Accounting for derivative instruments - forecasted trans (Details) kJ in Millions, MMBTU in Millions, $ in Millions |
3 Months Ended | 12 Months Ended |
|---|---|---|
|
Mar. 31, 2016
USD ($)
kJ
MMBTU
|
Dec. 31, 2015
USD ($)
kJ
MMBTU
|
|
| Natural gas swaps | ||
| Derivative instruments | ||
| Volume of forecasted transactions, energy (swaps: Mmbtu, agreements: joules) | MMBTU | 6.7 | 2.8 |
| Gas purchase agreements | ||
| Derivative instruments | ||
| Volume of forecasted transactions, energy (swaps: Mmbtu, agreements: joules) | kJ | 22.4 | 25.0 |
| Interest rate swaps | ||
| Derivative instruments | ||
| Volume of forecasted transactions, (in dollars) | $ | $ 228.9 | $ 302.3 |