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Leases (Tables) | 12 Months Ended
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Dec. 31, 2017
Schedule of Future Minimum Rental Payments for Operating Leases | At December 31, 2017, future minimum operating lease payments, excluding contingent rentals, were as follows (in millions):
| 2018 |  | 2019 |  | 2020 |  | 2021 |  | 2022 |  | Thereafter |  | Total
Alliant Energy |  | $6 |  |  |  | $5 |  |  |  | $2 |  |  |  | $2 |  |  |  | $1 |  |  |  | $13 |  |  |  | $29 |
IPL | 3 |  |  | 2 |  |  | 1 |  |  | 1 |  |  | 1 |  |  | 13 |  |  | 21 |
WPL | 3 |  |  | 3 |  |  | 1 |  |  | — |  |  | — |  |  | — |  |  | 7 |
IPL [Member] |
Schedule of Future Minimum Rental Payments for Operating Leases | At December 31, 2017, future minimum operating lease payments, excluding contingent rentals, were as follows (in millions):
| 2018 |  | 2019 |  | 2020 |  | 2021 |  | 2022 |  | Thereafter |  | Total
Alliant Energy |  | $6 |  |  |  | $5 |  |  |  | $2 |  |  |  | $2 |  |  |  | $1 |  |  |  | $13 |  |  |  | $29 |
IPL | 3 |  |  | 2 |  |  | 1 |  |  | 1 |  |  | 1 |  |  | 13 |  |  | 21 |
WPL | 3 |  |  | 3 |  |  | 1 |  |  | — |  |  | — |  |  | — |  |  | 7 |
WPL [Member] |
Schedule of Future Minimum Rental Payments for Operating Leases | At December 31, 2017, future minimum operating lease payments, excluding contingent rentals, were as follows (in millions):
| 2018 |  | 2019 |  | 2020 |  | 2021 |  | 2022 |  | Thereafter |  | Total
Alliant Energy |  | $6 |  |  |  | $5 |  |  |  | $2 |  |  |  | $2 |  |  |  | $1 |  |  |  | $13 |  |  |  | $29 |
IPL | 3 |  |  | 2 |  |  | 1 |  |  | 1 |  |  | 1 |  |  | 13 |  |  | 21 |
WPL | 3 |  |  | 3 |  |  | 1 |  |  | — |  |  | — |  |  | — |  |  | 7 |
WPL [Member] | Sheboygan Falls Energy Facility [Member] |
Schedule of Capital Lease Expense | The Sheboygan Falls Energy Facility lease expenses were included in WPL’s income statements as follows (in millions):
| 2017 |  | 2016 |  | 2015
Interest expense |  | $8.7 |  |  |  | $9.3 |  |  |  | $9.9 |
Depreciation and amortization | 6.2 |  |  | 6.2 |  |  | 6.2 |
|  | $14.9 |  |  |  | $15.5 |  |  |  | $16.1 |
Schedule of Future Minimum Lease Payments for Capital Leases | At December 31, 2017, WPL’s estimated future minimum capital lease payments for the Sheboygan Falls Energy Facility were as follows (in millions):
| 2018 |  | 2019 |  | 2020 |  | 2021 |  | 2022 |  | Thereafter |  | Total |  | Less: amount representing interest |  | Present value of minimum capital lease payments
Sheboygan Falls Energy Facility | $15 |  | $15 |  | $15 |  | $15 |  | $15 |  | $35 |  | $110 |  | $33 |  | $77

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- Definition Tabular disclosure of future minimum lease payments as of the date of the latest balance sheet presented, in aggregate and for each of the five years succeeding fiscal years, with separate deductions from the total for the amount representing executor costs, including any profit thereon, included in the minimum lease payments and for the amount of the imputed interest necessary to reduce the net minimum lease payments to present value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6455398&loc=d3e45280-112737 + Details
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- Definition Tabular disclosure of future minimum payments required in the aggregate and for each of the five succeeding fiscal years for operating leases having initial or remaining noncancelable lease terms in excess of one year and the total minimum rentals to be received in the future under noncancelable subleases as of the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 20 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6453985&loc=d3e41502-112717 + Details
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