Overview and Summary of Significant Accounting Policies (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2024 USD ($) mi² customer	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Jan. 01, 2025 USD ($)	Dec. 31, 2021 USD ($)
Significant Accounting Policies [Line Items]
Other Investments	$ 0.1	$ 0.2
Cash and Cash Equivalents, at Carrying Value	54.0	41.0
Restricted Cash and Cash Equivalents, Current	0.1	0.1
Capitalized Software, estimated amortization expense for year after next	$ 15.5
Service area, square miles | mi²	6,000
Capitalized interest for unregulated generation property	$ 7.7	$ 6.5	$ 1.3
Straight-line depreciation average annual composite basis (percent)	2.90%	3.20%	3.30%
Depreciation and amortization	$ 95.2	$ 82.1	$ 80.0
Insurance and claims costs	2.2	1.8
Insurance costs below coverage thresholds of third-party providers	7.3	8.0
Capitalized Computer Software, Amortization	9.8	4.1	3.3
Capitalized Software, estimated amortization over remaining useful life	75.8
Capitalized Software, estimated amortization expense for next twelve months	15.7
Capitalized Software, estimated amortization expense for three years in the future	15.2
Capitalized Software, estimated amortization expense for four years in the future	14.9
Capitalized Software, estimated amortization expense for five years in the future	14.5
Restricted Cash and Cash Equivalents	54.1	41.1	30.6
Carrying Value	2,571.4	2,221.0
Other Assets, Noncurrent	45.9	52.4
Customer receivables	79.8	71.0
Unbilled revenue	24.1	19.4
Accounts Receivable, Allowance for Credit Loss	(6.1)	(0.9)
Accounts receivable, net	106.8	92.5
Accounts Receivable, Allowance for Credit Loss, Current	6.1	0.9	0.5
Accounts Receivable, Credit Loss Expense (Reversal)	8.3	5.4
Accounts Receivable, Allowance for Credit Loss, Writeoff	(3.7)	(6.0)
Accounts Receivable, Allowance for Credit Loss, Recovery	0.6	1.0
Income Tax Expense (Benefit)	(3.0)	6.6	(9.6)
Net income (loss)	13.8	35.7	(4.7)
Interest expense	85.0	63.6	67.8
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax	(0.8)	(0.8)	(0.8)
Accumulated other comprehensive income/(loss)	(5.3)	(4.6)	(2.4)
Other comprehensive loss before reclassifications	0.0	(1.6)
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent	0.7	0.6
Other Comprehensive Income (Loss), Net of Tax	(0.7)	(2.2)	2.4
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax	(0.8)	(0.8)	(0.8)
Other Comprehensive Income (Loss), Defined Benefit Plan, Transition Asset (Obligation), Reclassification Adjustment from AOCI, after Tax		(0.2)	(1.0)
Allowance for Funds Used During Construction, Equity Portion	6.2	5.0	5.7
Capitalized Computer Software, Gross	197.7	146.5
Capitalized Computer Software, Accumulated Amortization	(22.6)	(32.5)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Significant Accounting Policies [Line Items]
Accumulated other comprehensive income/(loss)	(15.7)	(15.8)	(14.4)
Other comprehensive loss before reclassifications		(1.6)
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent		(0.2)
Other Comprehensive Income (Loss), Net of Tax	0.1	(1.4)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Significant Accounting Policies [Line Items]
Accumulated other comprehensive income/(loss)	10.4	11.2	12.0
Other comprehensive loss before reclassifications		0.0
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent		0.8
Other Comprehensive Income (Loss), Net of Tax	(0.8)	(0.8)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Significant Accounting Policies [Line Items]
Income Tax Expense (Benefit)		0.0	0.3
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Significant Accounting Policies [Line Items]
Income Tax Expense (Benefit)	(0.2)	(0.2)	(0.2)
Related Party
Significant Accounting Policies [Line Items]
Other	3.0	0.8
Nonrelated Party
Significant Accounting Policies [Line Items]
Other	6.0	2.2
Prepaid Implementation Costs for Software as a Service
Significant Accounting Policies [Line Items]
Other Assets, Noncurrent	4.0	14.8
THE DAYTON POWER AND LIGHT COMPANY [Member]
Significant Accounting Policies [Line Items]
Cash and Cash Equivalents, at Carrying Value	24.6	15.5
Restricted Cash and Cash Equivalents, Current	0.1	0.1
Payments of Ordinary Dividends, Common Stock	40.0		64.0
Capitalized Software, estimated amortization expense for year after next	$ 15.1
Approximate number of retail customers | customer	537,000
Service area, square miles | mi²	6,000
Capitalized interest for unregulated generation property	$ 7.7	$ 6.5	$ 1.3
Straight-line depreciation average annual composite basis (percent)	2.40%	2.60%	2.80%
Depreciation and amortization	$ 93.4	$ 80.7	$ 78.7
Insurance and claims costs		3.7
Insurance costs below coverage thresholds of third-party providers	3.7	3.5
Capitalized Computer Software, Amortization	9.3	3.9	3.1
Capitalized Software, estimated amortization over remaining useful life	74.3
Capitalized Software, estimated amortization expense for next twelve months	15.3
Capitalized Software, estimated amortization expense for three years in the future	14.8
Capitalized Software, estimated amortization expense for four years in the future	14.6
Capitalized Software, estimated amortization expense for five years in the future	14.5
Restricted Cash and Cash Equivalents	24.7	15.6	19.8		$ 14.5
Carrying Value	2,546.2	2,195.9
Other Assets, Noncurrent	43.2	52.9
Customer receivables	79.0	70.0
Unbilled revenue	24.1	19.4
Accounts Receivable, Allowance for Credit Loss	(6.1)	(0.9)
Accounts receivable, net	106.6	93.1
Accounts Receivable, Allowance for Credit Loss, Current	6.1	0.9	0.5
Accounts Receivable, Credit Loss Expense (Reversal)	8.3	5.4
Accounts Receivable, Allowance for Credit Loss, Writeoff	(3.7)	(6.0)
Accounts Receivable, Allowance for Credit Loss, Recovery	0.6	1.0
Income Tax Expense (Benefit)	3.2	13.5	(3.1)
Net income (loss)	36.9	61.4	18.9
Interest expense	48.2	25.8	28.8
Accumulated other comprehensive income/(loss)	(26.4)	(27.9)
Other Comprehensive Income (Loss), Net of Tax	1.5	(1.1)	5.0
Other Comprehensive Income (Loss), Defined Benefit Plan, Transition Asset (Obligation), Reclassification Adjustment from AOCI, after Tax		(0.4)	(2.7)
Allowance for Funds Used During Construction, Equity Portion	6.2	5.0	5.7
Capitalized Computer Software, Gross	193.8	142.2
Capitalized Computer Software, Accumulated Amortization	(20.7)	(30.8)
THE DAYTON POWER AND LIGHT COMPANY [Member] | Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Significant Accounting Policies [Line Items]
Accumulated other comprehensive income/(loss)	(26.4)	(27.9)	(26.8)
Other comprehensive loss before reclassifications		(1.5)
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent		(0.4)
Other Comprehensive Income (Loss), Net of Tax	1.5	(1.1)
THE DAYTON POWER AND LIGHT COMPANY [Member] | Related Party
Significant Accounting Policies [Line Items]
Other	3.6	2.4
THE DAYTON POWER AND LIGHT COMPANY [Member] | Nonrelated Party
Significant Accounting Policies [Line Items]
Other	6.0	2.2
THE DAYTON POWER AND LIGHT COMPANY [Member] | Prepaid Implementation Costs for Software as a Service
Significant Accounting Policies [Line Items]
Other Assets, Noncurrent	4.0	14.8
Note to DPL Capital Trust II Maturing in 2031 - 8.125% [Member]
Significant Accounting Policies [Line Items]
Note payable to trust	15.6	15.6
Electric Generation, Transmission and Distribution Equipment [Member]
Significant Accounting Policies [Line Items]
Depreciation and amortization	85.4	78.0	76.7
Electric Generation, Transmission and Distribution Equipment [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Significant Accounting Policies [Line Items]
Depreciation and amortization	$ 84.1	$ 76.8	$ 75.6
Forecast [Member]
Significant Accounting Policies [Line Items]
Ohio Holdings Investment Percent				15.00%
Ohio Investment Percent				17.65%
Ohio Investments Purchase price				$ 273.0
CDPQ Investment percent				30.00%
CDPQ Investment total				$ 546.0
Forecast [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Significant Accounting Policies [Line Items]
Ohio Holdings Investment Percent				15.00%
Ohio Investment Percent				17.65%
Ohio Investments Purchase price				$ 273.0
CDPQ Investment percent				30.00%
CDPQ Investment total				$ 546.0
Ohio Holdings Purchase price				$ 273.0