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Fair Value Measurements | 9 Months Ended
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Sep. 30, 2019
Fair Value Measurements | FAIR VALUE MEASUREMENTS Fair Value of Financial Instruments - The carrying amounts of current assets and current liabilities approximate fair value because of the short maturity of such financial instruments. Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions):
Alliant Energy | September 30, 2019 |  | December 31, 2018
|  |  | 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 |  | $174.4 |  |  |  | $174.4 |  |  |  | $— |  |  |  | $— |  |  |  | $174.4 |  |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | $— |
Derivatives | 30.3 |  |  | — |  |  | 8.1 |  |  | 22.2 |  |  | 30.3 |  |  | 28.3 |  |  | — |  |  | 8.9 |  |  | 19.4 |  |  | 28.3 |
Deferred proceeds | 237.0 |  |  | — |  |  | — |  |  | 237.0 |  |  | 237.0 |  |  | 119.4 |  |  | — |  |  | — |  |  | 119.4 |  |  | 119.4 |
Liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives | 31.8 |  |  | — |  |  | 31.3 |  |  | 0.5 |  |  | 31.8 |  |  | 23.3 |  |  | — |  |  | 16.1 |  |  | 7.2 |  |  | 23.3 |
Long-term debt (incl. current maturities) | 6,191.9 |  |  | — |  |  | 7,016.4 |  |  | 2.0 |  |  | 7,018.4 |  |  | 5,502.8 |  |  | — |  |  | 5,858.4 |  |  | 2.4 |  |  | 5,860.8 |
IPL | September 30, 2019 |  | December 31, 2018
|  |  | 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 |  | $173.7 |  |  |  | $173.7 |  |  |  | $— |  |  |  | $— |  |  |  | $173.7 |  |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | $— |
Derivatives | 23.3 |  |  | — |  |  | 4.8 |  |  | 18.5 |  |  | 23.3 |  |  | 17.7 |  |  | — |  |  | 4.0 |  |  | 13.7 |  |  | 17.7 |
Deferred proceeds | 237.0 |  |  | — |  |  | — |  |  | 237.0 |  |  | 237.0 |  |  | 119.4 |  |  | — |  |  | — |  |  | 119.4 |  |  | 119.4 |
Liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives | 13.4 |  |  | — |  |  | 12.9 |  |  | 0.5 |  |  | 13.4 |  |  | 11.2 |  |  | — |  |  | 6.5 |  |  | 4.7 |  |  | 11.2 |
Long-term debt (incl. current maturities) | 3,146.8 |  |  | — |  |  | 3,537.0 |  |  | — |  |  | 3,537.0 |  |  | 2,552.3 |  |  | — |  |  | 2,691.2 |  |  | — |  |  | 2,691.2 |
WPL | September 30, 2019 |  | December 31, 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 |  | $7.0 |  |  |  | $— |  |  |  | $3.3 |  |  |  | $3.7 |  |  |  | $7.0 |  |  |  | $10.6 |  |  |  | $— |  |  |  | $4.9 |  |  |  | $5.7 |  |  |  | $10.6 |
Liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives | 18.4 |  |  | — |  |  | 18.4 |  |  | — |  |  | 18.4 |  |  | 12.1 |  |  | — |  |  | 9.6 |  |  | 2.5 |  |  | 12.1 |
Long-term debt (incl. current maturities) | 1,932.3 |  |  | — |  |  | 2,314.1 |  |  | — |  |  | 2,314.1 |  |  | 1,834.9 |  |  | — |  |  | 2,043.7 |  |  | — |  |  | 2,043.7 |
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 | 2019 |  | 2018 |  | 2019 |  | 2018
Beginning balance, July 1 |  | $13.2 |  |  |  | ($10.7 | ) |  |  | $214.6 |  |  |  | $208.3 |
Total net gains included in changes in net assets (realized/unrealized) | 12.7 |  |  | 25.7 |  |  | — |  |  | — |
Transfers out of Level 3 | (1.2 | ) |  | 15.6 |  |  | — |  |  | — |
Sales | — |  |  | (0.2 | ) |  | — |  |  | — |
Settlements (a) | (3.0 | ) |  | (6.2 | ) |  | 22.4 |  |  | 35.4 |
Ending balance, September 30 |  | $21.7 |  |  |  | $24.2 |  |  |  | $237.0 |  |  |  | $243.7 |
