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Fair Value Measurements (Tables) | 3 Months Ended
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Mar. 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [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
| Carrying Amount |  | Fair Value |  | Carrying Amount |  | Fair Value |  | Carrying Amount |  | Fair Value
March 31, 2013 |  |  |  |  |  |  |  |  |  |  |
Assets: |  |  |  |  |  |  |  |  |  |  |
Derivative assets (Note 11) |  | $23.6 |  |  |  | $23.6 |  |  |  | $12.5 |  |  |  | $12.5 |  |  |  | $11.1 |  |  |  | $11.1 |
Deferred proceeds (sales of receivables) (Note 3(a)) | 122.1 |  |  | 122.1 |  |  | 122.1 |  |  | 122.1 |  |  | — |  |  | — |
Capitalization and liabilities: |  |  |  |  |  |  |  |  |  |  |
Long-term debt (including current maturities) (Note 8(b)) | 3,123.4 |  |  | 3,806.5 |  |  | 1,344.5 |  |  | 1,643.8 |  |  | 1,331.7 |  |  | 1,691.6 |
Cumulative preferred stock (Note 7) | 200.0 |  |  | 201.8 |  |  | 200.0 |  |  | 201.8 |  |  | — |  |  | — |
Derivative liabilities (Note 11) | 17.1 |  |  | 17.1 |  |  | 6.1 |  |  | 6.1 |  |  | 11.0 |  |  | 11.0 |
| Alliant Energy |  | IPL |  | WPL
| Carrying Amount |  | Fair Value |  | Carrying Amount |  | Fair Value |  | Carrying Amount |  | Fair Value
December 31, 2012 |  |  |  |  |  |  |  |  |  |  |
Assets: |  |  |  |  |  |  |  |  |  |  |
Derivative assets (Note 11) |  | $26.2 |  |  |  | $26.2 |  |  |  | $17.5 |  |  |  | $17.5 |  |  |  | $8.7 |  |  |  | $8.7 |
Deferred proceeds (sales of receivables) (Note 3(a)) | 66.8 |  |  | 66.8 |  |  | 66.8 |  |  | 66.8 |  |  | — |  |  | — |
Capitalization and liabilities: |  |  |  |  |  |  |  |  |  |  |
Long-term debt (including current maturities) (Note 8(b)) | 3,138.1 |  |  | 3,860.5 |  |  | 1,359.5 |  |  | 1,679.9 |  |  | 1,331.5 |  |  | 1,713.3 |
Cumulative preferred stock (Note 7) | 205.1 |  |  | 212.6 |  |  | 145.1 |  |  | 151.8 |  |  | 60.0 |  |  | 60.8 |
Derivative liabilities (Note 11) | 40.4 |  |  | 40.4 |  |  | 16.1 |  |  | 16.1 |  |  | 24.3 |  |  | 24.3 |
Recurring Fair Value Measurements | Items subject to fair value measurement disclosure requirements were as follows (in millions):
Alliant Energy | March 31, 2013 |  | December 31, 2012
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
| Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives - commodity contracts |  | $23.6 |  |  |  | $— |  |  |  | $14.4 |  |  |  | $9.2 |  |  |  | $26.2 |  |  |  | $— |  |  |  | $4.8 |  |  |  | $21.4 |
Deferred proceeds | 122.1 |  |  | — |  |  | — |  |  | 122.1 |  |  | 66.8 |  |  | — |  |  | — |  |  | 66.8 |
Capitalization and liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt (including current maturities) | 3,806.5 |  |  | — |  |  | 3,806.0 |  |  | 0.5 |  |  | 3,860.5 |  |  | — |  |  | 3,860.0 |  |  | 0.5 |
Cumulative preferred stock | 201.8 |  |  | 201.8 |  |  | — |  |  | — |  |  | 212.6 |  |  | 162.3 |  |  | 50.3 |  |  | — |
Derivatives - commodity contracts | 17.1 |  |  | — |  |  | 12.8 |  |  | 4.3 |  |  | 40.4 |  |  | — |  |  | 30.9 |  |  | 9.5 |
IPL | March 31, 2013 |  | December 31, 2012
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
| Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives - commodity contracts |  | $12.5 |  |  |  | $— |  |  |  | $6.5 |  |  |  | $6.0 |  |  |  | $17.5 |  |  |  | $— |  |  |  | $3.1 |  |  |  | $14.4 |
