Goodwill And Other Intangible Assets (Gross Carrying Amount And Accumulated Amortization Expense) (Details) (USD $) In Millions	3 Months Ended
Sep. 30, 2011 Cross State Air Pollution Rule [Member] Alliant Energy And IPL [Member]	Dec. 31, 2010 Alliant Energy Corporation [Member] RMT [Member]	Sep. 30, 2011 Alliant Energy Corporation [Member]	Dec. 31, 2010 Alliant Energy Corporation [Member]	Sep. 30, 2011 IPL [Member]	Dec. 31, 2010 IPL [Member]	Sep. 30, 2011 WPL [Member]	Dec. 31, 2010 WPL [Member]
Gross carrying amount			$ 12.6	$ 50.9	$ 12.1	$ 47.0	$ 0.5	$ 3.9
Accumulated amortization			10.7	16.5	10.2	13.1	0.5	3.4
Goodwill		3
Impairment of the intangible assets	$ 22.7

Carrying amount as of the balance sheet date, which is the cumulative amount paid and (if applicable) the fair value of any noncontrolling interest in the acquiree, adjusted for any amortization recognized prior to the adoption of any changes in generally accepted accounting principles (as applicable) and for any impairment charges, in excess of the fair value of net assets acquired in one or more business combination transactions.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 5: http://www.xbrl.org/2003/role/presentationRef

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Reference 6: http://www.xbrl.org/2003/role/presentationRef

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-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.

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