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Fair Value Measurements (Tables) | 9 Months Ended
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Sep. 30, 2025
Statement [Line Items] |
Fair Value Measurements | Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions):
Alliant Energy | September 30, 2025 |  | December 31, 2024
|  |  | Fair Value |  |  |  | Fair Value
| Carrying |  | Level |  | Level |  | Level |  |  |  | Carrying |  | Level |  | Level |  | Level |  |
| Amount |  | 1 |  | 2 |  | 3 |  | Total |  | Amount |  | 1 |  | 2 |  | 3 |  | Total
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Money market fund investments | $477 |  |  | $477 |  |  | $— |  |  | $— |  |  | $477 |  |  | $52 |  |  | $52 |  |  | $— |  |  | $— |  |  | $52 |
Time deposits | 250 |  |  | — |  |  | 250 |  |  | — |  |  | 250 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
Commodity derivatives | 82 |  |  | — |  |  | 42 |  |  | 40 |  |  | 82 |  |  | 75 |  |  | — |  |  | 48 |  |  | 27 |  |  | 75 |
Deferred proceeds | 231 |  |  | — |  |  | — |  |  | 231 |  |  | 231 |  |  | 163 |  |  | — |  |  | — |  |  | 163 |  |  | 163 |
Liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Commodity derivatives | 48 |  |  | — |  |  | 47 |  |  | 1 |  |  | 48 |  |  | 58 |  |  | — |  |  | 56 |  |  | 2 |  |  | 58 |
Long-term debt (incl. current maturities) | 11,729 |  |  | — |  |  | 11,504 |  |  | — |  |  | 11,504 |  |  | 9,848 |  |  | — |  |  | 9,577 |  |  | — |  |  | 9,577 |
IPL | September 30, 2025 |  | December 31, 2024
|  |  | Fair Value |  |  |  | Fair Value
| Carrying |  | Level |  | Level |  | Level |  |  |  | Carrying |  | Level |  | Level |  | Level |  |
| Amount |  | 1 |  | 2 |  | 3 |  | Total |  | Amount |  | 1 |  | 2 |  | 3 |  | Total
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Money market fund investments | $194 |  |  | $194 |  |  | $— |  |  | $— |  |  | $194 |  |  | $9 |  |  | $9 |  |  | $— |  |  | $— |  |  | $9 |
Commodity derivatives | 52 |  |  | — |  |  | 21 |  |  | 31 |  |  | 52 |  |  | 48 |  |  | — |  |  | 26 |  |  | 22 |  |  | 48 |
Deferred proceeds | 231 |  |  | — |  |  | — |  |  | 231 |  |  | 231 |  |  | 163 |  |  | — |  |  | — |  |  | 163 |  |  | 163 |
Liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Commodity derivatives | 10 |  |  | — |  |  | 9 |  |  | 1 |  |  | 10 |  |  | 13 |  |  | — |  |  | 11 |  |  | 2 |  |  | 13 |
Long-term debt (incl. current maturities) | 4,679 |  |  | — |  |  | 4,465 |  |  | — |  |  | 4,465 |  |  | 4,090 |  |  | — |  |  | 3,736 |  |  | — |  |  | 3,736 |
WPL | September 30, 2025 |  | December 31, 2024
|  |  | Fair Value |  |  |  | Fair Value
| Carrying |  | Level |  | Level |  | Level |  |  |  | Carrying |  | Level |  | Level |  | Level |  |
| Amount |  | 1 |  | 2 |  | 3 |  | Total |  | Amount |  | 1 |  | 2 |  | 3 |  | Total
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Money market fund investments | $— |  |  | $— |  |  | $— |  |  | $— |  |  | $— |  |  | $43 |  |  | $43 |  |  | $— |  |  | $— |  |  | $43 |
Commodity derivatives | 30 |  |  | — |  |  | 21 |  |  | 9 |  |  | 30 |  |  | 27 |  |  | — |  |  | 22 |  |  | 5 |  |  | 27 |
Liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Commodity derivatives | 38 |  |  | — |  |  | 38 |  |  | — |  |  | 38 |  |  | 45 |  |  | — |  |  | 45 |  |  | — |  |  | 45 |
Long-term debt | 3,372 |  |  | — |  |  | 3,287 |  |  | — |  |  | 3,287 |  |  | 3,370 |  |  | — |  |  | 3,170 |  |  | — |  |  | 3,170 |
