Income Taxes

12 Months Ended

Dec. 31, 2023

Income Tax [Line Items]

Income Taxes

INCOME TAXES

Income Tax Expense (Benefit) - The components of “Income tax expense (benefit)” in the income statements were as follows (in millions):

	Alliant Energy			IPL			WPL
	2023	2022	2021	2023	2022	2021	2023	2022	2021
Current tax expense (benefit):
Federal	($3)	$7	$1	($44)	($29)	($21)	$48	$46	$22
State	(6)	2	3	(21)	(8)	(1)	25	16	6
Deferred tax expense (benefit):
Federal	100	109	9	87	91	73	10	10	(75)
State	36	28	15	17	1	—	3	12	11
Production tax credits	(121)	(123)	(101)	(95)	(105)	(87)	(26)	(18)	(14)
Investment tax credits	(1)	(1)	(1)	(1)	—	—	—	—	(1)
Provision recorded as a change in accrued interest	(1)	—	—	(1)	—	—	—	—	—
	$4	$22	($74)	($58)	($50)	($36)	$60	$66	($51)

Income Tax Rates - The overall income tax rates shown in the following table were computed by dividing income tax expense (benefit) by income before income taxes.

	Alliant Energy			IPL			WPL
	2023	2022	2021	2023	2022	2021	2023	2022	2021
Statutory federal income tax rate	21%	21%	21%	21%	21%	21%	21%	21%	21%
State income taxes, net of federal benefits	2	3	2	(2)	(2)	(1)	5	6	6
Production tax credits	(17)	(18)	(17)	(31)	(34)	(27)	(7)	(5)	(6)
Amortization of excess deferred taxes (Refer to Note 2)	(2)	(2)	(18)	(2)	(2)	(4)	(2)	(3)	(43)
Effect of rate-making on property-related differences	(4)	(1)	(1)	(5)	(1)	(2)	(3)	(2)	(1)
Adjustment for prior period taxes	—	1	1	—	1	2	—	—	—
Other items, net	1	(1)	—	—	1	—	1	—	(1)
Overall income tax rate	1%	3%	(12%)	(19%)	(16%)	(11%)	15%	17%	(24%)

Deferred Tax Assets and Liabilities - The deferred tax assets and liabilities included on the balance sheets at December 31 arise from the following temporary differences (in millions):

	Alliant Energy		IPL		WPL
	2023	2022	2023	2022	2023	2022
Deferred tax liabilities:
Property	$2,453	$2,442	$1,415	$1,440	$972	$938
ATC Holdings	127	125	—	—	—	—
Other	213	155	157	86	64	80
Total deferred tax liabilities	2,793	2,722	1,572	1,526	1,036	1,018
Deferred tax assets:
Federal credit carryforwards	649	672	449	450	191	209
Net operating losses carryforwards - state	26	32	1	—	—	—
Other	79	75	32	29	19	20
Subtotal deferred tax assets	754	779	482	479	210	229
Valuation allowances	(3)	—	(1)	—	(1)	—
Total deferred tax assets	751	779	481	479	209	229
Total deferred tax liabilities, net	$2,042	$1,943	$1,091	$1,047	$827	$789

Carryforwards - At December 31, 2023, carryforwards and expiration dates were estimated as follows (in millions):

	Range of Expiration Dates	Alliant Energy	IPL	WPL
State net operating losses	2025-2043	$428	$6	$1
Federal tax credits	2031-2043	649	449	191

Valuation Allowances - Refer to Note 1(c) for discussion of valuation allowances recorded in 2023 related to the expected transfer of renewable tax credits to other corporate taxpayers.

Uncertain Tax Positions - At December 31, 2023, 2022 and 2021, there were no uncertain tax positions or penalties accrued related to uncertain tax positions. As of December 31, 2023, no material changes to unrecognized tax benefits are expected during the next 12 months.

