|
Summary Of Significant Accounting Policies (Regulatory Liabilities) (Details) (USD $)
In Millions, unless otherwise specified |
Sep. 30, 2012
|
Dec. 31, 2011
|
|---|---|---|
| Regulatory Liabilities [Line Items] | ||
| Regulatory liabilities | $ 906.4 | $ 910.1 |
|
IPL [Member]
|
||
| Regulatory Liabilities [Line Items] | ||
| Regulatory liabilities | 688.1 | 721.3 |
|
WPL [Member]
|
||
| Regulatory Liabilities [Line Items] | ||
| Regulatory liabilities | 218.3 | 188.8 |
|
Cost of removal obligations [Member]
|
||
| Regulatory Liabilities [Line Items] | ||
| Regulatory liabilities | 406.6 | 404.9 |
|
Cost of removal obligations [Member] | IPL [Member]
|
||
| Regulatory Liabilities [Line Items] | ||
| Regulatory liabilities | 266.5 | 261.9 |
|
Cost of removal obligations [Member] | WPL [Member]
|
||
| Regulatory Liabilities [Line Items] | ||
| Regulatory liabilities | 140.1 | 143.0 |
|
IPL's tax benefit rider [Member]
|
||
| Regulatory Liabilities [Line Items] | ||
| Regulatory liabilities | 327.4 | 349.6 |
|
IPL's tax benefit rider [Member] | IPL [Member]
|
||
| Regulatory Liabilities [Line Items] | ||
| Regulatory liabilities | 327.4 | 349.6 |
|
IPL's tax benefit rider [Member] | WPL [Member]
|
||
| Regulatory Liabilities [Line Items] | ||
| Regulatory liabilities | 0 | 0 |
|
Energy conservation cost recovery [Member]
|
||
| Regulatory Liabilities [Line Items] | ||
| Regulatory liabilities | 48.8 | 29.6 |
|
Energy conservation cost recovery [Member] | IPL [Member]
|
||
| Regulatory Liabilities [Line Items] | ||
| Regulatory liabilities | 8.9 | 4.7 |
|
Energy conservation cost recovery [Member] | WPL [Member]
|
||
| Regulatory Liabilities [Line Items] | ||
| Regulatory liabilities | 39.9 | 24.9 |
|
IPL electric transmission assets sale [Member]
|
||
| Regulatory Liabilities [Line Items] | ||
| Regulatory liabilities | 35.2 | 45.1 |
|
IPL electric transmission assets sale [Member] | IPL [Member]
|
||
| Regulatory Liabilities [Line Items] | ||
| Regulatory liabilities | 35.2 | 45.1 |
|
IPL electric transmission assets sale [Member] | WPL [Member]
|
||
| Regulatory Liabilities [Line Items] | ||
| Regulatory liabilities | 0 | 0 |
|
Derivatives [Member]
|
||
| Regulatory Liabilities [Line Items] | ||
| Regulatory liabilities | 21.3 | 7.2 |
|
Derivatives [Member] | IPL [Member]
|
||
| Regulatory Liabilities [Line Items] | ||
| Regulatory liabilities | 10.2 | 3.6 |
|
Derivatives [Member] | WPL [Member]
|
||
| Regulatory Liabilities [Line Items] | ||
| Regulatory liabilities | 11.1 | 3.6 |
|
Commodity cost recovery [Member]
|
||
| Regulatory Liabilities [Line Items] | ||
| Regulatory liabilities | 20.4 | 23.8 |
|
Commodity cost recovery [Member] | IPL [Member]
|
||
| Regulatory Liabilities [Line Items] | ||
| Regulatory liabilities | 14.8 | 23.2 |
|
Commodity cost recovery [Member] | WPL [Member]
|
||
| Regulatory Liabilities [Line Items] | ||
| Regulatory liabilities | 5.6 | 0.6 |
|
Other [Member]
|
||
| Regulatory Liabilities [Line Items] | ||
| Regulatory liabilities | 46.7 | 49.9 |
|
Other [Member] | IPL [Member]
|
||
| Regulatory Liabilities [Line Items] | ||
| Regulatory liabilities | 25.1 | 33.2 |
|
Other [Member] | WPL [Member]
|
||
| Regulatory Liabilities [Line Items] | ||
| Regulatory liabilities | $ 21.6 | $ 16.7 |