Benefit Plans (Employees Participate In Defined Contribution Retirement Plans) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
401(k) costs	$ 18.5		$ 18.4		$ 18.5
IPL [Member]
401(k) costs	9.6	[1]	9.2	[1]	8.8	[1]
WPL [Member]
401(k) costs	$ 8.1	[1]	$ 8.4	[1]	$ 8.9	[1]

[1] IPL’s and WPL’s amounts include allocated costs associated with Corporate Services employees.