Utility Rate Cases	9 Months Ended
Sep. 30, 2011
Utility Rate Cases	(2) UTILITY RATE CASES IPL's Minnesota Retail Electric Rate Case (2009 Test Year)—In May 2010, IPL filed a request with the MPUC to increase annual rates for its Minnesota retail electric customers by $15 million, or approximately 22%. The request was based on a 2009 historical test year as adjusted for certain known and measurable items at the time of the filing. The key drivers for the filing included recovery of investments in the Whispering Willow—East wind project and emission control projects at Lansing Unit 4, and recovery of increased electric transmission service costs. In conjunction with the filing, IPL implemented an interim retail rate increase of $14 million, on an annual basis, effective July 6, 2010. During the nine months ended Sep. 30, 2011 and 2010, Alliant Energy and IPL recorded $9 million and $4 million, respectively, in electric revenues from IPL's Minnesota retail electric customers related to the interim retail electric rate increase and the reserve for rate refund discussed below. In August 2011, IPL received an order from the MPUC authorizing a final annual retail electric rate increase equivalent to $11 million. The final annual retail electric rate increase of $11 million includes $8 million of higher base rates, $2 million from the renewable energy rider and $1 million from the utilization of regulatory liabilities to offset higher electric transmission service costs. As of Sep. 30, 2011, Alliant Energy and IPL reserved $3 million, including interest, for refunds anticipated to be paid to IPL's Minnesota retail electric customers in 2012 in accordance with the MPUC's August 2011 order. Refer to Note 1(b) for discussion of changes to regulatory assets and regulatory liabilities during the nine months ended Sep. 30, 2011 based on the MPUC's decisions to provide IPL's retail electric customers in Minnesota additional refunds from the gain on the sale of electric transmission assets in 2007 and to provide IPL recovery of $2 million of previously incurred costs for Sutherland #4. Refer to Note 1(c) for discussion of an impairment recognized during the nine months ended Sep. 30, 2011 based on the MPUC's decision regarding the recovery of Whispering Willow—East wind project costs. IPL's Iowa Retail Electric Rate Case (2009 Test Year)—In March 2010, IPL filed a request with the IUB to increase annual rates for its Iowa retail electric customers. The request was based on a 2009 historical test year as adjusted for certain known and measurable changes occurring up to 12 months after the commencement of the proceeding. The key drivers for the filing included recovery of investments in the Whispering Willow—East wind project and emission control projects at Lansing Unit 4, and recovery of increased electric transmission service costs. In conjunction with the filing, IPL implemented an interim retail electric rate increase of $119 million, on an annual basis, effective March 20, 2010. During the nine months ended Sep. 30, 2011 and 2010, Alliant Energy and IPL recorded $95 million and $72 million, respectively, in electric revenues from IPL's Iowa retail electric customers related to the retail electric rate increase and the rate refund discussed below. In February 2011, IPL received an order from the IUB authorizing a final annual retail electric rate increase of $114 million, or approximately 10%. In 2011, IPL refunded $5 million, including interest, to its retail electric customers in Iowa. WPL's Retail Fuel-related Rate Case (2012 Test Year)—In May 2011, WPL filed a request with the PSCW to increase annual retail electric rates by $13 million to recover anticipated increases in retail fuel-related costs in 2012 due to higher purchased power energy costs and emission compliance costs. In July 2011, the EPA issued CSAPR, which requires SO2 and NOx emissions reductions from IPL's and WPL's fossil-fueled electric generating units (EGUs) with greater than 25 MW of capacity located in Iowa, Minnesota and Wisconsin beginning in 2012. After evaluating CSAPR, in August 2011, WPL revised its request for an annual retail electric rate increase to $20 million to reflect higher emission compliance costs. Any rate changes granted from this request are expected to be effective on Jan. 1, 2012. WPL's Retail Electric Rate Case (2011 Test Year)—In April 2010, WPL filed a request with the PSCW to reopen the rate order for its 2010 test year to increase annual retail electric rates for 2011. The request was based on a forward-looking test period that included 2011. The key drivers for the filing included recovery of investments in WPL's Bent Tree—Phase I wind project and expiring deferral credits, partially offset by lower variable fuel expenses. In December 2010, WPL received an order from the PSCW authorizing an annual retail electric rate increase of $8 million, or approximately 1%, effective Jan. 1, 2011. This $8 million increase in annual rates effective Jan. 1, 2011, combined with the termination of the $9 million interim fuel-related rate increase effective Dec. 31, 2010, resulted in a net $1 million