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Benefit Plans (Tables) | 3 Months Ended
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Mar. 31, 2021
Defined Benefit Plan Disclosure [Line Items] |
Net Periodic Benefit Costs | The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three months ended March 31 are included below (in millions). For IPL and WPL, amounts are for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans.
| Defined Benefit Pension Plans |  | OPEB Plans
Alliant Energy | 2021 |  | 2020 |  |  |  |  |  | 2021 |  | 2020 |  |  |  |
Service cost | $3 |  | $3 |  |  |  |  |  | $1 |  | $1 |  |  |  |
Interest cost | 8 |  | 11 |  |  |  |  |  | 1 |  | 2 |  |  |  |
Expected return on plan assets | (17) |  | (18) |  |  |  |  |  | (1) |  | (2) |  |  |  |
Amortization of actuarial loss | 10 |  | 9 |  |  |  |  |  | 1 |  | 1 |  |  |  |
Settlement losses (a) | — |  | 4 |  |  |  |  |  | — |  | — |  |  |  |
| $4 |  | $9 |  |  |  |  |  | $2 |  | $2 |  |  |  |
| Defined Benefit Pension Plans |  | OPEB Plans
IPL | 2021 |  | 2020 |  |  |  |  |  | 2021 |  | 2020 |  |  |  |
Service cost | $2 |  | $1 |  |  |  |  |  | $— |  | $— |  |  |  |
Interest cost | 4 |  | 5 |  |  |  |  |  | 1 |  | 1 |  |  |  |
Expected return on plan assets | (8) |  | (8) |  |  |  |  |  | (1) |  | (1) |  |  |  |
Amortization of actuarial loss | 4 |  | 4 |  |  |  |  |  | — |  | — |  |  |  |
| $2 |  | $2 |  |  |  |  |  | $— |  | $— |  |  |  |
| Defined Benefit Pension Plans |  | OPEB Plans
WPL | 2021 |  | 2020 |  |  |  |  |  | 2021 |  | 2020 |  |  |  |
Service cost | $1 |  | $1 |  |  |  |  |  | $— |  | $— |  |  |  |
Interest cost | 4 |  | 5 |  |  |  |  |  | — |  | 1 |  |  |  |
Expected return on plan assets | (8) |  | (8) |  |  |  |  |  | — |  | — |  |  |  |
Amortization of actuarial loss | 5 |  | 4 |  |  |  |  |  | 1 |  | — |  |  |  |
| $2 |  | $2 |  |  |  |  |  | $1 |  | $1 |  |  |  |
(a)Settlement losses related to payments made to retired executives of Alliant Energy.
Recognized Compensation Expense And Income Tax Benefits | A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three months ended March 31 was as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2021 |  | 2020 |  |  |  |  |  | 2021 |  | 2020 |  |  |  |  |  | 2021 |  | 2020 |  |  |  |
Compensation expense | $3 |  |  | $3 |  |  |  |  |  |  | $1 |  |  | $1 |  |  |  |  |  |  | $1 |  |  | $1 |  |  |  |  |
Income tax benefits | 1 |  |  | 1 |  |  |  |  |  |  | — |  |  | — |  |  |  |  |  |  | — |  |  | — |  |  |  |  |
Schedule Of Equity-based Compensation Plans Activity | For the three months ended March 31, 2021, performance shares, performance restricted stock units and restricted stock units were granted to key employees as follows. These shares and units will be paid out in shares of common stock, and are therefore accounted for as equity awards.
|  |  | Weighted Average
| Grants |  | Grant Date Fair Value
Performance shares | 72,774 |  | $46.19
Performance restricted stock units | 72,774 |  | 48.61
Restricted stock units | 79,862 |  | 48.61
IPL [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Net Periodic Benefit Costs | The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three months ended March 31 are included below (in millions). For IPL and WPL, amounts are for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans.
| Defined Benefit Pension Plans |  | OPEB Plans
Alliant Energy | 2021 |  | 2020 |  |  |  |  |  | 2021 |  | 2020 |  |  |  |
Service cost | $3 |  | $3 |  |  |  |  |  | $1 |  | $1 |  |  |  |
Interest cost | 8 |  | 11 |  |  |  |  |  | 1 |  | 2 |  |  |  |
Expected return on plan assets | (17) |  | (18) |  |  |  |  |  | (1) |  | (2) |  |  |  |
Amortization of actuarial loss | 10 |  | 9 |  |  |  |  |  | 1 |  | 1 |  |  |  |
Settlement losses (a) | — |  | 4 |  |  |  |  |  | — |  | — |  |  |  |
| $4 |  | $9 |  |  |  |  |  | $2 |  | $2 |  |  |  |
| Defined Benefit Pension Plans |  | OPEB Plans
IPL | 2021 |  | 2020 |  |  |  |  |  | 2021 |  | 2020 |  |  |  |
Service cost | $2 |  | $1 |  |  |  |  |  | $— |  | $— |  |  |  |
Interest cost | 4 |  | 5 |  |  |  |  |  | 1 |  | 1 |  |  |  |
Expected return on plan assets | (8) |  | (8) |  |  |  |  |  | (1) |  | (1) |  |  |  |
Amortization of actuarial loss | 4 |  | 4 |  |  |  |  |  | — |  | — |  |  |  |
| $2 |  | $2 |  |  |  |  |  | $— |  | $— |  |  |  |
| Defined Benefit Pension Plans |  | OPEB Plans
WPL | 2021 |  | 2020 |  |  |  |  |  | 2021 |  | 2020 |  |  |  |
Service cost | $1 |  | $1 |  |  |  |  |  | $— |  | $— |  |  |  |
Interest cost | 4 |  | 5 |  |  |  |  |  | — |  | 1 |  |  |  |
Expected return on plan assets | (8) |  | (8) |  |  |  |  |  | — |  | — |  |  |  |
Amortization of actuarial loss | 5 |  | 4 |  |  |  |  |  | 1 |  | — |  |  |  |
| $2 |  | $2 |  |  |  |  |  | $1 |  | $1 |  |  |  |
(a)Settlement losses related to payments made to retired executives of Alliant Energy.