Deferred proceeds | 122.1 |  |  | — |  |  | — |  |  | 122.1 |  |  | 66.8 |  |  | — |  |  | — |  |  | 66.8 |
Capitalization and liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt | 1,643.8 |  |  | — |  |  | 1,643.8 |  |  | — |  |  | 1,679.9 |  |  | — |  |  | 1,679.9 |  |  | — |
Cumulative preferred stock | 201.8 |  |  | 201.8 |  |  | — |  |  | — |  |  | 151.8 |  |  | 151.8 |  |  | — |  |  | — |
Derivatives - commodity contracts | 6.1 |  |  | — |  |  | 4.4 |  |  | 1.7 |  |  | 16.1 |  |  | — |  |  | 14.2 |  |  | 1.9 |
WPL | March 31, 2013 |  | December 31, 2012
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
| Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives - commodity contracts |  | $11.1 |  |  |  | $— |  |  |  | $7.9 |  |  |  | $3.2 |  |  |  | $8.7 |  |  |  | $— |  |  |  | $1.7 |  |  |  | $7.0 |
Capitalization and liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt | 1,691.6 |  |  | — |  |  | 1,691.6 |  |  | — |  |  | 1,713.3 |  |  | — |  |  | 1,713.3 |  |  | — |
Cumulative preferred stock | — |  |  | — |  |  | — |  |  | — |  |  | 60.8 |  |  | 10.5 |  |  | 50.3 |  |  | — |
Derivatives - commodity contracts | 11.0 |  |  | — |  |  | 8.4 |  |  | 2.6 |  |  | 24.3 |  |  | — |  |  | 16.7 |  |  | 7.6 |
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 | 2013 |  | 2012 |  | 2013 |  | 2012
Beginning balance, January 1 |  | $11.9 |  |  |  | ($0.9 | ) |  |  | $66.8 |  |  |  | $53.7 |
Total net losses (realized/unrealized) included in changes in net assets (a) | (2.4 | ) |  | (12.5 | ) |  | — |  |  | — |
Transfers into Level 3 (b) | — |  |  | (3.8 | ) |  | — |  |  | — |
Transfers out of Level 3 (c) | 3.6 |  |  | 5.3 |  |  | — |  |  | — |
Settlements (d) | (8.2 | ) |  | (3.2 | ) |  | 55.3 |  |  | (20.8 | )
Ending balance, March 31 |  | $4.9 |  |  |  | ($15.1 | ) |  |  | $122.1 |  |  |  | $32.9 |
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 (a) |  | ($2.4 | ) |  |  | ($12.5 | ) |  |  | $— |  |  |  | $— |
IPL | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
Three Months Ended March 31 | 2013 |  | 2012 |  | 2013 |  | 2012
Beginning balance, January 1 |  | $12.5 |  |  |  | $4.3 |  |  |  | $66.8 |  |  |  | $53.7 |
Total net losses (realized/unrealized) included in changes in net assets (a) | (2.9 | ) |  | (10.8 | ) |  | — |  |  | — |
Transfers into Level 3 (b) | — |  |  | (2.7 | ) |  | — |  |  | — |
Transfers out of Level 3 (c) | 1.1 |  |  | 0.1 |  |  | — |  |  | — |
Settlements (d) | (6.4 | ) |  | (2.3 | ) |  | 55.3 |  |  | (20.8 | )
Ending balance, March 31 |  | $4.3 |  |  |  | ($11.4 | ) |  |  | $122.1 |  |  |  | $32.9 |
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 (a) |  | ($2.9 | ) |  |  | ($10.8 | ) |  |  | $— |  |  |  | $— |
WPL | Commodity Contract Derivative
| Assets and (Liabilities), net
Three Months Ended March 31 | 2013 |  | 2012
Beginning balance, January 1 |  | ($0.6 | ) |  |  | ($5.2 | )
Total net gains (losses) (realized/unrealized) included in changes in net assets (a) | 0.5 |  |  | (1.7 | )
Transfers into Level 3 (b) | — |  |  | (1.1 | )
Transfers out of Level 3 (c) | 2.5 |  |  | 5.2 |
Settlements | (1.8 | ) |  | (0.9 | )
Ending balance, March 31 |  | $0.6 |  |  |  | ($3.7 | )
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 March 31 (a) |  | $0.5 |  |  |  | ($1.7 | )
(a) | Gains and losses related to derivative assets and derivative liabilities are recorded in “Regulatory assets” and “Regulatory liabilities” on the Condensed Consolidated Balance Sheets.
