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Fair Value Measurements (Tables) | 12 Months Ended
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Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |
Recurring Fair Value Measurements | Carrying amounts and the related estimated fair values of other financial instruments at December 31 were as follows (in millions):
Alliant Energy | 2019 |  | 2018
|  |  | Fair Value |  |  |  | Fair Value
| Carrying |  | Level |  | Level |  | Level |  |  |  | Carrying |  | Level |  | Level |  | Level |  |
| Amount |  | 1 |  | 2 |  | 3 |  | Total |  | Amount |  | 1 |  | 2 |  | 3 |  | Total
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives |  | $26.8 |  |  |  | $— |  |  |  | $4.8 |  |  |  | $22.0 |  |  |  | $26.8 |  |  |  | $28.3 |  |  |  | $— |  |  |  | $8.9 |  |  |  | $19.4 |  |  |  | $28.3 |
Deferred proceeds | 187.7 |  |  | — |  |  | — |  |  | 187.7 |  |  | 187.7 |  |  | 119.4 |  |  | — |  |  | — |  |  | 119.4 |  |  | 119.4 |
Liabilities and equity: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives | 37.6 |  |  | — |  |  | 36.8 |  |  | 0.8 |  |  | 37.6 |  |  | 23.3 |  |  | — |  |  | 16.1 |  |  | 7.2 |  |  | 23.3 |
Long-term debt (incl. current maturities) | 6,190.2 |  |  | — |  |  | 6,917.9 |  |  | 2.0 |  |  | 6,919.9 |  |  | 5,502.8 |  |  | — |  |  | 5,858.4 |  |  | 2.4 |  |  | 5,860.8 |
IPL | 2019 |  | 2018
|  |  | Fair Value |  |  |  | Fair Value
| Carrying |  | Level |  | Level |  | Level |  |  |  | Carrying |  | Level |  | Level |  | Level |  |
| Amount |  | 1 |  | 2 |  | 3 |  | Total |  | Amount |  | 1 |  | 2 |  | 3 |  | Total
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives |  | $22.3 |  |  |  | $— |  |  |  | $2.8 |  |  |  | $19.5 |  |  |  | $22.3 |  |  |  | $17.7 |  |  |  | $— |  |  |  | $4.0 |  |  |  | $13.7 |  |  |  | $17.7 |
Deferred proceeds | 187.7 |  |  | — |  |  | — |  |  | 187.7 |  |  | 187.7 |  |  | 119.4 |  |  | — |  |  | — |  |  | 119.4 |  |  | 119.4 |
Liabilities and equity: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives | 17.4 |  |  | — |  |  | 16.6 |  |  | 0.8 |  |  | 17.4 |  |  | 11.2 |  |  | — |  |  | 6.5 |  |  | 4.7 |  |  | 11.2 |
Long-term debt (incl. current maturities) | 3,147.3 |  |  | — |  |  | 3,489.1 |  |  | — |  |  | 3,489.1 |  |  | 2,552.3 |  |  | — |  |  | 2,691.2 |  |  | — |  |  | 2,691.2 |
WPL | 2019 |  | 2018
|  |  | Fair Value |  |  |  | Fair Value
| Carrying |  | Level |  | Level |  | Level |  |  |  | Carrying |  | Level |  | Level |  | Level |  |
| Amount |  | 1 |  | 2 |  | 3 |  | Total |  | Amount |  | 1 |  | 2 |  | 3 |  | Total
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives |  | $4.5 |  |  |  | $— |  |  |  | $2.0 |  |  |  | $2.5 |  |  |  | $4.5 |  |  |  | $10.6 |  |  |  | $— |  |  |  | $4.9 |  |  |  | $5.7 |  |  |  | $10.6 |
Liabilities and equity: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives | 20.2 |  |  | — |  |  | 20.2 |  |  | — |  |  | 20.2 |  |  | 12.1 |  |  | — |  |  | 9.6 |  |  | 2.5 |  |  | 12.1 |
Long-term debt (incl. current maturities) | 1,932.7 |  |  | — |  |  | 2,268.2 |  |  | — |  |  | 2,268.2 |  |  | 1,834.9 |  |  | — |  |  | 2,043.7 |  |  | — |  |  | 2,043.7 |
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
| 2019 |  | 2018 |  | 2019 |  | 2018
Beginning balance, January 1 |  | $12.2 |  |  |  | ($12.2 | ) |  |  | $119.4 |  |  |  | $222.1 |
Total net gains included in changes in net assets (realized/unrealized) | 8.2 |  |  | 9.1 |  |  | — |  |  | — |
Transfers out of Level 3 (a) | 4.0 |  |  | 16.1 |  |  | — |  |  | — |
Purchases | 13.8 |  |  | 26.7 |  |  | — |  |  | — |
Sales | (0.2 | ) |  | (0.5 | ) |  | — |  |  | — |
Settlements (b) | (16.8 | ) |  | (27.0 | ) |  | 68.3 |  |  | (102.7 | )
