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Income Taxes | 12 Months Ended
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Dec. 31, 2021
Income Tax [Line Items] |
Income Taxes | INCOME TAXES Income Tax Expense (Benefit) - The components of “Income tax expense (benefit)” in the income statements were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2021 |  | 2020 |  | 2019 |  | 2021 |  | 2020 |  | 2019 |  | 2021 |  | 2020 |  | 2019
Current tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal | $1 |  |  | $1 |  |  | ($7) |  |  | ($21) |  |  | $6 |  |  | ($11) |  |  | $22 |  |  | ($11) |  |  | $12 |
State | 3 |  |  | 8 |  |  | 24 |  |  | (1) |  |  | (1) |  |  | 24 |  |  | 6 |  |  | 7 |  |  | 13 |
IPL’s tax benefit riders | — |  |  | — |  |  | (4) |  |  | — |  |  | — |  |  | (4) |  |  | — |  |  | — |  |  | — |
Deferred tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal | 9 |  |  | 22 |  |  | 70 |  |  | 73 |  |  | 30 |  |  | 26 |  |  | (75) |  |  | (9) |  |  | 31 |
State | 15 |  |  | 8 |  |  | 42 |  |  | — |  |  | (2) |  |  | 31 |  |  | 11 |  |  | 10 |  |  | 6 |
Production tax credits | (101) |  |  | (95) |  |  | (55) |  |  | (87) |  |  | (80) |  |  | (42) |  |  | (14) |  |  | (15) |  |  | (13) |
Investment tax credits | (1) |  |  | (1) |  |  | (1) |  |  | — |  |  | — |  |  | — |  |  | (1) |  |  | (1) |  |  | — |
| ($74) |  |  | ($57) |  |  | $69 |  |  | ($36) |  |  | ($47) |  |  | $24 |  |  | ($51) |  |  | ($19) |  |  | $49 |
Income Tax Rates - The overall income tax rates shown in the following table were computed by dividing income tax expense (benefit) by income from continuing operations before income taxes.
| Alliant Energy |  | IPL |  | WPL
| 2021 |  | 2020 |  | 2019 |  | 2021 |  | 2020 |  | 2019 |  | 2021 |  | 2020 |  | 2019
Statutory federal income tax rate | 21 | % |  | 21 | % |  | 21 | % |  | 21 | % |  | 21 | % |  | 21 | % |  | 21 | % |  | 21 | % |  | 21 | %
State income taxes, net of federal benefits | 2 |  |  | 2 |  |  | 7 |  |  | (1) |  |  | (1) |  |  | 8 |  |  | 6 |  |  | 6 |  |  | 6 |
Amortization of excess deferred taxes (Refer to Note 2) | (18) |  |  | (13) |  |  | (1) |  |  | (4) |  |  | (5) |  |  | — |  |  | (43) |  |  | (26) |  |  | (2) |
Production tax credits | (17) |  |  | (17) |  |  | (9) |  |  | (27) |  |  | (28) |  |  | (13) |  |  | (6) |  |  | (7) |  |  | (5) |
Effect of rate-making on property-related differences | (1) |  |  | (3) |  |  | (6) |  |  | (2) |  |  | (4) |  |  | (10) |  |  | (1) |  |  | (2) |  |  | (3) |
Adjustment for prior period taxes | 1 |  |  | 1 |  |  | 1 |  |  | 2 |  |  | 1 |  |  | 3 |  |  | — |  |  | — |  |  | — |
IPL’s tax benefit riders | — |  |  | — |  |  | (1) |  |  | — |  |  | — |  |  | (1) |  |  | — |  |  | — |  |  | — |
Other items, net | — |  |  | (1) |  |  | (1) |  |  | — |  |  | — |  |  | — |  |  | (1) |  |  | — |  |  | — |
Overall income tax rate | (12 | %) |  | (10 | %) |  | 11 | % |  | (11 | %) |  | (16 | %) |  | 8 | % |  | (24 | %) |  | (8 | %) |  | 17 | %
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
| 2021 |  | 2020 |  | 2021 |  | 2020 |  | 2021 |  | 2020
Deferred tax liabilities: |  |  |  |  |  |  |  |  |  |  |
Property | $2,389 |  |  | $2,232 |  |  | $1,416 |  |  | $1,312 |  |  | $913 |  |  | $854 |
ATC Holdings | 123 |  |  | 116 |  |  | — |  |  | — |  |  | — |  |  | — |
Other | 111 |  |  | 101 |  |  | 76 |  |  | 83 |  |  | 50 |  |  | 41 |
Total deferred tax liabilities | 2,623 |  |  | 2,449 |  |  | 1,492 |  |  | 1,395 |  |  | 963 |  |  | 895 |
Deferred tax assets: |  |  |  |  |  |  |  |  |  |  |
Federal credit carryforwards | 560 |  |  | 454 |  |  | 345 |  |  | 258 |  |  | 192 |  |  | 175 |
Net operating losses carryforwards - federal | 39 |  |  | 77 |  |  | 36 |  |  | 71 |  |  | — |  |  | 1 |