(b) | Markets for similar assets and liabilities became inactive and observable market inputs became unavailable for transfers into Level 3. The transfers were valued as of the beginning of the period.
(c) | Observable market inputs became available for certain commodity contracts previously classified as Level 3 for transfers out of Level 3. The transfers were valued as of the beginning of the period.
(d) | 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.
IPL [Member] |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [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
| Carrying Amount |  | Fair Value |  | Carrying Amount |  | Fair Value |  | Carrying Amount |  | Fair Value
March 31, 2013 |  |  |  |  |  |  |  |  |  |  |
Assets: |  |  |  |  |  |  |  |  |  |  |
Derivative assets (Note 11) |  | $23.6 |  |  |  | $23.6 |  |  |  | $12.5 |  |  |  | $12.5 |  |  |  | $11.1 |  |  |  | $11.1 |
Deferred proceeds (sales of receivables) (Note 3(a)) | 122.1 |  |  | 122.1 |  |  | 122.1 |  |  | 122.1 |  |  | — |  |  | — |
Capitalization and liabilities: |  |  |  |  |  |  |  |  |  |  |
Long-term debt (including current maturities) (Note 8(b)) | 3,123.4 |  |  | 3,806.5 |  |  | 1,344.5 |  |  | 1,643.8 |  |  | 1,331.7 |  |  | 1,691.6 |
Cumulative preferred stock (Note 7) | 200.0 |  |  | 201.8 |  |  | 200.0 |  |  | 201.8 |  |  | — |  |  | — |
Derivative liabilities (Note 11) | 17.1 |  |  | 17.1 |  |  | 6.1 |  |  | 6.1 |  |  | 11.0 |  |  | 11.0 |
| Alliant Energy |  | IPL |  | WPL
| Carrying Amount |  | Fair Value |  | Carrying Amount |  | Fair Value |  | Carrying Amount |  | Fair Value
December 31, 2012 |  |  |  |  |  |  |  |  |  |  |
Assets: |  |  |  |  |  |  |  |  |  |  |
Derivative assets (Note 11) |  | $26.2 |  |  |  | $26.2 |  |  |  | $17.5 |  |  |  | $17.5 |  |  |  | $8.7 |  |  |  | $8.7 |
Deferred proceeds (sales of receivables) (Note 3(a)) | 66.8 |  |  | 66.8 |  |  | 66.8 |  |  | 66.8 |  |  | — |  |  | — |
Capitalization and liabilities: |  |  |  |  |  |  |  |  |  |  |
Long-term debt (including current maturities) (Note 8(b)) | 3,138.1 |  |  | 3,860.5 |  |  | 1,359.5 |  |  | 1,679.9 |  |  | 1,331.5 |  |  | 1,713.3 |
Cumulative preferred stock (Note 7) | 205.1 |  |  | 212.6 |  |  | 145.1 |  |  | 151.8 |  |  | 60.0 |  |  | 60.8 |
Derivative liabilities (Note 11) | 40.4 |  |  | 40.4 |  |  | 16.1 |  |  | 16.1 |  |  | 24.3 |  |  | 24.3 |
Recurring Fair Value Measurements | Items subject to fair value measurement disclosure requirements were as follows (in millions):
Alliant Energy | March 31, 2013 |  | December 31, 2012
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
| Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives - commodity contracts |  | $23.6 |  |  |  | $— |  |  |  | $14.4 |  |  |  | $9.2 |  |  |  | $26.2 |  |  |  | $— |  |  |  | $4.8 |  |  |  | $21.4 |
Deferred proceeds | 122.1 |  |  | — |  |  | — |  |  | 122.1 |  |  | 66.8 |  |  | — |  |  | — |  |  | 66.8 |