Ending balance, December 31 |  | $21.2 |  |  |  | $12.2 |  |  |  | $187.7 |  |  |  | $119.4 |
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 December 31 |  | $11.4 |  |  |  | $10.7 |  |  |  | $— |  |  |  | $— |
IPL | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
| 2019 |  | 2018 |  | 2019 |  | 2018
Beginning balance, January 1 |  | $9.0 |  |  |  | ($1.4 | ) |  |  | $119.4 |  |  |  | $222.1 |
Total net gains (losses) included in changes in net assets (realized/unrealized) | 10.7 |  |  | (0.5 | ) |  | — |  |  | — |
Transfers out of Level 3 (a) | 2.6 |  |  | 11.0 |  |  | — |  |  | — |
Purchases | 9.5 |  |  | 22.5 |  |  | — |  |  | — |
Sales | (0.1 | ) |  | (0.4 | ) |  | — |  |  | — |
Settlements (b) | (13.0 | ) |  | (22.2 | ) |  | 68.3 |  |  | (102.7 | )
Ending balance, December 31 |  | $18.7 |  |  |  | $9.0 |  |  |  | $187.7 |  |  |  | $119.4 |
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 December 31 |  | $12.6 |  |  |  | $0.2 |  |  |  | $— |  |  |  | $— |
WPL | Commodity Contract Derivative
| Assets and (Liabilities), net
| 2019 |  | 2018
Beginning balance, January 1 |  | $3.2 |  |  |  | ($10.8 | )
Total net gains (losses) included in changes in net assets (realized/unrealized) | (2.5 | ) |  | 9.6 |
Transfers out of Level 3 (a) | 1.4 |  |  | 5.1 |
Purchases | 4.3 |  |  | 4.2 |
Sales | (0.1 | ) |  | (0.1 | )
Settlements | (3.8 | ) |  | (4.8 | )
Ending balance, December 31 |  | $2.5 |  |  |  | $3.2 |
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 December 31 |  | ($1.2 | ) |  |  | $10.5 |
(a) | Observable market inputs became available for certain commodity contracts previously classified as Level 3 for transfers out of Level 3.
(b) | Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash amounts received from the receivables sold.
Fair Value Of Net Derivative Assets (Liabilities) | The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets at December 31 as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| Excluding FTRs |  | FTRs |  | Excluding FTRs |  | FTRs |  | Excluding FTRs |  | FTRs
2019 |  | $14.6 |  |  |  | $6.6 |  |  |  | $13.6 |  |  |  | $5.1 |  |  |  | $1.0 |  |  |  | $1.5 |
2018 | 3.2 |  |  | 9.0 |  |  | 1.8 |  |  | 7.2 |  |  | 1.4 |  |  | 1.8 |
IPL [Member] |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |
Recurring Fair Value Measurements | Carrying amounts and the related estimated fair values of other financial instruments at December 31 were as follows (in millions):
Alliant Energy | 2019 |  | 2018
|  |  | Fair Value |  |  |  | Fair Value
| Carrying |  | Level |  | Level |  | Level |  |  |  | Carrying |  | Level |  | Level |  | Level |  |
| Amount |  | 1 |  | 2 |  | 3 |  | Total |  | Amount |  | 1 |  | 2 |  | 3 |  | Total
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives |  | $26.8 |  |  |  | $— |  |  |  | $4.8 |  |  |  | $22.0 |  |  |  | $26.8 |  |  |  | $28.3 |  |  |  | $— |  |  |  | $8.9 |  |  |  | $19.4 |  |  |  | $28.3 |
Deferred proceeds | 187.7 |  |  | — |  |  | — |  |  | 187.7 |  |  | 187.7 |  |  | 119.4 |  |  | — |  |  | — |  |  | 119.4 |  |  | 119.4 |
Liabilities and equity: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives | 37.6 |  |  | — |  |  | 36.8 |  |  | 0.8 |  |  | 37.6 |  |  | 23.3 |  |  | — |  |  | 16.1 |  |  | 7.2 |  |  | 23.3 |
Long-term debt (incl. current maturities) | 6,190.2 |  |  | — |  |  | 6,917.9 |  |  | 2.0 |  |  | 6,919.9 |  |  | 5,502.8 |  |  | — |  |  | 5,858.4 |  |  | 2.4 |  |  | 5,860.8 |
IPL | 2019 |  | 2018
|  |  | Fair Value |  |  |  | Fair Value
| Carrying |  | Level |  | Level |  | Level |  |  |  | Carrying |  | Level |  | Level |  | Level |  |
| Amount |  | 1 |  | 2 |  | 3 |  | Total |  | Amount |  | 1 |  | 2 |  | 3 |  | Total
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives |  | $22.3 |  |  |  | $— |  |  |  | $2.8 |  |  |  | $19.5 |  |  |  | $22.3 |  |  |  | $17.7 |  |  |  | $— |  |  |  | $4.0 |  |  |  | $13.7 |  |  |  | $17.7 |
Deferred proceeds | 187.7 |  |  | — |  |  | — |  |  | 187.7 |  |  | 187.7 |  |  | 119.4 |  |  | — |  |  | — |  |  | 119.4 |  |  | 119.4 |
Liabilities and equity: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives | 17.4 |  |  | — |  |  | 16.6 |  |  | 0.8 |  |  | 17.4 |  |  | 11.2 |  |  | — |  |  | 6.5 |  |  | 4.7 |  |  | 11.2 |
Long-term debt (incl. current maturities) | 3,147.3 |  |  | — |  |  | 3,489.1 |  |  | — |  |  | 3,489.1 |  |  | 2,552.3 |  |  | — |  |  | 2,691.2 |  |  | — |  |  | 2,691.2 |
WPL | 2019 |  | 2018
|  |  | Fair Value |  |  |  | Fair Value
| Carrying |  | Level |  | Level |  | Level |  |  |  | Carrying |  | Level |  | Level |  | Level |  |
| Amount |  | 1 |  | 2 |  | 3 |  | Total |  | Amount |  | 1 |  | 2 |  | 3 |  | Total
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives |  | $4.5 |  |  |  | $— |  |  |  | $2.0 |  |  |  | $2.5 |  |  |  | $4.5 |  |  |  | $10.6 |  |  |  | $— |  |  |  | $4.9 |  |  |  | $5.7 |  |  |  | $10.6 |
Liabilities and equity: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives | 20.2 |  |  | — |  |  | 20.2 |  |  | — |  |  | 20.2 |  |  | 12.1 |  |  | — |  |  | 9.6 |  |  | 2.5 |  |  | 12.1 |
Long-term debt (incl. current maturities) | 1,932.7 |  |  | — |  |  | 2,268.2 |  |  | — |  |  | 2,268.2 |  |  | 1,834.9 |  |  | — |  |  | 2,043.7 |  |  | — |  |  | 2,043.7 |
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
| 2019 |  | 2018 |  | 2019 |  | 2018
Beginning balance, January 1 |  | $12.2 |  |  |  | ($12.2 | ) |  |  | $119.4 |  |  |  | $222.1 |
Total net gains included in changes in net assets (realized/unrealized) | 8.2 |  |  | 9.1 |  |  | — |  |  | — |
Transfers out of Level 3 (a) | 4.0 |  |  | 16.1 |  |  | — |  |  | — |
Purchases | 13.8 |  |  | 26.7 |  |  | — |  |  | — |
Sales | (0.2 | ) |  | (0.5 | ) |  | — |  |  | — |
Settlements (b) | (16.8 | ) |  | (27.0 | ) |  | 68.3 |  |  | (102.7 | )
Ending balance, December 31 |  | $21.2 |  |  |  | $12.2 |  |  |  | $187.7 |  |  |  | $119.4 |
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 December 31 |  | $11.4 |  |  |  | $10.7 |  |  |  | $— |  |  |  | $— |
IPL | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
| 2019 |  | 2018 |  | 2019 |  | 2018
Beginning balance, January 1 |  | $9.0 |  |  |  | ($1.4 | ) |  |  | $119.4 |  |  |  | $222.1 |
Total net gains (losses) included in changes in net assets (realized/unrealized) | 10.7 |  |  | (0.5 | ) |  | — |  |  | — |
Transfers out of Level 3 (a) | 2.6 |  |  | 11.0 |  |  | — |  |  | — |
Purchases | 9.5 |  |  | 22.5 |  |  | — |  |  | — |
Sales | (0.1 | ) |  | (0.4 | ) |  | — |  |  | — |
Settlements (b) | (13.0 | ) |  | (22.2 | ) |  | 68.3 |  |  | (102.7 | )
Ending balance, December 31 |  | $18.7 |  |  |  | $9.0 |  |  |  | $187.7 |  |  |  | $119.4 |
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 December 31 |  | $12.6 |  |  |  | $0.2 |  |  |  | $— |  |  |  | $— |
WPL | Commodity Contract Derivative
| Assets and (Liabilities), net
| 2019 |  | 2018
Beginning balance, January 1 |  | $3.2 |  |  |  | ($10.8 | )
Total net gains (losses) included in changes in net assets (realized/unrealized) | (2.5 | ) |  | 9.6 |
Transfers out of Level 3 (a) | 1.4 |  |  | 5.1 |
Purchases | 4.3 |  |  | 4.2 |
Sales | (0.1 | ) |  | (0.1 | )
Settlements | (3.8 | ) |  | (4.8 | )
Ending balance, December 31 |  | $2.5 |  |  |  | $3.2 |
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 December 31 |  | ($1.2 | ) |  |  | $10.5 |
(a) | Observable market inputs became available for certain commodity contracts previously classified as Level 3 for transfers out of Level 3.
(b) Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash amounts received from the receivables sold.
Fair Value Of Net Derivative Assets (Liabilities) | The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets at December 31 as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| Excluding FTRs |  | FTRs |  | Excluding FTRs |  | FTRs |  | Excluding FTRs |  | FTRs
2019 |  | $14.6 |  |  |  | $6.6 |  |  |  | $13.6 |  |  |  | $5.1 |  |  |  | $1.0 |  |  |  | $1.5 |
2018 | 3.2 |  |  | 9.0 |  |  | 1.8 |  |  | 7.2 |  |  | 1.4 |  |  | 1.8 |
WPL [Member] |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] |
Recurring Fair Value Measurements | Carrying amounts and the related estimated fair values of other financial instruments at December 31 were as follows (in millions):
Alliant Energy | 2019 |  | 2018
|  |  | Fair Value |  |  |  | Fair Value
| Carrying |  | Level |  | Level |  | Level |  |  |  | Carrying |  | Level |  | Level |  | Level |  |
| Amount |  | 1 |  | 2 |  | 3 |  | Total |  | Amount |  | 1 |  | 2 |  | 3 |  | Total
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives |  | $26.8 |  |  |  | $— |  |  |  | $4.8 |  |  |  | $22.0 |  |  |  | $26.8 |  |  |  | $28.3 |  |  |  | $— |  |  |  | $8.9 |  |  |  | $19.4 |  |  |  | $28.3 |
Deferred proceeds | 187.7 |  |  | — |  |  | — |  |  | 187.7 |  |  | 187.7 |  |  | 119.4 |  |  | — |  |  | — |  |  | 119.4 |  |  | 119.4 |
Liabilities and equity: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives | 37.6 |  |  | — |  |  | 36.8 |  |  | 0.8 |  |  | 37.6 |  |  | 23.3 |  |  | — |  |  | 16.1 |  |  | 7.2 |  |  | 23.3 |
Long-term debt (incl. current maturities) | 6,190.2 |  |  | — |  |  | 6,917.9 |  |  | 2.0 |  |  | 6,919.9 |  |  | 5,502.8 |  |  | — |  |  | 5,858.4 |  |  | 2.4 |  |  | 5,860.8 |
IPL | 2019 |  | 2018
|  |  | Fair Value |  |  |  | Fair Value
| Carrying |  | Level |  | Level |  | Level |  |  |  | Carrying |  | Level |  | Level |  | Level |  |
| Amount |  | 1 |  | 2 |  | 3 |  | Total |  | Amount |  | 1 |  | 2 |  | 3 |  | Total
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives |  | $22.3 |  |  |  | $— |  |  |  | $2.8 |  |  |  | $19.5 |  |  |  | $22.3 |  |  |  | $17.7 |  |  |  | $— |  |  |  | $4.0 |  |  |  | $13.7 |  |  |  | $17.7 |
Deferred proceeds | 187.7 |  |  | — |  |  | — |  |  | 187.7 |  |  | 187.7 |  |  | 119.4 |  |  | — |  |  | — |  |  | 119.4 |  |  | 119.4 |
Liabilities and equity: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives | 17.4 |  |  | — |  |  | 16.6 |  |  | 0.8 |  |  | 17.4 |  |  | 11.2 |  |  | — |  |  | 6.5 |  |  | 4.7 |  |  | 11.2 |
Long-term debt (incl. current maturities) | 3,147.3 |  |  | — |  |  | 3,489.1 |  |  | — |  |  | 3,489.1 |  |  | 2,552.3 |  |  | — |  |  | 2,691.2 |  |  | — |  |  | 2,691.2 |
WPL | 2019 |  | 2018
|  |  | Fair Value |  |  |  | Fair Value
| Carrying |  | Level |  | Level |  | Level |  |  |  | Carrying |  | Level |  | Level |  | Level |  |
| Amount |  | 1 |  | 2 |  | 3 |  | Total |  | Amount |  | 1 |  | 2 |  | 3 |  | Total
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives |  | $4.5 |  |  |  | $— |  |  |  | $2.0 |  |  |  | $2.5 |  |  |  | $4.5 |  |  |  | $10.6 |  |  |  | $— |  |  |  | $4.9 |  |  |  | $5.7 |  |  |  | $10.6 |