Net operating losses carryforwards - state | 38 |  |  | 37 |  |  | 3 |  |  | 1 |  |  | — |  |  | — |
Other | 65 |  |  | 73 |  |  | 25 |  |  | 30 |  |  | 18 |  |  | 18 |
Subtotal deferred tax assets | 702 |  |  | 641 |  |  | 409 |  |  | 360 |  |  | 210 |  |  | 194 |
Valuation allowances | (6) |  |  | (6) |  |  | — |  |  | — |  |  | — |  |  | (1) |
Total deferred tax assets | 696 |  |  | 635 |  |  | 409 |  |  | 360 |  |  | 210 |  |  | 193 |
Total deferred tax liabilities, net | $1,927 |  |  | $1,814 |  |  | $1,083 |  |  | $1,035 |  |  | $753 |  |  | $702 |
Carryforwards - At December 31, 2021, carryforwards and expiration dates were estimated as follows (in millions):
| Range of Expiration Dates |  | Alliant Energy |  | IPL |  | WPL
Federal net operating losses | 2037 |  | $186 |  | $172 |  | $1
State net operating losses | 2022-2041 |  | 619 |  | 28 |  | 2
Federal tax credits | 2022-2041 |  | 560 |  | 345 |  | 192
Valuation Allowances - Alliant Energy currently expects its federal net operating losses carryforwards will not be fully utilized until 2023. Because taxable income must be reduced by federal net operating losses carryforwards prior to utilizing federal tax credit carryforwards, Alliant Energy currently does not expect to utilize 2002 vintage federal credit carryforwards prior to their expiration in 2022, resulting in valuation allowances as of December 31, 2021. Uncertain Tax Positions - At December 31, 2021, 2020 and 2019, there were no uncertain tax positions or penalties accrued related to uncertain tax positions. As of December 31, 2021, no material changes to unrecognized tax benefits are expected during the next 12 months. 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) | 2018 | - | 2020
Consolidated Iowa income tax returns (b) | 2018 | - | 2020
Wisconsin combined tax returns (c) | 2017 | - | 2020
(a)The 2018 and 2019 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. Iowa Tax Reform - In 2018, Iowa tax reform was enacted, resulting in a reduction in the Iowa income tax rate from 12% to 9.8%, effective January 1, 2021, and the elimination of the deduction for federal income taxes, effective January 1, 2022, for taxes related to 2020 and prior.
IPL [Member] |
Income Tax [Line Items] |
Income Taxes | INCOME TAXES Income Tax Expense (Benefit) - The components of “Income tax expense (benefit)” in the income statements were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2021 |  | 2020 |  | 2019 |  | 2021 |  | 2020 |  | 2019 |  | 2021 |  | 2020 |  | 2019
Current tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal | $1 |  |  | $1 |  |  | ($7) |  |  | ($21) |  |  | $6 |  |  | ($11) |  |  | $22 |  |  | ($11) |  |  | $12 |
State | 3 |  |  | 8 |  |  | 24 |  |  | (1) |  |  | (1) |  |  | 24 |  |  | 6 |  |  | 7 |  |  | 13 |
IPL’s tax benefit riders | — |  |  | — |  |  | (4) |  |  | — |  |  | — |  |  | (4) |  |  | — |  |  | — |  |  | — |
Deferred tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal | 9 |  |  | 22 |  |  | 70 |  |  | 73 |  |  | 30 |  |  | 26 |  |  | (75) |  |  | (9) |  |  | 31 |
State | 15 |  |  | 8 |  |  | 42 |  |  | — |  |  | (2) |  |  | 31 |  |  | 11 |  |  | 10 |  |  | 6 |
Production tax credits | (101) |  |  | (95) |  |  | (55) |  |  | (87) |  |  | (80) |  |  | (42) |  |  | (14) |  |  | (15) |  |  | (13) |
Investment tax credits | (1) |  |  | (1) |  |  | (1) |  |  | — |  |  | — |  |  | — |  |  | (1) |  |  | (1) |  |  | — |
| ($74) |  |  | ($57) |  |  | $69 |  |  | ($36) |  |  | ($47) |  |  | $24 |  |  | ($51) |  |  | ($19) |  |  | $49 |
Income Tax Rates - The overall income tax rates shown in the following table were computed by dividing income tax expense (benefit) by income from continuing operations before income taxes.
