Overview and Summary of Significant Accounting Policies (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($) mi² customer	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Significant Accounting Policies [Line Items]
Other Investments	$ 0.1	$ 0.2
Cash and Cash Equivalents, at Carrying Value	41.0	30.5
Restricted Cash and Cash Equivalents, Current	0.1	0.1
Capitalized Software, estimated amortization expense for year after next	$ 6.3
Service area, square miles | mi²	6,000
Capitalized interest for unregulated generation property	$ 6.5	$ 1.3	$ 1.6
Straight-line depreciation average annual composite basis (percent)	3.20%	3.30%	3.70%
Depreciation and amortization	$ 82.1	$ 80.0	$ 76.1
Insurance and claims costs	1.8	1.6
Insurance costs below coverage thresholds of third-party providers	8.0	7.8
Capitalized Computer Software, Amortization	4.1	3.3	3.2
Capitalized Software, estimated amortization over remaining useful life	28.7
Capitalized Software, estimated amortization expense for next twelve months	6.3
Capitalized Software, estimated amortization expense for three years in the future	5.9
Capitalized Software, estimated amortization expense for four years in the future	5.3
Capitalized Software, estimated amortization expense for five years in the future	4.9
Restricted Cash and Cash Equivalents	41.1	30.6	26.7	$ 25.5
Carrying Value	2,221.0	1,885.0
Other Assets, Noncurrent	52.4	40.3
Customer receivables	71.0	61.3
Unbilled revenue	19.4	24.0
Accounts Receivable, Allowance for Credit Loss	(0.9)	(0.5)
Accounts receivable, net	92.5	91.9
Accounts Receivable, Allowance for Credit Loss, Current	0.9	0.5	0.3
Accounts Receivable, Credit Loss Expense (Reversal)	5.4	2.5
Accounts Receivable, Allowance for Credit Loss, Writeoff	(6.0)	(4.1)
Accounts Receivable, Allowance for Credit Loss, Recovery	1.0	1.8
Other income	(56.8)	(63.6)	(62.9)
Income Tax Expense (Benefit)	6.6	(9.6)	(0.5)
Interest expense	63.6	67.8	62.9
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax	(0.8)	(0.8)	(0.8)
Accumulated other comprehensive income/(loss)	(4.6)	(2.4)	(4.8)
Other comprehensive income before reclassifications	(1.6)	2.2
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent	0.6	(0.2)
Other Comprehensive Income (Loss), Net of Tax	(2.2)	2.4	7.5
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)	(1.9)
Allowance for Funds Used During Construction, Equity Portion	5.0	5.7	2.1
Capitalized Computer Software, Gross	146.5	105.0
Capitalized Computer Software, Accumulated Amortization	(32.5)	(36.1)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Significant Accounting Policies [Line Items]
Accumulated other comprehensive income/(loss)	(15.8)	(14.4)	(17.6)
Other comprehensive income before reclassifications	(1.6)	2.2
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent		(1.0)
Other Comprehensive Income (Loss), Net of Tax	(1.4)	3.2
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Significant Accounting Policies [Line Items]
Accumulated other comprehensive income/(loss)	11.2	12.0	12.8
Other comprehensive income before reclassifications	0.0	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]
Significant Accounting Policies [Line Items]
Net income (loss)	(0.6)	0.2	1.1
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Significant Accounting Policies [Line Items]
Other income	0.2	1.3	2.5
Income Tax Expense (Benefit)	0.0	0.3	0.6
Net income (loss)	0.2	1.0	1.9
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)
Interest expense	1.0	1.0	1.0
Related Party
Significant Accounting Policies [Line Items]
Other	0.8	3.2
Nonrelated Party
Significant Accounting Policies [Line Items]
Other	2.2	3.9
Prepaid Implementation Costs for Software as a Service
Significant Accounting Policies [Line Items]
Other Assets, Noncurrent	14.8	12.5
THE DAYTON POWER AND LIGHT COMPANY [Member]
Significant Accounting Policies [Line Items]
Cash and Cash Equivalents, at Carrying Value	15.5	19.7
Restricted Cash and Cash Equivalents, Current	0.1	0.1
Payments of Ordinary Dividends, Common Stock	83.0		52.0
Capitalized Software, estimated amortization expense for year after next	$ 5.6
Approximate number of retail customers | customer	539,000
Service area, square miles | mi²	6,000
Capitalized interest for unregulated generation property	$ 6.5	$ 1.3	$ 1.6
Straight-line depreciation average annual composite basis (percent)	2.60%	2.80%	2.80%
Depreciation and amortization	$ 80.7	$ 78.7	$ 74.6
Insurance costs below coverage thresholds of third-party providers	3.5	3.2
Capitalized Computer Software, Amortization	3.9	3.1	3.0
Capitalized Software, estimated amortization over remaining useful life	25.4
Capitalized Software, estimated amortization expense for next twelve months	5.6
Capitalized Software, estimated amortization expense for three years in the future	5.2
Capitalized Software, estimated amortization expense for four years in the future	4.6
Capitalized Software, estimated amortization expense for five years in the future	4.4
Restricted Cash and Cash Equivalents	15.6	19.8	14.5	$ 11.8
Carrying Value	2,195.9	1,861.5
Other Assets, Noncurrent	52.9	40.4
Customer receivables	70.0	60.6
Unbilled revenue	19.4	24.0
Accounts Receivable, Allowance for Credit Loss	(0.9)	(0.5)
Accounts receivable, net	93.1	92.3
Accounts Receivable, Allowance for Credit Loss, Current	0.9	0.5	0.3
Accounts Receivable, Credit Loss Expense (Reversal)	5.4	2.5
Accounts Receivable, Allowance for Credit Loss, Writeoff	(6.0)	(4.1)
Accounts Receivable, Allowance for Credit Loss, Recovery	1.0	1.8
Other income	(20.0)	(27.0)	(26.7)
Income Tax Expense (Benefit)	13.5	(3.1)	5.7
Interest expense	25.8	28.8	24.2
Accumulated other comprehensive income/(loss)	(27.9)	(26.8)	(31.8)
Other comprehensive income before reclassifications	(1.5)	2.3
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent		(2.7)
Other Comprehensive Income (Loss), Net of Tax	(1.1)	5.0	10.3
Other Comprehensive Income (Loss), Defined Benefit Plan, Transition Asset (Obligation), Reclassification Adjustment from AOCI, after Tax	(0.4)	(2.7)	(3.9)
Allowance for Funds Used During Construction, Equity Portion	5.0	5.7	2.1
Capitalized Computer Software, Gross	142.2	101.5
Capitalized Computer Software, Accumulated Amortization	(30.8)	(34.3)
THE DAYTON POWER AND LIGHT COMPANY [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Significant Accounting Policies [Line Items]
Net income (loss)	0.4	2.7	3.9
THE DAYTON POWER AND LIGHT COMPANY [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Significant Accounting Policies [Line Items]
Other income	0.6	3.6	5.0
Income Tax Expense (Benefit)	0.2	0.9	1.1
THE DAYTON POWER AND LIGHT COMPANY [Member] | Related Party
Significant Accounting Policies [Line Items]
Other	2.4	4.4
THE DAYTON POWER AND LIGHT COMPANY [Member] | Nonrelated Party
Significant Accounting Policies [Line Items]
Other	2.2	3.8
THE DAYTON POWER AND LIGHT COMPANY [Member] | Prepaid Implementation Costs for Software as a Service
Significant Accounting Policies [Line Items]
Other Assets, Noncurrent	14.8	12.5
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	78.0	76.7	72.9
Electric Generation, Transmission and Distribution Equipment [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Significant Accounting Policies [Line Items]
Depreciation and amortization	$ 76.8	$ 75.6	$ 71.6