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Fair Value Measurements (Tables) | 9 Months Ended
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Sep. 30, 2015
Statement [Line Items] |
Carrying Amount and Fair Value Of Financial Instruments | Carrying amounts and the related estimated fair values of other financial instruments were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
September 30, 2015 | Carrying Amount |  | Fair Value |  | Carrying Amount |  | Fair Value |  | Carrying Amount |  | Fair Value
Assets: |  |  |  |  |  |  |  |  |  |  |
Derivative assets (Note 12) |  | $20.3 |  |  |  | $20.3 |  |  |  | $18.5 |  |  |  | $18.5 |  |  |  | $1.8 |  |  |  | $1.8 |
Deferred proceeds (sales of receivables) (Note 4(a)) | 195.5 |  |  | 195.5 |  |  | 195.5 |  |  | 195.5 |  |  | — |  |  | — |
Capitalization and liabilities: |  |  |  |  |  |  |  |  |  |  |
Long-term debt (including current maturities) (Note 7(b)) | 3,858.8 |  |  | 4,394.3 |  |  | 1,868.5 |  |  | 2,115.3 |  |  | 1,543.6 |  |  | 1,825.5 |
Cumulative preferred stock | 200.0 |  |  | 201.3 |  |  | 200.0 |  |  | 201.3 |  |  | — |  |  | — |
Derivative liabilities (Note 12) | 59.1 |  |  | 59.1 |  |  | 22.0 |  |  | 22.0 |  |  | 37.1 |  |  | 37.1 |
| Alliant Energy |  | IPL |  | WPL
December 31, 2014 | Carrying Amount |  | Fair Value |  | Carrying Amount |  | Fair Value |  | Carrying Amount |  | Fair Value
Assets: |  |  |  |  |  |  |  |  |  |  |
Derivative assets (Note 12) |  | $38.6 |  |  |  | $38.6 |  |  |  | $28.0 |  |  |  | $28.0 |  |  |  | $10.6 |  |  |  | $10.6 |
Deferred proceeds (sales of receivables) (Note 4(a)) | 177.2 |  |  | 177.2 |  |  | 177.2 |  |  | 177.2 |  |  | — |  |  | — |
Capitalization and liabilities: |  |  |  |  |  |  |  |  |  |  |
Long-term debt (including current maturities) (Note 7(b)) | 3,789.7 |  |  | 4,418.2 |  |  | 1,768.7 |  |  | 2,053.0 |  |  | 1,573.9 |  |  | 1,908.9 |
Cumulative preferred stock | 200.0 |  |  | 200.2 |  |  | 200.0 |  |  | 200.2 |  |  | — |  |  | — |
Derivative liabilities (Note 12) | 37.6 |  |  | 37.6 |  |  | 19.5 |  |  | 19.5 |  |  | 18.1 |  |  | 18.1 |
Fair Value Measurements | Items subject to fair value measurement disclosure requirements were as follows (in millions):
Alliant Energy | September 30, 2015 |  | December 31, 2014
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
| Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives - commodity contracts |  | $20.3 |  |  |  | $— |  |  |  | $2.6 |  |  |  | $17.7 |  |  |  | $38.6 |  |  |  | $— |  |  |  | $2.6 |  |  |  | $36.0 |
Deferred proceeds | 195.5 |  |  | — |  |  | — |  |  | 195.5 |  |  | 177.2 |  |  | — |  |  | — |  |  | 177.2 |
Capitalization and liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt (including current maturities) | 4,394.3 |  |  | — |  |  | 4,390.6 |  |  | 3.7 |  |  | 4,418.2 |  |  | — |  |  | 4,414.9 |  |  | 3.3 |
Cumulative preferred stock | 201.3 |  |  | 201.3 |  |  | — |  |  | — |  |  | 200.2 |  |  | 200.2 |  |  | — |  |  | — |
Derivatives - commodity contracts | 59.1 |  |  | — |  |  | 16.8 |  |  | 42.3 |  |  | 37.6 |  |  | — |  |  | 19.5 |  |  | 18.1 |
IPL | September 30, 2015 |  | December 31, 2014
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
| Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives - commodity contracts |  | $18.5 |  |  |  | $— |  |  |  | $2.1 |  |  |  | $16.4 |  |  |  | $28.0 |  |  |  | $— |  |  |  | $2.4 |  |  |  | $25.6 |
Deferred proceeds | 195.5 |  |  | — |  |  | — |  |  | 195.5 |  |  | 177.2 |  |  | — |  |  | — |  |  | 177.2 |
