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Regulatory Matters (Tables) | 3 Months Ended
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Mar. 31, 2021
Regulatory Assets [Line Items] |
Regulatory Assets | 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
Regulatory Liabilities | 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
IPL [Member] |
Regulatory Assets [Line Items] |
Regulatory Assets | 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
Regulatory Liabilities | 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
WPL [Member] |
Regulatory Assets [Line Items] |
Regulatory Assets | 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
Regulatory Liabilities | 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

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