Common Equity And Preferred Stock (Capital Transactions With Subsidiaries) (Details) (USD $) In Millions	9 Months Ended
Sep. 30, 2011	Sep. 30, 2010
Common stock dividends to Alliant Energy	$ 141.1	$ 130.9
IPL [Member]
Common stock dividends to Alliant Energy	43.7
Repayments of capital to Alliant Energy	100.7	88.5
WPL [Member]
Common stock dividends to Alliant Energy	$ 83.3	$ 82.2

The cash outflow from the distribution of an entity's earnings in the form of dividends to common shareholders.

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

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-Name Accounting Standards Codification

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

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