Capitalization and liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt (including current maturities) | 3,806.5 |  |  | — |  |  | 3,806.0 |  |  | 0.5 |  |  | 3,860.5 |  |  | — |  |  | 3,860.0 |  |  | 0.5 |
Cumulative preferred stock | 201.8 |  |  | 201.8 |  |  | — |  |  | — |  |  | 212.6 |  |  | 162.3 |  |  | 50.3 |  |  | — |
Derivatives - commodity contracts | 17.1 |  |  | — |  |  | 12.8 |  |  | 4.3 |  |  | 40.4 |  |  | — |  |  | 30.9 |  |  | 9.5 |
IPL | March 31, 2013 |  | December 31, 2012
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
| Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives - commodity contracts |  | $12.5 |  |  |  | $— |  |  |  | $6.5 |  |  |  | $6.0 |  |  |  | $17.5 |  |  |  | $— |  |  |  | $3.1 |  |  |  | $14.4 |
Deferred proceeds | 122.1 |  |  | — |  |  | — |  |  | 122.1 |  |  | 66.8 |  |  | — |  |  | — |  |  | 66.8 |
Capitalization and liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt | 1,643.8 |  |  | — |  |  | 1,643.8 |  |  | — |  |  | 1,679.9 |  |  | — |  |  | 1,679.9 |  |  | — |
Cumulative preferred stock | 201.8 |  |  | 201.8 |  |  | — |  |  | — |  |  | 151.8 |  |  | 151.8 |  |  | — |  |  | — |
Derivatives - commodity contracts | 6.1 |  |  | — |  |  | 4.4 |  |  | 1.7 |  |  | 16.1 |  |  | — |  |  | 14.2 |  |  | 1.9 |
WPL | March 31, 2013 |  | December 31, 2012
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
| Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives - commodity contracts |  | $11.1 |  |  |  | $— |  |  |  | $7.9 |  |  |  | $3.2 |  |  |  | $8.7 |  |  |  | $— |  |  |  | $1.7 |  |  |  | $7.0 |
Capitalization and liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt | 1,691.6 |  |  | — |  |  | 1,691.6 |  |  | — |  |  | 1,713.3 |  |  | — |  |  | 1,713.3 |  |  | — |
Cumulative preferred stock | — |  |  | — |  |  | — |  |  | — |  |  | 60.8 |  |  | 10.5 |  |  | 50.3 |  |  | — |
Derivatives - commodity contracts | 11.0 |  |  | — |  |  | 8.4 |  |  | 2.6 |  |  | 24.3 |  |  | — |  |  | 16.7 |  |  | 7.6 |
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 | 2013 |  | 2012 |  | 2013 |  | 2012
Beginning balance, January 1 |  | $11.9 |  |  |  | ($0.9 | ) |  |  | $66.8 |  |  |  | $53.7 |
Total net losses (realized/unrealized) included in changes in net assets (a) | (2.4 | ) |  | (12.5 | ) |  | — |  |  | — |
Transfers into Level 3 (b) | — |  |  | (3.8 | ) |  | — |  |  | — |
Transfers out of Level 3 (c) | 3.6 |  |  | 5.3 |  |  | — |  |  | — |
Settlements (d) | (8.2 | ) |  | (3.2 | ) |  | 55.3 |  |  | (20.8 | )
Ending balance, March 31 |  | $4.9 |  |  |  | ($15.1 | ) |  |  | $122.1 |  |  |  | $32.9 |
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 (a) |  | ($2.4 | ) |  |  | ($12.5 | ) |  |  | $— |  |  |  | $— |
IPL | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
Three Months Ended March 31 | 2013 |  | 2012 |  | 2013 |  | 2012
Beginning balance, January 1 |  | $12.5 |  |  |  | $4.3 |  |  |  | $66.8 |  |  |  | $53.7 |
Total net losses (realized/unrealized) included in changes in net assets (a) | (2.9 | ) |  | (10.8 | ) |  | — |  |  | — |