Capitalization and liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt (including current maturities) | 2,115.3 |  |  | — |  |  | 2,115.3 |  |  | — |  |  | 2,053.0 |  |  | — |  |  | 2,053.0 |  |  | — |
Cumulative preferred stock | 201.3 |  |  | 201.3 |  |  | — |  |  | — |  |  | 200.2 |  |  | 200.2 |  |  | — |  |  | — |
Derivatives - commodity contracts | 22.0 |  |  | — |  |  | 9.4 |  |  | 12.6 |  |  | 19.5 |  |  | — |  |  | 13.3 |  |  | 6.2 |
WPL | September 30, 2015 |  | December 31, 2014
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
| Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives - commodity contracts |  | $1.8 |  |  |  | $— |  |  |  | $0.5 |  |  |  | $1.3 |  |  |  | $10.6 |  |  |  | $— |  |  |  | $0.2 |  |  |  | $10.4 |
Capitalization and liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt (including current maturities) | 1,825.5 |  |  | — |  |  | 1,825.5 |  |  | — |  |  | 1,908.9 |  |  | — |  |  | 1,908.9 |  |  | — |
Derivatives - commodity contracts | 37.1 |  |  | — |  |  | 7.4 |  |  | 29.7 |  |  | 18.1 |  |  | — |  |  | 6.2 |  |  | 11.9 |
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 September 30 | 2015 |  | 2014 |  | 2015 |  | 2014
Beginning balance, July 1 |  | $0.6 |  |  |  | $101.2 |  |  |  | $73.4 |  |  |  | $193.7 |
Total net losses (realized/unrealized) included in changes in net assets | (21.1 | ) |  | (12.7 | ) |  | — |  |  | — |
Sales | (0.4 | ) |  | (1.2 | ) |  | — |  |  | — |
Settlements (a) | (3.7 | ) |  | (19.0 | ) |  | 122.1 |  |  | (33.4 | )
Ending balance, September 30 |  | ($24.6 | ) |  |  | $68.3 |  |  |  | $195.5 |  |  |  | $160.3 |
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 |  | ($18.4 | ) |  |  | ($10.3 | ) |  |  | $— |  |  |  | $— |
Alliant Energy | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
Nine Months Ended September 30 | 2015 |  | 2014 |  | 2015 |  | 2014
Beginning balance, January 1 |  | $17.9 |  |  |  | $4.4 |  |  |  | $177.2 |  |  |  | $203.5 |
Total net gains (losses) (realized/unrealized) included in changes in net assets | (58.2 | ) |  | 43.0 |  |  | — |  |  | — |
Transfers out of Level 3 | 0.6 |  |  | — |  |  | — |  |  | — |
Purchases | 36.9 |  |  | 76.7 |  |  | — |  |  | — |
Sales | (1.7 | ) |  | (1.2 | ) |  | — |  |  | — |
Settlements (a) | (20.1 | ) |  | (54.6 | ) |  | 18.3 |  |  | (43.2 | )
Ending balance, September 30 |  | ($24.6 | ) |  |  | $68.3 |  |  |  | $195.5 |  |  |  | $160.3 |
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 |  | ($52.2 | ) |  |  | $34.6 |  |  |  | $— |  |  |  | $— |
IPL | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
Three Months Ended September 30 | 2015 |  | 2014 |  | 2015 |  | 2014
Beginning balance, July 1 |  | $18.3 |  |  |  | $64.2 |  |  |  | $73.4 |  |  |  | $193.7 |
Total net losses (realized/unrealized) included in changes in net assets | (8.6 | ) |  | (10.1 | ) |  | — |  |  | — |
Sales | (0.4 | ) |  | (1.0 | ) |  | — |  |  | — |
Settlements (a) | (5.5 | ) |  | (16.6 | ) |  | 122.1 |  |  | (33.4 | )
Ending balance, September 30 |  | $3.8 |  |  |  | $36.5 |  |  |  | $195.5 |  |  |  | $160.3 |
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 |  | ($8.0 | ) |  |  | ($9.6 | ) |  |  | $— |  |  |  | $— |
IPL | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
Nine Months Ended September 30 | 2015 |  | 2014 |  | 2015 |  | 2014
Beginning balance, January 1 |  | $19.4 |  |  |  | $14.6 |  |  |  | $177.2 |  |  |  | $203.5 |
Total net losses (realized/unrealized) included in changes in net assets | (26.0 | ) |  | (5.1 | ) |  | — |  |  | — |
Purchases | 33.1 |  |  | 68.8 |  |  | — |  |  | — |
Sales | (1.6 | ) |  | (1.0 | ) |  | — |  |  | — |
Settlements (a) | (21.1 | ) |  | (40.8 | ) |  | 18.3 |  |  | (43.2 | )
Ending balance, September 30 |  | $3.8 |  |  |  | $36.5 |  |  |  | $195.5 |  |  |  | $160.3 |
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 |  | ($21.2 | ) |  |  | ($6.0 | ) |  |  | $— |  |  |  | $— |
WPL | Commodity Contract Derivative
| Assets and (Liabilities), net
Three Months Ended September 30 | 2015 |  | 2014
Beginning balance, July 1 |  | ($17.7 | ) |  |  | $37.0 |
Total net losses (realized/unrealized) included in changes in net assets | (12.5 | ) |  | (2.6 | )
Sales | — |  |  | (0.2 | )
Settlements | 1.8 |  |  | (2.4 | )
Ending balance, September 30 |  | ($28.4 | ) |  |  | $31.8 |
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 |  | ($10.4 | ) |  |  | ($0.7 | )
WPL | Commodity Contract Derivative
| Assets and (Liabilities), net
Nine Months Ended September 30 | 2015 |  | 2014
Beginning balance, January 1 |  | ($1.5 | ) |  |  | ($10.2 | )
Total net gains (losses) (realized/unrealized) included in changes in net assets | (32.2 | ) |  | 48.1 |
Transfers out of Level 3 | 0.6 |  |  | — |
Purchases | 3.8 |  |  | 7.9 |
Sales | (0.1 | ) |  | (0.2 | )
Settlements | 1.0 |  |  | (13.8 | )
Ending balance, September 30 |  | ($28.4 | ) |  |  | $31.8 |
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 |  | ($31.0 | ) |  |  | $40.6 |
(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 proceeds received from the receivables sold.
Fair Value Of Net Derivative Assets (Liabilities) | The fair value of electric, natural gas and coal 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
September 30, 2015 |  | ($39.4 | ) |  |  | $14.8 |  |  |  | ($10.9 | ) |  |  | $14.7 |  |  |  | ($28.5 | ) |  |  | $0.1 |
December 31, 2014 | (7.0 | ) |  | 24.9 |  |  | (3.2 | ) |  | 22.6 |  |  | (3.8 | ) |  | 2.3 |
IPL [Member] |
Statement [Line Items] |
Carrying Amount and Fair Value Of Financial Instruments | Carrying amounts and the related estimated fair values of other financial instruments were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
September 30, 2015 | Carrying Amount |  | Fair Value |  | Carrying Amount |  | Fair Value |  | Carrying Amount |  | Fair Value
Assets: |  |  |  |  |  |  |  |  |  |  |
Derivative assets (Note 12) |  | $20.3 |  |  |  | $20.3 |  |  |  | $18.5 |  |  |  | $18.5 |  |  |  | $1.8 |  |  |  | $1.8 |
Deferred proceeds (sales of receivables) (Note 4(a)) | 195.5 |  |  | 195.5 |  |  | 195.5 |  |  | 195.5 |  |  | — |  |  | — |
Capitalization and liabilities: |  |  |  |  |  |  |  |  |  |  |
Long-term debt (including current maturities) (Note 7(b)) | 3,858.8 |  |  | 4,394.3 |  |  | 1,868.5 |  |  | 2,115.3 |  |  | 1,543.6 |  |  | 1,825.5 |
Cumulative preferred stock | 200.0 |  |  | 201.3 |  |  | 200.0 |  |  | 201.3 |  |  | — |  |  | — |
Derivative liabilities (Note 12) | 59.1 |  |  | 59.1 |  |  | 22.0 |  |  | 22.0 |  |  | 37.1 |  |  | 37.1 |
| Alliant Energy |  | IPL |  | WPL
December 31, 2014 | Carrying Amount |  | Fair Value |  | Carrying Amount |  | Fair Value |  | Carrying Amount |  | Fair Value
Assets: |  |  |  |  |  |  |  |  |  |  |
Derivative assets (Note 12) |  | $38.6 |  |  |  | $38.6 |  |  |  | $28.0 |  |  |  | $28.0 |  |  |  | $10.6 |  |  |  | $10.6 |
Deferred proceeds (sales of receivables) (Note 4(a)) | 177.2 |  |  | 177.2 |  |  | 177.2 |  |  | 177.2 |  |  | — |  |  | — |
