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Benefit Plans | 9 Months Ended
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Sep. 30, 2025
Benefit Plans | BENEFIT PLANS NOTE 10(a) Pension and OPEB Plans - Net Periodic Benefit Costs - The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three and nine months ended September 30 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
| Three Months |  | Nine Months |  | Three Months |  | Nine Months
Alliant Energy | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024
Service cost | $1 |  | $1 |  | $3 |  | $3 |  | $— |  | $1 |  | $1 |  | $2
Interest cost | 11 |  | 12 |  | 34 |  | 34 |  | 2 |  | 2 |  | 6 |  | 6
Expected return on plan assets | (13) |  | (14) |  | (40) |  | (41) |  | — |  | (2) |  | (3) |  | (4)
Amortization of prior service credit | (1) |  | — |  | (1) |  | — |  | — |  | — |  | — |  | —
Amortization of actuarial loss | 6 |  | 6 |  | 17 |  | 18 |  | — |  | — |  | — |  | —
| $4 |  | $5 |  | $13 |  | $14 |  | $2 |  | $1 |  | $4 |  | $4
| Defined Benefit Pension Plans |  | OPEB Plans
| Three Months |  | Nine Months |  | Three Months |  | Nine Months
IPL | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024
Service cost | $1 |  | $1 |  | $2 |  | $2 |  | $— |  | $— |  | $— |  | $—
Interest cost | 5 |  | 5 |  | 15 |  | 15 |  | — |  | 1 |  | 2 |  | 3
Expected return on plan assets | (7) |  | (7) |  | (19) |  | (20) |  | (1) |  | (1) |  | (3) |  | (3)
Amortization of actuarial loss | 3 |  | 2 |  | 7 |  | 7 |  | — |  | — |  | — |  | —
| $2 |  | $1 |  | $5 |  | $4 |  | ($1) |  | $— |  | ($1) |  | $—
| Defined Benefit Pension Plans |  | OPEB Plans
| Three Months |  | Nine Months |  | Three Months |  | Nine Months
WPL | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024
Service cost | $— |  | $— |  | $1 |  | $1 |  | $— |  | $— |  | $— |  | $—
Interest cost | 5 |  | 5 |  | 15 |  | 15 |  | 1 |  | 1 |  | 2 |  | 3
Expected return on plan assets | (5) |  | (6) |  | (17) |  | (18) |  | (1) |  | (1) |  | (1) |  | (1)
Amortization of actuarial loss | 3 |  | 3 |  | 8 |  | 9 |  | — |  | — |  | — |  | —
| $3 |  | $2 |  | $7 |  | $7 |  | $— |  | $— |  | $1 |  | $2
NOTE 10(b) Equity-based Compensation Plans - 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 and nine months ended September 30 was as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| Three Months |  | Nine Months |  | Three Months |  | Nine Months |  | Three Months |  | Nine Months
| 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024
Compensation expense | $6 |  | $3 |  | $13 |  | $10 |  | $3 |  | $2 |  | $7 |  | $5 |  | $2 |  | $1 |  | $6 |  | $4
Income tax benefits | 2 |  | 1 |  | 4 |  | 3 |  | 1 |  | — |  | 2 |  | 1 |  | 1 |  | — |  | 2 |  | 1
As of September 30, 2025, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $17 million, $8 million and $8 million, respectively, which is expected to be recognized over a weighted average period of between 1 year and 2 years. For the nine months ended September 30, 2025, performance shares and restricted stock units were granted to key employees under the equity-based compensation plans 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 (total shareowner return metric) | 105,896 |  | $66.52
Performance shares (net income and environmental metrics) | 118,883 |  | 61.63
Restricted stock units | 100,245 |  | 61.66
As of September 30, 2025, 598,077 shares were included in the calculation of diluted EPS related to the nonvested equity awards.
