Business Segments (Segment Financial Information) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Segment Reporting Information [Line Items]
External customer revenues	$ 188.2	$ 178.8	$ 511.5	$ 505.1
Intersegment revenues	0.0	0.0	0.0	0.0
Total revenues	188.2	178.8	511.5	505.1
Depreciation and amortization	18.9	18.6	56.9	54.8
Interest expense	15.8	17.1	47.0	55.4
Gain (Loss) on Extinguishment of Debt	0.0	31.7	0.0	31.7
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	7.7	(19.7)	23.1	(13.6)
Total assets	2,088.7		2,088.7		$ 2,036.0
Operating Segments [Member] | Utility [Member]
Segment Reporting Information [Line Items]
External customer revenues	185.9	176.8	504.2	498.4
Intersegment revenues	0.2	0.2	0.6	0.7
Total revenues	186.1	177.0	504.8	499.1
Depreciation and amortization	18.6	18.2	55.8	53.7
Interest expense	6.1	5.9	18.1	18.5
Gain (Loss) on Extinguishment of Debt		0.0		0.0
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	16.1	21.3	46.7	49.7
Total assets					2,014.7
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
External customer revenues	2.3	2.0	7.3	6.7
Intersegment revenues	0.8	1.0	2.6	2.7
Total revenues	3.1	3.0	9.9	9.4
Depreciation and amortization	0.3	0.4	1.1	1.1
Interest expense	9.7	11.2	28.9	36.9
Gain (Loss) on Extinguishment of Debt		31.7		31.7
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	(8.4)	(41.0)	(23.6)	(63.3)
Total assets	21.1		21.1		21.3
Adjustments and Eliminations [Member]
Segment Reporting Information [Line Items]
External customer revenues	0.0	0.0		0.0
Intersegment revenues	(1.0)	(1.2)	(3.2)	(3.4)
Total revenues	(1.0)	(1.2)	(3.2)	(3.4)
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		0.0
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	0.0	0.0	0.0	0.0
Subsidiaries [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization	18.6	18.2	55.8	53.7
Interest expense	6.1	5.9	18.1	18.5
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	16.1	$ 21.3	46.7	$ 49.7
Total assets	$ 2,067.6		$ 2,067.6		$ 2,014.7