Business Segments (Segment Financial Information) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Segment Reporting Information [Line Items]
External customer revenues	$ 869.0	$ 672.7	$ 660.5
Intersegment revenues	0.0	0.0	0.0
Total revenues	869.0	672.7	660.5
Fuel Costs	0.1	0.5	1.7
Depreciation and amortization	80.0	76.1	73.3
Interest expense	67.8	62.9	71.3
Gain (Loss) on Extinguishment of Debt	0.1	0.0	31.7
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	(14.3)	22.4	(11.9)
Net loss from continuing operations	(4.7)	22.9	(6.4)
Discontinued operations, net of tax	0.0	(0.8)	5.4
Cash capital expenditures	287.3	191.3	157.3
Total assets (end of year)	2,422.4	2,171.8	2,036.0
Operating Segments [Member] | Utility [Member]
Segment Reporting Information [Line Items]
External customer revenues	859.3	663.0	651.2
Intersegment revenues	0.8	0.7	0.9
Total revenues	860.1	663.7	652.1
Depreciation and amortization	78.7	74.6	71.8
Interest expense	28.8	24.2	24.3
Gain (Loss) on Extinguishment of Debt			0.0
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	15.8	52.8	58.1
Cash capital expenditures	283.7	189.3	153.3
Total assets (end of year)		2,162.6	2,014.7
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
External customer revenues	9.7	9.7	9.3
Intersegment revenues	3.6	3.5	3.6
Total revenues	13.3	13.2	12.9
Depreciation and amortization	1.3	1.5	1.5
Interest expense	39.0	38.7	47.0
Gain (Loss) on Extinguishment of Debt			31.7
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	(30.1)	(30.4)	(70.0)
Cash capital expenditures	3.6	2.0	4.0
Total assets (end of year)	16.5	9.2	21.3
Consolidation, Eliminations [Member]
Segment Reporting Information [Line Items]
External customer revenues	0.0	0.0	0.0
Intersegment revenues	(4.4)	(4.2)	(4.5)
Total revenues	(4.4)	(4.2)	(4.5)
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
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	0.0	0.5	1.6
Depreciation and amortization	78.7	74.6	71.8
Interest expense	28.8	24.2	24.3
Gain (Loss) on Extinguishment of Debt	0.1	0.0	0.0
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	15.8	52.8	$ 58.1
Total assets (end of year)	$ 2,405.9	$ 2,162.6