Regulatory Matters (Details) - USD ($) $ in Millions		12 Months Ended
	Nov. 30, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Aug. 01, 2018
Regulatory assets earning a return		$ 8.1
Regulatory Assets, Noncurrent		176.8	$ 193.6
Regulatory Assets, Current		24.5	27.5
Regulatory Assets		201.3	221.1
Regulatory Liability, Noncurrent		229.3	218.3
Regulatory Liability, Current		14.6	18.0
Regulatory Liabilities		243.9	236.3
Distribution Investment Rider	$ 120.8
TCJA Yearly Refund to Customers Per DRO		4.0
DRO Vegetation Management Cost Baseline					$ 10.7
DRO Vegetation Management Cost Deferral Cap		4.6
RSC Rider		$ 79.0
Return on Equity SEET Threshold		9.85%
Due from PJM transmission settlement		$ 1.7	1.7			$ 40.6
PJM transmission enhancement repayment amount		33.8
Recovery of Smart Grid Plan Phase 1 capital investments		249.0
Aggregate cap of recoverable Smart Grid Plan investments and expenses		267.6
DP&L shareholder funding under Smart Grid Plan		30.0
Transmission System Refund		4.4
Cash Contribution from Parent Company		150.0	150.0
Equity Contribution from Parent		132.5	98.0	$ 0.0
Proceeds from Capital Contribution from Parent		150.0
TFR True-Up Liability		12.6
TFR True-up Liability, Current		0.4
Vegetation Management and Other [Member]
Regulatory Assets, Noncurrent		$ 18.7
Undercollections to be collected [Member]
Regulatory Assets Type of Recovery		A/B
Regulatory Assets, Current		$ 23.9	26.8
Amounts being recovered through base rates [Member]
Regulatory Assets Type of Recovery		B
Regulatory Assets, Current		$ 0.6	0.7
Pension Costs [Member]
Regulatory Assets Type of Recovery		B
Regulatory Assets, Noncurrent		$ 76.2	94.4
Unrecovered OVEC Charges [Member]
Regulatory Assets Type of Recovery		C
Regulatory Assets, Noncurrent		$ 28.9	28.9
Deferred Regulatory Compliance Costs [Member]
Regulatory Assets Type of Recovery		B
Regulatory Assets, Noncurrent		$ 6.3	6.3
Ccem Smart Grid And Advanced Metering Infrastructure Cost [Member]
Regulatory Assets Type of Recovery		B
Regulatory Assets, Noncurrent		$ 5.2	8.5
Loss on Reacquired Debt [Member]
Regulatory Assets Type of Recovery		B
Regulatory Assets, Noncurrent		$ 4.3	7.1
Storm Costs [Member]
Regulatory Assets Type of Recovery		A
Regulatory Assets, Noncurrent		$ 15.2	11.5
Vegetation Management [Member]
Regulatory Assets Type of Recovery		A/B
Regulatory Assets, Noncurrent			15.7
Decoupling Deferral and Other [Member] [Domain]
Regulatory Assets Type of Recovery		C
Regulatory Assets, Noncurrent		$ 13.8	13.8
Uncollectible and Other [Member] [Domain]
Regulatory Assets Type of Recovery		C
Regulatory Assets, Noncurrent		$ 6.4	7.4
COVID-19 Deferral [Member]
Regulatory Assets, Noncurrent		$ 0.9	1.2
Storm Costs
Regulatory Assets Type of Recovery		B
Regulatory Assets, Noncurrent		$ 1.8	0.0
Subsidiaries [Member]
Regulatory assets earning a return		8.1
Regulatory Assets, Noncurrent		176.8	193.6
Regulatory Assets, Current		24.5	27.5
Regulatory Assets		201.3	221.1
Regulatory Liability, Noncurrent		229.3	218.3
Regulatory Liability, Current		14.6	18.0
Regulatory Liabilities		243.9	236.3
Distribution Investment Rider	$ 120.8
TCJA Yearly Refund to Customers Per DRO		4.0
DRO Vegetation Management Cost Baseline					$ 10.7
DRO Vegetation Management Cost Deferral Cap		4.6
RSC Rider		$ 79.0
Return on Equity SEET Threshold		9.85%
Due from PJM transmission settlement		$ 1.7	1.7			$ 40.6
PJM transmission enhancement repayment amount		33.8
Recovery of Smart Grid Plan Phase 1 capital investments		249.0
Aggregate cap of recoverable Smart Grid Plan investments and expenses		267.6
DP&L shareholder funding under Smart Grid Plan		30.0
Transmission System Refund		4.4
Equity Contribution from Parent		150.0	150.0	$ 0.0
TFR True-Up Liability		12.6
TFR True-up Liability, Current		0.4
Subsidiaries [Member] | Vegetation Management and Other [Member]
Regulatory Assets, Noncurrent		$ 18.7
Subsidiaries [Member] | Undercollections to be collected [Member]
Regulatory Assets Type of Recovery		A/B
Regulatory Assets, Current		$ 23.9	26.8
Subsidiaries [Member] | Amounts being recovered through base rates [Member]
Regulatory Assets Type of Recovery		B
Regulatory Assets, Current		$ 0.6	0.7
Subsidiaries [Member] | Pension Costs [Member]
Regulatory Assets Type of Recovery		B
Regulatory Current Asset, End Date for Recovery		Ongoing
Regulatory Assets, Noncurrent		$ 76.2	94.4
Subsidiaries [Member] | Unrecovered OVEC Charges [Member]
Regulatory Assets Type of Recovery		C