Capitalization and liabilities: |  |  |  |  |  |  |  |  |  |  |
Long-term debt (including current maturities) (Note 7(b)) | 3,789.7 |  |  | 4,418.2 |  |  | 1,768.7 |  |  | 2,053.0 |  |  | 1,573.9 |  |  | 1,908.9 |
Cumulative preferred stock | 200.0 |  |  | 200.2 |  |  | 200.0 |  |  | 200.2 |  |  | — |  |  | — |
Derivative liabilities (Note 12) | 37.6 |  |  | 37.6 |  |  | 19.5 |  |  | 19.5 |  |  | 18.1 |  |  | 18.1 |
Fair Value Measurements | Items subject to fair value measurement disclosure requirements were as follows (in millions):
Alliant Energy | September 30, 2015 |  | December 31, 2014
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
| Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives - commodity contracts |  | $20.3 |  |  |  | $— |  |  |  | $2.6 |  |  |  | $17.7 |  |  |  | $38.6 |  |  |  | $— |  |  |  | $2.6 |  |  |  | $36.0 |
Deferred proceeds | 195.5 |  |  | — |  |  | — |  |  | 195.5 |  |  | 177.2 |  |  | — |  |  | — |  |  | 177.2 |
Capitalization and liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt (including current maturities) | 4,394.3 |  |  | — |  |  | 4,390.6 |  |  | 3.7 |  |  | 4,418.2 |  |  | — |  |  | 4,414.9 |  |  | 3.3 |
Cumulative preferred stock | 201.3 |  |  | 201.3 |  |  | — |  |  | — |  |  | 200.2 |  |  | 200.2 |  |  | — |  |  | — |
Derivatives - commodity contracts | 59.1 |  |  | — |  |  | 16.8 |  |  | 42.3 |  |  | 37.6 |  |  | — |  |  | 19.5 |  |  | 18.1 |
IPL | September 30, 2015 |  | December 31, 2014
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
| Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives - commodity contracts |  | $18.5 |  |  |  | $— |  |  |  | $2.1 |  |  |  | $16.4 |  |  |  | $28.0 |  |  |  | $— |  |  |  | $2.4 |  |  |  | $25.6 |
Deferred proceeds | 195.5 |  |  | — |  |  | — |  |  | 195.5 |  |  | 177.2 |  |  | — |  |  | — |  |  | 177.2 |
Capitalization and liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt (including current maturities) | 2,115.3 |  |  | — |  |  | 2,115.3 |  |  | — |  |  | 2,053.0 |  |  | — |  |  | 2,053.0 |  |  | — |
Cumulative preferred stock | 201.3 |  |  | 201.3 |  |  | — |  |  | — |  |  | 200.2 |  |  | 200.2 |  |  | — |  |  | — |
Derivatives - commodity contracts | 22.0 |  |  | — |  |  | 9.4 |  |  | 12.6 |  |  | 19.5 |  |  | — |  |  | 13.3 |  |  | 6.2 |
WPL | September 30, 2015 |  | December 31, 2014
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
| Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives - commodity contracts |  | $1.8 |  |  |  | $— |  |  |  | $0.5 |  |  |  | $1.3 |  |  |  | $10.6 |  |  |  | $— |  |  |  | $0.2 |  |  |  | $10.4 |
Capitalization and liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt (including current maturities) | 1,825.5 |  |  | — |  |  | 1,825.5 |  |  | — |  |  | 1,908.9 |  |  | — |  |  | 1,908.9 |  |  | — |
Derivatives - commodity contracts | 37.1 |  |  | — |  |  | 7.4 |  |  | 29.7 |  |  | 18.1 |  |  | — |  |  | 6.2 |  |  | 11.9 |
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 September 30 | 2015 |  | 2014 |  | 2015 |  | 2014
Beginning balance, July 1 |  | $0.6 |  |  |  | $101.2 |  |  |  | $73.4 |  |  |  | $193.7 |
Total net losses (realized/unrealized) included in changes in net assets | (21.1 | ) |  | (12.7 | ) |  | — |  |  | — |
Sales | (0.4 | ) |  | (1.2 | ) |  | — |  |  | — |
Settlements (a) | (3.7 | ) |  | (19.0 | ) |  | 122.1 |  |  | (33.4 | )
Ending balance, September 30 |  | ($24.6 | ) |  |  | $68.3 |  |  |  | $195.5 |  |  |  | $160.3 |
