|
Derivative instruments and hedging activities (Details 2)
In Millions, unless otherwise specified |
Mar. 31, 2013
Gas purchase agreements
gigajoule
|
Dec. 31, 2012
Gas purchase agreements
gigajoule
|
Mar. 31, 2013
Interest rate swaps
USD ($)
|
Dec. 31, 2012
Interest rate swaps
USD ($)
|
Mar. 31, 2013
Currency forward
CAD
|
Dec. 31, 2012
Currency forward
CAD
|
|---|---|---|---|---|---|---|
| Derivative instruments | ||||||
| Volume of forecasted transactions | 46,800,000 | 49,800,000 | ||||
| Volume of forecasted transactions, (in dollars) | $ 170.6 | $ 172.0 | 153.7 | 176.6 |