Debt (Narrative) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended		1 Months Ended	9 Months Ended		1 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Jul. 31, 2014 IPL [Member]	Sep. 30, 2014 IPL [Member]	Sep. 30, 2013 IPL [Member]	Oct. 31, 2014 Subsequent Event [Member]	Oct. 31, 2014 Subsequent Event [Member] WPL [Member]
Debt [Line Items]
Retirement of long-term debt	$ 47.7	$ 0.8	$ 38.4	$ 38.4	$ 0	$ 250.0
Interest rate			5.00%			4.00%	4.10%
Proceeds from issuance of long-term debt						$ 250	$ 250
Interest rate, variable						0.75%