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Income Taxes (Tables) | 12 Months Ended
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Dec. 31, 2022
Income Tax [Line Items] |
Schedule of Components of Income Tax Expense (Benefit) | The components of “Income tax expense (benefit)” in the income statements were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2022 |  | 2021 |  | 2020 |  | 2022 |  | 2021 |  | 2020 |  | 2022 |  | 2021 |  | 2020
Current tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal | $7 |  | $1 |  | $1 |  | ($29) |  | ($21) |  | $6 |  | $46 |  | $22 |  | ($11)
State | 2 |  | 3 |  | 8 |  | (8) |  | (1) |  | (1) |  | 16 |  | 6 |  | 7
Deferred tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal | 109 |  | 9 |  | 22 |  | 91 |  | 73 |  | 30 |  | 10 |  | (75) |  | (9)
State | 28 |  | 15 |  | 8 |  | 1 |  | — |  | (2) |  | 12 |  | 11 |  | 10
Production tax credits | (123) |  | (101) |  | (95) |  | (105) |  | (87) |  | (80) |  | (18) |  | (14) |  | (15)
Investment tax credits | (1) |  | (1) |  | (1) |  | — |  | — |  | — |  | — |  | (1) |  | (1)
| $22 |  | ($74) |  | ($57) |  | ($50) |  | ($36) |  | ($47) |  | $66 |  | ($51) |  | ($19)
Schedule Of Effective Income Tax Rates | The overall income tax rates shown in the following table were computed by dividing income tax expense (benefit) by income before income taxes.
| Alliant Energy |  | IPL |  | WPL
| 2022 |  | 2021 |  | 2020 |  | 2022 |  | 2021 |  | 2020 |  | 2022 |  | 2021 |  | 2020
Statutory federal income tax rate | 21% |  | 21% |  | 21% |  | 21% |  | 21% |  | 21% |  | 21% |  | 21% |  | 21%
State income taxes, net of federal benefits | 3 |  | 2 |  | 2 |  | (2) |  | (1) |  | (1) |  | 6 |  | 6 |  | 6
Production tax credits | (18) |  | (17) |  | (17) |  | (34) |  | (27) |  | (28) |  | (5) |  | (6) |  | (7)
Amortization of excess deferred taxes (Refer to Note 2) | (2) |  | (18) |  | (13) |  | (2) |  | (4) |  | (5) |  | (3) |  | (43) |  | (26)
Effect of rate-making on property-related differences | (1) |  | (1) |  | (3) |  | (1) |  | (2) |  | (4) |  | (2) |  | (1) |  | (2)
Adjustment for prior period taxes | 1 |  | 1 |  | 1 |  | 1 |  | 2 |  | 1 |  | — |  | — |  | —
Other items, net | (1) |  | — |  | (1) |  | 1 |  | — |  | — |  | — |  | (1) |  | —
Overall income tax rate | 3% |  | (12%) |  | (10%) |  | (16%) |  | (11%) |  | (16%) |  | 17% |  | (24%) |  | (8%)
Schedule of Deferred Tax Assets and Liabilities | The deferred tax assets and liabilities included on the balance sheets at December 31 arise from the following temporary differences (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2022 |  | 2021 |  | 2022 |  | 2021 |  | 2022 |  | 2021
Deferred tax liabilities: |  |  |  |  |  |  |  |  |  |  |
Property | $2,442 |  |  | $2,389 |  |  | $1,440 |  |  | $1,416 |  |  | $938 |  |  | $913 |
ATC Holdings | 125 |  |  | 123 |  |  | — |  |  | — |  |  | — |  |  | — |
Other | 155 |  |  | 111 |  |  | 86 |  |  | 76 |  |  | 80 |  |  | 50 |
Total deferred tax liabilities | 2,722 |  |  | 2,623 |  |  | 1,526 |  |  | 1,492 |  |  | 1,018 |  |  | 963 |
Deferred tax assets: |  |  |  |  |  |  |  |  |  |  |
Federal credit carryforwards | 672 |  |  | 560 |  |  | 450 |  |  | 345 |  |  | 209 |  |  | 192 |
Net operating losses carryforwards - federal | — |  |  | 39 |  |  | — |  |  | 36 |  |  | — |  |  | — |
Net operating losses carryforwards - state | 32 |  |  | 38 |  |  | — |  |  | 3 |  |  | — |  |  | — |
Other | 75 |  |  | 65 |  |  | 29 |  |  | 25 |  |  | 20 |  |  | 18 |
Subtotal deferred tax assets | 779 |  |  | 702 |  |  | 479 |  |  | 409 |  |  | 229 |  |  | 210 |
Valuation allowances | — |  |  | (6) |  |  | — |  |  | — |  |  | — |  |  | — |
Total deferred tax assets | 779 |  |  | 696 |  |  | 479 |  |  | 409 |  |  | 229 |  |  | 210 |
Total deferred tax liabilities, net | $1,943 |  |  | $1,927 |  |  | $1,047 |  |  | $1,083 |  |  | $789 |  |  | $753 |
Summary Of Tax Credit Carryforwards | At December 31, 2022, carryforwards and expiration dates were estimated as follows (in millions):
| Range of Expiration Dates |  | Alliant Energy |  | IPL |  | WPL
State net operating losses | 2025-2042 |  | $527 |  | $10 |  | $1
Federal tax credits | 2024-2042 |  | 672 |  | 450 |  | 209
Schedule Of Open Tax Years | Tax years that remain subject to the statute of limitations in the major jurisdictions for each of Alliant Energy, IPL and WPL are as follows:
Consolidated federal income tax returns (a) | 2019 | - | 2021
Consolidated Iowa income tax returns (b) | 2019 | - | 2021
Wisconsin combined tax returns (c) | 2018 | - | 2021
(a)The 2019 and 2020 federal tax returns are effectively settled as a result of participation in the IRS Compliance Assurance Program, which allows Alliant Energy and the IRS to work together to resolve issues related to Alliant Energy’s current tax year before filing its federal income tax return. The statute of limitations for these federal tax returns expires three years from each filing date. (b)The statute of limitations for these Iowa tax returns expires three years from each filing date. (c)The statute of limitations for these Wisconsin combined tax returns expires four years from each filing date.
IPL [Member] |
Income Tax [Line Items] |
Schedule of Components of Income Tax Expense (Benefit) | The components of “Income tax expense (benefit)” in the income statements were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2022 |  | 2021 |  | 2020 |  | 2022 |  | 2021 |  | 2020 |  | 2022 |  | 2021 |  | 2020
Current tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal | $7 |  | $1 |  | $1 |  | ($29) |  | ($21) |  | $6 |  | $46 |  | $22 |  | ($11)
State | 2 |  | 3 |  | 8 |  | (8) |  | (1) |  | (1) |  | 16 |  | 6 |  | 7
Deferred tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal | 109 |  | 9 |  | 22 |  | 91 |  | 73 |  | 30 |  | 10 |  | (75) |  | (9)
State | 28 |  | 15 |  | 8 |  | 1 |  | — |  | (2) |  | 12 |  | 11 |  | 10
Production tax credits | (123) |  | (101) |  | (95) |  | (105) |  | (87) |  | (80) |  | (18) |  | (14) |  | (15)
Investment tax credits | (1) |  | (1) |  | (1) |  | — |  | — |  | — |  | — |  | (1) |  | (1)
| $22 |  | ($74) |  | ($57) |  | ($50) |  | ($36) |  | ($47) |  | $66 |  | ($51) |  | ($19)
Schedule Of Effective Income Tax Rates | The overall income tax rates shown in the following table were computed by dividing income tax expense (benefit) by income before income taxes.
| Alliant Energy |  | IPL |  | WPL
| 2022 |  | 2021 |  | 2020 |  | 2022 |  | 2021 |  | 2020 |  | 2022 |  | 2021 |  | 2020
Statutory federal income tax rate | 21% |  | 21% |  | 21% |  | 21% |  | 21% |  | 21% |  | 21% |  | 21% |  | 21%
State income taxes, net of federal benefits | 3 |  | 2 |  | 2 |  | (2) |  | (1) |  | (1) |  | 6 |  | 6 |  | 6
Production tax credits | (18) |  | (17) |  | (17) |  | (34) |  | (27) |  | (28) |  | (5) |  | (6) |  | (7)
Amortization of excess deferred taxes (Refer to Note 2) | (2) |  | (18) |  | (13) |  | (2) |  | (4) |  | (5) |  | (3) |  | (43) |  | (26)
Effect of rate-making on property-related differences | (1) |  | (1) |  | (3) |  | (1) |  | (2) |  | (4) |  | (2) |  | (1) |  | (2)
Adjustment for prior period taxes | 1 |  | 1 |  | 1 |  | 1 |  | 2 |  | 1 |  | — |  | — |  | —
Other items, net | (1) |  | — |  | (1) |  | 1 |  | — |  | — |  | — |  | (1) |  | —
Overall income tax rate | 3% |  | (12%) |  | (10%) |  | (16%) |  | (11%) |  | (16%) |  | 17% |  | (24%) |  | (8%)
Schedule of Deferred Tax Assets and Liabilities | The deferred tax assets and liabilities included on the balance sheets at December 31 arise from the following temporary differences (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2022 |  | 2021 |  | 2022 |  | 2021 |  | 2022 |  | 2021