decrease in annual retail electric rates charged to customers effective January 2011. Refer to "WPL's Retail Fuel-related Rate Case (2010 Test Year)" below for additional details of the interim fuel-related rate increase implemented in 2010 and a $5 million reduction to the 2011 test year base rate increase for refunds owed to retail electric customers related to interim fuel cost collections in 2010. WPL's Retail Fuel-related Rate Case (2010 Test Year)—In April 2010, WPL filed a request with the PSCW to increase annual retail electric rates by $9 million to recover anticipated increased electric production fuel and energy purchases (fuel-related costs) in 2010. Actual fuel-related costs through March 2010, combined with projections of continued higher fuel-related costs for the remainder of 2010, significantly exceeded the amounts being recovered in retail electric rates at the time of the filing. WPL received approval from the PSCW to implement an interim rate increase of $9 million, on an annual basis, effective in June 2010. Updated annual 2010 fuel-related costs during the proceeding resulted in WPL no longer qualifying for a fuel-related rate increase for 2010. In December 2010, the PSCW issued an order authorizing no increase in retail electric rates in 2010 related to fuel-related costs and required the interim rate increase to terminate at the end of 2010. The order also authorized WPL to use $5 million of the interim fuel rates collected in 2010 as a reduction to the 2011 test year base rate increase. As of Sep. 30, 2011, Alliant Energy's and WPL's remaining reserves were $2 million, including interest, for interim fuel cost collections in 2010. Refer to Note 1(b) for discussion of various other rate matters.
IPL [Member]
Utility Rate Cases	(2) UTILITY RATE CASES IPL's Minnesota Retail Electric Rate Case (2009 Test Year)—In May 2010, IPL filed a request with the MPUC to increase annual rates for its Minnesota retail electric customers by $15 million, or approximately 22%. The request was based on a 2009 historical test year as adjusted for certain known and measurable items at the time of the filing. The key drivers for the filing included recovery of investments in the Whispering Willow—East wind project and emission control projects at Lansing Unit 4, and recovery of increased electric transmission service costs. In conjunction with the filing, IPL implemented an interim retail rate increase of $14 million, on an annual basis, effective July 6, 2010. During the nine months ended Sep. 30, 2011 and 2010, Alliant Energy and IPL recorded $9 million and $4 million, respectively, in electric revenues from IPL's Minnesota retail electric customers related to the interim retail electric rate increase and the reserve for rate refund discussed below. In August 2011, IPL received an order from the MPUC authorizing a final annual retail electric rate increase equivalent to $11 million. The final annual retail electric rate increase of $11 million includes $8 million of higher base rates, $2 million from the renewable energy rider and $1 million from the utilization of regulatory liabilities to offset higher electric transmission service costs. As of Sep. 30, 2011, Alliant Energy and IPL reserved $3 million, including interest, for refunds anticipated to be paid to IPL's Minnesota retail electric customers in 2012 in accordance with the MPUC's August 2011 order. Refer to Note 1(b) for discussion of changes to regulatory assets and regulatory liabilities during the nine months ended Sep. 30, 2011 based on the MPUC's decisions to provide IPL's retail electric customers in Minnesota additional refunds from the gain on the sale of electric transmission assets in 2007 and to provide IPL recovery of $2 million of previously incurred costs for Sutherland #4. Refer to Note 1(c) for discussion of an impairment recognized during the nine months ended Sep. 30, 2011 based on the MPUC's decision regarding the recovery of Whispering Willow—East wind project costs. IPL's Iowa Retail Electric Rate Case (2009 Test Year)—In March 2010, IPL filed a request with the IUB to increase annual rates for its Iowa retail electric customers. The request was based on a 2009 historical test year as adjusted for certain known and measurable changes occurring up to 12 months after the commencement of the proceeding. The key drivers for the filing included recovery of investments in the Whispering Willow—East wind project and emission control projects at Lansing Unit 4, and recovery of increased electric transmission service costs. In conjunction with the filing, IPL implemented an interim retail electric rate increase of $119 million, on an annual basis, effective March 20, 2010. During the nine months ended Sep. 30, 2011 and 2010, Alliant Energy and IPL recorded $95 million and $72 million, respectively, in electric revenues from IPL's Iowa retail electric customers related to the retail electric rate increase and the rate refund discussed below. In February 2011, IPL received an order from the IUB authorizing a final annual retail electric rate increase of $114 million, or approximately 10%. In 2011, IPL refunded $5 million, including interest, to its retail electric customers in Iowa. WPL's Retail Fuel-related Rate Case (2012 Test Year)—In May 2011, WPL filed a request with the PSCW to increase annual retail electric rates by $13 million to recover anticipated increases in retail fuel-related costs in 2012 due to higher purchased power energy costs and emission compliance costs. In July 2011, the EPA issued CSAPR, which requires SO2 and NOx emissions reductions from IPL's and WPL's fossil-fueled electric generating units (EGUs) with greater than 25 MW of capacity located in Iowa, Minnesota and Wisconsin beginning in 2012. After evaluating CSAPR, in August 2011, WPL revised its request for an annual retail electric rate increase to $20 million to reflect higher emission compliance costs. Any rate changes granted from this request are expected to be effective on Jan. 1, 2012. WPL's Retail Electric Rate Case (2011 Test Year)—In April 2010, WPL filed a request with the PSCW to reopen the rate order for its 2010 test year to increase annual retail electric rates for 2011. The request was based on a forward-looking test period that included 2011. The key drivers for the filing included recovery of investments in WPL's Bent Tree—Phase I wind project and expiring deferral credits, partially offset by lower variable fuel expenses. In December 2010, WPL received an order from the PSCW authorizing an annual retail electric rate increase of $8 million, or approximately 1%, effective Jan. 1, 2011. This $8 million increase in annual rates effective Jan. 1, 2011, combined with the termination of the $9 million interim fuel-related rate increase effective Dec. 31, 2010, resulted in a net $1 million decrease in annual retail electric rates charged to customers effective January 2011. Refer to "WPL's Retail Fuel-related Rate Case (2010 Test Year)" below for additional details of the interim fuel-related rate increase implemented in 2010 and a $5 million reduction to the 2011 test year base rate increase for refunds owed to retail electric customers related to interim fuel cost collections in 2010. WPL's Retail Fuel-related Rate Case (2010 Test Year)—In April 2010, WPL filed a request with the PSCW to increase annual retail electric rates by $9 million to recover anticipated increased electric production fuel and energy purchases (fuel-related costs) in 2010. Actual fuel-related costs through March 2010, combined with projections of continued higher fuel-related costs for the remainder of 2010, significantly exceeded the amounts being recovered in retail electric rates at the time of the filing. WPL received approval from the PSCW to implement an interim rate increase of $9 million, on an annual basis, effective in June 2010. Updated annual 2010 fuel-related costs during the proceeding resulted in WPL no longer qualifying for a fuel-related rate increase for 2010. In December 2010, the PSCW issued an order authorizing no increase in retail electric rates in 2010 related to fuel-related costs and required the interim rate increase to terminate at the end of 2010. The order also authorized WPL to use $5 million of the interim fuel rates collected in 2010 as a reduction to the 2011 test year base rate increase. As of Sep. 30, 2011, Alliant Energy's and WPL's remaining reserves were $2 million, including interest, for interim fuel cost collections in 2010. Refer to Note 1(b) for discussion of various other rate matters.
WPL [Member]
Utility Rate Cases	(2) UTILITY RATE CASES IPL's Minnesota Retail Electric Rate Case (2009 Test Year)—In May 2010, IPL filed a request with the MPUC to increase annual rates for its Minnesota retail electric customers by $15 million, or approximately 22%. The request was based on a 2009 historical test year as adjusted for certain known and measurable items at the time of the filing. The key drivers for the filing included recovery of investments in the Whispering Willow—East wind project and emission control projects at Lansing Unit 4, and recovery of increased electric transmission service costs. In conjunction with the filing, IPL implemented an interim retail rate increase of $14 million, on an annual basis, effective July 6, 2010. During the nine months ended Sep. 30, 2011 and 2010, Alliant Energy and IPL recorded $9 million and $4 million, respectively, in electric revenues from IPL's Minnesota retail electric customers related to the interim retail electric rate increase and the reserve for rate refund discussed below. In August 2011, IPL received an order from the MPUC authorizing a final annual retail electric rate increase equivalent to $11 million. The final annual retail electric rate increase of $11 million includes $8 million of higher base rates, $2 million from the renewable energy rider and $1 million from the utilization of regulatory liabilities to offset higher electric transmission service costs. As of Sep. 30, 2011, Alliant Energy and IPL reserved $3 million, including interest, for refunds anticipated to be paid to IPL's Minnesota retail electric customers in 2012 in accordance with the MPUC's August 2011 order. Refer to Note 1(b) for discussion of