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Commitments And Contingencies (Tables) | 12 Months Ended
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Dec. 31, 2018
Long-term Purchase Commitment [Line Items] |
Other Purchase Commitments | At December 31, 2018, the related minimum future commitments were as follows (in millions):
Alliant Energy | 2019 |  | 2020 |  | 2021 |  | 2022 |  | 2023 |  | Thereafter |  | Total
Purchased power (a) |  | $159 |  |  |  | $135 |  |  |  | $149 |  |  |  | $140 |  |  |  | $155 |  |  |  | $307 |  |  |  | $1,045 |
Natural gas | 254 |  |  | 151 |  |  | 119 |  |  | 94 |  |  | 67 |  |  | 196 |  |  | 881 |
Coal (b) | 102 |  |  | 49 |  |  | 26 |  |  | 9 |  |  | 9 |  |  | — |  |  | 195 |
Other (c) | 60 |  |  | 4 |  |  | 3 |  |  | 2 |  |  | 2 |  |  | — |  |  | 71 |
|  | $575 |  |  |  | $339 |  |  |  | $297 |  |  |  | $245 |  |  |  | $233 |  |  |  | $503 |  |  |  | $2,192 |
IPL | 2019 |  | 2020 |  | 2021 |  | 2022 |  | 2023 |  | Thereafter |  | Total
Purchased power (a) |  | $144 |  |  |  | $135 |  |  |  | $149 |  |  |  | $140 |  |  |  | $155 |  |  |  | $307 |  |  |  | $1,030 |
Natural gas | 124 |  |  | 55 |  |  | 42 |  |  | 33 |  |  | 26 |  |  | 83 |  |  | 363 |
Coal (b) | 52 |  |  | 29 |  |  | 20 |  |  | 9 |  |  | 9 |  |  | — |  |  | 119 |
Other (c) | 24 |  |  | 3 |  |  | 3 |  |  | 2 |  |  | 2 |  |  | — |  |  | 34 |
|  | $344 |  |  |  | $222 |  |  |  | $214 |  |  |  | $184 |  |  |  | $192 |  |  |  | $390 |  |  |  | $1,546 |
WPL | 2019 |  | 2020 |  | 2021 |  | 2022 |  | 2023 |  | Thereafter |  | Total
Purchased power |  | $15 |  |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | $15 |
Natural gas | 130 |  |  | 96 |  |  | 77 |  |  | 61 |  |  | 41 |  |  | 113 |  |  | 518 |
Coal (b) | 50 |  |  | 20 |  |  | 6 |  |  | — |  |  | — |  |  | — |  |  | 76 |
Other (c) | 23 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | 23 |
|  | $218 |  |  |  | $116 |  |  |  | $83 |  |  |  | $61 |  |  |  | $41 |  |  |  | $113 |  |  |  | $632 |
(a) | Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. In July 2018, IPL entered into an amendment to shorten the term of the DAEC PPA by five years in exchange for a $110 million buyout payment by IPL in September 2020, subject to IUB approval. In December 2018, IPL received an order from the IUB, which was effective in January 2019, approving recovery of the buyout payment. As a result, Alliant Energy’s and IPL’s amounts in the above table do not include the September 2020 buyout payment, and the minimum future commitments reflect IPL’s purchase of capacity and the resulting energy from DAEC through December 2025, the original term of the PPA prior to the amendment. Amounts in the above table for 2021 and beyond relate to the DAEC PPA.
(b) | Corporate Services entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. These commitments were assigned to IPL and WPL based on information available as of December 31, 2018 regarding expected future usage, which is subject to change.
(c) | Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2018.
