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Commitments And Contingencies (Tables) | 3 Months Ended
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Mar. 31, 2013
Long-term Purchase Commitment [Line Items] |
Operating Expense Purchase Obligations | At March 31, 2013, minimum future commitments related to these operating expense purchase obligations were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
Purchased power (a): |  |  |  |  |
Duane Arnold Energy Center (DAEC) (IPL) (b) |  | $1,808 |  |  |  | $1,808 |  |  |  | $— |
Kewaunee Nuclear Power Plant (Kewaunee) (WPL) | 57 |  |  | — |  |  | 57 |
Other | 52 |  |  | 1 |  |  | 51 |
| 1,917 |  |  | 1,809 |  |  | 108 |
Natural gas | 365 |  |  | 240 |  |  | 125 |
Coal (c) | 235 |  |  | 71 |  |  | 42 |
SO2 emission allowances | 34 |  |  | 34 |  |  | — |
Other (d) | 47 |  |  | 26 |  |  | 15 |
|  | $2,598 |  |  |  | $2,180 |  |  |  | $290 |
(a) | Includes payments required by purchased power agreements (PPAs) for capacity rights and minimum quantities of MWhs required to be purchased.
(b) | Includes commitments incurred under an existing PPA that expires February 2014 and a new PPA completed in March 2013. The new PPA grants IPL rights to purchase 431 MWs of capacity and the resulting energy from DAEC for a term from the expiration of the existing PPA in February 2014 through December 31, 2025. If energy delivered under the new PPA is less than the targeted energy amount, an adjustment payment will be made to IPL, which will be reflected in IPL’s energy adjustment clause.
(c) | Corporate Services entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments of $122 million that have not been directly assigned to IPL and WPL since the specific needs of each utility were not yet known as of March 31, 2013.
(d) | Includes individual commitments incurred during the normal course of business that exceeded $1 million at March 31, 2013.
IPL [Member] |
Long-term Purchase Commitment [Line Items] |
Operating Expense Purchase Obligations | At March 31, 2013, minimum future commitments related to these operating expense purchase obligations were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
Purchased power (a): |  |  |  |  |
Duane Arnold Energy Center (DAEC) (IPL) (b) |  | $1,808 |  |  |  | $1,808 |  |  |  | $— |
Kewaunee Nuclear Power Plant (Kewaunee) (WPL) | 57 |  |  | — |  |  | 57 |
Other | 52 |  |  | 1 |  |  | 51 |
| 1,917 |  |  | 1,809 |  |  | 108 |
Natural gas | 365 |  |  | 240 |  |  | 125 |
Coal (c) | 235 |  |  | 71 |  |  | 42 |
SO2 emission allowances | 34 |  |  | 34 |  |  | — |
Other (d) | 47 |  |  | 26 |  |  | 15 |
|  | $2,598 |  |  |  | $2,180 |  |  |  | $290 |
(a) | Includes payments required by purchased power agreements (PPAs) for capacity rights and minimum quantities of MWhs required to be purchased.
(b) | Includes commitments incurred under an existing PPA that expires February 2014 and a new PPA completed in March 2013. The new PPA grants IPL rights to purchase 431 MWs of capacity and the resulting energy from DAEC for a term from the expiration of the existing PPA in February 2014 through December 31, 2025. If energy delivered under the new PPA is less than the targeted energy amount, an adjustment payment will be made to IPL, which will be reflected in IPL’s energy adjustment clause.
(c) | Corporate Services entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments of $122 million that have not been directly assigned to IPL and WPL since the specific needs of each utility were not yet known as of March 31, 2013.
(d) | Includes individual commitments incurred during the normal course of business that exceeded $1 million at March 31, 2013.
WPL [Member] |
Long-term Purchase Commitment [Line Items] |
Operating Expense Purchase Obligations | At March 31, 2013, minimum future commitments related to these operating expense purchase obligations were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
Purchased power (a): |  |  |  |  |
Duane Arnold Energy Center (DAEC) (IPL) (b) |  | $1,808 |  |  |  | $1,808 |  |  |  | $— |
Kewaunee Nuclear Power Plant (Kewaunee) (WPL) | 57 |  |  | — |  |  | 57 |
Other | 52 |  |  | 1 |  |  | 51 |
| 1,917 |  |  | 1,809 |  |  | 108 |
Natural gas | 365 |  |  | 240 |  |  | 125 |
Coal (c) | 235 |  |  | 71 |  |  | 42 |
SO2 emission allowances | 34 |  |  | 34 |  |  | — |
Other (d) | 47 |  |  | 26 |  |  | 15 |
|  | $2,598 |  |  |  | $2,180 |  |  |  | $290 |
(a) | Includes payments required by purchased power agreements (PPAs) for capacity rights and minimum quantities of MWhs required to be purchased.
(b) | Includes commitments incurred under an existing PPA that expires February 2014 and a new PPA completed in March 2013. The new PPA grants IPL rights to purchase 431 MWs of capacity and the resulting energy from DAEC for a term from the expiration of the existing PPA in February 2014 through December 31, 2025. If energy delivered under the new PPA is less than the targeted energy amount, an adjustment payment will be made to IPL, which will be reflected in IPL’s energy adjustment clause.
(c) | Corporate Services entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments of $122 million that have not been directly assigned to IPL and WPL since the specific needs of each utility were not yet known as of March 31, 2013.
(d) | Includes individual commitments incurred during the normal course of business that exceeded $1 million at March 31, 2013.

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