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Fair Value Measurements (Fair Value Of Financial Instruments) (Details) (USD $) In Millions, unless otherwise specified | Sep. 30, 2014 | Dec. 31, 2013
--- | --- | ---
Assets: |  |
Derivative assets | $ 83.1 | $ 26.7
Deferred proceeds (sales of receivables) | 160.3 | 203.5
Capitalization and liabilities: |  |
Long-term debt (including current maturities) | 3,852.6 | 3,712.3
Cumulative preferred stock | 200.0 | 200.0
Cumulative preferred stock | 200.2 | 167.0
Derivative liabilities | 14.1 | 20.8
IPL [Member] |  |
Assets: |  |
Derivative assets | 44.7 | 21.1
Deferred proceeds (sales of receivables) | 160.3 | 203.5
Capitalization and liabilities: |  |
Long-term debt (including current maturities) | 1,778.2 | 1,726.4
Cumulative preferred stock | 200.0 | 200.0
Cumulative preferred stock | 200.2 | 167.0
Derivative liabilities | 8.2 | 5.2
WPL [Member] |  |
Assets: |  |
Derivative assets | 38.4 | 5.6
Capitalization and liabilities: |  |
Long-term debt (including current maturities) | 1,618.0 | 1,532.9
Derivative liabilities | 5.9 | 15.6
Carrying Amount [Member] |  |
Assets: |  |
Derivative assets | 83.1 | 26.7
Deferred proceeds (sales of receivables) | 160.3 | 203.5
Capitalization and liabilities: |  |
Long-term debt (including current maturities) | 3,292.3 | 3,336.3
Cumulative preferred stock | 200.0 | 200.0
Derivative liabilities | 14.1 | 20.8
Carrying Amount [Member] | IPL [Member] |  |
Assets: |  |
Derivative assets | 44.7 | 21.1
Deferred proceeds (sales of receivables) | 160.3 | 203.5
Capitalization and liabilities: |  |
Long-term debt (including current maturities) | 1,520.3 | 1,558.4
Cumulative preferred stock | 200.0 | 200.0
Derivative liabilities | 8.2 | 5.2
Carrying Amount [Member] | WPL [Member] |  |
Assets: |  |
Derivative assets | 38.4 | 5.6
Capitalization and liabilities: |  |
Long-term debt (including current maturities) | 1,324.0 | 1,332.1
Derivative liabilities | 5.9 | 15.6
Fair Value [Member] |  |
Assets: |  |
Derivative assets | 83.1 | 26.7
Deferred proceeds (sales of receivables) | 160.3 | 203.5
Capitalization and liabilities: |  |
Long-term debt (including current maturities) | 3,852.6 | 3,712.3
Cumulative preferred stock | 200.2 | 167.0
Derivative liabilities | 14.1 | 20.8
Fair Value [Member] | IPL [Member] |  |
Assets: |  |
Derivative assets | 44.7 | 21.1
Deferred proceeds (sales of receivables) | 160.3 | 203.5
Capitalization and liabilities: |  |
Long-term debt (including current maturities) | 1,778.2 | 1,726.4
Cumulative preferred stock | 200.2 | 167.0
Derivative liabilities | 8.2 | 5.2
Fair Value [Member] | WPL [Member] |  |
Assets: |  |
Derivative assets | 38.4 | 5.6
Capitalization and liabilities: |  |
Long-term debt (including current maturities) | 1,618.0 | 1,532.9
Derivative liabilities | $ 5.9 | $ 15.6

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- Definition Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 16 -Article 7 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.16) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 16 -Article 9 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 20, 22 -Article 5 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.16) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 + Details
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