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 |  | $12.7 |  |  |  | $26.1 |  |  |  | $— |  |  |  | $— |
Alliant Energy | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
Nine Months Ended September 30 | 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) | 6.9 |  |  | 15.7 |  |  | — |  |  | — |
Transfers out of Level 3 | 2.8 |  |  | 15.6 |  |  | — |  |  | — |
Purchases | 13.8 |  |  | 26.7 |  |  | — |  |  | — |
Sales | (0.2 | ) |  | (0.2 | ) |  | — |  |  | — |
Settlements (a) | (13.8 | ) |  | (21.4 | ) |  | 117.6 |  |  | 21.6 |
Ending balance, September 30 |  | $21.7 |  |  |  | $24.2 |  |  |  | $237.0 |  |  |  | $243.7 |
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 |  | $10.1 |  |  |  | $16.5 |  |  |  | $— |  |  |  | $— |
IPL | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
Three Months Ended September 30 | 2019 |  | 2018 |  | 2019 |  | 2018
Beginning balance, July 1 |  | $9.3 |  |  |  | ($4.1 | ) |  |  | $214.6 |  |  |  | $208.3 |
Total net gains included in changes in net assets (realized/unrealized) | 11.5 |  |  | 16.8 |  |  | — |  |  | — |
Transfers out of Level 3 | (0.6 | ) |  | 10.5 |  |  | — |  |  | — |
Sales | — |  |  | (0.1 | ) |  | — |  |  | — |
Settlements (a) | (2.2 | ) |  | (4.9 | ) |  | 22.4 |  |  | 35.4 |
Ending balance, September 30 |  | $18.0 |  |  |  | $18.2 |  |  |  | $237.0 |  |  |  | $243.7 |
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 |  | $11.5 |  |  |  | $16.8 |  |  |  | $— |  |  |  | $— |
IPL | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
Nine Months Ended September 30 | 2019 |  | 2018 |  | 2019 |  | 2018
Beginning balance, January 1 |  | $9.0 |  |  |  | ($1.4 | ) |  |  | $119.4 |  |  |  | $222.1 |
Total net gains included in changes in net assets (realized/unrealized) | 8.6 |  |  | 7.6 |  |  | — |  |  | — |
Transfers out of Level 3 | 2.0 |  |  | 10.5 |  |  | — |  |  | — |
Purchases | 9.5 |  |  | 19.3 |  |  | — |  |  | — |
Sales | (0.1 | ) |  | (0.1 | ) |  | — |  |  | — |
Settlements (a) | (11.0 | ) |  | (17.7 | ) |  | 117.6 |  |  | 21.6 |
Ending balance, September 30 |  | $18.0 |  |  |  | $18.2 |  |  |  | $237.0 |  |  |  | $243.7 |
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 |  | $10.5 |  |  |  | $7.9 |  |  |  | $— |  |  |  | $— |
WPL | Commodity Contract Derivative
| Assets and (Liabilities), net
Three Months Ended September 30 | 2019 |  | 2018
Beginning balance, July 1 |  | $3.9 |  |  |  | ($6.6 | )
Total net gains included in changes in net assets (realized/unrealized) | 1.2 |  |  | 8.9 |
Transfers out of Level 3 | (0.6 | ) |  | 5.1 |
Sales | — |  |  | (0.1 | )
Settlements | (0.8 | ) |  | (1.3 | )
Ending balance, September 30 |  | $3.7 |  |  |  | $6.0 |
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 |  | $1.2 |  |  |  | $9.3 |
WPL | Commodity Contract Derivative
| Assets and (Liabilities), net
Nine Months Ended September 30 | 2019 |  | 2018
Beginning balance, January 1 |  | $3.2 |  |  |  | ($10.8 | )
Total net gains (losses) included in changes in net assets (realized/unrealized) | (1.7 | ) |  | 8.1 |
Transfers out of Level 3 | 0.8 |  |  | 5.1 |
Purchases | 4.3 |  |  | 7.4 |
Sales | (0.1 | ) |  | (0.1 | )
Settlements | (2.8 | ) |  | (3.7 | )
Ending balance, September 30 |  | $3.7 |  |  |  | $6.0 |
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 |  | ($0.4 | ) |  |  | $8.6 |
(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.