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 |  | ($18.4 | ) |  |  | ($10.3 | ) |  |  | $— |  |  |  | $— |
Alliant Energy | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
Nine Months Ended September 30 | 2015 |  | 2014 |  | 2015 |  | 2014
Beginning balance, January 1 |  | $17.9 |  |  |  | $4.4 |  |  |  | $177.2 |  |  |  | $203.5 |
Total net gains (losses) (realized/unrealized) included in changes in net assets | (58.2 | ) |  | 43.0 |  |  | — |  |  | — |
Transfers out of Level 3 | 0.6 |  |  | — |  |  | — |  |  | — |
Purchases | 36.9 |  |  | 76.7 |  |  | — |  |  | — |
Sales | (1.7 | ) |  | (1.2 | ) |  | — |  |  | — |
Settlements (a) | (20.1 | ) |  | (54.6 | ) |  | 18.3 |  |  | (43.2 | )
Ending balance, September 30 |  | ($24.6 | ) |  |  | $68.3 |  |  |  | $195.5 |  |  |  | $160.3 |
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 |  | ($52.2 | ) |  |  | $34.6 |  |  |  | $— |  |  |  | $— |
IPL | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
Three Months Ended September 30 | 2015 |  | 2014 |  | 2015 |  | 2014
Beginning balance, July 1 |  | $18.3 |  |  |  | $64.2 |  |  |  | $73.4 |  |  |  | $193.7 |
Total net losses (realized/unrealized) included in changes in net assets | (8.6 | ) |  | (10.1 | ) |  | — |  |  | — |
Sales | (0.4 | ) |  | (1.0 | ) |  | — |  |  | — |
Settlements (a) | (5.5 | ) |  | (16.6 | ) |  | 122.1 |  |  | (33.4 | )
Ending balance, September 30 |  | $3.8 |  |  |  | $36.5 |  |  |  | $195.5 |  |  |  | $160.3 |
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 |  | ($8.0 | ) |  |  | ($9.6 | ) |  |  | $— |  |  |  | $— |
IPL | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
Nine Months Ended September 30 | 2015 |  | 2014 |  | 2015 |  | 2014
Beginning balance, January 1 |  | $19.4 |  |  |  | $14.6 |  |  |  | $177.2 |  |  |  | $203.5 |
Total net losses (realized/unrealized) included in changes in net assets | (26.0 | ) |  | (5.1 | ) |  | — |  |  | — |
Purchases | 33.1 |  |  | 68.8 |  |  | — |  |  | — |
Sales | (1.6 | ) |  | (1.0 | ) |  | — |  |  | — |
Settlements (a) | (21.1 | ) |  | (40.8 | ) |  | 18.3 |  |  | (43.2 | )
Ending balance, September 30 |  | $3.8 |  |  |  | $36.5 |  |  |  | $195.5 |  |  |  | $160.3 |
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 |  | ($21.2 | ) |  |  | ($6.0 | ) |  |  | $— |  |  |  | $— |
WPL | Commodity Contract Derivative
| Assets and (Liabilities), net
Three Months Ended September 30 | 2015 |  | 2014
Beginning balance, July 1 |  | ($17.7 | ) |  |  | $37.0 |
Total net losses (realized/unrealized) included in changes in net assets | (12.5 | ) |  | (2.6 | )
Sales | — |  |  | (0.2 | )
Settlements | 1.8 |  |  | (2.4 | )
Ending balance, September 30 |  | ($28.4 | ) |  |  | $31.8 |
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 |  | ($10.4 | ) |  |  | ($0.7 | )
WPL | Commodity Contract Derivative
| Assets and (Liabilities), net
Nine Months Ended September 30 | 2015 |  | 2014
Beginning balance, January 1 |  | ($1.5 | ) |  |  | ($10.2 | )
Total net gains (losses) (realized/unrealized) included in changes in net assets | (32.2 | ) |  | 48.1 |
Transfers out of Level 3 | 0.6 |  |  | — |
Purchases | 3.8 |  |  | 7.9 |
Sales | (0.1 | ) |  | (0.2 | )
Settlements | 1.0 |  |  | (13.8 | )
Ending balance, September 30 |  | ($28.4 | ) |  |  | $31.8 |
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 |  | ($31.0 | ) |  |  | $40.6 |
(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 proceeds received from the receivables sold.
