Electric Rate and Regulatory Matters (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Vectren South Electric Environmental Compliance Filing [Abstract]
Amount of capital investments to date in equipment for mercury control	$ 30.0		$ 30.0
Amount of capital investments to date in equipment to control sulfur trioxide emissions	40.0		40.0
Regulatory Assets, Noncurrent	290.0		290.0		$ 249.4
Estimated cost of equipment to comply with MATS	35.0		35.0
Estimated cost of equipment required by the NOV	40.0		$ 40.0
Vectren South Electric Demand Side Management Program Filing [Abstract]
Number of Years in Initial Demand Side Management Program			3 years
Electric Domestic Regulated Revenue	$ 173.5	$ 164.4	$ 463.3	$ 466.0
Percent of industrial load opt out of applicable energy efficiency programs	80.00%		80.00%
Maximum period for recovery under energy efficiency program			4 years
FERC Return On Equity Complaint [Abstract]
Current return on equity used in MISO transmission owners rates	12.38%		12.38%
Reduced return on equity percentage sought by third party through joint complaint	9.15%		9.15%
FERC authorized base ROE percentage for first refund period	10.32%		10.32%
FERC authorized base ROE percentage for second refund period	9.70%		9.70%
Gross Investment In Qualifying Transmission Projects	$ 157.7		$ 157.7
Net Investment in Qualifying Transmission Projects	$ 137.7		$ 137.7
Number of incentive basis point above the FERC approved ROE	50		50
Maximum [Member]
Vectren South Electric Environmental Compliance Filing [Abstract]
Amount requested for approval of capital investments on coal-fired generation units	$ 75.0		$ 75.0
Minimum [Member]
Vectren South Electric Environmental Compliance Filing [Abstract]
Amount requested for approval of capital investments on coal-fired generation units	70.0		70.0
SIGECO Electric Environmental Compliance Filing [Member] | Depreciation, property taxes and operating expense [Member]
Vectren South Electric Environmental Compliance Filing [Abstract]
Regulatory Assets, Noncurrent	5.8		5.8
SIGECO Electric Environmental Compliance Filing [Member] | Post-in service carrying costs [Member]
Vectren South Electric Environmental Compliance Filing [Abstract]
Regulatory Assets, Noncurrent	$ 2.3		2.3
Electric Demand Side Management Program [Member]
Vectren South Electric Demand Side Management Program Filing [Abstract]
Electric Domestic Regulated Revenue			$ 8.2	$ 7.5