Schedule of Environmental Liabilities | At December 31, 2018, estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, which are not discounted, were as follows (in millions). At December 31, 2018, such amounts for WPL were not material.
| Alliant Energy |  | IPL
Range of estimated future costs |  | $11 |  | - | $29 |  |  | $8 |  | - | $24
Current and non-current environmental liabilities | 15 |  | 12
IPL [Member] |
Long-term Purchase Commitment [Line Items] |
Other Purchase Commitments | At December 31, 2018, the related minimum future commitments were as follows (in millions):
Alliant Energy | 2019 |  | 2020 |  | 2021 |  | 2022 |  | 2023 |  | Thereafter |  | Total
Purchased power (a) |  | $159 |  |  |  | $135 |  |  |  | $149 |  |  |  | $140 |  |  |  | $155 |  |  |  | $307 |  |  |  | $1,045 |
Natural gas | 254 |  |  | 151 |  |  | 119 |  |  | 94 |  |  | 67 |  |  | 196 |  |  | 881 |
Coal (b) | 102 |  |  | 49 |  |  | 26 |  |  | 9 |  |  | 9 |  |  | — |  |  | 195 |
Other (c) | 60 |  |  | 4 |  |  | 3 |  |  | 2 |  |  | 2 |  |  | — |  |  | 71 |
|  | $575 |  |  |  | $339 |  |  |  | $297 |  |  |  | $245 |  |  |  | $233 |  |  |  | $503 |  |  |  | $2,192 |
IPL | 2019 |  | 2020 |  | 2021 |  | 2022 |  | 2023 |  | Thereafter |  | Total
Purchased power (a) |  | $144 |  |  |  | $135 |  |  |  | $149 |  |  |  | $140 |  |  |  | $155 |  |  |  | $307 |  |  |  | $1,030 |
Natural gas | 124 |  |  | 55 |  |  | 42 |  |  | 33 |  |  | 26 |  |  | 83 |  |  | 363 |
Coal (b) | 52 |  |  | 29 |  |  | 20 |  |  | 9 |  |  | 9 |  |  | — |  |  | 119 |
Other (c) | 24 |  |  | 3 |  |  | 3 |  |  | 2 |  |  | 2 |  |  | — |  |  | 34 |
|  | $344 |  |  |  | $222 |  |  |  | $214 |  |  |  | $184 |  |  |  | $192 |  |  |  | $390 |  |  |  | $1,546 |
WPL | 2019 |  | 2020 |  | 2021 |  | 2022 |  | 2023 |  | Thereafter |  | Total
Purchased power |  | $15 |  |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | $15 |
Natural gas | 130 |  |  | 96 |  |  | 77 |  |  | 61 |  |  | 41 |  |  | 113 |  |  | 518 |
Coal (b) | 50 |  |  | 20 |  |  | 6 |  |  | — |  |  | — |  |  | — |  |  | 76 |
Other (c) | 23 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | 23 |
|  | $218 |  |  |  | $116 |  |  |  | $83 |  |  |  | $61 |  |  |  | $41 |  |  |  | $113 |  |  |  | $632 |
(a) | Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. In July 2018, IPL entered into an amendment to shorten the term of the DAEC PPA by five years in exchange for a $110 million buyout payment by IPL in September 2020, subject to IUB approval. In December 2018, IPL received an order from the IUB, which was effective in January 2019, approving recovery of the buyout payment. As a result, Alliant Energy’s and IPL’s amounts in the above table do not include the September 2020 buyout payment, and the minimum future commitments reflect IPL’s purchase of capacity and the resulting energy from DAEC through December 2025, the original term of the PPA prior to the amendment. Amounts in the above table for 2021 and beyond relate to the DAEC PPA.
(b) | Corporate Services entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. These commitments were assigned to IPL and WPL based on information available as of December 31, 2018 regarding expected future usage, which is subject to change.
(c) | Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2018.
Schedule of Environmental Liabilities | At December 31, 2018, estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, which are not discounted, were as follows (in millions). At December 31, 2018, such amounts for WPL were not material.
