Business Segments (Segment Financial Information) (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
External customer revenues	$ 155.1		$ 179.6		$ 326.3	$ 383.6
Intersegment revenues	0.0		0.0		0.0	0.0
Total revenues	155.1		179.6		326.3	383.6
Depreciation and amortization	18.5		17.9		36.2	36.3
Fuel Costs	0.3		0.5		0.9	1.4
Depreciation and amortization					36.4	13.9
Interest expense	19.4		21.7		38.3	45.4
Gain (Loss) on Extinguishment of Debt	0.0		44.9		0.0	44.9
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	3.7		(22.1)		6.1	(1.4)
Net income / (loss) from continuing operations	0.9		(18.5)		3.4	1.3
Discontinued operations, net of tax	2.6		2.4		2.0	24.7
Net income/ (loss)	3.5	$ 1.9	(16.1)	$ 42.1	5.4	26.0
Capital expenditures	39.4		29.1		84.0	63.4
Total assets	2,257.4				2,257.4		$ 1,935.8
Operating Segments [Member] | Utility [Member]
Segment Reporting Information [Line Items]
External customer revenues	152.8		177.4		321.6	378.5
Intersegment revenues	0.3		0.3		0.5	0.6
Total revenues	153.1		177.7		322.1	379.1
Depreciation and amortization	18.2		17.5		35.5	35.5
Interest expense	6.4		6.7		12.6	13.8
Gain (Loss) on Extinguishment of Debt			0.0			0.0
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	15.5		36.0		28.4	71.1
Capital expenditures	36.8		28.5		80.5	62.2
Total assets	1,933.1				1,933.1		1,883.2
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
External customer revenues	2.3		2.2		4.7	5.1
Intersegment revenues	0.9		0.8		1.7	1.6
Total revenues	3.2		3.0		6.4	6.7
Depreciation and amortization	0.3		0.4		0.7	0.8
Interest expense	13.0		15.0		25.7	31.6
Gain (Loss) on Extinguishment of Debt			44.9			44.9
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	(11.8)		(58.1)		(22.3)	(72.5)
Capital expenditures	2.6		0.6		3.5	1.2
Total assets	324.3				324.3		52.6
Adjustments and Eliminations [Member]
Segment Reporting Information [Line Items]
External customer revenues	0.0		0.0		0.0	0.0
Intersegment revenues	(1.2)		(1.1)		(2.2)	(2.2)
Total revenues	(1.2)		(1.1)		(2.2)	(2.2)
Depreciation and amortization	0.0		0.0		0.0	0.0
Interest expense			0.0			0.0
Gain (Loss) on Extinguishment of Debt			0.0			0.0
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	0.0		0.0		0.0	0.0
Capital expenditures	0.0		0.0		0.0	0.0
Subsidiaries [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	18.2		17.5		35.5	35.5
Fuel Costs	0.3		0.5		0.9	1.4
Depreciation and amortization					35.5	35.5
Interest expense	6.4		6.7		12.6	13.8
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	15.5		36.0		28.4	71.1
Net income/ (loss)	17.8		$ 29.8		29.5	$ 58.8
Total assets	$ 1,933.1				$ 1,933.1		$ 1,883.2