Property, Plant and Equipment	6 Months Ended
Property, Plant and Equipment	Jun. 30, 2016
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	PROPERTY, PLANT AND EQUIPMENT Utility - Emission Controls Project - WPL’s Edgewater Unit 5 - Construction of the scrubber and baghouse at Edgewater Unit 5 was completed in July 2016. As of June 30, 2016, Alliant Energy and WPL recorded capitalized expenditures for construction work in progress of $217 million and AFUDC of $12 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 June 30, 2016, Alliant Energy and IPL recorded capitalized expenditures for construction work in progress of $558 million and AFUDC of $44 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 2015, IPL completed the sale of its Minnesota natural gas distribution assets and received proceeds of $11 million and a promissory note of $2 million. In 2015, IPL completed the sale of its Minnesota electric distribution assets and received proceeds of $129 million. 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 amounts 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 for the three and six months ended June 30, 2015.
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 - Construction of the scrubber and baghouse at Edgewater Unit 5 was completed in July 2016. As of June 30, 2016, Alliant Energy and WPL recorded capitalized expenditures for construction work in progress of $217 million and AFUDC of $12 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 June 30, 2016, Alliant Energy and IPL recorded capitalized expenditures for construction work in progress of $558 million and AFUDC of $44 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 2015, IPL completed the sale of its Minnesota natural gas distribution assets and received proceeds of $11 million and a promissory note of $2 million. In 2015, IPL completed the sale of its Minnesota electric distribution assets and received proceeds of $129 million. 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 amounts 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 for the three and six months ended June 30, 2015.
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 - Construction of the scrubber and baghouse at Edgewater Unit 5 was completed in July 2016. As of June 30, 2016, Alliant Energy and WPL recorded capitalized expenditures for construction work in progress of $217 million and AFUDC of $12 million for the scrubber and baghouse in “Property, plant and equipment, net” on their balance sheets.