XML 51 R31.htm IDEA: XBRL DOCUMENT v3.25.3

Derivative Instruments (Tables)

9 Months Ended

Sep. 30, 2025

Derivative Instruments [Line Items]

Notional Amounts Of Derivative Instruments

As of September 30, 2025, gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and FTRs that were accounted for as commodity derivative instruments were as follows (units in thousands):

			Electricity												FTRs												Natural Gas																		Diesel Fuel
			MWhs						Years						MWhs						Years						Dths						Years																		Gallons						Years
Alliant Energy			1,689						2025-2026						17,992						2025-2026						136,910						2025-2032																		630						2025
IPL			563						2025-2026						7,143						2025-2026						56,355						2025-2030																		—						—
WPL			1,126						2025-2026						10,849						2025-2026						80,555						2025-2032																		630						2025

Fair Value Of Financial Instruments

Derivative instruments are recorded at fair value each reporting date on the balance sheets as assets or liabilities as follows (in millions):

			Alliant Energy												IPL												WPL
			September 30, 2025						December 31, 2024						September 30, 2025						December 31, 2024						September 30, 2025						December 31, 2024
Current derivative assets			$55						$41						$38						$29						$17						$12
Non-current derivative assets			27						34						14						19						13						15
Current derivative liabilities			22						26						8						11						14						15
Non-current derivative liabilities			26						32						2						2						24						30

Balance Sheet Offsetting

However, if the fair value amounts of derivative instruments by counterparty were netted, derivative assets and derivative liabilities related to commodity contracts would have been presented on the balance sheets as follows (in millions):

			Alliant Energy												IPL												WPL
			Gross												Gross												Gross
			(as reported)						Net						(as reported)						Net						(as reported)						Net
September 30, 2025
Derivative assets			$82						$72						$52						$47						$30						$25
Derivative liabilities			48						38						10						5						38						33
December 31, 2024
Derivative assets			75						64						48						43						27						21
Derivative liabilities			58						47						13						8						45						39

IPL [Member]

Derivative Instruments [Line Items]

Notional Amounts Of Derivative Instruments

As of September 30, 2025, gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and FTRs that were accounted for as commodity derivative instruments were as follows (units in thousands):

			Electricity												FTRs												Natural Gas																		Diesel Fuel
			MWhs						Years						MWhs						Years						Dths						Years																		Gallons						Years
Alliant Energy			1,689						2025-2026						17,992						2025-2026						136,910						2025-2032																		630						2025
IPL			563						2025-2026						7,143						2025-2026						56,355						2025-2030																		—						—
WPL			1,126						2025-2026						10,849						2025-2026						80,555						2025-2032																		630						2025

Fair Value Of Financial Instruments

Derivative instruments are recorded at fair value each reporting date on the balance sheets as assets or liabilities as follows (in millions):

			Alliant Energy												IPL												WPL
			September 30, 2025						December 31, 2024						September 30, 2025						December 31, 2024						September 30, 2025						December 31, 2024
Current derivative assets			$55						$41						$38						$29						$17						$12
Non-current derivative assets			27						34						14						19						13						15
Current derivative liabilities			22						26						8						11						14						15
Non-current derivative liabilities			26						32						2						2						24						30

Balance Sheet Offsetting

However, if the fair value amounts of derivative instruments by counterparty were netted, derivative assets and derivative liabilities related to commodity contracts would have been presented on the balance sheets as follows (in millions):

			Alliant Energy												IPL												WPL
			Gross												Gross												Gross
			(as reported)						Net						(as reported)						Net						(as reported)						Net
September 30, 2025
Derivative assets			$82						$72						$52						$47						$30						$25
Derivative liabilities			48						38						10						5						38						33
December 31, 2024
Derivative assets			75						64						48						43						27						21
Derivative liabilities			58						47						13						8						45						39

WPL [Member]

Derivative Instruments [Line Items]

Notional Amounts Of Derivative Instruments

As of September 30, 2025, gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and FTRs that were accounted for as commodity derivative instruments were as follows (units in thousands):

			Electricity												FTRs												Natural Gas																		Diesel Fuel
			MWhs						Years						MWhs						Years						Dths						Years																		Gallons						Years
Alliant Energy			1,689						2025-2026						17,992						2025-2026						136,910						2025-2032																		630						2025
IPL			563						2025-2026						7,143						2025-2026						56,355						2025-2030																		—						—
WPL			1,126						2025-2026						10,849						2025-2026						80,555						2025-2032																		630						2025

Fair Value Of Financial Instruments

Derivative instruments are recorded at fair value each reporting date on the balance sheets as assets or liabilities as follows (in millions):

			Alliant Energy												IPL												WPL
			September 30, 2025						December 31, 2024						September 30, 2025						December 31, 2024						September 30, 2025						December 31, 2024
Current derivative assets			$55						$41						$38						$29						$17						$12
Non-current derivative assets			27						34						14						19						13						15
Current derivative liabilities			22						26						8						11						14						15
Non-current derivative liabilities			26						32						2						2						24						30

Balance Sheet Offsetting

However, if the fair value amounts of derivative instruments by counterparty were netted, derivative assets and derivative liabilities related to commodity contracts would have been presented on the balance sheets as follows (in millions):

			Alliant Energy												IPL												WPL
			Gross												Gross												Gross
			(as reported)						Net						(as reported)						Net						(as reported)						Net
September 30, 2025
Derivative assets			$82						$72						$52						$47						$30						$25
Derivative liabilities			48						38						10						5						38						33
December 31, 2024
Derivative assets			75						64						48						43						27						21
Derivative liabilities			58						47						13						8						45						39

X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 20
-Name Accounting Standards Codification
-Section 25
-Paragraph 6A
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480682/815-20-25-6A

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480237/815-40-50-5

+ Details

Name:	us-gaap_DerivativeLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Tabular disclosure of derivative and other financial assets that are subject to offsetting, including master netting arrangements.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 7A
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-7A

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 210
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 10
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483444/210-20-55-10

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Topic 210
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 22
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483444/210-20-55-22

Reference 4: http://www.xbrl.org/2003/role/exampleRef
-Topic 210
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 21
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483444/210-20-55-21

Reference 5: http://www.xbrl.org/2003/role/exampleRef
-Topic 210
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 20
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483444/210-20-55-20

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 210
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483466/210-20-50-3

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 210
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483466/210-20-50-4

+ Details

Name:	us-gaap_OffsettingAssetsTableTextBlock
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:textBlockItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Tabular disclosure of the location and fair value amounts of derivative instruments (and nonderivative instruments that are designated and qualify as hedging instruments) reported in the statement of financial position.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 182
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480401/815-10-55-182

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4A
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-4A

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4E
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-4E

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-4B

+ Details

Name:	us-gaap_ScheduleOfDerivativeInstrumentsInStatementOfFinancialPositionFairValueTextBlock
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:textBlockItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Tabular disclosure of the notional amounts of outstanding derivative positions.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1A
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-1A

+ Details

Name:	us-gaap_ScheduleOfNotionalAmountsOfOutstandingDerivativePositionsTableTextBlock
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:textBlockItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	dei_LegalEntityAxis=lnt_IplMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	dei_LegalEntityAxis=lnt_WplMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: