Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Other, accum depr.	$ 5.6	$ 5.6
Non-regulated Generation, accum. depr.	40.0	31.0
Alliant Energy Corporate Services, Inc. and other, accum. depr.	214.2	200.2
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	240,000,000	240,000,000
Common stock, shares outstanding (in shares)	110,943,669	110,987,400
Shares in deferred compensation trust (in shares)	227,469	216,030
Shares in deferred compensation trust, weighted average cost per share (in dollars per share)	$ 35.25	$ 33.61
IPL [Member]
Other, accum depr.	4.1	4.1
Common stock, par value (in dollars per share)	$ 2.50	$ 2.50
Common stock, shares authorized (in shares)	24,000,000	24,000,000
Common stock, shares outstanding (in shares)	13,370,788	13,370,788
WPL [Member]
Leased Sheboygan Falls Energy Facility, accum. depr.	52.9	46.7
Other, accum depr.	$ 1.5	$ 1.5
Common stock, par value (in dollars per share)	$ 5	$ 5
Common stock, shares authorized (in shares)	18,000,000	18,000,000
Common stock, shares outstanding (in shares)	13,236,601	13,236,601