Property, Plant and Equipment	9 Months Ended
Property, Plant and Equipment	Sep. 30, 2015
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	PROPERTY, PLANT AND EQUIPMENT Utility - Emission Controls Project - WPL’s Edgewater Unit 5 - WPL is currently constructing a scrubber and baghouse at Edgewater Unit 5 to reduce SO2 and mercury emissions at the EGU. Construction began in 2014 and is expected to be completed in 2016. As of September 30, 2015, Alliant Energy and WPL recorded capitalized expenditures for construction work in progress of $171 million and AFUDC of $6 million for the scrubber and baghouse in “Property, plant and equipment, net” on their balance sheets. Natural Gas-Fired Generation Project - IPL’s Marshalltown Generating Station - IPL is currently constructing Marshalltown, an approximate 650 MW natural gas-fired combined-cycle EGU. Construction began in 2014 and is expected to be completed in 2017. As of September 30, 2015, Alliant Energy and IPL recorded capitalized expenditures for construction work in progress of $414 million and AFUDC of $17 million for Marshalltown in “Property, plant and equipment, net” on their balance sheets. Sales of IPL’s Minnesota Electric and Natural Gas Distribution Assets - In April 2015, IPL completed the sale of its Minnesota natural gas distribution assets and received proceeds of $11 million, subject to post-closing adjustments based on the value of the net assets as of the closing date, and a promissory note of $2 million. In July 2015, IPL completed the sale of its Minnesota electric distribution assets (primarily related to property, plant and equipment) and received proceeds of $127 million, subject to post-closing adjustments based on the value of the net assets as of the closing date. The proceeds from the natural gas distribution assets were used for general corporate purposes and the proceeds from the electric distribution assets were used to reduce cash proceeds received from IPL’s sales of accounts receivable program. The premium received over the book value of the property, plant and equipment sold was more than offset by a reduction in tax-related regulatory assets associated with the distribution assets. As a result, Alliant Energy and IPL recorded pre-tax charges of $9 million and $3 million for the Minnesota electric and natural gas distribution asset transactions, respectively, in “Other operation and maintenance” in their income statements during the nine months ended September 30, 2015. In July 2015, FERC approved the wholesale power supply agreement between IPL and Southern Minnesota Energy Cooperative, which became effective upon the sale of IPL’s Minnesota electric distribution assets. Non-regulated and Other - Corporate Services and Other - Corporate Services is implementing a new customer billing and information system for IPL and WPL. As of September 30, 2015, Alliant Energy recorded capitalized expenditures of $87 million and capitalized interest of $2 million for the system in “Property, plant and equipment, net” on its balance sheet.
IPL [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	PROPERTY, PLANT AND EQUIPMENT Utility - Emission Controls Project - WPL’s Edgewater Unit 5 - WPL is currently constructing a scrubber and baghouse at Edgewater Unit 5 to reduce SO2 and mercury emissions at the EGU. Construction began in 2014 and is expected to be completed in 2016. As of September 30, 2015, Alliant Energy and WPL recorded capitalized expenditures for construction work in progress of $171 million and AFUDC of $6 million for the scrubber and baghouse in “Property, plant and equipment, net” on their balance sheets. Natural Gas-Fired Generation Project - IPL’s Marshalltown Generating Station - IPL is currently constructing Marshalltown, an approximate 650 MW natural gas-fired combined-cycle EGU. Construction began in 2014 and is expected to be completed in 2017. As of September 30, 2015, Alliant Energy and IPL recorded capitalized expenditures for construction work in progress of $414 million and AFUDC of $17 million for Marshalltown in “Property, plant and equipment, net” on their balance sheets. Sales of IPL’s Minnesota Electric and Natural Gas Distribution Assets - In April 2015, IPL completed the sale of its Minnesota natural gas distribution assets and received proceeds of $11 million, subject to post-closing adjustments based on the value of the net assets as of the closing date, and a promissory note of $2 million. In July 2015, IPL completed the sale of its Minnesota electric distribution assets (primarily related to property, plant and equipment) and received proceeds of $127 million, subject to post-closing adjustments based on the value of the net assets as of the closing date. The proceeds from the natural gas distribution assets were used for general corporate purposes and the proceeds from the electric distribution assets were used to reduce cash proceeds received from IPL’s sales of accounts receivable program. The premium received over the book value of the property, plant and equipment sold was more than offset by a reduction in tax-related regulatory assets associated with the distribution assets. As a result, Alliant Energy and IPL recorded pre-tax charges of $9 million and $3 million for the Minnesota electric and natural gas distribution asset transactions, respectively, in “Other operation and maintenance” in their income statements during the nine months ended September 30, 2015. In July 2015, FERC approved the wholesale power supply agreement between IPL and Southern Minnesota Energy Cooperative, which became effective upon the sale of IPL’s Minnesota electric distribution assets.
WPL [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	PROPERTY, PLANT AND EQUIPMENT Utility - Emission Controls Project - WPL’s Edgewater Unit 5 - WPL is currently constructing a scrubber and baghouse at Edgewater Unit 5 to reduce SO2 and mercury emissions at the EGU. Construction began in 2014 and is expected to be completed in 2016. As of September 30, 2015, Alliant Energy and WPL recorded capitalized expenditures for construction work in progress of $171 million and AFUDC of $6 million for the scrubber and baghouse in “Property, plant and equipment, net” on their balance sheets.