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Fair Value Measurements (Tables) | 3 Months Ended
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Mar. 31, 2018
Statement [Line Items] |
Fair Value Measurements | Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions):
Alliant Energy | March 31, 2018 |  | December 31, 2017
|  |  | Fair Value |  |  |  | Fair Value
| Carrying |  | Level |  | Level |  | Level |  |  |  | Carrying |  | Level |  | Level |  | Level |  |
| Amount |  | 1 |  | 2 |  | 3 |  | Total |  | Amount |  | 1 |  | 2 |  | 3 |  | Total
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives |  | $14.1 |  |  |  | $— |  |  |  | $4.1 |  |  |  | $10.0 |  |  |  | $14.1 |  |  |  | $25.1 |  |  |  | $— |  |  |  | $4.1 |  |  |  | $21.0 |  |  |  | $25.1 |
Deferred proceeds | 120.9 |  |  | — |  |  | — |  |  | 120.9 |  |  | 120.9 |  |  | 222.1 |  |  | — |  |  | — |  |  | 222.1 |  |  | 222.1 |
Liabilities and equity: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives | 46.7 |  |  | — |  |  | 7.3 |  |  | 39.4 |  |  | 46.7 |  |  | 41.7 |  |  | — |  |  | 8.5 |  |  | 33.2 |  |  | 41.7 |
Long-term debt (incl. current maturities) | 4,912.5 |  |  | — |  |  | 5,366.6 |  |  | 2.5 |  |  | 5,369.1 |  |  | 4,866.3 |  |  | — |  |  | 5,444.6 |  |  | 2.9 |  |  | 5,447.5 |
Cumulative preferred stock of IPL | 200.0 |  |  | 198.4 |  |  | — |  |  | — |  |  | 198.4 |  |  | 200.0 |  |  | 203.8 |  |  | — |  |  | — |  |  | 203.8 |
IPL | March 31, 2018 |  | December 31, 2017
|  |  | Fair Value |  |  |  | Fair Value
| Carrying |  | Level |  | Level |  | Level |  |  |  | Carrying |  | Level |  | Level |  | Level |  |
| Amount |  | 1 |  | 2 |  | 3 |  | Total |  | Amount |  | 1 |  | 2 |  | 3 |  | Total
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives |  | $7.9 |  |  |  | $— |  |  |  | $1.7 |  |  |  | $6.2 |  |  |  | $7.9 |  |  |  | $17.1 |  |  |  | $— |  |  |  | $2.0 |  |  |  | $15.1 |  |  |  | $17.1 |
Deferred proceeds | 120.9 |  |  | — |  |  | — |  |  | 120.9 |  |  | 120.9 |  |  | 222.1 |  |  | — |  |  | — |  |  | 222.1 |  |  | 222.1 |
Liabilities and equity: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives | 24.7 |  |  | — |  |  | 3.1 |  |  | 21.6 |  |  | 24.7 |  |  | 19.4 |  |  | — |  |  | 2.9 |  |  | 16.5 |  |  | 19.4 |
Long-term debt (incl. current maturities) | 2,452.2 |  |  | — |  |  | 2,635.7 |  |  | — |  |  | 2,635.7 |  |  | 2,406.0 |  |  | — |  |  | 2,665.7 |  |  | — |  |  | 2,665.7 |
Cumulative preferred stock | 200.0 |  |  | 198.4 |  |  | — |  |  | — |  |  | 198.4 |  |  | 200.0 |  |  | 203.8 |  |  | — |  |  | — |  |  | 203.8 |
WPL | March 31, 2018 |  | December 31, 2017
|  |  | Fair Value |  |  |  | Fair Value
| Carrying |  | Level |  | Level |  | Level |  |  |  | Carrying |  | Level |  | Level |  | Level |  |
| Amount |  | 1 |  | 2 |  | 3 |  | Total |  | Amount |  | 1 |  | 2 |  | 3 |  | Total
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives |  | $6.2 |  |  |  | $— |  |  |  | $2.4 |  |  |  | $3.8 |  |  |  | $6.2 |  |  |  | $8.0 |  |  |  | $— |  |  |  | $2.1 |  |  |  | $5.9 |  |  |  | $8.0 |
Liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives | 22.0 |  |  | — |  |  | 4.2 |  |  | 17.8 |  |  | 22.0 |  |  | 22.3 |  |  | — |  |  | 5.6 |  |  | 16.7 |  |  | 22.3 |
Long-term debt | 1,833.7 |  |  | — |  |  | 2,102.7 |  |  | — |  |  | 2,102.7 |  |  | 1,833.4 |  |  | — |  |  | 2,147.9 |  |  | — |  |  | 2,147.9 |
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 March 31 | 2018 |  | 2017 |  | 2018 |  | 2017
Beginning balance, January 1 |  | ($12.2 | ) |  |  | $8.7 |  |  |  | $222.1 |  |  |  | $211.1 |
