Gas Rate and Regulatory Matters (Details) - USD ($)			1 Months Ended	12 Months Ended			30 Months Ended
	Feb. 21, 2018	Aug. 03, 2017	Aug. 31, 2014	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jan. 25, 2017	Oct. 31, 2017	Mar. 31, 2016
Public Utilities, General Disclosures [Line Items]
Regulatory assets				$ 416,800,000	$ 308,800,000
Other income – net				32,800,000	28,700,000	$ 20,300,000
INDIANA | Indiana Recovery and Deferral Mechanisms
Public Utilities, General Disclosures [Line Items]
Regulatory assets				22,700,000	21,900,000
Length of project plan required for recovery under new legislation			7 years
INDIANA | Senate Bill 251 and 560
Public Utilities, General Disclosures [Line Items]
Regulatory assets				78,000,000	51,100,000
Amount of project investment approved									$ 890,000,000
Amount of projects not approved for recovery									80,000,000
Additional investment increase								$ 105,000,000	$ 65,000,000
Project spend life to date							$ 482,000,000
Capital expenditures under plan								$ 995,000,000
INDIANA | Senate Bill 251
Public Utilities, General Disclosures [Line Items]
Operating expenses		$ 15,000,000
Capital investments		$ 17,000,000
Recovery period beginning in 2018		4 years
INDIANA | Indiana Gas | Indiana Recovery and Deferral Mechanisms
Public Utilities, General Disclosures [Line Items]
Allowable capital expenditures under Vectren programs				20,000,000
INDIANA | SIGECO | Indiana Recovery and Deferral Mechanisms
Public Utilities, General Disclosures [Line Items]
Allowable capital expenditures under Vectren programs				3,000,000
OHIO | Ohio Recovery and Deferral Mechanisms
Public Utilities, General Disclosures [Line Items]
Regulatory assets				31,200,000	24,400,000
Payments for capital improvements				321,100,000	261,100,000
OHIO | Ohio House Bill 95
Public Utilities, General Disclosures [Line Items]
Bill impact per customer per month				1.50
Other income – net				$ 66,100,000	$ 41,900,000
Subsequent Event | OHIO | Ohio House Bill 95
Public Utilities, General Disclosures [Line Items]
Period to recover costs of capital investments	10 years