Fair Value Of Net Derivative Assets (Liabilities) | The fair value of electric, natural gas and coal 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
September 30, 2015 |  | ($39.4 | ) |  |  | $14.8 |  |  |  | ($10.9 | ) |  |  | $14.7 |  |  |  | ($28.5 | ) |  |  | $0.1 |
December 31, 2014 | (7.0 | ) |  | 24.9 |  |  | (3.2 | ) |  | 22.6 |  |  | (3.8 | ) |  | 2.3 |
WPL [Member] |
Statement [Line Items] |
Carrying Amount and Fair Value Of Financial Instruments | Carrying amounts and the related estimated fair values of other financial instruments were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
September 30, 2015 | Carrying Amount |  | Fair Value |  | Carrying Amount |  | Fair Value |  | Carrying Amount |  | Fair Value
Assets: |  |  |  |  |  |  |  |  |  |  |
Derivative assets (Note 12) |  | $20.3 |  |  |  | $20.3 |  |  |  | $18.5 |  |  |  | $18.5 |  |  |  | $1.8 |  |  |  | $1.8 |
Deferred proceeds (sales of receivables) (Note 4(a)) | 195.5 |  |  | 195.5 |  |  | 195.5 |  |  | 195.5 |  |  | — |  |  | — |
Capitalization and liabilities: |  |  |  |  |  |  |  |  |  |  |
Long-term debt (including current maturities) (Note 7(b)) | 3,858.8 |  |  | 4,394.3 |  |  | 1,868.5 |  |  | 2,115.3 |  |  | 1,543.6 |  |  | 1,825.5 |
Cumulative preferred stock | 200.0 |  |  | 201.3 |  |  | 200.0 |  |  | 201.3 |  |  | — |  |  | — |
Derivative liabilities (Note 12) | 59.1 |  |  | 59.1 |  |  | 22.0 |  |  | 22.0 |  |  | 37.1 |  |  | 37.1 |
| Alliant Energy |  | IPL |  | WPL
December 31, 2014 | Carrying Amount |  | Fair Value |  | Carrying Amount |  | Fair Value |  | Carrying Amount |  | Fair Value
Assets: |  |  |  |  |  |  |  |  |  |  |
Derivative assets (Note 12) |  | $38.6 |  |  |  | $38.6 |  |  |  | $28.0 |  |  |  | $28.0 |  |  |  | $10.6 |  |  |  | $10.6 |
Deferred proceeds (sales of receivables) (Note 4(a)) | 177.2 |  |  | 177.2 |  |  | 177.2 |  |  | 177.2 |  |  | — |  |  | — |
Capitalization and liabilities: |  |  |  |  |  |  |  |  |  |  |
Long-term debt (including current maturities) (Note 7(b)) | 3,789.7 |  |  | 4,418.2 |  |  | 1,768.7 |  |  | 2,053.0 |  |  | 1,573.9 |  |  | 1,908.9 |
Cumulative preferred stock | 200.0 |  |  | 200.2 |  |  | 200.0 |  |  | 200.2 |  |  | — |  |  | — |
Derivative liabilities (Note 12) | 37.6 |  |  | 37.6 |  |  | 19.5 |  |  | 19.5 |  |  | 18.1 |  |  | 18.1 |
Fair Value Measurements | Items subject to fair value measurement disclosure requirements were as follows (in millions):
Alliant Energy | September 30, 2015 |  | December 31, 2014
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
| Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives - commodity contracts |  | $20.3 |  |  |  | $— |  |  |  | $2.6 |  |  |  | $17.7 |  |  |  | $38.6 |  |  |  | $— |  |  |  | $2.6 |  |  |  | $36.0 |
Deferred proceeds | 195.5 |  |  | — |  |  | — |  |  | 195.5 |  |  | 177.2 |  |  | — |  |  | — |  |  | 177.2 |
Capitalization and liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt (including current maturities) | 4,394.3 |  |  | — |  |  | 4,390.6 |  |  | 3.7 |  |  | 4,418.2 |  |  | — |  |  | 4,414.9 |  |  | 3.3 |
