Borrowing Arrangements (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Year end [Abstract]
Balance Outstanding, end of period	$ 227,100,000	$ 118,300,000
Long term debt [Abstract]
Total long term debt outstanding	1,524,200,000	1,718,200,000
Current maturities of long-term debt	(62,700,000)	(250,700,000)
Short-term borrowings expected to be refinanced	100,000,000	0
Debt subject to tender	0	(30,000,000)
Unamortized debt premium and discount - net	(1,900,000)	(2,300,000)
Long-term debt - net of current maturities and debt subject to tender	1,559,600,000	1,435,200,000
Long-term debt death put repayments	800,000	1,800,000	3,000,000
Maturities of long term debt [Abstract]
Debt maturing within 12 months following date of latest balance sheet	62,700,000
Debt maturing within two years following date of latest balance sheet	106,400,000
Debt maturing within three years following date of latest balance sheet	30,000,000
Debt maturing within four years following date of latest balance sheet	179,800,000
Debt maturing within five years following date of latest balance sheet	73,000,000
Debt maturing thereafter 5 years following date of the latest balance sheet	1,170,400,000
Covenants [Abstract]
Ratio of consolidated total debt to consolidated total capitalization, maximum ( in hundredths)	Not to exceed 65 percent
Fixed Rate Senior Unsecured Notes [Member] | Utility Holdings [Member]
Long term debt [Abstract]
Total long term debt outstanding	721,600,000	918,600,000
Proceeds from the sale of the notes, net of issuance costs	148,900,000
Debt guarantees [Abstract]
Long-term guarantees	722,000,000
Short-term debt guarantees	243,000,000
Fixed Rate Senior Unsecured Notes [Member] | Indiana Gas [Member]
Long term debt [Abstract]
Total long term debt outstanding	121,000,000	121,000,000
Fixed Rate Senior Unsecured Notes [Member] | Vectren Capital Corp. [Member]
Long term debt [Abstract]
Total long term debt outstanding	410,000,000	410,000,000
Proceeds from the sale of the notes, net of issuance costs		124,200,000	149,000,000
Amount of the proceeds that replaced the issuance of debt maturities due	48,000,000
Debt guarantees [Abstract]
Long-term guarantees	410,000,000
Short-term debt guarantees	84,000,000
Fixed Rate Senior Unsecured Notes [Member] | 2011, 6.625% [Member] | Utility Holdings [Member]
Long term debt [Abstract]
Total long term debt outstanding	0	250,000,000
Fixed Rate Senior Unsecured Notes [Member] | 2013, 5.25% [Member] | Utility Holdings [Member]
Long term debt [Abstract]
Total long term debt outstanding	100,000,000	100,000,000
Fixed Rate Senior Unsecured Notes [Member] | 2015, 5.45% [Member] | Utility Holdings [Member]
Long term debt [Abstract]
Total long term debt outstanding	75,000,000	75,000,000
Fixed Rate Senior Unsecured Notes [Member] | 2018, 5.75% [Member] | Utility Holdings [Member]
Long term debt [Abstract]
Total long term debt outstanding	100,000,000	100,000,000
Fixed Rate Senior Unsecured Notes [Member] | 2020, 6.28% [Member] | Utility Holdings [Member]
Long term debt [Abstract]
Total long term debt outstanding	100,000,000	100,000,000
Fixed rate stated percentage (in hundredths)	6.28%
Maturity date	Apr. 07, 2020
Debt Instrument Issuance Date	2009-04-07
Debt Issuance	100,000,000
Proceeds from the sale of the notes, net of issuance costs			99,500,000
Fixed Rate Senior Unsecured Notes [Member] | 2035, 6.10% [Member] | Utility Holdings [Member]
Long term debt [Abstract]
Total long term debt outstanding	75,000,000	75,000,000
Fixed Rate Senior Unsecured Notes [Member] | 2036, 5.95% [Member] | Utility Holdings [Member]
