XML 27 R7.htm IDEA: XBRL DOCUMENT
v3.21.2

Regulatory Matters | 9 Months Ended
--- | ---
Sep. 30, 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
| September 30, 2021 |  | December 31, 2020 |  | September 30, 2021 |  | December 31, 2020 |  | September 30, 2021 |  | December 31, 2020
Tax-related | $931 |  | $890 |  | $881 |  | $843 |  | $50 |  | $47
Pension and OPEB costs | 549 |  | 580 |  | 276 |  | 291 |  | 273 |  | 289
Asset retirement obligations | 124 |  | 119 |  | 85 |  | 81 |  | 39 |  | 38
Assets retired early | 98 |  | 113 |  | 69 |  | 77 |  | 29 |  | 36
IPL’s DAEC PPA amendment | 96 |  | 110 |  | 96 |  | 110 |  | — |  | —
WPL’s Western Wisconsin gas distribution expansion investments | 53 |  | 55 |  | — |  | — |  | 53 |  | 55
Commodity cost recovery | 32 |  | 4 |  | 17 |  | 1 |  | 15 |  | 3
Derivatives | 4 |  | 26 |  | 4 |  | 13 |  | — |  | 13
Other | 131 |  | 113 |  | 79 |  | 67 |  | 52 |  | 46
| $2,018 |  | $2,010 |  | $1,507 |  | $1,483 |  | $511 |  | $527
Commodity cost recovery - 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 September 30, 2021, IPL’s cumulative under-collection of natural gas costs was $15 million. 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. The cost recovery mechanism for WPL’s retail electric customers is based on forecasts of certain fuel-related costs expected to be incurred during forward-looking test periods and fuel monitoring ranges determined by the PSCW during each retail electric rate proceeding or in a separate fuel cost plan approval proceeding. In 2021, WPL’s actual fuel-related costs fell outside these fuel monitoring ranges, resulting in a $12 million deferral as of September 30, 2021. Regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| September 30, 2021 |  | December 31, 2020 |  | September 30, 2021 |  | December 31, 2020 |  | September 30, 2021 |  | December 31, 2020
Tax-related | $611 |  | $732 |  | $313 |  | $331 |  | $298 |  | $401
Cost of removal obligations | 383 |  | 367 |  | 252 |  | 238 |  | 131 |  | 129
Derivatives | 221 |  | 28 |  | 104 |  | 25 |  | 117 |  | 3
Electric transmission cost recovery | 53 |  | 68 |  | 29 |  | 39 |  | 24 |  | 29
WPL’s West Riverside liquidated damages | 40 |  | 38 |  | — |  | — |  | 40 |  | 38
Other | 53 |  | 73 |  | 22 |  | 43 |  | 31 |  | 30
| $1,361 |  | $1,306 |  | $720 |  | $676 |  | $641 |  | $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 nine months ended September 30, 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
| September 30, 2021 |  | December 31, 2020 |  | September 30, 2021 |  | December 31, 2020 |  | September 30, 2021 |  | December 31, 2020
Tax-related | $931 |  | $890 |  | $881 |  | $843 |  | $50 |  | $47
Pension and OPEB costs | 549 |  | 580 |  | 276 |  | 291 |  | 273 |  | 289
Asset retirement obligations | 124 |  | 119 |  | 85 |  | 81 |  | 39 |  | 38
Assets retired early | 98 |  | 113 |  | 69 |  | 77 |  | 29 |  | 36
IPL’s DAEC PPA amendment | 96 |  | 110 |  | 96 |  | 110 |  | — |  | —
WPL’s Western Wisconsin gas distribution expansion investments | 53 |  | 55 |  | — |  | — |  | 53 |  | 55
Commodity cost recovery | 32 |  | 4 |  | 17 |  | 1 |  | 15 |  | 3
Derivatives | 4 |  | 26 |  | 4 |  | 13 |  | — |  | 13
Other | 131 |  | 113 |  | 79 |  | 67 |  | 52 |  | 46
| $2,018 |  | $2,010 |  | $1,507 |  | $1,483 |  | $511 |  | $527
Commodity cost recovery - 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 September 30, 2021, IPL’s cumulative under-collection of natural gas costs was $15 million. 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. The cost recovery mechanism for WPL’s retail electric customers is based on forecasts of certain fuel-related costs expected to be incurred during forward-looking test periods and fuel monitoring ranges determined by the PSCW during each retail electric rate proceeding or in a separate fuel cost plan approval proceeding. In 2021, WPL’s actual fuel-related costs fell outside these fuel monitoring ranges, resulting in a $12 million deferral as of September 30, 2021. Regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| September 30, 2021 |  | December 31, 2020 |  | September 30, 2021 |  | December 31, 2020 |  | September 30, 2021 |  | December 31, 2020
