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Leases (Tables) | 12 Months Ended
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Dec. 31, 2014
Schedule of Operating Lease Rent Expense | Rental expenses associated with operating leases were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2014 |  | 2013 |  | 2012 |  | 2014 |  | 2013 |  | 2012 |  | 2014 |  | 2013 |  | 2012
Operating lease rental expenses (excluding contingent rentals) |  | $12 |  |  |  | $9 |  |  |  | $69 |  |  |  | $4 |  |  |  | $4 |  |  |  | $4 |  |  |  | $7 |  |  |  | $5 |  |  |  | $64 |
Contingent rentals (primarily related to the Riverside PPA) | — |  |  | — |  |  | 6 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | 5 |
|  | $12 |  |  |  | $9 |  |  |  | $75 |  |  |  | $4 |  |  |  | $4 |  |  |  | $4 |  |  |  | $7 |  |  |  | $5 |  |  |  | $69 |
Schedule of Future Minimum Rental Payments for Operating Leases | At December 31, 2014, future minimum operating lease payments, excluding contingent rentals, were as follows (in millions):
| 2015 |  | 2016 |  | 2017 |  | 2018 |  | 2019 |  | Thereafter |  | Total
Alliant Energy |  | $8 |  |  |  | $7 |  |  |  | $3 |  |  |  | $2 |  |  |  | $1 |  |  |  | $21 |  |  |  | $42 |
IPL | 3 |  |  | 2 |  |  | 2 |  |  | 1 |  |  | 1 |  |  | 15 |  |  | 24 |
WPL | 4 |  |  | 5 |  |  | 1 |  |  | — |  |  | — |  |  | — |  |  | 10 |
IPL [Member] |
Schedule of Operating Lease Rent Expense | Rental expenses associated with operating leases were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2014 |  | 2013 |  | 2012 |  | 2014 |  | 2013 |  | 2012 |  | 2014 |  | 2013 |  | 2012
Operating lease rental expenses (excluding contingent rentals) |  | $12 |  |  |  | $9 |  |  |  | $69 |  |  |  | $4 |  |  |  | $4 |  |  |  | $4 |  |  |  | $7 |  |  |  | $5 |  |  |  | $64 |
Contingent rentals (primarily related to the Riverside PPA) | — |  |  | — |  |  | 6 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | 5 |
|  | $12 |  |  |  | $9 |  |  |  | $75 |  |  |  | $4 |  |  |  | $4 |  |  |  | $4 |  |  |  | $7 |  |  |  | $5 |  |  |  | $69 |
Schedule of Future Minimum Rental Payments for Operating Leases | At December 31, 2014, future minimum operating lease payments, excluding contingent rentals, were as follows (in millions):
| 2015 |  | 2016 |  | 2017 |  | 2018 |  | 2019 |  | Thereafter |  | Total
Alliant Energy |  | $8 |  |  |  | $7 |  |  |  | $3 |  |  |  | $2 |  |  |  | $1 |  |  |  | $21 |  |  |  | $42 |
IPL | 3 |  |  | 2 |  |  | 2 |  |  | 1 |  |  | 1 |  |  | 15 |  |  | 24 |
WPL | 4 |  |  | 5 |  |  | 1 |  |  | — |  |  | — |  |  | — |  |  | 10 |
WPL [Member] |
Schedule of Operating Lease Rent Expense | Rental expenses associated with operating leases were as follows (in millions):
| Alliant Energy |  | IPL |  | WPL
| 2014 |  | 2013 |  | 2012 |  | 2014 |  | 2013 |  | 2012 |  | 2014 |  | 2013 |  | 2012
Operating lease rental expenses (excluding contingent rentals) |  | $12 |  |  |  | $9 |  |  |  | $69 |  |  |  | $4 |  |  |  | $4 |  |  |  | $4 |  |  |  | $7 |  |  |  | $5 |  |  |  | $64 |
Contingent rentals (primarily related to the Riverside PPA) | — |  |  | — |  |  | 6 |  |  | — |  |  | — |  |  | — |  |  | — |  |  | — |  |  | 5 |
|  | $12 |  |  |  | $9 |  |  |  | $75 |  |  |  | $4 |  |  |  | $4 |  |  |  | $4 |  |  |  | $7 |  |  |  | $5 |  |  |  | $69 |
Schedule of Future Minimum Rental Payments for Operating Leases | At December 31, 2014, future minimum operating lease payments, excluding contingent rentals, were as follows (in millions):
| 2015 |  | 2016 |  | 2017 |  | 2018 |  | 2019 |  | Thereafter |  | Total
Alliant Energy |  | $8 |  |  |  | $7 |  |  |  | $3 |  |  |  | $2 |  |  |  | $1 |  |  |  | $21 |  |  |  | $42 |
IPL | 3 |  |  | 2 |  |  | 2 |  |  | 1 |  |  | 1 |  |  | 15 |  |  | 24 |
WPL | 4 |  |  | 5 |  |  | 1 |  |  | — |  |  | — |  |  | — |  |  | 10 |
WPL [Member] | Sheboygan Falls Energy Facility [Member] |
Schedule of Capital Lease Expense | Sheboygan Falls lease expenses were included in WPL’s income statements as follows (in millions):
| 2014 |  | 2013 |  | 2012
Interest expense |  | $10.4 |  |  |  | $10.9 |  |  |  | $11.3 |
Depreciation and amortization | 6.2 |  |  | 6.2 |  |  | 6.2 |
|  | $16.6 |  |  |  | $17.1 |  |  |  | $17.5 |
Schedule of Future Minimum Lease Payments for Capital Leases | At December 31, 2014, WPL’s estimated future minimum capital lease payments for Sheboygan Falls were as follows (in millions):
| 2015 |  | 2016 |  | 2017 |  | 2018 |  | 2019 |  | Thereafter |  | Total |  | Less: amount representing interest |  | Present value of minimum capital lease payments
Sheboygan Falls | $15 |  | $15 |  | $15 |  | $15 |  | $15 |  | $83 |  | $158 |  | $63 |  | $95

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- Definition Tabular disclosure of a lessee's leasing arrangements including: (1) the basis on which contingent rental payments are determined, (2) the existence and terms of renewal or purchase options and escalation clauses, (3) restrictions imposed by lease arrangements, such as those concerning dividends, additional debt, and further leasing, (4) rent holidays, rent concessions, or leasehold improvement incentives and unusual provisions or conditions. Disclosure may also include the specific period used to amortize material leasehold improvements made at the inception of the lease or during the lease term. Additionally, for operating leases having initial or remaining noncancelable lease terms in excess of one year: (a) future minimum rental payments required as of the date of the latest balance sheet presented, in the aggregate and for each of the five succeeding fiscal years, (b) the total of minimum rentals to be received in the future under noncancelable subleases as of the date of the latest balance sheet presented, and (c) for all operating leases, rental expense for each period for which an income statement is presented, with separate amounts for minimum rentals, contingent rentals, and sublease rentals. Rental payments under leases with terms of a month or less that were not renewed need not be included. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 460 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=6851643&loc=d3e12069-110248 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6452660&loc=d3e36991-112694 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6453985&loc=d3e41499-112717 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 10 -Section 55 -Paragraph 40 -Subparagraph (Note 1,3) -URI http://asc.fasb.org/extlink&oid=6584154&loc=d3e38371-112697 Reference 5: 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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