IPL [Member] |
Benefit Plans | BENEFIT PLANS NOTE 10(a) Pension and OPEB Plans - Net Periodic Benefit Costs - The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three and nine months ended September 30 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
| Three Months |  | Nine Months |  | Three Months |  | Nine Months
Alliant Energy | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024
Service cost | $1 |  | $1 |  | $3 |  | $3 |  | $— |  | $1 |  | $1 |  | $2
Interest cost | 11 |  | 12 |  | 34 |  | 34 |  | 2 |  | 2 |  | 6 |  | 6
Expected return on plan assets | (13) |  | (14) |  | (40) |  | (41) |  | — |  | (2) |  | (3) |  | (4)
Amortization of prior service credit | (1) |  | — |  | (1) |  | — |  | — |  | — |  | — |  | —
Amortization of actuarial loss | 6 |  | 6 |  | 17 |  | 18 |  | — |  | — |  | — |  | —
| $4 |  | $5 |  | $13 |  | $14 |  | $2 |  | $1 |  | $4 |  | $4
| Defined Benefit Pension Plans |  | OPEB Plans
| Three Months |  | Nine Months |  | Three Months |  | Nine Months
IPL | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024
Service cost | $1 |  | $1 |  | $2 |  | $2 |  | $— |  | $— |  | $— |  | $—
Interest cost | 5 |  | 5 |  | 15 |  | 15 |  | — |  | 1 |  | 2 |  | 3
Expected return on plan assets | (7) |  | (7) |  | (19) |  | (20) |  | (1) |  | (1) |  | (3) |  | (3)
Amortization of actuarial loss | 3 |  | 2 |  | 7 |  | 7 |  | — |  | — |  | — |  | —
| $2 |  | $1 |  | $5 |  | $4 |  | ($1) |  | $— |  | ($1) |  | $—
| Defined Benefit Pension Plans |  | OPEB Plans
| Three Months |  | Nine Months |  | Three Months |  | Nine Months
WPL | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024
Service cost | $— |  | $— |  | $1 |  | $1 |  | $— |  | $— |  | $— |  | $—
Interest cost | 5 |  | 5 |  | 15 |  | 15 |  | 1 |  | 1 |  | 2 |  | 3
Expected return on plan assets | (5) |  | (6) |  | (17) |  | (18) |  | (1) |  | (1) |  | (1) |  | (1)
Amortization of actuarial loss | 3 |  | 3 |  | 8 |  | 9 |  | — |  | — |  | — |  | —
| $3 |  | $2 |  | $7 |  | $7 |  | $— |  | $— |  | $1 |  | $2
NOTE 10(b) Equity-based Compensation Plans - 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 and nine months ended September 30 was as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| Three Months |  | Nine Months |  | Three Months |  | Nine Months |  | Three Months |  | Nine Months
| 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024
Compensation expense | $6 |  | $3 |  | $13 |  | $10 |  | $3 |  | $2 |  | $7 |  | $5 |  | $2 |  | $1 |  | $6 |  | $4
Income tax benefits | 2 |  | 1 |  | 4 |  | 3 |  | 1 |  | — |  | 2 |  | 1 |  | 1 |  | — |  | 2 |  | 1
As of September 30, 2025, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $17 million, $8 million and $8 million, respectively, which is expected to be recognized over a weighted average period of between 1 year and 2 years. For the nine months ended September 30, 2025, performance shares and restricted stock units were granted to key employees under the equity-based compensation plans 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 (total shareowner return metric) | 105,896 |  | $66.52
Performance shares (net income and environmental metrics) | 118,883 |  | 61.63
Restricted stock units | 100,245 |  | 61.66
As of September 30, 2025, 598,077 shares were included in the calculation of diluted EPS related to the nonvested equity awards.
