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Benefit Plans (Tables) | 12 Months Ended
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Dec. 31, 2024
Defined Benefit Plan Disclosure [Line Items] |
Assumptions Used To Measure Benefit Plans | The weighted-average assumptions for defined benefit pension and OPEB plans at the measurement date of December 31 were as follows:
| Defined Benefit Pension Plans |  | OPEB Plans
Alliant Energy | 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022
Discount rate for benefit obligations | 5.65% |  | 5.36% |  | 5.54% |  | 5.62% |  | 5.40% |  | 5.53%
Discount rate for net periodic cost | 5.36% |  | 5.54% |  | 2.91% |  | 5.40% |  | 5.53% |  | 2.81%
Expected rate of return on plan assets | 7.73% |  | 7.80% |  | 7.80% |  | 6.22% |  | 6.50% |  | 6.40%
Interest crediting rate for Alliant Energy Cash Balance Pension Plan | 6.24% |  | 10.75% |  | 9.22% |  | N/A |  | N/A |  | N/A
Rate of compensation increase | 3.50% | - | 4.50% |  | 3.30% | - | 4.50% |  | 3.30% | - | 4.50% |  | N/A |  | N/A |  | N/A
| Qualified Defined Benefit Pension Plan |  | OPEB Plans
IPL | 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022
Discount rate for benefit obligations | 5.66% |  | 5.35% |  | 5.55% |  | 5.61% |  | 5.40% |  | 5.53%
Discount rate for net periodic cost | 5.35% |  | 5.55% |  | 2.94% |  | 5.40% |  | 5.53% |  | 2.80%
Expected rate of return on plan assets | 7.60% |  | 7.80% |  | 7.80% |  | 6.60% |  | 6.90% |  | 6.50%
Rate of compensation increase | 3.75% |  | 3.30% |  | 3.30% |  | N/A |  | N/A |  | N/A
| Qualified Defined Benefit Pension Plan |  | OPEB Plans
WPL | 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022
Discount rate for benefit obligations | 5.66% |  | 5.35% |  | 5.54% |  | 5.61% |  | 5.40% |  | 5.53%
Discount rate for net periodic cost | 5.35% |  | 5.54% |  | 2.94% |  | 5.40% |  | 5.53% |  | 2.79%
Expected rate of return on plan assets | 7.80% |  | 7.80% |  | 7.80% |  | 5.61% |  | 5.65% |  | 5.49%
Rate of compensation increase | 3.50% |  | 3.30% |  | 3.30% |  | N/A |  | N/A |  | N/A
Net Periodic Benefit Costs | The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans are included below (in millions). The service cost component of net periodic benefit costs is included in “Other operation and maintenance” expenses in the income statements and all other components of net periodic benefit costs are included in “Other (income) and deductions” in the income statements or regulatory assets on the balance sheets.
Alliant Energy | Defined Benefit Pension Plans |  | OPEB Plans
2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022
Service cost | $5 |  |  | $5 |  |  | $9 |  |  | $2 |  |  | $2 |  |  | $3 |
Interest cost | 45 |  |  | 47 |  |  | 36 |  |  | 8 |  |  | 9 |  |  | 6 |
Expected return on plan assets (a) | (55) |  |  | (53) |  |  | (69) |  |  | (5) |  |  | (5) |  |  | (5) |
Amortization of prior service credit (b) | (1) |  |  | (1) |  |  | (1) |  |  | — |  |  | — |  |  | — |
Amortization of actuarial loss (c) | 24 |  |  | 28 |  |  | 32 |  |  | — |  |  | 1 |  |  | 2 |
Settlement losses (d) | — |  |  | — |  |  | 26 |  |  | — |  |  | — |  |  | — |
| $18 |  |  | $26 |  |  | $33 |  |  | $5 |  |  | $7 |  |  | $6 |
IPL | Defined Benefit Pension Plans |  | OPEB Plans
2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022
Service cost | $3 |  |  | $3 |  |  | $6 |  |  | $1 |  |  | $1 |  |  | $1 |
Interest cost | 20 |  |  | 21 |  |  | 16 |  |  | 3 |  |  | 3 |  |  | 2 |
Expected return on plan assets (a) | (26) |  |  | (26) |  |  | (31) |  |  | (4) |  |  | (3) |  |  | (4) |
Amortization of actuarial loss (c) | 9 |  |  | 11 |  |  | 13 |  |  | — |  |  | 1 |  |  | 1 |
Settlement losses (d) | — |  |  | — |  |  | 13 |  |  | — |  |  | — |  |  | — |
| $6 |  |  | $9 |  |  | $17 |  |  | $— |  |  | $2 |  |  | $— |
WPL | Defined Benefit Pension Plans |  | OPEB Plans
2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022
Service cost | $2 |  |  | $2 |  |  | $3 |  |  | $1 |  |  | $1 |  |  | $1 |
Interest cost | 20 |  |  | 20 |  |  | 16 |  |  | 3 |  |  | 3 |  |  | 2 |
Expected return on plan assets (a) | (23) |  |  | (22) |  |  | (31) |  |  | (1) |  |  | (1) |  |  | (1) |
Amortization of actuarial loss (c) | 11 |  |  | 13 |  |  | 15 |  |  | — |  |  | 1 |  |  | 2 |
Settlement losses (d) | — |  |  | — |  |  | 13 |  |  | — |  |  | — |  |  | — |
| $10 |  |  | $13 |  |  | $16 |  |  | $3 |  |  | $4 |  |  | $4 |
(a)The expected return on plan assets is based on the expected rate of return on plan assets and the fair value approach to the market-related value of plan assets. (b)Unrecognized prior service credits for the OPEB plans are amortized over the average future service period to full eligibility of the participants of each plan. (c)Unrecognized net actuarial gains or losses in excess of 10% of the greater of the plans’ benefit obligations or assets are amortized over the average future service lives of plan participants, except for the Alliant Energy Cash Balance Pension Plan where gains or losses outside the 10% threshold are amortized over the time period the participants are expected to receive benefits. (d)Settlement losses related to payments made to retired executives of Alliant Energy and lump sum payments related to IPL’s and WPL’s qualified defined benefit pension plans. In 2022, the majority of Alliant Energy’s, IPL’s, and WPL’s pension settlement losses were recognized as regulatory assets in accordance with regulatory treatment, and $7 million was included in “Other (income) and deductions” in Alliant Energy’s and IPL’s income statements related to IPL’s qualified defined benefit pension plan.
Funded Status Of Benefit Plans | A reconciliation of the funded status of qualified and non-qualified defined benefit pension and OPEB plans to the amounts recognized on the balance sheets at December 31 was as follows (in millions):
| Defined Benefit Pension Plans |  | OPEB Plans
Alliant Energy | 2024 |  | 2023 |  | 2024 |  | 2023
Change in benefit obligation: |  |  |  |  |  |  |
Net benefit obligation at January 1 | $876 |  |  | $875 |  |  | $160 |  |  | $168 |
Service cost | 5 |  |  | 5 |  |  | 2 |  |  | 2 |
Interest cost | 45 |  |  | 47 |  |  | 8 |  |  | 9 |
Plan participants’ contributions | — |  |  | — |  |  | 3 |  |  | 4 |
Actuarial (gain) loss | (19) |  |  | 23 |  |  | (7) |  |  | (3) |
Gross benefits paid | (66) |  |  | (74) |  |  | (18) |  |  | (20) |
Net benefit obligation at December 31 | 841 |  |  | 876 |  |  | 148 |  |  | 160 |
Change in plan assets: |  |  |  |  |  |  |
Fair value of plan assets at January 1 | 732 |  |  | 706 |  |  | 83 |  |  | 83 |
Actual return on plan assets | 38 |  |  | 86 |  |  | 5 |  |  | 8 |
Employer contributions | 11 |  |  | 14 |  |  | 7 |  |  | 8 |
Plan participants’ contributions | — |  |  | — |  |  | 3 |  |  | 4 |
Gross benefits paid | (66) |  |  | (74) |  |  | (18) |  |  | (20) |
Fair value of plan assets at December 31 | 715 |  |  | 732 |  |  | 80 |  |  | 83 |
Under funded status at December 31 | ($126) |  |  | ($144) |  |  | ($68) |  |  | ($77) |
| Defined Benefit Pension Plans |  | OPEB Plans
Alliant Energy | 2024 |  | 2023 |  | 2024 |  | 2023
Amounts recognized on the balance sheets consist of: |  |  |  |  |  |  |
Non-current assets | $— |  |  | $— |  |  | $17 |  |  | $14 |
Current liabilities | (3) |  |  | (2) |  |  | (7) |  |  | (8) |
Pension and other benefit obligations | (123) |  |  | (142) |  |  | (78) |  |  | (83) |
Net amounts recognized at December 31 | ($126) |  |  | ($144) |  |  | ($68) |  |  | ($77) |
Amounts recognized in Regulatory Assets consist of: |  |  |  |  |  |  |
Net actuarial loss | $312 |  |  | $337 |  |  | $4 |  |  | $11 |
Prior service credit | (2) |  |  | (2) |  |  | — |  |  | — |
| $310 |  |  | $335 |  |  | $4 |  |  | $11 |
| Defined Benefit Pension Plans |  | OPEB Plans
IPL | 2024 |  | 2023 |  | 2024 |  | 2023
Change in benefit obligation: |  |  |  |  |  |  |
Net benefit obligation at January 1 | $387 |  |  | $389 |  |  | $65 |  |  | $68 |
Service cost | 3 |  |  | 3 |  |  | 1 |  |  | 1 |
Interest cost | 20 |  |  | 21 |  |  | 3 |  |  | 3 |
Plan participants’ contributions | — |  |  | — |  |  | 1 |  |  | 2 |
Actuarial (gain) loss | (8) |  |  | 9 |  |  | (3) |  |  | (1) |
Gross benefits paid | (30) |  |  | (35) |  |  | (8) |  |  | (8) |
Net benefit obligation at December 31 | 372 |  |  | 387 |  |  | 59 |  |  | 65 |
Change in plan assets: |  |  |  |  |  |  |
Fair value of plan assets at January 1 | 352 |  |  | 344 |  |  | 61 |  |  | 58 |
Actual return on plan assets | 18 |  |  | 42 |  |  | 4 |  |  | 7 |
Employer contributions | — |  |  | 1 |  |  | 1 |  |  | 2 |
Plan participants’ contributions | — |  |  | — |  |  | 1 |  |  | 2 |
Gross benefits paid | (30) |  |  | (35) |  |  | (8) |  |  | (8) |
Fair value of plan assets at December 31 | 340 |  |  | 352 |  |  | 59 |  |  | 61 |
Under funded status at December 31 | ($32) |  |  | ($35) |  |  | $— |  |  | ($4) |
| Defined Benefit Pension Plans |  | OPEB Plans
IPL | 2024 |  | 2023 |  | 2024 |  | 2023
Amounts recognized on the balance sheets consist of: |  |  |  |  |  |  |
Non-current assets | $— |  |  | $— |  |  | $13 |  |  | $10 |
Current liabilities | (1) |  |  | — |  |  | (1) |  |  | (1) |
Pension and other benefit obligations | (31) |  |  | (35) |  |  | (12) |  |  | (13) |
Net amounts recognized at December 31 | ($32) |  |  | ($35) |  |  | $— |  |  | ($4) |
Amounts recognized in Regulatory Assets consist of: |  |  |  |  |  |  |
