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Income Taxes (Tables) | 12 Months Ended
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Dec. 31, 2020
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
| 2020 |  | 2019 |  | 2018 |  | 2020 |  | 2019 |  | 2018 |  | 2020 |  | 2019 |  | 2018
Current tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal | $1 |  |  | ($7) |  |  | ($1) |  |  | $6 |  |  | ($11) |  |  | $15 |  |  | ($11) |  |  | $12 |  |  | ($9) |
State | 8 |  |  | 24 |  |  | (5) |  |  | (1) |  |  | 24 |  |  | (7) |  |  | 7 |  |  | 13 |  |  | (5) |
IPL’s tax benefit riders | — |  |  | (4) |  |  | (13) |  |  | — |  |  | (4) |  |  | (13) |  |  | — |  |  | — |  |  | — |
Deferred tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal | 22 |  |  | 70 |  |  | 68 |  |  | 30 |  |  | 26 |  |  | 10 |  |  | (9) |  |  | 31 |  |  | 44 |
State | 8 |  |  | 42 |  |  | 30 |  |  | (2) |  |  | 31 |  |  | 7 |  |  | 10 |  |  | 6 |  |  | 22 |
Production tax credits | (95) |  |  | (55) |  |  | (30) |  |  | (80) |  |  | (42) |  |  | (14) |  |  | (15) |  |  | (13) |  |  | (15) |
Investment tax credits | (1) |  |  | (1) |  |  | (1) |  |  | — |  |  | — |  |  | (1) |  |  | (1) |  |  | — |  |  | (1) |
| ($57) |  |  | $69 |  |  | $48 |  |  | ($47) |  |  | $24 |  |  | ($3) |  |  | ($19) |  |  | $49 |  |  | $36 |
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 from continuing operations before income taxes.
| Alliant Energy |  | IPL |  | WPL
| 2020 |  | 2019 |  | 2018 |  | 2020 |  | 2019 |  | 2018 |  | 2020 |  | 2019 |  | 2018
Statutory federal income tax rate | 21 | % |  | 21 | % |  | 21 | % |  | 21 | % |  | 21 | % |  | 21 | % |  | 21 | % |  | 21 | % |  | 21 | %
State income taxes, net of federal benefits | 2 |  |  | 7 |  |  | 7 |  |  | (1) |  |  | 8 |  |  | 8 |  |  | 6 |  |  | 6 |  |  | 6 |
Production tax credits | (17) |  |  | (9) |  |  | (5) |  |  | (28) |  |  | (13) |  |  | (5) |  |  | (7) |  |  | (5) |  |  | (7) |
Amortization of excess deferred taxes (Refer to Note 2) | (13) |  |  | (1) |  |  | (1) |  |  | (5) |  |  | — |  |  | — |  |  | (26) |  |  | (2) |  |  | — |
Effect of rate-making on property-related differences | (3) |  |  | (6) |  |  | (8) |  |  | (4) |  |  | (10) |  |  | (14) |  |  | (2) |  |  | (3) |  |  | (2) |
Adjustment for prior period taxes | 1 |  |  | 1 |  |  | (2) |  |  | 1 |  |  | 3 |  |  | (5) |  |  | — |  |  | — |  |  | — |
IPL’s tax benefit riders | — |  |  | (1) |  |  | (2) |  |  | — |  |  | (1) |  |  | (5) |  |  | — |  |  | — |  |  | — |
Federal Tax Reform adjustments | — |  |  | — |  |  | (1) |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | (2) |
Other items, net | (1) |  |  | (1) |  |  | (1) |  |  | — |  |  | — |  |  | (1) |  |  | — |  |  | — |  |  | (1) |
Overall income tax rate | (10 | %) |  | 11 | % |  | 8 | % |  | (16 | %) |  | 8 | % |  | (1 | %) |  | (8 | %) |  | 17 | % |  | 15 | %
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
| 2020 |  | 2019 |  | 2020 |  | 2019 |  | 2020 |  | 2019
Deferred tax liabilities: |  |  |  |  |  |  |  |  |  |  |
Property | $2,232 |  |  | $2,022 |  |  | $1,312 |  |  | $1,184 |  |  | $854 |  |  | $770 |
ATC Holdings | 116 |  |  | 111 |  |  | — |  |  | — |  |  | — |  |  | — |
Other | 101 |  |  | 84 |  |  | 83 |  |  | 76 |  |  | 41 |  |  | 32 |
Total deferred tax liabilities | 2,449 |  |  | 2,217 |  |  | 1,395 |  |  | 1,260 |  |  | 895 |  |  | 802 |
Deferred tax assets: |  |  |  |  |  |  |  |  |  |  |
Federal credit carryforwards | 454 |  |  | 355 |  |  | 258 |  |  | 175 |  |  | 175 |  |  | 160 |
Net operating losses carryforwards - federal | 77 |  |  | 60 |  |  | 71 |  |  | 56 |  |  | 1 |  |  | 1 |
Net operating losses carryforwards - state | 37 |  |  | 37 |  |  | 1 |  |  | 1 |  |  | — |  |  | — |
Other | 73 |  |  | 61 |  |  | 30 |  |  | 20 |  |  | 18 |  |  | 16 |
Subtotal deferred tax assets | 641 |  |  | 513 |  |  | 360 |  |  | 252 |  |  | 194 |  |  | 177 |
Valuation allowances | (6) |  |  | (10) |  |  | — |  |  | — |  |  | (1) |  |  | (1) |
Total deferred tax assets | 635 |  |  | 503 |  |  | 360 |  |  | 252 |  |  | 193 |  |  | 176 |
Total deferred tax liabilities, net | $1,814 |  |  | $1,714 |  |  | $1,035 |  |  | $1,008 |  |  | $702 |  |  | $626 |
Summary Of Tax Credit Carryforwards | At December 31, 2020, carryforwards and expiration dates were estimated as follows (in millions):
| Range of Expiration Dates |  | Alliant Energy |  | IPL |  | WPL
Federal net operating losses | 2037 |  | $366 |  | $339 |  | $3
State net operating losses | 2021-2040 |  | 622 |  | 10 |  | 2
Federal tax credits | 2022-2040 |  | 454 |  | 258 |  | 175
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) | 2017 | - | 2019
Consolidated Iowa income tax returns (b) | 2017 | - | 2019
Wisconsin combined tax returns (c) | 2016 | - | 2019
(a)The 2017 federal tax return is 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
| 2020 |  | 2019 |  | 2018 |  | 2020 |  | 2019 |  | 2018 |  | 2020 |  | 2019 |  | 2018
Current tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal | $1 |  |  | ($7) |  |  | ($1) |  |  | $6 |  |  | ($11) |  |  | $15 |  |  | ($11) |  |  | $12 |  |  | ($9) |
State | 8 |  |  | 24 |  |  | (5) |  |  | (1) |  |  | 24 |  |  | (7) |  |  | 7 |  |  | 13 |  |  | (5) |
IPL’s tax benefit riders | — |  |  | (4) |  |  | (13) |  |  | — |  |  | (4) |  |  | (13) |  |  | — |  |  | — |  |  | — |
Deferred tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal | 22 |  |  | 70 |  |  | 68 |  |  | 30 |  |  | 26 |  |  | 10 |  |  | (9) |  |  | 31 |  |  | 44 |
State | 8 |  |  | 42 |  |  | 30 |  |  | (2) |  |  | 31 |  |  | 7 |  |  | 10 |  |  | 6 |  |  | 22 |
Production tax credits | (95) |  |  | (55) |  |  | (30) |  |  | (80) |  |  | (42) |  |  | (14) |  |  | (15) |  |  | (13) |  |  | (15) |
Investment tax credits | (1) |  |  | (1) |  |  | (1) |  |  | — |  |  | — |  |  | (1) |  |  | (1) |  |  | — |  |  | (1) |
| ($57) |  |  | $69 |  |  | $48 |  |  | ($47) |  |  | $24 |  |  | ($3) |  |  | ($19) |  |  | $49 |  |  | $36 |
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 from continuing operations before income taxes.
| Alliant Energy |  | IPL |  | WPL
| 2020 |  | 2019 |  | 2018 |  | 2020 |  | 2019 |  | 2018 |  | 2020 |  | 2019 |  | 2018
Statutory federal income tax rate | 21 | % |  | 21 | % |  | 21 | % |  | 21 | % |  | 21 | % |  | 21 | % |  | 21 | % |  | 21 | % |  | 21 | %
State income taxes, net of federal benefits | 2 |  |  | 7 |  |  | 7 |  |  | (1) |  |  | 8 |  |  | 8 |  |  | 6 |  |  | 6 |  |  | 6 |
Production tax credits | (17) |  |  | (9) |  |  | (5) |  |  | (28) |  |  | (13) |  |  | (5) |  |  | (7) |  |  | (5) |  |  | (7) |
Amortization of excess deferred taxes (Refer to Note 2) | (13) |  |  | (1) |  |  | (1) |  |  | (5) |  |  | — |  |  | — |  |  | (26) |  |  | (2) |  |  | — |
Effect of rate-making on property-related differences | (3) |  |  | (6) |  |  | (8) |  |  | (4) |  |  | (10) |  |  | (14) |  |  | (2) |  |  | (3) |  |  | (2) |
Adjustment for prior period taxes | 1 |  |  | 1 |  |  | (2) |  |  | 1 |  |  | 3 |  |  | (5) |  |  | — |  |  | — |  |  | — |
IPL’s tax benefit riders | — |  |  | (1) |  |  | (2) |  |  | — |  |  | (1) |  |  | (5) |  |  | — |  |  | — |  |  | — |
Federal Tax Reform adjustments | — |  |  | — |  |  | (1) |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | (2) |
Other items, net | (1) |  |  | (1) |  |  | (1) |  |  | — |  |  | — |  |  | (1) |  |  | — |  |  | — |  |  | (1) |
Overall income tax rate | (10 | %) |  | 11 | % |  | 8 | % |  | (16 | %) |  | 8 | % |  | (1 | %) |  | (8 | %) |  | 17 | % |  | 15 | %
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
| 2020 |  | 2019 |  | 2020 |  | 2019 |  | 2020 |  | 2019
Deferred tax liabilities: |  |  |  |  |  |  |  |  |  |  |
Property | $2,232 |  |  | $2,022 |  |  | $1,312 |  |  | $1,184 |  |  | $854 |  |  | $770 |
ATC Holdings | 116 |  |  | 111 |  |  | — |  |  | — |  |  | — |  |  | — |
Other | 101 |  |  | 84 |  |  | 83 |  |  | 76 |  |  | 41 |  |  | 32 |
Total deferred tax liabilities | 2,449 |  |  | 2,217 |  |  | 1,395 |  |  | 1,260 |  |  | 895 |  |  | 802 |
Deferred tax assets: |  |  |  |  |  |  |  |  |  |  |
Federal credit carryforwards | 454 |  |  | 355 |  |  | 258 |  |  | 175 |  |  | 175 |  |  | 160 |
Net operating losses carryforwards - federal | 77 |  |  | 60 |  |  | 71 |  |  | 56 |  |  | 1 |  |  | 1 |
Net operating losses carryforwards - state | 37 |  |  | 37 |  |  | 1 |  |  | 1 |  |  | — |  |  | — |
Other | 73 |  |  | 61 |  |  | 30 |  |  | 20 |  |  | 18 |  |  | 16 |
Subtotal deferred tax assets | 641 |  |  | 513 |  |  | 360 |  |  | 252 |  |  | 194 |  |  | 177 |
Valuation allowances | (6) |  |  | (10) |  |  | — |  |  | — |  |  | (1) |  |  | (1) |
Total deferred tax assets | 635 |  |  | 503 |  |  | 360 |  |  | 252 |  |  | 193 |  |  | 176 |
Total deferred tax liabilities, net | $1,814 |  |  | $1,714 |  |  | $1,035 |  |  | $1,008 |  |  | $702 |  |  | $626 |
Summary Of Tax Credit Carryforwards | At December 31, 2020, carryforwards and expiration dates were estimated as follows (in millions):
| Range of Expiration Dates |  | Alliant Energy |  | IPL |  | WPL
Federal net operating losses | 2037 |  | $366 |  | $339 |  | $3
State net operating losses | 2021-2040 |  | 622 |  | 10 |  | 2
Federal tax credits | 2022-2040 |  | 454 |  | 258 |  | 175
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) | 2017 | - | 2019
Consolidated Iowa income tax returns (b) | 2017 | - | 2019
Wisconsin combined tax returns (c) | 2016 | - | 2019
(a)The 2017 federal tax return is 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
| 2020 |  | 2019 |  | 2018 |  | 2020 |  | 2019 |  | 2018 |  | 2020 |  | 2019 |  | 2018
Current tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal | $1 |  |  | ($7) |  |  | ($1) |  |  | $6 |  |  | ($11) |  |  | $15 |  |  | ($11) |  |  | $12 |  |  | ($9) |
State | 8 |  |  | 24 |  |  | (5) |  |  | (1) |  |  | 24 |  |  | (7) |  |  | 7 |  |  | 13 |  |  | (5) |
IPL’s tax benefit riders | — |  |  | (4) |  |  | (13) |  |  | — |  |  | (4) |  |  | (13) |  |  | — |  |  | — |  |  | — |
Deferred tax expense (benefit): |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Federal | 22 |  |  | 70 |  |  | 68 |  |  | 30 |  |  | 26 |  |  | 10 |  |  | (9) |  |  | 31 |  |  | 44 |
State | 8 |  |  | 42 |  |  | 30 |  |  | (2) |  |  | 31 |  |  | 7 |  |  | 10 |  |  | 6 |  |  | 22 |
Production tax credits | (95) |  |  | (55) |  |  | (30) |  |  | (80) |  |  | (42) |  |  | (14) |  |  | (15) |  |  | (13) |  |  | (15) |
Investment tax credits | (1) |  |  | (1) |  |  | (1) |  |  | — |  |  | — |  |  | (1) |  |  | (1) |  |  | — |  |  | (1) |
| ($57) |  |  | $69 |  |  | $48 |  |  | ($47) |  |  | $24 |  |  | ($3) |  |  | ($19) |  |  | $49 |  |  | $36 |
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 from continuing operations before income taxes.
| Alliant Energy |  | IPL |  | WPL
| 2020 |  | 2019 |  | 2018 |  | 2020 |  | 2019 |  | 2018 |  | 2020 |  | 2019 |  | 2018
Statutory federal income tax rate | 21 | % |  | 21 | % |  | 21 | % |  | 21 | % |  | 21 | % |  | 21 | % |  | 21 | % |  | 21 | % |  | 21 | %
State income taxes, net of federal benefits | 2 |  |  | 7 |  |  | 7 |  |  | (1) |  |  | 8 |  |  | 8 |  |  | 6 |  |  | 6 |  |  | 6 |
Production tax credits | (17) |  |  | (9) |  |  | (5) |  |  | (28) |  |  | (13) |  |  | (5) |  |  | (7) |  |  | (5) |  |  | (7) |
Amortization of excess deferred taxes (Refer to Note 2) | (13) |  |  | (1) |  |  | (1) |  |  | (5) |  |  | — |  |  | — |  |  | (26) |  |  | (2) |  |  | — |
Effect of rate-making on property-related differences | (3) |  |  | (6) |  |  | (8) |  |  | (4) |  |  | (10) |  |  | (14) |  |  | (2) |  |  | (3) |  |  | (2) |
Adjustment for prior period taxes | 1 |  |  | 1 |  |  | (2) |  |  | 1 |  |  | 3 |  |  | (5) |  |  | — |  |  | — |  |  | — |
IPL’s tax benefit riders | — |  |  | (1) |  |  | (2) |  |  | — |  |  | (1) |  |  | (5) |  |  | — |  |  | — |  |  | — |
Federal Tax Reform adjustments | — |  |  | — |  |  | (1) |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | (2) |
Other items, net | (1) |  |  | (1) |  |  | (1) |  |  | — |  |  | — |  |  | (1) |  |  | — |  |  | — |  |  | (1) |
Overall income tax rate | (10 | %) |  | 11 | % |  | 8 | % |  | (16 | %) |  | 8 | % |  | (1 | %) |  | (8 | %) |  | 17 | % |  | 15 | %
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
| 2020 |  | 2019 |  | 2020 |  | 2019 |  | 2020 |  | 2019
Deferred tax liabilities: |  |  |  |  |  |  |  |  |  |  |
Property | $2,232 |  |  | $2,022 |  |  | $1,312 |  |  | $1,184 |  |  | $854 |  |  | $770 |
ATC Holdings | 116 |  |  | 111 |  |  | — |  |  | — |  |  | — |  |  | — |