Transfers into Level 3 (b) | — |  |  | (2.7 | ) |  | — |  |  | — |
Transfers out of Level 3 (c) | 1.1 |  |  | 0.1 |  |  | — |  |  | — |
Settlements (d) | (6.4 | ) |  | (2.3 | ) |  | 55.3 |  |  | (20.8 | )
Ending balance, March 31 |  | $4.3 |  |  |  | ($11.4 | ) |  |  | $122.1 |  |  |  | $32.9 |
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 (a) |  | ($2.9 | ) |  |  | ($10.8 | ) |  |  | $— |  |  |  | $— |
WPL | Commodity Contract Derivative
| Assets and (Liabilities), net
Three Months Ended March 31 | 2013 |  | 2012
Beginning balance, January 1 |  | ($0.6 | ) |  |  | ($5.2 | )
Total net gains (losses) (realized/unrealized) included in changes in net assets (a) | 0.5 |  |  | (1.7 | )
Transfers into Level 3 (b) | — |  |  | (1.1 | )
Transfers out of Level 3 (c) | 2.5 |  |  | 5.2 |
Settlements | (1.8 | ) |  | (0.9 | )
Ending balance, March 31 |  | $0.6 |  |  |  | ($3.7 | )
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 March 31 (a) |  | $0.5 |  |  |  | ($1.7 | )
(a) | Gains and losses related to derivative assets and derivative liabilities are recorded in “Regulatory assets” and “Regulatory liabilities” on the Condensed Consolidated Balance Sheets.
(b) | Markets for similar assets and liabilities became inactive and observable market inputs became unavailable for transfers into Level 3. The transfers were valued as of the beginning of the period.
(c) | Observable market inputs became available for certain commodity contracts previously classified as Level 3 for transfers out of Level 3. The transfers were valued as of the beginning of the period.
(d) | 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.
WPL [Member] |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [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
| Carrying Amount |  | Fair Value |  | Carrying Amount |  | Fair Value |  | Carrying Amount |  | Fair Value
March 31, 2013 |  |  |  |  |  |  |  |  |  |  |
Assets: |  |  |  |  |  |  |  |  |  |  |
Derivative assets (Note 11) |  | $23.6 |  |  |  | $23.6 |  |  |  | $12.5 |  |  |  | $12.5 |  |  |  | $11.1 |  |  |  | $11.1 |
Deferred proceeds (sales of receivables) (Note 3(a)) | 122.1 |  |  | 122.1 |  |  | 122.1 |  |  | 122.1 |  |  | — |  |  | — |
Capitalization and liabilities: |  |  |  |  |  |  |  |  |  |  |
Long-term debt (including current maturities) (Note 8(b)) | 3,123.4 |  |  | 3,806.5 |  |  | 1,344.5 |  |  | 1,643.8 |  |  | 1,331.7 |  |  | 1,691.6 |
Cumulative preferred stock (Note 7) | 200.0 |  |  | 201.8 |  |  | 200.0 |  |  | 201.8 |  |  | — |  |  | — |
Derivative liabilities (Note 11) | 17.1 |  |  | 17.1 |  |  | 6.1 |  |  | 6.1 |  |  | 11.0 |  |  | 11.0 |
| Alliant Energy |  | IPL |  | WPL
| Carrying Amount |  | Fair Value |  | Carrying Amount |  | Fair Value |  | Carrying Amount |  | Fair Value
December 31, 2012 |  |  |  |  |  |  |  |  |  |  |
Assets: |  |  |  |  |  |  |  |  |  |  |
Derivative assets (Note 11) |  | $26.2 |  |  |  | $26.2 |  |  |  | $17.5 |  |  |  | $17.5 |  |  |  | $8.7 |  |  |  | $8.7 |