Net actuarial loss | $126 |  |  | $135 |  |  | $7 |  |  | $9 |
Prior service credit | (1) |  |  | (1) |  |  | — |  |  | — |
| $125 |  |  | $134 |  |  | $7 |  |  | $9 |
| Defined Benefit Pension Plans |  | OPEB Plans
WPL | 2024 |  | 2023 |  | 2024 |  | 2023
Change in benefit obligation: |  |  |  |  |  |  |
Net benefit obligation at January 1 | $381 |  |  | $381 |  |  | $61 |  |  | $65 |
Service cost | 2 |  |  | 2 |  |  | 1 |  |  | 1 |
Interest cost | 20 |  |  | 20 |  |  | 3 |  |  | 3 |
Plan participants’ contributions | — |  |  | — |  |  | 1 |  |  | 2 |
Actuarial (gain) loss | (8) |  |  | 10 |  |  | (3) |  |  | (2) |
Gross benefits paid | (30) |  |  | (32) |  |  | (7) |  |  | (8) |
Net benefit obligation at December 31 | 365 |  |  | 381 |  |  | 56 |  |  | 61 |
Change in plan assets: |  |  |  |  |  |  |
Fair value of plan assets at January 1 | 306 |  |  | 291 |  |  | 14 |  |  | 14 |
Actual return on plan assets | 17 |  |  | 35 |  |  | — |  |  | 1 |
Employer contributions | 10 |  |  | 12 |  |  | 5 |  |  | 5 |
Plan participants’ contributions | — |  |  | — |  |  | 1 |  |  | 2 |
Gross benefits paid | (30) |  |  | (32) |  |  | (7) |  |  | (8) |
Fair value of plan assets at December 31 | 303 |  |  | 306 |  |  | 13 |  |  | 14 |
Under funded status at December 31 | ($62) |  |  | ($75) |  |  | ($43) |  |  | ($47) |
| Defined Benefit Pension Plans |  | OPEB Plans
WPL | 2024 |  | 2023 |  | 2024 |  | 2023
Amounts recognized on the balance sheets consist of: |  |  |  |  |  |  |
Non-current assets | $— |  |  | $— |  |  | $4 |  |  | $4 |
Current liabilities | — |  |  | — |  |  | (6) |  |  | (6) |
Pension and other benefit obligations | (62) |  |  | (75) |  |  | (41) |  |  | (45) |
Net amounts recognized at December 31 | ($62) |  |  | ($75) |  |  | ($43) |  |  | ($47) |
Amounts recognized in Regulatory Assets consist of: |  |  |  |  |  |  |
Net actuarial loss | $135 |  |  | $148 |  |  | $— |  |  | $3 |
Accumulated Benefit Obligations | Accumulated benefit obligations, aggregate amounts applicable to defined benefit pension and OPEB plans with accumulated benefit obligations in excess of plan assets, as well as defined benefit pension plans with projected benefit obligations in excess of plan assets as of the December 31 measurement date are as follows (in millions):
| Defined Benefit Pension Plans |  | OPEB Plans
Alliant Energy | 2024 |  | 2023 |  | 2024 |  | 2023
Accumulated benefit obligations | $824 |  |  | $857 |  |  | $148 |  |  | $160 |
Plans with accumulated benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Accumulated benefit obligations | 824 |  |  | 857 |  |  | 148 |  |  | 160 |
Fair value of plan assets | 715 |  |  | 732 |  |  | 80 |  |  | 83 |
Plans with projected benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Projected benefit obligations | 841 |  |  | 876 |  |  | N/A |  | N/A
Fair value of plan assets | 715 |  |  | 732 |  |  | N/A |  | N/A
| Defined Benefit Pension Plans |  | OPEB Plans
IPL | 2024 |  | 2023 |  | 2024 |  | 2023
Accumulated benefit obligations | $362 |  |  | $377 |  |  | $59 |  |  | $65 |
Plans with accumulated benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Accumulated benefit obligations | 362 |  |  | 377 |  |  | N/A |  | 65 |
Fair value of plan assets | 340 |  |  | 352 |  |  | N/A |  | 61 |
Plans with projected benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Projected benefit obligations | 372 |  |  | 387 |  |  | N/A |  | N/A
Fair value of plan assets | 340 |  |  | 352 |  |  | N/A |  | N/A
| Defined Benefit Pension Plans |  | OPEB Plans
WPL | 2024 |  | 2023 |  | 2024 |  | 2023
Accumulated benefit obligations | $358 |  |  | $373 |  |  | $56 |  |  | $61 |
Plans with accumulated benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Accumulated benefit obligations | 358 |  |  | 373 |  |  | 56 |  |  | 61 |
Fair value of plan assets | 303 |  |  | 306 |  |  | 13 |  |  | 14 |
Plans with projected benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Projected benefit obligations | 365 |  |  | 381 |  |  | N/A |  | N/A
Fair value of plan assets | 303 |  |  | 306 |  |  | N/A |  | N/A
Regulatory Assets | In addition to the amounts recognized in regulatory assets in the above tables for IPL and WPL, regulatory assets were recognized for amounts associated with Corporate Services employees participating in other Alliant Energy sponsored benefit plans that were allocated to IPL and WPL at December 31 as follows (in millions):
| IPL |  | WPL
| 2024 |  | 2023 |  | 2024 |  | 2023
Regulatory assets | $25 |  | $28 |  | $22 |  | $24
Estimated Future Employer Contributions | Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2025 is as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
Defined benefit pension plans (a) | $20 |  | $1 |  | $14
OPEB plans | 7 |  | 1 |  | 6
(a)Alliant Energy sponsors several non-qualified defined benefit pension plans that cover certain current and former key employees of IPL and WPL. Alliant Energy allocates pension costs to IPL and WPL for these plans. In addition, IPL and WPL amounts reflect funding for their non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans.
Expected Benefit Payments | Expected benefit payments for the qualified and non-qualified defined benefit plans, which reflect expected future service, as appropriate, are as follows (in millions):
Alliant Energy | 2025 |  | 2026 |  | 2027 |  | 2028 |  | 2029 |  | 2030 - 2034
Defined benefit pension benefits | $79 |  |  | $75 |  |  | $74 |  |  | $74 |  |  | $74 |  |  | $329
OPEB | 16 |  |  | 16 |  |  | 15 |  |  | 15 |  |  | 14 |  |  | 62
| $95 |  |  | $91 |  |  | $89 |  |  | $89 |  |  | $88 |  |  | $391
IPL | 2025 |  | 2026 |  | 2027 |  | 2028 |  | 2029 |  | 2030 - 2034
Defined benefit pension benefits | $36 |  |  | $34 |  |  | $33 |  |  | $33 |  |  | $32 |  |  | $148
OPEB | 7 |  |  | 6 |  |  | 6 |  |  | 6 |  |  | 6 |  |  | 24
| $43 |  |  | $40 |  |  | $39 |  |  | $39 |  |  | $38 |  |  | $172
WPL | 2025 |  | 2026 |  | 2027 |  | 2028 |  | 2029 |  | 2030 - 2034
Defined benefit pension benefits | $33 |  |  | $31 |  |  | $31 |  |  | $31 |  |  | $31 |  |  | $144
OPEB | 7 |  |  | 6 |  |  | 6 |  |  | 5 |  |  | 5 |  |  | 23
| $40 |  |  | $37 |  |  | $37 |  |  | $36 |  |  | $36 |  |  | $167
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 was as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022
Compensation expense | $12 |  | $12 |  | $13 |  | $6 |  | $6 |  | $7 |  | $5 |  | $5 |  | $5
Income tax benefits | 3 |  | 3 |  | 3 |  | 2 |  | 2 |  | 2 |  | 1 |  | 1 |  | 1
Schedule of Carrying Value and Fair Market Value of the Deferred Compensation Obligation | At December 31, the carrying value of the deferred compensation obligation for the company stock account and the shares in the deferred compensation trust based on the historical value of the shares of Alliant Energy common stock contributed to the rabbi trust, and the fair market value of the shares held in the rabbi trust, were as follows (in millions):
| 2024 |  | 2023
Carrying value | $14 |  | $13
Fair market value | 22 |  | 19
IPL [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Assumptions Used To Measure Benefit Plans | The weighted-average assumptions for defined benefit pension and OPEB plans at the measurement date of December 31 were as follows:
| Defined Benefit Pension Plans |  | OPEB Plans
Alliant Energy | 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022
Discount rate for benefit obligations | 5.65% |  | 5.36% |  | 5.54% |  | 5.62% |  | 5.40% |  | 5.53%
Discount rate for net periodic cost | 5.36% |  | 5.54% |  | 2.91% |  | 5.40% |  | 5.53% |  | 2.81%
Expected rate of return on plan assets | 7.73% |  | 7.80% |  | 7.80% |  | 6.22% |  | 6.50% |  | 6.40%
Interest crediting rate for Alliant Energy Cash Balance Pension Plan | 6.24% |  | 10.75% |  | 9.22% |  | N/A |  | N/A |  | N/A
Rate of compensation increase | 3.50% | - | 4.50% |  | 3.30% | - | 4.50% |  | 3.30% | - | 4.50% |  | N/A |  | N/A |  | N/A
| Qualified Defined Benefit Pension Plan |  | OPEB Plans
IPL | 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022
Discount rate for benefit obligations | 5.66% |  | 5.35% |  | 5.55% |  | 5.61% |  | 5.40% |  | 5.53%
Discount rate for net periodic cost | 5.35% |  | 5.55% |  | 2.94% |  | 5.40% |  | 5.53% |  | 2.80%
Expected rate of return on plan assets | 7.60% |  | 7.80% |  | 7.80% |  | 6.60% |  | 6.90% |  | 6.50%
Rate of compensation increase | 3.75% |  | 3.30% |  | 3.30% |  | N/A |  | N/A |  | N/A
| Qualified Defined Benefit Pension Plan |  | OPEB Plans
WPL | 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022
Discount rate for benefit obligations | 5.66% |  | 5.35% |  | 5.54% |  | 5.61% |  | 5.40% |  | 5.53%
Discount rate for net periodic cost | 5.35% |  | 5.54% |  | 2.94% |  | 5.40% |  | 5.53% |  | 2.79%
Expected rate of return on plan assets | 7.80% |  | 7.80% |  | 7.80% |  | 5.61% |  | 5.65% |  | 5.49%
Rate of compensation increase | 3.50% |  | 3.30% |  | 3.30% |  | N/A |  | N/A |  | N/A
Net Periodic Benefit Costs | The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans are included below (in millions). The service cost component of net periodic benefit costs is included in “Other operation and maintenance” expenses in the income statements and all other components of net periodic benefit costs are included in “Other (income) and deductions” in the income statements or regulatory assets on the balance sheets.
