Variable Interest Entities (VIEs)	9 Months Ended
Sep. 30, 2011
Variable Interest Entities (VIEs)	(16) VARIABLE INTEREST ENTITIES (VIEs) After making an ongoing exhaustive effort, Alliant Energy and WPL concluded they were unable to obtain the information necessary from the counterparty (a subsidiary of Calpine Corporation) for the Riverside PPA for Alliant Energy and WPL to determine whether the counterparty is a VIE and if Alliant Energy is the primary beneficiary. This PPA is currently accounted for as an operating lease. The counterparty for the Riverside PPA sells a portion of its generating capacity to WPL and can sell its energy output to WPL. Alliant Energy's and WPL's maximum exposure to loss from this PPA is undeterminable due to the inability to obtain the necessary information to complete such evaluation. Alliant Energy's (primarily WPL's) costs, excluding fuel costs, related to the Riverside PPA were $28.5 million and $55.4 million for the three and nine months ended Sep. 30, 2011, and $28.2 million and $55.1 million for the three and nine months ended Sep. 30, 2010, respectively.
IPL [Member]
Variable Interest Entities (VIEs)	(16) VARIABLE INTEREST ENTITIES (VIEs) After making an ongoing exhaustive effort, Alliant Energy and WPL concluded they were unable to obtain the information necessary from the counterparty (a subsidiary of Calpine Corporation) for the Riverside PPA for Alliant Energy and WPL to determine whether the counterparty is a VIE and if Alliant Energy is the primary beneficiary. This PPA is currently accounted for as an operating lease. The counterparty for the Riverside PPA sells a portion of its generating capacity to WPL and can sell its energy output to WPL. Alliant Energy's and WPL's maximum exposure to loss from this PPA is undeterminable due to the inability to obtain the necessary information to complete such evaluation. Alliant Energy's (primarily WPL's) costs, excluding fuel costs, related to the Riverside PPA were $28.5 million and $55.4 million for the three and nine months ended Sep. 30, 2011, and $28.2 million and $55.1 million for the three and nine months ended Sep. 30, 2010, respectively.
WPL [Member]
Variable Interest Entities (VIEs)	(16) VARIABLE INTEREST ENTITIES (VIEs) After making an ongoing exhaustive effort, Alliant Energy and WPL concluded they were unable to obtain the information necessary from the counterparty (a subsidiary of Calpine Corporation) for the Riverside PPA for Alliant Energy and WPL to determine whether the counterparty is a VIE and if Alliant Energy is the primary beneficiary. This PPA is currently accounted for as an operating lease. The counterparty for the Riverside PPA sells a portion of its generating capacity to WPL and can sell its energy output to WPL. Alliant Energy's and WPL's maximum exposure to loss from this PPA is undeterminable due to the inability to obtain the necessary information to complete such evaluation. Alliant Energy's (primarily WPL's) costs, excluding fuel costs, related to the Riverside PPA were $28.5 million and $55.4 million for the three and nine months ended Sep. 30, 2011, and $28.2 million and $55.1 million for the three and nine months ended Sep. 30, 2010, respectively.

(16) VARIABLE INTEREST ENTITIES (VIEs)

After making an ongoing exhaustive effort, Alliant Energy and WPL concluded they were unable to obtain the information necessary from the counterparty (a subsidiary of Calpine Corporation) for the Riverside PPA for Alliant Energy and WPL to determine whether the counterparty is a VIE and if Alliant Energy is the primary beneficiary. This PPA is currently accounted for as an operating lease. The counterparty for the Riverside PPA sells a portion of its generating capacity to WPL and can sell its energy output to WPL. Alliant Energy's and WPL's maximum exposure to loss from this PPA is undeterminable due to the inability to obtain the necessary information to complete such evaluation. Alliant Energy's (primarily WPL's) costs, excluding fuel costs, related to the Riverside PPA were $28.5 million and $55.4 million for the three and nine months ended Sep. 30, 2011, and $28.2 million and $55.1 million for the three and nine months ended Sep. 30, 2010, respectively.

(16) VARIABLE INTEREST ENTITIES (VIEs)

After making an ongoing exhaustive effort, Alliant Energy and WPL concluded they were unable to obtain the information necessary from the counterparty (a subsidiary of Calpine Corporation) for the Riverside PPA for Alliant Energy and WPL to determine whether the counterparty is a VIE and if Alliant Energy is the primary beneficiary. This PPA is currently accounted for as an operating lease. The counterparty for the Riverside PPA sells a portion of its generating capacity to WPL and can sell its energy output to WPL. Alliant Energy's and WPL's maximum exposure to loss from this PPA is undeterminable due to the inability to obtain the necessary information to complete such evaluation. Alliant Energy's (primarily WPL's) costs, excluding fuel costs, related to the Riverside PPA were $28.5 million and $55.4 million for the three and nine months ended Sep. 30, 2011, and $28.2 million and $55.1 million for the three and nine months ended Sep. 30, 2010, respectively.

Variable Interest Entities (VIEs)

(16) VARIABLE INTEREST ENTITIES (VIEs)

After making an ongoing exhaustive effort, Alliant Energy and WPL concluded they were unable to obtain the information necessary from the counterparty (a subsidiary of Calpine Corporation) for the Riverside PPA for Alliant Energy and WPL to determine whether the counterparty is a VIE and if Alliant Energy is the primary beneficiary. This PPA is currently accounted for as an operating lease. The counterparty for the Riverside PPA sells a portion of its generating capacity to WPL and can sell its energy output to WPL. Alliant Energy's and WPL's maximum exposure to loss from this PPA is undeterminable due to the inability to obtain the necessary information to complete such evaluation. Alliant Energy's (primarily WPL's) costs, excluding fuel costs, related to the Riverside PPA were $28.5 million and $55.4 million for the three and nine months ended Sep. 30, 2011, and $28.2 million and $55.1 million for the three and nine months ended Sep. 30, 2010, respectively.