Derivative Instruments (Gains And Losses From Derivative Instruments Not Designated As Hedging Instruments) (Details) (Commodity Contracts [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Regulatory Assets [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) from derivative instruments not designated as heding instruments	$ (14.7)	$ (37.9)	$ (79.6)
Regulatory Assets [Member] | IPL [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) from derivative instruments not designated as heding instruments	(6.6)	(16.8)	(42.4)
Regulatory Assets [Member] | WPL [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) from derivative instruments not designated as heding instruments	(8.1)	(21.1)	(37.2)
Regulatory Liabilities [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) from derivative instruments not designated as heding instruments	22.2	20.3	9.3
Regulatory Liabilities [Member] | IPL [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) from derivative instruments not designated as heding instruments	11.8	13.5	6.4
Regulatory Liabilities [Member] | WPL [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) from derivative instruments not designated as heding instruments	$ 10.4	$ 6.8	$ 2.9