Benefit Plans (Amounts Recognized On The Consolidated Balance Sheets) (Details) - USD ($) $ in Millions		Dec. 31, 2015	Dec. 31, 2014
Amounts recognized on the balance sheets consist of:
Pension and other benefit obligations		$ (451.8)	$ (421.7)
Pension Plans, Defined Benefit [Member]
Amounts recognized on the balance sheets consist of:
Non-current assets		0.0	0.0
Other current liabilities		(2.6)	(2.5)
Pension and other benefit obligations		(308.7)	(280.9)
Net amounts recognized at December 31		(311.3)	(283.4)
Amounts recognized in Regulatory Assets and AOCL consist of:
Net actuarial loss	[1]	533.1	533.4
Prior service credit	[1]	(7.2)	(7.4)
Net amount recognized at December 31	[1]	525.9	526.0
Other Postretirement Benefits Plans [Member]
Amounts recognized on the balance sheets consist of:
Non-current assets		3.0	6.1
Other current liabilities		(6.2)	(5.6)
Pension and other benefit obligations		(111.3)	(110.0)
Net amounts recognized at December 31		(114.5)	(109.5)
Amounts recognized in Regulatory Assets and AOCL consist of:
Net actuarial loss	[1]	59.8	60.7
Prior service credit	[1]	(5.6)	(16.7)
Net amount recognized at December 31	[1]	54.2	44.0
IPL [Member]
Amounts recognized on the balance sheets consist of:
Pension and other benefit obligations		(160.2)	(142.4)
IPL [Member] | Pension Plans, Defined Benefit [Member]
Amounts recognized on the balance sheets consist of:
Non-current assets		0.0	0.0
Other current liabilities		(0.8)	(0.8)
Pension and other benefit obligations		(132.6)	(117.6)
Net amounts recognized at December 31		(133.4)	(118.4)
Amounts recognized in Regulatory Assets and AOCL consist of:
Net actuarial loss	[2]	235.5	233.1
Prior service credit	[2]	(2.5)	(2.6)
Net amount recognized at December 31	[2]	233.0	230.5
IPL [Member] | Other Postretirement Benefits Plans [Member]
Amounts recognized on the balance sheets consist of:
Non-current assets		0.0	1.2
Other current liabilities		0.0	0.0
Pension and other benefit obligations		(22.1)	(18.9)
Net amounts recognized at December 31		(22.1)	(17.7)
Amounts recognized in Regulatory Assets and AOCL consist of:
Net actuarial loss	[2]	29.8	27.9
Prior service credit	[2]	(2.7)	(8.7)
Net amount recognized at December 31	[2]	27.1	19.2
WPL [Member]
Amounts recognized on the balance sheets consist of:
Pension and other benefit obligations		(188.7)	(180.4)
WPL [Member] | Pension Plans, Defined Benefit [Member]
Amounts recognized on the balance sheets consist of:
Non-current assets		0.0	0.0
Other current liabilities		(0.1)	(0.1)
Pension and other benefit obligations		(119.0)	(107.2)
Net amounts recognized at December 31		(119.1)	(107.3)
Amounts recognized in Regulatory Assets and AOCL consist of:
Net actuarial loss	[3]	232.1	233.5
Prior service credit	[3]	(1.2)	(1.0)
Net amount recognized at December 31	[3]	230.9	232.5
WPL [Member] | Other Postretirement Benefits Plans [Member]
Amounts recognized on the balance sheets consist of:
Non-current assets		3.0	4.9
Other current liabilities		(6.0)	(5.5)
Pension and other benefit obligations		(68.0)	(71.6)
Net amounts recognized at December 31		(71.0)	(72.2)
Amounts recognized in Regulatory Assets and AOCL consist of:
Net actuarial loss	[3]	23.3	26.3
Prior service credit	[3]	(2.4)	(5.6)
Net amount recognized at December 31	[3]	$ 20.9	$ 20.7

[1] Refer to Note 2 and Alliant Energy’s common equity statements for amounts recognized in “Regulatory assets” and “AOCL,” respectively, on Alliant Energy’s balance sheets.

[2] Refer to Note 2 for amounts recognized in “Regulatory assets” on IPL’s balance sheets.

[3] Refer to Note 2 for amounts recognized in “Regulatory assets” on WPL’s balance sheets.