Regulatory Current Asset, End Date for Recovery		Undetermined
Regulatory Assets, Noncurrent		$ 28.9	28.9
Subsidiaries [Member] | Deferred Regulatory Compliance Costs [Member]
Regulatory Assets Type of Recovery		B
Regulatory Current Asset, End Date for Recovery		Undetermined
Regulatory Assets, Noncurrent		$ 6.3	6.3
Subsidiaries [Member] | Ccem Smart Grid And Advanced Metering Infrastructure Cost [Member]
Regulatory Assets Type of Recovery		B
Regulatory Current Asset, End Date for Recovery		2026
Regulatory Assets, Noncurrent		$ 5.2	8.5
Subsidiaries [Member] | Loss on Reacquired Debt [Member]
Regulatory Assets Type of Recovery		B
Regulatory Current Asset, End Date for Recovery		Various
Regulatory Assets, Noncurrent		$ 4.3	7.1
Subsidiaries [Member] | Storm Costs [Member]
Regulatory Assets Type of Recovery		A
Regulatory Current Asset, End Date for Recovery		Undetermined
Regulatory Assets, Noncurrent		$ 15.2	11.5
Subsidiaries [Member] | Vegetation Management [Member]
Regulatory Assets Type of Recovery		A/B
Regulatory Current Asset, End Date for Recovery		Undetermined
Regulatory Assets, Noncurrent			15.7
Subsidiaries [Member] | Decoupling Deferral and Other [Member] [Domain]
Regulatory Assets Type of Recovery		C
Regulatory Current Asset, End Date for Recovery		Undetermined
Regulatory Assets, Noncurrent		$ 13.8	13.8
Subsidiaries [Member] | Uncollectible Receivables [Member]
Regulatory Current Asset, End Date for Recovery		Undetermined
Subsidiaries [Member] | Uncollectible and Other [Member] [Domain]
Regulatory Assets Type of Recovery		C
Regulatory Assets, Noncurrent		$ 6.4	7.4
Subsidiaries [Member] | COVID-19 Deferral [Member]
Regulatory Assets, Noncurrent		$ 0.9	1.2
Subsidiaries [Member] | Storm Costs
Regulatory Assets Type of Recovery		B
Regulatory Current Asset, End Date for Recovery		Undetermined
Postretirement Benefit Costs [Member]
Regulatory Liabilities Type of Recovery		B
Regulatory Liability, Noncurrent		$ 2.8	4.1
Postretirement Benefit Costs [Member] | Subsidiaries [Member]
Regulatory Liabilities Type of Recovery		B
Regulatory Liability, Amortization Through		Ongoing
Regulatory Liability, Noncurrent		$ 2.8	4.1
PJM transmission enhancement settlement repayment amount [Member]
Regulatory Liabilities Type of Recovery		A
Regulatory Liability, Noncurrent		$ 5.1	7.0
PJM transmission enhancement settlement repayment amount [Member] | Subsidiaries [Member]
Regulatory Liabilities Type of Recovery		A
Regulatory Liability, Noncurrent		$ 5.1	7.0
Deferred Income Tax Charge [Member]
Regulatory Liability, Noncurrent		$ 57.5	61.2
Deferred Income Tax Charge [Member] | Subsidiaries [Member]
Regulatory Liability, Amortization Through		Various
Regulatory Liability, Noncurrent		$ 57.5	61.2
TCJA Regulatory Liability [Member] [Domain]
Regulatory Liabilities Type of Recovery		B
Regulatory Liability, Noncurrent		$ 6.5	7.2
TCJA Regulatory Liability [Member] [Domain] | Subsidiaries [Member]
Regulatory Liabilities Type of Recovery		B
Regulatory Liability, Amortization Through		Ongoing
Regulatory Liability, Noncurrent		$ 6.5	7.2
Removal Costs [Member]
Regulatory Liability, Noncurrent		145.2	138.8
Removal Costs [Member] | Subsidiaries [Member]
Regulatory Liability, Noncurrent		$ 145.2	138.8
Overcollection of costs to be refunded [Member]
Regulatory Liabilities Type of Recovery		A/B
Regulatory Liability, Noncurrent		$ 14.2	18.0
Overcollection of costs to be refunded [Member] | Subsidiaries [Member]
Regulatory Liabilities Type of Recovery		A/B
Regulatory Liability, Noncurrent		$ 14.2	18.0
Transmission Formula Rate Credits
Regulatory Liabilities Type of Recovery		A
Regulatory Liability, Noncurrent		$ 0.4	0.0
Transmission Formula Rate Credits | Subsidiaries [Member]
Regulatory Liabilities Type of Recovery		A
Regulatory Liability, Noncurrent		$ 0.4	0.0
Transmission Formula Rate Credits, Noncurrent
Regulatory Liability, Noncurrent		12.2	0.0
Transmission Formula Rate Credits, Noncurrent | Subsidiaries [Member]
Regulatory Liability, Noncurrent		12.2	$ 0.0
Forecast [Member]
DRO Vegetation Management Cost Baseline		15.7
Forecast [Member] | Subsidiaries [Member]
DRO Vegetation Management Cost Baseline		15.7
Long-term [Member]
Due from PJM transmission settlement		5.1
Long-term [Member] | Subsidiaries [Member]
Due from PJM transmission settlement		5.1
Short-term [Member]
Due from PJM transmission settlement		1.7
Short-term [Member] | Subsidiaries [Member]
Due from PJM transmission settlement		$ 1.7