Income Taxes (Schedule Of Uncertain Tax Positions) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Uncertain Tax Positions [Roll Forward]
Balance, January 1	$ 0.7		$ 23.5		$ 66.7
Additions based on tax positions related to the current year	0		0.7		0.7
Reductions for tax positions of prior years (a)	(0.7)	[1]	(23.5)	[1]	(43.9)	[1]
Balance, December 31	0		0.7		23.5
Statute of Limitations, Expiration Period from Extended Due Date of Federal Tax Return	3 years
Statute of Limitations, Expiration Period from Extended Due Date of Iowa Tax Return	3 years
Statute of Limitations, Expiration Period from Extended Due Date of Wisconsin Tax Return	4 years
IPL [Member]
Uncertain Tax Positions [Roll Forward]
Balance, January 1	0		10.9		33.0
Additions based on tax positions related to the current year	0		0		0.1
Reductions for tax positions of prior years (a)	0	[1]	(10.9)	[1]	(22.2)	[1]
Balance, December 31	0		0		10.9
WPL [Member]
Uncertain Tax Positions [Roll Forward]
Balance, January 1	0.7		12.6		33.7
Additions based on tax positions related to the current year	0		0.7		0.6
Reductions for tax positions of prior years (a)	(0.7)	[1]	(12.6)	[1]	(21.7)	[1]
Balance, December 31	$ 0		$ 0.7		$ 12.6

[1] In 2012, the reductions for tax positions of prior years were due to the finalization of Alliant Energy’s federal income tax return audits for calendar years 2005 through 2009. In 2011, the reductions for tax positions of prior years were related to guidance published by the IRS clarifying the treatment of repairs expenditures for electric distribution property.