|
Summary Of Significant Accounting Policies (Regulatory Assets) (Details) (USD $)
In Millions, unless otherwise specified |
Sep. 30, 2012
|
Dec. 31, 2011
|
|---|---|---|
| Regulatory Assets [Line Items] | ||
| Regulatory assets | $ 1,518.4 | $ 1,495.0 |
|
IPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 1,151.0 | 1,117.3 |
|
WPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 367.4 | 377.7 |
|
Tax-related [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 709.4 | 634.7 |
|
Tax-related [Member] | IPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 686.2 | 614.6 |
|
Tax-related [Member] | WPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 23.2 | 20.1 |
|
Pension and other postretirement benefits costs [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 495.4 | 514.1 |
|
Pension and other postretirement benefits costs [Member] | IPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 256.3 | 264.9 |
|
Pension and other postretirement benefits costs [Member] | WPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 239.1 | 249.2 |
|
Asset retirement obligations [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 57.8 | 65.9 |
|
Asset retirement obligations [Member] | IPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 38.7 | 48.7 |
|
Asset retirement obligations [Member] | WPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 19.1 | 17.2 |
|
Derivatives [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 56.6 | 77.7 |
|
Derivatives [Member] | IPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 22.6 | 33.5 |
|
Derivatives [Member] | WPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 34.0 | 44.2 |
|
Environmental-related costs [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 36.3 | 38.9 |
|
Environmental-related costs [Member] | IPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 31.5 | 32.2 |
|
Environmental-related costs [Member] | WPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 4.8 | 6.7 |
|
Emission allowances [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 30.0 | 30.0 |
|
Emission allowances [Member] | IPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 30.0 | 30.0 |
|
Emission allowances [Member] | WPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 0 | 0 |
|
Debt redemption costs [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 20.3 | 21.8 |
|
Debt redemption costs [Member] | IPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 14.0 | 15.1 |
|
Debt redemption costs [Member] | WPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 6.3 | 6.7 |
|
IPL's electric transmission service costs [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 18.7 | 24.9 |
|
IPL's electric transmission service costs [Member] | IPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 18.7 | 24.9 |
|
IPL's electric transmission service costs [Member] | WPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 0 | 0 |
|
Proposed base-load projects costs [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 16.0 | 21.5 |
|
Proposed base-load projects costs [Member] | IPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 11.4 | 15.3 |
|
Proposed base-load projects costs [Member] | WPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 4.6 | 6.2 |
|
Other [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 77.9 | 65.5 |
|
Other [Member] | IPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 41.6 | 38.1 |
|
Other [Member] | WPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | $ 36.3 | $ 27.4 |