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Derivative Instruments (Tables) | 12 Months Ended
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Dec. 31, 2018
Derivative [Line Items] |
Notional Amounts of Derivative Instruments | As of December 31, 2018, 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 | 10,399 |  |  | 2019 |  | 181,694 |  |  | 2019-2026 |  | 10,467 |  |  | 2019-2021 |  | 3,024 |  |  | 2019
IPL | 5,954 |  |  | 2019 |  | 80,150 |  |  | 2019-2026 |  | 4,410 |  |  | 2019-2021 |  | — |  |  |
WPL | 4,445 |  |  | 2019 |  | 101,544 |  |  | 2019-2026 |  | 6,057 |  |  | 2019-2021 |  | 3,024 |  |  | 2019
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
| 2018 |  | 2017 |  | 2018 |  | 2017 |  | 2018 |  | 2017
Current derivative assets |  | $24.6 |  |  |  | $21.1 |  |  |  | $16.1 |  |  |  | $15.8 |  |  |  | $8.5 |  |  |  | $5.3 |
Non-current derivative assets | 3.7 |  |  | 4.0 |  |  | 1.6 |  |  | 1.3 |  |  | 2.1 |  |  | 2.7 |
Current derivative liabilities | 5.6 |  |  | 18.7 |  |  | 3.1 |  |  | 5.0 |  |  | 2.5 |  |  | 13.7 |
Non-current derivative liabilities | 17.7 |  |  | 23.0 |  |  | 8.1 |  |  | 14.4 |  |  | 9.6 |  |  | 8.6 |
IPL [Member] |
Derivative [Line Items] |
Notional Amounts of Derivative Instruments | As of December 31, 2018, 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 | 10,399 |  |  | 2019 |  | 181,694 |  |  | 2019-2026 |  | 10,467 |  |  | 2019-2021 |  | 3,024 |  |  | 2019
IPL | 5,954 |  |  | 2019 |  | 80,150 |  |  | 2019-2026 |  | 4,410 |  |  | 2019-2021 |  | — |  |  |
WPL | 4,445 |  |  | 2019 |  | 101,544 |  |  | 2019-2026 |  | 6,057 |  |  | 2019-2021 |  | 3,024 |  |  | 2019
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
| 2018 |  | 2017 |  | 2018 |  | 2017 |  | 2018 |  | 2017
Current derivative assets |  | $24.6 |  |  |  | $21.1 |  |  |  | $16.1 |  |  |  | $15.8 |  |  |  | $8.5 |  |  |  | $5.3 |
Non-current derivative assets | 3.7 |  |  | 4.0 |  |  | 1.6 |  |  | 1.3 |  |  | 2.1 |  |  | 2.7 |
Current derivative liabilities | 5.6 |  |  | 18.7 |  |  | 3.1 |  |  | 5.0 |  |  | 2.5 |  |  | 13.7 |
Non-current derivative liabilities | 17.7 |  |  | 23.0 |  |  | 8.1 |  |  | 14.4 |  |  | 9.6 |  |  | 8.6 |
WPL [Member] |
Derivative [Line Items] |
Notional Amounts of Derivative Instruments | As of December 31, 2018, 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 | 10,399 |  |  | 2019 |  | 181,694 |  |  | 2019-2026 |  | 10,467 |  |  | 2019-2021 |  | 3,024 |  |  | 2019
IPL | 5,954 |  |  | 2019 |  | 80,150 |  |  | 2019-2026 |  | 4,410 |  |  | 2019-2021 |  | — |  |  |
WPL | 4,445 |  |  | 2019 |  | 101,544 |  |  | 2019-2026 |  | 6,057 |  |  | 2019-2021 |  | 3,024 |  |  | 2019
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
| 2018 |  | 2017 |  | 2018 |  | 2017 |  | 2018 |  | 2017
Current derivative assets |  | $24.6 |  |  |  | $21.1 |  |  |  | $16.1 |  |  |  | $15.8 |  |  |  | $8.5 |  |  |  | $5.3 |
Non-current derivative assets | 3.7 |  |  | 4.0 |  |  | 1.6 |  |  | 1.3 |  |  | 2.1 |  |  | 2.7 |
Current derivative liabilities | 5.6 |  |  | 18.7 |  |  | 3.1 |  |  | 5.0 |  |  | 2.5 |  |  | 13.7 |
Non-current derivative liabilities | 17.7 |  |  | 23.0 |  |  | 8.1 |  |  | 14.4 |  |  | 9.6 |  |  | 8.6 |

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- Definition Tabular disclosure of the location and fair value amounts of derivative instruments (and nonderivative instruments that are designated and qualify as hedging instruments) reported in the statement of financial position. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4B -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624163-113959 + Details
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- Definition Tabular disclosure of the notional amounts of outstanding derivative positions. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 1A -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5579245-113959 + Details
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