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Regulatory Matters | 3 Months Ended
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Mar. 31, 2021
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, 2021 |  | December 31, 2020 |  | March 31, 2021 |  | December 31, 2020 |  | March 31, 2021 |  | December 31, 2020
Tax-related | $901 |  | $890 |  | $853 |  | $843 |  | $48 |  | $47
Pension and OPEB costs | 570 |  | 580 |  | 286 |  | 291 |  | 284 |  | 289
Asset retirement obligations | 120 |  | 119 |  | 82 |  | 81 |  | 38 |  | 38
Assets retired early | 108 |  | 113 |  | 74 |  | 77 |  | 34 |  | 36
IPL’s DAEC PPA amendment | 108 |  | 110 |  | 108 |  | 110 |  | — |  | —
WPL’s Western Wisconsin gas distribution expansion investments | 55 |  | 55 |  | — |  | — |  | 55 |  | 55
Derivatives | 13 |  | 26 |  | 6 |  | 13 |  | 7 |  | 13
Other | 132 |  | 117 |  | 85 |  | 68 |  | 47 |  | 49
| $2,007 |  | $2,010 |  | $1,494 |  | $1,483 |  | $513 |  | $527
Other - In February 2021, portions of the central and southern U.S., including Alliant Energy’s service territories, experienced a prolonged period of very cold temperatures and a series of winter storms. These events created significant volatility and increases in commodity prices caused by higher demand for electricity and natural gas and disruptions in commodity supply, resulting in IPL under-recovering its natural gas costs. In March 2021, IPL received approval from the IUB to spread recovery of these higher natural gas costs from its retail customers through December 2021. As of March 31, 2021, IPL’s cumulative under-collection of these natural gas costs was $20 million, which is included in “Other” regulatory assets in the above table. The extreme temperatures in February 2021 did not impact WPL’s natural gas costs and IPL’s and WPL’s fuel-related costs to the extent of IPL’s natural gas costs. Regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| March 31, 2021 |  | December 31, 2020 |  | March 31, 2021 |  | December 31, 2020 |  | March 31, 2021 |  | December 31, 2020
Tax-related | $685 |  | $732 |  | $327 |  | $331 |  | $358 |  | $401
Cost of removal obligations | 371 |  | 367 |  | 242 |  | 238 |  | 129 |  | 129
Electric transmission cost recovery | 67 |  | 68 |  | 40 |  | 39 |  | 27 |  | 29
WPL’s West Riverside liquidated damages | 38 |  | 38 |  | — |  | — |  | 38 |  | 38
Derivatives | 26 |  | 28 |  | 18 |  | 25 |  | 8 |  | 3
Other | 68 |  | 73 |  | 34 |  | 43 |  | 34 |  | 30
| $1,255 |  | $1,306 |  | $661 |  | $676 |  | $594 |  | $630
Tax-related - Alliant Energy’s, IPL’s and WPL’s tax-related regulatory liabilities are primarily related to excess deferred tax benefits resulting from the remeasurement of accumulated deferred income taxes caused by Federal Tax Reform. During the three months ended March 31, 2021, Alliant Energy’s, IPL’s and WPL’s tax-related regulatory liabilities decreased primarily due to returning a portion of these excess deferred tax benefits back to customers.
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, 2021 |  | December 31, 2020 |  | March 31, 2021 |  | December 31, 2020 |  | March 31, 2021 |  | December 31, 2020
Tax-related | $901 |  | $890 |  | $853 |  | $843 |  | $48 |  | $47
Pension and OPEB costs | 570 |  | 580 |  | 286 |  | 291 |  | 284 |  | 289
Asset retirement obligations | 120 |  | 119 |  | 82 |  | 81 |  | 38 |  | 38
Assets retired early | 108 |  | 113 |  | 74 |  | 77 |  | 34 |  | 36
IPL’s DAEC PPA amendment | 108 |  | 110 |  | 108 |  | 110 |  | — |  | —
WPL’s Western Wisconsin gas distribution expansion investments | 55 |  | 55 |  | — |  | — |  | 55 |  | 55
Derivatives | 13 |  | 26 |  | 6 |  | 13 |  | 7 |  | 13
Other | 132 |  | 117 |  | 85 |  | 68 |  | 47 |  | 49
| $2,007 |  | $2,010 |  | $1,494 |  | $1,483 |  | $513 |  | $527
Other - In February 2021, portions of the central and southern U.S., including Alliant Energy’s service territories, experienced a prolonged period of very cold temperatures and a series of winter storms. These events created significant volatility and increases in commodity prices caused by higher demand for electricity and natural gas and disruptions in commodity supply, resulting in IPL under-recovering its natural gas costs. In March 2021, IPL received approval from the IUB to spread recovery of these higher natural gas costs from its retail customers through December 2021. As of March 31, 2021, IPL’s cumulative under-collection of these natural gas costs was $20 million, which is included in “Other” regulatory assets in the above table. The extreme temperatures in February 2021 did not impact WPL’s natural gas costs and IPL’s and WPL’s fuel-related costs to the extent of IPL’s natural gas costs. Regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| March 31, 2021 |  | December 31, 2020 |  | March 31, 2021 |  | December 31, 2020 |  | March 31, 2021 |  | December 31, 2020
