Income Taxes (Tables)

12 Months Ended

Dec. 31, 2024

Income Tax [Line Items]

Schedule of Components of Income Tax Expense (Benefit)

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

	Alliant Energy			IPL			WPL
	2024	2023	2022	2024	2023	2022	2024	2023	2022
Current tax expense (benefit):
Federal	$13	($3)	$7	($19)	($44)	($29)	$37	$48	$46
State	(10)	(6)	2	(19)	(21)	(8)	23	25	16
Deferred tax expense (benefit):
Federal	60	100	109	38	87	91	24	10	10
State	15	36	28	(17)	17	1	7	3	12
Production tax credits	(177)	(121)	(123)	(108)	(95)	(105)	(69)	(26)	(18)
Investment tax credits	(15)	(1)	(1)	(4)	(1)	—	(11)	—	—
Provision recorded as a change in accrued interest	—	(1)	—	—	(1)	—	—	—	—
	($114)	$4	$22	($129)	($58)	($50)	$11	$60	$66

Schedule Of Effective 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. In 2024, Alliant Energy’s and IPL’s effective income tax rates were impacted by the pre-tax non-cash charge of $60 million for IPL’s Lansing Generation Station discussed in Note 2.

	Alliant Energy			IPL			WPL
	2024	2023	2022	2024	2023	2022	2024	2023	2022
Statutory federal income tax rate	21%	21%	21%	21%	21%	21%	21%	21%	21%
State income taxes, net of federal benefits	(1)	2	3	(12)	(2)	(2)	6	5	6
Production tax credits	(31)	(17)	(18)	(46)	(31)	(34)	(20)	(7)	(5)
Investment tax credits	(3)	—	—	(2)	—	—	(3)	—	—
Amortization of excess deferred taxes (Refer to Note 2)	(2)	(2)	(2)	(5)	(2)	(2)	—	(2)	(3)
Effect of rate-making on property-related differences	(5)	(4)	(1)	(10)	(5)	(1)	(1)	(3)	(2)
Other items, net	1	1	—	(1)	—	2	—	1	—
Overall income tax rate	(20%)	1%	3%	(55%)	(19%)	(16%)	3%	15%	17%

Schedule of 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
	2024	2023	2024	2023	2024	2023
Deferred tax liabilities:
Property	$2,596	$2,453	$1,521	$1,415	$999	$972
ATC Holdings	135	127	—	—	—	—
Other	178	213	120	157	66	64
Total deferred tax liabilities	2,909	2,793	1,641	1,572	1,065	1,036
Deferred tax assets:
Federal credit carryforwards	605	649	426	449	166	191
Net operating losses carryforwards - state	20	26	1	1	—	—
Other	98	79	37	32	34	19
Subtotal deferred tax assets	723	754	464	482	200	210
Valuation allowances	(2)	(3)	(2)	(1)	—	(1)
Total deferred tax assets	721	751	462	481	200	209
Total deferred tax liabilities, net	$2,188	$2,042	$1,179	$1,091	$865	$827

Summary Of Tax Credit Carryforwards

At December 31, 2024, carryforwards and expiration dates were estimated as follows (in millions):

	Range of Expiration Dates	Alliant Energy	IPL	WPL
State net operating losses	2025-2044	$338	$7	$1
Federal tax credits	2033-2044	605	426	166

Schedule Of 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)	2021	-	2023
Consolidated Iowa income tax returns (b)	2021	-	2023
Wisconsin combined tax returns (c)	2020	-	2023

(a)The 2021 and 2022 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.

IPL [Member]

Income Tax [Line Items]

Schedule of Components of Income Tax Expense (Benefit)

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

	Alliant Energy			IPL			WPL
	2024	2023	2022	2024	2023	2022	2024	2023	2022
Current tax expense (benefit):
Federal	$13	($3)	$7	($19)	($44)	($29)	$37	$48	$46
State	(10)	(6)	2	(19)	(21)	(8)	23	25	16
Deferred tax expense (benefit):
Federal	60	100	109	38	87	91	24	10	10
State	15	36	28	(17)	17	1	7	3	12
Production tax credits	(177)	(121)	(123)	(108)	(95)	(105)	(69)	(26)	(18)
Investment tax credits	(15)	(1)	(1)	(4)	(1)	—	(11)	—	—
Provision recorded as a change in accrued interest	—	(1)	—	—	(1)	—	—	—	—
	($114)	$4	$22	($129)	($58)	($50)	$11	$60	$66

Schedule Of Effective 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. In 2024, Alliant Energy’s and IPL’s effective income tax rates were impacted by the pre-tax non-cash charge of $60 million for IPL’s Lansing Generation Station discussed in Note 2.

	Alliant Energy			IPL			WPL
	2024	2023	2022	2024	2023	2022	2024	2023	2022
Statutory federal income tax rate	21%	21%	21%	21%	21%	21%	21%	21%	21%
State income taxes, net of federal benefits	(1)	2	3	(12)	(2)	(2)	6	5	6
Production tax credits	(31)	(17)	(18)	(46)	(31)	(34)	(20)	(7)	(5)
Investment tax credits	(3)	—	—	(2)	—	—	(3)	—	—
Amortization of excess deferred taxes (Refer to Note 2)	(2)	(2)	(2)	(5)	(2)	(2)	—	(2)	(3)
Effect of rate-making on property-related differences	(5)	(4)	(1)	(10)	(5)	(1)	(1)	(3)	(2)
Other items, net	1	1	—	(1)	—	2	—	1	—
Overall income tax rate	(20%)	1%	3%	(55%)	(19%)	(16%)	3%	15%	17%

Schedule of 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
	2024	2023	2024	2023	2024	2023
Deferred tax liabilities:
Property	$2,596	$2,453	$1,521	$1,415	$999	$972
ATC Holdings	135	127	—	—	—	—
Other	178	213	120	157	66	64
Total deferred tax liabilities	2,909	2,793	1,641	1,572	1,065	1,036
Deferred tax assets:
Federal credit carryforwards	605	649	426	449	166	191
Net operating losses carryforwards - state	20	26	1	1	—	—
Other	98	79	37	32	34	19
Subtotal deferred tax assets	723	754	464	482	200	210
Valuation allowances	(2)	(3)	(2)	(1)	—	(1)
Total deferred tax assets	721	751	462	481	200	209
Total deferred tax liabilities, net	$2,188	$2,042	$1,179	$1,091	$865	$827

Summary Of Tax Credit Carryforwards

At December 31, 2024, carryforwards and expiration dates were estimated as follows (in millions):

	Range of Expiration Dates	Alliant Energy	IPL	WPL
State net operating losses	2025-2044	$338	$7	$1
Federal tax credits	2033-2044	605	426	166

Schedule Of 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)	2021	-	2023
Consolidated Iowa income tax returns (b)	2021	-	2023
Wisconsin combined tax returns (c)	2020	-	2023

(a)The 2021 and 2022 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.

WPL [Member]

Income Tax [Line Items]

Schedule of Components of Income Tax Expense (Benefit)

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

	Alliant Energy			IPL			WPL
	2024	2023	2022	2024	2023	2022	2024	2023	2022
Current tax expense (benefit):
Federal	$13	($3)	$7	($19)	($44)	($29)	$37	$48	$46
State	(10)	(6)	2	(19)	(21)	(8)	23	25	16
Deferred tax expense (benefit):
Federal	60	100	109	38	87	91	24	10	10
State	15	36	28	(17)	17	1	7	3	12
Production tax credits	(177)	(121)	(123)	(108)	(95)	(105)	(69)	(26)	(18)
Investment tax credits	(15)	(1)	(1)	(4)	(1)	—	(11)	—	—
Provision recorded as a change in accrued interest	—	(1)	—	—	(1)	—	—	—	—
	($114)	$4	$22	($129)	($58)	($50)	$11	$60	$66

Schedule Of Effective 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. In 2024, Alliant Energy’s and IPL’s effective income tax rates were impacted by the pre-tax non-cash charge of $60 million for IPL’s Lansing Generation Station discussed in Note 2.

	Alliant Energy			IPL			WPL
	2024	2023	2022	2024	2023	2022	2024	2023	2022
Statutory federal income tax rate	21%	21%	21%	21%	21%	21%	21%	21%	21%
State income taxes, net of federal benefits	(1)	2	3	(12)	(2)	(2)	6	5	6
Production tax credits	(31)	(17)	(18)	(46)	(31)	(34)	(20)	(7)	(5)
Investment tax credits	(3)	—	—	(2)	—	—	(3)	—	—
Amortization of excess deferred taxes (Refer to Note 2)	(2)	(2)	(2)	(5)	(2)	(2)	—	(2)	(3)
Effect of rate-making on property-related differences	(5)	(4)	(1)	(10)	(5)	(1)	(1)	(3)	(2)
Other items, net	1	1	—	(1)	—	2	—	1	—
Overall income tax rate	(20%)	1%	3%	(55%)	(19%)	(16%)	3%	15%	17%

Schedule of 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
	2024	2023	2024	2023	2024	2023
Deferred tax liabilities:
Property	$2,596	$2,453	$1,521	$1,415	$999	$972
ATC Holdings	135	127	—	—	—	—
Other	178	213	120	157	66	64
Total deferred tax liabilities	2,909	2,793	1,641	1,572	1,065	1,036
Deferred tax assets:
Federal credit carryforwards	605	649	426	449	166	191
Net operating losses carryforwards - state	20	26	1	1	—	—
Other	98	79	37	32	34	19
Subtotal deferred tax assets	723	754	464	482	200	210
Valuation allowances	(2)	(3)	(2)	(1)	—	(1)
Total deferred tax assets	721	751	462	481	200	209
Total deferred tax liabilities, net	$2,188	$2,042	$1,179	$1,091	$865	$827

Summary Of Tax Credit Carryforwards

At December 31, 2024, carryforwards and expiration dates were estimated as follows (in millions):

	Range of Expiration Dates	Alliant Energy	IPL	WPL
State net operating losses	2025-2044	$338	$7	$1
Federal tax credits	2033-2044	605	426	166

Schedule Of 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)	2021	-	2023
Consolidated Iowa income tax returns (b)	2021	-	2023
Wisconsin combined tax returns (c)	2020	-	2023

(a)The 2021 and 2022 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.