| Alliant Energy |  | IPL
Range of estimated future costs |  | $11 |  | - | $29 |  |  | $8 |  | - | $24
Current and non-current environmental liabilities | 15 |  | 12
WPL [Member] |
Long-term Purchase Commitment [Line Items] |
Other Purchase Commitments | At December 31, 2018, the related minimum future commitments were as follows (in millions):
Alliant Energy | 2019 |  | 2020 |  | 2021 |  | 2022 |  | 2023 |  | Thereafter |  | Total
Purchased power (a) |  | $159 |  |  |  | $135 |  |  |  | $149 |  |  |  | $140 |  |  |  | $155 |  |  |  | $307 |  |  |  | $1,045 |
Natural gas | 254 |  |  | 151 |  |  | 119 |  |  | 94 |  |  | 67 |  |  | 196 |  |  | 881 |
Coal (b) | 102 |  |  | 49 |  |  | 26 |  |  | 9 |  |  | 9 |  |  | — |  |  | 195 |
Other (c) | 60 |  |  | 4 |  |  | 3 |  |  | 2 |  |  | 2 |  |  | — |  |  | 71 |
|  | $575 |  |  |  | $339 |  |  |  | $297 |  |  |  | $245 |  |  |  | $233 |  |  |  | $503 |  |  |  | $2,192 |
IPL | 2019 |  | 2020 |  | 2021 |  | 2022 |  | 2023 |  | Thereafter |  | Total
Purchased power (a) |  | $144 |  |  |  | $135 |  |  |  | $149 |  |  |  | $140 |  |  |  | $155 |  |  |  | $307 |  |  |  | $1,030 |
Natural gas | 124 |  |  | 55 |  |  | 42 |  |  | 33 |  |  | 26 |  |  | 83 |  |  | 363 |
Coal (b) | 52 |  |  | 29 |  |  | 20 |  |  | 9 |  |  | 9 |  |  | — |  |  | 119 |
Other (c) | 24 |  |  | 3 |  |  | 3 |  |  | 2 |  |  | 2 |  |  | — |  |  | 34 |
|  | $344 |  |  |  | $222 |  |  |  | $214 |  |  |  | $184 |  |  |  | $192 |  |  |  | $390 |  |  |  | $1,546 |
WPL | 2019 |  | 2020 |  | 2021 |  | 2022 |  | 2023 |  | Thereafter |  | Total
Purchased power |  | $15 |  |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | $15 |
Natural gas | 130 |  |  | 96 |  |  | 77 |  |  | 61 |  |  | 41 |  |  | 113 |  |  | 518 |
Coal (b) | 50 |  |  | 20 |  |  | 6 |  |  | — |  |  | — |  |  | — |  |  | 76 |
Other (c) | 23 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | 23 |
|  | $218 |  |  |  | $116 |  |  |  | $83 |  |  |  | $61 |  |  |  | $41 |  |  |  | $113 |  |  |  | $632 |
(a) | Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased. In July 2018, IPL entered into an amendment to shorten the term of the DAEC PPA by five years in exchange for a $110 million buyout payment by IPL in September 2020, subject to IUB approval. In December 2018, IPL received an order from the IUB, which was effective in January 2019, approving recovery of the buyout payment. As a result, Alliant Energy’s and IPL’s amounts in the above table do not include the September 2020 buyout payment, and the minimum future commitments reflect IPL’s purchase of capacity and the resulting energy from DAEC through December 2025, the original term of the PPA prior to the amendment. Amounts in the above table for 2021 and beyond relate to the DAEC PPA.
(b) | Corporate Services entered into system-wide coal contracts on behalf of IPL and WPL that include minimum future commitments. These commitments were assigned to IPL and WPL based on information available as of December 31, 2018 regarding expected future usage, which is subject to change.
(c) | Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2018.

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- Definition Tabular disclosure of material liabilities for remediation, site restoration, postclosure, monitoring commitments, or other exit costs that may occur on the sale, disposal or abandonment of a property as a result of unanticipated contamination of the assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 5.Y.Q4) -URI http://asc.fasb.org/extlink&oid=27011672&loc=d3e149879-122751 + Details
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- Definition Tabular disclosure of unconditional purchase obligations that are not recognized as a liability on the balance sheet, including the nature and significant terms of an unconditional purchase obligation; the amount of the fixed and determinable portion of the obligation as of the date of the latest balance sheet presented in the aggregate and, if determinable, for each of the five succeeding fiscal years; the nature of any variable components of the obligation; the amount purchased under the obligation (for example, the take-or-pay or throughput contract) for the reporting period; and may include the amount of imputed interest necessary to reduce the obligation to present value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 440 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=77896938&loc=d3e25287-109308 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 440 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=77896938&loc=d3e25336-109308 + Details
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