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Regulatory Matters | 3 Months Ended
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Mar. 31, 2018
Public Utilities, General Disclosures [Line Items] |
Regulatory Matters | REGULATORY MATTERS Regulatory Assets and Regulatory Liabilities - Regulatory assets were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| March 31, 2018 |  | December 31, 2017 |  | March 31, 2018 |  | December 31, 2017 |  | March 31, 2018 |  | December 31, 2017
Tax-related |  | $795.1 |  |  |  | $778.2 |  |  |  | $762.8 |  |  |  | $750.5 |  |  |  | $32.3 |  |  |  | $27.7 |
Pension and OPEB costs | 538.6 |  |  | 548.0 |  |  | 270.0 |  |  | 274.4 |  |  | 268.6 |  |  | 273.6 |
Asset retirement obligations | 104.3 |  |  | 109.3 |  |  | 67.9 |  |  | 72.5 |  |  | 36.4 |  |  | 36.8 |
EGUs retired early | 60.1 |  |  | 63.8 |  |  | 30.4 |  |  | 31.6 |  |  | 29.7 |  |  | 32.2 |
Derivatives | 47.6 |  |  | 45.3 |  |  | 25.5 |  |  | 21.8 |  |  | 22.1 |  |  | 23.5 |
Emission allowances | 25.4 |  |  | 25.5 |  |  | 25.4 |  |  | 25.5 |  |  | — |  |  | — |
Other | 93.0 |  |  | 96.6 |  |  | 48.9 |  |  | 55.3 |  |  | 44.1 |  |  | 41.3 |
|  | $1,664.1 |  |  |  | $1,666.7 |  |  |  | $1,230.9 |  |  |  | $1,231.6 |  |  |  | $433.2 |  |  |  | $435.1 |
Regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| March 31, 2018 |  | December 31, 2017 |  | March 31, 2018 |  | December 31, 2017 |  | March 31, 2018 |  | December 31, 2017
Tax-related |  | $901.3 |  |  |  | $899.4 |  |  |  | $399.5 |  |  |  | $399.5 |  |  |  | $501.8 |  |  |  | $499.9 |
Cost of removal obligations | 415.6 |  |  | 410.0 |  |  | 274.7 |  |  | 274.5 |  |  | 140.9 |  |  | 135.5 |
Electric transmission cost recovery | 95.3 |  |  | 90.4 |  |  | 33.5 |  |  | 26.4 |  |  | 61.8 |  |  | 64.0 |
Commodity cost recovery | 31.2 |  |  | 21.0 |  |  | 24.2 |  |  | 14.6 |  |  | 7.0 |  |  | 6.4 |
IPL’s tax benefit riders | 25.0 |  |  | 25.0 |  |  | 25.0 |  |  | 25.0 |  |  | — |  |  | — |
Other | 69.5 |  |  | 51.4 |  |  | 20.4 |  |  | 15.4 |  |  | 49.1 |  |  | 36.0 |
|  | $1,537.9 |  |  |  | $1,497.2 |  |  |  | $777.3 |  |  |  | $755.4 |  |  |  | $760.6 |  |  |  | $741.8 |
Tax-related - Alliant Energy’s and IPL’s tax-related regulatory assets are generally impacted by certain property-related differences at IPL for which deferred tax is not recorded in the income statement pursuant to Iowa rate-making principles. Deferred tax amounts for such property-related differences at IPL are recorded to regulatory assets, along with the necessary revenue requirement tax gross-ups. During the three months ended March 31, 2018, Alliant Energy’s and IPL’s tax-related regulatory assets increased primarily due to property-related differences for qualifying repair expenditures. Other - In January 2018, the IUB issued an order requiring IPL and other investor-owned utilities in Iowa to track all calculated differences since January 1, 2018 resulting from Tax Reform, such that any over-collections can be refunded to its customers at a future date, if appropriate. In January 2018, the PSCW issued an order directing WPL and other investor-owned utilities in Wisconsin to defer the revenue requirement impacts resulting from Tax Reform since its inception. As a result of these orders, as of March 31, 2018, Alliant Energy, IPL and WPL deferred $19 million, $8 million and $11 million, respectively, related to Tax Reform, which is included in “Other” in the regulatory liabilities