v3.3.1.900
Accounting for derivative instruments and hedging activities (Details)
MMBTU in Millions, J in Millions, CAD in Millions, $ in Millions
1 Months Ended 3 Months Ended 12 Months Ended 24 Months Ended
Oct. 31, 2014
CAD
May. 05, 2014
USD ($)
Feb. 20, 2014
USD ($)
MMBTU
Jun. 30, 2014
J
Sep. 30, 2014
USD ($)
Dec. 31, 2015
USD ($)
MMBTU
item
Dec. 31, 2014
USD ($)
MMBTU
Dec. 31, 2013
USD ($)
Dec. 31, 2015
USD ($)
item
Apr. 02, 2014
CAD
CAD / $
Apr. 02, 2014
USD ($)
CAD / $
Feb. 14, 2014
USD ($)
Dec. 31, 2006
CAD
Derivative instruments                          
Long-term debt           $ 733.3     $ 733.3        
Deferred financing costs           42.5 $ 62.8   $ 42.5        
Repayment of debt           $ 403.3 639.8 $ 118.8          
Derivative instruments designated as cash flow hedges | Cash Flow Hedging [Member]                          
Derivative instruments                          
Derivative, Number of Instruments Held | item           1     1        
Piedmont term loan, due 2018                          
Derivative instruments                          
Long-term debt           $ 59.0 64.0   $ 59.0        
6.5% Debentures due October 2014                          
Derivative instruments                          
Aggregate principal amount of debt | CAD                         CAD 60.0
Repayment of debt | CAD CAD 44.8                        
Senior secured term loan, due 2021                          
Derivative instruments                          
Long-term debt           $ 473.2 $ 541.5   $ 473.2        
Senior secured term loan, due 2021 | London Interbank Offered Rate (LIBOR)                          
Derivative instruments                          
Minimum variable rate, as a percent           1.00%              
Gas purchase agreements | Ontario project                          
Derivative instruments                          
Notional amount, energy (in joules: Ontario, in Mbtu: Orlando) | J       2,900,000,000                  
Expected uncontracted gas requirements for 2014 | Ontario project                          
Derivative instruments                          
Percentage of requirements whose price is fixed by derivative                 98.00%        
Expected uncontracted gas requirements for 2015 | Ontario project                          
Derivative instruments                          
Percentage of requirements whose price is fixed by derivative           98.00%              
Expected uncontracted gas requirements for 2016 | Ontario project                          
Derivative instruments                          
Percentage of requirements whose price is fixed by derivative           32.00%              
Expected uncontracted gas requirements for 2017 | Ontario project                          
Derivative instruments                          
Percentage of requirements whose price is fixed by derivative           30.00%              
Natural gas swaps                          
Derivative instruments                          
Notional amount, energy (in joules: Ontario, in Mbtu: Orlando) | MMBTU           2.8 6.3            
Natural gas swaps | Orlando project                          
Derivative instruments                          
Notional amount, energy (in joules: Ontario, in Mbtu: Orlando) | MMBTU     4.5     6.3              
Percentage of ownership interest           50.00%     50.00%        
Amount paid to terminate contract     $ 4.0                    
Percentage of the entity's share in required natural gas purchases hedge           100.00%              
Natural gas swaps during 2015                          
Derivative instruments                          
Percentage of the entity's share in required natural gas purchases hedge           63.00%              
Natural gas swaps during 2016                          
Derivative instruments                          
Percentage of the entity's share in required natural gas purchases hedge           63.00%              
Interest rate swaps                          
Derivative instruments                          
Notional amount           $ 302.3 $ 333.9   $ 302.3        
Interest rate swaps | Senior secured term loan, due 2021 | London Interbank Offered Rate (LIBOR)                          
Derivative instruments                          
Applicable margin of derivative (as a percent)   3.75%                      
Notional amount   $ 199.0       153.6     153.6        
Aggregate principal amount of debt   $ 600.0       $ 473.2     $ 473.2        
Interest rate swaps | Adjusted Eurodollar (LIBOR) Below One Percent [Member] | Senior secured term loan, due 2021                          
Derivative instruments                          
Swaption all in one interest rate (as a percent)   4.75%                      
Interest rate swaps | Adjusted Eurodollar (LIBOR) Below One Percent [Member] | Senior secured term loan, due 2021 | London Interbank Offered Rate (LIBOR)                          
Derivative instruments                          
Applicable margin of derivative (as a percent)   1.16%                      
Interest rate swaps | Minimum | Senior secured term loan, due 2021                          
Derivative instruments                          
Swaption all in one interest rate (as a percent)   4.75%                      
Interest rate swaps | Minimum | Senior secured term loan, due 2021 | London Interbank Offered Rate (LIBOR)                          
Derivative instruments                          
Minimum variable rate, as a percent   1.00%                      
Interest rate swaps | Minimum | Adjusted Eurodollar (LIBOR) Above One Percent [Member] | Senior secured term loan, due 2021                          
Derivative instruments                          
Swaption all in one interest rate (as a percent)   4.91%                      
Interest rate swaps | Epsilon Power Partners                          
Derivative instruments                          
Amount paid to terminate contract     2.6                    
Swaption interest rate (as a percent)           7.37%     7.37%        
Interest rate swaps | Piedmont | Piedmont term loan, due 2018                          
Derivative instruments                          
Long-term debt                       $ 68.5  
Deferred financing costs           $ 1.0     $ 1.0        
Interest rate swaps | Swaption interest rate until February 15, 2015 | Cadillac Project                          
Derivative instruments                          
Swaption interest rate (as a percent)           6.00%     6.00%        
Interest rate swaps | Swaption interest rate from February 16, 2015 to February 15, 2019 | Cadillac Project                          
Derivative instruments                          
Swaption interest rate (as a percent)           6.10%     6.10%        
Interest rate swaps | Swaption interest rate from February 16, 2019 to February 15, 2023 | Cadillac Project                          
Derivative instruments                          
Swaption interest rate (as a percent)           6.30%     6.30%        
Interest rate swaps | Swaption interest rate after February 15, 2023 | Cadillac Project                          
Derivative instruments                          
Swaption interest rate (as a percent)           6.40%     6.40%        
Interest rate swaps | Swaption interest rate until February 29, 2016 | Piedmont                          
Derivative instruments                          
Swaption interest rate (as a percent)           1.70%     1.70%        
Applicable margin, low end of range (as a percent)           3.50%     3.50%        
Applicable margin, high end of range (as a percent)           3.80%     3.80%        
Interest rate swaps | Swaption interest rate From February, 2016 to August, 2018 | Piedmont                          
Derivative instruments                          
Swaption interest rate (as a percent)           4.47%     4.47%        
Applicable margin of derivative (as a percent)           4.00%     4.00%        
Swaption all in one interest rate (as a percent)           8.50%     8.50%        
Interest rate swaps | Swaption interest rate From August, 2018 to November, 2030 | Piedmont                          
Derivative instruments                          
Swaption interest rate (as a percent)           4.47%     4.47%        
Foreign currency forward contracts                          
Derivative instruments                          
Amount paid to terminate contract     $ 0.4                    
Notional amount                   CAD 45.3 $ 41.0    
Foreign exchange rate (Canadian dollars per US dollar) | CAD / $                   1.105 1.105    
Realized loss on expiration of contract         $ 0.5                
Foreign currency forward contracts | 6.5% Debentures due October 2014                          
Derivative instruments                          
Aggregate principal amount of debt | CAD                   CAD 44.8      
Repayment of debt | CAD CAD 44.8