Benefit Plans (Tables)

12 Months Ended

Dec. 31, 2024

Defined Benefit Plan Disclosure [Line Items]

Assumptions Used To Measure Benefit Plans

The weighted-average assumptions for defined benefit pension and OPEB plans at the measurement date of December 31 were as follows:

	Defined Benefit Pension Plans									OPEB Plans
Alliant Energy	2024			2023			2022			2024	2023	2022
Discount rate for benefit obligations	5.65%			5.36%			5.54%			5.62%	5.40%	5.53%
Discount rate for net periodic cost	5.36%			5.54%			2.91%			5.40%	5.53%	2.81%
Expected rate of return on plan assets	7.73%			7.80%			7.80%			6.22%	6.50%	6.40%
Interest crediting rate for Alliant Energy Cash Balance Pension Plan	6.24%			10.75%			9.22%			N/A	N/A	N/A
Rate of compensation increase	3.50%	-	4.50%	3.30%	-	4.50%	3.30%	-	4.50%	N/A	N/A	N/A

	Qualified Defined Benefit Pension Plan			OPEB Plans
IPL	2024	2023	2022	2024	2023	2022
Discount rate for benefit obligations	5.66%	5.35%	5.55%	5.61%	5.40%	5.53%
Discount rate for net periodic cost	5.35%	5.55%	2.94%	5.40%	5.53%	2.80%
Expected rate of return on plan assets	7.60%	7.80%	7.80%	6.60%	6.90%	6.50%
Rate of compensation increase	3.75%	3.30%	3.30%	N/A	N/A	N/A

	Qualified Defined Benefit Pension Plan			OPEB Plans
WPL	2024	2023	2022	2024	2023	2022
Discount rate for benefit obligations	5.66%	5.35%	5.54%	5.61%	5.40%	5.53%
Discount rate for net periodic cost	5.35%	5.54%	2.94%	5.40%	5.53%	2.79%
Expected rate of return on plan assets	7.80%	7.80%	7.80%	5.61%	5.65%	5.49%
Rate of compensation increase	3.50%	3.30%	3.30%	N/A	N/A	N/A

Net Periodic Benefit Costs

The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans are included below (in millions). The service cost component of net periodic benefit costs is included in “Other operation and maintenance” expenses in the income statements and all other components of net periodic benefit costs are included in “Other (income) and deductions” in the income statements or regulatory assets on the balance sheets.

Alliant Energy	Defined Benefit Pension Plans			OPEB Plans
	2024	2023	2022	2024	2023	2022
Service cost	$5	$5	$9	$2	$2	$3
Interest cost	45	47	36	8	9	6
Expected return on plan assets (a)	(55)	(53)	(69)	(5)	(5)	(5)
Amortization of prior service credit (b)	(1)	(1)	(1)	—	—	—
Amortization of actuarial loss (c)	24	28	32	—	1	2
Settlement losses (d)	—	—	26	—	—	—
	$18	$26	$33	$5	$7	$6

IPL	Defined Benefit Pension Plans			OPEB Plans
	2024	2023	2022	2024	2023	2022
Service cost	$3	$3	$6	$1	$1	$1
Interest cost	20	21	16	3	3	2
Expected return on plan assets (a)	(26)	(26)	(31)	(4)	(3)	(4)
Amortization of actuarial loss (c)	9	11	13	—	1	1
Settlement losses (d)	—	—	13	—	—	—
	$6	$9	$17	$—	$2	$—

WPL	Defined Benefit Pension Plans			OPEB Plans
	2024	2023	2022	2024	2023	2022
Service cost	$2	$2	$3	$1	$1	$1
Interest cost	20	20	16	3	3	2
Expected return on plan assets (a)	(23)	(22)	(31)	(1)	(1)	(1)
Amortization of actuarial loss (c)	11	13	15	—	1	2
Settlement losses (d)	—	—	13	—	—	—
	$10	$13	$16	$3	$4	$4

(a)The expected return on plan assets is based on the expected rate of return on plan assets and the fair value approach to the market-related value of plan assets.

(b)Unrecognized prior service credits for the OPEB plans are amortized over the average future service period to full eligibility of the participants of each plan.

(c)Unrecognized net actuarial gains or losses in excess of 10% of the greater of the plans’ benefit obligations or assets are amortized over the average future service lives of plan participants, except for the Alliant Energy Cash Balance Pension Plan where gains or losses outside the 10% threshold are amortized over the time period the participants are expected to receive benefits.

(d)Settlement losses related to payments made to retired executives of Alliant Energy and lump sum payments related to IPL’s and WPL’s qualified defined benefit pension plans. In 2022, the majority of Alliant Energy’s, IPL’s, and WPL’s pension settlement losses were recognized as regulatory assets in accordance with regulatory treatment, and $7 million was included in “Other (income) and deductions” in Alliant Energy’s and IPL’s income statements related to IPL’s qualified defined benefit pension plan.

Funded Status Of Benefit Plans

A reconciliation of the funded status of qualified and non-qualified defined benefit pension and OPEB plans to the amounts recognized on the balance sheets at December 31 was as follows (in millions):

	Defined Benefit Pension Plans		OPEB Plans
Alliant Energy	2024	2023	2024	2023
Change in benefit obligation:
Net benefit obligation at January 1	$876	$875	$160	$168
Service cost	5	5	2	2
Interest cost	45	47	8	9
Plan participants’ contributions	—	—	3	4
Actuarial (gain) loss	(19)	23	(7)	(3)
Gross benefits paid	(66)	(74)	(18)	(20)
Net benefit obligation at December 31	841	876	148	160
Change in plan assets:
Fair value of plan assets at January 1	732	706	83	83
Actual return on plan assets	38	86	5	8
Employer contributions	11	14	7	8
Plan participants’ contributions	—	—	3	4
Gross benefits paid	(66)	(74)	(18)	(20)
Fair value of plan assets at December 31	715	732	80	83
Under funded status at December 31	($126)	($144)	($68)	($77)

	Defined Benefit Pension Plans		OPEB Plans
Alliant Energy	2024	2023	2024	2023
Amounts recognized on the balance sheets consist of:
Non-current assets	$—	$—	$17	$14
Current liabilities	(3)	(2)	(7)	(8)
Pension and other benefit obligations	(123)	(142)	(78)	(83)
Net amounts recognized at December 31	($126)	($144)	($68)	($77)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	$312	$337	$4	$11
Prior service credit	(2)	(2)	—	—
	$310	$335	$4	$11

	Defined Benefit Pension Plans		OPEB Plans
IPL	2024	2023	2024	2023
Change in benefit obligation:
Net benefit obligation at January 1	$387	$389	$65	$68
Service cost	3	3	1	1
Interest cost	20	21	3	3
Plan participants’ contributions	—	—	1	2
Actuarial (gain) loss	(8)	9	(3)	(1)
Gross benefits paid	(30)	(35)	(8)	(8)
Net benefit obligation at December 31	372	387	59	65
Change in plan assets:
Fair value of plan assets at January 1	352	344	61	58
Actual return on plan assets	18	42	4	7
Employer contributions	—	1	1	2
Plan participants’ contributions	—	—	1	2
Gross benefits paid	(30)	(35)	(8)	(8)
Fair value of plan assets at December 31	340	352	59	61
Under funded status at December 31	($32)	($35)	$—	($4)

