Business Segments (Segment Financial Information) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Segment Reporting Information [Line Items]
External customer revenues	$ 199.0	$ 207.7	$ 592.2	$ 591.5
Intersegment revenues	0.0	0.0	0.0	0.0
Total revenues	199.0	207.7	592.2	591.5
Depreciation and amortization	17.7	19.7	54.1	58.8
Fuel Costs	5.2	4.6	13.0	12.7
Depreciation and amortization			34.2	62.4
Interest expense	18.3	22.6	63.7	74.4
Gain (Loss) on Extinguishment of Debt	0.0	0.0	(44.9)	(6.4)
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	26.5	19.8	23.0	13.7
Net income / (loss) from continuing operations	35.9	16.7	35.6	12.2
Discontinued operations, net of tax	(0.5)	4.3	25.8	29.2
Net income/ (loss)	35.4	21.0	61.4	41.4
Capital expenditures	59.0	25.1	122.4	75.8
Total assets	1,816.3		1,816.3		$ 1,883.1
Operating Segments [Member] | Utility [Member]
Segment Reporting Information [Line Items]
External customer revenues	190.9	198.5	569.4	562.9
Intersegment revenues	0.2	0.2	0.8	0.6
Total revenues	191.1	198.7	570.2	563.5
Depreciation and amortization	17.4	19.1	52.9	56.5
Interest expense	6.1	5.8	19.9	20.5
Gain (Loss) on Extinguishment of Debt			0.0
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	37.7	37.5	108.8	73.9
Capital expenditures	58.9	20.5	121.1	65.0
Total assets	1,779.4		1,779.4		1,819.6
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
External customer revenues	8.1	9.2	22.8	28.6
Intersegment revenues	0.8	0.7	2.4	2.1
Total revenues	8.9	9.9	25.2	30.7
Depreciation and amortization	0.3	0.6	1.2	2.3
Interest expense	12.2	16.8	43.8	53.9
Gain (Loss) on Extinguishment of Debt			(44.9)
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	(11.2)	(17.7)	(85.8)	(60.2)
Capital expenditures	0.1	4.6	1.3	10.8
Total assets	36.9		36.9		63.5
Adjustments and Eliminations [Member]
Segment Reporting Information [Line Items]
External customer revenues	0.0	0.0	0.0	0.0
Intersegment revenues	(1.0)	(0.9)	(3.2)	(2.7)
Total revenues	(1.0)	(0.9)	(3.2)	(2.7)
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
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]
Gain (Loss) on Disposition of Business	0.0	0.0	0.0	(12.4)
Depreciation and amortization	17.4	19.1	52.9	56.5
Fuel Costs	0.6	0.1	2.0	1.7
Depreciation and amortization			52.9	56.5
Interest expense	6.1	5.8	19.9	20.5
Gain (Loss) on Extinguishment of Debt	0.0	0.0	0.0	(0.6)
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	37.7	37.5	108.8	73.9
Net income/ (loss)	44.9	$ 31.2	103.7	$ 61.9
Total assets	$ 1,779.4		$ 1,779.4		$ 1,819.6