Environmental and Sustainability Matters (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) lb / MWh site MW	Dec. 31, 2015 USD ($)	Dec. 31, 2016 USD ($)
Site Contingency [Line Items]
Natural gas combined cycle plant power | MW	700
New renewable generation power | MW	54
Grid modernization costs	$ 450.0
Percentage reduction of lbs CO2/MWh since 2005 | lb / MWh	980
Coal Ash Waste Disposal, Ash Ponds and Water [Abstract]
Asset Retirement Obligation (ARO)	$ 107.0	$ 82.0	$ 106.7
Estimated spend for ash pond dam reinforcement and other operational changes	$ 17.0
Notification period of issuance of the renewal of its intent to retire a unit	1 year
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%
Climate Changes [Abstract]
Percent reduction of Vectren's CO2 emissions since 2005			35.00%
Manufactured Gas Plants
Cumulative costs recorded	$ 44.2
Accrued costs included in Other Liabilities	$ 2.5		$ 2.9
SIGECO
Manufactured Gas Plants
Number of sites identified with potential remedial responsibility for entity (in number of sites) | site	5
Cumulative costs recorded	$ 20.3
Insurance coverage, amount received	15.7
Total estimated insurance recoveries	15.8
SIGECO | Ash Ponds
Coal Ash Waste Disposal, Ash Ponds and Water [Abstract]
Asset Retirement Obligation (ARO)	$ 40.0
Indiana Gas
Manufactured Gas Plants
Number of sites identified with potential remedial responsibility for entity (in number of sites) | site	26
Cumulative costs recorded	$ 23.9
Insurance coverage, amount received	20.8
Minimum
Coal Ash Waste Disposal, Ash Ponds and Water [Abstract]
Estimated capital expenditures to comply with Ash Pond and Coal Ash disposal regulations		35.0
Ash Pond and Coal Ash disposal exit costs and revised anticipated cost	45.0
Estimated capital expenditures to comply with Clean Water Act	4.0
Maximum
Coal Ash Waste Disposal, Ash Ponds and Water [Abstract]
Estimated capital expenditures to comply with Ash Pond and Coal Ash disposal regulations		$ 80.0
Ash Pond and Coal Ash disposal exit costs and revised anticipated cost	135.0
Estimated capital expenditures to comply with Clean Water Act	$ 8.0