Total net losses included in changes in net assets (realized/unrealized) | (9.8 | ) |  | (35.2 | ) |  | — |  |  | — |
Sales | — |  |  | (0.1 | ) |  | — |  |  | — |
Settlements (a) | (7.4 | ) |  | (6.3 | ) |  | (101.2 | ) |  | (62.1 | )
Ending balance, March 31 |  | ($29.4 | ) |  |  | ($32.9 | ) |  |  | $120.9 |  |  |  | $149.0 |
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 March 31 |  | ($9.4 | ) |  |  | ($33.7 | ) |  |  | $— |  |  |  | $— |
IPL | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
Three Months Ended March 31 | 2018 |  | 2017 |  | 2018 |  | 2017
Beginning balance, January 1 |  | ($1.4 | ) |  |  | $10.1 |  |  |  | $222.1 |  |  |  | $211.1 |
Total net losses included in changes in net assets (realized/unrealized) | (7.6 | ) |  | (12.7 | ) |  | — |  |  | — |
Sales | — |  |  | (0.1 | ) |  | — |  |  | — |
Settlements (a) | (6.4 | ) |  | (5.6 | ) |  | (101.2 | ) |  | (62.1 | )
Ending balance, March 31 |  | ($15.4 | ) |  |  | ($8.3 | ) |  |  | $120.9 |  |  |  | $149.0 |
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 March 31 |  | ($7.3 | ) |  |  | ($11.4 | ) |  |  | $— |  |  |  | $— |
WPL | Commodity Contract Derivative
| Assets and (Liabilities), net
Three Months Ended March 31 | 2018 |  | 2017
Beginning balance, January 1 |  | ($10.8 | ) |  |  | ($1.4 | )
Total net losses included in changes in net assets (realized/unrealized) | (2.2 | ) |  | (22.5 | )
Settlements | (1.0 | ) |  | (0.7 | )
Ending balance, March 31 |  | ($14.0 | ) |  |  | ($24.6 | )
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 March 31 |  | ($2.1 | ) |  |  | ($22.3 | )
(a) | 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 electric, natural gas, coal and diesel fuel commodity contracts categorized as Level 3 was recognized as net derivative assets (liabilities) as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| Excluding FTRs |  | FTRs |  | Excluding FTRs |  | FTRs |  | Excluding FTRs |  | FTRs
March 31, 2018 |  | ($34.6 | ) |  |  | $5.2 |  |  |  | ($20.0 | ) |  |  | $4.6 |  |  |  | ($14.6 | ) |  |  | $0.6 |
December 31, 2017 | (23.5 | ) |  | 11.3 |  |  | (11.5 | ) |  | 10.1 |  |  | (12.0 | ) |  | 1.2 |
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 | March 31, 2018 |  | December 31, 2017
|  |  | Fair Value |  |  |  | Fair Value
| Carrying |  | Level |  | Level |  | Level |  |  |  | Carrying |  | Level |  | Level |  | Level |  |
| Amount |  | 1 |  | 2 |  | 3 |  | Total |  | Amount |  | 1 |  | 2 |  | 3 |  | Total
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives |  | $14.1 |  |  |  | $— |  |  |  | $4.1 |  |  |  | $10.0 |  |  |  | $14.1 |  |  |  | $25.1 |  |  |  | $— |  |  |  | $4.1 |  |  |  | $21.0 |  |  |  | $25.1 |
Deferred proceeds | 120.9 |  |  | — |  |  | — |  |  | 120.9 |  |  | 120.9 |  |  | 222.1 |  |  | — |  |  | — |  |  | 222.1 |  |  | 222.1 |
Liabilities and equity: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives | 46.7 |  |  | — |  |  | 7.3 |  |  | 39.4 |  |  | 46.7 |  |  | 41.7 |  |  | — |  |  | 8.5 |  |  | 33.2 |  |  | 41.7 |
Long-term debt (incl. current maturities) | 4,912.5 |  |  | — |  |  | 5,366.6 |  |  | 2.5 |  |  | 5,369.1 |  |  | 4,866.3 |  |  | — |  |  | 5,444.6 |  |  | 2.9 |  |  | 5,447.5 |
Cumulative preferred stock of IPL | 200.0 |  |  | 198.4 |  |  | — |  |  | — |  |  | 198.4 |  |  | 200.0 |  |  | 203.8 |  |  | — |  |  | — |  |  | 203.8 |
IPL | March 31, 2018 |  | December 31, 2017
|  |  | Fair Value |  |  |  | Fair Value
| Carrying |  | Level |  | Level |  | Level |  |  |  | Carrying |  | Level |  | Level |  | Level |  |
| Amount |  | 1 |  | 2 |  | 3 |  | Total |  | Amount |  | 1 |  | 2 |  | 3 |  | Total
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives |  | $7.9 |  |  |  | $— |  |  |  | $1.7 |  |  |  | $6.2 |  |  |  | $7.9 |  |  |  | $17.1 |  |  |  | $— |  |  |  | $2.0 |  |  |  | $15.1 |  |  |  | $17.1 |
Deferred proceeds | 120.9 |  |  | — |  |  | — |  |  | 120.9 |  |  | 120.9 |  |  | 222.1 |  |  | — |  |  | — |  |  | 222.1 |  |  | 222.1 |
Liabilities and equity: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives | 24.7 |  |  | — |  |  | 3.1 |  |  | 21.6 |  |  | 24.7 |  |  | 19.4 |  |  | — |  |  | 2.9 |  |  | 16.5 |  |  | 19.4 |
Long-term debt (incl. current maturities) | 2,452.2 |  |  | — |  |  | 2,635.7 |  |  | — |  |  | 2,635.7 |  |  | 2,406.0 |  |  | — |  |  | 2,665.7 |  |  | — |  |  | 2,665.7 |
Cumulative preferred stock | 200.0 |  |  | 198.4 |  |  | — |  |  | — |  |  | 198.4 |  |  | 200.0 |  |  | 203.8 |  |  | — |  |  | — |  |  | 203.8 |
WPL | March 31, 2018 |  | December 31, 2017
|  |  | Fair Value |  |  |  | Fair Value
| Carrying |  | Level |  | Level |  | Level |  |  |  | Carrying |  | Level |  | Level |  | Level |  |
| Amount |  | 1 |  | 2 |  | 3 |  | Total |  | Amount |  | 1 |  | 2 |  | 3 |  | Total
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives |  | $6.2 |  |  |  | $— |  |  |  | $2.4 |  |  |  | $3.8 |  |  |  | $6.2 |  |  |  | $8.0 |  |  |  | $— |  |  |  | $2.1 |  |  |  | $5.9 |  |  |  | $8.0 |
Liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives | 22.0 |  |  | — |  |  | 4.2 |  |  | 17.8 |  |  | 22.0 |  |  | 22.3 |  |  | — |  |  | 5.6 |  |  | 16.7 |  |  | 22.3 |
Long-term debt | 1,833.7 |  |  | — |  |  | 2,102.7 |  |  | — |  |  | 2,102.7 |  |  | 1,833.4 |  |  | — |  |  | 2,147.9 |  |  | — |  |  | 2,147.9 |
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 March 31 | 2018 |  | 2017 |  | 2018 |  | 2017
Beginning balance, January 1 |  | ($12.2 | ) |  |  | $8.7 |  |  |  | $222.1 |  |  |  | $211.1 |
Total net losses included in changes in net assets (realized/unrealized) | (9.8 | ) |  | (35.2 | ) |  | — |  |  | — |
Sales | — |  |  | (0.1 | ) |  | — |  |  | — |
Settlements (a) | (7.4 | ) |  | (6.3 | ) |  | (101.2 | ) |  | (62.1 | )
Ending balance, March 31 |  | ($29.4 | ) |  |  | ($32.9 | ) |  |  | $120.9 |  |  |  | $149.0 |
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 March 31 |  | ($9.4 | ) |  |  | ($33.7 | ) |  |  | $— |  |  |  | $— |
IPL | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
Three Months Ended March 31 | 2018 |  | 2017 |  | 2018 |  | 2017
Beginning balance, January 1 |  | ($1.4 | ) |  |  | $10.1 |  |  |  | $222.1 |  |  |  | $211.1 |
Total net losses included in changes in net assets (realized/unrealized) | (7.6 | ) |  | (12.7 | ) |  | — |  |  | — |
Sales | — |  |  | (0.1 | ) |  | — |  |  | — |
Settlements (a) | (6.4 | ) |  | (5.6 | ) |  | (101.2 | ) |  | (62.1 | )
Ending balance, March 31 |  | ($15.4 | ) |  |  | ($8.3 | ) |  |  | $120.9 |  |  |  | $149.0 |
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 March 31 |  | ($7.3 | ) |  |  | ($11.4 | ) |  |  | $— |  |  |  | $— |
WPL | Commodity Contract Derivative
| Assets and (Liabilities), net
Three Months Ended March 31 | 2018 |  | 2017
Beginning balance, January 1 |  | ($10.8 | ) |  |  | ($1.4 | )
Total net losses included in changes in net assets (realized/unrealized) | (2.2 | ) |  | (22.5 | )
Settlements | (1.0 | ) |  | (0.7 | )
Ending balance, March 31 |  | ($14.0 | ) |  |  | ($24.6 | )
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 March 31 |  | ($2.1 | ) |  |  | ($22.3 | )
(a) | 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 electric, natural gas, coal and diesel fuel commodity contracts categorized as Level 3 was recognized as net derivative assets (liabilities) as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| Excluding FTRs |  | FTRs |  | Excluding FTRs |  | FTRs |  | Excluding FTRs |  | FTRs
March 31, 2018 |  | ($34.6 | ) |  |  | $5.2 |  |  |  | ($20.0 | ) |  |  | $4.6 |  |  |  | ($14.6 | ) |  |  | $0.6 |
December 31, 2017 | (23.5 | ) |  | 11.3 |  |  | (11.5 | ) |  | 10.1 |  |  | (12.0 | ) |  | 1.2 |
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 | March 31, 2018 |  | December 31, 2017
|  |  | Fair Value |  |  |  | Fair Value
| Carrying |  | Level |  | Level |  | Level |  |  |  | Carrying |  | Level |  | Level |  | Level |  |
| Amount |  | 1 |  | 2 |  | 3 |  | Total |  | Amount |  | 1 |  | 2 |  | 3 |  | Total
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives |  | $14.1 |  |  |  | $— |  |  |  | $4.1 |  |  |  | $10.0 |  |  |  | $14.1 |  |  |  | $25.1 |  |  |  | $— |  |  |  | $4.1 |  |  |  | $21.0 |  |  |  | $25.1 |
Deferred proceeds | 120.9 |  |  | — |  |  | — |  |  | 120.9 |  |  | 120.9 |  |  | 222.1 |  |  | — |  |  | — |  |  | 222.1 |  |  | 222.1 |
Liabilities and equity: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives | 46.7 |  |  | — |  |  | 7.3 |  |  | 39.4 |  |  | 46.7 |  |  | 41.7 |  |  | — |  |  | 8.5 |  |  | 33.2 |  |  | 41.7 |
Long-term debt (incl. current maturities) | 4,912.5 |  |  | — |  |  | 5,366.6 |  |  | 2.5 |  |  | 5,369.1 |  |  | 4,866.3 |  |  | — |  |  | 5,444.6 |  |  | 2.9 |  |  | 5,447.5 |
Cumulative preferred stock of IPL | 200.0 |  |  | 198.4 |  |  | — |  |  | — |  |  | 198.4 |  |  | 200.0 |  |  | 203.8 |  |  | — |  |  | — |  |  | 203.8 |
IPL | March 31, 2018 |  | December 31, 2017
|  |  | Fair Value |  |  |  | Fair Value
| Carrying |  | Level |  | Level |  | Level |  |  |  | Carrying |  | Level |  | Level |  | Level |  |
| Amount |  | 1 |  | 2 |  | 3 |  | Total |  | Amount |  | 1 |  | 2 |  | 3 |  | Total
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives |  | $7.9 |  |  |  | $— |  |  |  | $1.7 |  |  |  | $6.2 |  |  |  | $7.9 |  |  |  | $17.1 |  |  |  | $— |  |  |  | $2.0 |  |  |  | $15.1 |  |  |  | $17.1 |
Deferred proceeds | 120.9 |  |  | — |  |  | — |  |  | 120.9 |  |  | 120.9 |  |  | 222.1 |  |  | — |  |  | — |  |  | 222.1 |  |  | 222.1 |
Liabilities and equity: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives | 24.7 |  |  | — |  |  | 3.1 |  |  | 21.6 |  |  | 24.7 |  |  | 19.4 |  |  | — |  |  | 2.9 |  |  | 16.5 |  |  | 19.4 |
Long-term debt (incl. current maturities) | 2,452.2 |  |  | — |  |  | 2,635.7 |  |  | — |  |  | 2,635.7 |  |  | 2,406.0 |  |  | — |  |  | 2,665.7 |  |  | — |  |  | 2,665.7 |
Cumulative preferred stock | 200.0 |  |  | 198.4 |  |  | — |  |  | — |  |  | 198.4 |  |  | 200.0 |  |  | 203.8 |  |  | — |  |  | — |  |  | 203.8 |
WPL | March 31, 2018 |  | December 31, 2017
|  |  | Fair Value |  |  |  | Fair Value
| Carrying |  | Level |  | Level |  | Level |  |  |  | Carrying |  | Level |  | Level |  | Level |  |
| Amount |  | 1 |  | 2 |  | 3 |  | Total |  | Amount |  | 1 |  | 2 |  | 3 |  | Total
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives |  | $6.2 |  |  |  | $— |  |  |  | $2.4 |  |  |  | $3.8 |  |  |  | $6.2 |  |  |  | $8.0 |  |  |  | $— |  |  |  | $2.1 |  |  |  | $5.9 |  |  |  | $8.0 |
Liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives | 22.0 |  |  | — |  |  | 4.2 |  |  | 17.8 |  |  | 22.0 |  |  | 22.3 |  |  | — |  |  | 5.6 |  |  | 16.7 |  |  | 22.3 |