changes to regulatory assets and regulatory liabilities during the nine months ended Sep. 30, 2011 based on the MPUC's decisions to provide IPL's retail electric customers in Minnesota additional refunds from the gain on the sale of electric transmission assets in 2007 and to provide IPL recovery of $2 million of previously incurred costs for Sutherland #4. Refer to Note 1(c) for discussion of an impairment recognized during the nine months ended Sep. 30, 2011 based on the MPUC's decision regarding the recovery of Whispering Willow—East wind project costs. IPL's Iowa Retail Electric Rate Case (2009 Test Year)—In March 2010, IPL filed a request with the IUB to increase annual rates for its Iowa retail electric customers. The request was based on a 2009 historical test year as adjusted for certain known and measurable changes occurring up to 12 months after the commencement of the proceeding. The key drivers for the filing included recovery of investments in the Whispering Willow—East wind project and emission control projects at Lansing Unit 4, and recovery of increased electric transmission service costs. In conjunction with the filing, IPL implemented an interim retail electric rate increase of $119 million, on an annual basis, effective March 20, 2010. During the nine months ended Sep. 30, 2011 and 2010, Alliant Energy and IPL recorded $95 million and $72 million, respectively, in electric revenues from IPL's Iowa retail electric customers related to the retail electric rate increase and the rate refund discussed below. In February 2011, IPL received an order from the IUB authorizing a final annual retail electric rate increase of $114 million, or approximately 10%. In 2011, IPL refunded $5 million, including interest, to its retail electric customers in Iowa. WPL's Retail Fuel-related Rate Case (2012 Test Year)—In May 2011, WPL filed a request with the PSCW to increase annual retail electric rates by $13 million to recover anticipated increases in retail fuel-related costs in 2012 due to higher purchased power energy costs and emission compliance costs. In July 2011, the EPA issued CSAPR, which requires SO2 and NOx emissions reductions from IPL's and WPL's fossil-fueled electric generating units (EGUs) with greater than 25 MW of capacity located in Iowa, Minnesota and Wisconsin beginning in 2012. After evaluating CSAPR, in August 2011, WPL revised its request for an annual retail electric rate increase to $20 million to reflect higher emission compliance costs. Any rate changes granted from this request are expected to be effective on Jan. 1, 2012. WPL's Retail Electric Rate Case (2011 Test Year)—In April 2010, WPL filed a request with the PSCW to reopen the rate order for its 2010 test year to increase annual retail electric rates for 2011. The request was based on a forward-looking test period that included 2011. The key drivers for the filing included recovery of investments in WPL's Bent Tree—Phase I wind project and expiring deferral credits, partially offset by lower variable fuel expenses. In December 2010, WPL received an order from the PSCW authorizing an annual retail electric rate increase of $8 million, or approximately 1%, effective Jan. 1, 2011. This $8 million increase in annual rates effective Jan. 1, 2011, combined with the termination of the $9 million interim fuel-related rate increase effective Dec. 31, 2010, resulted in a net $1 million decrease in annual retail electric rates charged to customers effective January 2011. Refer to "WPL's Retail Fuel-related Rate Case (2010 Test Year)" below for additional details of the interim fuel-related rate increase implemented in 2010 and a $5 million reduction to the 2011 test year base rate increase for refunds owed to retail electric customers related to interim fuel cost collections in 2010. WPL's Retail Fuel-related Rate Case (2010 Test Year)—In April 2010, WPL filed a request with the PSCW to increase annual retail electric rates by $9 million to recover anticipated increased electric production fuel and energy purchases (fuel-related costs) in 2010. Actual fuel-related costs through March 2010, combined with projections of continued higher fuel-related costs for the remainder of 2010, significantly exceeded the amounts being recovered in retail electric rates at the time of the filing. WPL received approval from the PSCW to implement an interim rate increase of $9 million, on an annual basis, effective in June 2010. Updated annual 2010 fuel-related costs during the proceeding resulted in WPL no longer qualifying for a fuel-related rate increase for 2010. In December 2010, the PSCW issued an order authorizing no increase in retail electric rates in 2010 related to fuel-related costs and required the interim rate increase to terminate at the end of 2010. The order also authorized WPL to use $5 million of the interim fuel rates collected in 2010 as a reduction to the 2011 test year base rate increase. As of Sep. 30, 2011, Alliant Energy's and WPL's remaining reserves were $2 million, including interest, for interim fuel cost collections in 2010. Refer to Note 1(b) for discussion of various other rate matters.

(2) UTILITY RATE CASES

IPL's Minnesota Retail Electric Rate Case (2009 Test Year)—In May 2010, IPL filed a request with the MPUC to increase annual rates for its Minnesota retail electric customers by $15 million, or approximately 22%. The request was based on a 2009 historical test year as adjusted for certain known and measurable items at the time of the filing. The key drivers for the filing included recovery of investments in the Whispering Willow—East wind project and emission control projects at Lansing Unit 4, and recovery of increased electric transmission service costs. In conjunction with the filing, IPL implemented an interim retail rate increase of $14 million, on an annual basis, effective July 6, 2010. During the nine months ended Sep. 30, 2011 and 2010, Alliant Energy and IPL recorded $9 million and $4 million, respectively, in electric revenues from IPL's Minnesota retail electric customers related to the interim retail electric rate increase and the reserve for rate refund discussed below. In August 2011, IPL received an order from the MPUC authorizing a final annual retail electric rate increase equivalent to $11 million. The final annual retail electric rate increase of $11 million includes $8 million of higher base rates, $2 million from the renewable energy rider and $1 million from the utilization of regulatory liabilities to offset higher electric transmission service costs. As of Sep. 30, 2011, Alliant Energy and IPL reserved $3 million, including interest, for refunds anticipated to be paid to IPL's Minnesota retail electric customers in 2012 in accordance with the MPUC's August 2011 order. Refer to Note 1(b) for discussion of changes to regulatory assets and regulatory liabilities during the nine months ended Sep. 30, 2011 based on the MPUC's decisions to provide IPL's retail electric customers in Minnesota additional refunds from the gain on the sale of electric transmission assets in 2007 and to provide IPL recovery of $2 million of previously incurred costs for Sutherland #4. Refer to Note 1(c) for discussion of an impairment recognized during the nine months ended Sep. 30, 2011 based on the MPUC's decision regarding the recovery of Whispering Willow—East wind project costs.

IPL's Iowa Retail Electric Rate Case (2009 Test Year)—In March 2010, IPL filed a request with the IUB to increase annual rates for its Iowa retail electric customers. The request was based on a 2009 historical test year as adjusted for certain known and measurable changes occurring up to 12 months after the commencement of the proceeding. The key drivers for the filing included recovery of investments in the Whispering Willow—East wind project and emission control projects at Lansing Unit 4, and recovery of increased electric transmission service costs. In conjunction with the filing, IPL implemented an interim retail electric rate increase of $119 million, on an annual basis, effective March 20, 2010. During the nine months ended Sep. 30, 2011 and 2010, Alliant Energy and IPL recorded $95 million and $72 million, respectively, in electric revenues from IPL's Iowa retail electric customers related to the retail electric rate increase and the rate refund discussed below. In February 2011, IPL received an order from the IUB authorizing a final annual retail electric rate increase of $114 million, or approximately 10%. In 2011, IPL refunded $5 million, including interest, to its retail electric customers in Iowa.

WPL's Retail Fuel-related Rate Case (2012 Test Year)—In May 2011, WPL filed a request with the PSCW to increase annual retail electric rates by $13 million to recover anticipated increases in retail fuel-related costs in 2012 due to higher purchased power energy costs and emission compliance costs. In July 2011, the EPA issued CSAPR, which requires SO2 and NOx emissions reductions from IPL's and WPL's fossil-fueled electric generating units (EGUs) with greater than 25 MW of capacity located in Iowa, Minnesota and Wisconsin beginning in 2012. After evaluating CSAPR, in August 2011, WPL revised its request for an annual retail electric rate increase to $20 million to reflect higher emission compliance costs. Any rate changes granted from this request are expected to be effective on Jan. 1, 2012.

WPL's Retail Electric Rate Case (2011 Test Year)—In April 2010, WPL filed a request with the PSCW to reopen the rate order for its 2010 test year to increase annual retail electric rates for 2011. The request was based on a forward-looking test period that included 2011. The key drivers for the filing included recovery of investments in WPL's Bent Tree—Phase I wind project and expiring deferral credits, partially offset by lower variable fuel expenses. In December 2010, WPL received an order from the PSCW authorizing an annual retail electric rate increase of $8 million, or approximately 1%, effective Jan. 1, 2011. This $8 million increase in annual rates effective Jan. 1, 2011, combined with the termination of the $9 million interim fuel-related rate increase effective Dec. 31, 2010, resulted in a net $1 million decrease in annual retail electric rates charged to customers effective January 2011. Refer to "WPL's Retail Fuel-related Rate Case (2010 Test Year)" below for additional details of the interim fuel-related rate increase implemented in 2010 and a $5 million reduction to the 2011 test year base rate increase for refunds owed to retail electric customers related to interim fuel cost collections in 2010.

