v2.4.0.6

Fair Value Measurements (Fair Value Of Financial Instruments) (Details) (USD $) In Millions, unless otherwise specified | Sep. 30, 2012 | Dec. 31, 2011
--- | --- | ---
Capitalization and liabilities: |  |
Cumulative preferred stock of subsidiaries | $ 145.1 | $ 145.1
Cumulative preferred stock of subsidiaries | 60.0 | 60.0
Alliant Energy [Member] |  |
Assets: |  |
Money market funds, at carrying value | 13.6 | 0
Capitalization and liabilities: |  |
Long-term debt (including current maturities) | 3,598.7 |
Cumulative preferred stock of subsidiaries | 215.6 |
IPL [Member] |  |
Assets: |  |
Money market funds, at carrying value | 1.1 | 0
Deferred proceeds (sales of receivables) | 155.9 | 55.3
Capitalization and liabilities: |  |
Long-term debt (including current maturities) | 1,696.1 |
Cumulative preferred stock of subsidiaries | 145.1 | 145.1
Cumulative preferred stock of subsidiaries | 154.8 |
WPL [Member] |  |
Assets: |  |
Money market funds, at carrying value | 12.5 | 0
Capitalization and liabilities: |  |
Long-term debt (including current maturities) | 1,492.4 |
Cumulative preferred stock of subsidiaries | 60.0 | 60.0
Cumulative preferred stock of subsidiaries | 60.8 |
Carrying Amount [Member] | Alliant Energy [Member] |  |
Assets: |  |
Money market funds, at carrying value | 13.6 |
Derivative assets | 46.5 | 15.7
Deferred proceeds (sales of receivables) | 153.9 | 53.7
Capitalization and liabilities: |  |
Long-term debt (including current maturities) | 2,829.5 | 2,704.5
Cumulative preferred stock of subsidiaries | 205.1 | 205.1
Derivative liabilities | 57.3 | 78.0
Carrying Amount [Member] | IPL [Member] |  |
Assets: |  |
Money market funds, at carrying value | 1.1 |
Derivative assets | 28.1 | 10.6
Deferred proceeds (sales of receivables) | 153.9 | 53.7
Capitalization and liabilities: |  |
Long-term debt (including current maturities) | 1,359.3 | 1,309.0
Cumulative preferred stock of subsidiaries | 145.1 | 145.1
Derivative liabilities | 22.8 | 33.6
Carrying Amount [Member] | WPL [Member] |  |
Assets: |  |
Money market funds, at carrying value | 12.5 |
Derivative assets | 18.4 | 5.1
Deferred proceeds (sales of receivables) | 0 | 0
Capitalization and liabilities: |  |
Long-term debt (including current maturities) | 1,082.5 | 1,082.2
Cumulative preferred stock of subsidiaries | 60.0 | 60.0
Derivative liabilities | 34.5 | 44.4
Fair Value [Member] | Alliant Energy [Member] |  |
Assets: |  |
Money market funds, at carrying value | 13.6 |
Derivative assets | 46.5 | 15.7
Deferred proceeds (sales of receivables) | 153.9 | 53.7
Capitalization and liabilities: |  |
Long-term debt (including current maturities) | 3,598.7 | 3,325.3
Cumulative preferred stock of subsidiaries | 215.6 | 222.5
Derivative liabilities | 57.3 | 78.0
Fair Value [Member] | IPL [Member] |  |
Assets: |  |
Money market funds, at carrying value | 1.1 |
Derivative assets | 28.1 | 10.6
Deferred proceeds (sales of receivables) | 153.9 | 53.7
Capitalization and liabilities: |  |
Long-term debt (including current maturities) | 1,696.1 | 1,560.4
Cumulative preferred stock of subsidiaries | 154.8 | 164.3
Derivative liabilities | 22.8 | 33.6
Fair Value [Member] | WPL [Member] |  |
Assets: |  |
Money market funds, at carrying value | 12.5 |
Derivative assets | 18.4 | 5.1
Deferred proceeds (sales of receivables) | 0 | 0
Capitalization and liabilities: |  |
Long-term debt (including current maturities) | 1,492.4 | 1,439.0
Cumulative preferred stock of subsidiaries | 60.8 | 58.2
Derivative liabilities | $ 34.5 | $ 44.4

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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=6947722&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=6947722&loc=d3e13476-108611 + Details
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- Definition Including current and noncurrent portions, aggregate carrying amount of long-term borrowings as of the balance sheet date. May include notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, which had initial maturities beyond one year or beyond the normal operating cycle, if longer, and after deducting unamortized discount or premiums, if any. + 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 210.5-02.22) -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 210.9-03.16) -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 -Article 7 -Section 03 -Paragraph 16 Reference 4: 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 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 Investment in short-term money-market instruments (such as commercial paper, banker's acceptances, repurchase agreements, government securities, certificates of deposit, and so forth) which are highly liquid (that is, readily convertible to known amounts of cash) and so near their maturity that they present an insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify as cash equivalents by definition. Original maturity means an original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 8, 9 -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 FASB -Name Accounting Standards Codification -Glossary Cash Equivalents -URI http://asc.fasb.org/extlink&oid=6507016 + 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 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. Reference 2: 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 3: 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 4: 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 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 5 -Section 02 -Paragraph 29 + Details
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- Definition The carrying value (book value) of an entity's issued and outstanding stock which is not included within permanent equity in Stockholders Equity. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. If convertible, the issuer does not control the actions or events necessary to issue the maximum number of shares that could be required to be delivered under the conversion option if the holder exercises the option to convert the stock to another class of equity. If the security is a warrant or a rights issue, the warrant or rights issue is considered to be temporary equity if the issuer cannot demonstrate that it would be able to deliver upon the exercise of the option by the holder in all cases. Includes stock with a put option held by an ESOP and stock redeemable by a holder only in the event of a change in control of the issuer. + 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 210.5-02.27(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Emerging Issues Task Force (EITF) -Number D-98 -Paragraph 2 -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 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 4 -Section 08 -Paragraph i Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 28 -Subparagraph a -Article 5 + Details
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