Property, Plant and Equipment	9 Months Ended
Property, Plant and Equipment	Sep. 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 September 30, 2016, Alliant Energy and WPL recorded capitalized expenditures of $223 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 the second quarter of 2017. As of September 30, 2016, Alliant Energy and IPL recorded capitalized expenditures for construction work in progress of $600 million and AFUDC of $56 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 nine months ended September 30, 2015. Non-regulated and Other - Non-regulated Generation - Franklin County Wind Farm - Based on an evaluation of the strategic options for the Franklin County wind farm performed in the third quarter of 2016, Alliant Energy concluded, as of September 30, 2016, it was probable the Franklin County wind farm will be transferred to IPL. As a result, Alliant Energy performed an impairment analysis of such assets in the third quarter of 2016. The impairment analysis evaluated the value of the assets and a reasonable estimate of the amount of costs associated with the Franklin County wind farm that would be allowed for recovery for IPL’s electric rate-making purposes. Based on various analyses, including discounted cash flows projected from the Franklin County wind farm, recently executed purchased power agreements associated with wind generating facilities located near the Franklin County wind farm, and the cost of new wind farms identified through IPL’s planned wind expansion, the current value of the Franklin County wind farm assets as of September 30, 2016 was determined to be approximately $33 million, subject to working capital adjustments. Alliant Energy concluded such value represents a reasonable estimate of the amount IPL will be allowed for recovery for IPL’s electric rate-making purposes. As a result, the carrying amount of the Franklin County wind farm was reduced to its current value, resulting in non-cash, pre-tax asset valuation charges of $86 million (after-tax charges of $51 million, or $0.23 per share) in the third quarter of 2016. Alliant Energy recorded such charges as a reduction to “Property, plant and equipment, net” on its balance sheet in 2016 and charges to “Asset valuation charges for Franklin County wind farm” in its income statements for the three and nine months ended September 30, 2016. IPL currently anticipates requesting approval from FERC in the fourth quarter of 2016 to transfer the Franklin County wind farm to IPL and expects to complete such transfer in the first quarter of 2017. The final amount to be recovered for IPL’s electric rate-making purposes will be determined by the IUB as part of IPL’s Iowa retail electric rate case for the 2016 Test Year, currently anticipated to be filed in the second quarter of 2017, and therefore the final asset valuation charges are subject to change.
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 September 30, 2016, Alliant Energy and WPL recorded capitalized expenditures of $223 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 the second quarter of 2017. As of September 30, 2016, Alliant Energy and IPL recorded capitalized expenditures for construction work in progress of $600 million and AFUDC of $56 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 nine months ended September 30, 2015. Non-regulated and Other - Non-regulated Generation - Franklin County Wind Farm - Based on an evaluation of the strategic options for the Franklin County wind farm performed in the third quarter of 2016, Alliant Energy concluded, as of September 30, 2016, it was probable the Franklin County wind farm will be transferred to IPL. As a result, Alliant Energy performed an impairment analysis of such assets in the third quarter of 2016. The impairment analysis evaluated the value of the assets and a reasonable estimate of the amount of costs associated with the Franklin County wind farm that would be allowed for recovery for IPL’s electric rate-making purposes. Based on various analyses, including discounted cash flows projected from the Franklin County wind farm, recently executed purchased power agreements associated with wind generating facilities located near the Franklin County wind farm, and the cost of new wind farms identified through IPL’s planned wind expansion, the current value of the Franklin County wind farm assets as of September 30, 2016 was determined to be approximately $33 million, subject to working capital adjustments. Alliant Energy concluded such value represents a reasonable estimate of the amount IPL will be allowed for recovery for IPL’s electric rate-making purposes. As a result, the carrying amount of the Franklin County wind farm was reduced to its current value, resulting in non-cash, pre-tax asset valuation charges of $86 million (after-tax charges of $51 million, or $0.23 per share) in the third quarter of 2016. Alliant Energy recorded such charges as a reduction to “Property, plant and equipment, net” on its balance sheet in 2016 and charges to “Asset valuation charges for Franklin County wind farm” in its income statements for the three and nine months ended September 30, 2016. IPL currently anticipates requesting approval from FERC in the fourth quarter of 2016 to transfer the Franklin County wind farm to IPL and expects to complete such transfer in the first quarter of 2017. The final amount to be recovered for IPL’s electric rate-making purposes will be determined by the IUB as part of IPL’s Iowa retail electric rate case for the 2016 Test Year, currently anticipated to be filed in the second quarter of 2017, and therefore the final asset valuation charges are subject to change.
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 September 30, 2016, Alliant Energy and WPL recorded capitalized expenditures of $223 million and AFUDC of $12 million for the scrubber and baghouse in “Property, plant and equipment, net” on their balance sheets.