WPL's Retail Fuel-related Rate Case (2010 Test Year)—In April 2010, WPL filed a request with the PSCW to increase annual retail electric rates by $9 million to recover anticipated increased electric production fuel and energy purchases (fuel-related costs) in 2010. Actual fuel-related costs through March 2010, combined with projections of continued higher fuel-related costs for the remainder of 2010, significantly exceeded the amounts being recovered in retail electric rates at the time of the filing. WPL received approval from the PSCW to implement an interim rate increase of $9 million, on an annual basis, effective in June 2010. Updated annual 2010 fuel-related costs during the proceeding resulted in WPL no longer qualifying for a fuel-related rate increase for 2010. In December 2010, the PSCW issued an order authorizing no increase in retail electric rates in 2010 related to fuel-related costs and required the interim rate increase to terminate at the end of 2010. The order also authorized WPL to use $5 million of the interim fuel rates collected in 2010 as a reduction to the 2011 test year base rate increase. As of Sep. 30, 2011, Alliant Energy's and WPL's remaining reserves were $2 million, including interest, for interim fuel cost collections in 2010.

Refer to Note 1(b) for discussion of various other rate matters.

Utility Rate Cases

(2) UTILITY RATE CASES

IPL's Minnesota Retail Electric Rate Case (2009 Test Year)—In May 2010, IPL filed a request with the MPUC to increase annual rates for its Minnesota retail electric customers by $15 million, or approximately 22%. The request was based on a 2009 historical test year as adjusted for certain known and measurable items at the time of the filing. The key drivers for the filing included recovery of investments in the Whispering Willow—East wind project and emission control projects at Lansing Unit 4, and recovery of increased electric transmission service costs. In conjunction with the filing, IPL implemented an interim retail rate increase of $14 million, on an annual basis, effective July 6, 2010. During the nine months ended Sep. 30, 2011 and 2010, Alliant Energy and IPL recorded $9 million and $4 million, respectively, in electric revenues from IPL's Minnesota retail electric customers related to the interim retail electric rate increase and the reserve for rate refund discussed below. In August 2011, IPL received an order from the MPUC authorizing a final annual retail electric rate increase equivalent to $11 million. The final annual retail electric rate increase of $11 million includes $8 million of higher base rates, $2 million from the renewable energy rider and $1 million from the utilization of regulatory liabilities to offset higher electric transmission service costs. As of Sep. 30, 2011, Alliant Energy and IPL reserved $3 million, including interest, for refunds anticipated to be paid to IPL's Minnesota retail electric customers in 2012 in accordance with the MPUC's August 2011 order. Refer to Note 1(b) for discussion of changes to regulatory assets and regulatory liabilities during the nine months ended Sep. 30, 2011 based on the MPUC's decisions to provide IPL's retail electric customers in Minnesota additional refunds from the gain on the sale of electric transmission assets in 2007 and to provide IPL recovery of $2 million of previously incurred costs for Sutherland #4. Refer to Note 1(c) for discussion of an impairment recognized during the nine months ended Sep. 30, 2011 based on the MPUC's decision regarding the recovery of Whispering Willow—East wind project costs.

IPL's Iowa Retail Electric Rate Case (2009 Test Year)—In March 2010, IPL filed a request with the IUB to increase annual rates for its Iowa retail electric customers. The request was based on a 2009 historical test year as adjusted for certain known and measurable changes occurring up to 12 months after the commencement of the proceeding. The key drivers for the filing included recovery of investments in the Whispering Willow—East wind project and emission control projects at Lansing Unit 4, and recovery of increased electric transmission service costs. In conjunction with the filing, IPL implemented an interim retail electric rate increase of $119 million, on an annual basis, effective March 20, 2010. During the nine months ended Sep. 30, 2011 and 2010, Alliant Energy and IPL recorded $95 million and $72 million, respectively, in electric revenues from IPL's Iowa retail electric customers related to the retail electric rate increase and the rate refund discussed below. In February 2011, IPL received an order from the IUB authorizing a final annual retail electric rate increase of $114 million, or approximately 10%. In 2011, IPL refunded $5 million, including interest, to its retail electric customers in Iowa.