Long term debt [Abstract]
Total long term debt outstanding	0	96,700,000
Fixed rate stated percentage (in hundredths)	5.95%
Maturity date	Dec. 31, 2036
Call date	2011-10-21
Debt Issuance	96,200,000
Debt Instrument Put And Call Exercise Date			Nov. 21, 2011
Fixed Rate Senior Unsecured Notes [Member] | 2039, 6.25% [Member] | Utility Holdings [Member]
Long term debt [Abstract]
Total long term debt outstanding	121,600,000	121,900,000
Fixed Rate Senior Unsecured Notes [Member] | 2013, Series E, 6.69% [Member] | Indiana Gas [Member]
Long term debt [Abstract]
Total long term debt outstanding	5,000,000	5,000,000
Fixed Rate Senior Unsecured Notes [Member] | 2015, Series E, 7.15% [Member] | Indiana Gas [Member]
Long term debt [Abstract]
Total long term debt outstanding	5,000,000	5,000,000
Fixed Rate Senior Unsecured Notes [Member] | 2015, Series E1, 6.69% [Member] | Indiana Gas [Member]
Long term debt [Abstract]
Total long term debt outstanding	5,000,000	5,000,000
Fixed Rate Senior Unsecured Notes [Member] | 2015, Series E, 6.69% [Member] | Indiana Gas [Member]
Long term debt [Abstract]
Total long term debt outstanding	10,000,000	10,000,000
Fixed Rate Senior Unsecured Notes [Member] | 2025, Series E, 6.53% [Member] | Indiana Gas [Member]
Long term debt [Abstract]
Total long term debt outstanding	10,000,000	10,000,000
Fixed Rate Senior Unsecured Notes [Member] | 2027, Series E, 6.42% [Member] | Indiana Gas [Member]
Long term debt [Abstract]
Total long term debt outstanding	5,000,000	5,000,000
Fixed Rate Senior Unsecured Notes [Member] | 2027, Series E, 6.68% [Member] | Indiana Gas [Member]
Long term debt [Abstract]
Total long term debt outstanding	1,000,000	1,000,000
Fixed Rate Senior Unsecured Notes [Member] | 2027, Series F, 6.34% [Member] | Indiana Gas [Member]
Long term debt [Abstract]
Total long term debt outstanding	20,000,000	20,000,000
Fixed Rate Senior Unsecured Notes [Member] | 2028, Series F, 6.36% [Member] | Indiana Gas [Member]
Long term debt [Abstract]
Total long term debt outstanding	10,000,000	10,000,000
Fixed Rate Senior Unsecured Notes [Member] | 2028, Series F, 6.55% [Member] | Indiana Gas [Member]
Long term debt [Abstract]
Total long term debt outstanding	20,000,000	20,000,000
Fixed Rate Senior Unsecured Notes [Member] | 2029, Series G, 7.08% [Member] | Indiana Gas [Member]
Long term debt [Abstract]
Total long term debt outstanding	30,000,000	30,000,000
Fixed Rate Senior Unsecured Notes [Member] | 2010, 7.98% [Member] | Vectren Capital Corp. [Member]
Long term debt [Abstract]
Total long term debt outstanding			22,500,000
Fixed Rate Senior Unsecured Notes [Member] | 2012, 5.13% [Member] | Vectren Capital Corp. [Member]
Long term debt [Abstract]
Total long term debt outstanding	25,000,000	25,000,000
Fixed Rate Senior Unsecured Notes [Member] | 2012, 7.43% [Member] | Vectren Capital Corp. [Member]
Long term debt [Abstract]
Total long term debt outstanding	35,000,000	35,000,000
Fixed Rate Senior Unsecured Notes [Member] | 2014, 6.37% [Member] | Vectren Capital Corp. [Member]
Long term debt [Abstract]
Total long term debt outstanding	30,000,000	30,000,000
Fixed rate stated percentage (in hundredths)	6.37%
Maturity date	Dec. 31, 2014
Debt Instrument Issuance Date	2009-03-11
Debt Issuance	30,000,000
Fixed Rate Senior Unsecured Notes [Member] | 2015, 5.31% [Member] | Vectren Capital Corp. [Member]
Long term debt [Abstract]
Total long term debt outstanding	75,000,000	75,000,000
Fixed Rate Senior Unsecured Notes [Member] | 2016, 6.92% [Member] | Vectren Capital Corp. [Member]