Commodity Contracts - The fair value of FTR 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, 2019 |  | $13.1 |  |  |  | $8.6 |  |  |  | $12.5 |  |  |  | $5.5 |  |  |  | $0.6 |  |  |  | $3.1 |
December 31, 2018 | 3.2 |  |  | 9.0 |  |  | 1.8 |  |  | 7.2 |  |  | 1.4 |  |  | 1.8 |
IPL [Member] |
Fair Value Measurements | FAIR VALUE MEASUREMENTS Fair Value of Financial Instruments - The carrying amounts of current assets and current liabilities approximate fair value because of the short maturity of such financial instruments. Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions):
Alliant Energy | September 30, 2019 |  | December 31, 2018
|  |  | 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 |  | $174.4 |  |  |  | $174.4 |  |  |  | $— |  |  |  | $— |  |  |  | $174.4 |  |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | $— |
Derivatives | 30.3 |  |  | — |  |  | 8.1 |  |  | 22.2 |  |  | 30.3 |  |  | 28.3 |  |  | — |  |  | 8.9 |  |  | 19.4 |  |  | 28.3 |
Deferred proceeds | 237.0 |  |  | — |  |  | — |  |  | 237.0 |  |  | 237.0 |  |  | 119.4 |  |  | — |  |  | — |  |  | 119.4 |  |  | 119.4 |
Liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives | 31.8 |  |  | — |  |  | 31.3 |  |  | 0.5 |  |  | 31.8 |  |  | 23.3 |  |  | — |  |  | 16.1 |  |  | 7.2 |  |  | 23.3 |
Long-term debt (incl. current maturities) | 6,191.9 |  |  | — |  |  | 7,016.4 |  |  | 2.0 |  |  | 7,018.4 |  |  | 5,502.8 |  |  | — |  |  | 5,858.4 |  |  | 2.4 |  |  | 5,860.8 |
IPL | September 30, 2019 |  | December 31, 2018
|  |  | 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 |  | $173.7 |  |  |  | $173.7 |  |  |  | $— |  |  |  | $— |  |  |  | $173.7 |  |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | $— |
Derivatives | 23.3 |  |  | — |  |  | 4.8 |  |  | 18.5 |  |  | 23.3 |  |  | 17.7 |  |  | — |  |  | 4.0 |  |  | 13.7 |  |  | 17.7 |
Deferred proceeds | 237.0 |  |  | — |  |  | — |  |  | 237.0 |  |  | 237.0 |  |  | 119.4 |  |  | — |  |  | — |  |  | 119.4 |  |  | 119.4 |
Liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives | 13.4 |  |  | — |  |  | 12.9 |  |  | 0.5 |  |  | 13.4 |  |  | 11.2 |  |  | — |  |  | 6.5 |  |  | 4.7 |  |  | 11.2 |
Long-term debt (incl. current maturities) | 3,146.8 |  |  | — |  |  | 3,537.0 |  |  | — |  |  | 3,537.0 |  |  | 2,552.3 |  |  | — |  |  | 2,691.2 |  |  | — |  |  | 2,691.2 |
WPL | September 30, 2019 |  | December 31, 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 |  | $7.0 |  |  |  | $— |  |  |  | $3.3 |  |  |  | $3.7 |  |  |  | $7.0 |  |  |  | $10.6 |  |  |  | $— |  |  |  | $4.9 |  |  |  | $5.7 |  |  |  | $10.6 |
Liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives | 18.4 |  |  | — |  |  | 18.4 |  |  | — |  |  | 18.4 |  |  | 12.1 |  |  | — |  |  | 9.6 |  |  | 2.5 |  |  | 12.1 |
Long-term debt (incl. current maturities) | 1,932.3 |  |  | — |  |  | 2,314.1 |  |  | — |  |  | 2,314.1 |  |  | 1,834.9 |  |  | — |  |  | 2,043.7 |  |  | — |  |  | 2,043.7 |
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 | 2019 |  | 2018 |  | 2019 |  | 2018
Beginning balance, July 1 |  | $13.2 |  |  |  | ($10.7 | ) |  |  | $214.6 |  |  |  | $208.3 |
Total net gains included in changes in net assets (realized/unrealized) | 12.7 |  |  | 25.7 |  |  | — |  |  | — |
Transfers out of Level 3 | (1.2 | ) |  | 15.6 |  |  | — |  |  | — |
Sales | — |  |  | (0.2 | ) |  | — |  |  | — |
Settlements (a) | (3.0 | ) |  | (6.2 | ) |  | 22.4 |  |  | 35.4 |