WPL's Retail Fuel-related Rate Case (2012 Test Year)—In May 2011, WPL filed a request with the PSCW to increase annual retail electric rates by $13 million to recover anticipated increases in retail fuel-related costs in 2012 due to higher purchased power energy costs and emission compliance costs. In July 2011, the EPA issued CSAPR, which requires SO2 and NOx emissions reductions from IPL's and WPL's fossil-fueled electric generating units (EGUs) with greater than 25 MW of capacity located in Iowa, Minnesota and Wisconsin beginning in 2012. After evaluating CSAPR, in August 2011, WPL revised its request for an annual retail electric rate increase to $20 million to reflect higher emission compliance costs. Any rate changes granted from this request are expected to be effective on Jan. 1, 2012.

WPL's Retail Electric Rate Case (2011 Test Year)—In April 2010, WPL filed a request with the PSCW to reopen the rate order for its 2010 test year to increase annual retail electric rates for 2011. The request was based on a forward-looking test period that included 2011. The key drivers for the filing included recovery of investments in WPL's Bent Tree—Phase I wind project and expiring deferral credits, partially offset by lower variable fuel expenses. In December 2010, WPL received an order from the PSCW authorizing an annual retail electric rate increase of $8 million, or approximately 1%, effective Jan. 1, 2011. This $8 million increase in annual rates effective Jan. 1, 2011, combined with the termination of the $9 million interim fuel-related rate increase effective Dec. 31, 2010, resulted in a net $1 million decrease in annual retail electric rates charged to customers effective January 2011. Refer to "WPL's Retail Fuel-related Rate Case (2010 Test Year)" below for additional details of the interim fuel-related rate increase implemented in 2010 and a $5 million reduction to the 2011 test year base rate increase for refunds owed to retail electric customers related to interim fuel cost collections in 2010.

WPL's Retail Fuel-related Rate Case (2010 Test Year)—In April 2010, WPL filed a request with the PSCW to increase annual retail electric rates by $9 million to recover anticipated increased electric production fuel and energy purchases (fuel-related costs) in 2010. Actual fuel-related costs through March 2010, combined with projections of continued higher fuel-related costs for the remainder of 2010, significantly exceeded the amounts being recovered in retail electric rates at the time of the filing. WPL received approval from the PSCW to implement an interim rate increase of $9 million, on an annual basis, effective in June 2010. Updated annual 2010 fuel-related costs during the proceeding resulted in WPL no longer qualifying for a fuel-related rate increase for 2010. In December 2010, the PSCW issued an order authorizing no increase in retail electric rates in 2010 related to fuel-related costs and required the interim rate increase to terminate at the end of 2010. The order also authorized WPL to use $5 million of the interim fuel rates collected in 2010 as a reduction to the 2011 test year base rate increase. As of Sep. 30, 2011, Alliant Energy's and WPL's remaining reserves were $2 million, including interest, for interim fuel cost collections in 2010.

Refer to Note 1(b) for discussion of various other rate matters.

Utility Rate Cases

(2) UTILITY RATE CASES

IPL's Minnesota Retail Electric Rate Case (2009 Test Year)—In May 2010, IPL filed a request with the MPUC to increase annual rates for its Minnesota retail electric customers by $15 million, or approximately 22%. The request was based on a 2009 historical test year as adjusted for certain known and measurable items at the time of the filing. The key drivers for the filing included recovery of investments in the Whispering Willow—East wind project and emission control projects at Lansing Unit 4, and recovery of increased electric transmission service costs. In conjunction with the filing, IPL implemented an interim retail rate increase of $14 million, on an annual basis, effective July 6, 2010. During the nine months ended Sep. 30, 2011 and 2010, Alliant Energy and IPL recorded $9 million and $4 million, respectively, in electric revenues from IPL's Minnesota retail electric customers related to the interim retail electric rate increase and the reserve for rate refund discussed below. In August 2011, IPL received an order from the MPUC authorizing a final annual retail electric rate increase equivalent to $11 million. The final annual retail electric rate increase of $11 million includes $8 million of higher base rates, $2 million from the renewable energy rider and $1 million from the utilization of regulatory liabilities to offset higher electric transmission service costs. As of Sep. 30, 2011, Alliant Energy and IPL reserved $3 million, including interest, for refunds anticipated to be paid to IPL's Minnesota retail electric customers in 2012 in accordance with the MPUC's August 2011 order. Refer to Note 1(b) for discussion of changes to regulatory assets and regulatory liabilities during the nine months ended Sep. 30, 2011 based on the MPUC's decisions to provide IPL's retail electric customers in Minnesota additional refunds from the gain on the sale of electric transmission assets in 2007 and to provide IPL recovery of $2 million of previously incurred costs for Sutherland #4. Refer to Note 1(c) for discussion of an impairment recognized during the nine months ended Sep. 30, 2011 based on the MPUC's decision regarding the recovery of Whispering Willow—East wind project costs.

IPL's Iowa Retail Electric Rate Case (2009 Test Year)—In March 2010, IPL filed a request with the IUB to increase annual rates for its Iowa retail electric customers. The request was based on a 2009 historical test year as adjusted for certain known and measurable changes occurring up to 12 months after the commencement of the proceeding. The key drivers for the filing included recovery of investments in the Whispering Willow—East wind project and emission control projects at Lansing Unit 4, and recovery of increased electric transmission service costs. In conjunction with the filing, IPL implemented an interim retail electric rate increase of $119 million, on an annual basis, effective March 20, 2010. During the nine months ended Sep. 30, 2011 and 2010, Alliant Energy and IPL recorded $95 million and $72 million, respectively, in electric revenues from IPL's Iowa retail electric customers related to the retail electric rate increase and the rate refund discussed below. In February 2011, IPL received an order from the IUB authorizing a final annual retail electric rate increase of $114 million, or approximately 10%. In 2011, IPL refunded $5 million, including interest, to its retail electric customers in Iowa.

WPL's Retail Fuel-related Rate Case (2012 Test Year)—In May 2011, WPL filed a request with the PSCW to increase annual retail electric rates by $13 million to recover anticipated increases in retail fuel-related costs in 2012 due to higher purchased power energy costs and emission compliance costs. In July 2011, the EPA issued CSAPR, which requires SO2 and NOx emissions reductions from IPL's and WPL's fossil-fueled electric generating units (EGUs) with greater than 25 MW of capacity located in Iowa, Minnesota and Wisconsin beginning in 2012. After evaluating CSAPR, in August 2011, WPL revised its request for an annual retail electric rate increase to $20 million to reflect higher emission compliance costs. Any rate changes granted from this request are expected to be effective on Jan. 1, 2012.

WPL's Retail Electric Rate Case (2011 Test Year)—In April 2010, WPL filed a request with the PSCW to reopen the rate order for its 2010 test year to increase annual retail electric rates for 2011. The request was based on a forward-looking test period that included 2011. The key drivers for the filing included recovery of investments in WPL's Bent Tree—Phase I wind project and expiring deferral credits, partially offset by lower variable fuel expenses. In December 2010, WPL received an order from the PSCW authorizing an annual retail electric rate increase of $8 million, or approximately 1%, effective Jan. 1, 2011. This $8 million increase in annual rates effective Jan. 1, 2011, combined with the termination of the $9 million interim fuel-related rate increase effective Dec. 31, 2010, resulted in a net $1 million decrease in annual retail electric rates charged to customers effective January 2011. Refer to "WPL's Retail Fuel-related Rate Case (2010 Test Year)" below for additional details of the interim fuel-related rate increase implemented in 2010 and a $5 million reduction to the 2011 test year base rate increase for refunds owed to retail electric customers related to interim fuel cost collections in 2010.

WPL's Retail Fuel-related Rate Case (2010 Test Year)—In April 2010, WPL filed a request with the PSCW to increase annual retail electric rates by $9 million to recover anticipated increased electric production fuel and energy purchases (fuel-related costs) in 2010. Actual fuel-related costs through March 2010, combined with projections of continued higher fuel-related costs for the remainder of 2010, significantly exceeded the amounts being recovered in retail electric rates at the time of the filing. WPL received approval from the PSCW to implement an interim rate increase of $9 million, on an annual basis, effective in June 2010. Updated annual 2010 fuel-related costs during the proceeding resulted in WPL no longer qualifying for a fuel-related rate increase for 2010. In December 2010, the PSCW issued an order authorizing no increase in retail electric rates in 2010 related to fuel-related costs and required the interim rate increase to terminate at the end of 2010. The order also authorized WPL to use $5 million of the interim fuel rates collected in 2010 as a reduction to the 2011 test year base rate increase. As of Sep. 30, 2011, Alliant Energy's and WPL's remaining reserves were $2 million, including interest, for interim fuel cost collections in 2010.

Refer to Note 1(b) for discussion of various other rate matters.