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Commitments And Contingencies (Tables) | 12 Months Ended
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Dec. 31, 2016
Long-term Purchase Commitment [Line Items] |
Operating Expense Purchase Obligations | At December 31, 2016, minimum future commitments related to these operating expense purchase obligations were as follows (in millions):
Alliant Energy | 2017 |  | 2018 |  | 2019 |  | 2020 |  | 2021 |  | Thereafter |  | Total
Purchased power (a) |  | $185 |  |  |  | $189 |  |  |  | $159 |  |  |  | $137 |  |  |  | $149 |  |  |  | $599 |  |  |  | $1,418 |
Natural gas | 223 |  |  | 142 |  |  | 115 |  |  | 98 |  |  | 69 |  |  | 124 |  |  | 771 |
Coal (b) | 105 |  |  | 54 |  |  | 18 |  |  | — |  |  | — |  |  | — |  |  | 177 |
Other (c) | 16 |  |  | 4 |  |  | 5 |  |  | 2 |  |  | 2 |  |  | 5 |  |  | 34 |
|  | $529 |  |  |  | $389 |  |  |  | $297 |  |  |  | $237 |  |  |  | $220 |  |  |  | $728 |  |  |  | $2,400 |
IPL | 2017 |  | 2018 |  | 2019 |  | 2020 |  | 2021 |  | Thereafter |  | Total
Purchased power (a) |  | $138 |  |  |  | $131 |  |  |  | $144 |  |  |  | $137 |  |  |  | $149 |  |  |  | $599 |  |  |  | $1,298 |
Natural gas | 120 |  |  | 74 |  |  | 55 |  |  | 39 |  |  | 23 |  |  | 71 |  |  | 382 |
Coal (b) | 49 |  |  | 19 |  |  | 9 |  |  | — |  |  | — |  |  | — |  |  | 77 |
Other (c) | 15 |  |  | 1 |  |  | 1 |  |  | — |  |  | — |  |  | — |  |  | 17 |
|  | $322 |  |  |  | $225 |  |  |  | $209 |  |  |  | $176 |  |  |  | $172 |  |  |  | $670 |  |  |  | $1,774 |
WPL | 2017 |  | 2018 |  | 2019 |  | 2020 |  | 2021 |  | Thereafter |  | Total
Purchased power (a) |  | $47 |  |  |  | $58 |  |  |  | $15 |  |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | $120 |
Natural gas | 103 |  |  | 68 |  |  | 60 |  |  | 59 |  |  | 46 |  |  | 53 |  |  | 389 |
Coal (b) | 56 |  |  | 35 |  |  | 9 |  |  | — |  |  | — |  |  | — |  |  | 100 |
Other (c) | — |  |  | 1 |  |  | 1 |  |  | — |  |  | — |  |  | — |  |  | 2 |
|  | $206 |  |  |  | $162 |  |  |  | $85 |  |  |  | $59 |  |  |  | $46 |  |  |  | $53 |  |  |  | $611 |
(a) | Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased.
(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, 2016 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, 2016.
Schedule of Environmental Liabilities | At December 31, 2016, 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, were as follows (in millions). At December 31, 2016, such amounts for WPL were not material.
| Alliant Energy |  | IPL
Range of estimated future costs |  | $14 |  | - | $27 |  |  | $12 |  | - | $24
Current and non-current environmental liabilities | 16 |  | 13
IPL [Member] |
Long-term Purchase Commitment [Line Items] |
Operating Expense Purchase Obligations | At December 31, 2016, minimum future commitments related to these operating expense purchase obligations were as follows (in millions):
Alliant Energy | 2017 |  | 2018 |  | 2019 |  | 2020 |  | 2021 |  | Thereafter |  | Total
Purchased power (a) |  | $185 |  |  |  | $189 |  |  |  | $159 |  |  |  | $137 |  |  |  | $149 |  |  |  | $599 |  |  |  | $1,418 |
Natural gas | 223 |  |  | 142 |  |  | 115 |  |  | 98 |  |  | 69 |  |  | 124 |  |  | 771 |
Coal (b) | 105 |  |  | 54 |  |  | 18 |  |  | — |  |  | — |  |  | — |  |  | 177 |
Other (c) | 16 |  |  | 4 |  |  | 5 |  |  | 2 |  |  | 2 |  |  | 5 |  |  | 34 |
|  | $529 |  |  |  | $389 |  |  |  | $297 |  |  |  | $237 |  |  |  | $220 |  |  |  | $728 |  |  |  | $2,400 |
IPL | 2017 |  | 2018 |  | 2019 |  | 2020 |  | 2021 |  | Thereafter |  | Total
Purchased power (a) |  | $138 |  |  |  | $131 |  |  |  | $144 |  |  |  | $137 |  |  |  | $149 |  |  |  | $599 |  |  |  | $1,298 |
Natural gas | 120 |  |  | 74 |  |  | 55 |  |  | 39 |  |  | 23 |  |  | 71 |  |  | 382 |
Coal (b) | 49 |  |  | 19 |  |  | 9 |  |  | — |  |  | — |  |  | — |  |  | 77 |
Other (c) | 15 |  |  | 1 |  |  | 1 |  |  | — |  |  | — |  |  | — |  |  | 17 |
|  | $322 |  |  |  | $225 |  |  |  | $209 |  |  |  | $176 |  |  |  | $172 |  |  |  | $670 |  |  |  | $1,774 |
WPL | 2017 |  | 2018 |  | 2019 |  | 2020 |  | 2021 |  | Thereafter |  | Total
Purchased power (a) |  | $47 |  |  |  | $58 |  |  |  | $15 |  |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | $120 |
Natural gas | 103 |  |  | 68 |  |  | 60 |  |  | 59 |  |  | 46 |  |  | 53 |  |  | 389 |
Coal (b) | 56 |  |  | 35 |  |  | 9 |  |  | — |  |  | — |  |  | — |  |  | 100 |
Other (c) | — |  |  | 1 |  |  | 1 |  |  | — |  |  | — |  |  | — |  |  | 2 |
|  | $206 |  |  |  | $162 |  |  |  | $85 |  |  |  | $59 |  |  |  | $46 |  |  |  | $53 |  |  |  | $611 |
(a) | Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased.
(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, 2016 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, 2016.
Schedule of Environmental Liabilities | At December 31, 2016, 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, were as follows (in millions). At December 31, 2016, such amounts for WPL were not material.
| Alliant Energy |  | IPL
Range of estimated future costs |  | $14 |  | - | $27 |  |  | $12 |  | - | $24
Current and non-current environmental liabilities | 16 |  | 13
WPL [Member] |
Long-term Purchase Commitment [Line Items] |
Operating Expense Purchase Obligations | At December 31, 2016, minimum future commitments related to these operating expense purchase obligations were as follows (in millions):
Alliant Energy | 2017 |  | 2018 |  | 2019 |  | 2020 |  | 2021 |  | Thereafter |  | Total
Purchased power (a) |  | $185 |  |  |  | $189 |  |  |  | $159 |  |  |  | $137 |  |  |  | $149 |  |  |  | $599 |  |  |  | $1,418 |
Natural gas | 223 |  |  | 142 |  |  | 115 |  |  | 98 |  |  | 69 |  |  | 124 |  |  | 771 |
Coal (b) | 105 |  |  | 54 |  |  | 18 |  |  | — |  |  | — |  |  | — |  |  | 177 |
Other (c) | 16 |  |  | 4 |  |  | 5 |  |  | 2 |  |  | 2 |  |  | 5 |  |  | 34 |
|  | $529 |  |  |  | $389 |  |  |  | $297 |  |  |  | $237 |  |  |  | $220 |  |  |  | $728 |  |  |  | $2,400 |
IPL | 2017 |  | 2018 |  | 2019 |  | 2020 |  | 2021 |  | Thereafter |  | Total
Purchased power (a) |  | $138 |  |  |  | $131 |  |  |  | $144 |  |  |  | $137 |  |  |  | $149 |  |  |  | $599 |  |  |  | $1,298 |
Natural gas | 120 |  |  | 74 |  |  | 55 |  |  | 39 |  |  | 23 |  |  | 71 |  |  | 382 |
Coal (b) | 49 |  |  | 19 |  |  | 9 |  |  | — |  |  | — |  |  | — |  |  | 77 |
Other (c) | 15 |  |  | 1 |  |  | 1 |  |  | — |  |  | — |  |  | — |  |  | 17 |
|  | $322 |  |  |  | $225 |  |  |  | $209 |  |  |  | $176 |  |  |  | $172 |  |  |  | $670 |  |  |  | $1,774 |
WPL | 2017 |  | 2018 |  | 2019 |  | 2020 |  | 2021 |  | Thereafter |  | Total
Purchased power (a) |  | $47 |  |  |  | $58 |  |  |  | $15 |  |  |  | $— |  |  |  | $— |  |  |  | $— |  |  |  | $120 |
Natural gas | 103 |  |  | 68 |  |  | 60 |  |  | 59 |  |  | 46 |  |  | 53 |  |  | 389 |
Coal (b) | 56 |  |  | 35 |  |  | 9 |  |  | — |  |  | — |  |  | — |  |  | 100 |
Other (c) | — |  |  | 1 |  |  | 1 |  |  | — |  |  | — |  |  | — |  |  | 2 |
|  | $206 |  |  |  | $162 |  |  |  | $85 |  |  |  | $59 |  |  |  | $46 |  |  |  | $53 |  |  |  | $611 |
(a) | Includes payments required by PPAs for capacity rights and minimum quantities of MWhs required to be purchased.
(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, 2016 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, 2016.

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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=73718637&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=73718637&loc=d3e25336-109308 + Details
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