Benefit Plans (Amounts Recognized On The Consolidated Balance Sheets) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Amounts recognized on the balance sheets consist of:
Pension and other benefit obligations	$ (421.7)		$ (206.6)
Amounts recognized in Regulatory Assets, Regulatory Liabilities and AOCL consist of (a):
Regulatory liability recognized related to other postretirement benefit plans	1.1		5.1
Pension Plans, Defined Benefit [Member]
Amounts recognized on the balance sheets consist of:
Non-current assets	0		0
Other current liabilities	(2.5)		(2.4)
Pension and other benefit obligations	(280.9)		(88.1)
Net amounts recognized at December 31	(283.4)		(90.5)
Amounts recognized in Regulatory Assets, Regulatory Liabilities and AOCL consist of (a):
Net actuarial loss	533.4	[1]	348.6	[1]
Prior service credit	(7.4)	[1]	(7.4)	[1]
Net amount recognized at December 31	526.0	[1]	341.2	[1]
Other Postretirement Benefits Plans [Member]
Amounts recognized on the balance sheets consist of:
Non-current assets	6.1		14.5
Other current liabilities	(5.6)		(4.8)
Pension and other benefit obligations	(110.0)		(93.5)
Net amounts recognized at December 31	(109.5)		(83.8)
Amounts recognized in Regulatory Assets, Regulatory Liabilities and AOCL consist of (a):
Net actuarial loss	60.7	[1]	38.1	[1]
Prior service credit	(16.7)	[1]	(28.6)	[1]
Net amount recognized at December 31	44.0	[1]	9.5	[1]
IPL [Member]
Amounts recognized on the balance sheets consist of:
Pension and other benefit obligations	(142.4)		(48.6)
Amounts recognized in Regulatory Assets, Regulatory Liabilities and AOCL consist of (a):
Regulatory liability recognized related to other postretirement benefit plans	0		1.0
IPL [Member] | Pension Plans, Defined Benefit [Member]
Amounts recognized on the balance sheets consist of:
Non-current assets	0		0
Other current liabilities	(0.8)		(0.8)
Pension and other benefit obligations	(117.6)		(27.3)
Net amounts recognized at December 31	(118.4)		(28.1)
Amounts recognized in Regulatory Assets, Regulatory Liabilities and AOCL consist of (a):
Net actuarial loss	233.1	[2]	146.1	[2]
Prior service credit	(2.6)	[2]	(2.6)	[2]
Net amount recognized at December 31	230.5	[2]	143.5	[2]
IPL [Member] | Other Postretirement Benefits Plans [Member]
Amounts recognized on the balance sheets consist of:
Non-current assets	1.2		8.8
Other current liabilities	0		0
Pension and other benefit obligations	(18.9)		(15.4)
Net amounts recognized at December 31	(17.7)		(6.6)
Amounts recognized in Regulatory Assets, Regulatory Liabilities and AOCL consist of (a):
Net actuarial loss	27.9	[2]	18.2	[2]
Prior service credit	(8.7)	[2]	(15.0)	[2]
Net amount recognized at December 31	19.2	[2]	3.2	[2]
WPL [Member]
Amounts recognized on the balance sheets consist of:
Pension and other benefit obligations	(180.4)		(88.4)
Amounts recognized in Regulatory Assets, Regulatory Liabilities and AOCL consist of (a):
Regulatory liability recognized related to other postretirement benefit plans	1.1		1.1
WPL [Member] | Pension Plans, Defined Benefit [Member]
Amounts recognized on the balance sheets consist of:
Non-current assets	0		0
Other current liabilities	(0.1)		(0.2)
Pension and other benefit obligations	(107.2)		(21.8)
Net amounts recognized at December 31	(107.3)		(22.0)
Amounts recognized in Regulatory Assets, Regulatory Liabilities and AOCL consist of (a):
Net actuarial loss	233.5	[3]	152.2	[3]
Prior service credit	(1.0)	[3]	(0.7)	[3]
Net amount recognized at December 31	232.5	[3]	151.5	[3]
WPL [Member] | Other Postretirement Benefits Plans [Member]
Amounts recognized on the balance sheets consist of:
Non-current assets	4.9		5.8
Other current liabilities	(5.5)		(4.8)
Pension and other benefit obligations	(71.6)		(64.9)
Net amounts recognized at December 31	(72.2)		(63.9)
Amounts recognized in Regulatory Assets, Regulatory Liabilities and AOCL consist of (a):
Net actuarial loss	26.3	[3]	18.3	[3]
Prior service credit	(5.6)	[3]	(9.5)	[3]
Net amount recognized at December 31	$ 20.7	[3]	$ 8.8	[3]

[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. At December 31, 2014 and 2013, $1.1 million and $5.1 million, respectively, of regulatory liabilities were recognized related to Alliant Energy’s OPEB plans.

[2] Refer to Note 2 for amounts recognized in “Regulatory assets” on IPL’s balance sheets. At December 31, 2014 and 2013, $0 and $1.0 million, respectively, of regulatory liabilities were recognized related to IPL’s OPEB plans.

[3] Refer to Note 2 for amounts recognized in “Regulatory assets” on WPL’s balance sheets. At December 31, 2014 and 2013, $1.1 million and $1.1 million, respectively, of regulatory liabilities were recognized related to WPL’s OPEB plans.