Property, Plant and Equipment	3 Months Ended
Property, Plant and Equipment	Mar. 31, 2017
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	PROPERTY, PLANT AND EQUIPMENT Utility - Natural Gas-Fired Generation Projects - IPL’s Marshalltown Generating Station - IPL’s construction of Marshalltown, an approximate 660 MW natural gas-fired combined-cycle EGU, was completed and the EGU was placed into service in April 2017. As of March 31, 2017, Alliant Energy and IPL recorded capitalized expenditures of $635 million and AFUDC of $79 million for Marshalltown in “Property, plant and equipment, net” on their balance sheets. WPL’s Riverside Expansion - WPL is currently constructing the Riverside expansion, an approximate 730 MW natural gas-fired combined-cycle EGU. Construction began in 2016 and is currently expected to be completed by early 2020. As of March 31, 2017, Alliant Energy and WPL recorded capitalized expenditures for construction work in progress of $129 million and AFUDC of $3 million for the Riverside expansion in “Property, plant and equipment, net” on their balance sheets. These capital expenditures do not yet reflect any potential impacts from the intent to exercise purchase options by certain WPL electric cooperatives for a partial ownership interest in the Riverside expansion. Wind Generation - Franklin County Wind Farm Transfer - In April 2017, the Franklin County wind farm was transferred from AEF to IPL pursuant to a February 2017 FERC order, at a value of approximately $33 million, subject to final working capital adjustments. 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 review for the 2016 Test Year, which was filed in April 2017.
IPL [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	PROPERTY, PLANT AND EQUIPMENT Utility - Natural Gas-Fired Generation Projects - IPL’s Marshalltown Generating Station - IPL’s construction of Marshalltown, an approximate 660 MW natural gas-fired combined-cycle EGU, was completed and the EGU was placed into service in April 2017. As of March 31, 2017, Alliant Energy and IPL recorded capitalized expenditures of $635 million and AFUDC of $79 million for Marshalltown in “Property, plant and equipment, net” on their balance sheets. WPL’s Riverside Expansion - WPL is currently constructing the Riverside expansion, an approximate 730 MW natural gas-fired combined-cycle EGU. Construction began in 2016 and is currently expected to be completed by early 2020. As of March 31, 2017, Alliant Energy and WPL recorded capitalized expenditures for construction work in progress of $129 million and AFUDC of $3 million for the Riverside expansion in “Property, plant and equipment, net” on their balance sheets. These capital expenditures do not yet reflect any potential impacts from the intent to exercise purchase options by certain WPL electric cooperatives for a partial ownership interest in the Riverside expansion. Wind Generation - Franklin County Wind Farm Transfer - In April 2017, the Franklin County wind farm was transferred from AEF to IPL pursuant to a February 2017 FERC order, at a value of approximately $33 million, subject to final working capital adjustments. 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 review for the 2016 Test Year, which was filed in April 2017.
WPL [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	PROPERTY, PLANT AND EQUIPMENT Utility - Natural Gas-Fired Generation Projects - IPL’s Marshalltown Generating Station - IPL’s construction of Marshalltown, an approximate 660 MW natural gas-fired combined-cycle EGU, was completed and the EGU was placed into service in April 2017. As of March 31, 2017, Alliant Energy and IPL recorded capitalized expenditures of $635 million and AFUDC of $79 million for Marshalltown in “Property, plant and equipment, net” on their balance sheets. WPL’s Riverside Expansion - WPL is currently constructing the Riverside expansion, an approximate 730 MW natural gas-fired combined-cycle EGU. Construction began in 2016 and is currently expected to be completed by early 2020. As of March 31, 2017, Alliant Energy and WPL recorded capitalized expenditures for construction work in progress of $129 million and AFUDC of $3 million for the Riverside expansion in “Property, plant and equipment, net” on their balance sheets. These capital expenditures do not yet reflect any potential impacts from the intent to exercise purchase options by certain WPL electric cooperatives for a partial ownership interest in the Riverside expansion.