Commitments And Contingencies (Narrative) (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended			3 Months Ended						9 Months Ended	12 Months Ended	1 Months Ended				3 Months Ended
	Jul. 31, 2012 subclass	Dec. 31, 2010	Mar. 31, 2013	Mar. 31, 2013 IPL [Member] site	Mar. 31, 2013 WPL [Member] site	Mar. 31, 2013 Manufactured Gas Plant Sites [Member]	Mar. 31, 2013 Manufactured Gas Plant Sites [Member] IPL [Member]	Mar. 31, 2013 Manufactured Gas Plant Sites [Member] WPL [Member]	Mar. 31, 2013 Indemnifications [Member] RMT [Member]	Sep. 30, 2012 Defined benefit pension plans [Member]	Dec. 31, 2011 Defined benefit pension plans [Member]	Feb. 28, 2013 Defined benefit pension plans [Member] Cash Balance Plan [Member]	Mar. 31, 2013 Performance guarantees outstanding, 2013 [Member]	Mar. 31, 2013 Performance guarantees outstanding, 2014 [Member]	Mar. 31, 2013 Performance guarantees outstanding, 2015 [Member]	Mar. 31, 2013 Scenario, Forecast [Member]	Mar. 31, 2013 Scenario, Forecast [Member] IPL [Member]	Mar. 31, 2013 Scenario, Forecast [Member] WPL [Member]	Mar. 31, 2013 Scenario, Forecast [Member] Capital Purchase Obligation [Member]	Mar. 31, 2013 Scenario, Forecast [Member] Capital Purchase Obligation [Member] IPL [Member]	Mar. 31, 2013 Scenario, Forecast [Member] Capital Purchase Obligation [Member] WPL [Member]	Mar. 31, 2013 Civil Penalty [Member] WPL [Member]	Mar. 31, 2013 Environmental Issue [Member] WPL [Member]	Mar. 31, 2013 Minimum [Member]	Mar. 31, 2013 Maximum [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments																$ 2,598	$ 2,180	$ 290	$ 63	$ 12	$ 51
Interest crediting rate		8.20%
Aggregate additional payments to certain plan participants											10
Number of new subclasses certified as a result of court opinion and order	2
Estimated damages from court opinion and order										18.7
Loss contingency, estimate of possible loss									3
Warranty period																								12 months	60 months
Loss contingency, damages sought, value										9.6
Damages to be paid out of common fund										4.3
Loss contingency, damages awarded, value												6.4										2.0	7.0
Performance guarantees outstanding			617										270	294	53
Present value abandonment obligation			30
Number of sites with ownership interest (in sites)				40	14
Number of sites with no further action (in sites)				13	9
Sites with no further action for soil remediation (in sites)				3
Minimum remaining estimated cost incurred for investigation, remediation and monitoring																20	17	3
Maximum remaining estimated cost incurred for investigation, remediation and monitoring																35	31	4
Current and non-current environmental liabilities						$ 26	$ 23	$ 3