Deferred tax liabilities: |  |  |  |  |  |  |  |  |  |  |
Property | $2,442 |  |  | $2,389 |  |  | $1,440 |  |  | $1,416 |  |  | $938 |  |  | $913 |
ATC Holdings | 125 |  |  | 123 |  |  | — |  |  | — |  |  | — |  |  | — |
Other | 155 |  |  | 111 |  |  | 86 |  |  | 76 |  |  | 80 |  |  | 50 |
Total deferred tax liabilities | 2,722 |  |  | 2,623 |  |  | 1,526 |  |  | 1,492 |  |  | 1,018 |  |  | 963 |
Deferred tax assets: |  |  |  |  |  |  |  |  |  |  |
Federal credit carryforwards | 672 |  |  | 560 |  |  | 450 |  |  | 345 |  |  | 209 |  |  | 192 |
Net operating losses carryforwards - federal | — |  |  | 39 |  |  | — |  |  | 36 |  |  | — |  |  | — |
Net operating losses carryforwards - state | 32 |  |  | 38 |  |  | — |  |  | 3 |  |  | — |  |  | — |
Other | 75 |  |  | 65 |  |  | 29 |  |  | 25 |  |  | 20 |  |  | 18 |
Subtotal deferred tax assets | 779 |  |  | 702 |  |  | 479 |  |  | 409 |  |  | 229 |  |  | 210 |
Valuation allowances | — |  |  | (6) |  |  | — |  |  | — |  |  | — |  |  | — |
Total deferred tax assets | 779 |  |  | 696 |  |  | 479 |  |  | 409 |  |  | 229 |  |  | 210 |
Total deferred tax liabilities, net | $1,943 |  |  | $1,927 |  |  | $1,047 |  |  | $1,083 |  |  | $789 |  |  | $753 |
Summary Of Tax Credit Carryforwards | At December 31, 2022, carryforwards and expiration dates were estimated as follows (in millions):
| Range of Expiration Dates |  | Alliant Energy |  | IPL |  | WPL
State net operating losses | 2025-2042 |  | $527 |  | $10 |  | $1
Federal tax credits | 2024-2042 |  | 672 |  | 450 |  | 209
Schedule Of Open Tax Years | Tax years that remain subject to the statute of limitations in the major jurisdictions for each of Alliant Energy, IPL and WPL are as follows:
Consolidated federal income tax returns (a) | 2019 | - | 2021
Consolidated Iowa income tax returns (b) | 2019 | - | 2021
Wisconsin combined tax returns (c) | 2018 | - | 2021
(a)The 2019 and 2020 federal tax returns are effectively settled as a result of participation in the IRS Compliance Assurance Program, which allows Alliant Energy and the IRS to work together to resolve issues related to Alliant Energy’s current tax year before filing its federal income tax return. The statute of limitations for these federal tax returns expires three years from each filing date. (b)The statute of limitations for these Iowa tax returns expires three years from each filing date. (c)The statute of limitations for these Wisconsin combined tax returns expires four years from each filing date.
WPL [Member] |
Income Tax [Line Items] |
Schedule of Components of Income Tax Expense (Benefit) | The components of “Income tax expense (benefit)” in the income statements were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2022 |  | 2021 |  | 2020 |  | 2022 |  | 2021 |  | 2020 |  | 2022 |  | 2021 |  | 2020
Current tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal | $7 |  | $1 |  | $1 |  | ($29) |  | ($21) |  | $6 |  | $46 |  | $22 |  | ($11)
State | 2 |  | 3 |  | 8 |  | (8) |  | (1) |  | (1) |  | 16 |  | 6 |  | 7
Deferred tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal | 109 |  | 9 |  | 22 |  | 91 |  | 73 |  | 30 |  | 10 |  | (75) |  | (9)
State | 28 |  | 15 |  | 8 |  | 1 |  | — |  | (2) |  | 12 |  | 11 |  | 10
Production tax credits | (123) |  | (101) |  | (95) |  | (105) |  | (87) |  | (80) |  | (18) |  | (14) |  | (15)
Investment tax credits | (1) |  | (1) |  | (1) |  | — |  | — |  | — |  | — |  | (1) |  | (1)
| $22 |  | ($74) |  | ($57) |  | ($50) |  | ($36) |  | ($47) |  | $66 |  | ($51) |  | ($19)
Schedule Of Effective Income Tax Rates | The overall income tax rates shown in the following table were computed by dividing income tax expense (benefit) by income before income taxes.
| Alliant Energy |  | IPL |  | WPL
| 2022 |  | 2021 |  | 2020 |  | 2022 |  | 2021 |  | 2020 |  | 2022 |  | 2021 |  | 2020
Statutory federal income tax rate | 21% |  | 21% |  | 21% |  | 21% |  | 21% |  | 21% |  | 21% |  | 21% |  | 21%
State income taxes, net of federal benefits | 3 |  | 2 |  | 2 |  | (2) |  | (1) |  | (1) |  | 6 |  | 6 |  | 6
Production tax credits | (18) |  | (17) |  | (17) |  | (34) |  | (27) |  | (28) |  | (5) |  | (6) |  | (7)
Amortization of excess deferred taxes (Refer to Note 2) | (2) |  | (18) |  | (13) |  | (2) |  | (4) |  | (5) |  | (3) |  | (43) |  | (26)
Effect of rate-making on property-related differences | (1) |  | (1) |  | (3) |  | (1) |  | (2) |  | (4) |  | (2) |  | (1) |  | (2)
Adjustment for prior period taxes | 1 |  | 1 |  | 1 |  | 1 |  | 2 |  | 1 |  | — |  | — |  | —
Other items, net | (1) |  | — |  | (1) |  | 1 |  | — |  | — |  | — |  | (1) |  | —
Overall income tax rate | 3% |  | (12%) |  | (10%) |  | (16%) |  | (11%) |  | (16%) |  | 17% |  | (24%) |  | (8%)
Schedule of Deferred Tax Assets and Liabilities | The deferred tax assets and liabilities included on the balance sheets at December 31 arise from the following temporary differences (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2022 |  | 2021 |  | 2022 |  | 2021 |  | 2022 |  | 2021
Deferred tax liabilities: |  |  |  |  |  |  |  |  |  |  |
Property | $2,442 |  |  | $2,389 |  |  | $1,440 |  |  | $1,416 |  |  | $938 |  |  | $913 |
ATC Holdings | 125 |  |  | 123 |  |  | — |  |  | — |  |  | — |  |  | — |
Other | 155 |  |  | 111 |  |  | 86 |  |  | 76 |  |  | 80 |  |  | 50 |
Total deferred tax liabilities | 2,722 |  |  | 2,623 |  |  | 1,526 |  |  | 1,492 |  |  | 1,018 |  |  | 963 |
Deferred tax assets: |  |  |  |  |  |  |  |  |  |  |
Federal credit carryforwards | 672 |  |  | 560 |  |  | 450 |  |  | 345 |  |  | 209 |  |  | 192 |
Net operating losses carryforwards - federal | — |  |  | 39 |  |  | — |  |  | 36 |  |  | — |  |  | — |
Net operating losses carryforwards - state | 32 |  |  | 38 |  |  | — |  |  | 3 |  |  | — |  |  | — |
Other | 75 |  |  | 65 |  |  | 29 |  |  | 25 |  |  | 20 |  |  | 18 |
Subtotal deferred tax assets | 779 |  |  | 702 |  |  | 479 |  |  | 409 |  |  | 229 |  |  | 210 |
Valuation allowances | — |  |  | (6) |  |  | — |  |  | — |  |  | — |  |  | — |
Total deferred tax assets | 779 |  |  | 696 |  |  | 479 |  |  | 409 |  |  | 229 |  |  | 210 |
Total deferred tax liabilities, net | $1,943 |  |  | $1,927 |  |  | $1,047 |  |  | $1,083 |  |  | $789 |  |  | $753 |
Summary Of Tax Credit Carryforwards | At December 31, 2022, carryforwards and expiration dates were estimated as follows (in millions):
| Range of Expiration Dates |  | Alliant Energy |  | IPL |  | WPL
State net operating losses | 2025-2042 |  | $527 |  | $10 |  | $1
Federal tax credits | 2024-2042 |  | 672 |  | 450 |  | 209
Schedule Of Open Tax Years | Tax years that remain subject to the statute of limitations in the major jurisdictions for each of Alliant Energy, IPL and WPL are as follows:
Consolidated federal income tax returns (a) | 2019 | - | 2021
Consolidated Iowa income tax returns (b) | 2019 | - | 2021
Wisconsin combined tax returns (c) | 2018 | - | 2021
(a)The 2019 and 2020 federal tax returns are effectively settled as a result of participation in the IRS Compliance Assurance Program, which allows Alliant Energy and the IRS to work together to resolve issues related to Alliant Energy’s current tax year before filing its federal income tax return. The statute of limitations for these federal tax returns expires three years from each filing date. (b)The statute of limitations for these Iowa tax returns expires three years from each filing date. (c)The statute of limitations for these Wisconsin combined tax returns expires four years from each filing date.

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