table above. Utility Rate Reviews - IPL’s Retail Gas Rate Review (2017 Test Year) - In May 2018, IPL filed a request with the IUB to increase annual gas base rates for its Iowa retail gas customers by $20 million, or approximately 8%. The request was based on a 2017 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 capital projects, partially offset by the benefits of Tax Reform. An interim retail gas rate increase of $11 million, or approximately 5%, on an annual basis, will be implemented effective May 14, 2018. The interim rate increase does not require regulatory approval; however, it will be subject to refund pending determination of final rates. IPL currently expects a decision from the IUB in 2019 with final rates effective by the second quarter of 2019. The IUB must issue a decision on requests for retail rate changes within 10 months of the date of the application for which changes are filed. IPL’s Retail Electric Rate Review (2016 Test Year) - In April 2017, IPL filed a request with the IUB to increase annual electric base rates for its Iowa retail electric customers. An interim retail electric base rate increase of $102 million, or approximately 7%, on an annual basis, was implemented effective April 13, 2017. In September 2017, IPL reached a partial, non-unanimous settlement agreement with the Iowa Office of Consumer Advocate, the Iowa Business Energy Coalition and the Large Energy Group for an annual electric base rate increase of $130 million, or approximately 9%. In February 2018, the IUB issued an order approving the settlement. Final rates were effective May 1, 2018. For the three months ended March 31, 2018, Alliant Energy and IPL recorded increases in electric base rates of $23 million in conjunction with the interim retail electric base rate increase.
IPL [Member] |
Public Utilities, General Disclosures [Line Items] |
Regulatory Matters | REGULATORY MATTERS Regulatory Assets and Regulatory Liabilities - Regulatory assets were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| March 31, 2018 |  | December 31, 2017 |  | March 31, 2018 |  | December 31, 2017 |  | March 31, 2018 |  | December 31, 2017
Tax-related |  | $795.1 |  |  |  | $778.2 |  |  |  | $762.8 |  |  |  | $750.5 |  |  |  | $32.3 |  |  |  | $27.7 |
Pension and OPEB costs | 538.6 |  |  | 548.0 |  |  | 270.0 |  |  | 274.4 |  |  | 268.6 |  |  | 273.6 |
Asset retirement obligations | 104.3 |  |  | 109.3 |  |  | 67.9 |  |  | 72.5 |  |  | 36.4 |  |  | 36.8 |
EGUs retired early | 60.1 |  |  | 63.8 |  |  | 30.4 |  |  | 31.6 |  |  | 29.7 |  |  | 32.2 |
Derivatives | 47.6 |  |  | 45.3 |  |  | 25.5 |  |  | 21.8 |  |  | 22.1 |  |  | 23.5 |
Emission allowances | 25.4 |  |  | 25.5 |  |  | 25.4 |  |  | 25.5 |  |  | — |  |  | — |
Other | 93.0 |  |  | 96.6 |  |  | 48.9 |  |  | 55.3 |  |  | 44.1 |  |  | 41.3 |
|  | $1,664.1 |  |  |  | $1,666.7 |  |  |  | $1,230.9 |  |  |  | $1,231.6 |  |  |  | $433.2 |  |  |  | $435.1 |
Regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| March 31, 2018 |  | December 31, 2017 |  | March 31, 2018 |  | December 31, 2017 |  | March 31, 2018 |  | December 31, 2017
Tax-related |  | $901.3 |  |  |  | $899.4 |  |  |  | $399.5 |  |  |  | $399.5 |  |  |  | $501.8 |  |  |  | $499.9 |
Cost of removal obligations | 415.6 |  |  | 410.0 |  |  | 274.7 |  |  | 274.5 |  |  | 140.9 |  |  | 135.5 |
Electric transmission cost recovery | 95.3 |  |  | 90.4 |  |  | 33.5 |  |  | 26.4 |  |  | 61.8 |  |  | 64.0 |