Open tax years - Tax years that remain subject to the statute of limitations in the major jurisdictions for each of Alliant Energy, IPL and WPL are as follows:

Consolidated federal income tax returns (a)	2019	-	2022
Consolidated Iowa income tax returns (b)	2020	-	2022
Wisconsin combined tax returns (c)	2019	-	2022

(a)The 2020 and 2021 federal tax returns are effectively settled as a result of participation in the IRS Compliance Assurance Program, which allows Alliant Energy and the IRS to work together to resolve issues related to Alliant Energy’s current tax year before filing its federal income tax return. The statute of limitations for these federal tax returns expires three years from each filing date.

(b)The statute of limitations for these Iowa tax returns expires three years from each filing date.

(c)The statute of limitations for these Wisconsin combined tax returns expires four years from each filing date.

Iowa Tax Reform - In 2018, Iowa tax reform was enacted, resulting in a reduction in the Iowa income tax rate from 12% to 9.8%, effective January 1, 2021, and the elimination of the deduction for federal income taxes, effective January 1, 2022, for taxes related to 2020 and prior.

In March 2022, additional Iowa tax reform was enacted. Annually, and by each November 1, the Iowa Department of Revenue will establish corporate income tax rates for the next tax year based on net corporate income tax receipts for the prior tax year, and reduce such rates if certain state income tax revenue triggers are satisfied. These corporate income tax rate reductions are currently expected to occur over a period of several years, with a target corporate income tax rate of 5.5%, compared to the 9.8% Iowa corporate income tax rate in effect at the time the Iowa tax reform was enacted. In September 2022 and September 2023, the Iowa Department of Revenue announced an Iowa corporate income tax rate of 8.4% effective January 1, 2023, and 7.1% effective January 1, 2024, respectively. Deferred tax assets and liabilities are measured at the enacted tax rate expected to be applied when temporary differences are to be realized or settled. Given the announcements of the new Iowa corporate income tax rates, Alliant Energy’s and IPL’s deferred tax liabilities were remeasured in 2022 and 2023 based upon the new rates effective January 1, 2023 and January 1, 2024, which resulted in a $77 million and $74 million reduction of Alliant Energy’s and IPL’s tax-related regulatory assets and a corresponding decrease in their deferred tax liabilities in 2022 and 2023, respectively. The reduction in tax-related regulatory assets is expected to provide cost benefits to IPL’s customers in the future. Alliant Energy parent company’s deferred tax assets were remeasured based upon the new rates effective January 1, 2023 and January 1, 2024, which resulted in charges of $8 million and $10 million recorded to income tax expense in Alliant Energy’s income statement and an increase in deferred income tax liabilities on Alliant Energy’s balance sheets in 2022 and 2023, respectively. Alliant Energy is currently unable to predict with certainty the timing or amount of any future rate reductions.

IPL [Member]

Income Tax [Line Items]

Income Taxes

INCOME TAXES

Income Tax Expense (Benefit) - The components of “Income tax expense (benefit)” in the income statements were as follows (in millions):

	Alliant Energy			IPL			WPL
	2023	2022	2021	2023	2022	2021	2023	2022	2021
Current tax expense (benefit):
Federal	($3)	$7	$1	($44)	($29)	($21)	$48	$46	$22
State	(6)	2	3	(21)	(8)	(1)	25	16	6
Deferred tax expense (benefit):
Federal	100	109	9	87	91	73	10	10	(75)
State	36	28	15	17	1	—	3	12	11
Production tax credits	(121)	(123)	(101)	(95)	(105)	(87)	(26)	(18)	(14)
Investment tax credits	(1)	(1)	(1)	(1)	—	—	—	—	(1)
Provision recorded as a change in accrued interest	(1)	—	—	(1)	—	—	—	—	—
	$4	$22	($74)	($58)	($50)	($36)	$60	$66	($51)

Income Tax Rates - The overall income tax rates shown in the following table were computed by dividing income tax expense (benefit) by income before income taxes.

	Alliant Energy			IPL			WPL
	2023	2022	2021	2023	2022	2021	2023	2022	2021
Statutory federal income tax rate	21%	21%	21%	21%	21%	21%	21%	21%	21%
State income taxes, net of federal benefits	2	3	2	(2)	(2)	(1)	5	6	6
Production tax credits	(17)	(18)	(17)	(31)	(34)	(27)	(7)	(5)	(6)
Amortization of excess deferred taxes (Refer to Note 2)	(2)	(2)	(18)	(2)	(2)	(4)	(2)	(3)	(43)
Effect of rate-making on property-related differences	(4)	(1)	(1)	(5)	(1)	(2)	(3)	(2)	(1)
Adjustment for prior period taxes	—	1	1	—	1	2	—	—	—
Other items, net	1	(1)	—	—	1	—	1	—	(1)
Overall income tax rate	1%	3%	(12%)	(19%)	(16%)	(11%)	15%	17%	(24%)

Deferred Tax Assets and Liabilities - The deferred tax assets and liabilities included on the balance sheets at December 31 arise from the following temporary differences (in millions):

	Alliant Energy		IPL		WPL
	2023	2022	2023	2022	2023	2022
Deferred tax liabilities:
Property	$2,453	$2,442	$1,415	$1,440	$972	$938
ATC Holdings	127	125	—	—	—	—
Other	213	155	157	86	64	80
Total deferred tax liabilities	2,793	2,722	1,572	1,526	1,036	1,018
Deferred tax assets:
Federal credit carryforwards	649	672	449	450	191	209
Net operating losses carryforwards - state	26	32	1	—	—	—
Other	79	75	32	29	19	20
Subtotal deferred tax assets	754	779	482	479	210	229
Valuation allowances	(3)	—	(1)	—	(1)	—
Total deferred tax assets	751	779	481	479	209	229
Total deferred tax liabilities, net	$2,042	$1,943	$1,091	$1,047	$827	$789

Carryforwards - At December 31, 2023, carryforwards and expiration dates were estimated as follows (in millions):

	Range of Expiration Dates	Alliant Energy	IPL	WPL
State net operating losses	2025-2043	$428	$6	$1
Federal tax credits	2031-2043	649	449	191

Valuation Allowances - Refer to Note 1(c) for discussion of valuation allowances recorded in 2023 related to the expected transfer of renewable tax credits to other corporate taxpayers.

Uncertain Tax Positions - At December 31, 2023, 2022 and 2021, there were no uncertain tax positions or penalties accrued related to uncertain tax positions. As of December 31, 2023, no material changes to unrecognized tax benefits are expected during the next 12 months.

Open tax years - Tax years that remain subject to the statute of limitations in the major jurisdictions for each of Alliant Energy, IPL and WPL are as follows:

Consolidated federal income tax returns (a)	2019	-	2022
Consolidated Iowa income tax returns (b)	2020	-	2022
Wisconsin combined tax returns (c)	2019	-	2022

(a)The 2020 and 2021 federal tax returns are effectively settled as a result of participation in the IRS Compliance Assurance Program, which allows Alliant Energy and the IRS to work together to resolve issues related to Alliant Energy’s current tax year before filing its federal income tax return. The statute of limitations for these federal tax returns expires three years from each filing date.

(b)The statute of limitations for these Iowa tax returns expires three years from each filing date.

(c)The statute of limitations for these Wisconsin combined tax returns expires four years from each filing date.

Iowa Tax Reform - In 2018, Iowa tax reform was enacted, resulting in a reduction in the Iowa income tax rate from 12% to 9.8%, effective January 1, 2021, and the elimination of the deduction for federal income taxes, effective January 1, 2022, for taxes related to 2020 and prior.

In March 2022, additional Iowa tax reform was enacted. Annually, and by each November 1, the Iowa Department of Revenue will establish corporate income tax rates for the next tax year based on net corporate income tax receipts for the prior tax year, and reduce such rates if certain state income tax revenue triggers are satisfied. These corporate income tax rate reductions are currently expected to occur over a period of several years, with a target corporate income tax rate of 5.5%, compared to the 9.8% Iowa corporate income tax rate in effect at the time the Iowa tax reform was enacted. In September 2022 and September 2023, the Iowa Department of Revenue announced an Iowa corporate income tax rate of 8.4% effective January 1, 2023, and 7.1% effective January 1, 2024, respectively. Deferred tax assets and liabilities are measured at the enacted tax rate expected to be applied when temporary differences are to be realized or settled. Given the announcements of the new Iowa corporate income tax rates, Alliant Energy’s and IPL’s deferred tax liabilities were remeasured in 2022 and 2023 based upon the new rates effective January 1, 2023 and January 1, 2024, which resulted in a $77 million and $74 million reduction of Alliant Energy’s and IPL’s tax-related regulatory assets and a corresponding decrease in their deferred tax liabilities in 2022 and 2023, respectively. The reduction in tax-related regulatory assets is expected to provide cost benefits to IPL’s customers in the future. Alliant Energy parent company’s deferred tax assets were remeasured based upon the new rates effective January 1, 2023 and January 1, 2024, which resulted in charges of $8 million and $10 million recorded to income tax expense in Alliant Energy’s income statement and an increase in deferred income tax liabilities on Alliant Energy’s balance sheets in 2022 and 2023, respectively. Alliant Energy is currently unable to predict with certainty the timing or amount of any future rate reductions.

WPL [Member]

Income Tax [Line Items]

Income Taxes

INCOME TAXES

Income Tax Expense (Benefit) - The components of “Income tax expense (benefit)” in the income statements were as follows (in millions):

	Alliant Energy			IPL			WPL
	2023	2022	2021	2023	2022	2021	2023	2022	2021
Current tax expense (benefit):
Federal	($3)	$7	$1	($44)	($29)	($21)	$48	$46	$22
State	(6)	2	3	(21)	(8)	(1)	25	16	6
Deferred tax expense (benefit):
Federal	100	109	9	87	91	73	10	10	(75)
State	36	28	15	17	1	—	3	12	11
Production tax credits	(121)	(123)	(101)	(95)	(105)	(87)	(26)	(18)	(14)
Investment tax credits	(1)	(1)	(1)	(1)	—	—	—	—	(1)
Provision recorded as a change in accrued interest	(1)	—	—	(1)	—	—	—	—	—
	$4	$22	($74)	($58)	($50)	($36)	$60	$66	($51)

Income Tax Rates - The overall income tax rates shown in the following table were computed by dividing income tax expense (benefit) by income before income taxes.

	Alliant Energy			IPL			WPL
	2023	2022	2021	2023	2022	2021	2023	2022	2021
Statutory federal income tax rate	21%	21%	21%	21%	21%	21%	21%	21%	21%
State income taxes, net of federal benefits	2	3	2	(2)	(2)	(1)	5	6	6
Production tax credits	(17)	(18)	(17)	(31)	(34)	(27)	(7)	(5)	(6)
Amortization of excess deferred taxes (Refer to Note 2)	(2)	(2)	(18)	(2)	(2)	(4)	(2)	(3)	(43)
Effect of rate-making on property-related differences	(4)	(1)	(1)	(5)	(1)	(2)	(3)	(2)	(1)
Adjustment for prior period taxes	—	1	1	—	1	2	—	—	—
Other items, net	1	(1)	—	—	1	—	1	—	(1)
Overall income tax rate	1%	3%	(12%)	(19%)	(16%)	(11%)	15%	17%	(24%)

Deferred Tax Assets and Liabilities - The deferred tax assets and liabilities included on the balance sheets at December 31 arise from the following temporary differences (in millions):

	Alliant Energy		IPL		WPL
	2023	2022	2023	2022	2023	2022
Deferred tax liabilities:
Property	$2,453	$2,442	$1,415	$1,440	$972	$938
ATC Holdings	127	125	—	—	—	—
Other	213	155	157	86	64	80
Total deferred tax liabilities	2,793	2,722	1,572	1,526	1,036	1,018
Deferred tax assets:
Federal credit carryforwards	649	672	449	450	191	209
Net operating losses carryforwards - state	26	32	1	—	—	—
Other	79	75	32	29	19	20
Subtotal deferred tax assets	754	779	482	479	210	229
Valuation allowances	(3)	—	(1)	—	(1)	—
Total deferred tax assets	751	779	481	479	209	229
Total deferred tax liabilities, net	$2,042	$1,943	$1,091	$1,047	$827	$789

Carryforwards - At December 31, 2023, carryforwards and expiration dates were estimated as follows (in millions):

	Range of Expiration Dates	Alliant Energy	IPL	WPL
State net operating losses	2025-2043	$428	$6	$1
Federal tax credits	2031-2043	649	449	191

Valuation Allowances - Refer to Note 1(c) for discussion of valuation allowances recorded in 2023 related to the expected transfer of renewable tax credits to other corporate taxpayers.

Uncertain Tax Positions - At December 31, 2023, 2022 and 2021, there were no uncertain tax positions or penalties accrued related to uncertain tax positions. As of December 31, 2023, no material changes to unrecognized tax benefits are expected during the next 12 months.

Open tax years - Tax years that remain subject to the statute of limitations in the major jurisdictions for each of Alliant Energy, IPL and WPL are as follows:

Consolidated federal income tax returns (a)	2019	-	2022
Consolidated Iowa income tax returns (b)	2020	-	2022
Wisconsin combined tax returns (c)	2019	-	2022

(a)The 2020 and 2021 federal tax returns are effectively settled as a result of participation in the IRS Compliance Assurance Program, which allows Alliant Energy and the IRS to work together to resolve issues related to Alliant Energy’s current tax year before filing its federal income tax return. The statute of limitations for these federal tax returns expires three years from each filing date.

(b)The statute of limitations for these Iowa tax returns expires three years from each filing date.

(c)The statute of limitations for these Wisconsin combined tax returns expires four years from each filing date.

Iowa Tax Reform - In 2018, Iowa tax reform was enacted, resulting in a reduction in the Iowa income tax rate from 12% to 9.8%, effective January 1, 2021, and the elimination of the deduction for federal income taxes, effective January 1, 2022, for taxes related to 2020 and prior.

In March 2022, additional Iowa tax reform was enacted. Annually, and by each November 1, the Iowa Department of Revenue will establish corporate income tax rates for the next tax year based on net corporate income tax receipts for the prior tax year, and reduce such rates if certain state income tax revenue triggers are satisfied. These corporate income tax rate reductions are currently expected to occur over a period of several years, with a target corporate income tax rate of 5.5%, compared to the 9.8% Iowa corporate income tax rate in effect at the time the Iowa tax reform was enacted. In September 2022 and September 2023, the Iowa Department of Revenue announced an Iowa corporate income tax rate of 8.4% effective January 1, 2023, and 7.1% effective January 1, 2024, respectively. Deferred tax assets and liabilities are measured at the enacted tax rate expected to be applied when temporary differences are to be realized or settled. Given the announcements of the new Iowa corporate income tax rates, Alliant Energy’s and IPL’s deferred tax liabilities were remeasured in 2022 and 2023 based upon the new rates effective January 1, 2023 and January 1, 2024, which resulted in a $77 million and $74 million reduction of Alliant Energy’s and IPL’s tax-related regulatory assets and a corresponding decrease in their deferred tax liabilities in 2022 and 2023, respectively. The reduction in tax-related regulatory assets is expected to provide cost benefits to IPL’s customers in the future. Alliant Energy parent company’s deferred tax assets were remeasured based upon the new rates effective January 1, 2023 and January 1, 2024, which resulted in charges of $8 million and $10 million recorded to income tax expense in Alliant Energy’s income statement and an increase in deferred income tax liabilities on Alliant Energy’s balance sheets in 2022 and 2023, respectively. Alliant Energy is currently unable to predict with certainty the timing or amount of any future rate reductions.