Tax-related | $685 |  | $732 |  | $327 |  | $331 |  | $358 |  | $401
Cost of removal obligations | 371 |  | 367 |  | 242 |  | 238 |  | 129 |  | 129
Electric transmission cost recovery | 67 |  | 68 |  | 40 |  | 39 |  | 27 |  | 29
WPL’s West Riverside liquidated damages | 38 |  | 38 |  | — |  | — |  | 38 |  | 38
Derivatives | 26 |  | 28 |  | 18 |  | 25 |  | 8 |  | 3
Other | 68 |  | 73 |  | 34 |  | 43 |  | 34 |  | 30
| $1,255 |  | $1,306 |  | $661 |  | $676 |  | $594 |  | $630
Tax-related - Alliant Energy’s, IPL’s and WPL’s tax-related regulatory liabilities are primarily related to excess deferred tax benefits resulting from the remeasurement of accumulated deferred income taxes caused by Federal Tax Reform. During the three months ended March 31, 2021, Alliant Energy’s, IPL’s and WPL’s tax-related regulatory liabilities decreased primarily due to returning a portion of these excess deferred tax benefits back to customers.
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, 2021 |  | December 31, 2020 |  | March 31, 2021 |  | December 31, 2020 |  | March 31, 2021 |  | December 31, 2020
Tax-related | $901 |  | $890 |  | $853 |  | $843 |  | $48 |  | $47
Pension and OPEB costs | 570 |  | 580 |  | 286 |  | 291 |  | 284 |  | 289
Asset retirement obligations | 120 |  | 119 |  | 82 |  | 81 |  | 38 |  | 38
Assets retired early | 108 |  | 113 |  | 74 |  | 77 |  | 34 |  | 36
IPL’s DAEC PPA amendment | 108 |  | 110 |  | 108 |  | 110 |  | — |  | —
WPL’s Western Wisconsin gas distribution expansion investments | 55 |  | 55 |  | — |  | — |  | 55 |  | 55
Derivatives | 13 |  | 26 |  | 6 |  | 13 |  | 7 |  | 13
Other | 132 |  | 117 |  | 85 |  | 68 |  | 47 |  | 49
| $2,007 |  | $2,010 |  | $1,494 |  | $1,483 |  | $513 |  | $527
Other - In February 2021, portions of the central and southern U.S., including Alliant Energy’s service territories, experienced a prolonged period of very cold temperatures and a series of winter storms. These events created significant volatility and increases in commodity prices caused by higher demand for electricity and natural gas and disruptions in commodity supply, resulting in IPL under-recovering its natural gas costs. In March 2021, IPL received approval from the IUB to spread recovery of these higher natural gas costs from its retail customers through December 2021. As of March 31, 2021, IPL’s cumulative under-collection of these natural gas costs was $20 million, which is included in “Other” regulatory assets in the above table. The extreme temperatures in February 2021 did not impact WPL’s natural gas costs and IPL’s and WPL’s fuel-related costs to the extent of IPL’s natural gas costs. Regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| March 31, 2021 |  | December 31, 2020 |  | March 31, 2021 |  | December 31, 2020 |  | March 31, 2021 |  | December 31, 2020
Tax-related | $685 |  | $732 |  | $327 |  | $331 |  | $358 |  | $401
Cost of removal obligations | 371 |  | 367 |  | 242 |  | 238 |  | 129 |  | 129
Electric transmission cost recovery | 67 |  | 68 |  | 40 |  | 39 |  | 27 |  | 29
WPL’s West Riverside liquidated damages | 38 |  | 38 |  | — |  | — |  | 38 |  | 38
Derivatives | 26 |  | 28 |  | 18 |  | 25 |  | 8 |  | 3
Other | 68 |  | 73 |  | 34 |  | 43 |  | 34 |  | 30
| $1,255 |  | $1,306 |  | $661 |  | $676 |  | $594 |  | $630
Tax-related - Alliant Energy’s, IPL’s and WPL’s tax-related regulatory liabilities are primarily related to excess deferred tax benefits resulting from the remeasurement of accumulated deferred income taxes caused by Federal Tax Reform. During the three months ended March 31, 2021, Alliant Energy’s, IPL’s and WPL’s tax-related regulatory liabilities decreased primarily due to returning a portion of these excess deferred tax benefits back to customers.

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