Fair Value Measurements Using Significant Unobservable Inputs | Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions):
Alliant Energy | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
Three Months Ended September 30 | 2025 |  | 2024 |  | 2025 |  | 2024
Beginning balance, July 1 | $56 |  | $51 |  | $235 |  | $171
Total n et gains (losses) i ncluded in changes in net assets (realized/unrealized) | (2) |  | 2 |  | — |  | —
Sales | (2) |  | — |  | — |  | —
Settlements (a) | (13) |  | (16) |  | (4) |  | 41
Ending balance, September 30 | $39 |  | $37 |  | $231 |  | $212
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 | ($4) |  | $2 |  | $— |  | $—
Alliant Energy | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
Nine Months Ended September 30 | 2025 |  | 2024 |  | 2025 |  | 2024
Beginning balance, January 1 | $25 |  | $24 |  | $163 |  | $216
Total net gains (losses) included in changes in net assets (realized/unrealized) | 5 |  | (7) |  | — |  | —
Purchases | 50 |  | 59 |  | — |  | —
Sales | (2) |  | (1) |  | — |  | —
Settlements (a) | (39) |  | (38) |  | 68 |  | (4)
Ending balance, September 30 | $39 |  | $37 |  | $231 |  | $212
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 | $4 |  | ($7) |  | $— |  | $—
IPL | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
Three Months Ended September 30 | 2025 |  | 2024 |  | 2025 |  | 2024
Beginning balance, July 1 | $44 |  | $40 |  | $235 |  | $171
Total net losses included in changes in net assets (realized/unrealized) | (5) |  | — |  | — |  | —
Sales | (1) |  | — |  | — |  | —
Settlements (a) | (8) |  | (11) |  | (4) |  | 41
Ending balance, September 30 | $30 |  | $29 |  | $231 |  | $212
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at September 30 | ($6) |  | $— |  | $— |  | $—
IPL | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
Nine Months Ended September 30 | 2025 |  | 2024 |  | 2025 |  | 2024
Beginning balance, January 1 | $20 |  | $19 |  | $163 |  | $216
Total net gains (losses) included in changes in net assets (realized/unrealized) | 1 |  | (7) |  | — |  | —
Purchases | 40 |  | 45 |  | — |  | —
Sales | (1) |  | (1) |  | — |  | —
Settlements (a) | (30) |  | (27) |  | 68 |  | (4)
Ending balance, September 30 | $30 |  | $29 |  | $231 |  | $212
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 | $1 |  | ($7) |  | $— |  | $—
WPL | Commodity Contract Derivative
| Assets and (Liabilities), net
Three Months Ended September 30 | 2025 |  | 2024
Beginning balance, July 1 | $12 |  | $11
Total net gains included in changes in net assets (realized/unrealized) | 3 |  | 2
Sales | (1) |  | —
Settlements | (5) |  | (5)
Ending balance, September 30 | $9 |  | $8
The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 | $2 |  | $2
WPL | Commodity Contract Derivative
| Assets and (Liabilities), net
Nine Months Ended September 30 | 2025 |  | 2024
Beginning balance, January 1 | $5 |  | $5
Total net gains included in changes in net assets (realized/unrealized) | 4 |  | —
Purchases | 10 |  | 14
Sales | (1) |  | —
Settlements | (9) |  | (11)
Ending balance, September 30 | $9 |  | $8
The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 | $3 |  | $—
(a)Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for expected credit losses associated with the receivables sold and cash amounts received from the receivables sold.
Fair Value Of Net Derivative Assets (Liabilities) | The fair value of FTRs and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| Excluding FTRs |  | FTRs |  | Excluding FTRs |  | FTRs |  | Excluding FTRs |  | FTRs
September 30, 2025 | $3 |  | $36 |  | $3 |  | $27 |  | $— |  | $9
December 31, 2024 | — |  | 25 |  | — |  | 20 |  | — |  | 5
IPL [Member] |
Statement [Line Items] |
Fair Value Measurements | Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions):
Alliant Energy | September 30, 2025 |  | December 31, 2024
|  |  | Fair Value |  |  |  | Fair Value
| Carrying |  | Level |  | Level |  | Level |  |  |  | Carrying |  | Level |  | Level |  | Level |  |
| Amount |  | 1 |  | 2 |  | 3 |  | Total |  | Amount |  | 1 |  | 2 |  | 3 |  | Total
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Money market fund investments | $477 |  |  | $477 |  |  | $— |  |  | $— |  |  | $477 |  |  | $52 |  |  | $52 |  |  | $— |  |  | $— |  |  | $52 |
Time deposits | 250 |  |  | — |  |  | 250 |  |  | — |  |  | 250 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
Commodity derivatives | 82 |  |  | — |  |  | 42 |  |  | 40 |  |  | 82 |  |  | 75 |  |  | — |  |  | 48 |  |  | 27 |  |  | 75 |
Deferred proceeds | 231 |  |  | — |  |  | — |  |  | 231 |  |  | 231 |  |  | 163 |  |  | — |  |  | — |  |  | 163 |  |  | 163 |
Liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Commodity derivatives | 48 |  |  | — |  |  | 47 |  |  | 1 |  |  | 48 |  |  | 58 |  |  | — |  |  | 56 |  |  | 2 |  |  | 58 |
Long-term debt (incl. current maturities) | 11,729 |  |  | — |  |  | 11,504 |  |  | — |  |  | 11,504 |  |  | 9,848 |  |  | — |  |  | 9,577 |  |  | — |  |  | 9,577 |
IPL | September 30, 2025 |  | December 31, 2024
|  |  | Fair Value |  |  |  | Fair Value
| Carrying |  | Level |  | Level |  | Level |  |  |  | Carrying |  | Level |  | Level |  | Level |  |
| Amount |  | 1 |  | 2 |  | 3 |  | Total |  | Amount |  | 1 |  | 2 |  | 3 |  | Total
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Money market fund investments | $194 |  |  | $194 |  |  | $— |  |  | $— |  |  | $194 |  |  | $9 |  |  | $9 |  |  | $— |  |  | $— |  |  | $9 |
Commodity derivatives | 52 |  |  | — |  |  | 21 |  |  | 31 |  |  | 52 |  |  | 48 |  |  | — |  |  | 26 |  |  | 22 |  |  | 48 |
Deferred proceeds | 231 |  |  | — |  |  | — |  |  | 231 |  |  | 231 |  |  | 163 |  |  | — |  |  | — |  |  | 163 |  |  | 163 |
Liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Commodity derivatives | 10 |  |  | — |  |  | 9 |  |  | 1 |  |  | 10 |  |  | 13 |  |  | — |  |  | 11 |  |  | 2 |  |  | 13 |
Long-term debt (incl. current maturities) | 4,679 |  |  | — |  |  | 4,465 |  |  | — |  |  | 4,465 |  |  | 4,090 |  |  | — |  |  | 3,736 |  |  | — |  |  | 3,736 |
WPL | September 30, 2025 |  | December 31, 2024
|  |  | Fair Value |  |  |  | Fair Value
| Carrying |  | Level |  | Level |  | Level |  |  |  | Carrying |  | Level |  | Level |  | Level |  |
| Amount |  | 1 |  | 2 |  | 3 |  | Total |  | Amount |  | 1 |  | 2 |  | 3 |  | Total
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Money market fund investments | $— |  |  | $— |  |  | $— |  |  | $— |  |  | $— |  |  | $43 |  |  | $43 |  |  | $— |  |  | $— |  |  | $43 |
Commodity derivatives | 30 |  |  | — |  |  | 21 |  |  | 9 |  |  | 30 |  |  | 27 |  |  | — |  |  | 22 |  |  | 5 |  |  | 27 |
Liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Commodity derivatives | 38 |  |  | — |  |  | 38 |  |  | — |  |  | 38 |  |  | 45 |  |  | — |  |  | 45 |  |  | — |  |  | 45 |
Long-term debt | 3,372 |  |  | — |  |  | 3,287 |  |  | — |  |  | 3,287 |  |  | 3,370 |  |  | — |  |  | 3,170 |  |  | — |  |  | 3,170 |
Fair Value Measurements Using Significant Unobservable Inputs | Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions):
Alliant Energy | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
Three Months Ended September 30 | 2025 |  | 2024 |  | 2025 |  | 2024
Beginning balance, July 1 | $56 |  | $51 |  | $235 |  | $171
Total n et gains (losses) i ncluded in changes in net assets (realized/unrealized) | (2) |  | 2 |  | — |  | —
Sales | (2) |  | — |  | — |  | —
Settlements (a) | (13) |  | (16) |  | (4) |  | 41
Ending balance, September 30 | $39 |  | $37 |  | $231 |  | $212
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 | ($4) |  | $2 |  | $— |  | $—
Alliant Energy | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
Nine Months Ended September 30 | 2025 |  | 2024 |  | 2025 |  | 2024
Beginning balance, January 1 | $25 |  | $24 |  | $163 |  | $216
Total net gains (losses) included in changes in net assets (realized/unrealized) | 5 |  | (7) |  | — |  | —
Purchases | 50 |  | 59 |  | — |  | —
Sales | (2) |  | (1) |  | — |  | —
Settlements (a) | (39) |  | (38) |  | 68 |  | (4)
Ending balance, September 30 | $39 |  | $37 |  | $231 |  | $212
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 | $4 |  | ($7) |  | $— |  | $—
IPL | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
Three Months Ended September 30 | 2025 |  | 2024 |  | 2025 |  | 2024
Beginning balance, July 1 | $44 |  | $40 |  | $235 |  | $171
Total net losses included in changes in net assets (realized/unrealized) | (5) |  | — |  | — |  | —
Sales | (1) |  | — |  | — |  | —
Settlements (a) | (8) |  | (11) |  | (4) |  | 41
Ending balance, September 30 | $30 |  | $29 |  | $231 |  | $212
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at September 30 | ($6) |  | $— |  | $— |  | $—
IPL | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
Nine Months Ended September 30 | 2025 |  | 2024 |  | 2025 |  | 2024
Beginning balance, January 1 | $20 |  | $19 |  | $163 |  | $216
Total net gains (losses) included in changes in net assets (realized/unrealized) | 1 |  | (7) |  | — |  | —
Purchases | 40 |  | 45 |  | — |  | —
Sales | (1) |  | (1) |  | — |  | —
Settlements (a) | (30) |  | (27) |  | 68 |  | (4)
Ending balance, September 30 | $30 |  | $29 |  | $231 |  | $212
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 | $1 |  | ($7) |  | $— |  | $—
WPL | Commodity Contract Derivative
| Assets and (Liabilities), net
Three Months Ended September 30 | 2025 |  | 2024
Beginning balance, July 1 | $12 |  | $11
Total net gains included in changes in net assets (realized/unrealized) | 3 |  | 2
Sales | (1) |  | —
Settlements | (5) |  | (5)
Ending balance, September 30 | $9 |  | $8
The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 | $2 |  | $2
WPL | Commodity Contract Derivative
| Assets and (Liabilities), net
Nine Months Ended September 30 | 2025 |  | 2024
Beginning balance, January 1 | $5 |  | $5
Total net gains included in changes in net assets (realized/unrealized) | 4 |  | —
Purchases | 10 |  | 14
Sales | (1) |  | —
Settlements | (9) |  | (11)
Ending balance, September 30 | $9 |  | $8
The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 | $3 |  | $—
(a)Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for expected credit losses associated with the receivables sold and cash amounts received from the receivables sold.