Commodity cost recovery | 31.2 |  |  | 21.0 |  |  | 24.2 |  |  | 14.6 |  |  | 7.0 |  |  | 6.4 |
IPL’s tax benefit riders | 25.0 |  |  | 25.0 |  |  | 25.0 |  |  | 25.0 |  |  | — |  |  | — |
Other | 69.5 |  |  | 51.4 |  |  | 20.4 |  |  | 15.4 |  |  | 49.1 |  |  | 36.0 |
|  | $1,537.9 |  |  |  | $1,497.2 |  |  |  | $777.3 |  |  |  | $755.4 |  |  |  | $760.6 |  |  |  | $741.8 |
Tax-related - Alliant Energy’s and IPL’s tax-related regulatory assets are generally impacted by certain property-related differences at IPL for which deferred tax is not recorded in the income statement pursuant to Iowa rate-making principles. Deferred tax amounts for such property-related differences at IPL are recorded to regulatory assets, along with the necessary revenue requirement tax gross-ups. During the three months ended March 31, 2018, Alliant Energy’s and IPL’s tax-related regulatory assets increased primarily due to property-related differences for qualifying repair expenditures. Other - In January 2018, the IUB issued an order requiring IPL and other investor-owned utilities in Iowa to track all calculated differences since January 1, 2018 resulting from Tax Reform, such that any over-collections can be refunded to its customers at a future date, if appropriate. In January 2018, the PSCW issued an order directing WPL and other investor-owned utilities in Wisconsin to defer the revenue requirement impacts resulting from Tax Reform since its inception. As a result of these orders, as of March 31, 2018, Alliant Energy, IPL and WPL deferred $19 million, $8 million and $11 million, respectively, related to Tax Reform, which is included in “Other” in the regulatory liabilities table above. Utility Rate Reviews - IPL’s Retail Gas Rate Review (2017 Test Year) - In May 2018, IPL filed a request with the IUB to increase annual gas base rates for its Iowa retail gas customers by $20 million, or approximately 8%. The request was based on a 2017 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 capital projects, partially offset by the benefits of Tax Reform. An interim retail gas rate increase of $11 million, or approximately 5%, on an annual basis, will be implemented effective May 14, 2018. The interim rate increase does not require regulatory approval; however, it will be subject to refund pending determination of final rates. IPL currently expects a decision from the IUB in 2019 with final rates effective by the second quarter of 2019. The IUB must issue a decision on requests for retail rate changes within 10 months of the date of the application for which changes are filed. IPL’s Retail Electric Rate Review (2016 Test Year) - In April 2017, IPL filed a request with the IUB to increase annual electric base rates for its Iowa retail electric customers. An interim retail electric base rate increase of $102 million, or approximately 7%, on an annual basis, was implemented effective April 13, 2017. In September 2017, IPL reached a partial, non-unanimous settlement agreement with the Iowa Office of Consumer Advocate, the Iowa Business Energy Coalition and the Large Energy Group for an annual electric base rate increase of $130 million, or approximately 9%. In February 2018, the IUB issued an order approving the settlement. Final rates were effective May 1, 2018. For the three months ended March 31, 2018, Alliant Energy and IPL recorded increases in electric base rates of $23 million in conjunction with the interim retail electric base rate increase.