Deferred proceeds (sales of receivables) (Note 3(a)) | 66.8 |  |  | 66.8 |  |  | 66.8 |  |  | 66.8 |  |  | — |  |  | — |
Capitalization and liabilities: |  |  |  |  |  |  |  |  |  |  |
Long-term debt (including current maturities) (Note 8(b)) | 3,138.1 |  |  | 3,860.5 |  |  | 1,359.5 |  |  | 1,679.9 |  |  | 1,331.5 |  |  | 1,713.3 |
Cumulative preferred stock (Note 7) | 205.1 |  |  | 212.6 |  |  | 145.1 |  |  | 151.8 |  |  | 60.0 |  |  | 60.8 |
Derivative liabilities (Note 11) | 40.4 |  |  | 40.4 |  |  | 16.1 |  |  | 16.1 |  |  | 24.3 |  |  | 24.3 |
Recurring Fair Value Measurements | Items subject to fair value measurement disclosure requirements were as follows (in millions):
Alliant Energy | March 31, 2013 |  | December 31, 2012
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
| Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives - commodity contracts |  | $23.6 |  |  |  | $— |  |  |  | $14.4 |  |  |  | $9.2 |  |  |  | $26.2 |  |  |  | $— |  |  |  | $4.8 |  |  |  | $21.4 |
Deferred proceeds | 122.1 |  |  | — |  |  | — |  |  | 122.1 |  |  | 66.8 |  |  | — |  |  | — |  |  | 66.8 |
Capitalization and liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt (including current maturities) | 3,806.5 |  |  | — |  |  | 3,806.0 |  |  | 0.5 |  |  | 3,860.5 |  |  | — |  |  | 3,860.0 |  |  | 0.5 |
Cumulative preferred stock | 201.8 |  |  | 201.8 |  |  | — |  |  | — |  |  | 212.6 |  |  | 162.3 |  |  | 50.3 |  |  | — |
Derivatives - commodity contracts | 17.1 |  |  | — |  |  | 12.8 |  |  | 4.3 |  |  | 40.4 |  |  | — |  |  | 30.9 |  |  | 9.5 |
IPL | March 31, 2013 |  | December 31, 2012
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
| Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives - commodity contracts |  | $12.5 |  |  |  | $— |  |  |  | $6.5 |  |  |  | $6.0 |  |  |  | $17.5 |  |  |  | $— |  |  |  | $3.1 |  |  |  | $14.4 |
Deferred proceeds | 122.1 |  |  | — |  |  | — |  |  | 122.1 |  |  | 66.8 |  |  | — |  |  | — |  |  | 66.8 |
Capitalization and liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt | 1,643.8 |  |  | — |  |  | 1,643.8 |  |  | — |  |  | 1,679.9 |  |  | — |  |  | 1,679.9 |  |  | — |
Cumulative preferred stock | 201.8 |  |  | 201.8 |  |  | — |  |  | — |  |  | 151.8 |  |  | 151.8 |  |  | — |  |  | — |
Derivatives - commodity contracts | 6.1 |  |  | — |  |  | 4.4 |  |  | 1.7 |  |  | 16.1 |  |  | — |  |  | 14.2 |  |  | 1.9 |
WPL | March 31, 2013 |  | December 31, 2012
| Fair |  | Level |  | Level |  | Level |  | Fair |  | Level |  | Level |  | Level
| Value |  | 1 |  | 2 |  | 3 |  | Value |  | 1 |  | 2 |  | 3
Assets: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivatives - commodity contracts |  | $11.1 |  |  |  | $— |  |  |  | $7.9 |  |  |  | $3.2 |  |  |  | $8.7 |  |  |  | $— |  |  |  | $1.7 |  |  |  | $7.0 |
Capitalization and liabilities: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Long-term debt | 1,691.6 |  |  | — |  |  | 1,691.6 |  |  | — |  |  | 1,713.3 |  |  | — |  |  | 1,713.3 |  |  | — |
