Additional Balance Sheet & Operational Information (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Inventories [Abstract]
Gas in storage - at average cost	$ 0	$ 23.6
Gas in storage - at LIFO cost	31.8	26.2
Total Gas in storage	31.8	49.8
Materials and supplies	54.9	48.8
Coal and Oil for electric generation - at average cost	60.6	70.1
Nonutility Coal - at LIFO cost	13.0	16.2
Other	1.6	2.2
Total inventories	161.9	187.1
Amount by which cost of replacing inventories carried at LIFO cost exceeded carrying value	12.0	16.0
Prepayments and other current assets [Abstract]
Prepaid gas delivery service	42.4	40.7
Deferred income taxes	16.0	3.8
Prepaid taxes	5.1	31.5
Other prepayments and current assets	20.8	25.2
Total prepayments and other current assets	84.3	101.2
Investments in unconsolidated affiliates [Abstract]
Total investments in unconsolidated affiliates	92.9	135.2
Equity in earnings (loss) of unconsolidated affiliates [Abstract]
Total equity in earnings (losses) of unconsolidated affiliates	(32.0)	(8.6)	3.4
Other utility and corporate investments [Abstract]
Cash surrender value of life insurance policies	27.3	27.5
Municipal bond	3.9	4.1
Restricted cash	1.9	1.2
Other investments	1.3	1.3
Other utility and corporate investments	34.4	34.1
Segment Reporting Information [Line Items]
Goodwill	262.3	242.0
Accrued liabilities [Abstract]
Refunds to customers and customer deposits	56.4	54.8
Accrued taxes	33.5	40.9
Accrued interest	21.7	23.8
Accrued retirement and deferred compensation benefits	6.5	5.8
Accrued salaries and other	63.0	53.1
Total accrued liabilities	181.1	178.4
Asset Retirement Obligation [Roll Forward]
Accrued liabilities	181.1	178.4
Deferred credits and other liabilities	239.4	220.6
Other - net in the consolidated statement of income [Abstract]
AFUDC - borrowed funds	2.5	1.4	1.3
AFUDC - equity funds	0.2	0.3	0.7
Nonutility plant capitalized interest	2.1	2.1	6.0
Interest income, net	1.4	1.7	1.4
Other nonutility investment impairment charges	(9.9)	(4.7)	0
Cash surrender value of life insurance policies	0.1	1.9	4.1
All other income	0.1	2.1	0.2
Total other - net	(3.5)	4.8	13.7
Cash paid for [Abstract]
Interest	108.6	104.5	95.5
Income taxes	(9.0)	8.1	(12.2)
Accruals related to utility and nonutility plant purchases [Abstract]
Accruals related to utility and nonutility plant purchases	15.9	13.9
Asset Retirement Obligation Costs [Member]
Accrued liabilities [Abstract]
Total accrued liabilities	0.2	0.3
Asset Retirement Obligation [Roll Forward]
Asset retirement obligation, beginning balance	38.7	36.1
Accretion	2.5	2.1
Increases (decreases) in estimates, net of cash payments	2.5	0.5
Asset retirement obligation, ending balance	43.7	38.7
Accrued liabilities	0.2	0.3
Deferred credits and other liabilities	43.5	38.4
Utility Group [Member] | Gas Utility Services [Member]
Segment Reporting Information [Line Items]
Goodwill	205.0	205.0
Nonutility Group [Member]
Investments in unconsolidated affiliates [Abstract]
Total investments in unconsolidated affiliates	7.3
Nonutility Group [Member] | Infrastructure Services [Member]
Segment Reporting Information [Line Items]
Goodwill	55.2	34.9
Nonutility Group [Member] | Energy Services [Member]
Segment Reporting Information [Line Items]
Goodwill	2.1	2.1
ProLiance Holdings, LLC [Member]
Investments in unconsolidated affiliates [Abstract]
Total investments in unconsolidated affiliates	85.4	123.2
Equity in earnings (loss) of unconsolidated affiliates [Abstract]
Total equity in earnings (losses) of unconsolidated affiliates	(28.6)	(2.5)	3.6
Haddington Energy Partners, LP [Member]
Investments in unconsolidated affiliates [Abstract]
Total investments in unconsolidated affiliates	3.4	3.4
Equity in earnings (loss) of unconsolidated affiliates [Abstract]
Total equity in earnings (losses) of unconsolidated affiliates	0	(6.1)	0.9
Other Nonutility Partnerships and Corporations [Member]
Investments in unconsolidated affiliates [Abstract]
Total investments in unconsolidated affiliates	3.9	8.4
Other Utility Investments [Member]
Investments in unconsolidated affiliates [Abstract]
Total investments in unconsolidated affiliates	0.2	0.2
Other Unconsolidated Affiliates [Member]
Equity in earnings (loss) of unconsolidated affiliates [Abstract]
Total equity in earnings (losses) of unconsolidated affiliates	$ (3.4)	$ 0	$ (1.1)