XML 75 R41.htm IDEA: XBRL DOCUMENT
v3.24.0.1

Benefit Plans (Tables) | 12 Months Ended
--- | ---
Dec. 31, 2023
Defined Benefit Plan Disclosure [Line Items] |
Assumptions Used To Measure Benefit Plans | The 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 | 2023 |  | 2022 |  | 2021 |  | 2023 |  | 2022 |  | 2021
Discount rate for benefit obligations | 5.36% |  | 5.54% |  | 2.91% |  | 5.40% |  | 5.53% |  | 2.81%
Discount rate for net periodic cost | 5.54% |  | 2.91% |  | 2.57% |  | 5.53% |  | 2.81% |  | 2.31%
Expected rate of return on plan assets | 7.80% |  | 7.80% |  | 7.10% |  | 6.50% |  | 6.40% |  | 4.80%
Interest crediting rate for Alliant Energy Cash Balance Pension Plan | 10.75% |  | 9.22% |  | 4.18% |  | N/A |  | N/A |  | N/A
Rate of compensation increase | 3.30% | - | 4.50% |  | 3.30% | - | 4.50% |  | 3.30% | - | 4.50% |  | N/A |  | N/A |  | N/A
| Qualified Defined Benefit Pension Plan |  | OPEB Plans
IPL | 2023 |  | 2022 |  | 2021 |  | 2023 |  | 2022 |  | 2021
Discount rate for benefit obligations | 5.35% |  | 5.55% |  | 2.94% |  | 5.40% |  | 5.53% |  | 2.80%
Discount rate for net periodic cost | 5.55% |  | 2.94% |  | 2.61% |  | 5.53% |  | 2.80% |  | 2.28%
Expected rate of return on plan assets | 7.80% |  | 7.80% |  | 7.10% |  | 6.90% |  | 6.50% |  | 5.10%
Rate of compensation increase | 3.30% |  | 3.30% |  | 3.30% |  | N/A |  | N/A |  | N/A
| Qualified Defined Benefit Pension Plan |  | OPEB Plans
WPL | 2023 |  | 2022 |  | 2021 |  | 2023 |  | 2022 |  | 2021
Discount rate for benefit obligations | 5.35% |  | 5.54% |  | 2.94% |  | 5.40% |  | 5.53% |  | 2.79%
Discount rate for net periodic cost | 5.54% |  | 2.94% |  | 2.64% |  | 5.53% |  | 2.79% |  | 2.27%
Expected rate of return on plan assets | 7.80% |  | 7.80% |  | 7.10% |  | 5.65% |  | 5.49% |  | 4.02%
Rate of compensation increase | 3.30% |  | 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
2023 |  | 2022 |  | 2021 |  | 2023 |  | 2022 |  | 2021
Service cost | $5 |  |  | $9 |  |  | $11 |  |  | $2 |  |  | $3 |  |  | $4 |
Interest cost | 47 |  |  | 36 |  |  | 34 |  |  | 9 |  |  | 6 |  |  | 5 |
Expected return on plan assets (a) | (53) |  |  | (69) |  |  | (69) |  |  | (5) |  |  | (5) |  |  | (5) |
Amortization of prior service credit (b) | (1) |  |  | (1) |  |  | — |  |  | — |  |  | — |  |  | — |
Amortization of actuarial loss (c) | 28 |  |  | 32 |  |  | 39 |  |  | 1 |  |  | 2 |  |  | 5 |
Settlement losses (d) | — |  |  | 26 |  |  | — |  |  | — |  |  | — |  |  | — |
| $26 |  |  | $33 |  |  | $15 |  |  | $7 |  |  | $6 |  |  | $9 |
IPL | Defined Benefit Pension Plans |  | OPEB Plans
2023 |  | 2022 |  | 2021 |  | 2023 |  | 2022 |  | 2021
Service cost | $3 |  |  | $6 |  |  | $7 |  |  | $1 |  |  | $1 |  |  | $1 |
Interest cost | 21 |  |  | 16 |  |  | 16 |  |  | 3 |  |  | 2 |  |  | 2 |
Expected return on plan assets (a) | (26) |  |  | (31) |  |  | (32) |  |  | (3) |  |  | (4) |  |  | (3) |
Amortization of actuarial loss (c) | 11 |  |  | 13 |  |  | 17 |  |  | 1 |  |  | 1 |  |  | 2 |
Settlement losses (d) | — |  |  | 13 |  |  | — |  |  | — |  |  | — |  |  | — |
| $9 |  |  | $17 |  |  | $8 |  |  | $2 |  |  | $— |  |  | $2 |
WPL | Defined Benefit Pension Plans |  | OPEB Plans
2023 |  | 2022 |  | 2021 |  | 2023 |  | 2022 |  | 2021
Service cost | $2 |  |  | $3 |  |  | $4 |  |  | $1 |  |  | $1 |  |  | $1 |
Interest cost | 20 |  |  | 16 |  |  | 15 |  |  | 3 |  |  | 2 |  |  | 2 |
Expected return on plan assets (a) | (22) |  |  | (31) |  |  | (31) |  |  | (1) |  |  | (1) |  |  | — |
Amortization of actuarial loss (c) | 13 |  |  | 15 |  |  | 19 |  |  | 1 |  |  | 2 |  |  | 2 |
Settlement losses (d) | — |  |  | 13 |  |  | — |  |  | — |  |  | — |  |  | — |
| $13 |  |  | $16 |  |  | $7 |  |  | $4 |  |  | $4 |  |  | $5 |
(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 | 2023 |  | 2022 |  | 2023 |  | 2022
Change in benefit obligation: |  |  |  |  |  |  |
Net benefit obligation at January 1 | $875 |  |  | $1,251 |  |  | $168 |  |  | $210 |
Service cost | 5 |  |  | 9 |  |  | 2 |  |  | 3 |
Interest cost | 47 |  |  | 36 |  |  | 9 |  |  | 6 |
Plan participants’ contributions | — |  |  | — |  |  | 4 |  |  | 4 |
Actuarial (gain) loss | 23 |  |  | (269) |  |  | (3) |  |  | (37) |
Gross benefits paid | (74) |  |  | (152) |  |  | (20) |  |  | (18) |
Net benefit obligation at December 31 | 876 |  |  | 875 |  |  | 160 |  |  | 168 |
Change in plan assets: |  |  |  |  |  |  |
Fair value of plan assets at January 1 | 706 |  |  | 1,011 |  |  | 83 |  |  | 106 |
Actual return on plan assets | 86 |  |  | (204) |  |  | 8 |  |  | (17) |
Employer contributions | 14 |  |  | 51 |  |  | 8 |  |  | 8 |
Plan participants’ contributions | — |  |  | — |  |  | 4 |  |  | 4 |
Gross benefits paid | (74) |  |  | (152) |  |  | (20) |  |  | (18) |
Fair value of plan assets at December 31 | 732 |  |  | 706 |  |  | 83 |  |  | 83 |
Under funded status at December 31 | ($144) |  |  | ($169) |  |  | ($77) |  |  | ($85) |
| Defined Benefit Pension Plans |  | OPEB Plans
Alliant Energy | 2023 |  | 2022 |  | 2023 |  | 2022
Amounts recognized on the balance sheets consist of: |  |  |  |  |  |  |
Non-current assets | $— |  |  | $— |  |  | $14 |  |  | $9 |
Current liabilities | (2) |  |  | (2) |  |  | (8) |  |  | (8) |
Pension and other benefit obligations | (142) |  |  | (167) |  |  | (83) |  |  | (86) |
Net amounts recognized at December 31 | ($144) |  |  | ($169) |  |  | ($77) |  |  | ($85) |
Amounts recognized in Regulatory Assets consist of: |  |  |  |  |  |  |
Net actuarial loss | $337 |  |  | $376 |  |  | $11 |  |  | $20 |
Prior service credit | (2) |  |  | (3) |  |  | — |  |  | — |
| $335 |  |  | $373 |  |  | $11 |  |  | $20 |
| Defined Benefit Pension Plans |  | OPEB Plans
IPL | 2023 |  | 2022 |  | 2023 |  | 2022
Change in benefit obligation: |  |  |  |  |  |  |
Net benefit obligation at January 1 | $389 |  |  | $567 |  |  | $68 |  |  | $84 |
Service cost | 3 |  |  | 6 |  |  | 1 |  |  | 1 |
Interest cost | 21 |  |  | 16 |  |  | 3 |  |  | 2 |
Plan participants’ contributions | — |  |  | — |  |  | 2 |  |  | 2 |
Actuarial (gain) loss | 9 |  |  | (123) |  |  | (1) |  |  | (14) |
Gross benefits paid | (35) |  |  | (77) |  |  | (8) |  |  | (7) |
Net benefit obligation at December 31 | 387 |  |  | 389 |  |  | 65 |  |  | 68 |
Change in plan assets: |  |  |  |  |  |  |
Fair value of plan assets at January 1 | 344 |  |  | 462 |  |  | 58 |  |  | 74 |
Actual return on plan assets | 42 |  |  | (92) |  |  | 7 |  |  | (12) |
Employer contributions | 1 |  |  | 51 |  |  | 2 |  |  | 1 |
Plan participants’ contributions | — |  |  | — |  |  | 2 |  |  | 2 |
Gross benefits paid | (35) |  |  | (77) |  |  | (8) |  |  | (7) |
Fair value of plan assets at December 31 | 352 |  |  | 344 |  |  | 61 |  |  | 58 |
Under funded status at December 31 | ($35) |  |  | ($45) |  |  | ($4) |  |  | ($10) |
| Defined Benefit Pension Plans |  | OPEB Plans
IPL | 2023 |  | 2022 |  | 2023 |  | 2022
Amounts recognized on the balance sheets consist of: |  |  |  |  |  |  |
Non-current assets | $— |  |  | $— |  |  | $10 |  |  | $6 |
Current liabilities | — |  |  | — |  |  | (1) |  |  | (2) |
Pension and other benefit obligations | (35) |  |  | (45) |  |  | (13) |  |  | (14) |
Net amounts recognized at December 31 | ($35) |  |  | ($45) |  |  | ($4) |  |  | ($10) |
Amounts recognized in Regulatory Assets consist of: |  |  |  |  |  |  |
Net actuarial loss | $135 |  |  | $154 |  |  | $9 |  |  | $14 |
Prior service credit | (1) |  |  | (1) |  |  | — |  |  | — |
| $134 |  |  | $153 |  |  | $9 |  |  | $14 |
| Defined Benefit Pension Plans |  | OPEB Plans
WPL | 2023 |  | 2022 |  | 2023 |  | 2022
Change in benefit obligation: |  |  |  |  |  |  |
Net benefit obligation at January 1 | $381 |  |  | $546 |  |  | $65 |  |  | $81 |
Service cost | 2 |  |  | 3 |  |  | 1 |  |  | 1 |
Interest cost | 20 |  |  | 16 |  |  | 3 |  |  | 2 |
Plan participants’ contributions | — |  |  | — |  |  | 2 |  |  | 2 |
Actuarial (gain) loss | 10 |  |  | (117) |  |  | (2) |  |  | (13) |