Ending balance, September 30 |  | $21.7 |  |  |  | $24.2 |  |  |  | $237.0 |  |  |  | $243.7 |
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 |  | $12.7 |  |  |  | $26.1 |  |  |  | $— |  |  |  | $— |
Alliant Energy | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
Nine Months Ended September 30 | 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) | 6.9 |  |  | 15.7 |  |  | — |  |  | — |
Transfers out of Level 3 | 2.8 |  |  | 15.6 |  |  | — |  |  | — |
Purchases | 13.8 |  |  | 26.7 |  |  | — |  |  | — |
Sales | (0.2 | ) |  | (0.2 | ) |  | — |  |  | — |
Settlements (a) | (13.8 | ) |  | (21.4 | ) |  | 117.6 |  |  | 21.6 |
Ending balance, September 30 |  | $21.7 |  |  |  | $24.2 |  |  |  | $237.0 |  |  |  | $243.7 |
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 |  | $10.1 |  |  |  | $16.5 |  |  |  | $— |  |  |  | $— |
IPL | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
Three Months Ended September 30 | 2019 |  | 2018 |  | 2019 |  | 2018
Beginning balance, July 1 |  | $9.3 |  |  |  | ($4.1 | ) |  |  | $214.6 |  |  |  | $208.3 |
Total net gains included in changes in net assets (realized/unrealized) | 11.5 |  |  | 16.8 |  |  | — |  |  | — |
Transfers out of Level 3 | (0.6 | ) |  | 10.5 |  |  | — |  |  | — |
Sales | — |  |  | (0.1 | ) |  | — |  |  | — |
Settlements (a) | (2.2 | ) |  | (4.9 | ) |  | 22.4 |  |  | 35.4 |
Ending balance, September 30 |  | $18.0 |  |  |  | $18.2 |  |  |  | $237.0 |  |  |  | $243.7 |
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 |  | $11.5 |  |  |  | $16.8 |  |  |  | $— |  |  |  | $— |
IPL | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
Nine Months Ended September 30 | 2019 |  | 2018 |  | 2019 |  | 2018
Beginning balance, January 1 |  | $9.0 |  |  |  | ($1.4 | ) |  |  | $119.4 |  |  |  | $222.1 |
Total net gains included in changes in net assets (realized/unrealized) | 8.6 |  |  | 7.6 |  |  | — |  |  | — |
Transfers out of Level 3 | 2.0 |  |  | 10.5 |  |  | — |  |  | — |
Purchases | 9.5 |  |  | 19.3 |  |  | — |  |  | — |
Sales | (0.1 | ) |  | (0.1 | ) |  | — |  |  | — |
Settlements (a) | (11.0 | ) |  | (17.7 | ) |  | 117.6 |  |  | 21.6 |
Ending balance, September 30 |  | $18.0 |  |  |  | $18.2 |  |  |  | $237.0 |  |  |  | $243.7 |
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 |  | $10.5 |  |  |  | $7.9 |  |  |  | $— |  |  |  | $— |
WPL | Commodity Contract Derivative
| Assets and (Liabilities), net
Three Months Ended September 30 | 2019 |  | 2018
Beginning balance, July 1 |  | $3.9 |  |  |  | ($6.6 | )
Total net gains included in changes in net assets (realized/unrealized) | 1.2 |  |  | 8.9 |
Transfers out of Level 3 | (0.6 | ) |  | 5.1 |
Sales | — |  |  | (0.1 | )
Settlements | (0.8 | ) |  | (1.3 | )
Ending balance, September 30 |  | $3.7 |  |  |  | $6.0 |
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 |  | $1.2 |  |  |  | $9.3 |
WPL | Commodity Contract Derivative
| Assets and (Liabilities), net
Nine Months Ended September 30 | 2019 |  | 2018
Beginning balance, January 1 |  | $3.2 |  |  |  | ($10.8 | )
Total net gains (losses) included in changes in net assets (realized/unrealized) | (1.7 | ) |  | 8.1 |
Transfers out of Level 3 | 0.8 |  |  | 5.1 |
Purchases | 4.3 |  |  | 7.4 |
Sales | (0.1 | ) |  | (0.1 | )
Settlements | (2.8 | ) |  | (3.7 | )
Ending balance, September 30 |  | $3.7 |  |  |  | $6.0 |
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 |  | ($0.4 | ) |  |  | $8.6 |
(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.
