Business Segments (Segment Financial Information) (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
External customer revenues	$ 148.1		$ 155.1		$ 323.3	$ 326.3
Intersegment revenues	0.0		0.0		0.0	0.0
Total revenues	148.1		155.1		323.3	326.3
Depreciation and amortization	18.9		18.5		38.0	36.2
Fuel Costs	0.1		0.3		0.5	0.9
Depreciation and amortization					38.0	36.4
Interest expense	15.6		19.4		31.2	38.3
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	1.5		3.7		15.4	6.1
Net income / (loss) from continuing operations	0.6		0.9		14.8	3.4
Discontinued operations, net of tax	(0.2)		2.6		(0.8)	2.0
Net income/ (loss)	0.4	$ 13.6	3.5	$ 1.9	14.0	5.4
Capital expenditures	43.0		26.7		94.9	66.9
Total assets	2,048.9				2,048.9		$ 2,036.0
Operating Segments [Member] | Utility [Member]
Segment Reporting Information [Line Items]
External customer revenues	145.7		152.8		318.3	321.6
Intersegment revenues	0.2		0.3		0.4	0.5
Total revenues	145.9		153.1		318.7	322.1
Depreciation and amortization	18.5		18.2		37.2	35.5
Interest expense	6.0		6.4		12.0	12.6
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	9.1		15.5		30.6	28.4
Capital expenditures	42.4		24.1		94.0	63.4
Total assets							2,014.7
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
External customer revenues	2.4		2.3		5.0	4.7
Intersegment revenues	0.9		0.9		1.8	1.7
Total revenues	3.3		3.2		6.8	6.4
Depreciation and amortization	0.4		0.3		0.8	0.7
Interest expense	9.6		13.0		19.2	25.7
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	(7.6)		(11.8)		(15.2)	(22.3)
Capital expenditures	0.6		2.6		0.9	3.5
Total assets	23.4				23.4		21.3
Adjustments and Eliminations [Member]
Segment Reporting Information [Line Items]
External customer revenues	0.0		0.0			0.0
Intersegment revenues	(1.1)		(1.2)		(2.2)	(2.2)
Total revenues	(1.1)		(1.2)		(2.2)	(2.2)
Depreciation and amortization	0.0		0.0		0.0	0.0
Interest expense	0.0		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	18.5		18.2		37.2	35.5
Fuel Costs	0.1		0.3		0.5	0.9
Depreciation and amortization					37.2	35.5
Interest expense	6.0		6.4		12.0	12.6
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	9.1		15.5		30.6	28.4
Net income/ (loss)	8.6		$ 17.8		26.9	$ 29.5
Total assets	$ 2,025.5				$ 2,025.5		$ 2,014.7