Benefit Plans (Tables)

12 Months Ended

Dec. 31, 2020

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	2020			2019			2018			2020	2019	2018
Discount rate for benefit obligations	2.57%			3.48%			4.34%			2.31%	3.40%	4.24%
Discount rate for net periodic cost	3.48%			4.34%			3.66%			3.40%	4.24%	3.53%
Expected rate of return on plan assets	7.10%			7.60%			7.60%			4.50%	5.44%	5.44%
Interest crediting rate for Alliant Energy Cash Balance Pension Plan	4.76%			5.52%			5.04%			N/A	N/A	N/A
Rate of compensation increase	3.65%	-	4.50%	3.65%	-	4.50%	3.65%	-	4.50%	N/A	N/A	N/A

	Qualified Defined Benefit Pension Plan			OPEB Plans
IPL	2020	2019	2018	2020	2019	2018
Discount rate for benefit obligations	2.61%	3.51%	4.35%	2.28%	3.39%	4.23%
Discount rate for net periodic cost	3.51%	4.35%	3.68%	3.39%	4.23%	3.51%
Expected rate of return on plan assets	7.10%	7.60%	7.60%	4.50%	5.60%	5.60%
Rate of compensation increase	3.65%	3.65%	3.65%	N/A	N/A	N/A

	Qualified Defined Benefit Pension Plan			OPEB Plans
WPL	2020	2019	2018	2020	2019	2018
Discount rate for benefit obligations	2.64%	3.50%	4.35%	2.27%	3.39%	4.23%
Discount rate for net periodic cost	3.50%	4.35%	3.69%	3.39%	4.23%	3.51%
Expected rate of return on plan assets	7.10%	7.60%	7.60%	3.28%	3.81%	3.84%
Rate of compensation increase	3.65%	3.65%	3.65%	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.

Alliant Energy	Defined Benefit Pension Plans			OPEB Plans
	2020	2019	2018	2020	2019	2018
Service cost	$11	$10	$12	$3	$3	$4
Interest cost	43	50	47	7	9	8
Expected return on plan assets (a)	(70)	(60)	(69)	(5)	(5)	(6)
Amortization of prior service credit (b)	—	(1)	(1)	—	—	—
Amortization of actuarial loss (c)	34	36	35	3	3	3
Settlement losses (d)	12	—	—	—	—	—
	$30	$35	$24	$8	$10	$9

IPL	Defined Benefit Pension Plans			OPEB Plans
	2020	2019	2018	2020	2019	2018
Service cost	$7	$6	$7	$1	$1	$2
Interest cost	20	23	21	3	3	3
Expected return on plan assets (a)	(33)	(28)	(32)	(4)	(4)	(4)
Amortization of actuarial loss (c)	15	15	15	1	2	1
Settlement losses (d)	7	—	—	—	—	—
	$16	$16	$11	$1	$2	$2

WPL	Defined Benefit Pension Plans			OPEB Plans
	2020	2019	2018	2020	2019	2018
Service cost	$4	$3	$4	$2	$1	$2
Interest cost	19	21	20	3	3	3
Expected return on plan assets (a)	(31)	(26)	(30)	(1)	(1)	(1)
Amortization of prior service credit (b)	—	—	—	(1)	—	—
Amortization of actuarial loss (c)	16	18	17	2	2	2
	$8	$16	$11	$5	$5	$6

(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 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	2020	2019	2020	2019
Change in benefit obligation:
Net benefit obligation at January 1	$1,280	$1,175	$214	$206
Service cost	11	10	3	3
Interest cost	43	50	7	9
Plan participants’ contributions	—	—	4	3
Actuarial loss	132	124	18	14
Gross benefits paid	(115)	(79)	(19)	(21)
Net benefit obligation at December 31	1,351	1,280	227	214
Change in plan assets:
Fair value of plan assets at January 1	931	809	105	99
Actual return on plan assets	108	168	11	15
Employer contributions	60	33	7	9
Plan participants’ contributions	—	—	4	3
Gross benefits paid	(115)	(79)	(19)	(21)
Fair value of plan assets at December 31	984	931	108	105
Under funded status at December 31	($367)	($349)	($119)	($109)

	Defined Benefit Pension Plans		OPEB Plans
Alliant Energy	2020	2019	2020	2019
Amounts recognized on the balance sheets consist of:
Non-current assets	$—	$—	$8	$10
Current liabilities	(2)	(14)	(8)	(8)
Pension and other benefit obligations	(365)	(335)	(119)	(111)
Net amounts recognized at December 31	($367)	($349)	($119)	($109)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	$533	$485	$54	$45
Prior service credit	(5)	(5)	(1)	(1)
	$528	$480	$53	$44

	Defined Benefit Pension Plans		OPEB Plans
IPL	2020	2019	2020	2019
Change in benefit obligation:
Net benefit obligation at January 1	$581	$534	$86	$83
Service cost	7	6	1	1
Interest cost	20	23	3	3
Plan participants’ contributions	—	—	1	1
Actuarial loss	60	56	8	6
Gross benefits paid	(53)	(38)	(8)	(8)
Net benefit obligation at December 31	615	581	91	86
Change in plan assets:
Fair value of plan assets at January 1	436	378	72	67
Actual return on plan assets	51	79	7	10
Employer contributions	19	17	2	2
Plan participants’ contributions	—	—	1	1
Gross benefits paid	(53)	(38)	(8)	(8)
Fair value of plan assets at December 31	453	436	74	72
Under funded status at December 31	($162)	($145)	($17)	($14)

	Defined Benefit Pension Plans		OPEB Plans
IPL	2020	2019	2020	2019
Amounts recognized on the balance sheets consist of:
Non-current assets	$—	$—	$4	$7
Current liabilities	(1)	(1)	(2)	(2)
Pension and other benefit obligations	(161)	(144)	(19)	(19)
Net amounts recognized at December 31	($162)	($145)	($17)	($14)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	$228	$208	$20	$17
Prior service credit	(1)	(1)	—	—
	$227	$207	$20	$17

	Defined Benefit Pension Plans		OPEB Plans
WPL	2020	2019	2020	2019
Change in benefit obligation:
Net benefit obligation at January 1	$550	$507	$85	$83
Service cost	4	3	2	1
Interest cost	19	21	3	3
Plan participants’ contributions	—	—	2	2
Actuarial loss	55	54	5	5
Gross benefits paid	(40)	(35)	(8)	(9)
Net benefit obligation at December 31	588	550	89	85
Change in plan assets:
Fair value of plan assets at January 1	406	352	17	17
Actual return on plan assets	48	73	2	1
Employer contributions	22	16	5	6
Plan participants’ contributions	—	—	2	2
Gross benefits paid	(40)	(35)	(8)	(9)
Fair value of plan assets at December 31	436	406	18	17
Under funded status at December 31	($152)	($144)	($71)	($68)

	Defined Benefit Pension Plans		OPEB Plans
WPL	2020	2019	2020	2019
Amounts recognized on the balance sheets consist of:
Non-current assets	$—	$—	$3	$3
Current liabilities	—	—	(6)	(6)
Pension and other benefit obligations	(152)	(144)	(68)	(65)
Net amounts recognized at December 31	($152)	($144)	($71)	($68)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	$233	$212	$25	$22
Prior service credit	(1)	(1)	(1)	(1)
	$232	$211	$24	$21

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	2020	2019	2020	2019
Accumulated benefit obligations	$1,305	$1,234	$227	$214
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	1,305	1,234	227	214
Fair value of plan assets	984	931	108	105
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	1,351	1,280	N/A	N/A
Fair value of plan assets	984	931	N/A	N/A

	Defined Benefit Pension Plans		OPEB Plans
IPL	2020	2019	2020	2019
Accumulated benefit obligations	$589	$558	$91	$86
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	589	558	91	86
Fair value of plan assets	453	436	74	72
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	615	581	N/A	N/A
Fair value of plan assets	453	436	N/A	N/A

	Defined Benefit Pension Plans		OPEB Plans
WPL	2020	2019	2020	2019
Accumulated benefit obligations	$573	$536	$89	$85
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	573	536	89	85
Fair value of plan assets	436	406	18	17
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	588	550	N/A	N/A
Fair value of plan assets	436	406	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
	2020	2019	2020	2019
Regulatory assets	$44	$39	$34	$29

Estimated Future Employer Contributions

Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2021 is as follows (in millions):

	Alliant Energy	IPL	WPL
Defined benefit pension plans (a)	$39	$17	$18
OPEB plans	8	2	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	2021	2022	2023	2024	2025	2026 - 2030
Defined benefit pension benefits	$76	$78	$79	$79	$80	$398
OPEB	18	18	17	17	17	74
	$94	$96	$96	$96	$97	$472

IPL	2021	2022	2023	2024	2025	2026 - 2030
Defined benefit pension benefits	$38	$38	$39	$38	$38	$181
OPEB	7	7	7	7	7	29
	$45	$45	$46	$45	$45	$210

WPL	2021	2022	2023	2024	2025	2026 - 2030
Defined benefit pension benefits	$32	$32	$32	$33	$33	$162
OPEB	7	7	7	7	6	29
	$39	$39	$39	$40	$39	$191

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
	2020	2019	2018	2020	2019	2018	2020	2019	2018
Compensation expense	$16	$26	$17	$9	$15	$9	$6	$10	$7
Income tax benefits	4	7	5	2	4	3	2	3	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):

	2020	2019
Carrying value	$11	$10
Fair market value	20	21

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	2020			2019			2018			2020	2019	2018
Discount rate for benefit obligations	2.57%			3.48%			4.34%			2.31%	3.40%	4.24%
Discount rate for net periodic cost	3.48%			4.34%			3.66%			3.40%	4.24%	3.53%
Expected rate of return on plan assets	7.10%			7.60%			7.60%			4.50%	5.44%	5.44%
Interest crediting rate for Alliant Energy Cash Balance Pension Plan	4.76%			5.52%			5.04%			N/A	N/A	N/A
Rate of compensation increase	3.65%	-	4.50%	3.65%	-	4.50%	3.65%	-	4.50%	N/A	N/A	N/A

	Qualified Defined Benefit Pension Plan			OPEB Plans
IPL	2020	2019	2018	2020	2019	2018
Discount rate for benefit obligations	2.61%	3.51%	4.35%	2.28%	3.39%	4.23%
Discount rate for net periodic cost	3.51%	4.35%	3.68%	3.39%	4.23%	3.51%
Expected rate of return on plan assets	7.10%	7.60%	7.60%	4.50%	5.60%	5.60%
Rate of compensation increase	3.65%	3.65%	3.65%	N/A	N/A	N/A

	Qualified Defined Benefit Pension Plan			OPEB Plans
WPL	2020	2019	2018	2020	2019	2018
Discount rate for benefit obligations	2.64%	3.50%	4.35%	2.27%	3.39%	4.23%
Discount rate for net periodic cost	3.50%	4.35%	3.69%	3.39%	4.23%	3.51%
Expected rate of return on plan assets	7.10%	7.60%	7.60%	3.28%	3.81%	3.84%
Rate of compensation increase	3.65%	3.65%	3.65%	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.

Alliant Energy	Defined Benefit Pension Plans			OPEB Plans
	2020	2019	2018	2020	2019	2018
Service cost	$11	$10	$12	$3	$3	$4
Interest cost	43	50	47	7	9	8
Expected return on plan assets (a)	(70)	(60)	(69)	(5)	(5)	(6)
Amortization of prior service credit (b)	—	(1)	(1)	—	—	—
Amortization of actuarial loss (c)	34	36	35	3	3	3
Settlement losses (d)	12	—	—	—	—	—
	$30	$35	$24	$8	$10	$9

IPL	Defined Benefit Pension Plans			OPEB Plans
	2020	2019	2018	2020	2019	2018
Service cost	$7	$6	$7	$1	$1	$2
Interest cost	20	23	21	3	3	3
Expected return on plan assets (a)	(33)	(28)	(32)	(4)	(4)	(4)
Amortization of actuarial loss (c)	15	15	15	1	2	1
Settlement losses (d)	7	—	—	—	—	—
	$16	$16	$11	$1	$2	$2

WPL	Defined Benefit Pension Plans			OPEB Plans
	2020	2019	2018	2020	2019	2018
Service cost	$4	$3	$4	$2	$1	$2
Interest cost	19	21	20	3	3	3
Expected return on plan assets (a)	(31)	(26)	(30)	(1)	(1)	(1)
Amortization of prior service credit (b)	—	—	—	(1)	—	—
Amortization of actuarial loss (c)	16	18	17	2	2	2
	$8	$16	$11	$5	$5	$6

(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 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	2020	2019	2020	2019
Change in benefit obligation:
Net benefit obligation at January 1	$1,280	$1,175	$214	$206
Service cost	11	10	3	3
Interest cost	43	50	7	9
Plan participants’ contributions	—	—	4	3
Actuarial loss	132	124	18	14
Gross benefits paid	(115)	(79)	(19)	(21)
Net benefit obligation at December 31	1,351	1,280	227	214
Change in plan assets:
Fair value of plan assets at January 1	931	809	105	99
Actual return on plan assets	108	168	11	15
Employer contributions	60	33	7	9
Plan participants’ contributions	—	—	4	3
Gross benefits paid	(115)	(79)	(19)	(21)
Fair value of plan assets at December 31	984	931	108	105
Under funded status at December 31	($367)	($349)	($119)	($109)

	Defined Benefit Pension Plans		OPEB Plans
Alliant Energy	2020	2019	2020	2019
Amounts recognized on the balance sheets consist of:
Non-current assets	$—	$—	$8	$10
Current liabilities	(2)	(14)	(8)	(8)
Pension and other benefit obligations	(365)	(335)	(119)	(111)
Net amounts recognized at December 31	($367)	($349)	($119)	($109)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	$533	$485	$54	$45
Prior service credit	(5)	(5)	(1)	(1)
	$528	$480	$53	$44

	Defined Benefit Pension Plans		OPEB Plans
IPL	2020	2019	2020	2019
Change in benefit obligation:
Net benefit obligation at January 1	$581	$534	$86	$83
Service cost	7	6	1	1
Interest cost	20	23	3	3
Plan participants’ contributions	—	—	1	1
Actuarial loss	60	56	8	6
Gross benefits paid	(53)	(38)	(8)	(8)
Net benefit obligation at December 31	615	581	91	86
Change in plan assets:
Fair value of plan assets at January 1	436	378	72	67
Actual return on plan assets	51	79	7	10
Employer contributions	19	17	2	2
Plan participants’ contributions	—	—	1	1
Gross benefits paid	(53)	(38)	(8)	(8)
Fair value of plan assets at December 31	453	436	74	72
Under funded status at December 31	($162)	($145)	($17)	($14)

	Defined Benefit Pension Plans		OPEB Plans
IPL	2020	2019	2020	2019
Amounts recognized on the balance sheets consist of:
Non-current assets	$—	$—	$4	$7
Current liabilities	(1)	(1)	(2)	(2)
Pension and other benefit obligations	(161)	(144)	(19)	(19)
Net amounts recognized at December 31	($162)	($145)	($17)	($14)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	$228	$208	$20	$17
Prior service credit	(1)	(1)	—	—
	$227	$207	$20	$17

	Defined Benefit Pension Plans		OPEB Plans
WPL	2020	2019	2020	2019
Change in benefit obligation:
Net benefit obligation at January 1	$550	$507	$85	$83
Service cost	4	3	2	1
Interest cost	19	21	3	3
Plan participants’ contributions	—	—	2	2
Actuarial loss	55	54	5	5
Gross benefits paid	(40)	(35)	(8)	(9)
Net benefit obligation at December 31	588	550	89	85
Change in plan assets:
Fair value of plan assets at January 1	406	352	17	17
Actual return on plan assets	48	73	2	1
Employer contributions	22	16	5	6
Plan participants’ contributions	—	—	2	2
Gross benefits paid	(40)	(35)	(8)	(9)
Fair value of plan assets at December 31	436	406	18	17
Under funded status at December 31	($152)	($144)	($71)	($68)

	Defined Benefit Pension Plans		OPEB Plans
WPL	2020	2019	2020	2019
Amounts recognized on the balance sheets consist of:
Non-current assets	$—	$—	$3	$3
Current liabilities	—	—	(6)	(6)
Pension and other benefit obligations	(152)	(144)	(68)	(65)
Net amounts recognized at December 31	($152)	($144)	($71)	($68)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	$233	$212	$25	$22
Prior service credit	(1)	(1)	(1)	(1)
	$232	$211	$24	$21

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	2020	2019	2020	2019
Accumulated benefit obligations	$1,305	$1,234	$227	$214
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	1,305	1,234	227	214
Fair value of plan assets	984	931	108	105
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	1,351	1,280	N/A	N/A
Fair value of plan assets	984	931	N/A	N/A

	Defined Benefit Pension Plans		OPEB Plans
IPL	2020	2019	2020	2019
Accumulated benefit obligations	$589	$558	$91	$86
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	589	558	91	86
Fair value of plan assets	453	436	74	72
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	615	581	N/A	N/A
Fair value of plan assets	453	436	N/A	N/A

	Defined Benefit Pension Plans		OPEB Plans
WPL	2020	2019	2020	2019
Accumulated benefit obligations	$573	$536	$89	$85
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	573	536	89	85
Fair value of plan assets	436	406	18	17
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	588	550	N/A	N/A
Fair value of plan assets	436	406	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
	2020	2019	2020	2019
Regulatory assets	$44	$39	$34	$29

Estimated Future Employer Contributions

Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2021 is as follows (in millions):

	Alliant Energy	IPL	WPL
Defined benefit pension plans (a)	$39	$17	$18
OPEB plans	8	2	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	2021	2022	2023	2024	2025	2026 - 2030
Defined benefit pension benefits	$76	$78	$79	$79	$80	$398
OPEB	18	18	17	17	17	74
	$94	$96	$96	$96	$97	$472

IPL	2021	2022	2023	2024	2025	2026 - 2030
Defined benefit pension benefits	$38	$38	$39	$38	$38	$181
OPEB	7	7	7	7	7	29
	$45	$45	$46	$45	$45	$210

WPL	2021	2022	2023	2024	2025	2026 - 2030
Defined benefit pension benefits	$32	$32	$32	$33	$33	$162
OPEB	7	7	7	7	6	29
	$39	$39	$39	$40	$39	$191

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
	2020	2019	2018	2020	2019	2018	2020	2019	2018
Compensation expense	$16	$26	$17	$9	$15	$9	$6	$10	$7
Income tax benefits	4	7	5	2	4	3	2	3	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	2020			2019			2018			2020	2019	2018
Discount rate for benefit obligations	2.57%			3.48%			4.34%			2.31%	3.40%	4.24%
Discount rate for net periodic cost	3.48%			4.34%			3.66%			3.40%	4.24%	3.53%
Expected rate of return on plan assets	7.10%			7.60%			7.60%			4.50%	5.44%	5.44%
Interest crediting rate for Alliant Energy Cash Balance Pension Plan	4.76%			5.52%			5.04%			N/A	N/A	N/A
Rate of compensation increase	3.65%	-	4.50%	3.65%	-	4.50%	3.65%	-	4.50%	N/A	N/A	N/A

	Qualified Defined Benefit Pension Plan			OPEB Plans
IPL	2020	2019	2018	2020	2019	2018
Discount rate for benefit obligations	2.61%	3.51%	4.35%	2.28%	3.39%	4.23%
Discount rate for net periodic cost	3.51%	4.35%	3.68%	3.39%	4.23%	3.51%
Expected rate of return on plan assets	7.10%	7.60%	7.60%	4.50%	5.60%	5.60%
Rate of compensation increase	3.65%	3.65%	3.65%	N/A	N/A	N/A

	Qualified Defined Benefit Pension Plan			OPEB Plans
WPL	2020	2019	2018	2020	2019	2018
Discount rate for benefit obligations	2.64%	3.50%	4.35%	2.27%	3.39%	4.23%
Discount rate for net periodic cost	3.50%	4.35%	3.69%	3.39%	4.23%	3.51%
Expected rate of return on plan assets	7.10%	7.60%	7.60%	3.28%	3.81%	3.84%
Rate of compensation increase	3.65%	3.65%	3.65%	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.

Alliant Energy	Defined Benefit Pension Plans			OPEB Plans
	2020	2019	2018	2020	2019	2018
Service cost	$11	$10	$12	$3	$3	$4
Interest cost	43	50	47	7	9	8
Expected return on plan assets (a)	(70)	(60)	(69)	(5)	(5)	(6)
Amortization of prior service credit (b)	—	(1)	(1)	—	—	—
Amortization of actuarial loss (c)	34	36	35	3	3	3
Settlement losses (d)	12	—	—	—	—	—
	$30	$35	$24	$8	$10	$9

IPL	Defined Benefit Pension Plans			OPEB Plans
	2020	2019	2018	2020	2019	2018
Service cost	$7	$6	$7	$1	$1	$2
Interest cost	20	23	21	3	3	3
Expected return on plan assets (a)	(33)	(28)	(32)	(4)	(4)	(4)
Amortization of actuarial loss (c)	15	15	15	1	2	1
Settlement losses (d)	7	—	—	—	—	—
	$16	$16	$11	$1	$2	$2

WPL	Defined Benefit Pension Plans			OPEB Plans
	2020	2019	2018	2020	2019	2018
Service cost	$4	$3	$4	$2	$1	$2
Interest cost	19	21	20	3	3	3
Expected return on plan assets (a)	(31)	(26)	(30)	(1)	(1)	(1)
Amortization of prior service credit (b)	—	—	—	(1)	—	—
Amortization of actuarial loss (c)	16	18	17	2	2	2
	$8	$16	$11	$5	$5	$6

(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 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	2020	2019	2020	2019
Change in benefit obligation:
Net benefit obligation at January 1	$1,280	$1,175	$214	$206
Service cost	11	10	3	3
Interest cost	43	50	7	9
Plan participants’ contributions	—	—	4	3
Actuarial loss	132	124	18	14
Gross benefits paid	(115)	(79)	(19)	(21)
Net benefit obligation at December 31	1,351	1,280	227	214
Change in plan assets:
Fair value of plan assets at January 1	931	809	105	99
Actual return on plan assets	108	168	11	15
Employer contributions	60	33	7	9
Plan participants’ contributions	—	—	4	3
Gross benefits paid	(115)	(79)	(19)	(21)
Fair value of plan assets at December 31	984	931	108	105
Under funded status at December 31	($367)	($349)	($119)	($109)

	Defined Benefit Pension Plans		OPEB Plans
Alliant Energy	2020	2019	2020	2019
Amounts recognized on the balance sheets consist of:
Non-current assets	$—	$—	$8	$10
Current liabilities	(2)	(14)	(8)	(8)
Pension and other benefit obligations	(365)	(335)	(119)	(111)
Net amounts recognized at December 31	($367)	($349)	($119)	($109)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	$533	$485	$54	$45
Prior service credit	(5)	(5)	(1)	(1)
	$528	$480	$53	$44

	Defined Benefit Pension Plans		OPEB Plans
IPL	2020	2019	2020	2019
Change in benefit obligation:
Net benefit obligation at January 1	$581	$534	$86	$83
Service cost	7	6	1	1
Interest cost	20	23	3	3
Plan participants’ contributions	—	—	1	1
Actuarial loss	60	56	8	6
Gross benefits paid	(53)	(38)	(8)	(8)
Net benefit obligation at December 31	615	581	91	86
Change in plan assets:
Fair value of plan assets at January 1	436	378	72	67
Actual return on plan assets	51	79	7	10
Employer contributions	19	17	2	2
Plan participants’ contributions	—	—	1	1
Gross benefits paid	(53)	(38)	(8)	(8)
Fair value of plan assets at December 31	453	436	74	72
Under funded status at December 31	($162)	($145)	($17)	($14)

	Defined Benefit Pension Plans		OPEB Plans
IPL	2020	2019	2020	2019
Amounts recognized on the balance sheets consist of:
Non-current assets	$—	$—	$4	$7
Current liabilities	(1)	(1)	(2)	(2)
Pension and other benefit obligations	(161)	(144)	(19)	(19)
Net amounts recognized at December 31	($162)	($145)	($17)	($14)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	$228	$208	$20	$17
Prior service credit	(1)	(1)	—	—
	$227	$207	$20	$17

	Defined Benefit Pension Plans		OPEB Plans
WPL	2020	2019	2020	2019
Change in benefit obligation:
Net benefit obligation at January 1	$550	$507	$85	$83
Service cost	4	3	2	1
Interest cost	19	21	3	3
Plan participants’ contributions	—	—	2	2
Actuarial loss	55	54	5	5
Gross benefits paid	(40)	(35)	(8)	(9)
Net benefit obligation at December 31	588	550	89	85
Change in plan assets:
Fair value of plan assets at January 1	406	352	17	17
Actual return on plan assets	48	73	2	1
Employer contributions	22	16	5	6
Plan participants’ contributions	—	—	2	2
Gross benefits paid	(40)	(35)	(8)	(9)
Fair value of plan assets at December 31	436	406	18	17
Under funded status at December 31	($152)	($144)	($71)	($68)

	Defined Benefit Pension Plans		OPEB Plans
WPL	2020	2019	2020	2019
Amounts recognized on the balance sheets consist of:
Non-current assets	$—	$—	$3	$3
Current liabilities	—	—	(6)	(6)
Pension and other benefit obligations	(152)	(144)	(68)	(65)
Net amounts recognized at December 31	($152)	($144)	($71)	($68)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	$233	$212	$25	$22
Prior service credit	(1)	(1)	(1)	(1)
	$232	$211	$24	$21

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	2020	2019	2020	2019
Accumulated benefit obligations	$1,305	$1,234	$227	$214
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	1,305	1,234	227	214
Fair value of plan assets	984	931	108	105
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	1,351	1,280	N/A	N/A
Fair value of plan assets	984	931	N/A	N/A

	Defined Benefit Pension Plans		OPEB Plans
IPL	2020	2019	2020	2019
Accumulated benefit obligations	$589	$558	$91	$86
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	589	558	91	86
Fair value of plan assets	453	436	74	72
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	615	581	N/A	N/A
Fair value of plan assets	453	436	N/A	N/A

	Defined Benefit Pension Plans		OPEB Plans
WPL	2020	2019	2020	2019
Accumulated benefit obligations	$573	$536	$89	$85
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	573	536	89	85
Fair value of plan assets	436	406	18	17
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	588	550	N/A	N/A
Fair value of plan assets	436	406	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
	2020	2019	2020	2019
Regulatory assets	$44	$39	$34	$29

Estimated Future Employer Contributions

Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2021 is as follows (in millions):

	Alliant Energy	IPL	WPL
Defined benefit pension plans (a)	$39	$17	$18
OPEB plans	8	2	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	2021	2022	2023	2024	2025	2026 - 2030
Defined benefit pension benefits	$76	$78	$79	$79	$80	$398
OPEB	18	18	17	17	17	74
	$94	$96	$96	$96	$97	$472

IPL	2021	2022	2023	2024	2025	2026 - 2030
Defined benefit pension benefits	$38	$38	$39	$38	$38	$181
OPEB	7	7	7	7	7	29
	$45	$45	$46	$45	$45	$210

WPL	2021	2022	2023	2024	2025	2026 - 2030
Defined benefit pension benefits	$32	$32	$32	$33	$33	$162
OPEB	7	7	7	7	6	29
	$39	$39	$39	$40	$39	$191

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
	2020	2019	2018	2020	2019	2018	2020	2019	2018
Compensation expense	$16	$26	$17	$9	$15	$9	$6	$10	$7
Income tax benefits	4	7	5	2	4	3	2	3	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, 2020, 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%	5%
Equity securities - U.S.	11%	-	41%	26%
Equity securities - international	14%	-	34%	23%
Global asset securities	5%	-	15%	9%
Risk parity securities	5%	-	15%	9%
Fixed income securities	20%	-	40%	28%

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

	2020				2019
	Fair	Level	Level	Level	Fair	Level	Level	Level
Alliant Energy	Value	1	2	3	Value	1	2	3
Cash and equivalents	$46	$—	$46	$—	$46	$4	$42	$—
Equity securities - U.S.	182	182	—	—	161	161	—	—
Equity securities - international	151	151	—	—	136	136	—	—
Global asset securities	45	45	—	—	47	47	—	—
Fixed income securities	134	56	78	—	131	58	73	—
Total assets in fair value hierarchy	558	$434	$124	$—	521	$406	$115	$—
Assets measured at net asset value	426				410
Accrued investment income	1				1
Due to brokers, net (pending trades with brokers)	(1)				(1)
Total pension plan assets	$984				$931

	2020				2019
	Fair	Level	Level	Level	Fair	Level	Level	Level
IPL	Value	1	2	3	Value	1	2	3
Cash and equivalents	$21	$—	$21	$—	$22	$2	$20	$—
Equity securities - U.S.	84	84	—	—	75	75	—	—
Equity securities - international	69	69	—	—	64	64	—	—
Global asset securities	21	21	—	—	22	22	—	—
Fixed income securities	62	26	36	—	61	27	34	—
Total assets in fair value hierarchy	257	$200	$57	$—	244	$190	$54	$—
Assets measured at net asset value	196				192
Total pension plan assets	$453				$436

	2020				2019
	Fair	Level	Level	Level	Fair	Level	Level	Level
WPL	Value	1	2	3	Value	1	2	3
Cash and equivalents	$20	$—	$20	$—	$20	$2	$18	$—
Equity securities - U.S.	81	81	—	—	70	70	—	—
Equity securities - international	67	67	—	—	59	59	—	—
Global asset securities	20	20	—	—	21	21	—	—
Fixed income securities	59	25	34	—	57	25	32	—
Total assets in fair value hierarchy	247	$193	$54	$—	227	$177	$50	$—
Assets measured at net asset value	189				179
Total pension plan assets	$436				$406

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, 2020, 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%	5%
Equity securities - U.S.	11%	-	41%	26%
Equity securities - international	14%	-	34%	23%
Global asset securities	5%	-	15%	9%
Risk parity securities	5%	-	15%	9%
Fixed income securities	20%	-	40%	28%

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

	2020				2019
	Fair	Level	Level	Level	Fair	Level	Level	Level
Alliant Energy	Value	1	2	3	Value	1	2	3
Cash and equivalents	$46	$—	$46	$—	$46	$4	$42	$—
Equity securities - U.S.	182	182	—	—	161	161	—	—
Equity securities - international	151	151	—	—	136	136	—	—
Global asset securities	45	45	—	—	47	47	—	—
Fixed income securities	134	56	78	—	131	58	73	—
Total assets in fair value hierarchy	558	$434	$124	$—	521	$406	$115	$—
Assets measured at net asset value	426				410
Accrued investment income	1				1
Due to brokers, net (pending trades with brokers)	(1)				(1)
Total pension plan assets	$984				$931

	2020				2019
	Fair	Level	Level	Level	Fair	Level	Level	Level
IPL	Value	1	2	3	Value	1	2	3
Cash and equivalents	$21	$—	$21	$—	$22	$2	$20	$—
Equity securities - U.S.	84	84	—	—	75	75	—	—
Equity securities - international	69	69	—	—	64	64	—	—
Global asset securities	21	21	—	—	22	22	—	—
Fixed income securities	62	26	36	—	61	27	34	—
Total assets in fair value hierarchy	257	$200	$57	$—	244	$190	$54	$—
Assets measured at net asset value	196				192
Total pension plan assets	$453				$436

	2020				2019
	Fair	Level	Level	Level	Fair	Level	Level	Level
WPL	Value	1	2	3	Value	1	2	3
Cash and equivalents	$20	$—	$20	$—	$20	$2	$18	$—
Equity securities - U.S.	81	81	—	—	70	70	—	—
Equity securities - international	67	67	—	—	59	59	—	—
Global asset securities	20	20	—	—	21	21	—	—
Fixed income securities	59	25	34	—	57	25	32	—
Total assets in fair value hierarchy	247	$193	$54	$—	227	$177	$50	$—
Assets measured at net asset value	189				179
Total pension plan assets	$436				$406

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, 2020, 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%	5%
Equity securities - U.S.	11%	-	41%	26%
Equity securities - international	14%	-	34%	23%
Global asset securities	5%	-	15%	9%
Risk parity securities	5%	-	15%	9%
Fixed income securities	20%	-	40%	28%

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

	2020				2019
	Fair	Level	Level	Level	Fair	Level	Level	Level
Alliant Energy	Value	1	2	3	Value	1	2	3
Cash and equivalents	$46	$—	$46	$—	$46	$4	$42	$—
Equity securities - U.S.	182	182	—	—	161	161	—	—
Equity securities - international	151	151	—	—	136	136	—	—
Global asset securities	45	45	—	—	47	47	—	—
Fixed income securities	134	56	78	—	131	58	73	—
Total assets in fair value hierarchy	558	$434	$124	$—	521	$406	$115	$—
Assets measured at net asset value	426				410
Accrued investment income	1				1
Due to brokers, net (pending trades with brokers)	(1)				(1)
Total pension plan assets	$984				$931

	2020				2019
	Fair	Level	Level	Level	Fair	Level	Level	Level
IPL	Value	1	2	3	Value	1	2	3
Cash and equivalents	$21	$—	$21	$—	$22	$2	$20	$—
Equity securities - U.S.	84	84	—	—	75	75	—	—
Equity securities - international	69	69	—	—	64	64	—	—
Global asset securities	21	21	—	—	22	22	—	—
Fixed income securities	62	26	36	—	61	27	34	—
Total assets in fair value hierarchy	257	$200	$57	$—	244	$190	$54	$—
Assets measured at net asset value	196				192
Total pension plan assets	$453				$436

	2020				2019
	Fair	Level	Level	Level	Fair	Level	Level	Level
WPL	Value	1	2	3	Value	1	2	3
Cash and equivalents	$20	$—	$20	$—	$20	$2	$18	$—
Equity securities - U.S.	81	81	—	—	70	70	—	—
Equity securities - international	67	67	—	—	59	59	—	—
Global asset securities	20	20	—	—	21	21	—	—
Fixed income securities	59	25	34	—	57	25	32	—
Total assets in fair value hierarchy	247	$193	$54	$—	227	$177	$50	$—
Assets measured at net asset value	189				179
Total pension plan assets	$436				$406

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, 2020, 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 - U.S.	0%	-	46%	25%
Equity securities - international	0%	-	34%	1%
Fixed income securities	20%	-	100%	73%

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

	2020				2019
	Fair	Level	Level	Level	Fair	Level	Level	Level
Alliant Energy	Value	1	2	3	Value	1	2	3
Cash and equivalents	$2	$—	$2	$—	$3	$3	$—	$—
Equity securities - U.S.	4	4	—	—	4	4	—	—
Equity securities - international	3	3	—	—	3	3	—	—
Fixed income securities	72	71	1	—	69	68	1	—
Total assets in fair value hierarchy	81	$78	$3	$—	79	$78	$1	$—
Assets measured at net asset value	27				26
Total OPEB plan assets	$108				$105

	2020				2019
	Fair	Level	Level	Level	Fair	Level	Level	Level
IPL	Value	1	2	3	Value	1	2	3
Cash and equivalents	$1	$—	$1	$—	$2	$2	$—	$—
Fixed income securities	51	51	—	—	48	48	—	—
Total assets in fair value hierarchy	52	$51	$1	$—	50	$50	$—	$—
Assets measured at net asset value	22				22
Total OPEB plan assets	$74				$72

	2020				2019
	Fair	Level	Level	Level	Fair	Level	Level	Level
WPL	Value	1	2	3	Value	1	2	3
Fixed income securities	$18	$18	$—	$—	$17	$17	$—	$—
Total OPEB plan assets	$18	$18	$—	$—	$17	$17	$—	$—

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, 2020, 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 - U.S.	0%	-	46%	25%
Equity securities - international	0%	-	34%	1%
Fixed income securities	20%	-	100%	73%

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

	2020				2019
	Fair	Level	Level	Level	Fair	Level	Level	Level
Alliant Energy	Value	1	2	3	Value	1	2	3
Cash and equivalents	$2	$—	$2	$—	$3	$3	$—	$—
Equity securities - U.S.	4	4	—	—	4	4	—	—
Equity securities - international	3	3	—	—	3	3	—	—
Fixed income securities	72	71	1	—	69	68	1	—
Total assets in fair value hierarchy	81	$78	$3	$—	79	$78	$1	$—
Assets measured at net asset value	27				26
Total OPEB plan assets	$108				$105

	2020				2019
	Fair	Level	Level	Level	Fair	Level	Level	Level
IPL	Value	1	2	3	Value	1	2	3
Cash and equivalents	$1	$—	$1	$—	$2	$2	$—	$—
Fixed income securities	51	51	—	—	48	48	—	—
Total assets in fair value hierarchy	52	$51	$1	$—	50	$50	$—	$—
Assets measured at net asset value	22				22
Total OPEB plan assets	$74				$72

	2020				2019
	Fair	Level	Level	Level	Fair	Level	Level	Level
WPL	Value	1	2	3	Value	1	2	3
Fixed income securities	$18	$18	$—	$—	$17	$17	$—	$—
Total OPEB plan assets	$18	$18	$—	$—	$17	$17	$—	$—

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, 2020, 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 - U.S.	0%	-	46%	25%
Equity securities - international	0%	-	34%	1%
Fixed income securities	20%	-	100%	73%

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

	2020				2019
	Fair	Level	Level	Level	Fair	Level	Level	Level
Alliant Energy	Value	1	2	3	Value	1	2	3
Cash and equivalents	$2	$—	$2	$—	$3	$3	$—	$—
Equity securities - U.S.	4	4	—	—	4	4	—	—
Equity securities - international	3	3	—	—	3	3	—	—
Fixed income securities	72	71	1	—	69	68	1	—
Total assets in fair value hierarchy	81	$78	$3	$—	79	$78	$1	$—
Assets measured at net asset value	27				26
Total OPEB plan assets	$108				$105

	2020				2019
	Fair	Level	Level	Level	Fair	Level	Level	Level
IPL	Value	1	2	3	Value	1	2	3
Cash and equivalents	$1	$—	$1	$—	$2	$2	$—	$—
Fixed income securities	51	51	—	—	48	48	—	—
Total assets in fair value hierarchy	52	$51	$1	$—	50	$50	$—	$—
Assets measured at net asset value	22				22
Total OPEB plan assets	$74				$72

	2020				2019
	Fair	Level	Level	Level	Fair	Level	Level	Level
WPL	Value	1	2	3	Value	1	2	3
Fixed income securities	$18	$18	$—	$—	$17	$17	$—	$—
Total OPEB plan assets	$18	$18	$—	$—	$17	$17	$—	$—

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
	2020	2019	2018	2020	2019	2018	2020	2019	2018
401(k) costs	$25	$25	$25	$13	$13	$13	$12	$12	$11

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
	2020	2019	2018	2020	2019	2018	2020	2019	2018
401(k) costs	$25	$25	$25	$13	$13	$13	$12	$12	$11

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
	2020	2019	2018	2020	2019	2018	2020	2019	2018
401(k) costs	$25	$25	$25	$13	$13	$13	$12	$12	$11

Performance Shares Equity Awards [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule Of Equity-based Compensation Plans Activity

A summary of the 2020 and 2019 performance shares activity, with amounts representing the target number of awards, was as follows:

	2020		2019
	Performance Shares - Equity	Weighted Average Grant Date Fair Value	Performance Shares - Equity	Weighted Average Grant Date Fair Value
Nonvested awards, January 1	74,193	$47.44	—	$—
Granted	56,204	64.04	91,816	47.23
Forfeited	(1,241)	50.94	(17,623)	46.35
Nonvested awards, December 31	129,156	54.63	74,193	47.44

Performance Shares and Performance Units Liability Awards [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule Of Equity-based Compensation Plans Activity

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

	Performance Shares (granted prior to 2019)			Performance Units (granted prior to 2019)
	2020	2019	2018	2020	2019	2018
Nonvested awards, January 1	131,872	203,188	223,511	34,574	57,761	71,737
Granted	—	—	74,163	—	—	19,840
Vested	(63,565)	(66,322)	(90,806)	(16,661)	(20,131)	(31,910)
Forfeited	—	(4,994)	(3,680)	(1,112)	(3,056)	(1,906)
Nonvested awards, December 31	68,307	131,872	203,188	16,801	34,574	57,761

At December 31, 2020, the Alliant Energy common stock closing price was $51.53, and additional information related to the fair value of nonvested performance shares and performance units granted in 2018 was as follows:

	Performance Shares	Performance Units
Nonvested awards at target	68,307	16,801
Estimated payout percentage based on performance criteria	172.5%	172.5%
Fair values of each nonvested award	$88.89	$88.89

Certain performance shares and performance units vested, resulting in payouts (a combination of cash and common stock for the performance shares and cash only for the performance units) as follows:

	Performance Shares (granted prior to 2019)			Performance Units (granted prior to 2019)
	2020	2019	2018	2020	2019	2018
	2017 Grant	2016 Grant	2015 Grant	2017 Grant	2016 Grant	2015 Grant
Performance awards vested	63,565	66,322	90,806	16,661	20,131	31,910
Percentage of target number of performance awards	155.0%	142.5%	137.5%	155.0%	142.5%	137.5%
Aggregate payout value (in millions)	$6	$4	$5	$2	$1	$1
Payout - cash (in millions)	$5	$4	$5	$2	$1	$1
Payout - common stock shares issued	9,543	6,447	5,078	N/A	N/A	N/A

Restricted Stock Units Equity Awards [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule Of Equity-based Compensation Plans Activity

A summary of the 2020 and 2019 restricted stock units activity was as follows:

	2020		2019
	Restricted Stock Units - Equity	Weighted Average Grant Date Fair Value	Restricted Stock Units - Equity	Weighted Average Grant Date Fair Value
Nonvested units, January 1	89,281	$46.04	—	$—
Granted	61,056	59.42	105,348	45.98
Forfeited	(3,788)	49.01	(16,067)	45.63
Nonvested units, December 31	146,549	51.54	89,281	46.04

Restricted Stock Unit Liability Awards [Member]

Defined Benefit Plan Disclosure [Line Items]

Schedule Of Equity-based Compensation Plans Activity

A summary of the restricted stock units granted prior to 2019 activity was as follows:

	2020	2019	2018
Nonvested units, January 1	113,033	174,163	113,749
Granted	—	—	63,568
Vested	(54,483)	(56,849)	—
Forfeited	—	(4,281)	(3,154)
Nonvested units, December 31	58,550	113,033	174,163

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:

	2020		2019		2018
	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	206,065	$41.50	203,188	$37.23	132,705	$36.50
Granted	56,204	59.37	91,816	46.10	74,163	38.60
Vested	(63,565)	39.12	(66,322)	33.93	—	—
Forfeited	(1,241)	49.25	(22,617)	44.00	(3,680)	38.60
Nonvested units, December 31	197,463	47.31	206,065	41.50	203,188	37.23