Commodity Contracts - The fair value of FTR 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, 2019 |  | $13.1 |  |  |  | $8.6 |  |  |  | $12.5 |  |  |  | $5.5 |  |  |  | $0.6 |  |  |  | $3.1 |
December 31, 2018 | 3.2 |  |  | 9.0 |  |  | 1.8 |  |  | 7.2 |  |  | 1.4 |  |  | 1.8 |
WPL [Member] |
Fair Value Measurements | FAIR VALUE MEASUREMENTS Fair Value of Financial Instruments - The carrying amounts of current assets and current liabilities approximate fair value because of the short maturity of such financial instruments. Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions):
Alliant Energy | September 30, 2019 |  | December 31, 2018
|  |  | 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 |  | $174.4 |  |  |  | $174.4 |  |  |  | $— |  |  |  | $— |  |  |  | $174.4 |  |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | $— |
Derivatives | 30.3 |  |  | — |  |  | 8.1 |  |  | 22.2 |  |  | 30.3 |  |  | 28.3 |  |  | — |  |  | 8.9 |  |  | 19.4 |  |  | 28.3 |
Deferred proceeds | 237.0 |  |  | — |  |  | — |  |  | 237.0 |  |  | 237.0 |  |  | 119.4 |  |  | — |  |  | — |  |  | 119.4 |  |  | 119.4 |
Liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives | 31.8 |  |  | — |  |  | 31.3 |  |  | 0.5 |  |  | 31.8 |  |  | 23.3 |  |  | — |  |  | 16.1 |  |  | 7.2 |  |  | 23.3 |
Long-term debt (incl. current maturities) | 6,191.9 |  |  | — |  |  | 7,016.4 |  |  | 2.0 |  |  | 7,018.4 |  |  | 5,502.8 |  |  | — |  |  | 5,858.4 |  |  | 2.4 |  |  | 5,860.8 |
IPL | September 30, 2019 |  | December 31, 2018
|  |  | 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 |  | $173.7 |  |  |  | $173.7 |  |  |  | $— |  |  |  | $— |  |  |  | $173.7 |  |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | $— |
Derivatives | 23.3 |  |  | — |  |  | 4.8 |  |  | 18.5 |  |  | 23.3 |  |  | 17.7 |  |  | — |  |  | 4.0 |  |  | 13.7 |  |  | 17.7 |
Deferred proceeds | 237.0 |  |  | — |  |  | — |  |  | 237.0 |  |  | 237.0 |  |  | 119.4 |  |  | — |  |  | — |  |  | 119.4 |  |  | 119.4 |
Liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives | 13.4 |  |  | — |  |  | 12.9 |  |  | 0.5 |  |  | 13.4 |  |  | 11.2 |  |  | — |  |  | 6.5 |  |  | 4.7 |  |  | 11.2 |
Long-term debt (incl. current maturities) | 3,146.8 |  |  | — |  |  | 3,537.0 |  |  | — |  |  | 3,537.0 |  |  | 2,552.3 |  |  | — |  |  | 2,691.2 |  |  | — |  |  | 2,691.2 |
WPL | September 30, 2019 |  | December 31, 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 |  | $7.0 |  |  |  | $— |  |  |  | $3.3 |  |  |  | $3.7 |  |  |  | $7.0 |  |  |  | $10.6 |  |  |  | $— |  |  |  | $4.9 |  |  |  | $5.7 |  |  |  | $10.6 |
Liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives | 18.4 |  |  | — |  |  | 18.4 |  |  | — |  |  | 18.4 |  |  | 12.1 |  |  | — |  |  | 9.6 |  |  | 2.5 |  |  | 12.1 |
Long-term debt (incl. current maturities) | 1,932.3 |  |  | — |  |  | 2,314.1 |  |  | — |  |  | 2,314.1 |  |  | 1,834.9 |  |  | — |  |  | 2,043.7 |  |  | — |  |  | 2,043.7 |
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 | 2019 |  | 2018 |  | 2019 |  | 2018
Beginning balance, July 1 |  | $13.2 |  |  |  | ($10.7 | ) |  |  | $214.6 |  |  |  | $208.3 |
Total net gains included in changes in net assets (realized/unrealized) | 12.7 |  |  | 25.7 |  |  | — |  |  | — |
Transfers out of Level 3 | (1.2 | ) |  | 15.6 |  |  | — |  |  | — |
Sales | — |  |  | (0.2 | ) |  | — |  |  | — |
Settlements (a) | (3.0 | ) |  | (6.2 | ) |  | 22.4 |  |  | 35.4 |
Ending balance, September 30 |  | $21.7 |  |  |  | $24.2 |  |  |  | $237.0 |  |  |  | $243.7 |
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 |  | $12.7 |  |  |  | $26.1 |  |  |  | $— |  |  |  | $— |
Alliant Energy | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