	Defined Benefit Pension Plans		OPEB Plans
IPL	2024	2023	2024	2023
Amounts recognized on the balance sheets consist of:
Non-current assets	$—	$—	$13	$10
Current liabilities	(1)	—	(1)	(1)
Pension and other benefit obligations	(31)	(35)	(12)	(13)
Net amounts recognized at December 31	($32)	($35)	$—	($4)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	$126	$135	$7	$9
Prior service credit	(1)	(1)	—	—
	$125	$134	$7	$9

	Defined Benefit Pension Plans		OPEB Plans
WPL	2024	2023	2024	2023
Change in benefit obligation:
Net benefit obligation at January 1	$381	$381	$61	$65
Service cost	2	2	1	1
Interest cost	20	20	3	3
Plan participants’ contributions	—	—	1	2
Actuarial (gain) loss	(8)	10	(3)	(2)
Gross benefits paid	(30)	(32)	(7)	(8)
Net benefit obligation at December 31	365	381	56	61
Change in plan assets:
Fair value of plan assets at January 1	306	291	14	14
Actual return on plan assets	17	35	—	1
Employer contributions	10	12	5	5
Plan participants’ contributions	—	—	1	2
Gross benefits paid	(30)	(32)	(7)	(8)
Fair value of plan assets at December 31	303	306	13	14
Under funded status at December 31	($62)	($75)	($43)	($47)

	Defined Benefit Pension Plans		OPEB Plans
WPL	2024	2023	2024	2023
Amounts recognized on the balance sheets consist of:
Non-current assets	$—	$—	$4	$4
Current liabilities	—	—	(6)	(6)
Pension and other benefit obligations	(62)	(75)	(41)	(45)
Net amounts recognized at December 31	($62)	($75)	($43)	($47)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	$135	$148	$—	$3

Accumulated Benefit Obligations

Accumulated benefit obligations, aggregate amounts applicable to defined benefit pension and OPEB plans with accumulated benefit obligations in excess of plan assets, as well as defined benefit pension plans with projected benefit obligations in excess of plan assets as of the December 31 measurement date are as follows (in millions):

	Defined Benefit Pension Plans		OPEB Plans
Alliant Energy	2024	2023	2024	2023
Accumulated benefit obligations	$824	$857	$148	$160
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	824	857	148	160
Fair value of plan assets	715	732	80	83
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	841	876	N/A	N/A
Fair value of plan assets	715	732	N/A	N/A

	Defined Benefit Pension Plans		OPEB Plans
IPL	2024	2023	2024	2023
Accumulated benefit obligations	$362	$377	$59	$65
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	362	377	N/A	65
Fair value of plan assets	340	352	N/A	61
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	372	387	N/A	N/A
Fair value of plan assets	340	352	N/A	N/A

	Defined Benefit Pension Plans		OPEB Plans
WPL	2024	2023	2024	2023
Accumulated benefit obligations	$358	$373	$56	$61
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	358	373	56	61
Fair value of plan assets	303	306	13	14
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	365	381	N/A	N/A
Fair value of plan assets	303	306	N/A	N/A

Regulatory Assets

In addition to the amounts recognized in regulatory assets in the above tables for IPL and WPL, regulatory assets were recognized for amounts associated with Corporate Services employees participating in other Alliant Energy sponsored benefit plans that were allocated to IPL and WPL at December 31 as follows (in millions):

	IPL		WPL
	2024	2023	2024	2023
Regulatory assets	$25	$28	$22	$24

Estimated Future Employer Contributions

Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2025 is as follows (in millions):

	Alliant Energy	IPL	WPL
Defined benefit pension plans (a)	$20	$1	$14
OPEB plans	7	1	6

(a)Alliant Energy sponsors several non-qualified defined benefit pension plans that cover certain current and former key employees of IPL and WPL. Alliant Energy allocates pension costs to IPL and WPL for these plans. In addition, IPL and WPL amounts reflect funding for their non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans.

Expected Benefit Payments

Expected benefit payments for the qualified and non-qualified defined benefit plans, which reflect expected future service, as appropriate, are as follows (in millions):

Alliant Energy	2025	2026	2027	2028	2029	2030 - 2034
Defined benefit pension benefits	$79	$75	$74	$74	$74	$329
OPEB	16	16	15	15	14	62
	$95	$91	$89	$89	$88	$391

IPL	2025	2026	2027	2028	2029	2030 - 2034
Defined benefit pension benefits	$36	$34	$33	$33	$32	$148
OPEB	7	6	6	6	6	24
	$43	$40	$39	$39	$38	$172

WPL	2025	2026	2027	2028	2029	2030 - 2034
Defined benefit pension benefits	$33	$31	$31	$31	$31	$144
OPEB	7	6	6	5	5	23
	$40	$37	$37	$36	$36	$167

Recognized Compensation Expense And Income Tax Benefits

A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards was as follows (in millions):

	Alliant Energy			IPL			WPL
	2024	2023	2022	2024	2023	2022	2024	2023	2022
Compensation expense	$12	$12	$13	$6	$6	$7	$5	$5	$5
Income tax benefits	3	3	3	2	2	2	1	1	1

Schedule of Carrying Value and Fair Market Value of the Deferred Compensation Obligation

At December 31, the carrying value of the deferred compensation obligation for the company stock account and the shares in the deferred compensation trust based on the historical value of the shares of Alliant Energy common stock contributed to the rabbi trust, and the fair market value of the shares held in the rabbi trust, were as follows (in millions):

	2024	2023
Carrying value	$14	$13
Fair market value	22	19

IPL [Member]

Defined Benefit Plan Disclosure [Line Items]

Assumptions Used To Measure Benefit Plans

The weighted-average assumptions for defined benefit pension and OPEB plans at the measurement date of December 31 were as follows:

	Defined Benefit Pension Plans									OPEB Plans
Alliant Energy	2024			2023			2022			2024	2023	2022
Discount rate for benefit obligations	5.65%			5.36%			5.54%			5.62%	5.40%	5.53%
Discount rate for net periodic cost	5.36%			5.54%			2.91%			5.40%	5.53%	2.81%
Expected rate of return on plan assets	7.73%			7.80%			7.80%			6.22%	6.50%	6.40%
Interest crediting rate for Alliant Energy Cash Balance Pension Plan	6.24%			10.75%			9.22%			N/A	N/A	N/A
Rate of compensation increase	3.50%	-	4.50%	3.30%	-	4.50%	3.30%	-	4.50%	N/A	N/A	N/A

