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Derivative Instruments (Tables) | 12 Months Ended
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Dec. 31, 2019
Derivative [Line Items] |
Notional Amounts of Derivative Instruments | As of December 31, 2019, gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and FTRs that were accounted for as commodity derivative instruments were as follows (units in thousands):
| FTRs |  | Natural Gas |  | Coal |  | Diesel Fuel
| MWhs |  | Years |  | Dths |  | Years |  | Tons |  | Years |  | Gallons |  | Years
Alliant Energy | 11,671 |  |  | 2020 |  | 189,287 |  |  | 2020-2026 |  | 6,194 |  |  | 2020-2021 |  | 5,040 |  |  | 2020-2021
IPL | 5,497 |  |  | 2020 |  | 102,758 |  |  | 2020-2026 |  | 2,700 |  |  | 2020-2021 |  | — |  |  |
WPL | 6,174 |  |  | 2020 |  | 86,529 |  |  | 2020-2026 |  | 3,494 |  |  | 2020-2021 |  | 5,040 |  |  | 2020-2021
Fair Value of Financial Instruments | At December 31, the fair values of current derivative assets are included in “Other current assets,” non-current derivative assets are included in “Deferred charges and other,” current derivative liabilities are included in “Other current liabilities” and non-current derivative liabilities are included in “Other liabilities” on the balance sheets as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018
Current derivative assets |  | $15.8 |  |  |  | $24.6 |  |  |  | $12.1 |  |  |  | $16.1 |  |  |  | $3.7 |  |  |  | $8.5 |
Non-current derivative assets | 11.0 |  |  | 3.7 |  |  | 10.2 |  |  | 1.6 |  |  | 0.8 |  |  | 2.1 |
Current derivative liabilities | 19.0 |  |  | 5.6 |  |  | 8.9 |  |  | 3.1 |  |  | 10.1 |  |  | 2.5 |
Non-current derivative liabilities | 18.6 |  |  | 17.7 |  |  | 8.5 |  |  | 8.1 |  |  | 10.1 |  |  | 9.6 |
IPL [Member] |
Derivative [Line Items] |
Notional Amounts of Derivative Instruments | As of December 31, 2019, gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and FTRs that were accounted for as commodity derivative instruments were as follows (units in thousands):
| FTRs |  | Natural Gas |  | Coal |  | Diesel Fuel
| MWhs |  | Years |  | Dths |  | Years |  | Tons |  | Years |  | Gallons |  | Years
Alliant Energy | 11,671 |  |  | 2020 |  | 189,287 |  |  | 2020-2026 |  | 6,194 |  |  | 2020-2021 |  | 5,040 |  |  | 2020-2021
IPL | 5,497 |  |  | 2020 |  | 102,758 |  |  | 2020-2026 |  | 2,700 |  |  | 2020-2021 |  | — |  |  |
WPL | 6,174 |  |  | 2020 |  | 86,529 |  |  | 2020-2026 |  | 3,494 |  |  | 2020-2021 |  | 5,040 |  |  | 2020-2021
Fair Value of Financial Instruments | At December 31, the fair values of current derivative assets are included in “Other current assets,” non-current derivative assets are included in “Deferred charges and other,” current derivative liabilities are included in “Other current liabilities” and non-current derivative liabilities are included in “Other liabilities” on the balance sheets as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018
Current derivative assets |  | $15.8 |  |  |  | $24.6 |  |  |  | $12.1 |  |  |  | $16.1 |  |  |  | $3.7 |  |  |  | $8.5 |
Non-current derivative assets | 11.0 |  |  | 3.7 |  |  | 10.2 |  |  | 1.6 |  |  | 0.8 |  |  | 2.1 |
Current derivative liabilities | 19.0 |  |  | 5.6 |  |  | 8.9 |  |  | 3.1 |  |  | 10.1 |  |  | 2.5 |
Non-current derivative liabilities | 18.6 |  |  | 17.7 |  |  | 8.5 |  |  | 8.1 |  |  | 10.1 |  |  | 9.6 |
WPL [Member] |
Derivative [Line Items] |
Notional Amounts of Derivative Instruments | As of December 31, 2019, gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and FTRs that were accounted for as commodity derivative instruments were as follows (units in thousands):
| FTRs |  | Natural Gas |  | Coal |  | Diesel Fuel
| MWhs |  | Years |  | Dths |  | Years |  | Tons |  | Years |  | Gallons |  | Years
Alliant Energy | 11,671 |  |  | 2020 |  | 189,287 |  |  | 2020-2026 |  | 6,194 |  |  | 2020-2021 |  | 5,040 |  |  | 2020-2021
IPL | 5,497 |  |  | 2020 |  | 102,758 |  |  | 2020-2026 |  | 2,700 |  |  | 2020-2021 |  | — |  |  |
WPL | 6,174 |  |  | 2020 |  | 86,529 |  |  | 2020-2026 |  | 3,494 |  |  | 2020-2021 |  | 5,040 |  |  | 2020-2021
Fair Value of Financial Instruments | At December 31, the fair values of current derivative assets are included in “Other current assets,” non-current derivative assets are included in “Deferred charges and other,” current derivative liabilities are included in “Other current liabilities” and non-current derivative liabilities are included in “Other liabilities” on the balance sheets as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2019 |  | 2018 |  | 2019 |  | 2018 |  | 2019 |  | 2018
Current derivative assets |  | $15.8 |  |  |  | $24.6 |  |  |  | $12.1 |  |  |  | $16.1 |  |  |  | $3.7 |  |  |  | $8.5 |
Non-current derivative assets | 11.0 |  |  | 3.7 |  |  | 10.2 |  |  | 1.6 |  |  | 0.8 |  |  | 2.1 |
Current derivative liabilities | 19.0 |  |  | 5.6 |  |  | 8.9 |  |  | 3.1 |  |  | 10.1 |  |  | 2.5 |
Non-current derivative liabilities | 18.6 |  |  | 17.7 |  |  | 8.5 |  |  | 8.1 |  |  | 10.1 |  |  | 9.6 |

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