided by (used in) investing activities (5.5)  
Cash flows provided by (used in) financing activities:    
Payments for revolving credit facility borrowings (20.0)  
Equity investment from noncontrolling interest 1.9  
Dividends paid (43.2)  
Net cash provided by financing activities (61.3)  
Net increase (decrease) in cash and cash equivalents (16.9)  
Cash and cash equivalents at beginning of period $ 16.9