	Qualified Defined Benefit Pension Plan			OPEB Plans
IPL	2024	2023	2022	2024	2023	2022
Discount rate for benefit obligations	5.66%	5.35%	5.55%	5.61%	5.40%	5.53%
Discount rate for net periodic cost	5.35%	5.55%	2.94%	5.40%	5.53%	2.80%
Expected rate of return on plan assets	7.60%	7.80%	7.80%	6.60%	6.90%	6.50%
Rate of compensation increase	3.75%	3.30%	3.30%	N/A	N/A	N/A

	Qualified Defined Benefit Pension Plan			OPEB Plans
WPL	2024	2023	2022	2024	2023	2022
Discount rate for benefit obligations	5.66%	5.35%	5.54%	5.61%	5.40%	5.53%
Discount rate for net periodic cost	5.35%	5.54%	2.94%	5.40%	5.53%	2.79%
Expected rate of return on plan assets	7.80%	7.80%	7.80%	5.61%	5.65%	5.49%
Rate of compensation increase	3.50%	3.30%	3.30%	N/A	N/A	N/A

Net Periodic Benefit Costs

The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans are included below (in millions). The service cost component of net periodic benefit costs is included in “Other operation and maintenance” expenses in the income statements and all other components of net periodic benefit costs are included in “Other (income) and deductions” in the income statements or regulatory assets on the balance sheets.

Alliant Energy	Defined Benefit Pension Plans			OPEB Plans
	2024	2023	2022	2024	2023	2022
Service cost	$5	$5	$9	$2	$2	$3
Interest cost	45	47	36	8	9	6
Expected return on plan assets (a)	(55)	(53)	(69)	(5)	(5)	(5)
Amortization of prior service credit (b)	(1)	(1)	(1)	—	—	—
Amortization of actuarial loss (c)	24	28	32	—	1	2
Settlement losses (d)	—	—	26	—	—	—
	$18	$26	$33	$5	$7	$6

IPL	Defined Benefit Pension Plans			OPEB Plans
	2024	2023	2022	2024	2023	2022
Service cost	$3	$3	$6	$1	$1	$1
Interest cost	20	21	16	3	3	2
Expected return on plan assets (a)	(26)	(26)	(31)	(4)	(3)	(4)
Amortization of actuarial loss (c)	9	11	13	—	1	1
Settlement losses (d)	—	—	13	—	—	—
	$6	$9	$17	$—	$2	$—

WPL	Defined Benefit Pension Plans			OPEB Plans
	2024	2023	2022	2024	2023	2022
Service cost	$2	$2	$3	$1	$1	$1
Interest cost	20	20	16	3	3	2
Expected return on plan assets (a)	(23)	(22)	(31)	(1)	(1)	(1)
Amortization of actuarial loss (c)	11	13	15	—	1	2
Settlement losses (d)	—	—	13	—	—	—
	$10	$13	$16	$3	$4	$4

(a)The expected return on plan assets is based on the expected rate of return on plan assets and the fair value approach to the market-related value of plan assets.

(b)Unrecognized prior service credits for the OPEB plans are amortized over the average future service period to full eligibility of the participants of each plan.

(c)Unrecognized net actuarial gains or losses in excess of 10% of the greater of the plans’ benefit obligations or assets are amortized over the average future service lives of plan participants, except for the Alliant Energy Cash Balance Pension Plan where gains or losses outside the 10% threshold are amortized over the time period the participants are expected to receive benefits.

(d)Settlement losses related to payments made to retired executives of Alliant Energy and lump sum payments related to IPL’s and WPL’s qualified defined benefit pension plans. In 2022, the majority of Alliant Energy’s, IPL’s, and WPL’s pension settlement losses were recognized as regulatory assets in accordance with regulatory treatment, and $7 million was included in “Other (income) and deductions” in Alliant Energy’s and IPL’s income statements related to IPL’s qualified defined benefit pension plan.

Funded Status Of Benefit Plans

A reconciliation of the funded status of qualified and non-qualified defined benefit pension and OPEB plans to the amounts recognized on the balance sheets at December 31 was as follows (in millions):

	Defined Benefit Pension Plans		OPEB Plans
Alliant Energy	2024	2023	2024	2023
Change in benefit obligation:
Net benefit obligation at January 1	$876	$875	$160	$168
Service cost	5	5	2	2
Interest cost	45	47	8	9
Plan participants’ contributions	—	—	3	4
Actuarial (gain) loss	(19)	23	(7)	(3)
Gross benefits paid	(66)	(74)	(18)	(20)
Net benefit obligation at December 31	841	876	148	160
Change in plan assets:
Fair value of plan assets at January 1	732	706	83	83
Actual return on plan assets	38	86	5	8
Employer contributions	11	14	7	8
Plan participants’ contributions	—	—	3	4
Gross benefits paid	(66)	(74)	(18)	(20)
Fair value of plan assets at December 31	715	732	80	83
Under funded status at December 31	($126)	($144)	($68)	($77)

	Defined Benefit Pension Plans		OPEB Plans
Alliant Energy	2024	2023	2024	2023
Amounts recognized on the balance sheets consist of:
Non-current assets	$—	$—	$17	$14
Current liabilities	(3)	(2)	(7)	(8)
Pension and other benefit obligations	(123)	(142)	(78)	(83)
Net amounts recognized at December 31	($126)	($144)	($68)	($77)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	$312	$337	$4	$11
Prior service credit	(2)	(2)	—	—
	$310	$335	$4	$11

	Defined Benefit Pension Plans		OPEB Plans
IPL	2024	2023	2024	2023
Change in benefit obligation:
Net benefit obligation at January 1	$387	$389	$65	$68
Service cost	3	3	1	1
Interest cost	20	21	3	3
Plan participants’ contributions	—	—	1	2
Actuarial (gain) loss	(8)	9	(3)	(1)
Gross benefits paid	(30)	(35)	(8)	(8)
Net benefit obligation at December 31	372	387	59	65
Change in plan assets:
Fair value of plan assets at January 1	352	344	61	58
Actual return on plan assets	18	42	4	7
Employer contributions	—	1	1	2
Plan participants’ contributions	—	—	1	2
Gross benefits paid	(30)	(35)	(8)	(8)
Fair value of plan assets at December 31	340	352	59	61
Under funded status at December 31	($32)	($35)	$—	($4)

	Defined Benefit Pension Plans		OPEB Plans
IPL	2024	2023	2024	2023
Amounts recognized on the balance sheets consist of:
Non-current assets	$—	$—	$13	$10
Current liabilities	(1)	—	(1)	(1)
Pension and other benefit obligations	(31)	(35)	(12)	(13)
Net amounts recognized at December 31	($32)	($35)	$—	($4)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	$126	$135	$7	$9
Prior service credit	(1)	(1)	—	—
	$125	$134	$7	$9

	Defined Benefit Pension Plans		OPEB Plans
WPL	2024	2023	2024	2023
Change in benefit obligation:
Net benefit obligation at January 1	$381	$381	$61	$65
Service cost	2	2	1	1
Interest cost	20	20	3	3
Plan participants’ contributions	—	—	1	2
Actuarial (gain) loss	(8)	10	(3)	(2)
Gross benefits paid	(30)	(32)	(7)	(8)
Net benefit obligation at December 31	365	381	56	61
Change in plan assets:
Fair value of plan assets at January 1	306	291	14	14
Actual return on plan assets	17	35	—	1
Employer contributions	10	12	5	5
Plan participants’ contributions	—	—	1	2
Gross benefits paid	(30)	(32)	(7)	(8)
Fair value of plan assets at December 31	303	306	13	14
Under funded status at December 31	($62)	($75)	($43)	($47)

	Defined Benefit Pension Plans		OPEB Plans
WPL	2024	2023	2024	2023
Amounts recognized on the balance sheets consist of:
Non-current assets	$—	$—	$4	$4
Current liabilities	—	—	(6)	(6)
Pension and other benefit obligations	(62)	(75)	(41)	(45)
Net amounts recognized at December 31	($62)	($75)	($43)	($47)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	$135	$148	$—	$3

Accumulated Benefit Obligations

Accumulated benefit obligations, aggregate amounts applicable to defined benefit pension and OPEB plans with accumulated benefit obligations in excess of plan assets, as well as defined benefit pension plans with projected benefit obligations in excess of plan assets as of the December 31 measurement date are as follows (in millions):

	Defined Benefit Pension Plans		OPEB Plans
Alliant Energy	2024	2023	2024	2023
Accumulated benefit obligations	$824	$857	$148	$160
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	824	857	148	160
Fair value of plan assets	715	732	80	83
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	841	876	N/A	N/A
Fair value of plan assets	715	732	N/A	N/A

	Defined Benefit Pension Plans		OPEB Plans
IPL	2024	2023	2024	2023
Accumulated benefit obligations	$362	$377	$59	$65
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	362	377	N/A	65
Fair value of plan assets	340	352	N/A	61
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	372	387	N/A	N/A
Fair value of plan assets	340	352	N/A	N/A

	Defined Benefit Pension Plans		OPEB Plans
WPL	2024	2023	2024	2023
Accumulated benefit obligations	$358	$373	$56	$61
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	358	373	56	61
Fair value of plan assets	303	306	13	14
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	365	381	N/A	N/A
Fair value of plan assets	303	306	N/A	N/A

Regulatory Assets

In addition to the amounts recognized in regulatory assets in the above tables for IPL and WPL, regulatory assets were recognized for amounts associated with Corporate Services employees participating in other Alliant Energy sponsored benefit plans that were allocated to IPL and WPL at December 31 as follows (in millions):

	IPL		WPL
	2024	2023	2024	2023
Regulatory assets	$25	$28	$22	$24

Estimated Future Employer Contributions

Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2025 is as follows (in millions):

	Alliant Energy	IPL	WPL
Defined benefit pension plans (a)	$20	$1	$14
OPEB plans	7	1	6

(a)Alliant Energy sponsors several non-qualified defined benefit pension plans that cover certain current and former key employees of IPL and WPL. Alliant Energy allocates pension costs to IPL and WPL for these plans. In addition, IPL and WPL amounts reflect funding for their non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans.

Expected Benefit Payments

Expected benefit payments for the qualified and non-qualified defined benefit plans, which reflect expected future service, as appropriate, are as follows (in millions):

Alliant Energy	2025	2026	2027	2028	2029	2030 - 2034
Defined benefit pension benefits	$79	$75	$74	$74	$74	$329
OPEB	16	16	15	15	14	62
	$95	$91	$89	$89	$88	$391

IPL	2025	2026	2027	2028	2029	2030 - 2034
Defined benefit pension benefits	$36	$34	$33	$33	$32	$148
OPEB	7	6	6	6	6	24
	$43	$40	$39	$39	$38	$172

WPL	2025	2026	2027	2028	2029	2030 - 2034
Defined benefit pension benefits	$33	$31	$31	$31	$31	$144
OPEB	7	6	6	5	5	23
	$40	$37	$37	$36	$36	$167

Recognized Compensation Expense And Income Tax Benefits

A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards was as follows (in millions):

	Alliant Energy			IPL			WPL
	2024	2023	2022	2024	2023	2022	2024	2023	2022
Compensation expense	$12	$12	$13	$6	$6	$7	$5	$5	$5
Income tax benefits	3	3	3	2	2	2	1	1	1

WPL [Member]

Defined Benefit Plan Disclosure [Line Items]

Assumptions Used To Measure Benefit Plans

The weighted-average assumptions for defined benefit pension and OPEB plans at the measurement date of December 31 were as follows:

	Defined Benefit Pension Plans									OPEB Plans
Alliant Energy	2024			2023			2022			2024	2023	2022
Discount rate for benefit obligations	5.65%			5.36%			5.54%			5.62%	5.40%	5.53%
Discount rate for net periodic cost	5.36%			5.54%			2.91%			5.40%	5.53%	2.81%
Expected rate of return on plan assets	7.73%			7.80%			7.80%			6.22%	6.50%	6.40%
Interest crediting rate for Alliant Energy Cash Balance Pension Plan	6.24%			10.75%			9.22%			N/A	N/A	N/A
Rate of compensation increase	3.50%	-	4.50%	3.30%	-	4.50%	3.30%	-	4.50%	N/A	N/A	N/A

	Qualified Defined Benefit Pension Plan			OPEB Plans
IPL	2024	2023	2022	2024	2023	2022
Discount rate for benefit obligations	5.66%	5.35%	5.55%	5.61%	5.40%	5.53%
Discount rate for net periodic cost	5.35%	5.55%	2.94%	5.40%	5.53%	2.80%
Expected rate of return on plan assets	7.60%	7.80%	7.80%	6.60%	6.90%	6.50%
Rate of compensation increase	3.75%	3.30%	3.30%	N/A	N/A	N/A

	Qualified Defined Benefit Pension Plan			OPEB Plans
WPL	2024	2023	2022	2024	2023	2022
Discount rate for benefit obligations	5.66%	5.35%	5.54%	5.61%	5.40%	5.53%
Discount rate for net periodic cost	5.35%	5.54%	2.94%	5.40%	5.53%	2.79%
Expected rate of return on plan assets	7.80%	7.80%	7.80%	5.61%	5.65%	5.49%
Rate of compensation increase	3.50%	3.30%	3.30%	N/A	N/A	N/A

Net Periodic Benefit Costs

The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans are included below (in millions). The service cost component of net periodic benefit costs is included in “Other operation and maintenance” expenses in the income statements and all other components of net periodic benefit costs are included in “Other (income) and deductions” in the income statements or regulatory assets on the balance sheets.

Alliant Energy	Defined Benefit Pension Plans			OPEB Plans
	2024	2023	2022	2024	2023	2022
Service cost	$5	$5	$9	$2	$2	$3
Interest cost	45	47	36	8	9	6
Expected return on plan assets (a)	(55)	(53)	(69)	(5)	(5)	(5)
Amortization of prior service credit (b)	(1)	(1)	(1)	—	—	—
Amortization of actuarial loss (c)	24	28	32	—	1	2
Settlement losses (d)	—	—	26	—	—	—
	$18	$26	$33	$5	$7	$6

IPL	Defined Benefit Pension Plans			OPEB Plans
	2024	2023	2022	2024	2023	2022
Service cost	$3	$3	$6	$1	$1	$1
Interest cost	20	21	16	3	3	2
Expected return on plan assets (a)	(26)	(26)	(31)	(4)	(3)	(4)
Amortization of actuarial loss (c)	9	11	13	—	1	1
Settlement losses (d)	—	—	13	—	—	—
	$6	$9	$17	$—	$2	$—

WPL	Defined Benefit Pension Plans			OPEB Plans
	2024	2023	2022	2024	2023	2022
Service cost	$2	$2	$3	$1	$1	$1
Interest cost	20	20	16	3	3	2
Expected return on plan assets (a)	(23)	(22)	(31)	(1)	(1)	(1)
Amortization of actuarial loss (c)	11	13	15	—	1	2
Settlement losses (d)	—	—	13	—	—	—
	$10	$13	$16	$3	$4	$4

(a)The expected return on plan assets is based on the expected rate of return on plan assets and the fair value approach to the market-related value of plan assets.

(b)Unrecognized prior service credits for the OPEB plans are amortized over the average future service period to full eligibility of the participants of each plan.

(c)Unrecognized net actuarial gains or losses in excess of 10% of the greater of the plans’ benefit obligations or assets are amortized over the average future service lives of plan participants, except for the Alliant Energy Cash Balance Pension Plan where gains or losses outside the 10% threshold are amortized over the time period the participants are expected to receive benefits.

(d)Settlement losses related to payments made to retired executives of Alliant Energy and lump sum payments related to IPL’s and WPL’s qualified defined benefit pension plans. In 2022, the majority of Alliant Energy’s, IPL’s, and WPL’s pension settlement losses were recognized as regulatory assets in accordance with regulatory treatment, and $7 million was included in “Other (income) and deductions” in Alliant Energy’s and IPL’s income statements related to IPL’s qualified defined benefit pension plan.

Funded Status Of Benefit Plans

A reconciliation of the funded status of qualified and non-qualified defined benefit pension and OPEB plans to the amounts recognized on the balance sheets at December 31 was as follows (in millions):

	Defined Benefit Pension Plans		OPEB Plans
Alliant Energy	2024	2023	2024	2023
Change in benefit obligation:
Net benefit obligation at January 1	$876	$875	$160	$168
Service cost	5	5	2	2
Interest cost	45	47	8	9
Plan participants’ contributions	—	—	3	4
Actuarial (gain) loss	(19)	23	(7)	(3)
Gross benefits paid	(66)	(74)	(18)	(20)
Net benefit obligation at December 31	841	876	148	160
Change in plan assets:
Fair value of plan assets at January 1	732	706	83	83
Actual return on plan assets	38	86	5	8
Employer contributions	11	14	7	8
Plan participants’ contributions	—	—	3	4
Gross benefits paid	(66)	(74)	(18)	(20)
Fair value of plan assets at December 31	715	732	80	83
Under funded status at December 31	($126)	($144)	($68)	($77)

	Defined Benefit Pension Plans		OPEB Plans
Alliant Energy	2024	2023	2024	2023
Amounts recognized on the balance sheets consist of:
Non-current assets	$—	$—	$17	$14
Current liabilities	(3)	(2)	(7)	(8)
Pension and other benefit obligations	(123)	(142)	(78)	(83)
Net amounts recognized at December 31	($126)	($144)	($68)	($77)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	$312	$337	$4	$11
Prior service credit	(2)	(2)	—	—
	$310	$335	$4	$11

	Defined Benefit Pension Plans		OPEB Plans
IPL	2024	2023	2024	2023
Change in benefit obligation:
Net benefit obligation at January 1	$387	$389	$65	$68
Service cost	3	3	1	1
Interest cost	20	21	3	3
Plan participants’ contributions	—	—	1	2
Actuarial (gain) loss	(8)	9	(3)	(1)
Gross benefits paid	(30)	(35)	(8)	(8)
Net benefit obligation at December 31	372	387	59	65
Change in plan assets:
Fair value of plan assets at January 1	352	344	61	58
Actual return on plan assets	18	42	4	7
Employer contributions	—	1	1	2
Plan participants’ contributions	—	—	1	2
Gross benefits paid	(30)	(35)	(8)	(8)
Fair value of plan assets at December 31	340	352	59	61
Under funded status at December 31	($32)	($35)	$—	($4)

	Defined Benefit Pension Plans		OPEB Plans
IPL	2024	2023	2024	2023
Amounts recognized on the balance sheets consist of:
Non-current assets	$—	$—	$13	$10
Current liabilities	(1)	—	(1)	(1)
Pension and other benefit obligations	(31)	(35)	(12)	(13)
Net amounts recognized at December 31	($32)	($35)	$—	($4)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	$126	$135	$7	$9
Prior service credit	(1)	(1)	—	—
	$125	$134	$7	$9

	Defined Benefit Pension Plans		OPEB Plans
WPL	2024	2023	2024	2023
Change in benefit obligation:
Net benefit obligation at January 1	$381	$381	$61	$65
Service cost	2	2	1	1
Interest cost	20	20	3	3
Plan participants’ contributions	—	—	1	2
Actuarial (gain) loss	(8)	10	(3)	(2)
Gross benefits paid	(30)	(32)	(7)	(8)
Net benefit obligation at December 31	365	381	56	61
Change in plan assets:
Fair value of plan assets at January 1	306	291	14	14
Actual return on plan assets	17	35	—	1
Employer contributions	10	12	5	5
Plan participants’ contributions	—	—	1	2
Gross benefits paid	(30)	(32)	(7)	(8)
Fair value of plan assets at December 31	303	306	13	14
Under funded status at December 31	($62)	($75)	($43)	($47)

	Defined Benefit Pension Plans		OPEB Plans
WPL	2024	2023	2024	2023
Amounts recognized on the balance sheets consist of:
Non-current assets	$—	$—	$4	$4
Current liabilities	—	—	(6)	(6)
Pension and other benefit obligations	(62)	(75)	(41)	(45)
Net amounts recognized at December 31	($62)	($75)	($43)	($47)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	$135	$148	$—	$3

Accumulated Benefit Obligations

Accumulated benefit obligations, aggregate amounts applicable to defined benefit pension and OPEB plans with accumulated benefit obligations in excess of plan assets, as well as defined benefit pension plans with projected benefit obligations in excess of plan assets as of the December 31 measurement date are as follows (in millions):

	Defined Benefit Pension Plans		OPEB Plans
Alliant Energy	2024	2023	2024	2023
Accumulated benefit obligations	$824	$857	$148	$160
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	824	857	148	160
Fair value of plan assets	715	732	80	83
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	841	876	N/A	N/A
Fair value of plan assets	715	732	N/A	N/A

	Defined Benefit Pension Plans		OPEB Plans
IPL	2024	2023	2024	2023
Accumulated benefit obligations	$362	$377	$59	$65
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	362	377	N/A	65
Fair value of plan assets	340	352	N/A	61
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	372	387	N/A	N/A
Fair value of plan assets	340	352	N/A	N/A

	Defined Benefit Pension Plans		OPEB Plans
WPL	2024	2023	2024	2023
Accumulated benefit obligations	$358	$373	$56	$61
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	358	373	56	61
Fair value of plan assets	303	306	13	14
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	365	381	N/A	N/A
Fair value of plan assets	303	306	N/A	N/A

Regulatory Assets

In addition to the amounts recognized in regulatory assets in the above tables for IPL and WPL, regulatory assets were recognized for amounts associated with Corporate Services employees participating in other Alliant Energy sponsored benefit plans that were allocated to IPL and WPL at December 31 as follows (in millions):

	IPL		WPL
	2024	2023	2024	2023
Regulatory assets	$25	$28	$22	$24

Estimated Future Employer Contributions

Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2025 is as follows (in millions):

	Alliant Energy	IPL	WPL
Defined benefit pension plans (a)	$20	$1	$14
OPEB plans	7	1	6

(a)Alliant Energy sponsors several non-qualified defined benefit pension plans that cover certain current and former key employees of IPL and WPL. Alliant Energy allocates pension costs to IPL and WPL for these plans. In addition, IPL and WPL amounts reflect funding for their non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans.

Expected Benefit Payments

Expected benefit payments for the qualified and non-qualified defined benefit plans, which reflect expected future service, as appropriate, are as follows (in millions):

Alliant Energy	2025	2026	2027	2028	2029	2030 - 2034
Defined benefit pension benefits	$79	$75	$74	$74	$74	$329
OPEB	16	16	15	15	14	62
	$95	$91	$89	$89	$88	$391

IPL	2025	2026	2027	2028	2029	2030 - 2034
Defined benefit pension benefits	$36	$34	$33	$33	$32	$148
OPEB	7	6	6	6	6	24
	$43	$40	$39	$39	$38	$172

WPL	2025	2026	2027	2028	2029	2030 - 2034
Defined benefit pension benefits	$33	$31	$31	$31	$31	$144
OPEB	7	6	6	5	5	23
	$40	$37	$37	$36	$36	$167

Recognized Compensation Expense And Income Tax Benefits

A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards was as follows (in millions):

	Alliant Energy			IPL			WPL
	2024	2023	2022	2024	2023	2022	2024	2023	2022
Compensation expense	$12	$12	$13	$6	$6	$7	$5	$5	$5
Income tax benefits	3	3	3	2	2	2	1	1	1

Pension Plans, Defined Benefit [Member]

Defined Benefit Plan Disclosure [Line Items]

Fair Value Of Plan Assets By Asset Category, Fair Value Hierarchy Level and Allocations

At December 31, 2024, the current target ranges and actual allocations for the defined benefit pension plan assets were as follows:

	Target Range			Actual
	Allocation			Allocation
Public equity securities	32%	-	49%	44%
Liquid alternative securities	0%	-	12%	6%
Return-seeking fixed income securities	4%	-	18%	8%
Liability-hedging fixed income securities (including cash and equivalents)	34%	-	53%	42%

At December 31, the fair values of qualified and non-qualified defined benefit pension plan assets were as follows (in millions):

	2024				2023
	Fair	Level	Level	Level	Fair	Level	Level	Level
Alliant Energy	Value	1	2	3	Value	1	2	3
Cash and equivalents	$49	$—	$49	$—	$19	$—	$19	$—
Equity securities	—	—	—	—	223	223	—	—
Global asset securities	—	—	—	—	39	39	—	—
Fixed income securities	—	—	—	—	143	31	112	—
Total assets in fair value hierarchy	49	$—	$49	$—	424	$293	$131	$—
Assets measured at net asset value	667				306
Accrued investment income	—				2
Due to brokers, net (pending trades with brokers)	(1)				—
Total pension plan assets	$715				$732

	2024				2023
	Fair	Level	Level	Level	Fair	Level	Level	Level
IPL	Value	1	2	3	Value	1	2	3
Cash and equivalents	$21	$—	$21	$—	$9	$—	$9	$—
Equity securities	—	—	—	—	107	107	—	—
Global asset securities	—	—	—	—	19	19	—	—
Fixed income securities	—	—	—	—	69	15	54	—
Total assets in fair value hierarchy	21	$—	$21	$—	204	$141	$63	$—
Assets measured at net asset value	319				147
Accrued investment income	—				1
Total pension plan assets	$340				$352

	2024				2023
	Fair	Level	Level	Level	Fair	Level	Level	Level
WPL	Value	1	2	3	Value	1	2	3
Cash and equivalents	$22	$—	$22	$—	$8	$—	$8	$—
Equity securities	—	—	—	—	93	93	—	—
Global asset securities	—	—	—	—	16	16	—	—
Fixed income securities	—	—	—	—	60	13	47	—
Total assets in fair value hierarchy	22	$—	$22	$—	177	$122	$55	$—
Assets measured at net asset value	281				128
Accrued investment income	—				1
Total pension plan assets	$303				$306

Pension Plans, Defined Benefit [Member] | IPL [Member]

Defined Benefit Plan Disclosure [Line Items]

Fair Value Of Plan Assets By Asset Category, Fair Value Hierarchy Level and Allocations

At December 31, 2024, the current target ranges and actual allocations for the defined benefit pension plan assets were as follows:

	Target Range			Actual
	Allocation			Allocation
Public equity securities	32%	-	49%	44%
Liquid alternative securities	0%	-	12%	6%
Return-seeking fixed income securities	4%	-	18%	8%
Liability-hedging fixed income securities (including cash and equivalents)	34%	-	53%	42%

At December 31, the fair values of qualified and non-qualified defined benefit pension plan assets were as follows (in millions):

	2024				2023
	Fair	Level	Level	Level	Fair	Level	Level	Level
Alliant Energy	Value	1	2	3	Value	1	2	3
Cash and equivalents	$49	$—	$49	$—	$19	$—	$19	$—
Equity securities	—	—	—	—	223	223	—	—
Global asset securities	—	—	—	—	39	39	—	—
Fixed income securities	—	—	—	—	143	31	112	—
Total assets in fair value hierarchy	49	$—	$49	$—	424	$293	$131	$—
Assets measured at net asset value	667				306
Accrued investment income	—				2
Due to brokers, net (pending trades with brokers)	(1)				—
Total pension plan assets	$715				$732

	2024				2023
	Fair	Level	Level	Level	Fair	Level	Level	Level
IPL	Value	1	2	3	Value	1	2	3
Cash and equivalents	$21	$—	$21	$—	$9	$—	$9	$—
Equity securities	—	—	—	—	107	107	—	—
Global asset securities	—	—	—	—	19	19	—	—
Fixed income securities	—	—	—	—	69	15	54	—
Total assets in fair value hierarchy	21	$—	$21	$—	204	$141	$63	$—
Assets measured at net asset value	319				147
Accrued investment income	—				1
Total pension plan assets	$340				$352

	2024				2023
	Fair	Level	Level	Level	Fair	Level	Level	Level
WPL	Value	1	2	3	Value	1	2	3
Cash and equivalents	$22	$—	$22	$—	$8	$—	$8	$—
Equity securities	—	—	—	—	93	93	—	—
Global asset securities	—	—	—	—	16	16	—	—
Fixed income securities	—	—	—	—	60	13	47	—
Total assets in fair value hierarchy	22	$—	$22	$—	177	$122	$55	$—
Assets measured at net asset value	281				128
Accrued investment income	—				1
Total pension plan assets	$303				$306

Pension Plans, Defined Benefit [Member] | WPL [Member]

Defined Benefit Plan Disclosure [Line Items]

Fair Value Of Plan Assets By Asset Category, Fair Value Hierarchy Level and Allocations

At December 31, 2024, the current target ranges and actual allocations for the defined benefit pension plan assets were as follows:

	Target Range			Actual
	Allocation			Allocation
Public equity securities	32%	-	49%	44%
Liquid alternative securities	0%	-	12%	6%
Return-seeking fixed income securities	4%	-	18%	8%
Liability-hedging fixed income securities (including cash and equivalents)	34%	-	53%	42%

At December 31, the fair values of qualified and non-qualified defined benefit pension plan assets were as follows (in millions):

	2024				2023
	Fair	Level	Level	Level	Fair	Level	Level	Level
Alliant Energy	Value	1	2	3	Value	1	2	3
Cash and equivalents	$49	$—	$49	$—	$19	$—	$19	$—
Equity securities	—	—	—	—	223	223	—	—
Global asset securities	—	—	—	—	39	39	—	—
Fixed income securities	—	—	—	—	143	31	112	—
Total assets in fair value hierarchy	49	$—	$49	$—	424	$293	$131	$—
Assets measured at net asset value	667				306
Accrued investment income	—				2
Due to brokers, net (pending trades with brokers)	(1)				—
Total pension plan assets	$715				$732

	2024				2023
	Fair	Level	Level	Level	Fair	Level	Level	Level
IPL	Value	1	2	3	Value	1	2	3
Cash and equivalents	$21	$—	$21	$—	$9	$—	$9	$—
Equity securities	—	—	—	—	107	107	—	—
Global asset securities	—	—	—	—	19	19	—	—
Fixed income securities	—	—	—	—	69	15	54	—
Total assets in fair value hierarchy	21	$—	$21	$—	204	$141	$63	$—
Assets measured at net asset value	319				147
Accrued investment income	—				1
Total pension plan assets	$340				$352

	2024				2023
	Fair	Level	Level	Level	Fair	Level	Level	Level
WPL	Value	1	2	3	Value	1	2	3
Cash and equivalents	$22	$—	$22	$—	$8	$—	$8	$—
Equity securities	—	—	—	—	93	93	—	—
Global asset securities	—	—	—	—	16	16	—	—
Fixed income securities	—	—	—	—	60	13	47	—
Total assets in fair value hierarchy	22	$—	$22	$—	177	$122	$55	$—
Assets measured at net asset value	281				128
Accrued investment income	—				1
Total pension plan assets	$303				$306

Other Postretirement Benefits Plans [Member]

Defined Benefit Plan Disclosure [Line Items]

Fair Value Of Plan Assets By Asset Category, Fair Value Hierarchy Level and Allocations

At December 31, 2024, the current target ranges and actual allocations for assets with a long-term investment horizon were as follows:

	Target Range			Actual
	Allocation			Allocation
Cash and equivalents	0%	-	5%	1%
Public equity securities	0%	-	40%	27%
Fixed income securities	40%	-	100%	72%

At December 31, the fair values of OPEB plan assets were as follows (in millions):

	2024				2023
	Fair	Level	Level	Level	Fair	Level	Level	Level
Alliant Energy	Value	1	2	3	Value	1	2	3
Cash and equivalents	$8	$—	$8	$—	$9	$—	$9	$—
Equity securities	20	20	—	—	8	8	—	—
Fixed income securities	52	52	—	—	47	47	—	—
Total assets in fair value hierarchy	80	$72	$8	$—	64	$55	$9	$—
Assets measured at net asset value	—				19
Total OPEB plan assets	$80				$83

	2024				2023
	Fair	Level	Level	Level	Fair	Level	Level	Level
IPL	Value	1	2	3	Value	1	2	3
Cash and equivalents	$1	$—	$1	$—	$1	$—	$1	$—
Equity securities	18	18	—	—	6	6	—	—
Fixed income securities	40	40	—	—	36	36	—	—
Total assets in fair value hierarchy	59	$58	$1	$—	43	$42	$1	$—
Assets measured at net asset value	—				18
Total OPEB plan assets	$59				$61

	2024				2023
	Fair	Level	Level	Level	Fair	Level	Level	Level
WPL	Value	1	2	3	Value	1	2	3
Cash and equivalents	$—	$—	$—	$—	$1	$—	$1	$—
Equity securities	2	2	—	—	2	2	—	—
Fixed income securities	11	11	—	—	11	11	—	—
Total OPEB plan assets	$13	$13	$—	$—	$14	$13	$1	$—

Other Postretirement Benefits Plans [Member] | IPL [Member]

Defined Benefit Plan Disclosure [Line Items]

Fair Value Of Plan Assets By Asset Category, Fair Value Hierarchy Level and Allocations

At December 31, 2024, the current target ranges and actual allocations for assets with a long-term investment horizon were as follows:

	Target Range			Actual
	Allocation			Allocation
Cash and equivalents	0%	-	5%	1%
Public equity securities	0%	-	40%	27%
Fixed income securities	40%	-	100%	72%

At December 31, the fair values of OPEB plan assets were as follows (in millions):

	2024				2023
	Fair	Level	Level	Level	Fair	Level	Level	Level
Alliant Energy	Value	1	2	3	Value	1	2	3
Cash and equivalents	$8	$—	$8	$—	$9	$—	$9	$—
Equity securities	20	20	—	—	8	8	—	—
Fixed income securities	52	52	—	—	47	47	—	—
Total assets in fair value hierarchy	80	$72	$8	$—	64	$55	$9	$—
Assets measured at net asset value	—				19
Total OPEB plan assets	$80				$83

	2024				2023
	Fair	Level	Level	Level	Fair	Level	Level	Level
IPL	Value	1	2	3	Value	1	2	3
Cash and equivalents	$1	$—	$1	$—	$1	$—	$1	$—
Equity securities	18	18	—	—	6	6	—	—
Fixed income securities	40	40	—	—	36	36	—	—
Total assets in fair value hierarchy	59	$58	$1	$—	43	$42	$1	$—
Assets measured at net asset value	—				18
Total OPEB plan assets	$59				$61

	2024				2023
	Fair	Level	Level	Level	Fair	Level	Level	Level
WPL	Value	1	2	3	Value	1	2	3
Cash and equivalents	$—	$—	$—	$—	$1	$—	$1	$—
Equity securities	2	2	—	—	2	2	—	—
Fixed income securities	11	11	—	—	11	11	—	—
Total OPEB plan assets	$13	$13	$—	$—	$14	$13	$1	$—

Other Postretirement Benefits Plans [Member] | WPL [Member]

Defined Benefit Plan Disclosure [Line Items]

Fair Value Of Plan Assets By Asset Category, Fair Value Hierarchy Level and Allocations

At December 31, 2024, the current target ranges and actual allocations for assets with a long-term investment horizon were as follows:

	Target Range			Actual
	Allocation			Allocation
Cash and equivalents	0%	-	5%	1%
Public equity securities	0%	-	40%	27%
Fixed income securities	40%	-	100%	72%

At December 31, the fair values of OPEB plan assets were as follows (in millions):

	2024				2023
	Fair	Level	Level	Level	Fair	Level	Level	Level
Alliant Energy	Value	1	2	3	Value	1	2	3
Cash and equivalents	$8	$—	$8	$—	$9	$—	$9	$—
Equity securities	20	20	—	—	8	8	—	—
Fixed income securities	52	52	—	—	47	47	—	—
Total assets in fair value hierarchy	80	$72	$8	$—	64	$55	$9	$—
Assets measured at net asset value	—				19
Total OPEB plan assets	$80				$83

	2024				2023
	Fair	Level	Level	Level	Fair	Level	Level	Level
IPL	Value	1	2	3	Value	1	2	3
Cash and equivalents	$1	$—	$1	$—	$1	$—	$1	$—
Equity securities	18	18	—	—	6	6	—	—
Fixed income securities	40	40	—	—	36	36	—	—
Total assets in fair value hierarchy	59	$58	$1	$—	43	$42	$1	$—
Assets measured at net asset value	—				18
Total OPEB plan assets	$59				$61

	2024				2023
	Fair	Level	Level	Level	Fair	Level	Level	Level
WPL	Value	1	2	3	Value	1	2	3
Cash and equivalents	$—	$—	$—	$—	$1	$—	$1	$—
Equity securities	2	2	—	—	2	2	—	—
Fixed income securities	11	11	—	—	11	11	—	—
Total OPEB plan assets	$13	$13	$—	$—	$14	$13	$1	$—

401(k) Savings Plan [Member]

Defined Benefit Plan Disclosure [Line Items]

Employees Participate In Defined Contribution Retirement Plans

Costs related to the 401(k) savings plans, which are partially based on the participants’ contributions and include allocated costs associated with Corporate Services employees for IPL and WPL, were as follows (in millions):

	Alliant Energy			IPL			WPL
	2024	2023	2022	2024	2023	2022	2024	2023	2022
401(k) costs	$31	$30	$28	$14	$14	$13	$15	$14	$13

401(k) Savings Plan [Member] | IPL [Member]

Defined Benefit Plan Disclosure [Line Items]

Employees Participate In Defined Contribution Retirement Plans

Costs related to the 401(k) savings plans, which are partially based on the participants’ contributions and include allocated costs associated with Corporate Services employees for IPL and WPL, were as follows (in millions):

	Alliant Energy			IPL			WPL
	2024	2023	2022	2024	2023	2022	2024	2023	2022
401(k) costs	$31	$30	$28	$14	$14	$13	$15	$14	$13

401(k) Savings Plan [Member] | WPL [Member]

Defined Benefit Plan Disclosure [Line Items]

Employees Participate In Defined Contribution Retirement Plans

Costs related to the 401(k) savings plans, which are partially based on the participants’ contributions and include allocated costs associated with Corporate Services employees for IPL and WPL, were as follows (in millions):

	Alliant Energy			IPL			WPL
	2024	2023	2022	2024	2023	2022	2024	2023	2022
401(k) costs	$31	$30	$28	$14	$14	$13	$15	$14	$13

Performance Shares (TSR Metric) [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule Of Equity-based Compensation Plans Activity

A summary of the performance shares activity, with amounts representing the target number of awards, was as follows:

	2024		2023		2022
	Shares	Weighted Average Grant Date Fair Value	Shares	Weighted Average Grant Date Fair Value	Shares	Weighted Average Grant Date Fair Value
Nonvested awards, January 1	233,954	$52.60	190,273	$54.13	196,429	$51.59
Granted	127,874	46.04	108,712	55.68	74,106	54.45
Vested	(47,497)	46.19	(53,431)	64.04	(71,101)	47.48
Forfeited	(24,932)	46.16	(11,600)	53.88	(9,161)	53.99
Nonvested awards, December 31	289,399	51.31	233,954	52.60	190,273	54.13

Restricted Stock Units [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule Of Equity-based Compensation Plans Activity

A summary of the restricted stock units activity was as follows:

	2024		2023		2022
	Units	Weighted Average Grant Date Fair Value	Units	Weighted Average Grant Date Fair Value	Units	Weighted Average Grant Date Fair Value
Nonvested awards, January 1	234,259	$52.58	198,275	$54.53	217,819	$50.54
Granted	129,854	48.69	106,124	52.77	77,122	56.88
Vested	(71,441)	48.65	(55,345)	59.40	(82,770)	46.08
Forfeited	(3,524)	48.40	(14,795)	54.53	(13,896)	55.53
Nonvested awards, December 31	289,148	51.85	234,259	52.58	198,275	54.53

Performance Shares (Net Income and Workforce Composition Metrics) [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule Of Equity-based Compensation Plans Activity

A summary of the performance shares activity, with amounts representing the target number of awards, was as follows:

	2024		2023		2022
	Shares	Weighted Average Grant Date Fair Value	Shares	Weighted Average Grant Date Fair Value	Shares	Weighted Average Grant Date Fair Value
Nonvested awards, January 1	257,639	$52.76	199,874	$54.74	196,429	$50.74
Granted	146,143	48.55	124,217	52.71	84,670	57.01
Vested	(67,852)	48.66	(53,431)	59.36	(71,101)	46.24
Forfeited	(5,230)	48.40	(13,021)	55.47	(10,124)	55.92
Nonvested awards, December 31	330,700	51.81	257,639	52.76	199,874	54.74