Business Segments (Segment Financial Information) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
External customer revenues	$ 672.7	$ 660.5	$ 743.7
Intersegment revenues	0.0	0.0	0.0
Total revenues	672.7	660.5	743.7
Fuel Costs	0.5	1.7	2.5
Depreciation and amortization	76.1	73.3	72.3
Interest expense	62.9	71.3	82.2
Gain (Loss) on Extinguishment of Debt	0.0	31.7	44.9
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	22.4	(11.9)	31.5
Net loss from continuing operations	22.9	(6.4)	51.8
Discontinued operations, net of tax	(0.8)	5.4	53.6
Cash capital expenditures	191.3	157.3	156.5
Total assets (end of year)	2,171.8	2,036.0	1,935.8
Operating Segments [Member] | Utility [Member]
Segment Reporting Information [Line Items]
External customer revenues	663.0	651.2	734.3
Intersegment revenues	0.7	0.9	1.1
Total revenues	663.7	652.1	735.4
Depreciation and amortization	74.6	71.8	70.8
Interest expense	24.2	24.3	26.0
Gain (Loss) on Extinguishment of Debt		0.0	0.0
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	52.8	58.1	124.3
Cash capital expenditures	189.3	153.3	155.5
Total assets (end of year)	2,171.8	2,014.7	1,883.2
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
External customer revenues	9.7	9.3	9.4
Intersegment revenues	3.5	3.6	3.2
Total revenues	13.2	12.9	12.6
Depreciation and amortization	1.5	1.5	1.5
Interest expense	38.7	47.0	56.2
Gain (Loss) on Extinguishment of Debt		31.7	44.9
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	(30.4)	(70.0)	(92.8)
Cash capital expenditures	2.0	4.0	1.0
Total assets (end of year)	9.2	21.3	52.6
Consolidation, Eliminations [Member]
Segment Reporting Information [Line Items]
External customer revenues	0.0	0.0	0.0
Intersegment revenues	(4.2)	(4.5)	(4.3)
Total revenues	(4.2)	(4.5)	(4.3)
Depreciation and amortization	0.0	0.0	0.0
Interest expense	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
Cash capital expenditures	0.0	0.0	0.0
THE DAYTON POWER AND LIGHT COMPANY [Member]
Segment Reporting Information [Line Items]
Fuel Costs	0.5	1.6	2.5
Depreciation and amortization	74.6	71.8	70.8
Interest expense	24.2	24.3	26.0
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	52.8	58.1	$ 124.3
Total assets (end of year)	$ 2,162.6	$ 2,014.7