Nine Months Ended September 30 | 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) | 6.9 |  |  | 15.7 |  |  | — |  |  | — |
Transfers out of Level 3 | 2.8 |  |  | 15.6 |  |  | — |  |  | — |
Purchases | 13.8 |  |  | 26.7 |  |  | — |  |  | — |
Sales | (0.2 | ) |  | (0.2 | ) |  | — |  |  | — |
Settlements (a) | (13.8 | ) |  | (21.4 | ) |  | 117.6 |  |  | 21.6 |
Ending balance, September 30 |  | $21.7 |  |  |  | $24.2 |  |  |  | $237.0 |  |  |  | $243.7 |
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 |  | $10.1 |  |  |  | $16.5 |  |  |  | $— |  |  |  | $— |
IPL | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
Three Months Ended September 30 | 2019 |  | 2018 |  | 2019 |  | 2018
Beginning balance, July 1 |  | $9.3 |  |  |  | ($4.1 | ) |  |  | $214.6 |  |  |  | $208.3 |
Total net gains included in changes in net assets (realized/unrealized) | 11.5 |  |  | 16.8 |  |  | — |  |  | — |
Transfers out of Level 3 | (0.6 | ) |  | 10.5 |  |  | — |  |  | — |
Sales | — |  |  | (0.1 | ) |  | — |  |  | — |
Settlements (a) | (2.2 | ) |  | (4.9 | ) |  | 22.4 |  |  | 35.4 |
Ending balance, September 30 |  | $18.0 |  |  |  | $18.2 |  |  |  | $237.0 |  |  |  | $243.7 |
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 |  | $11.5 |  |  |  | $16.8 |  |  |  | $— |  |  |  | $— |
IPL | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
Nine Months Ended September 30 | 2019 |  | 2018 |  | 2019 |  | 2018
Beginning balance, January 1 |  | $9.0 |  |  |  | ($1.4 | ) |  |  | $119.4 |  |  |  | $222.1 |
Total net gains included in changes in net assets (realized/unrealized) | 8.6 |  |  | 7.6 |  |  | — |  |  | — |
Transfers out of Level 3 | 2.0 |  |  | 10.5 |  |  | — |  |  | — |
Purchases | 9.5 |  |  | 19.3 |  |  | — |  |  | — |
Sales | (0.1 | ) |  | (0.1 | ) |  | — |  |  | — |
Settlements (a) | (11.0 | ) |  | (17.7 | ) |  | 117.6 |  |  | 21.6 |
Ending balance, September 30 |  | $18.0 |  |  |  | $18.2 |  |  |  | $237.0 |  |  |  | $243.7 |
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 |  | $10.5 |  |  |  | $7.9 |  |  |  | $— |  |  |  | $— |
WPL | Commodity Contract Derivative
| Assets and (Liabilities), net
Three Months Ended September 30 | 2019 |  | 2018
Beginning balance, July 1 |  | $3.9 |  |  |  | ($6.6 | )
Total net gains included in changes in net assets (realized/unrealized) | 1.2 |  |  | 8.9 |
Transfers out of Level 3 | (0.6 | ) |  | 5.1 |
Sales | — |  |  | (0.1 | )
Settlements | (0.8 | ) |  | (1.3 | )
Ending balance, September 30 |  | $3.7 |  |  |  | $6.0 |
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 |  | $1.2 |  |  |  | $9.3 |
WPL | Commodity Contract Derivative
| Assets and (Liabilities), net
Nine Months Ended September 30 | 2019 |  | 2018
Beginning balance, January 1 |  | $3.2 |  |  |  | ($10.8 | )
Total net gains (losses) included in changes in net assets (realized/unrealized) | (1.7 | ) |  | 8.1 |
Transfers out of Level 3 | 0.8 |  |  | 5.1 |
Purchases | 4.3 |  |  | 7.4 |
Sales | (0.1 | ) |  | (0.1 | )
Settlements | (2.8 | ) |  | (3.7 | )
Ending balance, September 30 |  | $3.7 |  |  |  | $6.0 |
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 |  | ($0.4 | ) |  |  | $8.6 |
(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.
Commodity Contracts - The fair value of FTR 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, 2019 |  | $13.1 |  |  |  | $8.6 |  |  |  | $12.5 |  |  |  | $5.5 |  |  |  | $0.6 |  |  |  | $3.1 |
December 31, 2018 | 3.2 |  |  | 9.0 |  |  | 1.8 |  |  | 7.2 |  |  | 1.4 |  |  | 1.8 |

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- Definition The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258 + Details
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