Alliant Energy | Defined Benefit Pension Plans |  | OPEB Plans
2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022
Service cost | $5 |  |  | $5 |  |  | $9 |  |  | $2 |  |  | $2 |  |  | $3 |
Interest cost | 45 |  |  | 47 |  |  | 36 |  |  | 8 |  |  | 9 |  |  | 6 |
Expected return on plan assets (a) | (55) |  |  | (53) |  |  | (69) |  |  | (5) |  |  | (5) |  |  | (5) |
Amortization of prior service credit (b) | (1) |  |  | (1) |  |  | (1) |  |  | — |  |  | — |  |  | — |
Amortization of actuarial loss (c) | 24 |  |  | 28 |  |  | 32 |  |  | — |  |  | 1 |  |  | 2 |
Settlement losses (d) | — |  |  | — |  |  | 26 |  |  | — |  |  | — |  |  | — |
| $18 |  |  | $26 |  |  | $33 |  |  | $5 |  |  | $7 |  |  | $6 |
IPL | Defined Benefit Pension Plans |  | OPEB Plans
2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022
Service cost | $3 |  |  | $3 |  |  | $6 |  |  | $1 |  |  | $1 |  |  | $1 |
Interest cost | 20 |  |  | 21 |  |  | 16 |  |  | 3 |  |  | 3 |  |  | 2 |
Expected return on plan assets (a) | (26) |  |  | (26) |  |  | (31) |  |  | (4) |  |  | (3) |  |  | (4) |
Amortization of actuarial loss (c) | 9 |  |  | 11 |  |  | 13 |  |  | — |  |  | 1 |  |  | 1 |
Settlement losses (d) | — |  |  | — |  |  | 13 |  |  | — |  |  | — |  |  | — |
| $6 |  |  | $9 |  |  | $17 |  |  | $— |  |  | $2 |  |  | $— |
WPL | Defined Benefit Pension Plans |  | OPEB Plans
2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022
Service cost | $2 |  |  | $2 |  |  | $3 |  |  | $1 |  |  | $1 |  |  | $1 |
Interest cost | 20 |  |  | 20 |  |  | 16 |  |  | 3 |  |  | 3 |  |  | 2 |
Expected return on plan assets (a) | (23) |  |  | (22) |  |  | (31) |  |  | (1) |  |  | (1) |  |  | (1) |
Amortization of actuarial loss (c) | 11 |  |  | 13 |  |  | 15 |  |  | — |  |  | 1 |  |  | 2 |
Settlement losses (d) | — |  |  | — |  |  | 13 |  |  | — |  |  | — |  |  | — |
| $10 |  |  | $13 |  |  | $16 |  |  | $3 |  |  | $4 |  |  | $4 |
(a)The expected return on plan assets is based on the expected rate of return on plan assets and the fair value approach to the market-related value of plan assets. (b)Unrecognized prior service credits for the OPEB plans are amortized over the average future service period to full eligibility of the participants of each plan. (c)Unrecognized net actuarial gains or losses in excess of 10% of the greater of the plans’ benefit obligations or assets are amortized over the average future service lives of plan participants, except for the Alliant Energy Cash Balance Pension Plan where gains or losses outside the 10% threshold are amortized over the time period the participants are expected to receive benefits. (d)Settlement losses related to payments made to retired executives of Alliant Energy and lump sum payments related to IPL’s and WPL’s qualified defined benefit pension plans. In 2022, the majority of Alliant Energy’s, IPL’s, and WPL’s pension settlement losses were recognized as regulatory assets in accordance with regulatory treatment, and $7 million was included in “Other (income) and deductions” in Alliant Energy’s and IPL’s income statements related to IPL’s qualified defined benefit pension plan.
Funded Status Of Benefit Plans | A reconciliation of the funded status of qualified and non-qualified defined benefit pension and OPEB plans to the amounts recognized on the balance sheets at December 31 was as follows (in millions):
| Defined Benefit Pension Plans |  | OPEB Plans
Alliant Energy | 2024 |  | 2023 |  | 2024 |  | 2023
Change in benefit obligation: |  |  |  |  |  |  |
Net benefit obligation at January 1 | $876 |  |  | $875 |  |  | $160 |  |  | $168 |
Service cost | 5 |  |  | 5 |  |  | 2 |  |  | 2 |
Interest cost | 45 |  |  | 47 |  |  | 8 |  |  | 9 |
Plan participants’ contributions | — |  |  | — |  |  | 3 |  |  | 4 |
Actuarial (gain) loss | (19) |  |  | 23 |  |  | (7) |  |  | (3) |
Gross benefits paid | (66) |  |  | (74) |  |  | (18) |  |  | (20) |
Net benefit obligation at December 31 | 841 |  |  | 876 |  |  | 148 |  |  | 160 |
Change in plan assets: |  |  |  |  |  |  |
Fair value of plan assets at January 1 | 732 |  |  | 706 |  |  | 83 |  |  | 83 |
Actual return on plan assets | 38 |  |  | 86 |  |  | 5 |  |  | 8 |
Employer contributions | 11 |  |  | 14 |  |  | 7 |  |  | 8 |
Plan participants’ contributions | — |  |  | — |  |  | 3 |  |  | 4 |
Gross benefits paid | (66) |  |  | (74) |  |  | (18) |  |  | (20) |
Fair value of plan assets at December 31 | 715 |  |  | 732 |  |  | 80 |  |  | 83 |
Under funded status at December 31 | ($126) |  |  | ($144) |  |  | ($68) |  |  | ($77) |
| Defined Benefit Pension Plans |  | OPEB Plans
Alliant Energy | 2024 |  | 2023 |  | 2024 |  | 2023
Amounts recognized on the balance sheets consist of: |  |  |  |  |  |  |
Non-current assets | $— |  |  | $— |  |  | $17 |  |  | $14 |
Current liabilities | (3) |  |  | (2) |  |  | (7) |  |  | (8) |
Pension and other benefit obligations | (123) |  |  | (142) |  |  | (78) |  |  | (83) |
Net amounts recognized at December 31 | ($126) |  |  | ($144) |  |  | ($68) |  |  | ($77) |
Amounts recognized in Regulatory Assets consist of: |  |  |  |  |  |  |
Net actuarial loss | $312 |  |  | $337 |  |  | $4 |  |  | $11 |
Prior service credit | (2) |  |  | (2) |  |  | — |  |  | — |
| $310 |  |  | $335 |  |  | $4 |  |  | $11 |
| Defined Benefit Pension Plans |  | OPEB Plans
IPL | 2024 |  | 2023 |  | 2024 |  | 2023
Change in benefit obligation: |  |  |  |  |  |  |
Net benefit obligation at January 1 | $387 |  |  | $389 |  |  | $65 |  |  | $68 |
Service cost | 3 |  |  | 3 |  |  | 1 |  |  | 1 |
Interest cost | 20 |  |  | 21 |  |  | 3 |  |  | 3 |
Plan participants’ contributions | — |  |  | — |  |  | 1 |  |  | 2 |
Actuarial (gain) loss | (8) |  |  | 9 |  |  | (3) |  |  | (1) |
Gross benefits paid | (30) |  |  | (35) |  |  | (8) |  |  | (8) |
Net benefit obligation at December 31 | 372 |  |  | 387 |  |  | 59 |  |  | 65 |
Change in plan assets: |  |  |  |  |  |  |
Fair value of plan assets at January 1 | 352 |  |  | 344 |  |  | 61 |  |  | 58 |
Actual return on plan assets | 18 |  |  | 42 |  |  | 4 |  |  | 7 |
Employer contributions | — |  |  | 1 |  |  | 1 |  |  | 2 |
Plan participants’ contributions | — |  |  | — |  |  | 1 |  |  | 2 |
Gross benefits paid | (30) |  |  | (35) |  |  | (8) |  |  | (8) |
Fair value of plan assets at December 31 | 340 |  |  | 352 |  |  | 59 |  |  | 61 |
Under funded status at December 31 | ($32) |  |  | ($35) |  |  | $— |  |  | ($4) |
| Defined Benefit Pension Plans |  | OPEB Plans
IPL | 2024 |  | 2023 |  | 2024 |  | 2023
Amounts recognized on the balance sheets consist of: |  |  |  |  |  |  |
Non-current assets | $— |  |  | $— |  |  | $13 |  |  | $10 |
Current liabilities | (1) |  |  | — |  |  | (1) |  |  | (1) |
Pension and other benefit obligations | (31) |  |  | (35) |  |  | (12) |  |  | (13) |
Net amounts recognized at December 31 | ($32) |  |  | ($35) |  |  | $— |  |  | ($4) |
Amounts recognized in Regulatory Assets consist of: |  |  |  |  |  |  |
Net actuarial loss | $126 |  |  | $135 |  |  | $7 |  |  | $9 |
Prior service credit | (1) |  |  | (1) |  |  | — |  |  | — |
| $125 |  |  | $134 |  |  | $7 |  |  | $9 |
| Defined Benefit Pension Plans |  | OPEB Plans
WPL | 2024 |  | 2023 |  | 2024 |  | 2023
Change in benefit obligation: |  |  |  |  |  |  |
Net benefit obligation at January 1 | $381 |  |  | $381 |  |  | $61 |  |  | $65 |
Service cost | 2 |  |  | 2 |  |  | 1 |  |  | 1 |
Interest cost | 20 |  |  | 20 |  |  | 3 |  |  | 3 |
Plan participants’ contributions | — |  |  | — |  |  | 1 |  |  | 2 |
Actuarial (gain) loss | (8) |  |  | 10 |  |  | (3) |  |  | (2) |
Gross benefits paid | (30) |  |  | (32) |  |  | (7) |  |  | (8) |
Net benefit obligation at December 31 | 365 |  |  | 381 |  |  | 56 |  |  | 61 |
Change in plan assets: |  |  |  |  |  |  |
Fair value of plan assets at January 1 | 306 |  |  | 291 |  |  | 14 |  |  | 14 |
Actual return on plan assets | 17 |  |  | 35 |  |  | — |  |  | 1 |