Cumulative preferred stock | 201.3 |  |  | 201.3 |  |  | — |  |  | — |  |  | 200.2 |  |  | 200.2 |  |  | — |  |  | — |
Derivatives - commodity contracts | 59.1 |  |  | — |  |  | 16.8 |  |  | 42.3 |  |  | 37.6 |  |  | — |  |  | 19.5 |  |  | 18.1 |
IPL | September 30, 2015 |  | December 31, 2014
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
| Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives - commodity contracts |  | $18.5 |  |  |  | $— |  |  |  | $2.1 |  |  |  | $16.4 |  |  |  | $28.0 |  |  |  | $— |  |  |  | $2.4 |  |  |  | $25.6 |
Deferred proceeds | 195.5 |  |  | — |  |  | — |  |  | 195.5 |  |  | 177.2 |  |  | — |  |  | — |  |  | 177.2 |
Capitalization and liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt (including current maturities) | 2,115.3 |  |  | — |  |  | 2,115.3 |  |  | — |  |  | 2,053.0 |  |  | — |  |  | 2,053.0 |  |  | — |
Cumulative preferred stock | 201.3 |  |  | 201.3 |  |  | — |  |  | — |  |  | 200.2 |  |  | 200.2 |  |  | — |  |  | — |
Derivatives - commodity contracts | 22.0 |  |  | — |  |  | 9.4 |  |  | 12.6 |  |  | 19.5 |  |  | — |  |  | 13.3 |  |  | 6.2 |
WPL | September 30, 2015 |  | December 31, 2014
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
| Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives - commodity contracts |  | $1.8 |  |  |  | $— |  |  |  | $0.5 |  |  |  | $1.3 |  |  |  | $10.6 |  |  |  | $— |  |  |  | $0.2 |  |  |  | $10.4 |
Capitalization and liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt (including current maturities) | 1,825.5 |  |  | — |  |  | 1,825.5 |  |  | — |  |  | 1,908.9 |  |  | — |  |  | 1,908.9 |  |  | — |
Derivatives - commodity contracts | 37.1 |  |  | — |  |  | 7.4 |  |  | 29.7 |  |  | 18.1 |  |  | — |  |  | 6.2 |  |  | 11.9 |
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 September 30 | 2015 |  | 2014 |  | 2015 |  | 2014
Beginning balance, July 1 |  | $0.6 |  |  |  | $101.2 |  |  |  | $73.4 |  |  |  | $193.7 |
Total net losses (realized/unrealized) included in changes in net assets | (21.1 | ) |  | (12.7 | ) |  | — |  |  | — |
Sales | (0.4 | ) |  | (1.2 | ) |  | — |  |  | — |
Settlements (a) | (3.7 | ) |  | (19.0 | ) |  | 122.1 |  |  | (33.4 | )
Ending balance, September 30 |  | ($24.6 | ) |  |  | $68.3 |  |  |  | $195.5 |  |  |  | $160.3 |
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 |  | ($18.4 | ) |  |  | ($10.3 | ) |  |  | $— |  |  |  | $— |
Alliant Energy | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
Nine Months Ended September 30 | 2015 |  | 2014 |  | 2015 |  | 2014
Beginning balance, January 1 |  | $17.9 |  |  |  | $4.4 |  |  |  | $177.2 |  |  |  | $203.5 |
Total net gains (losses) (realized/unrealized) included in changes in net assets | (58.2 | ) |  | 43.0 |  |  | — |  |  | — |
Transfers out of Level 3 | 0.6 |  |  | — |  |  | — |  |  | — |
Purchases | 36.9 |  |  | 76.7 |  |  | — |  |  | — |
Sales | (1.7 | ) |  | (1.2 | ) |  | — |  |  | — |
Settlements (a) | (20.1 | ) |  | (54.6 | ) |  | 18.3 |  |  | (43.2 | )
Ending balance, September 30 |  | ($24.6 | ) |  |  | $68.3 |  |  |  | $195.5 |  |  |  | $160.3 |