Long term debt [Abstract]
Total long term debt outstanding	60,000,000	60,000,000
Fixed rate stated percentage (in hundredths)	6.92%
Maturity date	Dec. 31, 2016
Debt Instrument Issuance Date	2009-03-11
Debt Issuance	60,000,000
Fixed Rate Senior Unsecured Notes [Member] | 2017, 3.48% [Member] | Vectren Capital Corp. [Member]
Long term debt [Abstract]
Total long term debt outstanding	75,000,000	75,000,000
Fixed rate stated percentage (in hundredths)	3.48%
Maturity date	Dec. 31, 2017
Debt Instrument Issuance Date	2010-12-15
Debt Issuance	75,000,000
Fixed Rate Senior Unsecured Notes [Member] | 2019, 7.30% [Member] | Vectren Capital Corp. [Member]
Long term debt [Abstract]
Total long term debt outstanding	60,000,000	60,000,000
Fixed rate stated percentage (in hundredths)	7.30%
Maturity date	Dec. 31, 2019
Debt Instrument Issuance Date	2009-03-11
Debt Issuance	60,000,000
Fixed Rate Senior Unsecured Notes [Member] | 2025, 4.53% [Member] | Vectren Capital Corp. [Member]
Long term debt [Abstract]
Total long term debt outstanding	50,000,000	50,000,000
Fixed rate stated percentage (in hundredths)	4.53%
Maturity date	Dec. 31, 2025
Debt Instrument Issuance Date	2010-12-15
Debt Issuance	50,000,000
Fixed Rate Senior Unsecured Notes [Member] | 2021, 4.67 [Member] | Utility Holdings [Member]
Long term debt [Abstract]
Total long term debt outstanding	55,000,000	0
Fixed rate stated percentage (in hundredths)	4.67%
Maturity date	Nov. 30, 2021
Debt Instrument Issuance Date	2011-11-30
Debt Issuance	55,000,000
Fixed Rate Senior Unsecured Notes [Member] | 2026, 5.02% [Member] | Utility Holdings [Member]
Long term debt [Abstract]
Total long term debt outstanding	60,000,000	0
Fixed rate stated percentage (in hundredths)	5.02%
Maturity date	Nov. 30, 2026
Debt Instrument Issuance Date	2011-11-30
Debt Issuance	60,000,000
Fixed Rate Senior Unsecured Notes [Member] | 2041, 5.99% [Member] | Utility Holdings [Member]
Long term debt [Abstract]
Total long term debt outstanding	35,000,000	0
Fixed rate stated percentage (in hundredths)	5.99%
Maturity date	Dec. 02, 2041
Debt Instrument Issuance Date	2011-11-30
Debt Issuance	35,000,000
Fixed Rate Senior Unsecured Notes [Member] | Fixed Rate Senior Unsecured Notes 2042500 [Member] | Utility Holdings [Member]
Long term debt [Abstract]
Total long term debt outstanding	100,000,000
Fixed rate stated percentage (in hundredths)	5.00%
Maturity date	Feb. 03, 2042
Debt Instrument Issuance Date	2012-02-01
Debt Issuance	100,000,000
Proceeds from the sale of the notes, net of issuance costs	99,500,000
First Mortgage Bonds [Member] | SIGECO [Member]
Long term debt [Abstract]
Total long term debt outstanding	267,500,000	267,500,000
Debt Instrument Issuance Date	2009-03-26
Proceeds from the sale of the notes, net of issuance costs			40,600,000
Tax-exempt auction rate mode long-term debt remarketed			41,300,000
Future long term debt sinking fund fund requirements and maturities [Abstract]
Annual sinking fund requirement fixed percentage (in hundredths)	1.00%
Utility plant remaining unfunded under mortgage indenture	1,300,000,000
Gross utility plant balance subject to the mortgage indenture	2,700,000
First Mortgage Bonds [Member] | 2015, 1985 Pollution Control Series A, current adjustable rate 0.10%, tax exempt, 2011 weighted average: 0.19% | SIGECO [Member]
Long term debt [Abstract]
Total long term debt outstanding	9,800,000	9,800,000
First Mortgage Bonds [Member] | 2016, 1986 Series, 8.875% [Member] | SIGECO [Member]
Long term debt [Abstract]
Total long term debt outstanding	13,000,000	13,000,000
First Mortgage Bonds [Member] | 2020, 1998 Pollution Control Series B, 4.50%, tax exempt [Member] | SIGECO [Member]
Long term debt [Abstract]
Total long term debt outstanding	4,600,000	4,600,000
First Mortgage Bonds [Member] | 2023, 1993 Environmental Improvement Series B, 5.15%, tax exempt [Member] | SIGECO [Member]
Long term debt [Abstract]
Total long term debt outstanding	22,600,000	22,600,000
First Mortgage Bonds [Member] | 2024, 2000 Environmental Improvement Series A, 4.65%, tax exempt [Member] | SIGECO [Member]
Long term debt [Abstract]
Total long term debt outstanding	22,500,000	22,500,000
First Mortgage Bonds [Member] | 2025, 1998 Pollution Control Series A, current adjustable rate 0.08%, tax exempt, 2011 weighted average: 0.19% | SIGECO [Member]
Long term debt [Abstract]
Total long term debt outstanding	31,500,000	31,500,000
First Mortgage Bonds [Member] | 2029, 1999 Senior Notes, 6.72% [Member] | SIGECO [Member]
Long term debt [Abstract]
Total long term debt outstanding	80,000,000	80,000,000
First Mortgage Bonds [Member] | 2030, 1998 Pollution Control Series B, 5.00%, tax exempt [Member] | SIGECO [Member]
Long term debt [Abstract]
Total long term debt outstanding	22,000,000	22,000,000
First Mortgage Bonds [Member] | 2030, 1998 Pollution Control Series C, 5.35%, tax exempt [Member] | SIGECO [Member]
Long term debt [Abstract]
Total long term debt outstanding	22,200,000	22,200,000
First Mortgage Bonds [Member] | 2040, 2009 Environmental Improvement Series, 5.40%, tax exempt [Member] | SIGECO [Member]
Long term debt [Abstract]
Total long term debt outstanding	22,300,000	22,300,000
Fixed rate stated percentage (in hundredths)			5.40%
Maturity date			Dec. 31, 2040
Debt Instrument Issuance Date	2009-08-19
Debt Issuance			22,300,000
Proceeds from the sale of the notes, net of issuance costs			21,300,000
First Mortgage Bonds [Member] | 2041, 2007 Pollution Control Series, 5.45%, tax exempt [Member] | SIGECO [Member]
Long term debt [Abstract]
Total long term debt outstanding	17,000,000	17,000,000
Other Long Term Notes Payable [Member]
Long term debt [Abstract]
Total long term debt outstanding	4,100,000	1,100,000
Short Term Credit Facility [Member]
Short-term borrowings [Abstract]
Short-term borrowing capacity	600,000,000
Short term credit facilities expiration date	2016-12-31
Short Term Credit Facility [Member] | Utility Group [Member]
Short-term borrowings [Abstract]
Short-term borrowing capacity	350,000,000
Short term borrowings available	107,000,000
Year end [Abstract]
Balance Outstanding, end of period	242,800,000	47,000,000	16,400,000
Weighted Average Interest Rate, end of period (in hundredths)	0.57%	0.41%	0.25%
Annual Average [Abstract]
Balance Outstanding, annual average	39,600,000	14,000,000	29,200,000
Weighted Average Interest Rate, annual average (in hundredths)	0.48%	0.40%	1.28%
Maximum Month End Balance Outstanding	242,800,000	47,000,000	151,100,000
Short Term Credit Facility [Member] | Nonutility Group [Member]
Short-term borrowings [Abstract]
Short-term borrowing capacity	250,000,000
Short term borrowings available	166,000,000
Year end [Abstract]
Balance Outstanding, end of period	84,300,000	71,300,000	197,100,000
Weighted Average Interest Rate, end of period (in hundredths)	1.45%	2.01%	0.60%
Annual Average [Abstract]
Balance Outstanding, annual average	124,900,000	143,200,000	151,800,000
Weighted Average Interest Rate, annual average (in hundredths)	1.92%	0.93%	0.78%
Maximum Month End Balance Outstanding	$ 180,100,000	$ 174,600,000	$ 256,500,000