|
Derivative Instruments (Details) (USD $)
In Millions, unless otherwise specified |
3 Months Ended | 9 Months Ended | |||
|---|---|---|---|---|---|
|
Sep. 30, 2013
|
Sep. 30, 2012
|
Sep. 30, 2013
|
Sep. 30, 2012
|
Dec. 31, 2012
|
|
| Derivatives, Fair Value [Line Items] | |||||
| Derivative asset | $ 12.4 | $ 12.4 | $ 19.2 | ||
| Derivative liability | 2.1 | 2.1 | 1.9 | ||
| Gains (losses) | 4.2 | (2.3) | 5.4 | (29.1) | |
| Derivative Instruments (Textuals) | |||||
| Collateral in margin accounts | 2.6 | 2.6 | 2.9 | ||
|
Other Deferred Charges and Other Assets [Member]
|
|||||
| Derivatives, Fair Value [Line Items] | |||||
| Long-term portion of derivative assets | 0.8 | 0.8 | |||
|
Other Deferred Credits and Other Liabilities [Member]
|
|||||
| Derivatives, Fair Value [Line Items] | |||||
| Long-term portion of derivative liabilities | 0.2 | 0.2 | |||
|
Natural Gas [Member]
|
|||||
| Derivatives, Fair Value [Line Items] | |||||
| Derivative asset | 3.1 | 3.1 | 3.0 | ||
| Derivative liability | 2.1 | 2.1 | 1.9 | ||
| Volume of derivative instruments | 6.3 million Dth | 17.2 million Dth | 36.4 million Dth | 56.0 million Dth | |
| Gains (losses) | (1.1) | (5.3) | (5.7) | (35.7) | |
|
Fuel Oil [Member]
|
|||||
| Derivatives, Fair Value [Line Items] | |||||
| Derivative asset | 0.3 | 0.3 | 0.4 | ||
| Derivative liability | 0 | 0 | 0 | ||
| Volume of derivative instruments | 2.5 million gallons | 1.7 million gallons | 6.2 million gallons | 5.5 million gallons | |
| Gains (losses) | (0.1) | 0.1 | 0.1 | 1.5 | |
|
Ftrs [Member]
|
|||||
| Derivatives, Fair Value [Line Items] | |||||
| Derivative asset | 5.6 | 5.6 | 4.7 | ||
| Derivative liability | 0 | 0 | 0 | ||
| Volume of derivative instruments | 6,322 MW | 5,927 MW | 17,410 MW | 16,581 MW | |
| Gains (losses) | 5.4 | 2.9 | 11.0 | 5.1 | |
|
Coal [Member]
|
|||||
| Derivatives, Fair Value [Line Items] | |||||
| Derivative asset | 3.4 | 3.4 | 11.1 | ||
| Derivative liability | $ 0 | $ 0 | $ 0 | ||