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Fair Value Measurements (Fair Value Of Financial Instruments) (Details) (USD $) In Millions, unless otherwise specified | Jun. 30, 2013 | Dec. 31, 2012
--- | --- | ---
Assets: |  |
Derivative assets | $ 60.5 | $ 26.2
Deferred proceeds (sales of receivables) | 69.3 | 66.8
Capitalization and liabilities: |  |
Long-term debt (including current maturities) | 3,619.5 | 3,860.5
Cumulative preferred stock | 200.0 | 145.1
Cumulative preferred stock | 188.4 |
Cumulative preferred stock | 0 | 60.0
Cumulative preferred stock |  | 212.6
Derivative liabilities | 37.1 | 40.4
IPL [Member] |  |
Assets: |  |
Derivative assets | 45.1 | 17.5
Deferred proceeds (sales of receivables) | 69.3 | 66.8
Capitalization and liabilities: |  |
Long-term debt (including current maturities) | 1,586.8 | 1,679.9
Cumulative preferred stock | 200.0 | 145.1
Cumulative preferred stock | 188.4 | 151.8
Derivative liabilities | 9.7 | 16.1
WPL [Member] |  |
Assets: |  |
Derivative assets | 15.4 | 8.7
Capitalization and liabilities: |  |
Long-term debt (including current maturities) | 1,572.1 | 1,713.3
Cumulative preferred stock | 0 | 60.0
Cumulative preferred stock | 0 | 60.8
Derivative liabilities | 27.4 | 24.3
Carrying Amount [Member] |  |
Assets: |  |
Derivative assets | 60.5 | 26.2
Deferred proceeds (sales of receivables) | 69.3 | 66.8
Capitalization and liabilities: |  |
Long-term debt (including current maturities) | 3,142.9 | 3,138.1
Cumulative preferred stock | 200.0 |
Cumulative preferred stock |  | 205.1
Derivative liabilities | 37.1 | 40.4
Carrying Amount [Member] | IPL [Member] |  |
Assets: |  |
Derivative assets | 45.1 | 17.5
Deferred proceeds (sales of receivables) | 69.3 | 66.8
Capitalization and liabilities: |  |
Long-term debt (including current maturities) | 1,364.7 | 1,359.5
Cumulative preferred stock | 200.0 | 145.1
Derivative liabilities | 9.7 | 16.1
Carrying Amount [Member] | WPL [Member] |  |
Assets: |  |
Derivative assets | 15.4 | 8.7
Deferred proceeds (sales of receivables) | 0 | 0
Capitalization and liabilities: |  |
Long-term debt (including current maturities) | 1,331.9 | 1,331.5
Cumulative preferred stock | 0 | 60.0
Derivative liabilities | 27.4 | 24.3
Fair Value [Member] |  |
Assets: |  |
Derivative assets | 60.5 | 26.2
Deferred proceeds (sales of receivables) | 69.3 | 66.8
Capitalization and liabilities: |  |
Long-term debt (including current maturities) | 3,619.5 | 3,860.5
Cumulative preferred stock | 188.4 |
Cumulative preferred stock |  | 212.6
Derivative liabilities | 37.1 | 40.4
Fair Value [Member] | IPL [Member] |  |
Assets: |  |
Derivative assets | 45.1 | 17.5
Deferred proceeds (sales of receivables) | 69.3 | 66.8
Capitalization and liabilities: |  |
Long-term debt (including current maturities) | 1,586.8 | 1,679.9
Cumulative preferred stock | 188.4 | 151.8
Derivative liabilities | 9.7 | 16.1
Fair Value [Member] | WPL [Member] |  |
Assets: |  |
Derivative assets | 15.4 | 8.7
Deferred proceeds (sales of receivables) | 0 | 0
Capitalization and liabilities: |  |
Long-term debt (including current maturities) | 1,572.1 | 1,713.3
Cumulative preferred stock | 0 | 60.8
Derivative liabilities | $ 27.4 | $ 24.3

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- Definition This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13433-108611 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13476-108611 + Details
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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 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.16) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 4: 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 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 16 -Article 9 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 20, 22 -Article 5 + Details
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- Definition Aggregate par or stated value of issued nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer). This item includes treasury stock repurchased by the entity. Note: elements for number of nonredeemable preferred shares, par value and other disclosure concepts are in another section within stockholders' equity. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Principles Board Opinion (APB) -Number 12 -Paragraph 10 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=6959260&loc=d3e187085-122770 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 29 -Article 5 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.28) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 129 -Paragraph 2, 3, 4, 5, 6, 7, 8 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
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