Environmental Matters (Details) $ in Millions	9 Months Ended
	Sep. 30, 2016 USD ($) MW	Dec. 31, 2015 USD ($)
Air Quality [Abstract]
Percentage of coal fired generating fleet currently being scrubbed for SO2 (in hundredths)	100.00%
Percentage of coal fired generating fleet currently controlled for NOx (in hundredths)	90.00%
Coal Ash Waste Disposal, Ash Ponds and Water [Abstract]
Asset Retirement Obligation	$ 25.0
Estimated spend for ash pond dam reinforcement and other operational changes	$ 12.0
Climate Changes [Abstract]
Vectren's share of Indiana's CO2 emissions in 2013 (as a percent)	6.00%
Percent reduction of Vectren's CO2 emissions since 2005	31.00%
Long term contract for purchase of electric power generated by wind energy (in megawatts) | MW	80
Percentage of total electricity obtained by the supplier to meet the energy needs of its retail customers provided by clean energy sources (in hundredths)	4.00%
Vectren's emission rate (as measured in lbs CO2/MWh) prior to installation of new technology	1,967
Vectren's emission rate (as measured in lbs CO2/MWh) after installation of new technology	1,922
Percentage reduction of lbs CO2/MWh since 2005	3.00%
Manufactured Gas Plants
Environmental Remediation Expense	$ 43.4
Accrual for Environmental Loss Contingencies Included In Other Liabilities	$ 2.5	$ 3.3
Indiana Gas [Member]
Manufactured Gas Plants
Number of sites identified with potential remedial responsibility for entity (in number of sites)	26
Environmental Remediation Expense	$ 23.2
Insurance Recoveries	$ 20.8
SIGECO [Member]
Manufactured Gas Plants
Number of sites identified with potential remedial responsibility for entity (in number of sites)	5
Environmental Remediation Expense	$ 20.2
Insurance Recoveries	14.8
Total estimated insurance recoveries	15.8
Minimum [Member]
Coal Ash Waste Disposal, Ash Ponds and Water [Abstract]
Ash Pond and Coal Ash Retirement, Anticipated Cost	35.0
Estimated capital expenditures to comply with Clean Water Act	4.0
Maximum [Member]
Coal Ash Waste Disposal, Ash Ponds and Water [Abstract]
Ash Pond and Coal Ash Retirement, Anticipated Cost	80.0
Estimated capital expenditures to comply with Clean Water Act	$ 8.0