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Income Taxes (Schedule Of Uncertain Tax Positions) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011
Uncertain Tax Positions [Roll Forward] |  |  |  |  |  |
Balance, January 1 | $ 0.7 |  | $ 23.5 |  | $ 66.7 |
Additions based on tax positions related to the current year | 0 |  | 0.7 |  | 0.7 |
Reductions for tax positions of prior years (a) | (0.7) | [1] | (23.5) | [1] | (43.9) | [1]
Balance, December 31 | 0 |  | 0.7 |  | 23.5 |
Statute of Limitations, Expiration Period from Extended Due Date of Federal Tax Return | 3 years |  |  |  |  |
Statute of Limitations, Expiration Period from Extended Due Date of Iowa Tax Return | 3 years |  |  |  |  |
Statute of Limitations, Expiration Period from Extended Due Date of Wisconsin Tax Return | 4 years |  |  |  |  |
IPL [Member] |  |  |  |  |  |
Uncertain Tax Positions [Roll Forward] |  |  |  |  |  |
Balance, January 1 | 0 |  | 10.9 |  | 33.0 |
Additions based on tax positions related to the current year | 0 |  | 0 |  | 0.1 |
Reductions for tax positions of prior years (a) | 0 | [1] | (10.9) | [1] | (22.2) | [1]
Balance, December 31 | 0 |  | 0 |  | 10.9 |
WPL [Member] |  |  |  |  |  |
Uncertain Tax Positions [Roll Forward] |  |  |  |  |  |
Balance, January 1 | 0.7 |  | 12.6 |  | 33.7 |
Additions based on tax positions related to the current year | 0 |  | 0.7 |  | 0.6 |
Reductions for tax positions of prior years (a) | (0.7) | [1] | (12.6) | [1] | (21.7) | [1]
Balance, December 31 | $ 0 |  | $ 0.7 |  | $ 12.6 |
[1] | In 2012, the reductions for tax positions of prior years were due to the finalization of Alliant Energy’s federal income tax return audits for calendar years 2005 through 2009. In 2011, the reductions for tax positions of prior years were related to guidance published by the IRS clarifying the treatment of repairs expenditures for electric distribution property.

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- Definition Amount of unrecognized tax benefits pertaining to uncertain tax positions taken in tax returns. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Unrecognized Tax Benefit -URI http://asc.fasb.org/extlink&oid=6527854 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319 + Details
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- Definition Amount of decrease in unrecognized tax benefits resulting from tax positions taken in prior period tax returns. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319 + Details
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