Business Segments (Segment Financial Information) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Gain (Loss) on Disposition of Business			$ (13.5)	$ 0.0
External customer revenues	$ 178.1	$ 174.5	383.8	370.0
Intersegment revenues	0.0	0.0	0.0	0.0
Total revenues	178.1	174.5	383.8	370.0
Depreciation and amortization	20.3	18.8	39.1	37.1
Fuel Costs	3.6	2.3	8.1	4.3
Depreciation and amortization			41.6	54.5
Impairment of Long-Lived Assets Held-for-use			1.2	66.4
Interest expense	24.0	27.6	51.8	54.9
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	(6.9)	(9.1)	(6.1)	(10.1)
Net income / (loss) from continuing operations	(5.4)	(6.4)	(4.5)	(6.8)
Discontinued operations, net of tax	8.9	6.9	24.9	(44.4)
Net income/ (loss)	3.5	0.5	20.4	(51.2)
Capital expenditures	23.4	25.0	50.7	66.4
Total assets	1,792.5		1,792.5		$ 2,049.2
Operating Segments [Member] | Utility [Member]
Segment Reporting Information [Line Items]
External customer revenues	168.6	167.9	364.4	357.7
Intersegment revenues	0.2	0.3	0.4	0.6
Total revenues	168.8	168.2	364.8	358.3
Depreciation and amortization	18.8	18.6	37.4	36.7
Interest expense	6.5	8.0	14.7	15.6
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	17.1	15.1	36.4	40.1
Capital expenditures	19.9	19.4	44.5	45.7
Total assets	1,700.6		1,700.6		1,689.4
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
External customer revenues	9.5	6.6	19.4	12.3
Intersegment revenues	0.8	1.3	1.4	2.7
Total revenues	10.3	7.9	20.8	15.0
Depreciation and amortization	1.5	0.2	1.7	0.4
Interest expense	17.5	19.6	37.1	39.3
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	(24.0)	(24.2)	(42.5)	(50.2)
Capital expenditures	3.5	5.6	6.2	20.7
Total assets	479.5		479.5		743.0
Adjustments and Eliminations [Member]
Segment Reporting Information [Line Items]
External customer revenues	0.0	0.0	0.0	0.0
Intersegment revenues	(1.0)	(1.6)	(1.8)	(3.3)
Total revenues	(1.0)	(1.6)	(1.8)	(3.3)
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
Total assets	(387.6)		(387.6)		(383.2)
Subsidiaries [Member]
Segment Reporting Information [Line Items]
Gain (Loss) on Disposition of Business	0.0	0.0	(12.4)	0.0
Depreciation and amortization	18.8	18.6	37.4	36.7
Fuel Costs	0.7	0.0	1.6	0.0
Depreciation and amortization			37.4	45.5
Impairment of Long-Lived Assets Held-for-use			0.0	66.3
Interest expense	6.5	8.0	14.7	15.6
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	17.1	15.1	36.4	40.1
Net income / (loss) from continuing operations	15.0	11.3	30.7	28.3
Discontinued operations, net of tax	0.0	4.8	0.0	(54.0)
Net income/ (loss)	15.0	16.1	30.7	(25.7)
Total assets	$ 1,700.6		$ 1,700.6		$ 1,689.4
Subsidiaries [Member] | Generation [Member]
Segment Reporting Information [Line Items]
Discontinued operations, net of tax		$ 4.8		$ (54.0)