Cumulative preferred stock | — |  |  | — |  |  | — |  |  | — |  |  | 60.8 |  |  | 10.5 |  |  | 50.3 |  |  | — |
Derivatives - commodity contracts | 11.0 |  |  | — |  |  | 8.4 |  |  | 2.6 |  |  | 24.3 |  |  | — |  |  | 16.7 |  |  | 7.6 |
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 | 2013 |  | 2012 |  | 2013 |  | 2012
Beginning balance, January 1 |  | $11.9 |  |  |  | ($0.9 | ) |  |  | $66.8 |  |  |  | $53.7 |
Total net losses (realized/unrealized) included in changes in net assets (a) | (2.4 | ) |  | (12.5 | ) |  | — |  |  | — |
Transfers into Level 3 (b) | — |  |  | (3.8 | ) |  | — |  |  | — |
Transfers out of Level 3 (c) | 3.6 |  |  | 5.3 |  |  | — |  |  | — |
Settlements (d) | (8.2 | ) |  | (3.2 | ) |  | 55.3 |  |  | (20.8 | )
Ending balance, March 31 |  | $4.9 |  |  |  | ($15.1 | ) |  |  | $122.1 |  |  |  | $32.9 |
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 (a) |  | ($2.4 | ) |  |  | ($12.5 | ) |  |  | $— |  |  |  | $— |
IPL | Commodity Contract Derivative |  |
| Assets and (Liabilities), net |  | Deferred Proceeds
Three Months Ended March 31 | 2013 |  | 2012 |  | 2013 |  | 2012
Beginning balance, January 1 |  | $12.5 |  |  |  | $4.3 |  |  |  | $66.8 |  |  |  | $53.7 |
Total net losses (realized/unrealized) included in changes in net assets (a) | (2.9 | ) |  | (10.8 | ) |  | — |  |  | — |
Transfers into Level 3 (b) | — |  |  | (2.7 | ) |  | — |  |  | — |
Transfers out of Level 3 (c) | 1.1 |  |  | 0.1 |  |  | — |  |  | — |
Settlements (d) | (6.4 | ) |  | (2.3 | ) |  | 55.3 |  |  | (20.8 | )
Ending balance, March 31 |  | $4.3 |  |  |  | ($11.4 | ) |  |  | $122.1 |  |  |  | $32.9 |
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 (a) |  | ($2.9 | ) |  |  | ($10.8 | ) |  |  | $— |  |  |  | $— |
WPL | Commodity Contract Derivative
| Assets and (Liabilities), net
Three Months Ended March 31 | 2013 |  | 2012
Beginning balance, January 1 |  | ($0.6 | ) |  |  | ($5.2 | )
Total net gains (losses) (realized/unrealized) included in changes in net assets (a) | 0.5 |  |  | (1.7 | )
Transfers into Level 3 (b) | — |  |  | (1.1 | )
Transfers out of Level 3 (c) | 2.5 |  |  | 5.2 |
Settlements | (1.8 | ) |  | (0.9 | )
Ending balance, March 31 |  | $0.6 |  |  |  | ($3.7 | )
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 March 31 (a) |  | $0.5 |  |  |  | ($1.7 | )
(a) | Gains and losses related to derivative assets and derivative liabilities are recorded in “Regulatory assets” and “Regulatory liabilities” on the Condensed Consolidated Balance Sheets.
(b) | Markets for similar assets and liabilities became inactive and observable market inputs became unavailable for transfers into Level 3. The transfers were valued as of the beginning of the period.
(c) | Observable market inputs became available for certain commodity contracts previously classified as Level 3 for transfers out of Level 3. The transfers were valued as of the beginning of the period.
(d) | 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.

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