Other | 101 |  |  | 84 |  |  | 83 |  |  | 76 |  |  | 41 |  |  | 32 |
Total deferred tax liabilities | 2,449 |  |  | 2,217 |  |  | 1,395 |  |  | 1,260 |  |  | 895 |  |  | 802 |
Deferred tax assets: |  |  |  |  |  |  |  |  |  |  |
Federal credit carryforwards | 454 |  |  | 355 |  |  | 258 |  |  | 175 |  |  | 175 |  |  | 160 |
Net operating losses carryforwards - federal | 77 |  |  | 60 |  |  | 71 |  |  | 56 |  |  | 1 |  |  | 1 |
Net operating losses carryforwards - state | 37 |  |  | 37 |  |  | 1 |  |  | 1 |  |  | — |  |  | — |
Other | 73 |  |  | 61 |  |  | 30 |  |  | 20 |  |  | 18 |  |  | 16 |
Subtotal deferred tax assets | 641 |  |  | 513 |  |  | 360 |  |  | 252 |  |  | 194 |  |  | 177 |
Valuation allowances | (6) |  |  | (10) |  |  | — |  |  | — |  |  | (1) |  |  | (1) |
Total deferred tax assets | 635 |  |  | 503 |  |  | 360 |  |  | 252 |  |  | 193 |  |  | 176 |
Total deferred tax liabilities, net | $1,814 |  |  | $1,714 |  |  | $1,035 |  |  | $1,008 |  |  | $702 |  |  | $626 |
Summary Of Tax Credit Carryforwards | At December 31, 2020, carryforwards and expiration dates were estimated as follows (in millions):
| Range of Expiration Dates |  | Alliant Energy |  | IPL |  | WPL
Federal net operating losses | 2037 |  | $366 |  | $339 |  | $3
State net operating losses | 2021-2040 |  | 622 |  | 10 |  | 2
Federal tax credits | 2022-2040 |  | 454 |  | 258 |  | 175
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) | 2017 | - | 2019
Consolidated Iowa income tax returns (b) | 2017 | - | 2019
Wisconsin combined tax returns (c) | 2016 | - | 2019
(a)The 2017 federal tax return is 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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- Definition Tabular disclosure of the components of income tax expense attributable to continuing operations for each year presented including, but not limited to: current tax expense (benefit), deferred tax expense (benefit), investment tax credits, government grants, the benefits of operating loss carryforwards, tax expense that results from allocating certain tax benefits either directly to contributed capital or to reduce goodwill or other noncurrent intangible assets of an acquired entity, adjustments of a deferred tax liability or asset for enacted changes in tax laws or rates or a change in the tax status of the entity, and adjustments of the beginning-of-the-year balances of a valuation allowance because of a change in circumstances that causes a change in judgment about the realizability of the related deferred tax asset in future years. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 9 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32639-109319 + Details
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- Definition Tabular disclosure of the components of net deferred tax asset or liability recognized in an entity's statement of financial position, including the following: the total of all deferred tax liabilities, the total of all deferred tax assets, the total valuation allowance recognized for deferred tax assets. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32537-109319 + Details
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