| Alliant Energy |  | IPL |  | WPL
| 2021 |  | 2020 |  | 2019 |  | 2021 |  | 2020 |  | 2019 |  | 2021 |  | 2020 |  | 2019
Statutory federal income tax rate | 21 | % |  | 21 | % |  | 21 | % |  | 21 | % |  | 21 | % |  | 21 | % |  | 21 | % |  | 21 | % |  | 21 | %
State income taxes, net of federal benefits | 2 |  |  | 2 |  |  | 7 |  |  | (1) |  |  | (1) |  |  | 8 |  |  | 6 |  |  | 6 |  |  | 6 |
Amortization of excess deferred taxes (Refer to Note 2) | (18) |  |  | (13) |  |  | (1) |  |  | (4) |  |  | (5) |  |  | — |  |  | (43) |  |  | (26) |  |  | (2) |
Production tax credits | (17) |  |  | (17) |  |  | (9) |  |  | (27) |  |  | (28) |  |  | (13) |  |  | (6) |  |  | (7) |  |  | (5) |
Effect of rate-making on property-related differences | (1) |  |  | (3) |  |  | (6) |  |  | (2) |  |  | (4) |  |  | (10) |  |  | (1) |  |  | (2) |  |  | (3) |
Adjustment for prior period taxes | 1 |  |  | 1 |  |  | 1 |  |  | 2 |  |  | 1 |  |  | 3 |  |  | — |  |  | — |  |  | — |
IPL’s tax benefit riders | — |  |  | — |  |  | (1) |  |  | — |  |  | — |  |  | (1) |  |  | — |  |  | — |  |  | — |
Other items, net | — |  |  | (1) |  |  | (1) |  |  | — |  |  | — |  |  | — |  |  | (1) |  |  | — |  |  | — |
Overall income tax rate | (12 | %) |  | (10 | %) |  | 11 | % |  | (11 | %) |  | (16 | %) |  | 8 | % |  | (24 | %) |  | (8 | %) |  | 17 | %
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
| 2021 |  | 2020 |  | 2021 |  | 2020 |  | 2021 |  | 2020
Deferred tax liabilities: |  |  |  |  |  |  |  |  |  |  |
Property | $2,389 |  |  | $2,232 |  |  | $1,416 |  |  | $1,312 |  |  | $913 |  |  | $854 |
ATC Holdings | 123 |  |  | 116 |  |  | — |  |  | — |  |  | — |  |  | — |
Other | 111 |  |  | 101 |  |  | 76 |  |  | 83 |  |  | 50 |  |  | 41 |
Total deferred tax liabilities | 2,623 |  |  | 2,449 |  |  | 1,492 |  |  | 1,395 |  |  | 963 |  |  | 895 |
Deferred tax assets: |  |  |  |  |  |  |  |  |  |  |
Federal credit carryforwards | 560 |  |  | 454 |  |  | 345 |  |  | 258 |  |  | 192 |  |  | 175 |
Net operating losses carryforwards - federal | 39 |  |  | 77 |  |  | 36 |  |  | 71 |  |  | — |  |  | 1 |
Net operating losses carryforwards - state | 38 |  |  | 37 |  |  | 3 |  |  | 1 |  |  | — |  |  | — |
Other | 65 |  |  | 73 |  |  | 25 |  |  | 30 |  |  | 18 |  |  | 18 |
Subtotal deferred tax assets | 702 |  |  | 641 |  |  | 409 |  |  | 360 |  |  | 210 |  |  | 194 |
Valuation allowances | (6) |  |  | (6) |  |  | — |  |  | — |  |  | — |  |  | (1) |
Total deferred tax assets | 696 |  |  | 635 |  |  | 409 |  |  | 360 |  |  | 210 |  |  | 193 |
Total deferred tax liabilities, net | $1,927 |  |  | $1,814 |  |  | $1,083 |  |  | $1,035 |  |  | $753 |  |  | $702 |
Carryforwards - At December 31, 2021, carryforwards and expiration dates were estimated as follows (in millions):
| Range of Expiration Dates |  | Alliant Energy |  | IPL |  | WPL
Federal net operating losses | 2037 |  | $186 |  | $172 |  | $1
State net operating losses | 2022-2041 |  | 619 |  | 28 |  | 2
Federal tax credits | 2022-2041 |  | 560 |  | 345 |  | 192
Valuation Allowances - Alliant Energy currently expects its federal net operating losses carryforwards will not be fully utilized until 2023. Because taxable income must be reduced by federal net operating losses carryforwards prior to utilizing federal tax credit carryforwards, Alliant Energy currently does not expect to utilize 2002 vintage federal credit carryforwards prior to their expiration in 2022, resulting in valuation allowances as of December 31, 2021. Uncertain Tax Positions - At December 31, 2021, 2020 and 2019, there were no uncertain tax positions or penalties accrued related to uncertain tax positions. As of December 31, 2021, no material changes to unrecognized tax benefits are expected during the next 12 months. 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) | 2018 | - | 2020
Consolidated Iowa income tax returns (b) | 2018 | - | 2020
Wisconsin combined tax returns (c) | 2017 | - | 2020
(a)The 2018 and 2019 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. Iowa Tax Reform - In 2018, Iowa tax reform was enacted, resulting in a reduction in the Iowa income tax rate from 12% to 9.8%, effective January 1, 2021, and the elimination of the deduction for federal income taxes, effective January 1, 2022, for taxes related to 2020 and prior.
WPL [Member] |
Income Tax [Line Items] |
Income Taxes | INCOME TAXES Income Tax Expense (Benefit) - The components of “Income tax expense (benefit)” in the income statements were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2021 |  | 2020 |  | 2019 |  | 2021 |  | 2020 |  | 2019 |  | 2021 |  | 2020 |  | 2019
Current tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal | $1 |  |  | $1 |  |  | ($7) |  |  | ($21) |  |  | $6 |  |  | ($11) |  |  | $22 |  |  | ($11) |  |  | $12 |
State | 3 |  |  | 8 |  |  | 24 |  |  | (1) |  |  | (1) |  |  | 24 |  |  | 6 |  |  | 7 |  |  | 13 |
IPL’s tax benefit riders | — |  |  | — |  |  | (4) |  |  | — |  |  | — |  |  | (4) |  |  | — |  |  | — |  |  | — |
Deferred tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal | 9 |  |  | 22 |  |  | 70 |  |  | 73 |  |  | 30 |  |  | 26 |  |  | (75) |  |  | (9) |  |  | 31 |
State | 15 |  |  | 8 |  |  | 42 |  |  | — |  |  | (2) |  |  | 31 |  |  | 11 |  |  | 10 |  |  | 6 |
Production tax credits | (101) |  |  | (95) |  |  | (55) |  |  | (87) |  |  | (80) |  |  | (42) |  |  | (14) |  |  | (15) |  |  | (13) |
Investment tax credits | (1) |  |  | (1) |  |  | (1) |  |  | — |  |  | — |  |  | — |  |  | (1) |  |  | (1) |  |  | — |
| ($74) |  |  | ($57) |  |  | $69 |  |  | ($36) |  |  | ($47) |  |  | $24 |  |  | ($51) |  |  | ($19) |  |  | $49 |
Income Tax Rates - The overall income tax rates shown in the following table were computed by dividing income tax expense (benefit) by income from continuing operations before income taxes.