Fair Value Of Net Derivative Assets (Liabilities) | The fair value of FTRs and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| Excluding FTRs |  | FTRs |  | Excluding FTRs |  | FTRs |  | Excluding FTRs |  | FTRs
September 30, 2025 | $3 |  | $36 |  | $3 |  | $27 |  | $— |  | $9
December 31, 2024 | — |  | 25 |  | — |  | 20 |  | — |  | 5
WPL [Member] |
Statement [Line Items] |
Fair Value Measurements | Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions):
Alliant Energy | September 30, 2025 |  | December 31, 2024
|  |  | Fair Value |  |  |  | Fair Value
| Carrying |  | Level |  | Level |  | Level |  |  |  | Carrying |  | Level |  | Level |  | Level |  |
| Amount |  | 1 |  | 2 |  | 3 |  | Total |  | Amount |  | 1 |  | 2 |  | 3 |  | Total
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Money market fund investments | $477 |  |  | $477 |  |  | $— |  |  | $— |  |  | $477 |  |  | $52 |  |  | $52 |  |  | $— |  |  | $— |  |  | $52 |
Time deposits | 250 |  |  | — |  |  | 250 |  |  | — |  |  | 250 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |
Commodity derivatives | 82 |  |  | — |  |  | 42 |  |  | 40 |  |  | 82 |  |  | 75 |  |  | — |  |  | 48 |  |  | 27 |  |  | 75 |
Deferred proceeds | 231 |  |  | — |  |  | — |  |  | 231 |  |  | 231 |  |  | 163 |  |  | — |  |  | — |  |  | 163 |  |  | 163 |
Liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Commodity derivatives | 48 |  |  | — |  |  | 47 |  |  | 1 |  |  | 48 |  |  | 58 |  |  | — |  |  | 56 |  |  | 2 |  |  | 58 |
Long-term debt (incl. current maturities) | 11,729 |  |  | — |  |  | 11,504 |  |  | — |  |  | 11,504 |  |  | 9,848 |  |  | — |  |  | 9,577 |  |  | — |  |  | 9,577 |
IPL | September 30, 2025 |  | December 31, 2024
|  |  | Fair Value |  |  |  | Fair Value
| Carrying |  | Level |  | Level |  | Level |  |  |  | Carrying |  | Level |  | Level |  | Level |  |
| Amount |  | 1 |  | 2 |  | 3 |  | Total |  | Amount |  | 1 |  | 2 |  | 3 |  | Total
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Money market fund investments | $194 |  |  | $194 |  |  | $— |  |  | $— |  |  | $194 |  |  | $9 |  |  | $9 |  |  | $— |  |  | $— |  |  | $9 |
Commodity derivatives | 52 |  |  | — |  |  | 21 |  |  | 31 |  |  | 52 |  |  | 48 |  |  | — |  |  | 26 |  |  | 22 |  |  | 48 |
Deferred proceeds | 231 |  |  | — |  |  | — |  |  | 231 |  |  | 231 |  |  | 163 |  |  | — |  |  | — |  |  | 163 |  |  | 163 |
Liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Commodity derivatives | 10 |  |  | — |  |  | 9 |  |  | 1 |  |  | 10 |  |  | 13 |  |  | — |  |  | 11 |  |  | 2 |  |  | 13 |
Long-term debt (incl. current maturities) | 4,679 |  |  | — |  |  | 4,465 |  |  | — |  |  | 4,465 |  |  | 4,090 |  |  | — |  |  | 3,736 |  |  | — |  |  | 3,736 |
WPL | September 30, 2025 |  | December 31, 2024
|  |  | Fair Value |  |  |  | Fair Value
| Carrying |  | Level |  | Level |  | Level |  |  |  | Carrying |  | Level |  | Level |  | Level |  |
| Amount |  | 1 |  | 2 |  | 3 |  | Total |  | Amount |  | 1 |  | 2 |  | 3 |  | Total
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Money market fund investments | $— |  |  | $— |  |  | $— |  |  | $— |  |  | $— |  |  | $43 |  |  | $43 |  |  | $— |  |  | $— |  |  | $43 |
Commodity derivatives | 30 |  |  | — |  |  | 21 |  |  | 9 |  |  | 30 |  |  | 27 |  |  | — |  |  | 22 |  |  | 5 |  |  | 27 |
Liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Commodity derivatives | 38 |  |  | — |  |  | 38 |  |  | — |  |  | 38 |  |  | 45 |  |  | — |  |  | 45 |  |  | — |  |  | 45 |
Long-term debt | 3,372 |  |  | — |  |  | 3,287 |  |  | — |  |  | 3,287 |  |  | 3,370 |  |  | — |  |  | 3,170 |  |  | — |  |  | 3,170 |
