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Benefit Plans | 12 Months Ended
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Dec. 31, 2023
Benefit Plans | BENEFIT PLANS(a) Pension and Other Postretirement Benefits Plans - Retirement benefits are provided to substantially all employees through various qualified and non-qualified non-contributory defined benefit pension plans (currently closed to new hires), and/or through defined contribution plans (including 401(k) savings plans). Benefits of the non-contributory defined benefit pension plans are based on the plan participant’s years of service, age and compensation. Benefits of the defined contribution plans are based on the plan participant’s years of service, age, compensation and contributions. Certain defined benefit postretirement health care and life benefits are provided to eligible retirees. In general, the retiree health care plans consist of fixed benefit subsidy structures and the retiree life insurance plans are non-contributory. IPL and WPL account for their participation in Alliant Energy and Corporate Services sponsored plans as multiple-employer plans. For IPL and WPL, amounts below represent the amounts for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans. Assumptions - 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
Expected rate of return on plan assets - The expected rate of return on plan assets is based on projected asset class returns using target allocations. A forward-looking building blocks approach is used, and historical returns, survey information and capital market information are analyzed to support the expected rate of return on plan assets assumption. Refer to “Investment Strategy for Plan Assets” below for additional information related to investment strategy and mix of assets for the pension and OPEB plans. Life Expectancy - The life expectancy assumption is used in determining the benefit obligation and net periodic benefit cost for defined benefit pension and OPEB plans. This assumption utilizes base mortality tables that were released in 2019 by the Society of Actuaries and mortality projection tables that were released in 2021 by the Society of Actuaries. 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. Benefit Plan Assets and Obligations - 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 |
In 2023, actuarial losses related to benefit obligations for defined benefit pension plans were primarily due to decreases in the discount rates. In 2022, actuarial gains related to benefit obligations for defined benefit pension and OPEB plans were primarily due to increases in the discount rates. 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
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 and Benefit Payments - 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 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
Investment Strategy for Plan Assets - Investment strategies for defined benefit pension and OPEB plan assets combine preservation of principal and prudent risk-taking to protect the integrity of plan assets, in order to meet the obligations to plan participants while minimizing benefit costs over the long term. Investment risk of plan assets is mitigated through diversification, including equity, fixed income and global asset strategies. Global asset strategies may include investments in global equity, global debt and currencies. Defined Benefit Pension Plan Assets - The asset mix of defined benefit pension plans is governed by allocation targets. The asset allocation is monitored regularly, and appropriate steps are taken as needed to rebalance the assets within the prescribed ranges. An overlay management service is also used to help maintain target allocations and meet liquidity needs. The overlay manager is authorized to use derivative financial instruments to facilitate this service. For separately managed accounts, prohibited investments include, but are not limited to, direct ownership of real estate, oil and gas limited partnerships, securities of the managers’ firms or affiliate firms, and Alliant Energy securities. The allocations shown below exclude market exposure obtained through the overlay management service. 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%
Other Postretirement Benefits Plan Assets - OPEB plan assets are comprised of specific assets within certain defined benefit pension plans (401(h) assets) as well as assets held in VEBA trusts. For VEBA trusts with assets greater than $5 million and the WPL 401(h) assets, the mix among asset classes is governed by allocation targets. The asset allocation is monitored regularly, and appropriate steps are taken as needed to rebalance the assets within the prescribed ranges. 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%
Fair Value Measurements - Fair value measurement accounting establishes three levels of fair value hierarchy that prioritize the inputs to valuation techniques used to measure fair value. Refer to Note 16 for discussion of levels within the fair value hierarchy. Level 1 items include investments in securities held in registered investment companies and directly held equity securities, which are valued at the closing price reported in the active market in which the securities are traded. Level 2 items include cash and equivalents and fixed income securities. Cash and equivalents include money market fund investments and cash collateral supporting derivative financial instruments. Fixed income securities include corporate and government bonds, which are valued at the closing price reported in the active market for similar assets in which the individual securities are traded or based on yields currently available on comparable securities of issuers with similar credit ratings. Certain investments that are measured at fair value using the net asset value practical expedient have not been classified in the fair value hierarchy. These fair value amounts are included below to reconcile the fair value hierarchy to the respective total plan assets. 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 |  |  |  |  |  |  |
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 |  |  | $— |  |  | $— |
For the various defined benefit pension and OPEB plans, Alliant Energy common stock represented less than 1% of assets directly held in the plans at December 31, 2023 and 2022. 401(k) Savings Plans - A significant number of employees participate in defined contribution retirement plans (401(k) savings plans). Alliant Energy common stock directly held by participants represented 8% and 10% of total assets in the 401(k) savings plans at December 31, 2023 and 2022, respectively. 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 |
(b) Equity-based Compensation Plans - In 2020, Alliant Energy’s shareowners approved the 2020 OIP, which permits the grant of shares of Alliant Energy common stock, restricted stock, restricted stock units, performance shares, performance units, and other stock-based or cash-based awards to key employees. At December 31, 2023, performance shares and restricted stock units (performance- and time-vesting) were outstanding under the 2020 OIP, and 8 million shares of Alliant Energy common stock remained available for grants under the 2020 OIP. Alliant Energy satisfies share payouts related to equity awards through the issuance of new shares of its common stock. Nonvested awards generally do not have non-forfeitable rights to dividends or dividend equivalents when dividends are paid to common shareowners. 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
As of December 31, 2023, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $8 million, $4 million and $3 million, respectively, which is expected to be recognized over a weighted average period of between one year and two years. Share-based compensation expense is recognized on a straight-line basis over the requisite service periods and is recorded in “Other operation and maintenance” in the income statements. As of December 31, 2023, 429,804 shares were included in the calculation of diluted EPS related to the nonvested equity awards. Performance Shares - Equity Awards - Payouts of performance shares are contingent upon achievement over a three-year period of specified performance criteria, which currently is total shareowner return relative to an investor-owned utility peer group. Performance shares grants are to be paid out in shares of Alliant Energy common stock and are accounted for as equity awards. The fair value of each of these performance shares is based on the fair value of the underlying common stock on the grant date and the probability of satisfying the market condition contained in the agreement during a three-year performance period. The actual number of these performance shares that will be paid out upon vesting is dependent upon actual performance and may range from zero to 200% of the target number of shares. If minimum performance targets are not met during the performance period, these performance shares are forfeited. Compensation expense is recorded ratably over the performance period based on the fair value of the awards at the grant date. 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 - Payouts of restricted stock units are based on the expiration of a three-year time-vesting period. Restricted stock unit grants are to be paid out in shares of Alliant Energy common stock and are accounted for as equity awards. The fair value of each of these restricted stock units is based on the closing market price of one share of Alliant Energy common stock on the grant date of the award. Compensation expense is recorded ratably over the performance period based on the fair value of the awards on the grant date. 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 - Payouts of performance restricted stock units are based upon achievement of certain performance targets during a three-year performance period, which currently includes specified growth of consolidated net income from continuing operations, as well as a diversity metric for the 2022 and 2023 grants. The actual number of units that will be paid out upon vesting is dependent upon actual performance and may range from zero to 200% of the target number of units under each award type. If minimum performance targets are not met during the performance period, these units are forfeited. Performance restricted stock units are to be paid out in shares and are accounted for as equity awards. The fair value of each performance restricted stock unit is based on the closing market price of one share of Alliant Energy common stock on the grant date of the award. Compensation expense is recorded ratably over the performance period based on a probability assessment of payouts for the awards at each reporting period. 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
(c) Deferred Compensation Plan - Alliant Energy maintains a DCP under which certain key employees may defer up to 100% of base salary and short-term cash incentive compensation and members of its Board of Directors may elect to defer all or part of their retainer and committee fees. Key employees who have made the maximum allowed contribution to the Alliant Energy 401(k) Savings Plan may receive an additional credit to the DCP. Key employees and Board of Directors members may elect to have their deferrals credited to a company stock account, an interest account, equity accounts or mutual fund accounts based on certain benchmark funds. Company Stock Account - The DCP does not permit diversification of deferrals credited to the company stock account and all distributions from participants’ company stock accounts are made in the form of shares of Alliant Energy common stock. The deferred compensation obligations for participants’ company stock accounts are recorded in “Additional paid-in capital” and the shares of Alliant Energy common stock held in a rabbi trust to satisfy this obligation are recorded in “Shares in deferred compensation trust” on Alliant Energy’s balance sheets. 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
Interest, Equity and Mutual Fund Accounts - Distributions from participants’ interest, equity and mutual fund accounts are in the form of cash payments. The deferred compensation obligations for participants’ interest, equity and mutual fund accounts are recorded in “Pension and other benefit obligations” on the balance sheets. At December 31, 2023 and 2022, the carrying value of Alliant Energy’s deferred compensation obligations for participants’ interest, equity and mutual fund accounts, which approximates fair market value, was $21 million and $19 million, respectively.
IPL [Member] |
Benefit Plans | BENEFIT PLANS(a) Pension and Other Postretirement Benefits Plans - Retirement benefits are provided to substantially all employees through various qualified and non-qualified non-contributory defined benefit pension plans (currently closed to new hires), and/or through defined contribution plans (including 401(k) savings plans). Benefits of the non-contributory defined benefit pension plans are based on the plan participant’s years of service, age and compensation. Benefits of the defined contribution plans are based on the plan participant’s years of service, age, compensation and contributions. Certain defined benefit postretirement health care and life benefits are provided to eligible retirees. In general, the retiree health care plans consist of fixed benefit subsidy structures and the retiree life insurance plans are non-contributory. IPL and WPL account for their participation in Alliant Energy and Corporate Services sponsored plans as multiple-employer plans. For IPL and WPL, amounts below represent the amounts for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans. Assumptions - 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
Expected rate of return on plan assets - The expected rate of return on plan assets is based on projected asset class returns using target allocations. A forward-looking building blocks approach is used, and historical returns, survey information and capital market information are analyzed to support the expected rate of return on plan assets assumption. Refer to “Investment Strategy for Plan Assets” below for additional information related to investment strategy and mix of assets for the pension and OPEB plans. Life Expectancy - The life expectancy assumption is used in determining the benefit obligation and net periodic benefit cost for defined benefit pension and OPEB plans. This assumption utilizes base mortality tables that were released in 2019 by the Society of Actuaries and mortality projection tables that were released in 2021 by the Society of Actuaries. 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. Benefit Plan Assets and Obligations - 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 |
In 2023, actuarial losses related to benefit obligations for defined benefit pension plans were primarily due to decreases in the discount rates. In 2022, actuarial gains related to benefit obligations for defined benefit pension and OPEB plans were primarily due to increases in the discount rates. 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
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 and Benefit Payments - 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 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
Investment Strategy for Plan Assets - Investment strategies for defined benefit pension and OPEB plan assets combine preservation of principal and prudent risk-taking to protect the integrity of plan assets, in order to meet the obligations to plan participants while minimizing benefit costs over the long term. Investment risk of plan assets is mitigated through diversification, including equity, fixed income and global asset strategies. Global asset strategies may include investments in global equity, global debt and currencies. Defined Benefit Pension Plan Assets - The asset mix of defined benefit pension plans is governed by allocation targets. The asset allocation is monitored regularly, and appropriate steps are taken as needed to rebalance the assets within the prescribed ranges. An overlay management service is also used to help maintain target allocations and meet liquidity needs. The overlay manager is authorized to use derivative financial instruments to facilitate this service. For separately managed accounts, prohibited investments include, but are not limited to, direct ownership of real estate, oil and gas limited partnerships, securities of the managers’ firms or affiliate firms, and Alliant Energy securities. The allocations shown below exclude market exposure obtained through the overlay management service. 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%
Other Postretirement Benefits Plan Assets - OPEB plan assets are comprised of specific assets within certain defined benefit pension plans (401(h) assets) as well as assets held in VEBA trusts. For VEBA trusts with assets greater than $5 million and the WPL 401(h) assets, the mix among asset classes is governed by allocation targets. The asset allocation is monitored regularly, and appropriate steps are taken as needed to rebalance the assets within the prescribed ranges. 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%
Fair Value Measurements - Fair value measurement accounting establishes three levels of fair value hierarchy that prioritize the inputs to valuation techniques used to measure fair value. Refer to Note 16 for discussion of levels within the fair value hierarchy. Level 1 items include investments in securities held in registered investment companies and directly held equity securities, which are valued at the closing price reported in the active market in which the securities are traded. Level 2 items include cash and equivalents and fixed income securities. Cash and equivalents include money market fund investments and cash collateral supporting derivative financial instruments. Fixed income securities include corporate and government bonds, which are valued at the closing price reported in the active market for similar assets in which the individual securities are traded or based on yields currently available on comparable securities of issuers with similar credit ratings. Certain investments that are measured at fair value using the net asset value practical expedient have not been classified in the fair value hierarchy. These fair value amounts are included below to reconcile the fair value hierarchy to the respective total plan assets. 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 |  |  |  |  |  |  |
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 |  |  | $— |  |  | $— |
For the various defined benefit pension and OPEB plans, Alliant Energy common stock represented less than 1% of assets directly held in the plans at December 31, 2023 and 2022. 401(k) Savings Plans - A significant number of employees participate in defined contribution retirement plans (401(k) savings plans). Alliant Energy common stock directly held by participants represented 8% and 10% of total assets in the 401(k) savings plans at December 31, 2023 and 2022, respectively. 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 |
(b) Equity-based Compensation Plans - In 2020, Alliant Energy’s shareowners approved the 2020 OIP, which permits the grant of shares of Alliant Energy common stock, restricted stock, restricted stock units, performance shares, performance units, and other stock-based or cash-based awards to key employees. At December 31, 2023, performance shares and restricted stock units (performance- and time-vesting) were outstanding under the 2020 OIP, and 8 million shares of Alliant Energy common stock remained available for grants under the 2020 OIP. Alliant Energy satisfies share payouts related to equity awards through the issuance of new shares of its common stock. Nonvested awards generally do not have non-forfeitable rights to dividends or dividend equivalents when dividends are paid to common shareowners. 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
As of December 31, 2023, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $8 million, $4 million and $3 million, respectively, which is expected to be recognized over a weighted average period of between one year and two years. Share-based compensation expense is recognized on a straight-line basis over the requisite service periods and is recorded in “Other operation and maintenance” in the income statements. As of December 31, 2023, 429,804 shares were included in the calculation of diluted EPS related to the nonvested equity awards. Performance Shares - Equity Awards - Payouts of performance shares are contingent upon achievement over a three-year period of specified performance criteria, which currently is total shareowner return relative to an investor-owned utility peer group. Performance shares grants are to be paid out in shares of Alliant Energy common stock and are accounted for as equity awards. The fair value of each of these performance shares is based on the fair value of the underlying common stock on the grant date and the probability of satisfying the market condition contained in the agreement during a three-year performance period. The actual number of these performance shares that will be paid out upon vesting is dependent upon actual performance and may range from zero to 200% of the target number of shares. If minimum performance targets are not met during the performance period, these performance shares are forfeited. Compensation expense is recorded ratably over the performance period based on the fair value of the awards at the grant date. 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 - Payouts of restricted stock units are based on the expiration of a three-year time-vesting period. Restricted stock unit grants are to be paid out in shares of Alliant Energy common stock and are accounted for as equity awards. The fair value of each of these restricted stock units is based on the closing market price of one share of Alliant Energy common stock on the grant date of the award. Compensation expense is recorded ratably over the performance period based on the fair value of the awards on the grant date. 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 - Payouts of performance restricted stock units are based upon achievement of certain performance targets during a three-year performance period, which currently includes specified growth of consolidated net income from continuing operations, as well as a diversity metric for the 2022 and 2023 grants. The actual number of units that will be paid out upon vesting is dependent upon actual performance and may range from zero to 200% of the target number of units under each award type. If minimum performance targets are not met during the performance period, these units are forfeited. Performance restricted stock units are to be paid out in shares and are accounted for as equity awards. The fair value of each performance restricted stock unit is based on the closing market price of one share of Alliant Energy common stock on the grant date of the award. Compensation expense is recorded ratably over the performance period based on a probability assessment of payouts for the awards at each reporting period. 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
WPL [Member] |
Benefit Plans | BENEFIT PLANS(a) Pension and Other Postretirement Benefits Plans - Retirement benefits are provided to substantially all employees through various qualified and non-qualified non-contributory defined benefit pension plans (currently closed to new hires), and/or through defined contribution plans (including 401(k) savings plans). Benefits of the non-contributory defined benefit pension plans are based on the plan participant’s years of service, age and compensation. Benefits of the defined contribution plans are based on the plan participant’s years of service, age, compensation and contributions. Certain defined benefit postretirement health care and life benefits are provided to eligible retirees. In general, the retiree health care plans consist of fixed benefit subsidy structures and the retiree life insurance plans are non-contributory. IPL and WPL account for their participation in Alliant Energy and Corporate Services sponsored plans as multiple-employer plans. For IPL and WPL, amounts below represent the amounts for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans. Assumptions - 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
Expected rate of return on plan assets - The expected rate of return on plan assets is based on projected asset class returns using target allocations. A forward-looking building blocks approach is used, and historical returns, survey information and capital market information are analyzed to support the expected rate of return on plan assets assumption. Refer to “Investment Strategy for Plan Assets” below for additional information related to investment strategy and mix of assets for the pension and OPEB plans. Life Expectancy - The life expectancy assumption is used in determining the benefit obligation and net periodic benefit cost for defined benefit pension and OPEB plans. This assumption utilizes base mortality tables that were released in 2019 by the Society of Actuaries and mortality projection tables that were released in 2021 by the Society of Actuaries. 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. Benefit Plan Assets and Obligations - 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 |
In 2023, actuarial losses related to benefit obligations for defined benefit pension plans were primarily due to decreases in the discount rates. In 2022, actuarial gains related to benefit obligations for defined benefit pension and OPEB plans were primarily due to increases in the discount rates. 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
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 and Benefit Payments - 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 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
Investment Strategy for Plan Assets - Investment strategies for defined benefit pension and OPEB plan assets combine preservation of principal and prudent risk-taking to protect the integrity of plan assets, in order to meet the obligations to plan participants while minimizing benefit costs over the long term. Investment risk of plan assets is mitigated through diversification, including equity, fixed income and global asset strategies. Global asset strategies may include investments in global equity, global debt and currencies. Defined Benefit Pension Plan Assets - The asset mix of defined benefit pension plans is governed by allocation targets. The asset allocation is monitored regularly, and appropriate steps are taken as needed to rebalance the assets within the prescribed ranges. An overlay management service is also used to help maintain target allocations and meet liquidity needs. The overlay manager is authorized to use derivative financial instruments to facilitate this service. For separately managed accounts, prohibited investments include, but are not limited to, direct ownership of real estate, oil and gas limited partnerships, securities of the managers’ firms or affiliate firms, and Alliant Energy securities. The allocations shown below exclude market exposure obtained through the overlay management service. 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%
Other Postretirement Benefits Plan Assets - OPEB plan assets are comprised of specific assets within certain defined benefit pension plans (401(h) assets) as well as assets held in VEBA trusts. For VEBA trusts with assets greater than $5 million and the WPL 401(h) assets, the mix among asset classes is governed by allocation targets. The asset allocation is monitored regularly, and appropriate steps are taken as needed to rebalance the assets within the prescribed ranges. 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%
Fair Value Measurements - Fair value measurement accounting establishes three levels of fair value hierarchy that prioritize the inputs to valuation techniques used to measure fair value. Refer to Note 16 for discussion of levels within the fair value hierarchy. Level 1 items include investments in securities held in registered investment companies and directly held equity securities, which are valued at the closing price reported in the active market in which the securities are traded. Level 2 items include cash and equivalents and fixed income securities. Cash and equivalents include money market fund investments and cash collateral supporting derivative financial instruments. Fixed income securities include corporate and government bonds, which are valued at the closing price reported in the active market for similar assets in which the individual securities are traded or based on yields currently available on comparable securities of issuers with similar credit ratings. Certain investments that are measured at fair value using the net asset value practical expedient have not been classified in the fair value hierarchy. These fair value amounts are included below to reconcile the fair value hierarchy to the respective total plan assets. 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 |  |  |  |  |  |  |
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 |  |  | $— |  |  | $— |
For the various defined benefit pension and OPEB plans, Alliant Energy common stock represented less than 1% of assets directly held in the plans at December 31, 2023 and 2022. 401(k) Savings Plans - A significant number of employees participate in defined contribution retirement plans (401(k) savings plans). Alliant Energy common stock directly held by participants represented 8% and 10% of total assets in the 401(k) savings plans at December 31, 2023 and 2022, respectively. 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 |
(b) Equity-based Compensation Plans - In 2020, Alliant Energy’s shareowners approved the 2020 OIP, which permits the grant of shares of Alliant Energy common stock, restricted stock, restricted stock units, performance shares, performance units, and other stock-based or cash-based awards to key employees. At December 31, 2023, performance shares and restricted stock units (performance- and time-vesting) were outstanding under the 2020 OIP, and 8 million shares of Alliant Energy common stock remained available for grants under the 2020 OIP. Alliant Energy satisfies share payouts related to equity awards through the issuance of new shares of its common stock. Nonvested awards generally do not have non-forfeitable rights to dividends or dividend equivalents when dividends are paid to common shareowners. 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
As of December 31, 2023, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $8 million, $4 million and $3 million, respectively, which is expected to be recognized over a weighted average period of between one year and two years. Share-based compensation expense is recognized on a straight-line basis over the requisite service periods and is recorded in “Other operation and maintenance” in the income statements. As of December 31, 2023, 429,804 shares were included in the calculation of diluted EPS related to the nonvested equity awards. Performance Shares - Equity Awards - Payouts of performance shares are contingent upon achievement over a three-year period of specified performance criteria, which currently is total shareowner return relative to an investor-owned utility peer group. Performance shares grants are to be paid out in shares of Alliant Energy common stock and are accounted for as equity awards. The fair value of each of these performance shares is based on the fair value of the underlying common stock on the grant date and the probability of satisfying the market condition contained in the agreement during a three-year performance period. The actual number of these performance shares that will be paid out upon vesting is dependent upon actual performance and may range from zero to 200% of the target number of shares. If minimum performance targets are not met during the performance period, these performance shares are forfeited. Compensation expense is recorded ratably over the performance period based on the fair value of the awards at the grant date. 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 - Payouts of restricted stock units are based on the expiration of a three-year time-vesting period. Restricted stock unit grants are to be paid out in shares of Alliant Energy common stock and are accounted for as equity awards. The fair value of each of these restricted stock units is based on the closing market price of one share of Alliant Energy common stock on the grant date of the award. Compensation expense is recorded ratably over the performance period based on the fair value of the awards on the grant date. 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 - Payouts of performance restricted stock units are based upon achievement of certain performance targets during a three-year performance period, which currently includes specified growth of consolidated net income from continuing operations, as well as a diversity metric for the 2022 and 2023 grants. The actual number of units that will be paid out upon vesting is dependent upon actual performance and may range from zero to 200% of the target number of units under each award type. If minimum performance targets are not met during the performance period, these units are forfeited. Performance restricted stock units are to be paid out in shares and are accounted for as equity awards. The fair value of each performance restricted stock unit is based on the closing market price of one share of Alliant Energy common stock on the grant date of the award. Compensation expense is recorded ratably over the performance period based on a probability assessment of payouts for the awards at each reporting period. 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

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