Consolidated Statements of Common Equity (USD $) In Millions, unless otherwise specified	Total	IPL [Member]	WPL [Member]	Common Stock [Member]	Common Stock [Member] IPL [Member]	Common Stock [Member] WPL [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] IPL [Member]	Additional Paid-in Capital [Member] WPL [Member]	Retained Earnings [Member]	Retained Earnings [Member] IPL [Member]	Retained Earnings [Member] WPL [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Deferred Compensation, Share-based Payments [Member]
Beginning balance at Dec. 31, 2010	$ 2,893.6	$ 1,389.8	$ 1,369.3	$ 1.1	$ 33.4	$ 66.2	$ 1,506.8	$ 974.0	$ 844.0	$ 1,394.7	$ 382.4	$ 459.1	$ (1.4)	$ (7.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to Alliant Energy common shareowners	303.6	124.3	160.2							303.6	124.3	160.2
Common stock dividends	(188.1)	(73.4)	(112.1)							(188.1)	(73.4)	(112.1)
Capital contributions from parent		54.0	25.0					54.0	25.0
Repayment of capital to parent		(100.7)						(100.7)
Other	3.3	0.4					4.0	0.4						(0.7)
Other comprehensive income, net of tax	0.6												0.6
Ending balance at Dec. 31, 2011	3,013.0	1,394.4	1,442.4	1.1	33.4	66.2	1,510.8	927.7	869.0	1,510.2	433.3	507.2	(0.8)	(8.3)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to Alliant Energy common shareowners	34.9	(4.7)	31.1
Ending balance at Mar. 31, 2012
Beginning balance at Dec. 31, 2011	3,013.0	1,394.4	1,442.4	1.1	33.4	66.2	1,510.8	927.7	869.0	1,510.2	433.3	507.2		(8.3)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to Alliant Energy common shareowners	319.8	137.6	162.4							319.8	137.6	162.4
Common stock dividends	(199.3)	(122.9)	(112.0)							(199.3)	(122.9)	(112.0)
Capital contributions from parent		110.0	90.0					110.0	90.0
Other	1.4	0.1	0.2				0.4	0.1	0.2					1.0
Ending balance at Dec. 31, 2012	3,134.9	1,519.2	1,583.0	1.1	33.4	66.2	1,511.2	1,037.8	959.2	1,630.7	448.0	557.6		(7.3)
Beginning balance at Sep. 30, 2012
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to Alliant Energy common shareowners	68.3	22.4	40.2
Ending balance at Dec. 31, 2012	3,134.9	1,519.2	1,583.0	1.1	33.4	66.2
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to Alliant Energy common shareowners	69.9	22.9	42.0
Ending balance at Mar. 31, 2013
Beginning balance at Dec. 31, 2012	3,134.9	1,519.2	1,583.0	1.1	33.4	66.2	1,511.2	1,037.8	959.2	1,630.7	448.0	557.6	(0.8)	(7.3)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to Alliant Energy common shareowners	358.3	173.6	175.9							358.3	173.6	175.9
Common stock dividends	(208.3)	(128.1)	(116.3)							(208.3)	(128.1)	(116.3)
Capital contributions from parent		120.0	0					120.0
Preferred stock issuance costs	(5.4)	(5.4)					(5.4)	(5.4)
Other	1.3	0.4	(0.2)				2.0	0.4	(0.2)					(0.7)
Other comprehensive income, net of tax	0.6												0.6
Ending balance at Dec. 31, 2013	3,281.4	1,679.7	1,642.4	1.1	33.4	66.2	1,507.8	1,152.8	959.0	1,780.7	493.5	617.2	(0.2)	(8.0)
Beginning balance at Sep. 30, 2013
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income attributable to Alliant Energy common shareowners	65.5	18.5	38.2
Ending balance at Dec. 31, 2013	$ 3,281.4	$ 1,679.7	$ 1,642.4	$ 1.1	$ 33.4	$ 66.2