Business Segments (Segment Financial Information) (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
External customer revenues	$ 178.8		$ 192.9		$ 505.1	$ 576.5
Intersegment revenues	0.0		0.0		0.0	0.0
Total revenues	178.8		192.9		505.1	576.5
Depreciation and amortization	18.6		17.7		54.8	54.0
Fuel Costs	0.4		0.6		1.3	2.0
Depreciation and amortization					55.1	34.2
Interest expense	17.1		18.3		55.4	63.7
Gain (Loss) on Extinguishment of Debt	31.7		0.0		31.7	44.9
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	(19.7)		27.1		(13.6)	25.7
Net income / (loss) from continuing operations	(9.3)		36.2		(5.9)	37.5
Discontinued operations, net of tax	1.1		(0.8)		3.1	23.9
Net income/ (loss)	(8.2)	$ 1.9	35.4	$ 42.1	(2.8)	61.4
Capital expenditures	44.7		59.0		128.7	122.4
Total assets	1,907.5				1,907.5		$ 1,935.8
Operating Segments [Member] | Utility [Member]
Segment Reporting Information [Line Items]
External customer revenues	176.8		190.9		498.4	569.4
Intersegment revenues	0.2		0.2		0.7	0.8
Total revenues	177.0		191.1		499.1	570.2
Depreciation and amortization	18.2		17.4		53.7	52.9
Interest expense	5.9		6.1		18.5	19.9
Gain (Loss) on Extinguishment of Debt	0.0				0.0	0.0
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	21.3		37.7		49.7	108.8
Capital expenditures	44.6		58.9		125.1	121.1
Total assets	1,890.5				1,890.5		1,883.2
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
External customer revenues	2.0		2.0		6.7	7.1
Intersegment revenues	1.0		0.8		2.7	2.4
Total revenues	3.0		2.8		9.4	9.5
Depreciation and amortization	0.4		0.3		1.1	1.1
Interest expense	11.2		12.2		36.9	43.8
Gain (Loss) on Extinguishment of Debt	31.7				31.7	44.9
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	(41.0)		(10.6)		(63.3)	(83.1)
Capital expenditures	0.1		0.1		3.6	1.3
Total assets	17.0				17.0		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)		(1.0)		(3.4)	(3.2)
Total revenues	(1.2)		(1.0)		(3.4)	(3.2)
Depreciation and amortization	0.0		0.0		0.0	0.0
Interest expense	0.0		0.0		0.0	0.0
Gain (Loss) on Extinguishment of Debt	0.0				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		17.4		53.7	52.9
Fuel Costs	0.4		0.6		1.3	2.0
Depreciation and amortization					53.7	52.9
Interest expense	5.9		6.1		18.5	19.9
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	21.3		37.7		49.7	108.8
Net income/ (loss)	17.8		$ 44.9		47.3	$ 103.7
Total assets	$ 1,890.5				$ 1,890.5		$ 1,883.2