Business Segments (Segment Financial Information) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Segment Reporting Information [Line Items]
Gain (Loss) on Disposition of Business	$ 0.0	$ (11.7)
External customer revenues	209.0	207.4
Intersegment revenues	0.0	0.0
Total revenues	209.0	207.4
Depreciation and amortization	18.4	18.8
Fuel Costs	3.5	4.5
Depreciation and amortization	(3.1)	20.1
Interest expense	23.7	27.8
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	19.2	2.5
Net income / (loss) from continuing operations	16.5	2.3
Discontinued operations, net of tax	25.6	14.6
Net income/ (loss)	42.1	16.9
Capital expenditures	34.3	27.3
Total assets	1,865.7		$ 1,883.1
Operating Segments [Member] | Utility [Member]
Segment Reporting Information [Line Items]
External customer revenues	201.1	195.8
Intersegment revenues	0.3	0.2
Total revenues	201.4	196.0
Depreciation and amortization	18.0	18.6
Interest expense	7.1	8.2
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	35.1	19.3
Capital expenditures	33.7	24.6
Total assets	1,792.9		1,819.6
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
External customer revenues	7.9	11.6
Intersegment revenues	0.8	0.6
Total revenues	8.7	12.2
Depreciation and amortization	0.4	0.2
Interest expense	16.6	19.6
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	(15.9)	(16.8)
Capital expenditures	0.6	2.7
Total assets	607.9		545.9
Adjustments and Eliminations [Member]
Segment Reporting Information [Line Items]
External customer revenues	0.0	0.0
Intersegment revenues	(1.1)	(0.8)
Total revenues	(1.1)	(0.8)
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
Total assets	(535.1)		(482.4)
Subsidiaries [Member]
Segment Reporting Information [Line Items]
Gain (Loss) on Disposition of Business	0.0	(12.4)
Depreciation and amortization	18.0	18.6
Fuel Costs	0.9	0.9
Depreciation and amortization	18.0	18.6
Interest expense	7.1	8.2
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	35.1	19.3
Net income/ (loss)	29.0	$ 15.7
Total assets	$ 1,792.9		$ 1,819.6