Liabilities and equity: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives | 20.2 |  |  | — |  |  | 20.2 |  |  | — |  |  | 20.2 |  |  | 12.1 |  |  | — |  |  | 9.6 |  |  | 2.5 |  |  | 12.1 |
Long-term debt (incl. current maturities) | 1,932.7 |  |  | — |  |  | 2,268.2 |  |  | — |  |  | 2,268.2 |  |  | 1,834.9 |  |  | — |  |  | 2,043.7 |  |  | — |  |  | 2,043.7 |
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
| 2019 |  | 2018 |  | 2019 |  | 2018
Beginning balance, January 1 |  | $12.2 |  |  |  | ($12.2 | ) |  |  | $119.4 |  |  |  | $222.1 |
Total net gains included in changes in net assets (realized/unrealized) | 8.2 |  |  | 9.1 |  |  | — |  |  | — |
Transfers out of Level 3 (a) | 4.0 |  |  | 16.1 |  |  | — |  |  | — |
Purchases | 13.8 |  |  | 26.7 |  |  | — |  |  | — |
Sales | (0.2 | ) |  | (0.5 | ) |  | — |  |  | — |
Settlements (b) | (16.8 | ) |  | (27.0 | ) |  | 68.3 |  |  | (102.7 | )
Ending balance, December 31 |  | $21.2 |  |  |  | $12.2 |  |  |  | $187.7 |  |  |  | $119.4 |
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 December 31 |  | $11.4 |  |  |  | $10.7 |  |  |  | $— |  |  |  | $— |
IPL | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
| 2019 |  | 2018 |  | 2019 |  | 2018
Beginning balance, January 1 |  | $9.0 |  |  |  | ($1.4 | ) |  |  | $119.4 |  |  |  | $222.1 |
Total net gains (losses) included in changes in net assets (realized/unrealized) | 10.7 |  |  | (0.5 | ) |  | — |  |  | — |
Transfers out of Level 3 (a) | 2.6 |  |  | 11.0 |  |  | — |  |  | — |
Purchases | 9.5 |  |  | 22.5 |  |  | — |  |  | — |
Sales | (0.1 | ) |  | (0.4 | ) |  | — |  |  | — |
Settlements (b) | (13.0 | ) |  | (22.2 | ) |  | 68.3 |  |  | (102.7 | )
Ending balance, December 31 |  | $18.7 |  |  |  | $9.0 |  |  |  | $187.7 |  |  |  | $119.4 |
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 December 31 |  | $12.6 |  |  |  | $0.2 |  |  |  | $— |  |  |  | $— |
WPL | Commodity Contract Derivative
| Assets and (Liabilities), net
| 2019 |  | 2018
Beginning balance, January 1 |  | $3.2 |  |  |  | ($10.8 | )
Total net gains (losses) included in changes in net assets (realized/unrealized) | (2.5 | ) |  | 9.6 |
Transfers out of Level 3 (a) | 1.4 |  |  | 5.1 |
Purchases | 4.3 |  |  | 4.2 |
Sales | (0.1 | ) |  | (0.1 | )
Settlements | (3.8 | ) |  | (4.8 | )
Ending balance, December 31 |  | $2.5 |  |  |  | $3.2 |
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 December 31 |  | ($1.2 | ) |  |  | $10.5 |
(a) | Observable market inputs became available for certain commodity contracts previously classified as Level 3 for transfers out of Level 3.
(b) Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for doubtful accounts associated with the receivables sold and cash amounts received from the receivables sold.
Fair Value Of Net Derivative Assets (Liabilities) | The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets at December 31 as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| Excluding FTRs |  | FTRs |  | Excluding FTRs |  | FTRs |  | Excluding FTRs |  | FTRs
2019 |  | $14.6 |  |  |  | $6.6 |  |  |  | $13.6 |  |  |  | $5.1 |  |  |  | $1.0 |  |  |  | $1.5 |
2018 | 3.2 |  |  | 9.0 |  |  | 1.8 |  |  | 7.2 |  |  | 1.4 |  |  | 1.8 |

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