Tax-related | $611 |  | $732 |  | $313 |  | $331 |  | $298 |  | $401
Cost of removal obligations | 383 |  | 367 |  | 252 |  | 238 |  | 131 |  | 129
Derivatives | 221 |  | 28 |  | 104 |  | 25 |  | 117 |  | 3
Electric transmission cost recovery | 53 |  | 68 |  | 29 |  | 39 |  | 24 |  | 29
WPL’s West Riverside liquidated damages | 40 |  | 38 |  | — |  | — |  | 40 |  | 38
Other | 53 |  | 73 |  | 22 |  | 43 |  | 31 |  | 30
| $1,361 |  | $1,306 |  | $720 |  | $676 |  | $641 |  | $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 nine months ended September 30, 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
| September 30, 2021 |  | December 31, 2020 |  | September 30, 2021 |  | December 31, 2020 |  | September 30, 2021 |  | December 31, 2020
Tax-related | $931 |  | $890 |  | $881 |  | $843 |  | $50 |  | $47
Pension and OPEB costs | 549 |  | 580 |  | 276 |  | 291 |  | 273 |  | 289
Asset retirement obligations | 124 |  | 119 |  | 85 |  | 81 |  | 39 |  | 38
Assets retired early | 98 |  | 113 |  | 69 |  | 77 |  | 29 |  | 36
IPL’s DAEC PPA amendment | 96 |  | 110 |  | 96 |  | 110 |  | — |  | —
WPL’s Western Wisconsin gas distribution expansion investments | 53 |  | 55 |  | — |  | — |  | 53 |  | 55
Commodity cost recovery | 32 |  | 4 |  | 17 |  | 1 |  | 15 |  | 3
Derivatives | 4 |  | 26 |  | 4 |  | 13 |  | — |  | 13
Other | 131 |  | 113 |  | 79 |  | 67 |  | 52 |  | 46
| $2,018 |  | $2,010 |  | $1,507 |  | $1,483 |  | $511 |  | $527
Commodity cost recovery - 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 September 30, 2021, IPL’s cumulative under-collection of natural gas costs was $15 million. 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. The cost recovery mechanism for WPL’s retail electric customers is based on forecasts of certain fuel-related costs expected to be incurred during forward-looking test periods and fuel monitoring ranges determined by the PSCW during each retail electric rate proceeding or in a separate fuel cost plan approval proceeding. In 2021, WPL’s actual fuel-related costs fell outside these fuel monitoring ranges, resulting in a $12 million deferral as of September 30, 2021. Regulatory liabilities were comprised of the following items (in millions):
| Alliant Energy |  | IPL |  | WPL
| September 30, 2021 |  | December 31, 2020 |  | September 30, 2021 |  | December 31, 2020 |  | September 30, 2021 |  | December 31, 2020
Tax-related | $611 |  | $732 |  | $313 |  | $331 |  | $298 |  | $401
Cost of removal obligations | 383 |  | 367 |  | 252 |  | 238 |  | 131 |  | 129
Derivatives | 221 |  | 28 |  | 104 |  | 25 |  | 117 |  | 3
Electric transmission cost recovery | 53 |  | 68 |  | 29 |  | 39 |  | 24 |  | 29
WPL’s West Riverside liquidated damages | 40 |  | 38 |  | — |  | — |  | 40 |  | 38
Other | 53 |  | 73 |  | 22 |  | 43 |  | 31 |  | 30
| $1,361 |  | $1,306 |  | $720 |  | $676 |  | $641 |  | $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 nine months ended September 30, 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.

X
- Definition The entire disclosure for public utilities. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -URI http://asc.fasb.org/topic&trid=2156578 + Details
Name: | us-gaap_PublicUtilitiesDisclosureTextBlock
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_PublicUtilitiesGeneralDisclosuresLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | dei_LegalEntityAxis=lnt_IplMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=lnt_WplMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |