Selected Consolidated Quarterly Financial Data (Unaudited) (Details) $ / shares in Units, $ in Millions			3 Months Ended								12 Months Ended
		Apr. 20, 2016	Dec. 31, 2016 USD ($) $ / shares	Sep. 30, 2016 USD ($) $ / shares	Jun. 30, 2016 USD ($) $ / shares	Mar. 31, 2016 USD ($) $ / shares	Dec. 31, 2015 USD ($) $ / shares	Sep. 30, 2015 USD ($) $ / shares	Jun. 30, 2015 USD ($) $ / shares	Mar. 31, 2015 USD ($) $ / shares	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Operating revenues			$ 797.0	$ 924.6	$ 754.6	$ 843.8	$ 740.1	$ 898.9	$ 717.2	$ 897.4	$ 3,320.0	$ 3,253.6	$ 3,350.3
Operating income			99.9	162.6	128.6	145.9	79.2	235.9	109.0	152.9	537.0	577.0	543.6
Income from continuing operations, net of tax			63.0	128.8	84.4	97.6	35.2	180.0	68.9	96.6	373.8	380.7	385.5
Loss from discontinued operations, net of tax			(0.3)	(0.4)	(0.5)	(1.1)	(1.1)	(0.1)	(1.3)	0.0	(2.3)	(2.5)	(2.4)
Net income											381.7	388.4	393.3
Net income attributable to common shareowners			$ 62.7	$ 128.4	$ 83.9	$ 96.5	$ 34.1	$ 179.9	$ 67.6	$ 96.6	371.5	378.2	383.1
Income from continuing operations, net of tax (in dollars per share) | $ / shares	[1]		$ 0.28	$ 0.57	$ 0.37	$ 0.43	$ 0.16	$ 0.79	$ 0.31	$ 0.43
Loss from discontinued operations, net of tax (in dollars per share) | $ / shares	[1]		0.00	0.00	0.00	0.00	(0.01)	0.00	(0.01)	0.00
Net income (in dollars per share) | $ / shares	[1]		$ 0.28	$ 0.57	$ 0.37	$ 0.43	$ 0.15	$ 0.79	$ 0.30	$ 0.43
Common stock split conversion ratio (2:1)		2
IPL [Member]
Operating revenues			$ 434.5	$ 516.2	$ 411.0	$ 458.7	$ 398.7	$ 504.6	$ 382.2	$ 489.0	1,820.4	1,774.5	1,848.1
Operating income			34.9	125.9	48.0	62.0	25.6	117.0	33.8	65.5	270.8	241.9	209.2
Net income			26.5	116.7	34.4	48.2	8.0	119.1	19.0	50.1	225.8	196.2	191.8
Net income attributable to common shareowners			24.0	114.1	31.9	45.6	5.5	116.5	16.5	47.5	215.6	186.0	181.6
WPL [Member]
Operating revenues			352.2	397.0	334.3	375.6	330.7	382.6	324.7	397.1	1,459.1	1,435.1	1,449.1
Operating income			58.2	115.0	75.0	78.8	49.3	110.3	68.3	80.8	327.0	308.7	301.0
Net income			32.5	69.6	43.7	47.0	24.4	68.4	39.7	45.1	192.8	177.6	181.1
Net income attributable to common shareowners			$ 31.7	$ 69.0	$ 43.2	$ 46.5	$ 24.2	$ 68.0	$ 39.2	$ 44.9	$ 190.4	$ 176.3	$ 180.4

[1] Amounts reflect the effects of a two-for-one common stock split distributed in May 2016.