v2.4.0.6
Guarantees and condensed consolidating financial information (Details 5) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Condensed consolidating statement of cash flows    
Net cash provided by operating activities $ 74.2  
Cash flows used in investing activities:    
Construction in progress (9.7) (163.5)
Change in restricted cash (18.7) (6.4)
Purchase of property, plant and equipment (2.2)  
Net cash provided (used in) by investing activities (30.6)  
Cash flows provided by financing activities:    
Offering costs related to tax equity (0.6)  
Repayment of long-term debt (2.6) (2.7)
Proceeds from project-level debt 20.8 184.2
Payments for revolving credit facility borrowings (2.9) (8.0)
Equity contribution from noncontrolling interest 2.0  
Dividends paid (36.3) (36.0)
Net cash provided by financing activities (19.6)  
Net increase (decrease) in cash and cash equivalents 24.0  
Less cash at discontinued operations (5.0)  
Cash and cash equivalents at beginning of period at discontinued operations 6.5  
Cash and cash equivalents at beginning of period 60.2 60.6
Cash and cash equivalents at end of period 85.7 106.6
Guarantor Subsidiaries
    
Condensed consolidating statement of cash flows    
Net cash provided by operating activities 51.3  
Cash flows used in investing activities:    
Acquisitions and investments, net of cash acquired 3.0  
Construction in progress (9.7)  
Change in restricted cash (18.7)  
Purchase of property, plant and equipment (2.0)  
Net cash provided (used in) by investing activities (27.4)  
Cash flows provided by financing activities:    
Offering costs related to tax equity (0.6)  
Repayment of long-term debt (2.6)  
Proceeds from project-level debt 20.8  
Payments for revolving credit facility borrowings (2.9)  
Dividends paid (4.0)  
Net cash provided by financing activities 10.7  
Net increase (decrease) in cash and cash equivalents 34.6  
Less cash at discontinued operations (5.0)  
Cash and cash equivalents at beginning of period at discontinued operations 6.5  
Cash and cash equivalents at beginning of period 43.3  
Cash and cash equivalents at end of period 79.4  
Curtis Palmer
    
Condensed consolidating statement of cash flows    
Net cash provided by operating activities 0.2  
Cash flows used in investing activities:    
Purchase of property, plant and equipment (0.2)  
Net cash provided (used in) by investing activities (0.2)  
Atlantic Power
    
Condensed consolidating statement of cash flows    
Net cash provided by operating activities 22.7  
Cash flows used in investing activities:    
Acquisitions and investments, net of cash acquired (3.0)  
Net cash provided (used in) by investing activities (3.0)  
Cash flows provided by financing activities:    
Equity contribution from noncontrolling interest 2.0  
Dividends paid (32.3)  
Net cash provided by financing activities (30.3)  
Net increase (decrease) in cash and cash equivalents (10.6)  
Cash and cash equivalents at beginning of period 16.9  
Cash and cash equivalents at end of period $ 6.3