CONDENSED CONSOLIDATED STATEMENTS OF INCOME (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Income Statement [Abstract]
Utility revenues	$ 806.1	$ 694.4	$ 2,422.8	$ 1,818.2
Nonregulated revenues	626.5	421.6	1,934.7	976.0
Total revenues	1,432.6	1,116.0	4,357.5	2,794.2
Utility cost of fuel, natural gas, and purchased power	383.0	296.0	1,343.2	861.1
Nonregulated cost of sales	576.5	447.9	1,824.0	884.7
Operating and maintenance expense	334.3	288.7	698.9	583.8
Goodwill impairment loss	6.7	0	6.7	0
Merger transaction costs	5.9	0	5.9	0
Transaction costs related to pending sale of UPPCO	0.9	0	0.9	0
Transaction costs related to pending sale of IES retail energy business	0.8	0	0.8	0
Depreciation and amortization expense	72.9	65.5	144.2	126.4
Taxes other than income taxes	25.5	24.8	53.6	52.0
Operating income (loss)	26.1	(6.9)	279.3	286.2
Earnings from equity method investments	23.9	22.8	46.8	45.1
Miscellaneous income	5.0	5.5	11.0	11.2
Interest expense	38.7	28.6	77.8	57.9
Other expense	(9.8)	(0.3)	(20.0)	(1.6)
Income (loss) before taxes	16.3	(7.2)	259.3	284.6
Provision (benefit) for income taxes	8.2	(3.3)	98.0	106.3
Net income (loss) from continuing operations	8.1	(3.9)	161.3	178.3
Discontinued operations, net of tax	(0.1)	(0.8)	(0.2)	5.3
Net income (loss)	8.0	(4.7)	161.1	183.6
Preferred stock dividends of subsidiary	(0.8)	(0.8)	(1.6)	(1.6)
Noncontrolling interest in subsidiaries	0	0.1	0.1	0.1
Net income (loss) attributed to common shareholders	$ 7.2	$ (5.4)	$ 159.6	$ 182.1
Average shares of common stock
Basic (in shares)	80.2	79.4	80.2	79.0
Diluted (in shares)	80.5	79.4	80.5	79.7
Earnings (loss) per common share (basic)
Net income (loss) from continuing operations (in dollars per share)	$ 0.09	$ (0.06)	$ 1.99	$ 2.24
Discontinued operations, net of tax (in dollars per share)	$ 0.00	$ (0.01)	$ 0.00	$ 0.07
Earnings (loss) per common share (basic) (in dollars per share)	$ 0.09	$ (0.07)	$ 1.99	$ 2.31
Earnings (loss) per common share (diluted)
Net income (loss) from continuing operations (in dollars per share)	$ 0.09	$ (0.06)	$ 1.98	$ 2.22
Discontinued operations, net of tax (in dollars per share)	$ 0.00	$ (0.01)	$ 0.00	$ 0.07
Earnings (loss) per common share (diluted) (in dollars per share)	$ 0.09	$ (0.07)	$ 1.98	$ 2.29
Dividends per common share declared (in dollars per share)	$ 0.68	$ 0.68	$ 1.36	$ 1.36