Gross benefits paid | (32) |  |  | (67) |  |  | (8) |  |  | (8) |
Net benefit obligation at December 31 | 381 |  |  | 381 |  |  | 61 |  |  | 65 |
Change in plan assets: |  |  |  |  |  |  |
Fair value of plan assets at January 1 | 291 |  |  | 450 |  |  | 14 |  |  | 17 |
Actual return on plan assets | 35 |  |  | (92) |  |  | 1 |  |  | (2) |
Employer contributions | 12 |  |  | — |  |  | 5 |  |  | 5 |
Plan participants’ contributions | — |  |  | — |  |  | 2 |  |  | 2 |
Gross benefits paid | (32) |  |  | (67) |  |  | (8) |  |  | (8) |
Fair value of plan assets at December 31 | 306 |  |  | 291 |  |  | 14 |  |  | 14 |
Under funded status at December 31 | ($75) |  |  | ($90) |  |  | ($47) |  |  | ($51) |
| Defined Benefit Pension Plans |  | OPEB Plans
WPL | 2023 |  | 2022 |  | 2023 |  | 2022
Amounts recognized on the balance sheets consist of: |  |  |  |  |  |  |
Non-current assets | $— |  |  | $— |  |  | $4 |  |  | $3 |
Current liabilities | — |  |  | — |  |  | (6) |  |  | (5) |
Pension and other benefit obligations | (75) |  |  | (90) |  |  | (45) |  |  | (49) |
Net amounts recognized at December 31 | ($75) |  |  | ($90) |  |  | ($47) |  |  | ($51) |
Amounts recognized in Regulatory Assets consist of: |  |  |  |  |  |  |
Net actuarial loss | $148 |  |  | $165 |  |  | $3 |  |  | $6 |
Prior service credit | — |  |  | — |  |  | — |  |  | — |
| $148 |  |  | $165 |  |  | $3 |  |  | $6 |
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 | 2023 |  | 2022 |  | 2023 |  | 2022
Accumulated benefit obligations | $857 |  |  | $857 |  |  | $160 |  |  | $168 |
Plans with accumulated benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Accumulated benefit obligations | 857 |  |  | 857 |  |  | 160 |  |  | 168 |
Fair value of plan assets | 732 |  |  | 706 |  |  | 83 |  |  | 83 |
Plans with projected benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Projected benefit obligations | 876 |  |  | 875 |  |  | N/A |  | N/A
Fair value of plan assets | 732 |  |  | 706 |  |  | N/A |  | N/A
| Defined Benefit Pension Plans |  | OPEB Plans
IPL | 2023 |  | 2022 |  | 2023 |  | 2022
Accumulated benefit obligations | $377 |  |  | $379 |  |  | $65 |  |  | $68 |
Plans with accumulated benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Accumulated benefit obligations | 377 |  |  | 379 |  |  | 65 |  |  | 68 |
Fair value of plan assets | 352 |  |  | 344 |  |  | 61 |  |  | 58 |
Plans with projected benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Projected benefit obligations | 387 |  |  | 389 |  |  | N/A |  | N/A
Fair value of plan assets | 352 |  |  | 344 |  |  | N/A |  | N/A
| Defined Benefit Pension Plans |  | OPEB Plans
WPL | 2023 |  | 2022 |  | 2023 |  | 2022
Accumulated benefit obligations | $373 |  |  | $373 |  |  | $61 |  |  | $65 |
Plans with accumulated benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Accumulated benefit obligations | 373 |  |  | 373 |  |  | 61 |  |  | 65 |
Fair value of plan assets | 306 |  |  | 291 |  |  | 14 |  |  | 14 |
Plans with projected benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Projected benefit obligations | 381 |  |  | 381 |  |  | N/A |  | N/A
Fair value of plan assets | 306 |  |  | 291 |  |  | 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
| 2023 |  | 2022 |  | 2023 |  | 2022
Regulatory assets | $28 |  | $30 |  | $24 |  | $25
Estimated Future Employer Contributions | Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2024 is as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
Defined benefit pension plans (a) | $12 |  | $— |  | $10
OPEB plans | 8 |  | 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 | 2024 |  | 2025 |  | 2026 |  | 2027 |  | 2028 |  | 2029 - 2033
Defined benefit pension benefits | $73 |  |  | $73 |  |  | $74 |  |  | $75 |  |  | $75 |  |  | $343
OPEB | 17 |  |  | 17 |  |  | 16 |  |  | 16 |  |  | 15 |  |  | 65
| $90 |  |  | $90 |  |  | $90 |  |  | $91 |  |  | $90 |  |  | $408
IPL | 2024 |  | 2025 |  | 2026 |  | 2027 |  | 2028 |  | 2029 - 2033
Defined benefit pension benefits | $34 |  |  | $34 |  |  | $34 |  |  | $33 |  |  | $33 |  |  | $151
OPEB | 7 |  |  | 7 |  |  | 7 |  |  | 6 |  |  | 6 |  |  | 25
| $41 |  |  | $41 |  |  | $41 |  |  | $39 |  |  | $39 |  |  | $176
WPL | 2024 |  | 2025 |  | 2026 |  | 2027 |  | 2028 |  | 2029 - 2033
Defined benefit pension benefits | $32 |  |  | $32 |  |  | $31 |  |  | $31 |  |  | $31 |  |  | $146
OPEB | 7 |  |  | 7 |  |  | 6 |  |  | 6 |  |  | 6 |  |  | 24
| $39 |  |  | $39 |  |  | $37 |  |  | $37 |  |  | $37 |  |  | $170
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
| 2023 |  | 2022 |  | 2021 |  | 2023 |  | 2022 |  | 2021 |  | 2023 |  | 2022 |  | 2021
Compensation expense | $12 |  | $13 |  | $14 |  | $6 |  | $7 |  | $8 |  | $5 |  | $5 |  | $6
Income tax benefits | 3 |  | 3 |  | 4 |  | 2 |  | 2 |  | 2 |  | 1 |  | 1 |  | 2
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):
| 2023 |  | 2022
Carrying value | $13 |  | $13
Fair market value | 19 |  | 22
IPL [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Assumptions Used To Measure Benefit Plans | The 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 | 2023 |  | 2022 |  | 2021 |  | 2023 |  | 2022 |  | 2021
Discount rate for benefit obligations | 5.36% |  | 5.54% |  | 2.91% |  | 5.40% |  | 5.53% |  | 2.81%
Discount rate for net periodic cost | 5.54% |  | 2.91% |  | 2.57% |  | 5.53% |  | 2.81% |  | 2.31%
Expected rate of return on plan assets | 7.80% |  | 7.80% |  | 7.10% |  | 6.50% |  | 6.40% |  | 4.80%
Interest crediting rate for Alliant Energy Cash Balance Pension Plan | 10.75% |  | 9.22% |  | 4.18% |  | N/A |  | N/A |  | N/A
Rate of compensation increase | 3.30% | - | 4.50% |  | 3.30% | - | 4.50% |  | 3.30% | - | 4.50% |  | N/A |  | N/A |  | N/A
| Qualified Defined Benefit Pension Plan |  | OPEB Plans
IPL | 2023 |  | 2022 |  | 2021 |  | 2023 |  | 2022 |  | 2021
Discount rate for benefit obligations | 5.35% |  | 5.55% |  | 2.94% |  | 5.40% |  | 5.53% |  | 2.80%
Discount rate for net periodic cost | 5.55% |  | 2.94% |  | 2.61% |  | 5.53% |  | 2.80% |  | 2.28%
Expected rate of return on plan assets | 7.80% |  | 7.80% |  | 7.10% |  | 6.90% |  | 6.50% |  | 5.10%
Rate of compensation increase | 3.30% |  | 3.30% |  | 3.30% |  | N/A |  | N/A |  | N/A
| Qualified Defined Benefit Pension Plan |  | OPEB Plans
WPL | 2023 |  | 2022 |  | 2021 |  | 2023 |  | 2022 |  | 2021
Discount rate for benefit obligations | 5.35% |  | 5.54% |  | 2.94% |  | 5.40% |  | 5.53% |  | 2.79%
Discount rate for net periodic cost | 5.54% |  | 2.94% |  | 2.64% |  | 5.53% |  | 2.79% |  | 2.27%
Expected rate of return on plan assets | 7.80% |  | 7.80% |  | 7.10% |  | 5.65% |  | 5.49% |  | 4.02%
Rate of compensation increase | 3.30% |  | 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
2023 |  | 2022 |  | 2021 |  | 2023 |  | 2022 |  | 2021
Service cost | $5 |  |  | $9 |  |  | $11 |  |  | $2 |  |  | $3 |  |  | $4 |
Interest cost | 47 |  |  | 36 |  |  | 34 |  |  | 9 |  |  | 6 |  |  | 5 |
Expected return on plan assets (a) | (53) |  |  | (69) |  |  | (69) |  |  | (5) |  |  | (5) |  |  | (5) |
Amortization of prior service credit (b) | (1) |  |  | (1) |  |  | — |  |  | — |  |  | — |  |  | — |
Amortization of actuarial loss (c) | 28 |  |  | 32 |  |  | 39 |  |  | 1 |  |  | 2 |  |  | 5 |
Settlement losses (d) | — |  |  | 26 |  |  | — |  |  | — |  |  | — |  |  | — |
| $26 |  |  | $33 |  |  | $15 |  |  | $7 |  |  | $6 |  |  | $9 |
IPL | Defined Benefit Pension Plans |  | OPEB Plans
2023 |  | 2022 |  | 2021 |  | 2023 |  | 2022 |  | 2021
Service cost | $3 |  |  | $6 |  |  | $7 |  |  | $1 |  |  | $1 |  |  | $1 |
Interest cost | 21 |  |  | 16 |  |  | 16 |  |  | 3 |  |  | 2 |  |  | 2 |
Expected return on plan assets (a) | (26) |  |  | (31) |  |  | (32) |  |  | (3) |  |  | (4) |  |  | (3) |
Amortization of actuarial loss (c) | 11 |  |  | 13 |  |  | 17 |  |  | 1 |  |  | 1 |  |  | 2 |
Settlement losses (d) | — |  |  | 13 |  |  | — |  |  | — |  |  | — |  |  | — |
| $9 |  |  | $17 |  |  | $8 |  |  | $2 |  |  | $— |  |  | $2 |
WPL | Defined Benefit Pension Plans |  | OPEB Plans
2023 |  | 2022 |  | 2021 |  | 2023 |  | 2022 |  | 2021
Service cost | $2 |  |  | $3 |  |  | $4 |  |  | $1 |  |  | $1 |  |  | $1 |
Interest cost | 20 |  |  | 16 |  |  | 15 |  |  | 3 |  |  | 2 |  |  | 2 |
Expected return on plan assets (a) | (22) |  |  | (31) |  |  | (31) |  |  | (1) |  |  | (1) |  |  | — |
Amortization of actuarial loss (c) | 13 |  |  | 15 |  |  | 19 |  |  | 1 |  |  | 2 |  |  | 2 |
Settlement losses (d) | — |  |  | 13 |  |  | — |  |  | — |  |  | — |  |  | — |
| $13 |  |  | $16 |  |  | $7 |  |  | $4 |  |  | $4 |  |  | $5 |
(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 | 2023 |  | 2022 |  | 2023 |  | 2022
Change in benefit obligation: |  |  |  |  |  |  |
Net benefit obligation at January 1 | $875 |  |  | $1,251 |  |  | $168 |  |  | $210 |
Service cost | 5 |  |  | 9 |  |  | 2 |  |  | 3 |
Interest cost | 47 |  |  | 36 |  |  | 9 |  |  | 6 |
Plan participants’ contributions | — |  |  | — |  |  | 4 |  |  | 4 |
Actuarial (gain) loss | 23 |  |  | (269) |  |  | (3) |  |  | (37) |
Gross benefits paid | (74) |  |  | (152) |  |  | (20) |  |  | (18) |
Net benefit obligation at December 31 | 876 |  |  | 875 |  |  | 160 |  |  | 168 |
Change in plan assets: |  |  |  |  |  |  |
Fair value of plan assets at January 1 | 706 |  |  | 1,011 |  |  | 83 |  |  | 106 |
Actual return on plan assets | 86 |  |  | (204) |  |  | 8 |  |  | (17) |
Employer contributions | 14 |  |  | 51 |  |  | 8 |  |  | 8 |
Plan participants’ contributions | — |  |  | — |  |  | 4 |  |  | 4 |
Gross benefits paid | (74) |  |  | (152) |  |  | (20) |  |  | (18) |
Fair value of plan assets at December 31 | 732 |  |  | 706 |  |  | 83 |  |  | 83 |
Under funded status at December 31 | ($144) |  |  | ($169) |  |  | ($77) |  |  | ($85) |
| Defined Benefit Pension Plans |  | OPEB Plans
Alliant Energy | 2023 |  | 2022 |  | 2023 |  | 2022
Amounts recognized on the balance sheets consist of: |  |  |  |  |  |  |
Non-current assets | $— |  |  | $— |  |  | $14 |  |  | $9 |
Current liabilities | (2) |  |  | (2) |  |  | (8) |  |  | (8) |
Pension and other benefit obligations | (142) |  |  | (167) |  |  | (83) |  |  | (86) |
Net amounts recognized at December 31 | ($144) |  |  | ($169) |  |  | ($77) |  |  | ($85) |
Amounts recognized in Regulatory Assets consist of: |  |  |  |  |  |  |
Net actuarial loss | $337 |  |  | $376 |  |  | $11 |  |  | $20 |
Prior service credit | (2) |  |  | (3) |  |  | — |  |  | — |
| $335 |  |  | $373 |  |  | $11 |  |  | $20 |
| Defined Benefit Pension Plans |  | OPEB Plans
IPL | 2023 |  | 2022 |  | 2023 |  | 2022
Change in benefit obligation: |  |  |  |  |  |  |
Net benefit obligation at January 1 | $389 |  |  | $567 |  |  | $68 |  |  | $84 |
Service cost | 3 |  |  | 6 |  |  | 1 |  |  | 1 |
Interest cost | 21 |  |  | 16 |  |  | 3 |  |  | 2 |
Plan participants’ contributions | — |  |  | — |  |  | 2 |  |  | 2 |
Actuarial (gain) loss | 9 |  |  | (123) |  |  | (1) |  |  | (14) |
Gross benefits paid | (35) |  |  | (77) |  |  | (8) |  |  | (7) |
Net benefit obligation at December 31 | 387 |  |  | 389 |  |  | 65 |  |  | 68 |
Change in plan assets: |  |  |  |  |  |  |
Fair value of plan assets at January 1 | 344 |  |  | 462 |  |  | 58 |  |  | 74 |
Actual return on plan assets | 42 |  |  | (92) |  |  | 7 |  |  | (12) |
Employer contributions | 1 |  |  | 51 |  |  | 2 |  |  | 1 |
Plan participants’ contributions | — |  |  | — |  |  | 2 |  |  | 2 |
Gross benefits paid | (35) |  |  | (77) |  |  | (8) |  |  | (7) |
Fair value of plan assets at December 31 | 352 |  |  | 344 |  |  | 61 |  |  | 58 |
Under funded status at December 31 | ($35) |  |  | ($45) |  |  | ($4) |  |  | ($10) |
| Defined Benefit Pension Plans |  | OPEB Plans
IPL | 2023 |  | 2022 |  | 2023 |  | 2022
Amounts recognized on the balance sheets consist of: |  |  |  |  |  |  |
Non-current assets | $— |  |  | $— |  |  | $10 |  |  | $6 |
Current liabilities | — |  |  | — |  |  | (1) |  |  | (2) |
Pension and other benefit obligations | (35) |  |  | (45) |  |  | (13) |  |  | (14) |
Net amounts recognized at December 31 | ($35) |  |  | ($45) |  |  | ($4) |  |  | ($10) |
Amounts recognized in Regulatory Assets consist of: |  |  |  |  |  |  |
Net actuarial loss | $135 |  |  | $154 |  |  | $9 |  |  | $14 |
Prior service credit | (1) |  |  | (1) |  |  | — |  |  | — |
| $134 |  |  | $153 |  |  | $9 |  |  | $14 |
| Defined Benefit Pension Plans |  | OPEB Plans
WPL | 2023 |  | 2022 |  | 2023 |  | 2022
Change in benefit obligation: |  |  |  |  |  |  |
Net benefit obligation at January 1 | $381 |  |  | $546 |  |  | $65 |  |  | $81 |
Service cost | 2 |  |  | 3 |  |  | 1 |  |  | 1 |
Interest cost | 20 |  |  | 16 |  |  | 3 |  |  | 2 |
Plan participants’ contributions | — |  |  | — |  |  | 2 |  |  | 2 |
Actuarial (gain) loss | 10 |  |  | (117) |  |  | (2) |  |  | (13) |
Gross benefits paid | (32) |  |  | (67) |  |  | (8) |  |  | (8) |
Net benefit obligation at December 31 | 381 |  |  | 381 |  |  | 61 |  |  | 65 |
Change in plan assets: |  |  |  |  |  |  |
Fair value of plan assets at January 1 | 291 |  |  | 450 |  |  | 14 |  |  | 17 |
Actual return on plan assets | 35 |  |  | (92) |  |  | 1 |  |  | (2) |
Employer contributions | 12 |  |  | — |  |  | 5 |  |  | 5 |
Plan participants’ contributions | — |  |  | — |  |  | 2 |  |  | 2 |
Gross benefits paid | (32) |  |  | (67) |  |  | (8) |  |  | (8) |
Fair value of plan assets at December 31 | 306 |  |  | 291 |  |  | 14 |  |  | 14 |
Under funded status at December 31 | ($75) |  |  | ($90) |  |  | ($47) |  |  | ($51) |
| Defined Benefit Pension Plans |  | OPEB Plans
WPL | 2023 |  | 2022 |  | 2023 |  | 2022
Amounts recognized on the balance sheets consist of: |  |  |  |  |  |  |
Non-current assets | $— |  |  | $— |  |  | $4 |  |  | $3 |
Current liabilities | — |  |  | — |  |  | (6) |  |  | (5) |
Pension and other benefit obligations | (75) |  |  | (90) |  |  | (45) |  |  | (49) |
Net amounts recognized at December 31 | ($75) |  |  | ($90) |  |  | ($47) |  |  | ($51) |
Amounts recognized in Regulatory Assets consist of: |  |  |  |  |  |  |
Net actuarial loss | $148 |  |  | $165 |  |  | $3 |  |  | $6 |
Prior service credit | — |  |  | — |  |  | — |  |  | — |
| $148 |  |  | $165 |  |  | $3 |  |  | $6 |
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 | 2023 |  | 2022 |  | 2023 |  | 2022
Accumulated benefit obligations | $857 |  |  | $857 |  |  | $160 |  |  | $168 |
Plans with accumulated benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Accumulated benefit obligations | 857 |  |  | 857 |  |  | 160 |  |  | 168 |
Fair value of plan assets | 732 |  |  | 706 |  |  | 83 |  |  | 83 |
Plans with projected benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Projected benefit obligations | 876 |  |  | 875 |  |  | N/A |  | N/A
Fair value of plan assets | 732 |  |  | 706 |  |  | N/A |  | N/A
| Defined Benefit Pension Plans |  | OPEB Plans
IPL | 2023 |  | 2022 |  | 2023 |  | 2022
Accumulated benefit obligations | $377 |  |  | $379 |  |  | $65 |  |  | $68 |
Plans with accumulated benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Accumulated benefit obligations | 377 |  |  | 379 |  |  | 65 |  |  | 68 |
Fair value of plan assets | 352 |  |  | 344 |  |  | 61 |  |  | 58 |
Plans with projected benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Projected benefit obligations | 387 |  |  | 389 |  |  | N/A |  | N/A
Fair value of plan assets | 352 |  |  | 344 |  |  | N/A |  | N/A
| Defined Benefit Pension Plans |  | OPEB Plans
WPL | 2023 |  | 2022 |  | 2023 |  | 2022
Accumulated benefit obligations | $373 |  |  | $373 |  |  | $61 |  |  | $65 |
Plans with accumulated benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Accumulated benefit obligations | 373 |  |  | 373 |  |  | 61 |  |  | 65 |
Fair value of plan assets | 306 |  |  | 291 |  |  | 14 |  |  | 14 |
Plans with projected benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Projected benefit obligations | 381 |  |  | 381 |  |  | N/A |  | N/A
Fair value of plan assets | 306 |  |  | 291 |  |  | 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
| 2023 |  | 2022 |  | 2023 |  | 2022
Regulatory assets | $28 |  | $30 |  | $24 |  | $25
Estimated Future Employer Contributions | Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2024 is as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
Defined benefit pension plans (a) | $12 |  | $— |  | $10
OPEB plans | 8 |  | 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 | 2024 |  | 2025 |  | 2026 |  | 2027 |  | 2028 |  | 2029 - 2033
Defined benefit pension benefits | $73 |  |  | $73 |  |  | $74 |  |  | $75 |  |  | $75 |  |  | $343
OPEB | 17 |  |  | 17 |  |  | 16 |  |  | 16 |  |  | 15 |  |  | 65
| $90 |  |  | $90 |  |  | $90 |  |  | $91 |  |  | $90 |  |  | $408
IPL | 2024 |  | 2025 |  | 2026 |  | 2027 |  | 2028 |  | 2029 - 2033
Defined benefit pension benefits | $34 |  |  | $34 |  |  | $34 |  |  | $33 |  |  | $33 |  |  | $151
OPEB | 7 |  |  | 7 |  |  | 7 |  |  | 6 |  |  | 6 |  |  | 25
| $41 |  |  | $41 |  |  | $41 |  |  | $39 |  |  | $39 |  |  | $176
WPL | 2024 |  | 2025 |  | 2026 |  | 2027 |  | 2028 |  | 2029 - 2033
Defined benefit pension benefits | $32 |  |  | $32 |  |  | $31 |  |  | $31 |  |  | $31 |  |  | $146
OPEB | 7 |  |  | 7 |  |  | 6 |  |  | 6 |  |  | 6 |  |  | 24
| $39 |  |  | $39 |  |  | $37 |  |  | $37 |  |  | $37 |  |  | $170
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
| 2023 |  | 2022 |  | 2021 |  | 2023 |  | 2022 |  | 2021 |  | 2023 |  | 2022 |  | 2021
Compensation expense | $12 |  | $13 |  | $14 |  | $6 |  | $7 |  | $8 |  | $5 |  | $5 |  | $6
Income tax benefits | 3 |  | 3 |  | 4 |  | 2 |  | 2 |  | 2 |  | 1 |  | 1 |  | 2
WPL [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Assumptions Used To Measure Benefit Plans | The 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 | 2023 |  | 2022 |  | 2021 |  | 2023 |  | 2022 |  | 2021
Discount rate for benefit obligations | 5.36% |  | 5.54% |  | 2.91% |  | 5.40% |  | 5.53% |  | 2.81%
Discount rate for net periodic cost | 5.54% |  | 2.91% |  | 2.57% |  | 5.53% |  | 2.81% |  | 2.31%
Expected rate of return on plan assets | 7.80% |  | 7.80% |  | 7.10% |  | 6.50% |  | 6.40% |  | 4.80%
Interest crediting rate for Alliant Energy Cash Balance Pension Plan | 10.75% |  | 9.22% |  | 4.18% |  | N/A |  | N/A |  | N/A
Rate of compensation increase | 3.30% | - | 4.50% |  | 3.30% | - | 4.50% |  | 3.30% | - | 4.50% |  | N/A |  | N/A |  | N/A
| Qualified Defined Benefit Pension Plan |  | OPEB Plans
IPL | 2023 |  | 2022 |  | 2021 |  | 2023 |  | 2022 |  | 2021
Discount rate for benefit obligations | 5.35% |  | 5.55% |  | 2.94% |  | 5.40% |  | 5.53% |  | 2.80%
Discount rate for net periodic cost | 5.55% |  | 2.94% |  | 2.61% |  | 5.53% |  | 2.80% |  | 2.28%
Expected rate of return on plan assets | 7.80% |  | 7.80% |  | 7.10% |  | 6.90% |  | 6.50% |  | 5.10%
Rate of compensation increase | 3.30% |  | 3.30% |  | 3.30% |  | N/A |  | N/A |  | N/A
| Qualified Defined Benefit Pension Plan |  | OPEB Plans
WPL | 2023 |  | 2022 |  | 2021 |  | 2023 |  | 2022 |  | 2021
Discount rate for benefit obligations | 5.35% |  | 5.54% |  | 2.94% |  | 5.40% |  | 5.53% |  | 2.79%
Discount rate for net periodic cost | 5.54% |  | 2.94% |  | 2.64% |  | 5.53% |  | 2.79% |  | 2.27%
Expected rate of return on plan assets | 7.80% |  | 7.80% |  | 7.10% |  | 5.65% |  | 5.49% |  | 4.02%
Rate of compensation increase | 3.30% |  | 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
2023 |  | 2022 |  | 2021 |  | 2023 |  | 2022 |  | 2021
Service cost | $5 |  |  | $9 |  |  | $11 |  |  | $2 |  |  | $3 |  |  | $4 |
Interest cost | 47 |  |  | 36 |  |  | 34 |  |  | 9 |  |  | 6 |  |  | 5 |
Expected return on plan assets (a) | (53) |  |  | (69) |  |  | (69) |  |  | (5) |  |  | (5) |  |  | (5) |
Amortization of prior service credit (b) | (1) |  |  | (1) |  |  | — |  |  | — |  |  | — |  |  | — |
Amortization of actuarial loss (c) | 28 |  |  | 32 |  |  | 39 |  |  | 1 |  |  | 2 |  |  | 5 |
Settlement losses (d) | — |  |  | 26 |  |  | — |  |  | — |  |  | — |  |  | — |
| $26 |  |  | $33 |  |  | $15 |  |  | $7 |  |  | $6 |  |  | $9 |
IPL | Defined Benefit Pension Plans |  | OPEB Plans
2023 |  | 2022 |  | 2021 |  | 2023 |  | 2022 |  | 2021
Service cost | $3 |  |  | $6 |  |  | $7 |  |  | $1 |  |  | $1 |  |  | $1 |
Interest cost | 21 |  |  | 16 |  |  | 16 |  |  | 3 |  |  | 2 |  |  | 2 |
Expected return on plan assets (a) | (26) |  |  | (31) |  |  | (32) |  |  | (3) |  |  | (4) |  |  | (3) |
Amortization of actuarial loss (c) | 11 |  |  | 13 |  |  | 17 |  |  | 1 |  |  | 1 |  |  | 2 |
Settlement losses (d) | — |  |  | 13 |  |  | — |  |  | — |  |  | — |  |  | — |
| $9 |  |  | $17 |  |  | $8 |  |  | $2 |  |  | $— |  |  | $2 |
WPL | Defined Benefit Pension Plans |  | OPEB Plans
2023 |  | 2022 |  | 2021 |  | 2023 |  | 2022 |  | 2021
Service cost | $2 |  |  | $3 |  |  | $4 |  |  | $1 |  |  | $1 |  |  | $1 |
Interest cost | 20 |  |  | 16 |  |  | 15 |  |  | 3 |  |  | 2 |  |  | 2 |
Expected return on plan assets (a) | (22) |  |  | (31) |  |  | (31) |  |  | (1) |  |  | (1) |  |  | — |
Amortization of actuarial loss (c) | 13 |  |  | 15 |  |  | 19 |  |  | 1 |  |  | 2 |  |  | 2 |
Settlement losses (d) | — |  |  | 13 |  |  | — |  |  | — |  |  | — |  |  | — |
| $13 |  |  | $16 |  |  | $7 |  |  | $4 |  |  | $4 |  |  | $5 |
(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 | 2023 |  | 2022 |  | 2023 |  | 2022
Change in benefit obligation: |  |  |  |  |  |  |
Net benefit obligation at January 1 | $875 |  |  | $1,251 |  |  | $168 |  |  | $210 |
Service cost | 5 |  |  | 9 |  |  | 2 |  |  | 3 |
Interest cost | 47 |  |  | 36 |  |  | 9 |  |  | 6 |
Plan participants’ contributions | — |  |  | — |  |  | 4 |  |  | 4 |
Actuarial (gain) loss | 23 |  |  | (269) |  |  | (3) |  |  | (37) |
Gross benefits paid | (74) |  |  | (152) |  |  | (20) |  |  | (18) |
Net benefit obligation at December 31 | 876 |  |  | 875 |  |  | 160 |  |  | 168 |
Change in plan assets: |  |  |  |  |  |  |
Fair value of plan assets at January 1 | 706 |  |  | 1,011 |  |  | 83 |  |  | 106 |
Actual return on plan assets | 86 |  |  | (204) |  |  | 8 |  |  | (17) |
Employer contributions | 14 |  |  | 51 |  |  | 8 |  |  | 8 |
Plan participants’ contributions | — |  |  | — |  |  | 4 |  |  | 4 |
Gross benefits paid | (74) |  |  | (152) |  |  | (20) |  |  | (18) |
Fair value of plan assets at December 31 | 732 |  |  | 706 |  |  | 83 |  |  | 83 |
Under funded status at December 31 | ($144) |  |  | ($169) |  |  | ($77) |  |  | ($85) |
| Defined Benefit Pension Plans |  | OPEB Plans
Alliant Energy | 2023 |  | 2022 |  | 2023 |  | 2022
Amounts recognized on the balance sheets consist of: |  |  |  |  |  |  |
Non-current assets | $— |  |  | $— |  |  | $14 |  |  | $9 |
Current liabilities | (2) |  |  | (2) |  |  | (8) |  |  | (8) |
Pension and other benefit obligations | (142) |  |  | (167) |  |  | (83) |  |  | (86) |
Net amounts recognized at December 31 | ($144) |  |  | ($169) |  |  | ($77) |  |  | ($85) |
Amounts recognized in Regulatory Assets consist of: |  |  |  |  |  |  |
Net actuarial loss | $337 |  |  | $376 |  |  | $11 |  |  | $20 |
Prior service credit | (2) |  |  | (3) |  |  | — |  |  | — |
| $335 |  |  | $373 |  |  | $11 |  |  | $20 |
| Defined Benefit Pension Plans |  | OPEB Plans
IPL | 2023 |  | 2022 |  | 2023 |  | 2022
Change in benefit obligation: |  |  |  |  |  |  |
Net benefit obligation at January 1 | $389 |  |  | $567 |  |  | $68 |  |  | $84 |
Service cost | 3 |  |  | 6 |  |  | 1 |  |  | 1 |
Interest cost | 21 |  |  | 16 |  |  | 3 |  |  | 2 |
Plan participants’ contributions | — |  |  | — |  |  | 2 |  |  | 2 |
Actuarial (gain) loss | 9 |  |  | (123) |  |  | (1) |  |  | (14) |
Gross benefits paid | (35) |  |  | (77) |  |  | (8) |  |  | (7) |
Net benefit obligation at December 31 | 387 |  |  | 389 |  |  | 65 |  |  | 68 |
Change in plan assets: |  |  |  |  |  |  |
Fair value of plan assets at January 1 | 344 |  |  | 462 |  |  | 58 |  |  | 74 |
Actual return on plan assets | 42 |  |  | (92) |  |  | 7 |  |  | (12) |
Employer contributions | 1 |  |  | 51 |  |  | 2 |  |  | 1 |
Plan participants’ contributions | — |  |  | — |  |  | 2 |  |  | 2 |
Gross benefits paid | (35) |  |  | (77) |  |  | (8) |  |  | (7) |
Fair value of plan assets at December 31 | 352 |  |  | 344 |  |  | 61 |  |  | 58 |
Under funded status at December 31 | ($35) |  |  | ($45) |  |  | ($4) |  |  | ($10) |
| Defined Benefit Pension Plans |  | OPEB Plans
IPL | 2023 |  | 2022 |  | 2023 |  | 2022
Amounts recognized on the balance sheets consist of: |  |  |  |  |  |  |
Non-current assets | $— |  |  | $— |  |  | $10 |  |  | $6 |
Current liabilities | — |  |  | — |  |  | (1) |  |  | (2) |
Pension and other benefit obligations | (35) |  |  | (45) |  |  | (13) |  |  | (14) |
Net amounts recognized at December 31 | ($35) |  |  | ($45) |  |  | ($4) |  |  | ($10) |
Amounts recognized in Regulatory Assets consist of: |  |  |  |  |  |  |
Net actuarial loss | $135 |  |  | $154 |  |  | $9 |  |  | $14 |
Prior service credit | (1) |  |  | (1) |  |  | — |  |  | — |
| $134 |  |  | $153 |  |  | $9 |  |  | $14 |
| Defined Benefit Pension Plans |  | OPEB Plans
WPL | 2023 |  | 2022 |  | 2023 |  | 2022
Change in benefit obligation: |  |  |  |  |  |  |
Net benefit obligation at January 1 | $381 |  |  | $546 |  |  | $65 |  |  | $81 |
Service cost | 2 |  |  | 3 |  |  | 1 |  |  | 1 |
Interest cost | 20 |  |  | 16 |  |  | 3 |  |  | 2 |
Plan participants’ contributions | — |  |  | — |  |  | 2 |  |  | 2 |
Actuarial (gain) loss | 10 |  |  | (117) |  |  | (2) |  |  | (13) |
Gross benefits paid | (32) |  |  | (67) |  |  | (8) |  |  | (8) |
Net benefit obligation at December 31 | 381 |  |  | 381 |  |  | 61 |  |  | 65 |
Change in plan assets: |  |  |  |  |  |  |
Fair value of plan assets at January 1 | 291 |  |  | 450 |  |  | 14 |  |  | 17 |
Actual return on plan assets | 35 |  |  | (92) |  |  | 1 |  |  | (2) |
Employer contributions | 12 |  |  | — |  |  | 5 |  |  | 5 |
Plan participants’ contributions | — |  |  | — |  |  | 2 |  |  | 2 |
Gross benefits paid | (32) |  |  | (67) |  |  | (8) |  |  | (8) |
Fair value of plan assets at December 31 | 306 |  |  | 291 |  |  | 14 |  |  | 14 |
Under funded status at December 31 | ($75) |  |  | ($90) |  |  | ($47) |  |  | ($51) |
| Defined Benefit Pension Plans |  | OPEB Plans
WPL | 2023 |  | 2022 |  | 2023 |  | 2022
Amounts recognized on the balance sheets consist of: |  |  |  |  |  |  |
Non-current assets | $— |  |  | $— |  |  | $4 |  |  | $3 |
Current liabilities | — |  |  | — |  |  | (6) |  |  | (5) |
Pension and other benefit obligations | (75) |  |  | (90) |  |  | (45) |  |  | (49) |
Net amounts recognized at December 31 | ($75) |  |  | ($90) |  |  | ($47) |  |  | ($51) |
Amounts recognized in Regulatory Assets consist of: |  |  |  |  |  |  |
Net actuarial loss | $148 |  |  | $165 |  |  | $3 |  |  | $6 |
Prior service credit | — |  |  | — |  |  | — |  |  | — |
| $148 |  |  | $165 |  |  | $3 |  |  | $6 |
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 | 2023 |  | 2022 |  | 2023 |  | 2022
Accumulated benefit obligations | $857 |  |  | $857 |  |  | $160 |  |  | $168 |
Plans with accumulated benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Accumulated benefit obligations | 857 |  |  | 857 |  |  | 160 |  |  | 168 |
Fair value of plan assets | 732 |  |  | 706 |  |  | 83 |  |  | 83 |
Plans with projected benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Projected benefit obligations | 876 |  |  | 875 |  |  | N/A |  | N/A
Fair value of plan assets | 732 |  |  | 706 |  |  | N/A |  | N/A
| Defined Benefit Pension Plans |  | OPEB Plans
IPL | 2023 |  | 2022 |  | 2023 |  | 2022
Accumulated benefit obligations | $377 |  |  | $379 |  |  | $65 |  |  | $68 |
Plans with accumulated benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Accumulated benefit obligations | 377 |  |  | 379 |  |  | 65 |  |  | 68 |
Fair value of plan assets | 352 |  |  | 344 |  |  | 61 |  |  | 58 |
Plans with projected benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Projected benefit obligations | 387 |  |  | 389 |  |  | N/A |  | N/A
Fair value of plan assets | 352 |  |  | 344 |  |  | N/A |  | N/A
| Defined Benefit Pension Plans |  | OPEB Plans
WPL | 2023 |  | 2022 |  | 2023 |  | 2022
Accumulated benefit obligations | $373 |  |  | $373 |  |  | $61 |  |  | $65 |
Plans with accumulated benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Accumulated benefit obligations | 373 |  |  | 373 |  |  | 61 |  |  | 65 |
Fair value of plan assets | 306 |  |  | 291 |  |  | 14 |  |  | 14 |
Plans with projected benefit obligations in excess of plan assets: |  |  |  |  |  |  |
Projected benefit obligations | 381 |  |  | 381 |  |  | N/A |  | N/A
Fair value of plan assets | 306 |  |  | 291 |  |  | 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
| 2023 |  | 2022 |  | 2023 |  | 2022
Regulatory assets | $28 |  | $30 |  | $24 |  | $25
Estimated Future Employer Contributions | Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2024 is as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
Defined benefit pension plans (a) | $12 |  | $— |  | $10
OPEB plans | 8 |  | 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 | 2024 |  | 2025 |  | 2026 |  | 2027 |  | 2028 |  | 2029 - 2033
Defined benefit pension benefits | $73 |  |  | $73 |  |  | $74 |  |  | $75 |  |  | $75 |  |  | $343
OPEB | 17 |  |  | 17 |  |  | 16 |  |  | 16 |  |  | 15 |  |  | 65
| $90 |  |  | $90 |  |  | $90 |  |  | $91 |  |  | $90 |  |  | $408
IPL | 2024 |  | 2025 |  | 2026 |  | 2027 |  | 2028 |  | 2029 - 2033
Defined benefit pension benefits | $34 |  |  | $34 |  |  | $34 |  |  | $33 |  |  | $33 |  |  | $151
OPEB | 7 |  |  | 7 |  |  | 7 |  |  | 6 |  |  | 6 |  |  | 25
| $41 |  |  | $41 |  |  | $41 |  |  | $39 |  |  | $39 |  |  | $176
WPL | 2024 |  | 2025 |  | 2026 |  | 2027 |  | 2028 |  | 2029 - 2033
Defined benefit pension benefits | $32 |  |  | $32 |  |  | $31 |  |  | $31 |  |  | $31 |  |  | $146
OPEB | 7 |  |  | 7 |  |  | 6 |  |  | 6 |  |  | 6 |  |  | 24
| $39 |  |  | $39 |  |  | $37 |  |  | $37 |  |  | $37 |  |  | $170
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
| 2023 |  | 2022 |  | 2021 |  | 2023 |  | 2022 |  | 2021 |  | 2023 |  | 2022 |  | 2021
Compensation expense | $12 |  | $13 |  | $14 |  | $6 |  | $7 |  | $8 |  | $5 |  | $5 |  | $6
Income tax benefits | 3 |  | 3 |  | 4 |  | 2 |  | 2 |  | 2 |  | 1 |  | 1 |  | 2
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, 2023, the current target ranges and actual allocations for the defined benefit pension plan assets were as follows:
| Target Range |  | Actual
| Allocation |  | Allocation
Cash and equivalents | 0% | - | 5% |  | 2%
Equity securities | 47% | - | 67% |  | 56%
Global asset securities | 0% | - | 15% |  | 5%
Fixed income securities | 27% | - | 47% |  | 37%
At December 31, the fair values of qualified and non-qualified defined benefit pension plan assets were as follows (in millions):
| 2023 |  | 2022
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
Alliant Energy | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents | $19 |  |  | $— |  |  | $19 |  |  | $— |  |  | $79 |  |  | $— |  |  | $79 |  |  | $— |
Equity securities | 223 |  |  | 223 |  |  | — |  |  | — |  |  | 185 |  |  | 185 |  |  | — |  |  | — |
Global asset securities | 39 |  |  | 39 |  |  | — |  |  | — |  |  | 35 |  |  | 35 |  |  | — |  |  | — |
Fixed income securities | 143 |  |  | 31 |  |  | 112 |  |  | — |  |  | 130 |  |  | 30 |  |  | 100 |  |  | — |
Total assets in fair value hierarchy | 424 |  |  | $293 |  |  | $131 |  |  | $— |  |  | 429 |  |  | $250 |  |  | $179 |  |  | $— |
Assets measured at net asset value | 306 |  |  |  |  |  |  |  |  | 276 |  |  |  |  |  |  |
Accrued investment income | 2 |  |  |  |  |  |  |  |  | 1 |  |  |  |  |  |  |
Total pension plan assets | $732 |  |  |  |  |  |  |  |  | $706 |  |  |  |  |  |  |
| 2023 |  | 2022
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
IPL | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents | $9 |  |  | $— |  |  | $9 |  |  | $— |  |  | $62 |  |  | $— |  |  | $62 |  |  | $— |
Equity securities | 107 |  |  | 107 |  |  | — |  |  | — |  |  | 83 |  |  | 83 |  |  | — |  |  | — |
Global asset securities | 19 |  |  | 19 |  |  | — |  |  | — |  |  | 16 |  |  | 16 |  |  | — |  |  | — |
Fixed income securities | 69 |  |  | 15 |  |  | 54 |  |  | — |  |  | 58 |  |  | 13 |  |  | 45 |  |  | — |
Total assets in fair value hierarchy | 204 |  |  | $141 |  |  | $63 |  |  | $— |  |  | 219 |  |  | $112 |  |  | $107 |  |  | $— |
Assets measured at net asset value | 147 |  |  |  |  |  |  |  |  | 124 |  |  |  |  |  |  |
Accrued investment income | 1 |  |  |  |  |  |  |  |  | 1 |  |  |  |  |  |  |
Total pension plan assets | $352 |  |  |  |  |  |  |  |  | $344 |  |  |  |  |  |  |
| 2023 |  | 2022
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
WPL | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents | $8 |  |  | $— |  |  | $8 |  |  | $— |  |  | $13 |  |  | $— |  |  | $13 |  |  | $— |
Equity securities | 93 |  |  | 93 |  |  | — |  |  | — |  |  | 82 |  |  | 82 |  |  | — |  |  | — |
Global asset securities | 16 |  |  | 16 |  |  | — |  |  | — |  |  | 16 |  |  | 16 |  |  | — |  |  | — |
Fixed income securities | 60 |  |  | 13 |  |  | 47 |  |  | — |  |  | 57 |  |  | 13 |  |  | 44 |  |  | — |
Total assets in fair value hierarchy | 177 |  |  | $122 |  |  | $55 |  |  | $— |  |  | 168 |  |  | $111 |  |  | $57 |  |  | $— |
Assets measured at net asset value | 128 |  |  |  |  |  |  |  |  | 122 |  |  |  |  |  |  |
Accrued investment income | 1 |  |  |  |  |  |  |  |  | 1 |  |  |  |  |  |  |
Total pension plan assets | $306 |  |  |  |  |  |  |  |  | $291 |  |  |  |  |  |  |
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, 2023, the current target ranges and actual allocations for the defined benefit pension plan assets were as follows:
| Target Range |  | Actual
| Allocation |  | Allocation
Cash and equivalents | 0% | - | 5% |  | 2%
Equity securities | 47% | - | 67% |  | 56%
Global asset securities | 0% | - | 15% |  | 5%
Fixed income securities | 27% | - | 47% |  | 37%
At December 31, the fair values of qualified and non-qualified defined benefit pension plan assets were as follows (in millions):
| 2023 |  | 2022
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
Alliant Energy | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents | $19 |  |  | $— |  |  | $19 |  |  | $— |  |  | $79 |  |  | $— |  |  | $79 |  |  | $— |
Equity securities | 223 |  |  | 223 |  |  | — |  |  | — |  |  | 185 |  |  | 185 |  |  | — |  |  | — |
Global asset securities | 39 |  |  | 39 |  |  | — |  |  | — |  |  | 35 |  |  | 35 |  |  | — |  |  | — |
Fixed income securities | 143 |  |  | 31 |  |  | 112 |  |  | — |  |  | 130 |  |  | 30 |  |  | 100 |  |  | — |
Total assets in fair value hierarchy | 424 |  |  | $293 |  |  | $131 |  |  | $— |  |  | 429 |  |  | $250 |  |  | $179 |  |  | $— |
Assets measured at net asset value | 306 |  |  |  |  |  |  |  |  | 276 |  |  |  |  |  |  |
Accrued investment income | 2 |  |  |  |  |  |  |  |  | 1 |  |  |  |  |  |  |
Total pension plan assets | $732 |  |  |  |  |  |  |  |  | $706 |  |  |  |  |  |  |
| 2023 |  | 2022
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
IPL | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents | $9 |  |  | $— |  |  | $9 |  |  | $— |  |  | $62 |  |  | $— |  |  | $62 |  |  | $— |
Equity securities | 107 |  |  | 107 |  |  | — |  |  | — |  |  | 83 |  |  | 83 |  |  | — |  |  | — |
Global asset securities | 19 |  |  | 19 |  |  | — |  |  | — |  |  | 16 |  |  | 16 |  |  | — |  |  | — |
Fixed income securities | 69 |  |  | 15 |  |  | 54 |  |  | — |  |  | 58 |  |  | 13 |  |  | 45 |  |  | — |
Total assets in fair value hierarchy | 204 |  |  | $141 |  |  | $63 |  |  | $— |  |  | 219 |  |  | $112 |  |  | $107 |  |  | $— |
Assets measured at net asset value | 147 |  |  |  |  |  |  |  |  | 124 |  |  |  |  |  |  |
Accrued investment income | 1 |  |  |  |  |  |  |  |  | 1 |  |  |  |  |  |  |
Total pension plan assets | $352 |  |  |  |  |  |  |  |  | $344 |  |  |  |  |  |  |
| 2023 |  | 2022
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
WPL | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents | $8 |  |  | $— |  |  | $8 |  |  | $— |  |  | $13 |  |  | $— |  |  | $13 |  |  | $— |
Equity securities | 93 |  |  | 93 |  |  | — |  |  | — |  |  | 82 |  |  | 82 |  |  | — |  |  | — |
Global asset securities | 16 |  |  | 16 |  |  | — |  |  | — |  |  | 16 |  |  | 16 |  |  | — |  |  | — |
Fixed income securities | 60 |  |  | 13 |  |  | 47 |  |  | — |  |  | 57 |  |  | 13 |  |  | 44 |  |  | — |
Total assets in fair value hierarchy | 177 |  |  | $122 |  |  | $55 |  |  | $— |  |  | 168 |  |  | $111 |  |  | $57 |  |  | $— |
Assets measured at net asset value | 128 |  |  |  |  |  |  |  |  | 122 |  |  |  |  |  |  |
Accrued investment income | 1 |  |  |  |  |  |  |  |  | 1 |  |  |  |  |  |  |
Total pension plan assets | $306 |  |  |  |  |  |  |  |  | $291 |  |  |  |  |  |  |
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, 2023, the current target ranges and actual allocations for the defined benefit pension plan assets were as follows:
| Target Range |  | Actual
| Allocation |  | Allocation
Cash and equivalents | 0% | - | 5% |  | 2%
Equity securities | 47% | - | 67% |  | 56%
Global asset securities | 0% | - | 15% |  | 5%
Fixed income securities | 27% | - | 47% |  | 37%
At December 31, the fair values of qualified and non-qualified defined benefit pension plan assets were as follows (in millions):
| 2023 |  | 2022
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
Alliant Energy | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents | $19 |  |  | $— |  |  | $19 |  |  | $— |  |  | $79 |  |  | $— |  |  | $79 |  |  | $— |
Equity securities | 223 |  |  | 223 |  |  | — |  |  | — |  |  | 185 |  |  | 185 |  |  | — |  |  | — |
Global asset securities | 39 |  |  | 39 |  |  | — |  |  | — |  |  | 35 |  |  | 35 |  |  | — |  |  | — |
Fixed income securities | 143 |  |  | 31 |  |  | 112 |  |  | — |  |  | 130 |  |  | 30 |  |  | 100 |  |  | — |
Total assets in fair value hierarchy | 424 |  |  | $293 |  |  | $131 |  |  | $— |  |  | 429 |  |  | $250 |  |  | $179 |  |  | $— |
Assets measured at net asset value | 306 |  |  |  |  |  |  |  |  | 276 |  |  |  |  |  |  |
Accrued investment income | 2 |  |  |  |  |  |  |  |  | 1 |  |  |  |  |  |  |
Total pension plan assets | $732 |  |  |  |  |  |  |  |  | $706 |  |  |  |  |  |  |
| 2023 |  | 2022
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
IPL | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents | $9 |  |  | $— |  |  | $9 |  |  | $— |  |  | $62 |  |  | $— |  |  | $62 |  |  | $— |
Equity securities | 107 |  |  | 107 |  |  | — |  |  | — |  |  | 83 |  |  | 83 |  |  | — |  |  | — |
Global asset securities | 19 |  |  | 19 |  |  | — |  |  | — |  |  | 16 |  |  | 16 |  |  | — |  |  | — |
Fixed income securities | 69 |  |  | 15 |  |  | 54 |  |  | — |  |  | 58 |  |  | 13 |  |  | 45 |  |  | — |
Total assets in fair value hierarchy | 204 |  |  | $141 |  |  | $63 |  |  | $— |  |  | 219 |  |  | $112 |  |  | $107 |  |  | $— |
Assets measured at net asset value | 147 |  |  |  |  |  |  |  |  | 124 |  |  |  |  |  |  |
Accrued investment income | 1 |  |  |  |  |  |  |  |  | 1 |  |  |  |  |  |  |
Total pension plan assets | $352 |  |  |  |  |  |  |  |  | $344 |  |  |  |  |  |  |
| 2023 |  | 2022
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
WPL | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents | $8 |  |  | $— |  |  | $8 |  |  | $— |  |  | $13 |  |  | $— |  |  | $13 |  |  | $— |
Equity securities | 93 |  |  | 93 |  |  | — |  |  | — |  |  | 82 |  |  | 82 |  |  | — |  |  | — |
Global asset securities | 16 |  |  | 16 |  |  | — |  |  | — |  |  | 16 |  |  | 16 |  |  | — |  |  | — |
Fixed income securities | 60 |  |  | 13 |  |  | 47 |  |  | — |  |  | 57 |  |  | 13 |  |  | 44 |  |  | — |
Total assets in fair value hierarchy | 177 |  |  | $122 |  |  | $55 |  |  | $— |  |  | 168 |  |  | $111 |  |  | $57 |  |  | $— |
Assets measured at net asset value | 128 |  |  |  |  |  |  |  |  | 122 |  |  |  |  |  |  |
Accrued investment income | 1 |  |  |  |  |  |  |  |  | 1 |  |  |  |  |  |  |
Total pension plan assets | $306 |  |  |  |  |  |  |  |  | $291 |  |  |  |  |  |  |
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, 2023, the current target ranges and actual allocations for VEBA trusts with assets greater than $5 million and the WPL 401(h) assets were as follows:
| Target Range |  | Actual
| Allocation |  | Allocation
Cash and equivalents | 0% | - | 5% |  | 1%
Equity securities | 0% | - | 55% |  | 36%
Fixed income securities | 40% | - | 100% |  | 63%
At December 31, the fair values of OPEB plan assets were as follows (in millions):
| 2023 |  | 2022
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
Alliant Energy | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents | $9 |  |  | $— |  |  | $9 |  |  | $— |  |  | $3 |  |  | $— |  |  | $3 |  |  | $— |
Equity securities | 8 |  |  | 8 |  |  | — |  |  | — |  |  | 9 |  |  | 9 |  |  | — |  |  | — |
Global asset securities | — |  |  | — |  |  | — |  |  | — |  |  | 1 |  |  | 1 |  |  | — |  |  | — |
Fixed income securities | 47 |  |  | 47 |  |  | — |  |  | — |  |  | 47 |  |  | 46 |  |  | 1 |  |  | — |
Total assets in fair value hierarchy | 64 |  |  | $55 |  |  | $9 |  |  | $— |  |  | 60 |  |  | $56 |  |  | $4 |  |  | $— |
Assets measured at net asset value | 19 |  |  |  |  |  |  |  |  | 23 |  |  |  |  |  |  |
Total OPEB plan assets | $83 |  |  |  |  |  |  |  |  | $83 |  |  |  |  |  |  |
| 2023 |  | 2022
| 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 | 6 |  |  | 6 |  |  | — |  |  | — |  |  | 5 |  |  | 5 |  |  | — |  |  | — |
Fixed income securities | 36 |  |  | 36 |  |  | — |  |  | — |  |  | 34 |  |  | 34 |  |  | — |  |  | — |
Total assets in fair value hierarchy | 43 |  |  | $42 |  |  | $1 |  |  | $— |  |  | 40 |  |  | $39 |  |  | $1 |  |  | $— |
Assets measured at net asset value | 18 |  |  |  |  |  |  |  |  | 18 |  |  |  |  |  |  |
Total OPEB plan assets | $61 |  |  |  |  |  |  |  |  | $58 |  |  |  |  |  |  |
| 2023 |  | 2022
| 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 |  |  | — |  |  | — |  |  | 1 |  |  | 1 |  |  | — |  |  | — |
Fixed income securities | 11 |  |  | 11 |  |  | — |  |  | — |  |  | 13 |  |  | 13 |  |  | — |  |  | — |
Total OPEB plan assets | $14 |  |  | $13 |  |  | $1 |  |  | $— |  |  | $14 |  |  | $14 |  |  | $— |  |  | $— |
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, 2023, the current target ranges and actual allocations for VEBA trusts with assets greater than $5 million and the WPL 401(h) assets were as follows:
| Target Range |  | Actual
| Allocation |  | Allocation
Cash and equivalents | 0% | - | 5% |  | 1%
Equity securities | 0% | - | 55% |  | 36%
Fixed income securities | 40% | - | 100% |  | 63%
At December 31, the fair values of OPEB plan assets were as follows (in millions):
| 2023 |  | 2022
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
Alliant Energy | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents | $9 |  |  | $— |  |  | $9 |  |  | $— |  |  | $3 |  |  | $— |  |  | $3 |  |  | $— |
Equity securities | 8 |  |  | 8 |  |  | — |  |  | — |  |  | 9 |  |  | 9 |  |  | — |  |  | — |
Global asset securities | — |  |  | — |  |  | — |  |  | — |  |  | 1 |  |  | 1 |  |  | — |  |  | — |
Fixed income securities | 47 |  |  | 47 |  |  | — |  |  | — |  |  | 47 |  |  | 46 |  |  | 1 |  |  | — |
Total assets in fair value hierarchy | 64 |  |  | $55 |  |  | $9 |  |  | $— |  |  | 60 |  |  | $56 |  |  | $4 |  |  | $— |
Assets measured at net asset value | 19 |  |  |  |  |  |  |  |  | 23 |  |  |  |  |  |  |
Total OPEB plan assets | $83 |  |  |  |  |  |  |  |  | $83 |  |  |  |  |  |  |
| 2023 |  | 2022
| 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 | 6 |  |  | 6 |  |  | — |  |  | — |  |  | 5 |  |  | 5 |  |  | — |  |  | — |
Fixed income securities | 36 |  |  | 36 |  |  | — |  |  | — |  |  | 34 |  |  | 34 |  |  | — |  |  | — |
Total assets in fair value hierarchy | 43 |  |  | $42 |  |  | $1 |  |  | $— |  |  | 40 |  |  | $39 |  |  | $1 |  |  | $— |
Assets measured at net asset value | 18 |  |  |  |  |  |  |  |  | 18 |  |  |  |  |  |  |
Total OPEB plan assets | $61 |  |  |  |  |  |  |  |  | $58 |  |  |  |  |  |  |
| 2023 |  | 2022
| 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 |  |  | — |  |  | — |  |  | 1 |  |  | 1 |  |  | — |  |  | — |
Fixed income securities | 11 |  |  | 11 |  |  | — |  |  | — |  |  | 13 |  |  | 13 |  |  | — |  |  | — |
Total OPEB plan assets | $14 |  |  | $13 |  |  | $1 |  |  | $— |  |  | $14 |  |  | $14 |  |  | $— |  |  | $— |
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, 2023, the current target ranges and actual allocations for VEBA trusts with assets greater than $5 million and the WPL 401(h) assets were as follows:
| Target Range |  | Actual
| Allocation |  | Allocation
Cash and equivalents | 0% | - | 5% |  | 1%
Equity securities | 0% | - | 55% |  | 36%
Fixed income securities | 40% | - | 100% |  | 63%
At December 31, the fair values of OPEB plan assets were as follows (in millions):
| 2023 |  | 2022
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
Alliant Energy | Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Cash and equivalents | $9 |  |  | $— |  |  | $9 |  |  | $— |  |  | $3 |  |  | $— |  |  | $3 |  |  | $— |
Equity securities | 8 |  |  | 8 |  |  | — |  |  | — |  |  | 9 |  |  | 9 |  |  | — |  |  | — |
Global asset securities | — |  |  | — |  |  | — |  |  | — |  |  | 1 |  |  | 1 |  |  | — |  |  | — |
Fixed income securities | 47 |  |  | 47 |  |  | — |  |  | — |  |  | 47 |  |  | 46 |  |  | 1 |  |  | — |
Total assets in fair value hierarchy | 64 |  |  | $55 |  |  | $9 |  |  | $— |  |  | 60 |  |  | $56 |  |  | $4 |  |  | $— |
Assets measured at net asset value | 19 |  |  |  |  |  |  |  |  | 23 |  |  |  |  |  |  |
Total OPEB plan assets | $83 |  |  |  |  |  |  |  |  | $83 |  |  |  |  |  |  |
| 2023 |  | 2022
| 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 | 6 |  |  | 6 |  |  | — |  |  | — |  |  | 5 |  |  | 5 |  |  | — |  |  | — |
Fixed income securities | 36 |  |  | 36 |  |  | — |  |  | — |  |  | 34 |  |  | 34 |  |  | — |  |  | — |
Total assets in fair value hierarchy | 43 |  |  | $42 |  |  | $1 |  |  | $— |  |  | 40 |  |  | $39 |  |  | $1 |  |  | $— |
Assets measured at net asset value | 18 |  |  |  |  |  |  |  |  | 18 |  |  |  |  |  |  |
Total OPEB plan assets | $61 |  |  |  |  |  |  |  |  | $58 |  |  |  |  |  |  |
| 2023 |  | 2022
| 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 |  |  | — |  |  | — |  |  | 1 |  |  | 1 |  |  | — |  |  | — |
Fixed income securities | 11 |  |  | 11 |  |  | — |  |  | — |  |  | 13 |  |  | 13 |  |  | — |  |  | — |
Total OPEB plan assets | $14 |  |  | $13 |  |  | $1 |  |  | $— |  |  | $14 |  |  | $14 |  |  | $— |  |  | $— |
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
| 2023 |  | 2022 |  | 2021 |  | 2023 |  | 2022 |  | 2021 |  | 2023 |  | 2022 |  | 2021
401(k) costs | $30 |  |  | $28 |  |  | $26 |  |  | $14 |  |  | $13 |  |  | $13 |  |  | $14 |  |  | $13 |  |  | $12 |
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
| 2023 |  | 2022 |  | 2021 |  | 2023 |  | 2022 |  | 2021 |  | 2023 |  | 2022 |  | 2021
401(k) costs | $30 |  |  | $28 |  |  | $26 |  |  | $14 |  |  | $13 |  |  | $13 |  |  | $14 |  |  | $13 |  |  | $12 |
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
| 2023 |  | 2022 |  | 2021 |  | 2023 |  | 2022 |  | 2021 |  | 2023 |  | 2022 |  | 2021
401(k) costs | $30 |  |  | $28 |  |  | $26 |  |  | $14 |  |  | $13 |  |  | $13 |  |  | $14 |  |  | $13 |  |  | $12 |
Performance Shares Equity Awards [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:
| 2023 |  | 2022 |  | 2021
| 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 | 190,273 |  | $54.13 |  | 196,429 |  | $51.59 |  | 129,156 |  | $54.63
Granted | 108,712 |  | 55.68 |  | 74,106 |  | 54.45 |  | 73,112 |  | 46.19
Vested | (53,431) |  | 64.04 |  | (71,101) |  | 47.48 |  | — |  | —
Forfeited | (11,600) |  | 53.88 |  | (9,161) |  | 53.99 |  | (5,839) |  | 51.07
Nonvested awards, December 31 | 233,954 |  | 52.60 |  | 190,273 |  | 54.13 |  | 196,429 |  | 51.59
Restricted Stock Units Equity Awards [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:
| 2023 |  | 2022 |  | 2021
| Units |  | Weighted Average Grant Date Fair Value |  | Units |  | Weighted Average Grant Date Fair Value |  | Units |  | Weighted Average Grant Date Fair Value
Nonvested units, January 1 | 198,275 |  | $54.53 |  | 217,819 |  | $50.54 |  | 146,549 |  | $51.54
Granted | 106,124 |  | 52.77 |  | 77,122 |  | 56.88 |  | 80,152 |  | 48.65
Vested | (55,345) |  | 59.40 |  | (82,770) |  | 46.08 |  | — |  | —
Forfeited | (14,795) |  | 54.53 |  | (13,896) |  | 55.53 |  | (8,882) |  | 49.84
Nonvested units, December 31 | 234,259 |  | 52.58 |  | 198,275 |  | 54.53 |  | 217,819 |  | 50.54
Performance Restricted Stock Units Equity Awards [Member] |
Defined Benefit Plan Disclosure [Line Items] |
Schedule Of Equity-based Compensation Plans Activity | A summary of the performance restricted stock units activity, with amounts representing the target number of units, was as follows:
| 2023 |  | 2022 |  | 2021
| Units |  | Weighted Average Grant Date Fair Value |  | Units |  | Weighted Average Grant Date Fair Value |  | Units |  | Weighted Average Grant Date Fair Value
Nonvested units, January 1 | 199,874 |  | $54.74 |  | 196,429 |  | $50.74 |  | 197,463 |  | $47.31
Granted | 124,217 |  | 52.71 |  | 84,670 |  | 57.01 |  | 73,112 |  | 48.66
Vested | (53,431) |  | 59.36 |  | (71,101) |  | 46.24 |  | (68,307) |  | 38.60
Forfeited | (13,021) |  | 55.47 |  | (10,124) |  | 55.92 |  | (5,839) |  | 50.46
Nonvested units, December 31 | 257,639 |  | 52.76 |  | 199,874 |  | 54.74 |  | 196,429 |  | 50.74

X
- Definition Schedule of carrying value and fair market value of the deferred compensation obligation table text block + References No definition available. + Details
Name: | lnt_ScheduleOfCarryingValueAndFairMarketValueOfDeferredCompensationObligationTableTextBlock
Namespace Prefix: | lnt_
Data Type: | dtr-types1:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Schedule Of Define Benefit Plan Recognized In Regulatory Assets [Table Text Block] + References No definition available. + Details
Name: | lnt_ScheduleOfDefineBenefitPlanRecognizedInRegulatoryAssetsTableTextBlock
Namespace Prefix: | lnt_
Data Type: | dtr-types1:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Schedule of estimated future employer contributions table text block + References No definition available. + Details
Name: | lnt_ScheduleOfEstimatedFutureEmployerContributionsTableTextBlock
Namespace Prefix: | lnt_
Data Type: | dtr-types1:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_DefinedBenefitPlanDisclosureLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of share-based payment arrangement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 50 -Paragraph 1 -SubTopic 10 -Topic 718 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480429/718-10-50-1 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480429/718-10-50-2 + Details
Name: | us-gaap_DisclosureOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTextBlock
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of benefit obligation and plan assets of defined benefit plan with accumulated benefit obligation in excess of plan assets. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 17 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480482/715-20-55-17 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-3 Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-3 + Details
Name: | us-gaap_ScheduleOfAccumulatedBenefitObligationsInExcessOfFairValueOfPlanAssetsTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of the major categories of plan assets of pension plans and/or other employee benefit plans. This information may include, but is not limited to, the target allocation of plan assets, the fair value of each major category of plan assets, and the level within the fair value hierarchy in which the fair value measurements fall. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 715 -SubTopic 20 -Subparagraph (d)(5) -Name Accounting Standards Codification -Paragraph 1 -Section 50 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
Name: | us-gaap_ScheduleOfAllocationOfPlanAssetsTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of assumption used to determine benefit obligation and net periodic benefit cost of defined benefit plan. Includes, but is not limited to, discount rate, rate of compensation increase, expected long-term rate of return on plan assets and interest crediting rate. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (k) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
Name: | us-gaap_ScheduleOfAssumptionsUsedTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of the costs related to the various types of retirement plans including defined benefit pension plan cost, defined contribution plan cost, other postretirement benefit plan cost, and net periodic benefit cost. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 50 -Paragraph 1 -SubTopic 20 -Topic 715 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
Name: | us-gaap_ScheduleOfCostsOfRetirementPlansTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of allocation of amount expensed and capitalized for award under share-based payment arrangement to statement of income or comprehensive income and statement of financial position. Includes, but is not limited to, corresponding line item in financial statement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480429/718-10-50-2 + Details
Name: | us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTextBlock
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of benefits expected to be paid by pension plans and/or other employee benefit plans in each of the next five fiscal years and in the aggregate for the five fiscal years thereafter. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 715 -SubTopic 20 -Subparagraph (f) -Name Accounting Standards Codification -Paragraph 1 -Section 50 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
Name: | us-gaap_ScheduleOfExpectedBenefitPaymentsTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of the components of net benefit costs for pension plans and/or other employee benefit plans including service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) recognized due to settlements or curtailments. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 715 -SubTopic 20 -Subparagraph (h) -Name Accounting Standards Codification -Paragraph 1 -Section 50 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
Name: | us-gaap_ScheduleOfNetBenefitCostsTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Definition Tabular disclosure of net funded status of pension plans and/or other employee benefit plans. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 + Details
Name: | us-gaap_ScheduleOfNetFundedStatusTableTextBlock
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:textBlockItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | dei_LegalEntityAxis=lnt_IplMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=lnt_WplMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RetirementPlanTypeAxis=us-gaap_PensionPlansDefinedBenefitMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RetirementPlanTypeAxis=us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RetirementPlanTypeAxis=us-gaap_OtherPensionPlansPostretirementOrSupplementalPlansDefinedBenefitMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_AwardTypeAxis=us-gaap_PerformanceSharesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_AwardTypeAxis=us-gaap_RestrictedStockUnitsRSUMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_AwardTypeAxis=lnt_PerformanceRestrictedStockUnitMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |