Commitments And Contingencies (Schedule Of Environmental Liabilities) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Current environmental liabilities	$ 2.7	$ 2.0
Non-current environmental liabilities	12.8	13.5
Total environmental liabilities	15.5	15.5
Minimum range of estimated future cost incurred for investigation, remediation and monitoring	11.0
Maximum remaining estimated cost incurred for investigation, remediation and monitoring	28.0
IPL [Member]
Current environmental liabilities	1.7	1.7
Non-current environmental liabilities	11.2	11.9
Total environmental liabilities	12.9	13.6
Minimum range of estimated future cost incurred for investigation, remediation and monitoring	9.0
Maximum remaining estimated cost incurred for investigation, remediation and monitoring	25.0
WPL [Member]
Current environmental liabilities	1.0	0.3
Non-current environmental liabilities	1.5	1.6
Total environmental liabilities	2.5	$ 1.9
Minimum range of estimated future cost incurred for investigation, remediation and monitoring	2.0
Maximum remaining estimated cost incurred for investigation, remediation and monitoring	3.0
Manufactured Gas Plant [Member]
Total environmental liabilities	15.0
Manufactured Gas Plant [Member] | IPL [Member]
Total environmental liabilities	13.0
Manufactured Gas Plant [Member] | WPL [Member]
Total environmental liabilities	$ 2.0