Business Segments (Segment Financial Information) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
External customer revenues	$ 174.7	$ 209.0
Intersegment revenues	0.0	0.0
Total revenues	174.7	209.0
Depreciation and amortization	17.8	18.4
Fuel Costs	4.0	3.5
Depreciation and amortization	17.8	(3.1)
Interest expense	18.9	23.7
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	0.4	19.2
Net income / (loss) from continuing operations	0.9	16.5
Discontinued operations, net of tax	1.0	25.6
Net income/ (loss)	1.9	42.1
Capital expenditures	44.6	34.3
Total assets	1,918.4		$ 1,935.8
Operating Segments [Member] | Utility [Member]
Segment Reporting Information [Line Items]
External customer revenues	168.7	201.1
Intersegment revenues	0.3	0.3
Total revenues	169.0	201.4
Depreciation and amortization	17.3	18.0
Interest expense	6.2	7.1
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	12.9	35.1
Capital expenditures	43.7	33.7
Total assets	1,874.6		1,883.2
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
External customer revenues	6.0	7.9
Intersegment revenues	0.8	0.8
Total revenues	6.8	8.7
Depreciation and amortization	0.5	0.4
Interest expense	12.7	16.6
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	(12.5)	(15.9)
Capital expenditures	0.9	0.6
Total assets	43.8		52.6
Adjustments and Eliminations [Member]
Segment Reporting Information [Line Items]
External customer revenues	0.0	0.0
Intersegment revenues	(1.1)	(1.1)
Total revenues	(1.1)	(1.1)
Depreciation and amortization	0.0	0.0
Interest expense	0.0	0.0
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	0.0	0.0
Capital expenditures	0.0	0.0
Subsidiaries [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	17.3	18.0
Fuel Costs	0.6	0.9
Depreciation and amortization	17.3	18.0
Interest expense	6.2	7.1
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	12.9	35.1
Net income/ (loss)	11.7	$ 29.0
Total assets	$ 1,874.6		$ 1,883.2