Recognized Compensation Expense And Income Tax Benefits | A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three months ended March 31 was as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2021 |  | 2020 |  |  |  |  |  | 2021 |  | 2020 |  |  |  |  |  | 2021 |  | 2020 |  |  |  |
Compensation expense | $3 |  |  | $3 |  |  |  |  |  |  | $1 |  |  | $1 |  |  |  |  |  |  | $1 |  |  | $1 |  |  |  |  |
Income tax benefits | 1 |  |  | 1 |  |  |  |  |  |  | — |  |  | — |  |  |  |  |  |  | — |  |  | — |  |  |  |  |
Schedule Of Equity-based Compensation Plans Activity | For the three months ended March 31, 2021, performance shares, performance restricted stock units and restricted stock units were granted to key employees as follows. These shares and units will be paid out in shares of common stock, and are therefore accounted for as equity awards.
|  |  | Weighted Average
| Grants |  | Grant Date Fair Value
Performance shares | 72,774 |  | $46.19
Performance restricted stock units | 72,774 |  | 48.61
Restricted stock units | 79,862 |  | 48.61
WPL [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Net Periodic Benefit Costs | The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three months ended March 31 are included below (in millions). For IPL and WPL, amounts are for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans.
| Defined Benefit Pension Plans |  | OPEB Plans
Alliant Energy | 2021 |  | 2020 |  |  |  |  |  | 2021 |  | 2020 |  |  |  |
Service cost | $3 |  | $3 |  |  |  |  |  | $1 |  | $1 |  |  |  |
Interest cost | 8 |  | 11 |  |  |  |  |  | 1 |  | 2 |  |  |  |
Expected return on plan assets | (17) |  | (18) |  |  |  |  |  | (1) |  | (2) |  |  |  |
Amortization of actuarial loss | 10 |  | 9 |  |  |  |  |  | 1 |  | 1 |  |  |  |
Settlement losses (a) | — |  | 4 |  |  |  |  |  | — |  | — |  |  |  |
| $4 |  | $9 |  |  |  |  |  | $2 |  | $2 |  |  |  |
| Defined Benefit Pension Plans |  | OPEB Plans
IPL | 2021 |  | 2020 |  |  |  |  |  | 2021 |  | 2020 |  |  |  |
Service cost | $2 |  | $1 |  |  |  |  |  | $— |  | $— |  |  |  |
Interest cost | 4 |  | 5 |  |  |  |  |  | 1 |  | 1 |  |  |  |
Expected return on plan assets | (8) |  | (8) |  |  |  |  |  | (1) |  | (1) |  |  |  |
Amortization of actuarial loss | 4 |  | 4 |  |  |  |  |  | — |  | — |  |  |  |
| $2 |  | $2 |  |  |  |  |  | $— |  | $— |  |  |  |
| Defined Benefit Pension Plans |  | OPEB Plans
WPL | 2021 |  | 2020 |  |  |  |  |  | 2021 |  | 2020 |  |  |  |
Service cost | $1 |  | $1 |  |  |  |  |  | $— |  | $— |  |  |  |
Interest cost | 4 |  | 5 |  |  |  |  |  | — |  | 1 |  |  |  |
Expected return on plan assets | (8) |  | (8) |  |  |  |  |  | — |  | — |  |  |  |
Amortization of actuarial loss | 5 |  | 4 |  |  |  |  |  | 1 |  | — |  |  |  |
| $2 |  | $2 |  |  |  |  |  | $1 |  | $1 |  |  |  |
(a)Settlement losses related to payments made to retired executives of Alliant Energy.
Recognized Compensation Expense And Income Tax Benefits | A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three months ended March 31 was as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2021 |  | 2020 |  |  |  |  |  | 2021 |  | 2020 |  |  |  |  |  | 2021 |  | 2020 |  |  |  |
Compensation expense | $3 |  |  | $3 |  |  |  |  |  |  | $1 |  |  | $1 |  |  |  |  |  |  | $1 |  |  | $1 |  |  |  |  |
Income tax benefits | 1 |  |  | 1 |  |  |  |  |  |  | — |  |  | — |  |  |  |  |  |  | — |  |  | — |  |  |  |  |
Schedule Of Equity-based Compensation Plans Activity | For the three months ended March 31, 2021, performance shares, performance restricted stock units and restricted stock units were granted to key employees as follows. These shares and units will be paid out in shares of common stock, and are therefore accounted for as equity awards.
|  |  | Weighted Average
| Grants |  | Grant Date Fair Value
Performance shares | 72,774 |  | $46.19
Performance restricted stock units | 72,774 |  | 48.61
Restricted stock units | 79,862 |  | 48.61

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