Employer contributions | 10 |  |  | 12 |  |  | 5 |  |  | 5 |
Plan participants’ contributions | — |  |  | — |  |  | 1 |  |  | 2 |
Gross benefits paid | (30) |  |  | (32) |  |  | (7) |  |  | (8) |
Fair value of plan assets at December 31 | 303 |  |  | 306 |  |  | 13 |  |  | 14 |
Under funded status at December 31 | ($62) |  |  | ($75) |  |  | ($43) |  |  | ($47) |
| Defined Benefit Pension Plans |  | OPEB Plans
WPL | 2024 |  | 2023 |  | 2024 |  | 2023
Amounts recognized on the balance sheets consist of: |  |  |  |  |  |  |
Non-current assets | $— |  |  | $— |  |  | $4 |  |  | $4 |
Current liabilities | — |  |  | — |  |  | (6) |  |  | (6) |
Pension and other benefit obligations | (62) |  |  | (75) |  |  | (41) |  |  | (45) |
Net amounts recognized at December 31 | ($62) |  |  | ($75) |  |  | ($43) |  |  | ($47) |
Amounts recognized in Regulatory Assets consist of: |  |  |  |  |  |  |
Net actuarial loss | $135 |  |  | $148 |  |  | $— |  |  | $3 |
Accumulated Benefit Obligations | Accumulated benefit obligations, aggregate amounts applicable to defined benefit pension and OPEB plans with accumulated benefit obligations in excess of plan assets, as well as defined benefit pension plans with projected benefit obligations in excess of plan assets as of the December 31 measurement date are as follows (in millions):
| Defined Benefit Pension Plans |  | OPEB Plans
Alliant Energy | 2024 |  | 2023 |  | 2024 |  | 2023
Accumulated benefit obligations | $824 |  |  | $857 |  |  | $148 |  |  | $160 |
Plans with accumulated benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Accumulated benefit obligations | 824 |  |  | 857 |  |  | 148 |  |  | 160 |
Fair value of plan assets | 715 |  |  | 732 |  |  | 80 |  |  | 83 |
Plans with projected benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Projected benefit obligations | 841 |  |  | 876 |  |  | N/A |  | N/A
Fair value of plan assets | 715 |  |  | 732 |  |  | N/A |  | N/A
| Defined Benefit Pension Plans |  | OPEB Plans
IPL | 2024 |  | 2023 |  | 2024 |  | 2023
Accumulated benefit obligations | $362 |  |  | $377 |  |  | $59 |  |  | $65 |
Plans with accumulated benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Accumulated benefit obligations | 362 |  |  | 377 |  |  | N/A |  | 65 |
Fair value of plan assets | 340 |  |  | 352 |  |  | N/A |  | 61 |
Plans with projected benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Projected benefit obligations | 372 |  |  | 387 |  |  | N/A |  | N/A
Fair value of plan assets | 340 |  |  | 352 |  |  | N/A |  | N/A
| Defined Benefit Pension Plans |  | OPEB Plans
WPL | 2024 |  | 2023 |  | 2024 |  | 2023
Accumulated benefit obligations | $358 |  |  | $373 |  |  | $56 |  |  | $61 |
Plans with accumulated benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Accumulated benefit obligations | 358 |  |  | 373 |  |  | 56 |  |  | 61 |
Fair value of plan assets | 303 |  |  | 306 |  |  | 13 |  |  | 14 |
Plans with projected benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Projected benefit obligations | 365 |  |  | 381 |  |  | N/A |  | N/A
Fair value of plan assets | 303 |  |  | 306 |  |  | N/A |  | N/A
Regulatory Assets | In addition to the amounts recognized in regulatory assets in the above tables for IPL and WPL, regulatory assets were recognized for amounts associated with Corporate Services employees participating in other Alliant Energy sponsored benefit plans that were allocated to IPL and WPL at December 31 as follows (in millions):
| IPL |  | WPL
| 2024 |  | 2023 |  | 2024 |  | 2023
Regulatory assets | $25 |  | $28 |  | $22 |  | $24
Estimated Future Employer Contributions | Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2025 is as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
Defined benefit pension plans (a) | $20 |  | $1 |  | $14
OPEB plans | 7 |  | 1 |  | 6
(a)Alliant Energy sponsors several non-qualified defined benefit pension plans that cover certain current and former key employees of IPL and WPL. Alliant Energy allocates pension costs to IPL and WPL for these plans. In addition, IPL and WPL amounts reflect funding for their non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans.
Expected Benefit Payments | Expected benefit payments for the qualified and non-qualified defined benefit plans, which reflect expected future service, as appropriate, are as follows (in millions):
Alliant Energy | 2025 |  | 2026 |  | 2027 |  | 2028 |  | 2029 |  | 2030 - 2034
Defined benefit pension benefits | $79 |  |  | $75 |  |  | $74 |  |  | $74 |  |  | $74 |  |  | $329
OPEB | 16 |  |  | 16 |  |  | 15 |  |  | 15 |  |  | 14 |  |  | 62
| $95 |  |  | $91 |  |  | $89 |  |  | $89 |  |  | $88 |  |  | $391
IPL | 2025 |  | 2026 |  | 2027 |  | 2028 |  | 2029 |  | 2030 - 2034
Defined benefit pension benefits | $36 |  |  | $34 |  |  | $33 |  |  | $33 |  |  | $32 |  |  | $148
OPEB | 7 |  |  | 6 |  |  | 6 |  |  | 6 |  |  | 6 |  |  | 24
| $43 |  |  | $40 |  |  | $39 |  |  | $39 |  |  | $38 |  |  | $172
WPL | 2025 |  | 2026 |  | 2027 |  | 2028 |  | 2029 |  | 2030 - 2034
Defined benefit pension benefits | $33 |  |  | $31 |  |  | $31 |  |  | $31 |  |  | $31 |  |  | $144
OPEB | 7 |  |  | 6 |  |  | 6 |  |  | 5 |  |  | 5 |  |  | 23
| $40 |  |  | $37 |  |  | $37 |  |  | $36 |  |  | $36 |  |  | $167
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 was as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022
Compensation expense | $12 |  | $12 |  | $13 |  | $6 |  | $6 |  | $7 |  | $5 |  | $5 |  | $5
Income tax benefits | 3 |  | 3 |  | 3 |  | 2 |  | 2 |  | 2 |  | 1 |  | 1 |  | 1
WPL [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Assumptions Used To Measure Benefit Plans | The weighted-average assumptions for defined benefit pension and OPEB plans at the measurement date of December 31 were as follows:
| Defined Benefit Pension Plans |  | OPEB Plans
Alliant Energy | 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022
Discount rate for benefit obligations | 5.65% |  | 5.36% |  | 5.54% |  | 5.62% |  | 5.40% |  | 5.53%
Discount rate for net periodic cost | 5.36% |  | 5.54% |  | 2.91% |  | 5.40% |  | 5.53% |  | 2.81%
Expected rate of return on plan assets | 7.73% |  | 7.80% |  | 7.80% |  | 6.22% |  | 6.50% |  | 6.40%
Interest crediting rate for Alliant Energy Cash Balance Pension Plan | 6.24% |  | 10.75% |  | 9.22% |  | N/A |  | N/A |  | N/A
Rate of compensation increase | 3.50% | - | 4.50% |  | 3.30% | - | 4.50% |  | 3.30% | - | 4.50% |  | N/A |  | N/A |  | N/A
| Qualified Defined Benefit Pension Plan |  | OPEB Plans
IPL | 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022
Discount rate for benefit obligations | 5.66% |  | 5.35% |  | 5.55% |  | 5.61% |  | 5.40% |  | 5.53%
Discount rate for net periodic cost | 5.35% |  | 5.55% |  | 2.94% |  | 5.40% |  | 5.53% |  | 2.80%
Expected rate of return on plan assets | 7.60% |  | 7.80% |  | 7.80% |  | 6.60% |  | 6.90% |  | 6.50%
Rate of compensation increase | 3.75% |  | 3.30% |  | 3.30% |  | N/A |  | N/A |  | N/A
| Qualified Defined Benefit Pension Plan |  | OPEB Plans
WPL | 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022
Discount rate for benefit obligations | 5.66% |  | 5.35% |  | 5.54% |  | 5.61% |  | 5.40% |  | 5.53%
Discount rate for net periodic cost | 5.35% |  | 5.54% |  | 2.94% |  | 5.40% |  | 5.53% |  | 2.79%
Expected rate of return on plan assets | 7.80% |  | 7.80% |  | 7.80% |  | 5.61% |  | 5.65% |  | 5.49%
Rate of compensation increase | 3.50% |  | 3.30% |  | 3.30% |  | N/A |  | N/A |  | N/A
Net Periodic Benefit Costs | The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans are included below (in millions). The service cost component of net periodic benefit costs is included in “Other operation and maintenance” expenses in the income statements and all other components of net periodic benefit costs are included in “Other (income) and deductions” in the income statements or regulatory assets on the balance sheets.
