Property, Plant and Equipment (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended															12 Months Ended							12 Months Ended		12 Months Ended										12 Months Ended		12 Months Ended
	Dec. 31, 2013 MW	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 IPL [Member]	Dec. 31, 2012 IPL [Member]	Dec. 31, 2011 IPL [Member]	Dec. 31, 2013 WPL [Member]	Dec. 31, 2012 WPL [Member]	Dec. 31, 2011 WPL [Member]	Dec. 31, 2013 Franklin County Wind Project [Member]	Dec. 31, 2013 Sheboygan Falls Energy Facility [Member]	Dec. 31, 2013 Non-Regulated [Member] Minimum [Member]	Dec. 31, 2013 Non-Regulated [Member] Maximum [Member]	Dec. 31, 2011 Green Lake And Fond Du Lac Counties Wind Site [Member] WPL [Member]	Dec. 31, 2013 Whispering Willow - East Wind Project [Member]	Dec. 31, 2013 Whispering Willow - East Wind Project [Member] IPL [Member]	Dec. 31, 2009 Whispering Willow - East Wind Project [Member] IPL [Member] MW	Dec. 31, 2011 Whispering Willow - East Wind Project [Member] Alliant Energy and IPL [Member]	Dec. 31, 2013 Vestas Wind Turbine Generators [Member] MW	Dec. 31, 2013 Franklin County Wind Project [Member] MW	Dec. 31, 2011 Franklin County Wind Project [Member] MW	Dec. 31, 2013 George Neal Unit 3 [Member] IPL [Member]	Dec. 31, 2013 George Neal Unit 3 [Member] Alliant Energy and IPL [Member]	Dec. 31, 2013 George Neal Unit 4 [Member] IPL [Member]	Dec. 31, 2013 George Neal Unit 4 [Member] Alliant Energy and IPL [Member]	Dec. 31, 2013 Columbia Units 1-2 [Member] WPL [Member]	Dec. 31, 2012 Columbia Units 1-2 [Member] WPL [Member]	Dec. 31, 2011 Columbia Units 1-2 [Member] WPL [Member]	Dec. 31, 2013 Columbia Units 1-2 [Member] Alliant Energy and WPL [Member]	Dec. 31, 2013 IPL (FERC formula) [Member] IPL [Member]	Dec. 31, 2013 Franklin County Iowa Wind Site [Member] IPL [Member] MW	Dec. 31, 2007 Franklin County Iowa Wind Site [Member] IPL [Member] MW	Dec. 31, 2013 Bent Tree - Phase I Wind Project [Member] Whispering Willow - East Wind Project [Member] IPL and WPL [Member] MW	Dec. 31, 2013 Minnesota [Member] Whispering Willow - East Wind Project [Member] IPL [Member]	Dec. 31, 2011 Franklin County Wind Project [Member] IPL [Member]	Dec. 31, 2013 Ottumwa Unit 1 [Member] IPL [Member]	Dec. 31, 2013 Ottumwa Unit 1 [Member] Alliant Energy and IPL [Member]	Dec. 31, 2013 Scenario, Forecast [Member] IPL [Member]
Property, Plant and Equipment [Line Items]
Wind site capacity (in megawatts)																	200				100										200	500
Other property, plant and equipment	$ 22.3	$ 21.2		$ 21.2	$ 19.8		$ 1.1	$ 1.4																							$ 13.0
Disallowance of project costs																8
Project costs allocated by jurisdiction																																		30
Asset impairment charges														5				8
Electric plant	9,415.7	9,070.7		5,034.9	4,815.2		4,380.8	4,255.5							7.0									61.0	57.0
Wind EGU capacity (in megawatts)																			500	99													401
Proceeds from sale of wind project assets to affiliate				0	0	115.3																													115.3
Purchase of development rights	100
Ownership interest %																						28.00%		25.695%		46.20%										48.00%
Allowance for funds used during construction	30.8	21.9	12.0	21.0	8.4	5.8	9.8	13.5	6.2														2.0		4.0	7.2	3.9	0.2	11.0								10.0
George Neal Generating Station Unit 3 emission controls (IPL)	54.6	26.5		54.6	26.5																		53.0
Ottumwa Generating Station Unit 1 emission controls (IPL)	135.1	73.7		135.1	73.7																																125.0
Columbia Energy Center Units 1 and 2 emission controls (WPL)	265.0	130.4					265.0	130.4																					254.0
Expected proceeds from assets sales																																						128
Wholesale power supply agreement termination notice term				5 years
Wholesale power supply agreement term				10 years
Authorized return on common equity																														10.97%
Property, plant and equipment, useful life										30 years	35 years	5 years	30 years
Non-regulated Generation property, plant and equipment	$ 249.4	$ 258.6								$ 142.0	$ 107.0