Rate & Regulatory Matters (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011
Vectren South Electric Base Rate Filing [Abstract]
Amount of revised rate increase filed in rebuttal to original rate increase to IURC	$ 28.6
Amount of infrastructure construction in the three years leading up to December 2009 rate filing	325.0
Rate of return included in rate increase (in hundredths)	7.29%
Dollar amount of the rate base included in rate increase	1,295.6
Amount of rate of return on equity included in rate base (in hundredths)	10.40%
VEDO Gas Rate Design [Abstract]
Percentage of residential and commercial base rate covered by customer service charge (in hundredths)	90.00%
Vectren South Electric Demand Side Management Program Filing [Abstract]
Number of years in initial demand side management program approved by the IURC (in years)	3
Maximum deferral of lost margin associated with small customer demand side programs	1.0
VEDO Continues the Process to Exit the Merchant Function [Abstract]
Length of contract for customers who purchase natural gas through state certified natural gas suppliers (in months)	12 Months
Number of auctions requirement related to the plan approved by the PUCO (in number of auctions)	2
Number of tranches of customers secured in first auction	1
Number of tranches of customers secured in second auction	2
Approximate Number Of Customers In Tranche	28,000
Vectren South Electric Dense Pack Filing [Abstract]
Expected capital investment to improve the efficiency of generating station	32.0
Number of years in capital improvement program (in years)	2
Amount of expected capital investment invested to date	$ 19.0
Expected increase in efficiency for generating station following improvement (in hundredths)	5.00%
Vectren South Electric Fuel Cost Reduction [Abstract]
Number of years for recovery of coal costs	6