Benefit Plans (Tables)

12 Months Ended

Dec. 31, 2023

Defined Benefit Plan Disclosure [Line Items]

Assumptions Used To Measure Benefit Plans

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

	Defined Benefit Pension Plans									OPEB Plans
Alliant Energy	2023			2022			2021			2023	2022	2021
Discount rate for benefit obligations	5.36%			5.54%			2.91%			5.40%	5.53%	2.81%
Discount rate for net periodic cost	5.54%			2.91%			2.57%			5.53%	2.81%	2.31%
Expected rate of return on plan assets	7.80%			7.80%			7.10%			6.50%	6.40%	4.80%
Interest crediting rate for Alliant Energy Cash Balance Pension Plan	10.75%			9.22%			4.18%			N/A	N/A	N/A
Rate of compensation increase	3.30%	-	4.50%	3.30%	-	4.50%	3.30%	-	4.50%	N/A	N/A	N/A

	Qualified Defined Benefit Pension Plan			OPEB Plans
IPL	2023	2022	2021	2023	2022	2021
Discount rate for benefit obligations	5.35%	5.55%	2.94%	5.40%	5.53%	2.80%
Discount rate for net periodic cost	5.55%	2.94%	2.61%	5.53%	2.80%	2.28%
Expected rate of return on plan assets	7.80%	7.80%	7.10%	6.90%	6.50%	5.10%
Rate of compensation increase	3.30%	3.30%	3.30%	N/A	N/A	N/A

	Qualified Defined Benefit Pension Plan			OPEB Plans
WPL	2023	2022	2021	2023	2022	2021
Discount rate for benefit obligations	5.35%	5.54%	2.94%	5.40%	5.53%	2.79%
Discount rate for net periodic cost	5.54%	2.94%	2.64%	5.53%	2.79%	2.27%
Expected rate of return on plan assets	7.80%	7.80%	7.10%	5.65%	5.49%	4.02%
Rate of compensation increase	3.30%	3.30%	3.30%	N/A	N/A	N/A

Net Periodic Benefit Costs

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

Alliant Energy	Defined Benefit Pension Plans			OPEB Plans
	2023	2022	2021	2023	2022	2021
Service cost	$5	$9	$11	$2	$3	$4
Interest cost	47	36	34	9	6	5
Expected return on plan assets (a)	(53)	(69)	(69)	(5)	(5)	(5)
Amortization of prior service credit (b)	(1)	(1)	—	—	—	—
Amortization of actuarial loss (c)	28	32	39	1	2	5
Settlement losses (d)	—	26	—	—	—	—
	$26	$33	$15	$7	$6	$9

IPL	Defined Benefit Pension Plans			OPEB Plans
	2023	2022	2021	2023	2022	2021
Service cost	$3	$6	$7	$1	$1	$1
Interest cost	21	16	16	3	2	2
Expected return on plan assets (a)	(26)	(31)	(32)	(3)	(4)	(3)
Amortization of actuarial loss (c)	11	13	17	1	1	2
Settlement losses (d)	—	13	—	—	—	—
	$9	$17	$8	$2	$—	$2

WPL	Defined Benefit Pension Plans			OPEB Plans
	2023	2022	2021	2023	2022	2021
Service cost	$2	$3	$4	$1	$1	$1
Interest cost	20	16	15	3	2	2
Expected return on plan assets (a)	(22)	(31)	(31)	(1)	(1)	—
Amortization of actuarial loss (c)	13	15	19	1	2	2
Settlement losses (d)	—	13	—	—	—	—
	$13	$16	$7	$4	$4	$5

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

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

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

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

Funded Status Of Benefit Plans

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

	Defined Benefit Pension Plans		OPEB Plans
Alliant Energy	2023	2022	2023	2022
Change in benefit obligation:
Net benefit obligation at January 1	$875	$1,251	$168	$210
Service cost	5	9	2	3
Interest cost	47	36	9	6
Plan participants’ contributions	—	—	4	4
Actuarial (gain) loss	23	(269)	(3)	(37)
Gross benefits paid	(74)	(152)	(20)	(18)
Net benefit obligation at December 31	876	875	160	168
Change in plan assets:
Fair value of plan assets at January 1	706	1,011	83	106
Actual return on plan assets	86	(204)	8	(17)
Employer contributions	14	51	8	8
Plan participants’ contributions	—	—	4	4
Gross benefits paid	(74)	(152)	(20)	(18)
Fair value of plan assets at December 31	732	706	83	83
Under funded status at December 31	($144)	($169)	($77)	($85)

	Defined Benefit Pension Plans		OPEB Plans
Alliant Energy	2023	2022	2023	2022
Amounts recognized on the balance sheets consist of:
Non-current assets	$—	$—	$14	$9
Current liabilities	(2)	(2)	(8)	(8)
Pension and other benefit obligations	(142)	(167)	(83)	(86)
Net amounts recognized at December 31	($144)	($169)	($77)	($85)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	$337	$376	$11	$20
Prior service credit	(2)	(3)	—	—
	$335	$373	$11	$20

	Defined Benefit Pension Plans		OPEB Plans
IPL	2023	2022	2023	2022
Change in benefit obligation:
Net benefit obligation at January 1	$389	$567	$68	$84
Service cost	3	6	1	1
Interest cost	21	16	3	2
Plan participants’ contributions	—	—	2	2
Actuarial (gain) loss	9	(123)	(1)	(14)
Gross benefits paid	(35)	(77)	(8)	(7)
Net benefit obligation at December 31	387	389	65	68
Change in plan assets:
Fair value of plan assets at January 1	344	462	58	74
Actual return on plan assets	42	(92)	7	(12)
Employer contributions	1	51	2	1
Plan participants’ contributions	—	—	2	2
Gross benefits paid	(35)	(77)	(8)	(7)
Fair value of plan assets at December 31	352	344	61	58
Under funded status at December 31	($35)	($45)	($4)	($10)

	Defined Benefit Pension Plans		OPEB Plans
IPL	2023	2022	2023	2022
Amounts recognized on the balance sheets consist of:
Non-current assets	$—	$—	$10	$6
Current liabilities	—	—	(1)	(2)
Pension and other benefit obligations	(35)	(45)	(13)	(14)
Net amounts recognized at December 31	($35)	($45)	($4)	($10)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	$135	$154	$9	$14
Prior service credit	(1)	(1)	—	—
	$134	$153	$9	$14

	Defined Benefit Pension Plans		OPEB Plans
WPL	2023	2022	2023	2022
Change in benefit obligation:
Net benefit obligation at January 1	$381	$546	$65	$81
Service cost	2	3	1	1
Interest cost	20	16	3	2
Plan participants’ contributions	—	—	2	2
Actuarial (gain) loss	10	(117)	(2)	(13)
Gross benefits paid	(32)	(67)	(8)	(8)
Net benefit obligation at December 31	381	381	61	65
Change in plan assets:
Fair value of plan assets at January 1	291	450	14	17
Actual return on plan assets	35	(92)	1	(2)
Employer contributions	12	—	5	5
Plan participants’ contributions	—	—	2	2
Gross benefits paid	(32)	(67)	(8)	(8)
Fair value of plan assets at December 31	306	291	14	14
Under funded status at December 31	($75)	($90)	($47)	($51)

	Defined Benefit Pension Plans		OPEB Plans
WPL	2023	2022	2023	2022
Amounts recognized on the balance sheets consist of:
Non-current assets	$—	$—	$4	$3
Current liabilities	—	—	(6)	(5)
Pension and other benefit obligations	(75)	(90)	(45)	(49)
Net amounts recognized at December 31	($75)	($90)	($47)	($51)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	$148	$165	$3	$6
Prior service credit	—	—	—	—
	$148	$165	$3	$6

Accumulated Benefit Obligations

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

	Defined Benefit Pension Plans		OPEB Plans
Alliant Energy	2023	2022	2023	2022
Accumulated benefit obligations	$857	$857	$160	$168
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	857	857	160	168
Fair value of plan assets	732	706	83	83
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	876	875	N/A	N/A
Fair value of plan assets	732	706	N/A	N/A

	Defined Benefit Pension Plans		OPEB Plans
IPL	2023	2022	2023	2022
Accumulated benefit obligations	$377	$379	$65	$68
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	377	379	65	68
Fair value of plan assets	352	344	61	58
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	387	389	N/A	N/A
Fair value of plan assets	352	344	N/A	N/A

	Defined Benefit Pension Plans		OPEB Plans
WPL	2023	2022	2023	2022
Accumulated benefit obligations	$373	$373	$61	$65
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	373	373	61	65
Fair value of plan assets	306	291	14	14
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	381	381	N/A	N/A
Fair value of plan assets	306	291	N/A	N/A

Regulatory Assets

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

	IPL		WPL
	2023	2022	2023	2022
Regulatory assets	$28	$30	$24	$25

Estimated Future Employer Contributions

Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2024 is as follows (in millions):

	Alliant Energy	IPL	WPL
Defined benefit pension plans (a)	$12	$—	$10
OPEB plans	8	1	6

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

Expected Benefit Payments

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

Alliant Energy	2024	2025	2026	2027	2028	2029 - 2033
Defined benefit pension benefits	$73	$73	$74	$75	$75	$343
OPEB	17	17	16	16	15	65
	$90	$90	$90	$91	$90	$408

IPL	2024	2025	2026	2027	2028	2029 - 2033
Defined benefit pension benefits	$34	$34	$34	$33	$33	$151
OPEB	7	7	7	6	6	25
	$41	$41	$41	$39	$39	$176

WPL	2024	2025	2026	2027	2028	2029 - 2033
Defined benefit pension benefits	$32	$32	$31	$31	$31	$146
OPEB	7	7	6	6	6	24
	$39	$39	$37	$37	$37	$170

Recognized Compensation Expense And Income Tax Benefits

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

	Alliant Energy			IPL			WPL
	2023	2022	2021	2023	2022	2021	2023	2022	2021
Compensation expense	$12	$13	$14	$6	$7	$8	$5	$5	$6
Income tax benefits	3	3	4	2	2	2	1	1	2

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

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

	2023	2022
Carrying value	$13	$13
Fair market value	19	22

IPL [Member]

Defined Benefit Plan Disclosure [Line Items]

Assumptions Used To Measure Benefit Plans

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

	Defined Benefit Pension Plans									OPEB Plans
Alliant Energy	2023			2022			2021			2023	2022	2021
Discount rate for benefit obligations	5.36%			5.54%			2.91%			5.40%	5.53%	2.81%
Discount rate for net periodic cost	5.54%			2.91%			2.57%			5.53%	2.81%	2.31%
Expected rate of return on plan assets	7.80%			7.80%			7.10%			6.50%	6.40%	4.80%
Interest crediting rate for Alliant Energy Cash Balance Pension Plan	10.75%			9.22%			4.18%			N/A	N/A	N/A
Rate of compensation increase	3.30%	-	4.50%	3.30%	-	4.50%	3.30%	-	4.50%	N/A	N/A	N/A

	Qualified Defined Benefit Pension Plan			OPEB Plans
IPL	2023	2022	2021	2023	2022	2021
Discount rate for benefit obligations	5.35%	5.55%	2.94%	5.40%	5.53%	2.80%
Discount rate for net periodic cost	5.55%	2.94%	2.61%	5.53%	2.80%	2.28%
Expected rate of return on plan assets	7.80%	7.80%	7.10%	6.90%	6.50%	5.10%
Rate of compensation increase	3.30%	3.30%	3.30%	N/A	N/A	N/A

	Qualified Defined Benefit Pension Plan			OPEB Plans
WPL	2023	2022	2021	2023	2022	2021
Discount rate for benefit obligations	5.35%	5.54%	2.94%	5.40%	5.53%	2.79%
Discount rate for net periodic cost	5.54%	2.94%	2.64%	5.53%	2.79%	2.27%
Expected rate of return on plan assets	7.80%	7.80%	7.10%	5.65%	5.49%	4.02%
Rate of compensation increase	3.30%	3.30%	3.30%	N/A	N/A	N/A

Net Periodic Benefit Costs

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

Alliant Energy	Defined Benefit Pension Plans			OPEB Plans
	2023	2022	2021	2023	2022	2021
Service cost	$5	$9	$11	$2	$3	$4
Interest cost	47	36	34	9	6	5
Expected return on plan assets (a)	(53)	(69)	(69)	(5)	(5)	(5)
Amortization of prior service credit (b)	(1)	(1)	—	—	—	—
Amortization of actuarial loss (c)	28	32	39	1	2	5
Settlement losses (d)	—	26	—	—	—	—
	$26	$33	$15	$7	$6	$9

IPL	Defined Benefit Pension Plans			OPEB Plans
	2023	2022	2021	2023	2022	2021
Service cost	$3	$6	$7	$1	$1	$1
Interest cost	21	16	16	3	2	2
Expected return on plan assets (a)	(26)	(31)	(32)	(3)	(4)	(3)
Amortization of actuarial loss (c)	11	13	17	1	1	2
Settlement losses (d)	—	13	—	—	—	—
	$9	$17	$8	$2	$—	$2

WPL	Defined Benefit Pension Plans			OPEB Plans
	2023	2022	2021	2023	2022	2021
Service cost	$2	$3	$4	$1	$1	$1
Interest cost	20	16	15	3	2	2
Expected return on plan assets (a)	(22)	(31)	(31)	(1)	(1)	—
Amortization of actuarial loss (c)	13	15	19	1	2	2
Settlement losses (d)	—	13	—	—	—	—
	$13	$16	$7	$4	$4	$5

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

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

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

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

Funded Status Of Benefit Plans

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

	Defined Benefit Pension Plans		OPEB Plans
Alliant Energy	2023	2022	2023	2022
Change in benefit obligation:
Net benefit obligation at January 1	$875	$1,251	$168	$210
Service cost	5	9	2	3
Interest cost	47	36	9	6
Plan participants’ contributions	—	—	4	4
Actuarial (gain) loss	23	(269)	(3)	(37)
Gross benefits paid	(74)	(152)	(20)	(18)
Net benefit obligation at December 31	876	875	160	168
Change in plan assets:
Fair value of plan assets at January 1	706	1,011	83	106
Actual return on plan assets	86	(204)	8	(17)
Employer contributions	14	51	8	8
Plan participants’ contributions	—	—	4	4
Gross benefits paid	(74)	(152)	(20)	(18)
Fair value of plan assets at December 31	732	706	83	83
Under funded status at December 31	($144)	($169)	($77)	($85)

	Defined Benefit Pension Plans		OPEB Plans
Alliant Energy	2023	2022	2023	2022
Amounts recognized on the balance sheets consist of:
Non-current assets	$—	$—	$14	$9
Current liabilities	(2)	(2)	(8)	(8)
Pension and other benefit obligations	(142)	(167)	(83)	(86)
Net amounts recognized at December 31	($144)	($169)	($77)	($85)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	$337	$376	$11	$20
Prior service credit	(2)	(3)	—	—
	$335	$373	$11	$20

	Defined Benefit Pension Plans		OPEB Plans
IPL	2023	2022	2023	2022
Change in benefit obligation:
Net benefit obligation at January 1	$389	$567	$68	$84
Service cost	3	6	1	1
Interest cost	21	16	3	2
Plan participants’ contributions	—	—	2	2
Actuarial (gain) loss	9	(123)	(1)	(14)
Gross benefits paid	(35)	(77)	(8)	(7)
Net benefit obligation at December 31	387	389	65	68
Change in plan assets:
Fair value of plan assets at January 1	344	462	58	74
Actual return on plan assets	42	(92)	7	(12)
Employer contributions	1	51	2	1
Plan participants’ contributions	—	—	2	2
Gross benefits paid	(35)	(77)	(8)	(7)
Fair value of plan assets at December 31	352	344	61	58
Under funded status at December 31	($35)	($45)	($4)	($10)

	Defined Benefit Pension Plans		OPEB Plans
IPL	2023	2022	2023	2022
Amounts recognized on the balance sheets consist of:
Non-current assets	$—	$—	$10	$6
Current liabilities	—	—	(1)	(2)
Pension and other benefit obligations	(35)	(45)	(13)	(14)
Net amounts recognized at December 31	($35)	($45)	($4)	($10)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	$135	$154	$9	$14
Prior service credit	(1)	(1)	—	—
	$134	$153	$9	$14

	Defined Benefit Pension Plans		OPEB Plans
WPL	2023	2022	2023	2022
Change in benefit obligation:
Net benefit obligation at January 1	$381	$546	$65	$81
Service cost	2	3	1	1
Interest cost	20	16	3	2
Plan participants’ contributions	—	—	2	2
Actuarial (gain) loss	10	(117)	(2)	(13)
Gross benefits paid	(32)	(67)	(8)	(8)
Net benefit obligation at December 31	381	381	61	65
Change in plan assets:
Fair value of plan assets at January 1	291	450	14	17
Actual return on plan assets	35	(92)	1	(2)
Employer contributions	12	—	5	5
Plan participants’ contributions	—	—	2	2
Gross benefits paid	(32)	(67)	(8)	(8)
Fair value of plan assets at December 31	306	291	14	14
Under funded status at December 31	($75)	($90)	($47)	($51)

	Defined Benefit Pension Plans		OPEB Plans
WPL	2023	2022	2023	2022
Amounts recognized on the balance sheets consist of:
Non-current assets	$—	$—	$4	$3
Current liabilities	—	—	(6)	(5)
Pension and other benefit obligations	(75)	(90)	(45)	(49)
Net amounts recognized at December 31	($75)	($90)	($47)	($51)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	$148	$165	$3	$6
Prior service credit	—	—	—	—
	$148	$165	$3	$6

Accumulated Benefit Obligations

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

	Defined Benefit Pension Plans		OPEB Plans
Alliant Energy	2023	2022	2023	2022
Accumulated benefit obligations	$857	$857	$160	$168
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	857	857	160	168
Fair value of plan assets	732	706	83	83
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	876	875	N/A	N/A
Fair value of plan assets	732	706	N/A	N/A

	Defined Benefit Pension Plans		OPEB Plans
IPL	2023	2022	2023	2022
Accumulated benefit obligations	$377	$379	$65	$68
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	377	379	65	68
Fair value of plan assets	352	344	61	58
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	387	389	N/A	N/A
Fair value of plan assets	352	344	N/A	N/A

	Defined Benefit Pension Plans		OPEB Plans
WPL	2023	2022	2023	2022
Accumulated benefit obligations	$373	$373	$61	$65
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	373	373	61	65
Fair value of plan assets	306	291	14	14
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	381	381	N/A	N/A
Fair value of plan assets	306	291	N/A	N/A

Regulatory Assets

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

	IPL		WPL
	2023	2022	2023	2022
Regulatory assets	$28	$30	$24	$25

Estimated Future Employer Contributions

Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2024 is as follows (in millions):

	Alliant Energy	IPL	WPL
Defined benefit pension plans (a)	$12	$—	$10
OPEB plans	8	1	6

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

Expected Benefit Payments

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

Alliant Energy	2024	2025	2026	2027	2028	2029 - 2033
Defined benefit pension benefits	$73	$73	$74	$75	$75	$343
OPEB	17	17	16	16	15	65
	$90	$90	$90	$91	$90	$408

IPL	2024	2025	2026	2027	2028	2029 - 2033
Defined benefit pension benefits	$34	$34	$34	$33	$33	$151
OPEB	7	7	7	6	6	25
	$41	$41	$41	$39	$39	$176

WPL	2024	2025	2026	2027	2028	2029 - 2033
Defined benefit pension benefits	$32	$32	$31	$31	$31	$146
OPEB	7	7	6	6	6	24
	$39	$39	$37	$37	$37	$170

Recognized Compensation Expense And Income Tax Benefits

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

	Alliant Energy			IPL			WPL
	2023	2022	2021	2023	2022	2021	2023	2022	2021
Compensation expense	$12	$13	$14	$6	$7	$8	$5	$5	$6
Income tax benefits	3	3	4	2	2	2	1	1	2

WPL [Member]

Defined Benefit Plan Disclosure [Line Items]

Assumptions Used To Measure Benefit Plans

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

	Defined Benefit Pension Plans									OPEB Plans
Alliant Energy	2023			2022			2021			2023	2022	2021
Discount rate for benefit obligations	5.36%			5.54%			2.91%			5.40%	5.53%	2.81%
Discount rate for net periodic cost	5.54%			2.91%			2.57%			5.53%	2.81%	2.31%
Expected rate of return on plan assets	7.80%			7.80%			7.10%			6.50%	6.40%	4.80%
Interest crediting rate for Alliant Energy Cash Balance Pension Plan	10.75%			9.22%			4.18%			N/A	N/A	N/A
Rate of compensation increase	3.30%	-	4.50%	3.30%	-	4.50%	3.30%	-	4.50%	N/A	N/A	N/A

	Qualified Defined Benefit Pension Plan			OPEB Plans
IPL	2023	2022	2021	2023	2022	2021
Discount rate for benefit obligations	5.35%	5.55%	2.94%	5.40%	5.53%	2.80%
Discount rate for net periodic cost	5.55%	2.94%	2.61%	5.53%	2.80%	2.28%
Expected rate of return on plan assets	7.80%	7.80%	7.10%	6.90%	6.50%	5.10%
Rate of compensation increase	3.30%	3.30%	3.30%	N/A	N/A	N/A

	Qualified Defined Benefit Pension Plan			OPEB Plans
WPL	2023	2022	2021	2023	2022	2021
Discount rate for benefit obligations	5.35%	5.54%	2.94%	5.40%	5.53%	2.79%
Discount rate for net periodic cost	5.54%	2.94%	2.64%	5.53%	2.79%	2.27%
Expected rate of return on plan assets	7.80%	7.80%	7.10%	5.65%	5.49%	4.02%
Rate of compensation increase	3.30%	3.30%	3.30%	N/A	N/A	N/A

Net Periodic Benefit Costs

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

Alliant Energy	Defined Benefit Pension Plans			OPEB Plans
	2023	2022	2021	2023	2022	2021
Service cost	$5	$9	$11	$2	$3	$4
Interest cost	47	36	34	9	6	5
Expected return on plan assets (a)	(53)	(69)	(69)	(5)	(5)	(5)
Amortization of prior service credit (b)	(1)	(1)	—	—	—	—
Amortization of actuarial loss (c)	28	32	39	1	2	5
Settlement losses (d)	—	26	—	—	—	—
	$26	$33	$15	$7	$6	$9

IPL	Defined Benefit Pension Plans			OPEB Plans
	2023	2022	2021	2023	2022	2021
Service cost	$3	$6	$7	$1	$1	$1
Interest cost	21	16	16	3	2	2
Expected return on plan assets (a)	(26)	(31)	(32)	(3)	(4)	(3)
Amortization of actuarial loss (c)	11	13	17	1	1	2
Settlement losses (d)	—	13	—	—	—	—
	$9	$17	$8	$2	$—	$2

WPL	Defined Benefit Pension Plans			OPEB Plans
	2023	2022	2021	2023	2022	2021
Service cost	$2	$3	$4	$1	$1	$1
Interest cost	20	16	15	3	2	2
Expected return on plan assets (a)	(22)	(31)	(31)	(1)	(1)	—
Amortization of actuarial loss (c)	13	15	19	1	2	2
Settlement losses (d)	—	13	—	—	—	—
	$13	$16	$7	$4	$4	$5

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

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

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

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

Funded Status Of Benefit Plans

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

	Defined Benefit Pension Plans		OPEB Plans
Alliant Energy	2023	2022	2023	2022
Change in benefit obligation:
Net benefit obligation at January 1	$875	$1,251	$168	$210
Service cost	5	9	2	3
Interest cost	47	36	9	6
Plan participants’ contributions	—	—	4	4
Actuarial (gain) loss	23	(269)	(3)	(37)
Gross benefits paid	(74)	(152)	(20)	(18)
Net benefit obligation at December 31	876	875	160	168
Change in plan assets:
Fair value of plan assets at January 1	706	1,011	83	106
Actual return on plan assets	86	(204)	8	(17)
Employer contributions	14	51	8	8
Plan participants’ contributions	—	—	4	4
Gross benefits paid	(74)	(152)	(20)	(18)
Fair value of plan assets at December 31	732	706	83	83
Under funded status at December 31	($144)	($169)	($77)	($85)

	Defined Benefit Pension Plans		OPEB Plans
Alliant Energy	2023	2022	2023	2022
Amounts recognized on the balance sheets consist of:
Non-current assets	$—	$—	$14	$9
Current liabilities	(2)	(2)	(8)	(8)
Pension and other benefit obligations	(142)	(167)	(83)	(86)
Net amounts recognized at December 31	($144)	($169)	($77)	($85)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	$337	$376	$11	$20
Prior service credit	(2)	(3)	—	—
	$335	$373	$11	$20

	Defined Benefit Pension Plans		OPEB Plans
IPL	2023	2022	2023	2022
Change in benefit obligation:
Net benefit obligation at January 1	$389	$567	$68	$84
Service cost	3	6	1	1
Interest cost	21	16	3	2
Plan participants’ contributions	—	—	2	2
Actuarial (gain) loss	9	(123)	(1)	(14)
Gross benefits paid	(35)	(77)	(8)	(7)
Net benefit obligation at December 31	387	389	65	68
Change in plan assets:
Fair value of plan assets at January 1	344	462	58	74
Actual return on plan assets	42	(92)	7	(12)
Employer contributions	1	51	2	1
Plan participants’ contributions	—	—	2	2
Gross benefits paid	(35)	(77)	(8)	(7)
Fair value of plan assets at December 31	352	344	61	58
Under funded status at December 31	($35)	($45)	($4)	($10)

	Defined Benefit Pension Plans		OPEB Plans
IPL	2023	2022	2023	2022
Amounts recognized on the balance sheets consist of:
Non-current assets	$—	$—	$10	$6
Current liabilities	—	—	(1)	(2)
Pension and other benefit obligations	(35)	(45)	(13)	(14)
Net amounts recognized at December 31	($35)	($45)	($4)	($10)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	$135	$154	$9	$14
Prior service credit	(1)	(1)	—	—
	$134	$153	$9	$14

	Defined Benefit Pension Plans		OPEB Plans
WPL	2023	2022	2023	2022
Change in benefit obligation:
Net benefit obligation at January 1	$381	$546	$65	$81
Service cost	2	3	1	1
Interest cost	20	16	3	2
Plan participants’ contributions	—	—	2	2
Actuarial (gain) loss	10	(117)	(2)	(13)
Gross benefits paid	(32)	(67)	(8)	(8)
Net benefit obligation at December 31	381	381	61	65
Change in plan assets:
Fair value of plan assets at January 1	291	450	14	17
Actual return on plan assets	35	(92)	1	(2)
Employer contributions	12	—	5	5
Plan participants’ contributions	—	—	2	2
Gross benefits paid	(32)	(67)	(8)	(8)
Fair value of plan assets at December 31	306	291	14	14
Under funded status at December 31	($75)	($90)	($47)	($51)

	Defined Benefit Pension Plans		OPEB Plans
WPL	2023	2022	2023	2022
Amounts recognized on the balance sheets consist of:
Non-current assets	$—	$—	$4	$3
Current liabilities	—	—	(6)	(5)
Pension and other benefit obligations	(75)	(90)	(45)	(49)
Net amounts recognized at December 31	($75)	($90)	($47)	($51)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	$148	$165	$3	$6
Prior service credit	—	—	—	—
	$148	$165	$3	$6

Accumulated Benefit Obligations

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

	Defined Benefit Pension Plans		OPEB Plans
Alliant Energy	2023	2022	2023	2022
Accumulated benefit obligations	$857	$857	$160	$168
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	857	857	160	168
Fair value of plan assets	732	706	83	83
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	876	875	N/A	N/A
Fair value of plan assets	732	706	N/A	N/A

	Defined Benefit Pension Plans		OPEB Plans
IPL	2023	2022	2023	2022
Accumulated benefit obligations	$377	$379	$65	$68
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	377	379	65	68
Fair value of plan assets	352	344	61	58
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	387	389	N/A	N/A
Fair value of plan assets	352	344	N/A	N/A

	Defined Benefit Pension Plans		OPEB Plans
WPL	2023	2022	2023	2022
Accumulated benefit obligations	$373	$373	$61	$65
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	373	373	61	65
Fair value of plan assets	306	291	14	14
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	381	381	N/A	N/A
Fair value of plan assets	306	291	N/A	N/A

Regulatory Assets

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

	IPL		WPL
	2023	2022	2023	2022
Regulatory assets	$28	$30	$24	$25

Estimated Future Employer Contributions

Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2024 is as follows (in millions):

	Alliant Energy	IPL	WPL
Defined benefit pension plans (a)	$12	$—	$10
OPEB plans	8	1	6

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

Expected Benefit Payments

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

Alliant Energy	2024	2025	2026	2027	2028	2029 - 2033
Defined benefit pension benefits	$73	$73	$74	$75	$75	$343
OPEB	17	17	16	16	15	65
	$90	$90	$90	$91	$90	$408

IPL	2024	2025	2026	2027	2028	2029 - 2033
Defined benefit pension benefits	$34	$34	$34	$33	$33	$151
OPEB	7	7	7	6	6	25
	$41	$41	$41	$39	$39	$176

WPL	2024	2025	2026	2027	2028	2029 - 2033
Defined benefit pension benefits	$32	$32	$31	$31	$31	$146
OPEB	7	7	6	6	6	24
	$39	$39	$37	$37	$37	$170

Recognized Compensation Expense And Income Tax Benefits

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

	Alliant Energy			IPL			WPL
	2023	2022	2021	2023	2022	2021	2023	2022	2021
Compensation expense	$12	$13	$14	$6	$7	$8	$5	$5	$6
Income tax benefits	3	3	4	2	2	2	1	1	2

Pension Plans, Defined Benefit [Member]

Defined Benefit Plan Disclosure [Line Items]

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

At December 31, 2023, the current target ranges and actual allocations for the defined benefit pension plan assets were as follows:

	Target Range			Actual
	Allocation			Allocation
Cash and equivalents	0%	-	5%	2%
Equity securities	47%	-	67%	56%
Global asset securities	0%	-	15%	5%
Fixed income securities	27%	-	47%	37%

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

	2023				2022
	Fair	Level	Level	Level	Fair	Level	Level	Level
Alliant Energy	Value	1	2	3	Value	1	2	3
Cash and equivalents	$19	$—	$19	$—	$79	$—	$79	$—
Equity securities	223	223	—	—	185	185	—	—
Global asset securities	39	39	—	—	35	35	—	—
Fixed income securities	143	31	112	—	130	30	100	—
Total assets in fair value hierarchy	424	$293	$131	$—	429	$250	$179	$—
Assets measured at net asset value	306				276
Accrued investment income	2				1
Total pension plan assets	$732				$706

	2023				2022
	Fair	Level	Level	Level	Fair	Level	Level	Level
IPL	Value	1	2	3	Value	1	2	3
Cash and equivalents	$9	$—	$9	$—	$62	$—	$62	$—
Equity securities	107	107	—	—	83	83	—	—
Global asset securities	19	19	—	—	16	16	—	—
Fixed income securities	69	15	54	—	58	13	45	—
Total assets in fair value hierarchy	204	$141	$63	$—	219	$112	$107	$—
Assets measured at net asset value	147				124
Accrued investment income	1				1
Total pension plan assets	$352				$344

	2023				2022
	Fair	Level	Level	Level	Fair	Level	Level	Level
WPL	Value	1	2	3	Value	1	2	3
Cash and equivalents	$8	$—	$8	$—	$13	$—	$13	$—
Equity securities	93	93	—	—	82	82	—	—
Global asset securities	16	16	—	—	16	16	—	—
Fixed income securities	60	13	47	—	57	13	44	—
Total assets in fair value hierarchy	177	$122	$55	$—	168	$111	$57	$—
Assets measured at net asset value	128				122
Accrued investment income	1				1
Total pension plan assets	$306				$291

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

Defined Benefit Plan Disclosure [Line Items]

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

At December 31, 2023, the current target ranges and actual allocations for the defined benefit pension plan assets were as follows:

	Target Range			Actual
	Allocation			Allocation
Cash and equivalents	0%	-	5%	2%
Equity securities	47%	-	67%	56%
Global asset securities	0%	-	15%	5%
Fixed income securities	27%	-	47%	37%

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

	2023				2022
	Fair	Level	Level	Level	Fair	Level	Level	Level
Alliant Energy	Value	1	2	3	Value	1	2	3
Cash and equivalents	$19	$—	$19	$—	$79	$—	$79	$—
Equity securities	223	223	—	—	185	185	—	—
Global asset securities	39	39	—	—	35	35	—	—
Fixed income securities	143	31	112	—	130	30	100	—
Total assets in fair value hierarchy	424	$293	$131	$—	429	$250	$179	$—
Assets measured at net asset value	306				276
Accrued investment income	2				1
Total pension plan assets	$732				$706

	2023				2022
	Fair	Level	Level	Level	Fair	Level	Level	Level
IPL	Value	1	2	3	Value	1	2	3
Cash and equivalents	$9	$—	$9	$—	$62	$—	$62	$—
Equity securities	107	107	—	—	83	83	—	—
Global asset securities	19	19	—	—	16	16	—	—
Fixed income securities	69	15	54	—	58	13	45	—
Total assets in fair value hierarchy	204	$141	$63	$—	219	$112	$107	$—
Assets measured at net asset value	147				124
Accrued investment income	1				1
Total pension plan assets	$352				$344

	2023				2022
	Fair	Level	Level	Level	Fair	Level	Level	Level
WPL	Value	1	2	3	Value	1	2	3
Cash and equivalents	$8	$—	$8	$—	$13	$—	$13	$—
Equity securities	93	93	—	—	82	82	—	—
Global asset securities	16	16	—	—	16	16	—	—
Fixed income securities	60	13	47	—	57	13	44	—
Total assets in fair value hierarchy	177	$122	$55	$—	168	$111	$57	$—
Assets measured at net asset value	128				122
Accrued investment income	1				1
Total pension plan assets	$306				$291

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

Defined Benefit Plan Disclosure [Line Items]

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

At December 31, 2023, the current target ranges and actual allocations for the defined benefit pension plan assets were as follows:

	Target Range			Actual
	Allocation			Allocation
Cash and equivalents	0%	-	5%	2%
Equity securities	47%	-	67%	56%
Global asset securities	0%	-	15%	5%
Fixed income securities	27%	-	47%	37%

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

	2023				2022
	Fair	Level	Level	Level	Fair	Level	Level	Level
Alliant Energy	Value	1	2	3	Value	1	2	3
Cash and equivalents	$19	$—	$19	$—	$79	$—	$79	$—
Equity securities	223	223	—	—	185	185	—	—
Global asset securities	39	39	—	—	35	35	—	—
Fixed income securities	143	31	112	—	130	30	100	—
Total assets in fair value hierarchy	424	$293	$131	$—	429	$250	$179	$—
Assets measured at net asset value	306				276
Accrued investment income	2				1
Total pension plan assets	$732				$706

	2023				2022
	Fair	Level	Level	Level	Fair	Level	Level	Level
IPL	Value	1	2	3	Value	1	2	3
Cash and equivalents	$9	$—	$9	$—	$62	$—	$62	$—
Equity securities	107	107	—	—	83	83	—	—
Global asset securities	19	19	—	—	16	16	—	—
Fixed income securities	69	15	54	—	58	13	45	—
Total assets in fair value hierarchy	204	$141	$63	$—	219	$112	$107	$—
Assets measured at net asset value	147				124
Accrued investment income	1				1
Total pension plan assets	$352				$344

	2023				2022
	Fair	Level	Level	Level	Fair	Level	Level	Level
WPL	Value	1	2	3	Value	1	2	3
Cash and equivalents	$8	$—	$8	$—	$13	$—	$13	$—
Equity securities	93	93	—	—	82	82	—	—
Global asset securities	16	16	—	—	16	16	—	—
Fixed income securities	60	13	47	—	57	13	44	—
Total assets in fair value hierarchy	177	$122	$55	$—	168	$111	$57	$—
Assets measured at net asset value	128				122
Accrued investment income	1				1
Total pension plan assets	$306				$291

Other Postretirement Benefits Plans [Member]

Defined Benefit Plan Disclosure [Line Items]

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

At December 31, 2023, the current target ranges and actual allocations for VEBA trusts with assets greater than $5 million and the WPL 401(h) assets were as follows:

	Target Range			Actual
	Allocation			Allocation
Cash and equivalents	0%	-	5%	1%
Equity securities	0%	-	55%	36%
Fixed income securities	40%	-	100%	63%

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

	2023				2022
	Fair	Level	Level	Level	Fair	Level	Level	Level
Alliant Energy	Value	1	2	3	Value	1	2	3
Cash and equivalents	$9	$—	$9	$—	$3	$—	$3	$—
Equity securities	8	8	—	—	9	9	—	—
Global asset securities	—	—	—	—	1	1	—	—
Fixed income securities	47	47	—	—	47	46	1	—
Total assets in fair value hierarchy	64	$55	$9	$—	60	$56	$4	$—
Assets measured at net asset value	19				23
Total OPEB plan assets	$83				$83

	2023				2022
	Fair	Level	Level	Level	Fair	Level	Level	Level
IPL	Value	1	2	3	Value	1	2	3
Cash and equivalents	$1	$—	$1	$—	$1	$—	$1	$—
Equity securities	6	6	—	—	5	5	—	—
Fixed income securities	36	36	—	—	34	34	—	—
Total assets in fair value hierarchy	43	$42	$1	$—	40	$39	$1	$—
Assets measured at net asset value	18				18
Total OPEB plan assets	$61				$58

	2023				2022
	Fair	Level	Level	Level	Fair	Level	Level	Level
WPL	Value	1	2	3	Value	1	2	3
Cash and equivalents	$1	$—	$1	$—	$—	$—	$—	$—
Equity securities	2	2	—	—	1	1	—	—
Fixed income securities	11	11	—	—	13	13	—	—
Total OPEB plan assets	$14	$13	$1	$—	$14	$14	$—	$—

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

Defined Benefit Plan Disclosure [Line Items]

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

At December 31, 2023, the current target ranges and actual allocations for VEBA trusts with assets greater than $5 million and the WPL 401(h) assets were as follows:

	Target Range			Actual
	Allocation			Allocation
Cash and equivalents	0%	-	5%	1%
Equity securities	0%	-	55%	36%
Fixed income securities	40%	-	100%	63%

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

	2023				2022
	Fair	Level	Level	Level	Fair	Level	Level	Level
Alliant Energy	Value	1	2	3	Value	1	2	3
Cash and equivalents	$9	$—	$9	$—	$3	$—	$3	$—
Equity securities	8	8	—	—	9	9	—	—
Global asset securities	—	—	—	—	1	1	—	—
Fixed income securities	47	47	—	—	47	46	1	—
Total assets in fair value hierarchy	64	$55	$9	$—	60	$56	$4	$—
Assets measured at net asset value	19				23
Total OPEB plan assets	$83				$83

	2023				2022
	Fair	Level	Level	Level	Fair	Level	Level	Level
IPL	Value	1	2	3	Value	1	2	3
Cash and equivalents	$1	$—	$1	$—	$1	$—	$1	$—
Equity securities	6	6	—	—	5	5	—	—
Fixed income securities	36	36	—	—	34	34	—	—
Total assets in fair value hierarchy	43	$42	$1	$—	40	$39	$1	$—
Assets measured at net asset value	18				18
Total OPEB plan assets	$61				$58

	2023				2022
	Fair	Level	Level	Level	Fair	Level	Level	Level
WPL	Value	1	2	3	Value	1	2	3
Cash and equivalents	$1	$—	$1	$—	$—	$—	$—	$—
Equity securities	2	2	—	—	1	1	—	—
Fixed income securities	11	11	—	—	13	13	—	—
Total OPEB plan assets	$14	$13	$1	$—	$14	$14	$—	$—

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

Defined Benefit Plan Disclosure [Line Items]

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

At December 31, 2023, the current target ranges and actual allocations for VEBA trusts with assets greater than $5 million and the WPL 401(h) assets were as follows:

	Target Range			Actual
	Allocation			Allocation
Cash and equivalents	0%	-	5%	1%
Equity securities	0%	-	55%	36%
Fixed income securities	40%	-	100%	63%

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

	2023				2022
	Fair	Level	Level	Level	Fair	Level	Level	Level
Alliant Energy	Value	1	2	3	Value	1	2	3
Cash and equivalents	$9	$—	$9	$—	$3	$—	$3	$—
Equity securities	8	8	—	—	9	9	—	—
Global asset securities	—	—	—	—	1	1	—	—
Fixed income securities	47	47	—	—	47	46	1	—
Total assets in fair value hierarchy	64	$55	$9	$—	60	$56	$4	$—
Assets measured at net asset value	19				23
Total OPEB plan assets	$83				$83

	2023				2022
	Fair	Level	Level	Level	Fair	Level	Level	Level
IPL	Value	1	2	3	Value	1	2	3
Cash and equivalents	$1	$—	$1	$—	$1	$—	$1	$—
Equity securities	6	6	—	—	5	5	—	—
Fixed income securities	36	36	—	—	34	34	—	—
Total assets in fair value hierarchy	43	$42	$1	$—	40	$39	$1	$—
Assets measured at net asset value	18				18
Total OPEB plan assets	$61				$58

	2023				2022
	Fair	Level	Level	Level	Fair	Level	Level	Level
WPL	Value	1	2	3	Value	1	2	3
Cash and equivalents	$1	$—	$1	$—	$—	$—	$—	$—
Equity securities	2	2	—	—	1	1	—	—
Fixed income securities	11	11	—	—	13	13	—	—
Total OPEB plan assets	$14	$13	$1	$—	$14	$14	$—	$—

401(k) Savings Plan [Member]

Defined Benefit Plan Disclosure [Line Items]

Employees Participate In Defined Contribution Retirement Plans

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

	Alliant Energy			IPL			WPL
	2023	2022	2021	2023	2022	2021	2023	2022	2021
401(k) costs	$30	$28	$26	$14	$13	$13	$14	$13	$12

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

Defined Benefit Plan Disclosure [Line Items]

Employees Participate In Defined Contribution Retirement Plans

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

	Alliant Energy			IPL			WPL
	2023	2022	2021	2023	2022	2021	2023	2022	2021
401(k) costs	$30	$28	$26	$14	$13	$13	$14	$13	$12

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

Defined Benefit Plan Disclosure [Line Items]

Employees Participate In Defined Contribution Retirement Plans

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

	Alliant Energy			IPL			WPL
	2023	2022	2021	2023	2022	2021	2023	2022	2021
401(k) costs	$30	$28	$26	$14	$13	$13	$14	$13	$12

Performance Shares Equity Awards [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule Of Equity-based Compensation Plans Activity

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

	2023		2022		2021
	Shares	Weighted Average Grant Date Fair Value	Shares	Weighted Average Grant Date Fair Value	Shares	Weighted Average Grant Date Fair Value
Nonvested awards, January 1	190,273	$54.13	196,429	$51.59	129,156	$54.63
Granted	108,712	55.68	74,106	54.45	73,112	46.19
Vested	(53,431)	64.04	(71,101)	47.48	—	—
Forfeited	(11,600)	53.88	(9,161)	53.99	(5,839)	51.07
Nonvested awards, December 31	233,954	52.60	190,273	54.13	196,429	51.59

Restricted Stock Units Equity Awards [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule Of Equity-based Compensation Plans Activity

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

	2023		2022		2021
	Units	Weighted Average Grant Date Fair Value	Units	Weighted Average Grant Date Fair Value	Units	Weighted Average Grant Date Fair Value
Nonvested units, January 1	198,275	$54.53	217,819	$50.54	146,549	$51.54
Granted	106,124	52.77	77,122	56.88	80,152	48.65
Vested	(55,345)	59.40	(82,770)	46.08	—	—
Forfeited	(14,795)	54.53	(13,896)	55.53	(8,882)	49.84
Nonvested units, December 31	234,259	52.58	198,275	54.53	217,819	50.54

Performance Restricted Stock Units Equity Awards [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule Of Equity-based Compensation Plans Activity

A summary of the performance restricted stock units activity, with amounts representing the target number of units, was as follows:

	2023		2022		2021
	Units	Weighted Average Grant Date Fair Value	Units	Weighted Average Grant Date Fair Value	Units	Weighted Average Grant Date Fair Value
Nonvested units, January 1	199,874	$54.74	196,429	$50.74	197,463	$47.31
Granted	124,217	52.71	84,670	57.01	73,112	48.66
Vested	(53,431)	59.36	(71,101)	46.24	(68,307)	38.60
Forfeited	(13,021)	55.47	(10,124)	55.92	(5,839)	50.46
Nonvested units, December 31	257,639	52.76	199,874	54.74	196,429	50.74