Alliant Energy | Defined Benefit Pension Plans |  | OPEB Plans
2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022
Service cost | $5 |  |  | $5 |  |  | $9 |  |  | $2 |  |  | $2 |  |  | $3 |
Interest cost | 45 |  |  | 47 |  |  | 36 |  |  | 8 |  |  | 9 |  |  | 6 |
Expected return on plan assets (a) | (55) |  |  | (53) |  |  | (69) |  |  | (5) |  |  | (5) |  |  | (5) |
Amortization of prior service credit (b) | (1) |  |  | (1) |  |  | (1) |  |  | — |  |  | — |  |  | — |
Amortization of actuarial loss (c) | 24 |  |  | 28 |  |  | 32 |  |  | — |  |  | 1 |  |  | 2 |
Settlement losses (d) | — |  |  | — |  |  | 26 |  |  | — |  |  | — |  |  | — |
| $18 |  |  | $26 |  |  | $33 |  |  | $5 |  |  | $7 |  |  | $6 |
IPL | Defined Benefit Pension Plans |  | OPEB Plans
2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022
Service cost | $3 |  |  | $3 |  |  | $6 |  |  | $1 |  |  | $1 |  |  | $1 |
Interest cost | 20 |  |  | 21 |  |  | 16 |  |  | 3 |  |  | 3 |  |  | 2 |
Expected return on plan assets (a) | (26) |  |  | (26) |  |  | (31) |  |  | (4) |  |  | (3) |  |  | (4) |
Amortization of actuarial loss (c) | 9 |  |  | 11 |  |  | 13 |  |  | — |  |  | 1 |  |  | 1 |
Settlement losses (d) | — |  |  | — |  |  | 13 |  |  | — |  |  | — |  |  | — |
| $6 |  |  | $9 |  |  | $17 |  |  | $— |  |  | $2 |  |  | $— |
WPL | Defined Benefit Pension Plans |  | OPEB Plans
2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022
Service cost | $2 |  |  | $2 |  |  | $3 |  |  | $1 |  |  | $1 |  |  | $1 |
Interest cost | 20 |  |  | 20 |  |  | 16 |  |  | 3 |  |  | 3 |  |  | 2 |
Expected return on plan assets (a) | (23) |  |  | (22) |  |  | (31) |  |  | (1) |  |  | (1) |  |  | (1) |
Amortization of actuarial loss (c) | 11 |  |  | 13 |  |  | 15 |  |  | — |  |  | 1 |  |  | 2 |
Settlement losses (d) | — |  |  | — |  |  | 13 |  |  | — |  |  | — |  |  | — |
| $10 |  |  | $13 |  |  | $16 |  |  | $3 |  |  | $4 |  |  | $4 |
(a)The expected return on plan assets is based on the expected rate of return on plan assets and the fair value approach to the market-related value of plan assets. (b)Unrecognized prior service credits for the OPEB plans are amortized over the average future service period to full eligibility of the participants of each plan. (c)Unrecognized net actuarial gains or losses in excess of 10% of the greater of the plans’ benefit obligations or assets are amortized over the average future service lives of plan participants, except for the Alliant Energy Cash Balance Pension Plan where gains or losses outside the 10% threshold are amortized over the time period the participants are expected to receive benefits. (d)Settlement losses related to payments made to retired executives of Alliant Energy and lump sum payments related to IPL’s and WPL’s qualified defined benefit pension plans. In 2022, the majority of Alliant Energy’s, IPL’s, and WPL’s pension settlement losses were recognized as regulatory assets in accordance with regulatory treatment, and $7 million was included in “Other (income) and deductions” in Alliant Energy’s and IPL’s income statements related to IPL’s qualified defined benefit pension plan.
Funded Status Of Benefit Plans | A reconciliation of the funded status of qualified and non-qualified defined benefit pension and OPEB plans to the amounts recognized on the balance sheets at December 31 was as follows (in millions):
| Defined Benefit Pension Plans |  | OPEB Plans
Alliant Energy | 2024 |  | 2023 |  | 2024 |  | 2023
Change in benefit obligation: |  |  |  |  |  |  |
Net benefit obligation at January 1 | $876 |  |  | $875 |  |  | $160 |  |  | $168 |
Service cost | 5 |  |  | 5 |  |  | 2 |  |  | 2 |
Interest cost | 45 |  |  | 47 |  |  | 8 |  |  | 9 |
Plan participants’ contributions | — |  |  | — |  |  | 3 |  |  | 4 |
Actuarial (gain) loss | (19) |  |  | 23 |  |  | (7) |  |  | (3) |
Gross benefits paid | (66) |  |  | (74) |  |  | (18) |  |  | (20) |
Net benefit obligation at December 31 | 841 |  |  | 876 |  |  | 148 |  |  | 160 |
Change in plan assets: |  |  |  |  |  |  |
Fair value of plan assets at January 1 | 732 |  |  | 706 |  |  | 83 |  |  | 83 |
Actual return on plan assets | 38 |  |  | 86 |  |  | 5 |  |  | 8 |
Employer contributions | 11 |  |  | 14 |  |  | 7 |  |  | 8 |
Plan participants’ contributions | — |  |  | — |  |  | 3 |  |  | 4 |
Gross benefits paid | (66) |  |  | (74) |  |  | (18) |  |  | (20) |
Fair value of plan assets at December 31 | 715 |  |  | 732 |  |  | 80 |  |  | 83 |
Under funded status at December 31 | ($126) |  |  | ($144) |  |  | ($68) |  |  | ($77) |
| Defined Benefit Pension Plans |  | OPEB Plans
Alliant Energy | 2024 |  | 2023 |  | 2024 |  | 2023
Amounts recognized on the balance sheets consist of: |  |  |  |  |  |  |
Non-current assets | $— |  |  | $— |  |  | $17 |  |  | $14 |
Current liabilities | (3) |  |  | (2) |  |  | (7) |  |  | (8) |
Pension and other benefit obligations | (123) |  |  | (142) |  |  | (78) |  |  | (83) |
Net amounts recognized at December 31 | ($126) |  |  | ($144) |  |  | ($68) |  |  | ($77) |
Amounts recognized in Regulatory Assets consist of: |  |  |  |  |  |  |
Net actuarial loss | $312 |  |  | $337 |  |  | $4 |  |  | $11 |
Prior service credit | (2) |  |  | (2) |  |  | — |  |  | — |
| $310 |  |  | $335 |  |  | $4 |  |  | $11 |
| Defined Benefit Pension Plans |  | OPEB Plans
IPL | 2024 |  | 2023 |  | 2024 |  | 2023
Change in benefit obligation: |  |  |  |  |  |  |
Net benefit obligation at January 1 | $387 |  |  | $389 |  |  | $65 |  |  | $68 |
Service cost | 3 |  |  | 3 |  |  | 1 |  |  | 1 |
Interest cost | 20 |  |  | 21 |  |  | 3 |  |  | 3 |
Plan participants’ contributions | — |  |  | — |  |  | 1 |  |  | 2 |
Actuarial (gain) loss | (8) |  |  | 9 |  |  | (3) |  |  | (1) |
Gross benefits paid | (30) |  |  | (35) |  |  | (8) |  |  | (8) |
Net benefit obligation at December 31 | 372 |  |  | 387 |  |  | 59 |  |  | 65 |
Change in plan assets: |  |  |  |  |  |  |
Fair value of plan assets at January 1 | 352 |  |  | 344 |  |  | 61 |  |  | 58 |
Actual return on plan assets | 18 |  |  | 42 |  |  | 4 |  |  | 7 |
Employer contributions | — |  |  | 1 |  |  | 1 |  |  | 2 |
Plan participants’ contributions | — |  |  | — |  |  | 1 |  |  | 2 |
Gross benefits paid | (30) |  |  | (35) |  |  | (8) |  |  | (8) |
Fair value of plan assets at December 31 | 340 |  |  | 352 |  |  | 59 |  |  | 61 |
Under funded status at December 31 | ($32) |  |  | ($35) |  |  | $— |  |  | ($4) |
| Defined Benefit Pension Plans |  | OPEB Plans
IPL | 2024 |  | 2023 |  | 2024 |  | 2023
Amounts recognized on the balance sheets consist of: |  |  |  |  |  |  |
Non-current assets | $— |  |  | $— |  |  | $13 |  |  | $10 |
Current liabilities | (1) |  |  | — |  |  | (1) |  |  | (1) |
Pension and other benefit obligations | (31) |  |  | (35) |  |  | (12) |  |  | (13) |
Net amounts recognized at December 31 | ($32) |  |  | ($35) |  |  | $— |  |  | ($4) |
Amounts recognized in Regulatory Assets consist of: |  |  |  |  |  |  |
Net actuarial loss | $126 |  |  | $135 |  |  | $7 |  |  | $9 |
Prior service credit | (1) |  |  | (1) |  |  | — |  |  | — |
| $125 |  |  | $134 |  |  | $7 |  |  | $9 |
| Defined Benefit Pension Plans |  | OPEB Plans
WPL | 2024 |  | 2023 |  | 2024 |  | 2023
Change in benefit obligation: |  |  |  |  |  |  |
Net benefit obligation at January 1 | $381 |  |  | $381 |  |  | $61 |  |  | $65 |
Service cost | 2 |  |  | 2 |  |  | 1 |  |  | 1 |
Interest cost | 20 |  |  | 20 |  |  | 3 |  |  | 3 |
Plan participants’ contributions | — |  |  | — |  |  | 1 |  |  | 2 |
Actuarial (gain) loss | (8) |  |  | 10 |  |  | (3) |  |  | (2) |
Gross benefits paid | (30) |  |  | (32) |  |  | (7) |  |  | (8) |
Net benefit obligation at December 31 | 365 |  |  | 381 |  |  | 56 |  |  | 61 |
Change in plan assets: |  |  |  |  |  |  |
Fair value of plan assets at January 1 | 306 |  |  | 291 |  |  | 14 |  |  | 14 |
Actual return on plan assets | 17 |  |  | 35 |  |  | — |  |  | 1 |
Employer contributions | 10 |  |  | 12 |  |  | 5 |  |  | 5 |
Plan participants’ contributions | — |  |  | — |  |  | 1 |  |  | 2 |
Gross benefits paid | (30) |  |  | (32) |  |  | (7) |  |  | (8) |
Fair value of plan assets at December 31 | 303 |  |  | 306 |  |  | 13 |  |  | 14 |
Under funded status at December 31 | ($62) |  |  | ($75) |  |  | ($43) |  |  | ($47) |
| Defined Benefit Pension Plans |  | OPEB Plans
WPL | 2024 |  | 2023 |  | 2024 |  | 2023
Amounts recognized on the balance sheets consist of: |  |  |  |  |  |  |
Non-current assets | $— |  |  | $— |  |  | $4 |  |  | $4 |
Current liabilities | — |  |  | — |  |  | (6) |  |  | (6) |
Pension and other benefit obligations | (62) |  |  | (75) |  |  | (41) |  |  | (45) |
Net amounts recognized at December 31 | ($62) |  |  | ($75) |  |  | ($43) |  |  | ($47) |
Amounts recognized in Regulatory Assets consist of: |  |  |  |  |  |  |
Net actuarial loss | $135 |  |  | $148 |  |  | $— |  |  | $3 |
Accumulated Benefit Obligations | Accumulated benefit obligations, aggregate amounts applicable to defined benefit pension and OPEB plans with accumulated benefit obligations in excess of plan assets, as well as defined benefit pension plans with projected benefit obligations in excess of plan assets as of the December 31 measurement date are as follows (in millions):
| Defined Benefit Pension Plans |  | OPEB Plans
Alliant Energy | 2024 |  | 2023 |  | 2024 |  | 2023
Accumulated benefit obligations | $824 |  |  | $857 |  |  | $148 |  |  | $160 |
Plans with accumulated benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Accumulated benefit obligations | 824 |  |  | 857 |  |  | 148 |  |  | 160 |
Fair value of plan assets | 715 |  |  | 732 |  |  | 80 |  |  | 83 |
Plans with projected benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Projected benefit obligations | 841 |  |  | 876 |  |  | N/A |  | N/A
Fair value of plan assets | 715 |  |  | 732 |  |  | N/A |  | N/A
| Defined Benefit Pension Plans |  | OPEB Plans
IPL | 2024 |  | 2023 |  | 2024 |  | 2023
Accumulated benefit obligations | $362 |  |  | $377 |  |  | $59 |  |  | $65 |
Plans with accumulated benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Accumulated benefit obligations | 362 |  |  | 377 |  |  | N/A |  | 65 |
Fair value of plan assets | 340 |  |  | 352 |  |  | N/A |  | 61 |
Plans with projected benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Projected benefit obligations | 372 |  |  | 387 |  |  | N/A |  | N/A
Fair value of plan assets | 340 |  |  | 352 |  |  | N/A |  | N/A
| Defined Benefit Pension Plans |  | OPEB Plans
WPL | 2024 |  | 2023 |  | 2024 |  | 2023
Accumulated benefit obligations | $358 |  |  | $373 |  |  | $56 |  |  | $61 |
Plans with accumulated benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Accumulated benefit obligations | 358 |  |  | 373 |  |  | 56 |  |  | 61 |
Fair value of plan assets | 303 |  |  | 306 |  |  | 13 |  |  | 14 |
Plans with projected benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Projected benefit obligations | 365 |  |  | 381 |  |  | N/A |  | N/A
Fair value of plan assets | 303 |  |  | 306 |  |  | N/A |  | N/A
Regulatory Assets | In addition to the amounts recognized in regulatory assets in the above tables for IPL and WPL, regulatory assets were recognized for amounts associated with Corporate Services employees participating in other Alliant Energy sponsored benefit plans that were allocated to IPL and WPL at December 31 as follows (in millions):
| IPL |  | WPL
| 2024 |  | 2023 |  | 2024 |  | 2023
Regulatory assets | $25 |  | $28 |  | $22 |  | $24
Estimated Future Employer Contributions | Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2025 is as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
Defined benefit pension plans (a) | $20 |  | $1 |  | $14
OPEB plans | 7 |  | 1 |  | 6
(a)Alliant Energy sponsors several non-qualified defined benefit pension plans that cover certain current and former key employees of IPL and WPL. Alliant Energy allocates pension costs to IPL and WPL for these plans. In addition, IPL and WPL amounts reflect funding for their non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans.
Expected Benefit Payments | Expected benefit payments for the qualified and non-qualified defined benefit plans, which reflect expected future service, as appropriate, are as follows (in millions):
Alliant Energy | 2025 |  | 2026 |  | 2027 |  | 2028 |  | 2029 |  | 2030 - 2034
Defined benefit pension benefits | $79 |  |  | $75 |  |  | $74 |  |  | $74 |  |  | $74 |  |  | $329
OPEB | 16 |  |  | 16 |  |  | 15 |  |  | 15 |  |  | 14 |  |  | 62
| $95 |  |  | $91 |  |  | $89 |  |  | $89 |  |  | $88 |  |  | $391
IPL | 2025 |  | 2026 |  | 2027 |  | 2028 |  | 2029 |  | 2030 - 2034
Defined benefit pension benefits | $36 |  |  | $34 |  |  | $33 |  |  | $33 |  |  | $32 |  |  | $148
OPEB | 7 |  |  | 6 |  |  | 6 |  |  | 6 |  |  | 6 |  |  | 24
| $43 |  |  | $40 |  |  | $39 |  |  | $39 |  |  | $38 |  |  | $172
WPL | 2025 |  | 2026 |  | 2027 |  | 2028 |  | 2029 |  | 2030 - 2034
Defined benefit pension benefits | $33 |  |  | $31 |  |  | $31 |  |  | $31 |  |  | $31 |  |  | $144
OPEB | 7 |  |  | 6 |  |  | 6 |  |  | 5 |  |  | 5 |  |  | 23
| $40 |  |  | $37 |  |  | $37 |  |  | $36 |  |  | $36 |  |  | $167
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 was as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022
Compensation expense | $12 |  | $12 |  | $13 |  | $6 |  | $6 |  | $7 |  | $5 |  | $5 |  | $5
Income tax benefits | 3 |  | 3 |  | 3 |  | 2 |  | 2 |  | 2 |  | 1 |  | 1 |  | 1
Pension Plans, Defined Benefit [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Fair Value Of Plan Assets By Asset Category, Fair Value Hierarchy Level and Allocations | At December 31, 2024, the current target ranges and actual allocations for the defined benefit pension plan assets were as follows:
| Target Range |  | Actual
| Allocation |  | Allocation
Public equity securities | 32% | - | 49% |  | 44%
Liquid alternative securities | 0% | - | 12% |  | 6%
Return-seeking fixed income securities | 4% | - | 18% |  | 8%
Liability-hedging fixed income securities (including cash and equivalents) | 34% | - | 53% |  | 42%
At December 31, the fair values of qualified and non-qualified defined benefit pension plan assets were as follows (in millions):
| 2024 |  | 2023
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
Alliant Energy | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents | $49 |  |  | $— |  |  | $49 |  |  | $— |  |  | $19 |  |  | $— |  |  | $19 |  |  | $— |
Equity securities | — |  |  | — |  |  | — |  |  | — |  |  | 223 |  |  | 223 |  |  | — |  |  | — |
Global asset securities | — |  |  | — |  |  | — |  |  | — |  |  | 39 |  |  | 39 |  |  | — |  |  | — |
Fixed income securities | — |  |  | — |  |  | — |  |  | — |  |  | 143 |  |  | 31 |  |  | 112 |  |  | — |
Total assets in fair value hierarchy | 49 |  |  | $— |  |  | $49 |  |  | $— |  |  | 424 |  |  | $293 |  |  | $131 |  |  | $— |
Assets measured at net asset value | 667 |  |  |  |  |  |  |  |  | 306 |  |  |  |  |  |  |
Accrued investment income | — |  |  |  |  |  |  |  |  | 2 |  |  |  |  |  |  |
Due to brokers, net (pending trades with brokers) | (1) |  |  |  |  |  |  |  |  | — |  |  |  |  |  |  |
Total pension plan assets | $715 |  |  |  |  |  |  |  |  | $732 |  |  |  |  |  |  |
| 2024 |  | 2023
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
IPL | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents | $21 |  |  | $— |  |  | $21 |  |  | $— |  |  | $9 |  |  | $— |  |  | $9 |  |  | $— |
Equity securities | — |  |  | — |  |  | — |  |  | — |  |  | 107 |  |  | 107 |  |  | — |  |  | — |
Global asset securities | — |  |  | — |  |  | — |  |  | — |  |  | 19 |  |  | 19 |  |  | — |  |  | — |
Fixed income securities | — |  |  | — |  |  | — |  |  | — |  |  | 69 |  |  | 15 |  |  | 54 |  |  | — |
Total assets in fair value hierarchy | 21 |  |  | $— |  |  | $21 |  |  | $— |  |  | 204 |  |  | $141 |  |  | $63 |  |  | $— |
Assets measured at net asset value | 319 |  |  |  |  |  |  |  |  | 147 |  |  |  |  |  |  |
Accrued investment income | — |  |  |  |  |  |  |  |  | 1 |  |  |  |  |  |  |
Total pension plan assets | $340 |  |  |  |  |  |  |  |  | $352 |  |  |  |  |  |  |
| 2024 |  | 2023
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
WPL | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents | $22 |  |  | $— |  |  | $22 |  |  | $— |  |  | $8 |  |  | $— |  |  | $8 |  |  | $— |
Equity securities | — |  |  | — |  |  | — |  |  | — |  |  | 93 |  |  | 93 |  |  | — |  |  | — |
Global asset securities | — |  |  | — |  |  | — |  |  | — |  |  | 16 |  |  | 16 |  |  | — |  |  | — |
Fixed income securities | — |  |  | — |  |  | — |  |  | — |  |  | 60 |  |  | 13 |  |  | 47 |  |  | — |
Total assets in fair value hierarchy | 22 |  |  | $— |  |  | $22 |  |  | $— |  |  | 177 |  |  | $122 |  |  | $55 |  |  | $— |
Assets measured at net asset value | 281 |  |  |  |  |  |  |  |  | 128 |  |  |  |  |  |  |
Accrued investment income | — |  |  |  |  |  |  |  |  | 1 |  |  |  |  |  |  |
Total pension plan assets | $303 |  |  |  |  |  |  |  |  | $306 |  |  |  |  |  |  |
Pension Plans, Defined Benefit [Member] | IPL [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Fair Value Of Plan Assets By Asset Category, Fair Value Hierarchy Level and Allocations | At December 31, 2024, the current target ranges and actual allocations for the defined benefit pension plan assets were as follows:
| Target Range |  | Actual
| Allocation |  | Allocation
Public equity securities | 32% | - | 49% |  | 44%
Liquid alternative securities | 0% | - | 12% |  | 6%
Return-seeking fixed income securities | 4% | - | 18% |  | 8%
Liability-hedging fixed income securities (including cash and equivalents) | 34% | - | 53% |  | 42%
At December 31, the fair values of qualified and non-qualified defined benefit pension plan assets were as follows (in millions):
| 2024 |  | 2023
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
Alliant Energy | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents | $49 |  |  | $— |  |  | $49 |  |  | $— |  |  | $19 |  |  | $— |  |  | $19 |  |  | $— |
Equity securities | — |  |  | — |  |  | — |  |  | — |  |  | 223 |  |  | 223 |  |  | — |  |  | — |
Global asset securities | — |  |  | — |  |  | — |  |  | — |  |  | 39 |  |  | 39 |  |  | — |  |  | — |
Fixed income securities | — |  |  | — |  |  | — |  |  | — |  |  | 143 |  |  | 31 |  |  | 112 |  |  | — |
Total assets in fair value hierarchy | 49 |  |  | $— |  |  | $49 |  |  | $— |  |  | 424 |  |  | $293 |  |  | $131 |  |  | $— |
Assets measured at net asset value | 667 |  |  |  |  |  |  |  |  | 306 |  |  |  |  |  |  |
Accrued investment income | — |  |  |  |  |  |  |  |  | 2 |  |  |  |  |  |  |
Due to brokers, net (pending trades with brokers) | (1) |  |  |  |  |  |  |  |  | — |  |  |  |  |  |  |
Total pension plan assets | $715 |  |  |  |  |  |  |  |  | $732 |  |  |  |  |  |  |
| 2024 |  | 2023
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
IPL | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents | $21 |  |  | $— |  |  | $21 |  |  | $— |  |  | $9 |  |  | $— |  |  | $9 |  |  | $— |
Equity securities | — |  |  | — |  |  | — |  |  | — |  |  | 107 |  |  | 107 |  |  | — |  |  | — |
Global asset securities | — |  |  | — |  |  | — |  |  | — |  |  | 19 |  |  | 19 |  |  | — |  |  | — |
Fixed income securities | — |  |  | — |  |  | — |  |  | — |  |  | 69 |  |  | 15 |  |  | 54 |  |  | — |
Total assets in fair value hierarchy | 21 |  |  | $— |  |  | $21 |  |  | $— |  |  | 204 |  |  | $141 |  |  | $63 |  |  | $— |
Assets measured at net asset value | 319 |  |  |  |  |  |  |  |  | 147 |  |  |  |  |  |  |
Accrued investment income | — |  |  |  |  |  |  |  |  | 1 |  |  |  |  |  |  |
Total pension plan assets | $340 |  |  |  |  |  |  |  |  | $352 |  |  |  |  |  |  |
| 2024 |  | 2023
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
WPL | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents | $22 |  |  | $— |  |  | $22 |  |  | $— |  |  | $8 |  |  | $— |  |  | $8 |  |  | $— |
Equity securities | — |  |  | — |  |  | — |  |  | — |  |  | 93 |  |  | 93 |  |  | — |  |  | — |
Global asset securities | — |  |  | — |  |  | — |  |  | — |  |  | 16 |  |  | 16 |  |  | — |  |  | — |
Fixed income securities | — |  |  | — |  |  | — |  |  | — |  |  | 60 |  |  | 13 |  |  | 47 |  |  | — |
Total assets in fair value hierarchy | 22 |  |  | $— |  |  | $22 |  |  | $— |  |  | 177 |  |  | $122 |  |  | $55 |  |  | $— |
Assets measured at net asset value | 281 |  |  |  |  |  |  |  |  | 128 |  |  |  |  |  |  |
Accrued investment income | — |  |  |  |  |  |  |  |  | 1 |  |  |  |  |  |  |
Total pension plan assets | $303 |  |  |  |  |  |  |  |  | $306 |  |  |  |  |  |  |
Pension Plans, Defined Benefit [Member] | WPL [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Fair Value Of Plan Assets By Asset Category, Fair Value Hierarchy Level and Allocations | At December 31, 2024, the current target ranges and actual allocations for the defined benefit pension plan assets were as follows:
| Target Range |  | Actual
| Allocation |  | Allocation
Public equity securities | 32% | - | 49% |  | 44%
Liquid alternative securities | 0% | - | 12% |  | 6%
Return-seeking fixed income securities | 4% | - | 18% |  | 8%
Liability-hedging fixed income securities (including cash and equivalents) | 34% | - | 53% |  | 42%
At December 31, the fair values of qualified and non-qualified defined benefit pension plan assets were as follows (in millions):
| 2024 |  | 2023
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
Alliant Energy | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents | $49 |  |  | $— |  |  | $49 |  |  | $— |  |  | $19 |  |  | $— |  |  | $19 |  |  | $— |
Equity securities | — |  |  | — |  |  | — |  |  | — |  |  | 223 |  |  | 223 |  |  | — |  |  | — |
Global asset securities | — |  |  | — |  |  | — |  |  | — |  |  | 39 |  |  | 39 |  |  | — |  |  | — |
Fixed income securities | — |  |  | — |  |  | — |  |  | — |  |  | 143 |  |  | 31 |  |  | 112 |  |  | — |
Total assets in fair value hierarchy | 49 |  |  | $— |  |  | $49 |  |  | $— |  |  | 424 |  |  | $293 |  |  | $131 |  |  | $— |
Assets measured at net asset value | 667 |  |  |  |  |  |  |  |  | 306 |  |  |  |  |  |  |
Accrued investment income | — |  |  |  |  |  |  |  |  | 2 |  |  |  |  |  |  |
Due to brokers, net (pending trades with brokers) | (1) |  |  |  |  |  |  |  |  | — |  |  |  |  |  |  |
Total pension plan assets | $715 |  |  |  |  |  |  |  |  | $732 |  |  |  |  |  |  |
| 2024 |  | 2023
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
IPL | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents | $21 |  |  | $— |  |  | $21 |  |  | $— |  |  | $9 |  |  | $— |  |  | $9 |  |  | $— |
Equity securities | — |  |  | — |  |  | — |  |  | — |  |  | 107 |  |  | 107 |  |  | — |  |  | — |
Global asset securities | — |  |  | — |  |  | — |  |  | — |  |  | 19 |  |  | 19 |  |  | — |  |  | — |
Fixed income securities | — |  |  | — |  |  | — |  |  | — |  |  | 69 |  |  | 15 |  |  | 54 |  |  | — |
Total assets in fair value hierarchy | 21 |  |  | $— |  |  | $21 |  |  | $— |  |  | 204 |  |  | $141 |  |  | $63 |  |  | $— |
Assets measured at net asset value | 319 |  |  |  |  |  |  |  |  | 147 |  |  |  |  |  |  |
Accrued investment income | — |  |  |  |  |  |  |  |  | 1 |  |  |  |  |  |  |
Total pension plan assets | $340 |  |  |  |  |  |  |  |  | $352 |  |  |  |  |  |  |
| 2024 |  | 2023
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
WPL | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents | $22 |  |  | $— |  |  | $22 |  |  | $— |  |  | $8 |  |  | $— |  |  | $8 |  |  | $— |
Equity securities | — |  |  | — |  |  | — |  |  | — |  |  | 93 |  |  | 93 |  |  | — |  |  | — |
Global asset securities | — |  |  | — |  |  | — |  |  | — |  |  | 16 |  |  | 16 |  |  | — |  |  | — |
Fixed income securities | — |  |  | — |  |  | — |  |  | — |  |  | 60 |  |  | 13 |  |  | 47 |  |  | — |
Total assets in fair value hierarchy | 22 |  |  | $— |  |  | $22 |  |  | $— |  |  | 177 |  |  | $122 |  |  | $55 |  |  | $— |
Assets measured at net asset value | 281 |  |  |  |  |  |  |  |  | 128 |  |  |  |  |  |  |
Accrued investment income | — |  |  |  |  |  |  |  |  | 1 |  |  |  |  |  |  |
Total pension plan assets | $303 |  |  |  |  |  |  |  |  | $306 |  |  |  |  |  |  |
Other Postretirement Benefits Plans [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Fair Value Of Plan Assets By Asset Category, Fair Value Hierarchy Level and Allocations | At December 31, 2024, the current target ranges and actual allocations for assets with a long-term investment horizon were as follows:
| Target Range |  | Actual
| Allocation |  | Allocation
Cash and equivalents | 0% | - | 5% |  | 1%
Public equity securities | 0% | - | 40% |  | 27%
Fixed income securities | 40% | - | 100% |  | 72%
At December 31, the fair values of OPEB plan assets were as follows (in millions):
| 2024 |  | 2023
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
Alliant Energy | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents | $8 |  |  | $— |  |  | $8 |  |  | $— |  |  | $9 |  |  | $— |  |  | $9 |  |  | $— |
Equity securities | 20 |  |  | 20 |  |  | — |  |  | — |  |  | 8 |  |  | 8 |  |  | — |  |  | — |
Fixed income securities | 52 |  |  | 52 |  |  | — |  |  | — |  |  | 47 |  |  | 47 |  |  | — |  |  | — |
Total assets in fair value hierarchy | 80 |  |  | $72 |  |  | $8 |  |  | $— |  |  | 64 |  |  | $55 |  |  | $9 |  |  | $— |
Assets measured at net asset value | — |  |  |  |  |  |  |  |  | 19 |  |  |  |  |  |  |
Total OPEB plan assets | $80 |  |  |  |  |  |  |  |  | $83 |  |  |  |  |  |  |
| 2024 |  | 2023
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
IPL | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents | $1 |  |  | $— |  |  | $1 |  |  | $— |  |  | $1 |  |  | $— |  |  | $1 |  |  | $— |
Equity securities | 18 |  |  | 18 |  |  | — |  |  | — |  |  | 6 |  |  | 6 |  |  | — |  |  | — |
Fixed income securities | 40 |  |  | 40 |  |  | — |  |  | — |  |  | 36 |  |  | 36 |  |  | — |  |  | — |
Total assets in fair value hierarchy | 59 |  |  | $58 |  |  | $1 |  |  | $— |  |  | 43 |  |  | $42 |  |  | $1 |  |  | $— |
Assets measured at net asset value | — |  |  |  |  |  |  |  |  | 18 |  |  |  |  |  |  |
Total OPEB plan assets | $59 |  |  |  |  |  |  |  |  | $61 |  |  |  |  |  |  |
| 2024 |  | 2023
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
WPL | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents | $— |  |  | $— |  |  | $— |  |  | $— |  |  | $1 |  |  | $— |  |  | $1 |  |  | $— |
Equity securities | 2 |  |  | 2 |  |  | — |  |  | — |  |  | 2 |  |  | 2 |  |  | — |  |  | — |
Fixed income securities | 11 |  |  | 11 |  |  | — |  |  | — |  |  | 11 |  |  | 11 |  |  | — |  |  | — |
Total OPEB plan assets | $13 |  |  | $13 |  |  | $— |  |  | $— |  |  | $14 |  |  | $13 |  |  | $1 |  |  | $— |
Other Postretirement Benefits Plans [Member] | IPL [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Fair Value Of Plan Assets By Asset Category, Fair Value Hierarchy Level and Allocations | At December 31, 2024, the current target ranges and actual allocations for assets with a long-term investment horizon were as follows:
| Target Range |  | Actual
| Allocation |  | Allocation
Cash and equivalents | 0% | - | 5% |  | 1%
Public equity securities | 0% | - | 40% |  | 27%
Fixed income securities | 40% | - | 100% |  | 72%
At December 31, the fair values of OPEB plan assets were as follows (in millions):
| 2024 |  | 2023
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
Alliant Energy | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents | $8 |  |  | $— |  |  | $8 |  |  | $— |  |  | $9 |  |  | $— |  |  | $9 |  |  | $— |
Equity securities | 20 |  |  | 20 |  |  | — |  |  | — |  |  | 8 |  |  | 8 |  |  | — |  |  | — |
Fixed income securities | 52 |  |  | 52 |  |  | — |  |  | — |  |  | 47 |  |  | 47 |  |  | — |  |  | — |
Total assets in fair value hierarchy | 80 |  |  | $72 |  |  | $8 |  |  | $— |  |  | 64 |  |  | $55 |  |  | $9 |  |  | $— |
Assets measured at net asset value | — |  |  |  |  |  |  |  |  | 19 |  |  |  |  |  |  |
Total OPEB plan assets | $80 |  |  |  |  |  |  |  |  | $83 |  |  |  |  |  |  |
| 2024 |  | 2023
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
IPL | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents | $1 |  |  | $— |  |  | $1 |  |  | $— |  |  | $1 |  |  | $— |  |  | $1 |  |  | $— |
Equity securities | 18 |  |  | 18 |  |  | — |  |  | — |  |  | 6 |  |  | 6 |  |  | — |  |  | — |
Fixed income securities | 40 |  |  | 40 |  |  | — |  |  | — |  |  | 36 |  |  | 36 |  |  | — |  |  | — |
Total assets in fair value hierarchy | 59 |  |  | $58 |  |  | $1 |  |  | $— |  |  | 43 |  |  | $42 |  |  | $1 |  |  | $— |
Assets measured at net asset value | — |  |  |  |  |  |  |  |  | 18 |  |  |  |  |  |  |
Total OPEB plan assets | $59 |  |  |  |  |  |  |  |  | $61 |  |  |  |  |  |  |
| 2024 |  | 2023
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
WPL | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents | $— |  |  | $— |  |  | $— |  |  | $— |  |  | $1 |  |  | $— |  |  | $1 |  |  | $— |
Equity securities | 2 |  |  | 2 |  |  | — |  |  | — |  |  | 2 |  |  | 2 |  |  | — |  |  | — |
Fixed income securities | 11 |  |  | 11 |  |  | — |  |  | — |  |  | 11 |  |  | 11 |  |  | — |  |  | — |
Total OPEB plan assets | $13 |  |  | $13 |  |  | $— |  |  | $— |  |  | $14 |  |  | $13 |  |  | $1 |  |  | $— |
Other Postretirement Benefits Plans [Member] | WPL [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Fair Value Of Plan Assets By Asset Category, Fair Value Hierarchy Level and Allocations | At December 31, 2024, the current target ranges and actual allocations for assets with a long-term investment horizon were as follows:
| Target Range |  | Actual
| Allocation |  | Allocation
Cash and equivalents | 0% | - | 5% |  | 1%
Public equity securities | 0% | - | 40% |  | 27%
Fixed income securities | 40% | - | 100% |  | 72%
At December 31, the fair values of OPEB plan assets were as follows (in millions):
| 2024 |  | 2023
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
Alliant Energy | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents | $8 |  |  | $— |  |  | $8 |  |  | $— |  |  | $9 |  |  | $— |  |  | $9 |  |  | $— |
Equity securities | 20 |  |  | 20 |  |  | — |  |  | — |  |  | 8 |  |  | 8 |  |  | — |  |  | — |
Fixed income securities | 52 |  |  | 52 |  |  | — |  |  | — |  |  | 47 |  |  | 47 |  |  | — |  |  | — |
Total assets in fair value hierarchy | 80 |  |  | $72 |  |  | $8 |  |  | $— |  |  | 64 |  |  | $55 |  |  | $9 |  |  | $— |
Assets measured at net asset value | — |  |  |  |  |  |  |  |  | 19 |  |  |  |  |  |  |
Total OPEB plan assets | $80 |  |  |  |  |  |  |  |  | $83 |  |  |  |  |  |  |
| 2024 |  | 2023
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
IPL | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents | $1 |  |  | $— |  |  | $1 |  |  | $— |  |  | $1 |  |  | $— |  |  | $1 |  |  | $— |
Equity securities | 18 |  |  | 18 |  |  | — |  |  | — |  |  | 6 |  |  | 6 |  |  | — |  |  | — |
Fixed income securities | 40 |  |  | 40 |  |  | — |  |  | — |  |  | 36 |  |  | 36 |  |  | — |  |  | — |
Total assets in fair value hierarchy | 59 |  |  | $58 |  |  | $1 |  |  | $— |  |  | 43 |  |  | $42 |  |  | $1 |  |  | $— |
Assets measured at net asset value | — |  |  |  |  |  |  |  |  | 18 |  |  |  |  |  |  |
Total OPEB plan assets | $59 |  |  |  |  |  |  |  |  | $61 |  |  |  |  |  |  |
| 2024 |  | 2023
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
WPL | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents | $— |  |  | $— |  |  | $— |  |  | $— |  |  | $1 |  |  | $— |  |  | $1 |  |  | $— |
Equity securities | 2 |  |  | 2 |  |  | — |  |  | — |  |  | 2 |  |  | 2 |  |  | — |  |  | — |
Fixed income securities | 11 |  |  | 11 |  |  | — |  |  | — |  |  | 11 |  |  | 11 |  |  | — |  |  | — |
Total OPEB plan assets | $13 |  |  | $13 |  |  | $— |  |  | $— |  |  | $14 |  |  | $13 |  |  | $1 |  |  | $— |
401(k) Savings Plan [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Employees Participate In Defined Contribution Retirement Plans | Costs related to the 401(k) savings plans, which are partially based on the participants’ contributions and include allocated costs associated with Corporate Services employees for IPL and WPL, were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022
401(k) costs | $31 |  |  | $30 |  |  | $28 |  |  | $14 |  |  | $14 |  |  | $13 |  |  | $15 |  |  | $14 |  |  | $13 |
401(k) Savings Plan [Member] | IPL [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Employees Participate In Defined Contribution Retirement Plans | Costs related to the 401(k) savings plans, which are partially based on the participants’ contributions and include allocated costs associated with Corporate Services employees for IPL and WPL, were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022
401(k) costs | $31 |  |  | $30 |  |  | $28 |  |  | $14 |  |  | $14 |  |  | $13 |  |  | $15 |  |  | $14 |  |  | $13 |
401(k) Savings Plan [Member] | WPL [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Employees Participate In Defined Contribution Retirement Plans | Costs related to the 401(k) savings plans, which are partially based on the participants’ contributions and include allocated costs associated with Corporate Services employees for IPL and WPL, were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022 |  | 2024 |  | 2023 |  | 2022
401(k) costs | $31 |  |  | $30 |  |  | $28 |  |  | $14 |  |  | $14 |  |  | $13 |  |  | $15 |  |  | $14 |  |  | $13 |
Performance Shares (TSR Metric) [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Schedule Of Equity-based Compensation Plans Activity | A summary of the performance shares activity, with amounts representing the target number of awards, was as follows:
| 2024 |  | 2023 |  | 2022
| Shares |  | Weighted Average Grant Date Fair Value |  | Shares |  | Weighted Average Grant Date Fair Value |  | Shares |  | Weighted Average Grant Date Fair Value
Nonvested awards, January 1 | 233,954 |  | $52.60 |  | 190,273 |  | $54.13 |  | 196,429 |  | $51.59
Granted | 127,874 |  | 46.04 |  | 108,712 |  | 55.68 |  | 74,106 |  | 54.45
Vested | (47,497) |  | 46.19 |  | (53,431) |  | 64.04 |  | (71,101) |  | 47.48
Forfeited | (24,932) |  | 46.16 |  | (11,600) |  | 53.88 |  | (9,161) |  | 53.99
Nonvested awards, December 31 | 289,399 |  | 51.31 |  | 233,954 |  | 52.60 |  | 190,273 |  | 54.13
Restricted Stock Units [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Schedule Of Equity-based Compensation Plans Activity | A summary of the restricted stock units activity was as follows:
| 2024 |  | 2023 |  | 2022
| Units |  | Weighted Average Grant Date Fair Value |  | Units |  | Weighted Average Grant Date Fair Value |  | Units |  | Weighted Average Grant Date Fair Value
Nonvested awards, January 1 | 234,259 |  | $52.58 |  | 198,275 |  | $54.53 |  | 217,819 |  | $50.54
Granted | 129,854 |  | 48.69 |  | 106,124 |  | 52.77 |  | 77,122 |  | 56.88
Vested | (71,441) |  | 48.65 |  | (55,345) |  | 59.40 |  | (82,770) |  | 46.08
Forfeited | (3,524) |  | 48.40 |  | (14,795) |  | 54.53 |  | (13,896) |  | 55.53
Nonvested awards, December 31 | 289,148 |  | 51.85 |  | 234,259 |  | 52.58 |  | 198,275 |  | 54.53
Performance Shares (Net Income and Workforce Composition Metrics) [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Schedule Of Equity-based Compensation Plans Activity | A summary of the performance shares activity, with amounts representing the target number of awards, was as follows:
| 2024 |  | 2023 |  | 2022
| Shares |  | Weighted Average Grant Date Fair Value |  | Shares |  | Weighted Average Grant Date Fair Value |  | Shares |  | Weighted Average Grant Date Fair Value
Nonvested awards, January 1 | 257,639 |  | $52.76 |  | 199,874 |  | $54.74 |  | 196,429 |  | $50.74
Granted | 146,143 |  | 48.55 |  | 124,217 |  | 52.71 |  | 84,670 |  | 57.01
Vested | (67,852) |  | 48.66 |  | (53,431) |  | 59.36 |  | (71,101) |  | 46.24
Forfeited | (5,230) |  | 48.40 |  | (13,021) |  | 55.47 |  | (10,124) |  | 55.92
Nonvested awards, December 31 | 330,700 |  | 51.81 |  | 257,639 |  | 52.76 |  | 199,874 |  | 54.74

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