Selected Consolidated Quarterly Financial Data (Unaudited) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating revenues	$ 832.6	$ 866.6	$ 718.0	$ 859.6	$ 750.9	$ 887.6	$ 690.3	$ 765.7	$ 3,276.8	$ 3,094.5	$ 3,221.4
Operating income	108.6	201.4	103.2	120.7	101.6	213.7	108.8	95.6	533.9	519.7	513.3
Income from continuing operations, net of tax	66.5	158.9	65.9	72.9	71.1	149.0	65.5	39.3	364.2	324.9	323.1
Income (loss) from discontinued operations, net of tax	(1.0)	(1.3)	(0.6)	(3.0)	(2.8)	1.7	0.4	(4.4)	(5.9)	(5.1)	(19.5)
Net income (loss)									376.2	335.7	321.9
Net income (loss) attributable to common shareowners	65.5	157.6	65.3	69.9	68.3	150.7	65.9	34.9	358.3	319.8	303.6
Income from continuing operations, net of tax (in dollars per share)	$ 0.60	$ 1.43	$ 0.59	$ 0.66	$ 0.64	$ 1.34	$ 0.60	$ 0.36
Income (loss) from discontinued operations, net of tax (in dollars per share)	$ (0.01)	$ (0.01)	$ 0.00	$ (0.03)	$ (0.02)	$ 0.02	$ 0.00	$ (0.04)
Net income (in dollars per share)	$ 0.59	$ 1.42	$ 0.59	$ 0.63	$ 0.62	$ 1.36	$ 0.60	$ 0.32
IPL [Member]
Operating revenues	463.1	494.4	383.4	477.9	393.2	497.7	360.7	398.7	1,818.8	1,650.3	1,740.1
Operating income	36.2	100.0	34.7	41.1	29.0	112.0	35.4	23.9	212.0	200.3	208.4
Net income (loss)	21.1	112.6	24.7	31.5	25.6	106.5	19.6	(1.5)	189.9	150.2	139.3
Net income (loss) attributable to common shareowners	18.5	110.0	22.2	22.9	22.4	103.3	16.6	(4.7)	173.6	137.6	124.3
WPL [Member]
Operating revenues	355.7	360.9	319.9	369.8	345.2	376.6	315.7	354.5	1,406.3	1,392.0	1,434.4
Operating income	67.8	95.9	59.7	72.7	65.3	93.4	61.5	64.6	296.1	284.8	280.4
Net income (loss)	38.2	61.3	34.4	43.6	41.0	56.7	36.1	31.9	177.5	165.7	163.5
Net income (loss) attributable to common shareowners	$ 38.2	$ 61.3	$ 34.4	$ 42.0	$ 40.2	$ 55.9	$ 35.2	$ 31.1	$ 175.9	$ 162.4	$ 160.2