Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Contractual interest rate for funds borrowed, under the debt agreement.

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- Definition

Amount, after accumulated amortization, of debt discount (premium).

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Sum of the carrying values as of the balance sheet date of all long-term debt, which is debt initially having maturities due after one year from the balance sheet date or beyond the operating cycle, if longer, but excluding the portions thereof scheduled to be repaid within one year (current maturities) or the normal operating cycle, if longer, and after deducting unamortized discount or premiums, if any. Also excludes the portion of debt that could be repaid in one year at the option of the holder.

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Borrowing Arrangements - Long-Term Debt (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 15, 2017	Dec. 31, 2016
Long term debt [Abstract]
Total long-term debt outstanding	$ 1,848.7		$ 1,723.7
Current maturities of long-term debt	(100.0)		(124.1)
Debt issuance costs	(9.4)		(9.0)
Unamortized debt premium & discount-net	(0.6)		(0.7)
Total long-term debt-net	1,738.7		1,589.9
Utility Holdings \| Fixed Rate Senior Unsecured Notes
Long term debt [Abstract]
Total long-term debt outstanding	1,200.0		1,000.0
Utility Holdings \| Fixed Rate Senior Unsecured Notes \| 2018, 5.75%
Long term debt [Abstract]
Total long-term debt outstanding	$ 100.0		100.0
Interest rate	5.75%
Utility Holdings \| Fixed Rate Senior Unsecured Notes \| 2020, 6.28%
Long term debt [Abstract]
Total long-term debt outstanding	$ 100.0		100.0
Interest rate	6.28%
Utility Holdings \| Fixed Rate Senior Unsecured Notes \| 2021, 4.67%
Long term debt [Abstract]
Total long-term debt outstanding	$ 55.0		55.0
Interest rate	4.67%
Utility Holdings \| Fixed Rate Senior Unsecured Notes \| 2023, 3.72%
Long term debt [Abstract]
Total long-term debt outstanding	$ 150.0		150.0
Interest rate	3.72%
Utility Holdings \| Fixed Rate Senior Unsecured Notes \| 2026, 5.02%
Long term debt [Abstract]
Total long-term debt outstanding	$ 60.0		60.0
Interest rate	5.02%
Utility Holdings \| Fixed Rate Senior Unsecured Notes \| 2028, 3.20%
Long term debt [Abstract]
Total long-term debt outstanding	$ 45.0		45.0
Interest rate	3.20%
Utility Holdings \| Fixed Rate Senior Unsecured Notes \| 2032, 3.26%
Long term debt [Abstract]
Total long-term debt outstanding	$ 100.0		0.0
Interest rate	3.26%
Utility Holdings \| Fixed Rate Senior Unsecured Notes \| 2035, 6.10%
Long term debt [Abstract]
Total long-term debt outstanding	$ 75.0		75.0
Interest rate	6.10%
Utility Holdings \| Fixed Rate Senior Unsecured Notes \| 2035, 3.90%
Long term debt [Abstract]
Total long-term debt outstanding	$ 25.0		25.0
Interest rate	3.90%
Utility Holdings \| Fixed Rate Senior Unsecured Notes \| 2041, 5.99%
Long term debt [Abstract]
Total long-term debt outstanding	$ 35.0		35.0
Interest rate	5.99%
Utility Holdings \| Fixed Rate Senior Unsecured Notes \| 2042, 5.00%
Long term debt [Abstract]
Total long-term debt outstanding	$ 100.0		100.0
Interest rate	5.00%
Utility Holdings \| Fixed Rate Senior Unsecured Notes \| 2043, 4.25%
Long term debt [Abstract]
Total long-term debt outstanding	$ 80.0		80.0
Interest rate	4.25%
Utility Holdings \| Fixed Rate Senior Unsecured Notes \| 2045, 4.36%
Long term debt [Abstract]
Total long-term debt outstanding	$ 135.0		135.0
Interest rate	4.36%
Utility Holdings \| Fixed Rate Senior Unsecured Notes \| 2047, 3.93%
Long term debt [Abstract]
Total long-term debt outstanding	$ 100.0		0.0
Interest rate	3.93%
Utility Holdings \| Fixed Rate Senior Unsecured Notes \| 2055, 4.51%
Long term debt [Abstract]
Total long-term debt outstanding	$ 40.0		40.0
Interest rate	4.51%
Indiana Gas \| Fixed Rate Senior Unsecured Notes
Long term debt [Abstract]
Total long-term debt outstanding	$ 96.0		96.0
Indiana Gas \| Fixed Rate Senior Unsecured Notes \| 2025, Series E, 6.53%
Long term debt [Abstract]
Total long-term debt outstanding	$ 10.0		10.0
Interest rate	6.53%
Indiana Gas \| Fixed Rate Senior Unsecured Notes \| 2027, Series E, 6.42%
Long term debt [Abstract]
Total long-term debt outstanding	$ 5.0		5.0
Interest rate	6.42%
Indiana Gas \| Fixed Rate Senior Unsecured Notes \| 2027, Series E, 6.68%
Long term debt [Abstract]
Total long-term debt outstanding	$ 1.0		1.0
Interest rate	6.68%
Indiana Gas \| Fixed Rate Senior Unsecured Notes \| 2027, Series F, 6.34%
Long term debt [Abstract]
Total long-term debt outstanding	$ 20.0		20.0
Interest rate	6.34%
Indiana Gas \| Fixed Rate Senior Unsecured Notes \| 2028, Series F, 6.36%
Long term debt [Abstract]
Total long-term debt outstanding	$ 10.0		10.0
Interest rate	6.36%
Indiana Gas \| Fixed Rate Senior Unsecured Notes \| 2028, Series F, 6.55%
Long term debt [Abstract]
Total long-term debt outstanding	$ 20.0		20.0
Interest rate	6.55%
Indiana Gas \| Fixed Rate Senior Unsecured Notes \| 2029, Series G, 7.08%
Long term debt [Abstract]
Total long-term debt outstanding	$ 30.0		30.0
Interest rate	7.08%
SIGECO \| First Mortgage Bonds
Long term debt [Abstract]
Total long-term debt outstanding	$ 292.7		292.7
SIGECO \| First Mortgage Bonds \| 2022, 2013 Series C, current adjustable rate 1.565%, tax-exempt
Long term debt [Abstract]
Total long-term debt outstanding	$ 4.6		4.6
Interest rate	1.565%
SIGECO \| First Mortgage Bonds \| 2024, 2013 Series D, current adjustable rate 1.565%, tax-exempt
Long term debt [Abstract]
Total long-term debt outstanding	$ 22.5		22.5
Interest rate	1.565%
SIGECO \| First Mortgage Bonds \| 2025, 2014 Series B, current adjustable rate 1.565%, tax-exempt
Long term debt [Abstract]
Total long-term debt outstanding	$ 41.3		41.3
Interest rate	1.565%
SIGECO \| First Mortgage Bonds \| 2029, 1999 Series, 6.72%
Long term debt [Abstract]
Total long-term debt outstanding	$ 80.0		80.0
Interest rate	6.72%
SIGECO \| First Mortgage Bonds \| 2037, 2013 Series E, current adjustable rate 1.565%, tax-exempt
Long term debt [Abstract]
Total long-term debt outstanding	$ 22.0		22.0
Interest rate	1.565%
SIGECO \| First Mortgage Bonds \| 2038, 2013 Series A, 4.00%, tax-exempt
Long term debt [Abstract]
Total long-term debt outstanding	$ 22.2		22.2
Interest rate	4.00%
SIGECO \| First Mortgage Bonds \| 2043, 2013 Series B, 4.05%, tax-exempt
Long term debt [Abstract]
Total long-term debt outstanding	$ 39.6		39.6
Interest rate	4.05%
SIGECO \| First Mortgage Bonds \| 2044, 2014 Series A, 4.00% tax-exempt
Long term debt [Abstract]
Total long-term debt outstanding	$ 22.3		22.3
Interest rate	4.00%
SIGECO \| First Mortgage Bonds \| 2055, 2015 Series Mt. Vernon, 2.375%, tax-exempt
Long term debt [Abstract]
Total long-term debt outstanding	$ 23.0		23.0
Interest rate	2.375%
SIGECO \| First Mortgage Bonds \| 2055, 2015 Series Warrick County, 2.375%, tax-exempt
Long term debt [Abstract]
Total long-term debt outstanding	$ 15.2		15.2
Interest rate	2.375%
Vectren Capital Corp. \| Fixed Rate Senior Unsecured Notes
Long term debt [Abstract]
Total long-term debt outstanding	$ 260.0		335.0
Vectren Capital Corp. \| Fixed Rate Senior Unsecured Notes \| 2017, 3.48%
Long term debt [Abstract]
Total long-term debt outstanding	$ 0.0		75.0
Interest rate	3.48%	3.48%
Vectren Capital Corp. \| Fixed Rate Senior Unsecured Notes \| 2019, 7.30%
Long term debt [Abstract]
Total long-term debt outstanding	$ 60.0		60.0
Interest rate	7.30%
Vectren Capital Corp. \| Fixed Rate Senior Unsecured Notes \| 2022, 3.33%
Long term debt [Abstract]
Total long-term debt outstanding	$ 75.0		75.0
Interest rate	3.33%
Vectren Capital Corp. \| Fixed Rate Senior Unsecured Notes \| 2025, 4.53%
Long term debt [Abstract]
Total long-term debt outstanding	$ 50.0		50.0
Interest rate	4.53%
Vectren Capital Corp. \| Fixed Rate Senior Unsecured Notes \| 2030, 3.90%
Long term debt [Abstract]
Total long-term debt outstanding	$ 75.0		$ 75.0
Interest rate	3.90%