Fair Value Measurements Using Significant Unobservable Inputs | Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions):
Alliant Energy | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
Three Months Ended September 30 | 2025 |  | 2024 |  | 2025 |  | 2024
Beginning balance, July 1 | $56 |  | $51 |  | $235 |  | $171
Total n et gains (losses) i ncluded in changes in net assets (realized/unrealized) | (2) |  | 2 |  | — |  | —
Sales | (2) |  | — |  | — |  | —
Settlements (a) | (13) |  | (16) |  | (4) |  | 41
Ending balance, September 30 | $39 |  | $37 |  | $231 |  | $212
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 | ($4) |  | $2 |  | $— |  | $—
Alliant Energy | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
Nine Months Ended September 30 | 2025 |  | 2024 |  | 2025 |  | 2024
Beginning balance, January 1 | $25 |  | $24 |  | $163 |  | $216
Total net gains (losses) included in changes in net assets (realized/unrealized) | 5 |  | (7) |  | — |  | —
Purchases | 50 |  | 59 |  | — |  | —
Sales | (2) |  | (1) |  | — |  | —
Settlements (a) | (39) |  | (38) |  | 68 |  | (4)
Ending balance, September 30 | $39 |  | $37 |  | $231 |  | $212
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 | $4 |  | ($7) |  | $— |  | $—
IPL | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
Three Months Ended September 30 | 2025 |  | 2024 |  | 2025 |  | 2024
Beginning balance, July 1 | $44 |  | $40 |  | $235 |  | $171
Total net losses included in changes in net assets (realized/unrealized) | (5) |  | — |  | — |  | —
Sales | (1) |  | — |  | — |  | —
Settlements (a) | (8) |  | (11) |  | (4) |  | 41
Ending balance, September 30 | $30 |  | $29 |  | $231 |  | $212
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at September 30 | ($6) |  | $— |  | $— |  | $—
IPL | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
Nine Months Ended September 30 | 2025 |  | 2024 |  | 2025 |  | 2024
Beginning balance, January 1 | $20 |  | $19 |  | $163 |  | $216
Total net gains (losses) included in changes in net assets (realized/unrealized) | 1 |  | (7) |  | — |  | —
Purchases | 40 |  | 45 |  | — |  | —
Sales | (1) |  | (1) |  | — |  | —
Settlements (a) | (30) |  | (27) |  | 68 |  | (4)
Ending balance, September 30 | $30 |  | $29 |  | $231 |  | $212
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at September 30 | $1 |  | ($7) |  | $— |  | $—
WPL | Commodity Contract Derivative
| Assets and (Liabilities), net
Three Months Ended September 30 | 2025 |  | 2024
Beginning balance, July 1 | $12 |  | $11
Total net gains included in changes in net assets (realized/unrealized) | 3 |  | 2
Sales | (1) |  | —
Settlements | (5) |  | (5)
Ending balance, September 30 | $9 |  | $8
The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 | $2 |  | $2
WPL | Commodity Contract Derivative
| Assets and (Liabilities), net
Nine Months Ended September 30 | 2025 |  | 2024
Beginning balance, January 1 | $5 |  | $5
Total net gains included in changes in net assets (realized/unrealized) | 4 |  | —
Purchases | 10 |  | 14
Sales | (1) |  | —
Settlements | (9) |  | (11)
Ending balance, September 30 | $9 |  | $8
The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 | $3 |  | $—
(a)Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for expected credit losses associated with the receivables sold and cash amounts received from the receivables sold.
Fair Value Of Net Derivative Assets (Liabilities) | The fair value of FTRs and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| Excluding FTRs |  | FTRs |  | Excluding FTRs |  | FTRs |  | Excluding FTRs |  | FTRs
September 30, 2025 | $3 |  | $36 |  | $3 |  | $27 |  | $— |  | $9
December 31, 2024 | — |  | 25 |  | — |  | 20 |  | — |  | 5

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