|
Summary Of Significant Accounting Policies (Regulatory Assets) (Details) (USD $)
In Millions, unless otherwise specified |
Dec. 31, 2012
|
Dec. 31, 2011
|
|---|---|---|
| Regulatory Assets [Line Items] | ||
| Regulatory assets | $ 1,612.4 | $ 1,495.0 |
|
IPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 1,217.9 | 1,117.3 |
|
WPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 394.5 | 377.7 |
|
Tax-related [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 770.7 | 634.7 |
|
Tax-related [Member] | IPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 746.2 | 614.6 |
|
Tax-related [Member] | WPL [Member]
|
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| Regulatory Assets [Line Items] | ||
| Regulatory assets | 24.5 | 20.1 |
|
Pension and other postretirement benefits costs [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 549.2 | 514.1 |
|
Pension and other postretirement benefits costs [Member] | IPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 279.3 | 264.9 |
|
Pension and other postretirement benefits costs [Member] | WPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 269.9 | 249.2 |
|
Asset retirement obligations [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 62.4 | 65.9 |
|
Asset retirement obligations [Member] | IPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 38.6 | 48.7 |
|
Asset retirement obligations [Member] | WPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 23.8 | 17.2 |
|
Derivatives [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 40.2 | 77.7 |
|
Derivatives [Member] | IPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 16.3 | 33.5 |
|
Derivatives [Member] | WPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 23.9 | 44.2 |
|
Environmental-related costs [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 34.9 | 38.9 |
|
Environmental-related costs [Member] | IPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 30.3 | 32.2 |
|
Environmental-related costs [Member] | WPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 4.6 | 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 | 19.8 | 21.8 |
|
Debt redemption costs [Member] | IPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 13.6 | 15.1 |
|
Debt redemption costs [Member] | WPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 6.2 | 6.7 |
|
Proposed clean air compliance projects costs [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 16.7 | 14.9 |
|
Proposed clean air compliance projects costs [Member] | IPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 7.8 | 6.9 |
|
Proposed clean air compliance projects costs [Member] | WPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 8.9 | 8.0 |
|
IPL's electric transmission service costs [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 16.6 | 24.9 |
|
IPL's electric transmission service costs [Member] | IPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 16.6 | 24.9 |
|
IPL's electric transmission service costs [Member] | WPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 0 | 0 |
|
Proposed coal-fired base-load projects costs [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 14.2 | 21.5 |
|
Proposed coal-fired base-load projects costs [Member] | IPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 10.1 | 15.3 |
|
Proposed coal-fired base-load projects costs [Member] | WPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 4.1 | 6.2 |
|
Other [Member]
|
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| Regulatory Assets [Line Items] | ||
| Regulatory assets | 57.7 | 50.6 |
|
Other [Member] | IPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | 29.1 | 31.2 |
|
Other [Member] | WPL [Member]
|
||
| Regulatory Assets [Line Items] | ||
| Regulatory assets | $ 28.6 | $ 19.4 |