WPL [Member] |
Public Utilities, General Disclosures [Line Items] |
Regulatory Matters | REGULATORY MATTERS Regulatory Assets and Regulatory Liabilities - Regulatory assets were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| March 31, 2018 |  | December 31, 2017 |  | March 31, 2018 |  | December 31, 2017 |  | March 31, 2018 |  | December 31, 2017
Tax-related |  | $795.1 |  |  |  | $778.2 |  |  |  | $762.8 |  |  |  | $750.5 |  |  |  | $32.3 |  |  |  | $27.7 |
Pension and OPEB costs | 538.6 |  |  | 548.0 |  |  | 270.0 |  |  | 274.4 |  |  | 268.6 |  |  | 273.6 |
Asset retirement obligations | 104.3 |  |  | 109.3 |  |  | 67.9 |  |  | 72.5 |  |  | 36.4 |  |  | 36.8 |
EGUs retired early | 60.1 |  |  | 63.8 |  |  | 30.4 |  |  | 31.6 |  |  | 29.7 |  |  | 32.2 |
Derivatives | 47.6 |  |  | 45.3 |  |  | 25.5 |  |  | 21.8 |  |  | 22.1 |  |  | 23.5 |
Emission allowances | 25.4 |  |  | 25.5 |  |  | 25.4 |  |  | 25.5 |  |  | — |  |  | — |
Other | 93.0 |  |  | 96.6 |  |  | 48.9 |  |  | 55.3 |  |  | 44.1 |  |  | 41.3 |
|  | $1,664.1 |  |  |  | $1,666.7 |  |  |  | $1,230.9 |  |  |  | $1,231.6 |  |  |  | $433.2 |  |  |  | $435.1 |
Regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| March 31, 2018 |  | December 31, 2017 |  | March 31, 2018 |  | December 31, 2017 |  | March 31, 2018 |  | December 31, 2017
Tax-related |  | $901.3 |  |  |  | $899.4 |  |  |  | $399.5 |  |  |  | $399.5 |  |  |  | $501.8 |  |  |  | $499.9 |
Cost of removal obligations | 415.6 |  |  | 410.0 |  |  | 274.7 |  |  | 274.5 |  |  | 140.9 |  |  | 135.5 |
Electric transmission cost recovery | 95.3 |  |  | 90.4 |  |  | 33.5 |  |  | 26.4 |  |  | 61.8 |  |  | 64.0 |
Commodity cost recovery | 31.2 |  |  | 21.0 |  |  | 24.2 |  |  | 14.6 |  |  | 7.0 |  |  | 6.4 |
IPL’s tax benefit riders | 25.0 |  |  | 25.0 |  |  | 25.0 |  |  | 25.0 |  |  | — |  |  | — |
Other | 69.5 |  |  | 51.4 |  |  | 20.4 |  |  | 15.4 |  |  | 49.1 |  |  | 36.0 |
|  | $1,537.9 |  |  |  | $1,497.2 |  |  |  | $777.3 |  |  |  | $755.4 |  |  |  | $760.6 |  |  |  | $741.8 |
Tax-related - Alliant Energy’s and IPL’s tax-related regulatory assets are generally impacted by certain property-related differences at IPL for which deferred tax is not recorded in the income statement pursuant to Iowa rate-making principles. Deferred tax amounts for such property-related differences at IPL are recorded to regulatory assets, along with the necessary revenue requirement tax gross-ups. During the three months ended March 31, 2018, Alliant Energy’s and IPL’s tax-related regulatory assets increased primarily due to property-related differences for qualifying repair expenditures. Other - In January 2018, the IUB issued an order requiring IPL and other investor-owned utilities in Iowa to track all calculated differences since January 1, 2018 resulting from Tax Reform, such that any over-collections can be refunded to its customers at a future date, if appropriate. In January 2018, the PSCW issued an order directing WPL and other investor-owned utilities in Wisconsin to defer the revenue requirement impacts resulting from Tax Reform since its inception. As a result of these orders, as of March 31, 2018, Alliant Energy, IPL and WPL deferred $19 million, $8 million and $11 million, respectively, related to Tax Reform, which is included in “Other” in the regulatory liabilities table above.

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