Benefit Plans (Employees Participate In Defined Contribution Retirement Plans) (Details) (USD $) In Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2011		Sep. 30, 2010		Sep. 30, 2011		Sep. 30, 2010
Employees participate in defined contribution retirement plans (401(k) savings plans)	$ 4.5		$ 4.4		$ 14.5		$ 13.9
WPL [Member]
Employees participate in defined contribution retirement plans (401(k) savings plans)	2.0	[1]	2.2	[1]	6.6	[1]	6.8	[1]
IPL [Member]
Employees participate in defined contribution retirement plans (401(k) savings plans)	$ 2.2	[1]	$ 2.1	[1]	$ 7.1	[1]	$ 6.6	[1]

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