v2.4.0.6

Commitments And Contingencies (Tables) | 9 Months Ended
--- | ---
Sep. 30, 2012
Commitments and Contingencies Disclosure [Abstract] |
Operating Expense Purchase Obligations | At September 30, 2012, 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) |  | $271 |  |  |  | $271 |  |  |  | $— |
Kewaunee Nuclear Power Plant (Kewaunee) (WPL) | 95 |  |  | — |  |  | 95 |
Other | 63 |  |  | 4 |  |  | 59 |
| 429 |  |  | 275 |  |  | 154 |
Natural gas | 344 |  |  | 208 |  |  | 136 |
Coal (b) | 302 |  |  | 79 |  |  | 52 |
SO2 emission allowances | 34 |  |  | 34 |  |  | — |
Other (c) | 22 |  |  | 9 |  |  | 13 |
|  | $1,131 |  |  |  | $605 |  |  |  | $355 |
(a) | Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. Excludes contracts that are considered operating leases.
(b) | Corporate Services entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments of $171 million that have not been directly assigned to IPL and WPL since the specific needs of each utility were not yet known as of September 30, 2012.
(c) | Includes individual commitments incurred during the normal course of business that exceeded $1 million at September 30, 2012.

X
- Definition Long-Term Purchase Commitment, Operating Expenses Purchase Obligation [Table Text Block] + References No definition available. + Details
Name: | lnt_LongTermPurchaseCommitmentOperatingExpensesPurchaseObligationTableTextBlock
Namespace Prefix: | lnt_
Data Type: | nonnum:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_CommitmentsAndContingenciesDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration