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Income Taxes (Tables)

12 Months Ended

Dec. 31, 2023

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
			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)

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.

			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%)

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
			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

Summary Of Tax Credit 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

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)			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.

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
			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)

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.

			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%)

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
			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

Summary Of Tax Credit 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

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)			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.

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
			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)

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.

			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%)

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
			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

Summary Of Tax Credit 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

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)			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.

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