Common Equity (Capital Transactions With Subsidiaries) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Common stock dividends to Alliant Energy	$ 188.1	$ 174.6	$ 165.5
IPL [Member]
Common stock dividends to Alliant Energy	73.4
Repayments of capital to Alliant Energy	100.7	118.2	106.1
Total distributions from common equity	174.1	118.2	106.1
WPL [Member]
Common stock dividends to Alliant Energy	112.1	109.5	91.0
Total distributions from common equity	112.1	109.5	91.0
Resources [Member]
Repayments of capital to Alliant Energy		65.0	100.0
Total distributions from common equity		$ 65.0	$ 100.0