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Summary Of Significant Accounting Policies (Narrative) (Details) (USD $) In Millions, unless otherwise specified | 9 Months Ended
--- | ---
Sep. 30, 2013 | Sep. 30, 2012
Public Utility, Property, Plant and Equipment [Line Items] |  |
Regulatory liabilities utilized | $ (74.9) | $ 5.0
Increase in regulatory assets | 14.4 | 73.5
Wholesale power supply agreement termination notice minimum term (in years) | 5 years |
Wholesale power supply agreement minimum term (in years) | 10 years |
Alliant Energy and IPL [Member] | IPL's tax benefit riders [Member] |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |
Regulatory liabilities utilized | 67.0 |
IPL [Member] |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |
Regulatory liabilities utilized | (68.3) | (27.5)
Increase in regulatory assets | 9.8 | 57.7
IPL [Member] | Electric tax benefit rider [Member] |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |
Regulatory liabilities utilized | 59.0 |
IPL [Member] | Gas tax benefit rider [Member] |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |
Regulatory liabilities utilized | 8.0 |
WPL [Member] |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |
Regulatory liabilities utilized | (6.6) | 32.5
Increase in regulatory assets | 4.6 | 15.8
Wpl's Edgewater Unit 5 Purchase [Member] | WPL [Member] |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |
Jointly owned utility plant, proportionate ownership share | 25.00% |
2013 and 2014 Test Period Retail Electric And Gas Final Order [Member] | Alliant Energy and WPL [Member] |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |
Increase in regulatory assets |  | 5.0
Credit to utility other operation and maintenance |  | 5
IPL FERC Authorized Return On Common Equity [Member] | IPL [Member] |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |
Return on common equity wholesale electric rate | 10.97% |
Scenario, Forecast [Member] | IPL [Member] |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |
Expected proceeds from asset sales | $ 128 |

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- Definition The increase (decrease) during the reporting period in the value of other assets that are created when regulatory agencies permits public utilities to defer costs to the balance sheet. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 -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 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3602-108585 + Details
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- Definition The increase (decrease) during the reporting period in regulated liabilities. Regulated liabilities are created when regulatory agency permits an entity to defer revenues to the balance sheet. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 28 -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 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3602-108585 + Details
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- Definition The cash inflow from the sale of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Investing Activities -URI http://asc.fasb.org/extlink&oid=6516133 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 15 -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 FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 12 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3179-108585 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 95 -Paragraph 16 -Subparagraph c -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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