Business Segments (Segment Financial Information) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Segment Reporting Information [Line Items]
External customer revenues	$ 861.0	$ 869.0	$ 672.7
Total revenue	861.0	869.0	672.7
Fuel Costs	0.0	0.1	0.5
Depreciation and amortization	82.1	80.0	76.1
Interest expense	63.6	67.8	62.9
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	42.3	(14.3)	22.4
Net loss from continuing operations	35.7	(4.7)	22.9
Discontinued operations, net of tax	0.0	0.0	(0.8)
Cash capital expenditures	387.9	287.3	191.3
Total assets (end of year)	2,906.2	2,422.4	2,171.8
Revenues	861.0	869.0	672.7
Intersegment revenue
Segment Reporting Information [Line Items]
Revenues	0.0	0.0	0.0
Utility [Member]
Segment Reporting Information [Line Items]
Revenues	852.0	860.1	663.7
Operating Segments [Member] | Utility [Member]
Segment Reporting Information [Line Items]
External customer revenues	851.3	859.3	663.0
Total revenue	852.0	860.1	663.7
Depreciation and amortization	80.7	78.7	74.6
Interest expense	25.8	28.8	24.2
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	74.9	15.8	52.8
Cash capital expenditures	384.3	283.7	189.3
Total assets (end of year)		2,405.9	2,162.6
Operating Segments [Member] | Utility [Member] | Intersegment revenue
Segment Reporting Information [Line Items]
Revenues	0.7	0.8	0.7
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
External customer revenues	9.7	9.7	9.7
Total revenue	14.1	13.3	13.2
Depreciation and amortization	1.4	1.3	1.5
Interest expense	37.8	39.0	38.7
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	(32.6)	(30.1)	(30.4)
Cash capital expenditures	3.6	3.6	2.0
Total assets (end of year)	35.2	16.5	9.2
Corporate, Non-Segment [Member] | Intersegment revenue
Segment Reporting Information [Line Items]
Revenues	4.4	3.6	3.5
Consolidation, Eliminations [Member]
Segment Reporting Information [Line Items]
External customer revenues	0.0	0.0	0.0
Total revenue	(5.1)	(4.4)	(4.2)
Depreciation and amortization	0.0	0.0	0.0
Interest expense	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
Cash capital expenditures	0.0	0.0	0.0
Intersegment Eliminations | Intersegment revenue
Segment Reporting Information [Line Items]
Revenues	(5.1)	(4.4)	(4.2)
THE DAYTON POWER AND LIGHT COMPANY [Member]
Segment Reporting Information [Line Items]
Fuel Costs	0.0	0.0	0.5
Depreciation and amortization	80.7	78.7	74.6
Interest expense	25.8	28.8	24.2
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	74.9	15.8	52.8
Total assets (end of year)	2,871.0	2,405.9
Revenues	$ 852.0	$ 860.1	$ 663.7