WPL [Member] |
Benefit Plans | BENEFIT PLANS NOTE 10(a) Pension and OPEB Plans - Net Periodic Benefit Costs - The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three and nine months ended September 30 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
| Three Months |  | Nine Months |  | Three Months |  | Nine Months
Alliant Energy | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024
Service cost | $1 |  | $1 |  | $3 |  | $3 |  | $— |  | $1 |  | $1 |  | $2
Interest cost | 11 |  | 12 |  | 34 |  | 34 |  | 2 |  | 2 |  | 6 |  | 6
Expected return on plan assets | (13) |  | (14) |  | (40) |  | (41) |  | — |  | (2) |  | (3) |  | (4)
Amortization of prior service credit | (1) |  | — |  | (1) |  | — |  | — |  | — |  | — |  | —
Amortization of actuarial loss | 6 |  | 6 |  | 17 |  | 18 |  | — |  | — |  | — |  | —
| $4 |  | $5 |  | $13 |  | $14 |  | $2 |  | $1 |  | $4 |  | $4
| Defined Benefit Pension Plans |  | OPEB Plans
| Three Months |  | Nine Months |  | Three Months |  | Nine Months
IPL | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024
Service cost | $1 |  | $1 |  | $2 |  | $2 |  | $— |  | $— |  | $— |  | $—
Interest cost | 5 |  | 5 |  | 15 |  | 15 |  | — |  | 1 |  | 2 |  | 3
Expected return on plan assets | (7) |  | (7) |  | (19) |  | (20) |  | (1) |  | (1) |  | (3) |  | (3)
Amortization of actuarial loss | 3 |  | 2 |  | 7 |  | 7 |  | — |  | — |  | — |  | —
| $2 |  | $1 |  | $5 |  | $4 |  | ($1) |  | $— |  | ($1) |  | $—
| Defined Benefit Pension Plans |  | OPEB Plans
| Three Months |  | Nine Months |  | Three Months |  | Nine Months
WPL | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024
Service cost | $— |  | $— |  | $1 |  | $1 |  | $— |  | $— |  | $— |  | $—
Interest cost | 5 |  | 5 |  | 15 |  | 15 |  | 1 |  | 1 |  | 2 |  | 3
Expected return on plan assets | (5) |  | (6) |  | (17) |  | (18) |  | (1) |  | (1) |  | (1) |  | (1)
Amortization of actuarial loss | 3 |  | 3 |  | 8 |  | 9 |  | — |  | — |  | — |  | —
| $3 |  | $2 |  | $7 |  | $7 |  | $— |  | $— |  | $1 |  | $2
NOTE 10(b) Equity-based Compensation Plans - 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 and nine months ended September 30 was as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| Three Months |  | Nine Months |  | Three Months |  | Nine Months |  | Three Months |  | Nine Months
| 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024 |  | 2025 |  | 2024
Compensation expense | $6 |  | $3 |  | $13 |  | $10 |  | $3 |  | $2 |  | $7 |  | $5 |  | $2 |  | $1 |  | $6 |  | $4
Income tax benefits | 2 |  | 1 |  | 4 |  | 3 |  | 1 |  | — |  | 2 |  | 1 |  | 1 |  | — |  | 2 |  | 1
As of September 30, 2025, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $17 million, $8 million and $8 million, respectively, which is expected to be recognized over a weighted average period of between 1 year and 2 years. For the nine months ended September 30, 2025, performance shares and restricted stock units were granted to key employees under the equity-based compensation plans 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 (total shareowner return metric) | 105,896 |  | $66.52
Performance shares (net income and environmental metrics) | 118,883 |  | 61.63
Restricted stock units | 100,245 |  | 61.66
As of September 30, 2025, 598,077 shares were included in the calculation of diluted EPS related to the nonvested equity awards.

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- Definition The entire disclosure for an entity's employee compensation and benefit plans, including, but not limited to, postemployment and postretirement benefit plans, defined benefit pension plans, defined contribution plans, non-qualified and supplemental benefit plans, deferred compensation, share-based compensation, life insurance, severance, health care, unemployment and other benefit plans. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 715 -Name Accounting Standards Codification -Publisher FASB -URI https://asc.fasb.org/715/tableOfContent Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 712 -Name Accounting Standards Codification -Publisher FASB -URI https://asc.fasb.org/712/tableOfContent Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 710 -Name Accounting Standards Codification -Publisher FASB -URI https://asc.fasb.org/710/tableOfContent Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 718 -Name Accounting Standards Codification -Publisher FASB -URI https://asc.fasb.org/718/tableOfContent + Details
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