Long-term debt | 1,833.7 |  |  | — |  |  | 2,102.7 |  |  | — |  |  | 2,102.7 |  |  | 1,833.4 |  |  | — |  |  | 2,147.9 |  |  | — |  |  | 2,147.9 |
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 March 31 | 2018 |  | 2017 |  | 2018 |  | 2017
Beginning balance, January 1 |  | ($12.2 | ) |  |  | $8.7 |  |  |  | $222.1 |  |  |  | $211.1 |
Total net losses included in changes in net assets (realized/unrealized) | (9.8 | ) |  | (35.2 | ) |  | — |  |  | — |
Sales | — |  |  | (0.1 | ) |  | — |  |  | — |
Settlements (a) | (7.4 | ) |  | (6.3 | ) |  | (101.2 | ) |  | (62.1 | )
Ending balance, March 31 |  | ($29.4 | ) |  |  | ($32.9 | ) |  |  | $120.9 |  |  |  | $149.0 |
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 March 31 |  | ($9.4 | ) |  |  | ($33.7 | ) |  |  | $— |  |  |  | $— |
IPL | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
Three Months Ended March 31 | 2018 |  | 2017 |  | 2018 |  | 2017
Beginning balance, January 1 |  | ($1.4 | ) |  |  | $10.1 |  |  |  | $222.1 |  |  |  | $211.1 |
Total net losses included in changes in net assets (realized/unrealized) | (7.6 | ) |  | (12.7 | ) |  | — |  |  | — |
Sales | — |  |  | (0.1 | ) |  | — |  |  | — |
Settlements (a) | (6.4 | ) |  | (5.6 | ) |  | (101.2 | ) |  | (62.1 | )
Ending balance, March 31 |  | ($15.4 | ) |  |  | ($8.3 | ) |  |  | $120.9 |  |  |  | $149.0 |
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 March 31 |  | ($7.3 | ) |  |  | ($11.4 | ) |  |  | $— |  |  |  | $— |
WPL | Commodity Contract Derivative
| Assets and (Liabilities), net
Three Months Ended March 31 | 2018 |  | 2017
Beginning balance, January 1 |  | ($10.8 | ) |  |  | ($1.4 | )
Total net losses included in changes in net assets (realized/unrealized) | (2.2 | ) |  | (22.5 | )
Settlements | (1.0 | ) |  | (0.7 | )
Ending balance, March 31 |  | ($14.0 | ) |  |  | ($24.6 | )
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 March 31 |  | ($2.1 | ) |  |  | ($22.3 | )
(a) | 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 electric, natural gas, coal and diesel fuel commodity contracts categorized as Level 3 was recognized as net derivative assets (liabilities) as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| Excluding FTRs |  | FTRs |  | Excluding FTRs |  | FTRs |  | Excluding FTRs |  | FTRs
March 31, 2018 |  | ($34.6 | ) |  |  | $5.2 |  |  |  | ($20.0 | ) |  |  | $4.6 |  |  |  | ($14.6 | ) |  |  | $0.6 |
December 31, 2017 | (23.5 | ) |  | 11.3 |  |  | (11.5 | ) |  | 10.1 |  |  | (12.0 | ) |  | 1.2 |

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- Definition Tabular disclosure of the fair value measurement of assets using significant unobservable inputs (Level 3), a reconciliation of the beginning and ending balances, separately presenting changes during the period attributable to the following: (1) total gains or losses for the period (realized and unrealized), segregating those gains or losses included in earnings (or changes in net assets) and gains or losses recognized in other comprehensive income (loss), and a description of where those gains or losses included in earnings (or changes in net assets) are reported in the statement of income (or activities); (2) purchases, sales, issues, and settlements (each type disclosed separately); and (3) transfers in and transfers out of Level 3 (for example, transfers due to changes in the observability of significant inputs), by class of asset. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19279-110258 + Details
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