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 |  | ($52.2 | ) |  |  | $34.6 |  |  |  | $— |  |  |  | $— |
IPL | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
Three Months Ended September 30 | 2015 |  | 2014 |  | 2015 |  | 2014
Beginning balance, July 1 |  | $18.3 |  |  |  | $64.2 |  |  |  | $73.4 |  |  |  | $193.7 |
Total net losses (realized/unrealized) included in changes in net assets | (8.6 | ) |  | (10.1 | ) |  | — |  |  | — |
Sales | (0.4 | ) |  | (1.0 | ) |  | — |  |  | — |
Settlements (a) | (5.5 | ) |  | (16.6 | ) |  | 122.1 |  |  | (33.4 | )
Ending balance, September 30 |  | $3.8 |  |  |  | $36.5 |  |  |  | $195.5 |  |  |  | $160.3 |
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 |  | ($8.0 | ) |  |  | ($9.6 | ) |  |  | $— |  |  |  | $— |
IPL | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
Nine Months Ended September 30 | 2015 |  | 2014 |  | 2015 |  | 2014
Beginning balance, January 1 |  | $19.4 |  |  |  | $14.6 |  |  |  | $177.2 |  |  |  | $203.5 |
Total net losses (realized/unrealized) included in changes in net assets | (26.0 | ) |  | (5.1 | ) |  | — |  |  | — |
Purchases | 33.1 |  |  | 68.8 |  |  | — |  |  | — |
Sales | (1.6 | ) |  | (1.0 | ) |  | — |  |  | — |
Settlements (a) | (21.1 | ) |  | (40.8 | ) |  | 18.3 |  |  | (43.2 | )
Ending balance, September 30 |  | $3.8 |  |  |  | $36.5 |  |  |  | $195.5 |  |  |  | $160.3 |
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 |  | ($21.2 | ) |  |  | ($6.0 | ) |  |  | $— |  |  |  | $— |
WPL | Commodity Contract Derivative
| Assets and (Liabilities), net
Three Months Ended September 30 | 2015 |  | 2014
Beginning balance, July 1 |  | ($17.7 | ) |  |  | $37.0 |
Total net losses (realized/unrealized) included in changes in net assets | (12.5 | ) |  | (2.6 | )
Sales | — |  |  | (0.2 | )
Settlements | 1.8 |  |  | (2.4 | )
Ending balance, September 30 |  | ($28.4 | ) |  |  | $31.8 |
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 |  | ($10.4 | ) |  |  | ($0.7 | )
WPL | Commodity Contract Derivative
| Assets and (Liabilities), net
Nine Months Ended September 30 | 2015 |  | 2014
Beginning balance, January 1 |  | ($1.5 | ) |  |  | ($10.2 | )
Total net gains (losses) (realized/unrealized) included in changes in net assets | (32.2 | ) |  | 48.1 |
Transfers out of Level 3 | 0.6 |  |  | — |
Purchases | 3.8 |  |  | 7.9 |
Sales | (0.1 | ) |  | (0.2 | )
Settlements | 1.0 |  |  | (13.8 | )
Ending balance, September 30 |  | ($28.4 | ) |  |  | $31.8 |
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 |  | ($31.0 | ) |  |  | $40.6 |
(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 proceeds received from the receivables sold.
Fair Value Of Net Derivative Assets (Liabilities) | The fair value of electric, natural gas and coal 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
September 30, 2015 |  | ($39.4 | ) |  |  | $14.8 |  |  |  | ($10.9 | ) |  |  | $14.7 |  |  |  | ($28.5 | ) |  |  | $0.1 |
December 31, 2014 | (7.0 | ) |  | 24.9 |  |  | (3.2 | ) |  | 22.6 |  |  | (3.8 | ) |  | 2.3 |

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