GOODWILL AND OTHER INTANGIBLE ASSETS (Details) (USD $) In Millions, unless otherwise specified			3 Months Ended							3 Months Ended		3 Months Ended				3 Months Ended		3 Months Ended
	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2012 Nonregulated cost of sales	Mar. 31, 2011 Nonregulated cost of sales	Mar. 31, 2012 Depreciation and amortization	Mar. 31, 2011 Depreciation and amortization	Mar. 31, 2012 Customer-related year	Dec. 31, 2011 Customer-related	Dec. 31, 2011 Electric contract assets	Mar. 31, 2012 Patents year	Dec. 31, 2011 Patents	Mar. 31, 2012 Compressed natural gas fueling contract assets year	Dec. 31, 2011 Compressed natural gas fueling contract assets	Mar. 31, 2012 Renewable energy credits	Dec. 31, 2011 Renewable energy credits	Mar. 31, 2012 Nonregulated easements year	Dec. 31, 2011 Nonregulated easements	Mar. 31, 2012 Customer-owned equipment modifications year	Dec. 31, 2011 Customer-owned equipment modifications	Mar. 31, 2012 Emission allowances	Dec. 31, 2011 Emission allowances	Mar. 31, 2012 Other amortized intangible assets	Dec. 31, 2011 Other amortized intangible assets	Mar. 31, 2012 Trade name MGU	Dec. 31, 2011 Trade name MGU	Mar. 31, 2012 Trade name Trillium	Dec. 31, 2011 Trade name Trillium	Mar. 31, 2012 Trade name Pinnacle CNG Systems	Dec. 31, 2011 Trade name Pinnacle CNG Systems
Amortized intangible assets
Amortized intangible assets, carrying amount, gross	$ 60.6	$ 68.4					$ 34.5	$ 34.5	$ 7.8	$ 7.2	$ 7.2	$ 5.6	$ 5.6	$ 3.3	$ 2.8	$ 3.8	$ 3.8	$ 3.8	$ 3.6	$ 1.6	$ 1.7	$ 0.8	$ 1.4
Accumulated amortization of intangible assets	(27.5)	(33.1)					(25.4)	(24.8)	(6.6)	(0.1)		(0.6)	(0.3)			(0.7)	(0.7)	(0.3)	(0.2)	(0.1)	(0.2)	(0.3)	(0.3)
Amortized intangible assets, net	33.1	35.3					9.1	9.7	1.2	7.1	7.2	5.0	5.3	3.3	2.8	3.1	3.1	3.5	3.4	1.5	1.5	0.5	1.1
Weighted-average amortization period (in years)							10			18		9				12		12
Amortization expense			1.6	0.3	0.7	0.8
Unamortized intangible assets
Unamortized intangible asset, carrying amount																								5.2	5.2	3.5	3.5	1.5	1.5
Total intangible assets, gross	70.8	78.6
Total intangible assets	43.3	45.5
Amortization expense for the next five fiscal years
Amortization expense, 2012			5.9		2.5
Amortization expense, 2013			1.8		2.0
Amortization expense, 2014			1.4		1.7
Amortization expense, 2015			1.3		1.7
Amortization expense, 2016			$ 1.1		$ 1.5