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Debt (Credit Facilities) (Details) - USD ($) $ in Millions | 6 Months Ended |
--- | --- | ---
Jun. 30, 2015 | Dec. 31, 2014
Commercial paper: |  |  |
Amount outstanding |  | $ 120.9 | $ 141.3
Weighted average remaining maturity (in days) |  | 6 days |
Weighted average interest rates |  | 0.40% |
Available credit facility capacity | [1] | $ 767.9 |
Commercial paper, long-term |  | 111.2 |
Parent Company [Member] |  |  |
Commercial paper: |  |  |
Amount outstanding |  | $ 120.9 |
Weighted average remaining maturity (in days) |  | 6 days |
Weighted average interest rates |  | 0.40% |
Available credit facility capacity | [1] | $ 179.1 |
IPL [Member] |  |  |
Commercial paper: |  |  |
Amount outstanding |  | 0.0 |
Available credit facility capacity | [1] | 188.8 |
WPL [Member] |  |  |
Commercial paper: |  |  |
Amount outstanding |  | 0.0 |
Available credit facility capacity | [1] | $ 400.0 |
[1] | Alliant Energy’s and IPL’s available credit facility capacities reflect outstanding commercial paper classified as both short- and long-term debt at June 30, 2015. Refer to Note 7(b) for further discussion of $111.2 million of commercial paper outstanding at June 30, 2015 classified as long-term debt on Alliant Energy’s and IPL’s balance sheets.

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- Definition Carrying value as of the balance sheet date of short-term borrowings using unsecured obligations issued by banks, corporations and other borrowers to investors. The maturities of these money market securities generally do not exceed 270 days. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(a)(3)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.13(2)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19 -Subparagraph a(3) -Article 5 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 16 -Article 7 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 13 -Subparagraph 2 -Article 9 + Details
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