| Alliant Energy |  | IPL |  | WPL
| 2021 |  | 2020 |  | 2019 |  | 2021 |  | 2020 |  | 2019 |  | 2021 |  | 2020 |  | 2019
Statutory federal income tax rate | 21 | % |  | 21 | % |  | 21 | % |  | 21 | % |  | 21 | % |  | 21 | % |  | 21 | % |  | 21 | % |  | 21 | %
State income taxes, net of federal benefits | 2 |  |  | 2 |  |  | 7 |  |  | (1) |  |  | (1) |  |  | 8 |  |  | 6 |  |  | 6 |  |  | 6 |
Amortization of excess deferred taxes (Refer to Note 2) | (18) |  |  | (13) |  |  | (1) |  |  | (4) |  |  | (5) |  |  | — |  |  | (43) |  |  | (26) |  |  | (2) |
Production tax credits | (17) |  |  | (17) |  |  | (9) |  |  | (27) |  |  | (28) |  |  | (13) |  |  | (6) |  |  | (7) |  |  | (5) |
Effect of rate-making on property-related differences | (1) |  |  | (3) |  |  | (6) |  |  | (2) |  |  | (4) |  |  | (10) |  |  | (1) |  |  | (2) |  |  | (3) |
Adjustment for prior period taxes | 1 |  |  | 1 |  |  | 1 |  |  | 2 |  |  | 1 |  |  | 3 |  |  | — |  |  | — |  |  | — |
IPL’s tax benefit riders | — |  |  | — |  |  | (1) |  |  | — |  |  | — |  |  | (1) |  |  | — |  |  | — |  |  | — |
Other items, net | — |  |  | (1) |  |  | (1) |  |  | — |  |  | — |  |  | — |  |  | (1) |  |  | — |  |  | — |
Overall income tax rate | (12 | %) |  | (10 | %) |  | 11 | % |  | (11 | %) |  | (16 | %) |  | 8 | % |  | (24 | %) |  | (8 | %) |  | 17 | %
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
| 2021 |  | 2020 |  | 2021 |  | 2020 |  | 2021 |  | 2020
Deferred tax liabilities: |  |  |  |  |  |  |  |  |  |  |
Property | $2,389 |  |  | $2,232 |  |  | $1,416 |  |  | $1,312 |  |  | $913 |  |  | $854 |
ATC Holdings | 123 |  |  | 116 |  |  | — |  |  | — |  |  | — |  |  | — |
Other | 111 |  |  | 101 |  |  | 76 |  |  | 83 |  |  | 50 |  |  | 41 |
Total deferred tax liabilities | 2,623 |  |  | 2,449 |  |  | 1,492 |  |  | 1,395 |  |  | 963 |  |  | 895 |
Deferred tax assets: |  |  |  |  |  |  |  |  |  |  |
Federal credit carryforwards | 560 |  |  | 454 |  |  | 345 |  |  | 258 |  |  | 192 |  |  | 175 |
Net operating losses carryforwards - federal | 39 |  |  | 77 |  |  | 36 |  |  | 71 |  |  | — |  |  | 1 |
Net operating losses carryforwards - state | 38 |  |  | 37 |  |  | 3 |  |  | 1 |  |  | — |  |  | — |
Other | 65 |  |  | 73 |  |  | 25 |  |  | 30 |  |  | 18 |  |  | 18 |
Subtotal deferred tax assets | 702 |  |  | 641 |  |  | 409 |  |  | 360 |  |  | 210 |  |  | 194 |
Valuation allowances | (6) |  |  | (6) |  |  | — |  |  | — |  |  | — |  |  | (1) |
Total deferred tax assets | 696 |  |  | 635 |  |  | 409 |  |  | 360 |  |  | 210 |  |  | 193 |
Total deferred tax liabilities, net | $1,927 |  |  | $1,814 |  |  | $1,083 |  |  | $1,035 |  |  | $753 |  |  | $702 |
Carryforwards - At December 31, 2021, carryforwards and expiration dates were estimated as follows (in millions):
| Range of Expiration Dates |  | Alliant Energy |  | IPL |  | WPL
Federal net operating losses | 2037 |  | $186 |  | $172 |  | $1
State net operating losses | 2022-2041 |  | 619 |  | 28 |  | 2
Federal tax credits | 2022-2041 |  | 560 |  | 345 |  | 192
Valuation Allowances - Alliant Energy currently expects its federal net operating losses carryforwards will not be fully utilized until 2023. Because taxable income must be reduced by federal net operating losses carryforwards prior to utilizing federal tax credit carryforwards, Alliant Energy currently does not expect to utilize 2002 vintage federal credit carryforwards prior to their expiration in 2022, resulting in valuation allowances as of December 31, 2021. Uncertain Tax Positions - At December 31, 2021, 2020 and 2019, there were no uncertain tax positions or penalties accrued related to uncertain tax positions. As of December 31, 2021, no material changes to unrecognized tax benefits are expected during the next 12 months. 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) | 2018 | - | 2020
Consolidated Iowa income tax returns (b) | 2018 | - | 2020
Wisconsin combined tax returns (c) | 2017 | - | 2020
(a)The 2018 and 2019 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. Iowa Tax Reform - In 2018, Iowa tax reform was enacted, resulting in a reduction in the Iowa income tax rate from 12% to 9.8%, effective January 1, 2021, and the elimination of the deduction for federal income taxes, effective January 1, 2022, for taxes related to 2020 and prior.

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- Definition Income tax + References No definition available. + Details
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Namespace Prefix: | lnt_
Data Type: | xbrli:stringItemType
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