Business Segments (Segment Financial Information) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Segment Reporting Information [Line Items]
REVENUE	$ 876.5	$ 861.0	$ 869.0
Net purchased power	316.4	346.9	470.2
Operation and maintenance	259.1	232.1	184.7
Depreciation and amortization	95.2	82.1	80.0
Taxes other than income taxes	113.5	100.8	85.3
Interest expense	85.0	63.6	67.8
Other segment items (a)	(3.5)	(6.8)	(4.7)
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	10.8	42.3	(14.3)
Income Tax Expense (Benefit)	(3.0)	6.6	(9.6)
Net income (loss)	13.8	35.7	(4.7)
Segment Reporting Information, Income (Loss) before Income Taxes [Abstract]
Segment, Expenditure, Addition to Long-Lived Assets	549.5	387.9	287.3
Total assets (end of year)	3,417.4	2,906.2	2,422.4
Payments to Acquire Productive Assets	(549.5)	(387.9)	(287.3)
Intersegment revenue
Segment Reporting Information [Line Items]
REVENUE	0.0	0.0	0.0
Revenue from external customers
Segment Reporting Information [Line Items]
REVENUE	876.5	861.0	869.0
Utility [Member]
Segment Reporting Information [Line Items]
REVENUE	867.6	852.0	860.1
Operating Segments [Member] | Utility [Member]
Segment Reporting Information [Line Items]
REVENUE	867.6	852.0	860.1
Net purchased power	315.4	346.0	469.0
Operation and maintenance	258.3	229.8	185.1
Depreciation and amortization	93.4	80.7	78.7
Taxes other than income taxes	113.4	100.6	85.1
Interest expense	48.2	25.8	28.8
Other segment items (a)	(1.2)	(5.8)	(2.4)
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	40.1	74.9	15.8
Income Tax Expense (Benefit)	3.2	13.5	(3.1)
Net income (loss)	36.9	61.4	18.9
Segment Reporting Information, Income (Loss) before Income Taxes [Abstract]
Segment, Expenditure, Addition to Long-Lived Assets	547.9	384.3	283.7
Total assets (end of year)			2,405.9
Operating Segments [Member] | Utility [Member] | Intersegment revenue
Segment Reporting Information [Line Items]
REVENUE	0.9	0.7	0.8
Operating Segments [Member] | Utility [Member] | Revenue from external customers
Segment Reporting Information [Line Items]
REVENUE	866.7	851.3	859.3
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
REVENUE	14.7	14.1	13.3
Net purchased power	1.9	1.6	2.0
Operation and maintenance	5.7	6.7	3.2
Depreciation and amortization	1.8	1.4	1.3
Taxes other than income taxes	0.1	0.2	0.2
Interest expense	36.6	39.2	39.0
Other segment items (a)	(2.1)	(2.4)	(2.3)
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	(29.3)	(32.6)	(30.1)
Income Tax Expense (Benefit)	(6.2)	(6.9)	(6.5)
Net income (loss)	(23.1)	(25.7)	(23.6)
Segment Reporting Information, Income (Loss) before Income Taxes [Abstract]
Segment, Expenditure, Addition to Long-Lived Assets	1.6	3.6	3.6
Total assets (end of year)	62.2	35.2	16.5
Corporate, Non-Segment [Member] | Intersegment revenue
Segment Reporting Information [Line Items]
REVENUE	4.9	4.4	3.6
Corporate, Non-Segment [Member] | Revenue from external customers
Segment Reporting Information [Line Items]
REVENUE	9.8	9.7	9.7
Intersegment Eliminations
Segment Reporting Information [Line Items]
REVENUE	(5.8)	(5.1)	(4.4)
Net purchased power	(0.9)	(0.7)	(0.8)
Operation and maintenance	(4.9)	(4.4)	(3.6)
Depreciation and amortization	0.0	0.0	0.0
Taxes other than income taxes	0.0	0.0	0.0
Interest expense	0.2	(1.4)	(6.9)
Other segment items (a)	(0.2)	1.4	6.9
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	0.0	0.0	0.0
Income Tax Expense (Benefit)	0.0	0.0	0.0
Net income (loss)	0.0	0.0	0.0
Segment Reporting Information, Income (Loss) before Income Taxes [Abstract]
Segment, Expenditure, Addition to Long-Lived Assets	0.0	0.0	0.0
Intersegment Eliminations | Intersegment revenue
Segment Reporting Information [Line Items]
REVENUE	(5.8)	(5.1)	(4.4)
Intersegment Eliminations | Revenue from external customers
Segment Reporting Information [Line Items]
REVENUE	0.0	0.0	0.0
THE DAYTON POWER AND LIGHT COMPANY [Member]
Segment Reporting Information [Line Items]
REVENUE	867.6	852.0	860.1
Net purchased power	315.4	346.0	469.0
Operation and maintenance	258.3	229.8	185.1
Depreciation and amortization	93.4	80.7	78.7
Taxes other than income taxes	113.4	100.6	85.1
Interest expense	48.2	25.8	28.8
Other segment items (a)	(1.2)	(5.8)	(2.4)
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	40.1	74.9	15.8
Income Tax Expense (Benefit)	3.2	13.5	(3.1)
Net income (loss)	36.9	61.4	18.9
Segment Reporting Information, Income (Loss) before Income Taxes [Abstract]
Total assets (end of year)	3,355.2	2,871.0	2,405.9
Payments to Acquire Productive Assets	(547.9)	(384.3)	(283.7)
THE DAYTON POWER AND LIGHT COMPANY [Member] | Operating Segments [Member] | Utility [Member]
Segment Reporting Information, Income (Loss) before Income Taxes [Abstract]
Segment, Expenditure, Addition to Long-Lived Assets	$ 547.9	$ 384.3	$ 283.7