Regulatory Matters (Details) - USD ($) $ in Millions				12 Months Ended
	Nov. 30, 2020	Oct. 01, 2018	Oct. 20, 2017	Dec. 31, 2020	Dec. 31, 2018	Dec. 31, 2019	Aug. 01, 2018
Regulatory assets earning a return				$ 16.3
DRO revenue requirement		$ 248.0
Regulatory Assets, Noncurrent				193.6		$ 173.8
Regulatory Assets, Current				27.5		19.7
Regulatory Assets				221.1		193.5
Regulatory Liability, Noncurrent				218.3		243.6
Regulatory Liability, Current				18.0		27.9
Regulatory Liabilities				236.3		271.5
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
Distribution Modernization Rider			$ 105.0
RSC Rider				$ 79.0
Return on Equity SEET Threshold				9.85%
Due from PJM transmission settlement				$ 1.7		1.8	$ 40.8
PJM transmission enhancement repayment amount				$ 32.1
Tax rate after Tax Cuts and Jobs Act of 2017				21.00%
Refund of eligible excess ADIT and any related regulatory liability as required by the PUCO				$ 65.1
Refund of eligible excess ADIT and any related regulatory liability as required by the PUCO, including taxes				83.2
Reduction of Long-term regulatory liability related to deferred income taxes				23.4
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
Proposed annual increase in transmission rates to reflect effects on TCJA				$ 7.0
Proposed Increased Return on Equity SEET Threshold				9.99%
Vegetation Management and Other [Member]
Regulatory Assets, Noncurrent				$ 15.7
Undercollections to be collected [Member]
Regulatory Assets Type of Recovery				A/B
Regulatory Assets, Current				$ 26.8		19.1
Amounts being recovered through base rates [Member]
Regulatory Assets Type of Recovery				B
Regulatory Assets, Current				$ 0.7		0.6
Pension Costs [Member]
Regulatory Assets Type of Recovery				B
Regulatory Current Asset, End Date for Recovery				Ongoing
Regulatory Assets, Noncurrent				$ 94.4		83.9
Unrecovered OVEC Charges [Member]
Regulatory Assets Type of Recovery				C
Regulatory Current Asset, End Date for Recovery				Undetermined
Regulatory Assets, Noncurrent				$ 28.9		29.1
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
Ccem Smart Grid And Advanced Metering Infrastructure Cost [Member]
Regulatory Assets Type of Recovery				B
Regulatory Current Asset, End Date for Recovery				Undetermined
Regulatory Assets, Noncurrent				$ 8.5		8.5
Loss on Reacquired Debt [Member]
Regulatory Assets Type of Recovery				B
Regulatory Current Asset, End Date for Recovery				Various
Regulatory Assets, Noncurrent				$ 7.1		10.0
Storm Costs [Member]
Regulatory Assets Type of Recovery				A
Regulatory Current Asset, End Date for Recovery				Undetermined
Regulatory Assets, Noncurrent				$ 11.5		5.1
Vegetation Management [Member]
Regulatory Assets Type of Recovery				A/B
Regulatory Current Asset, End Date for Recovery				Undetermined
Regulatory Assets, Noncurrent						12.7
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
Uncollectible Receivables [Member]
Regulatory Current Asset, End Date for Recovery				Undetermined
Uncollectible and Other [Member] [Domain]
Regulatory Assets Type of Recovery				C
Regulatory Assets, Noncurrent				$ 7.4		4.4
COVID-19 Deferral [Member]
Regulatory Assets, Noncurrent				1.2
Subsidiaries [Member]
Regulatory assets earning a return				16.3
DRO revenue requirement		$ 248.0
Regulatory Assets, Noncurrent				193.6		173.8
Regulatory Assets, Current				27.5		19.7
Regulatory Assets				221.1		193.5
Regulatory Liability, Noncurrent				218.3		243.6
Regulatory Liability, Current				18.0		27.9
Regulatory Liabilities				236.3		271.5
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
Distribution Modernization Rider			$ 105.0
RSC Rider				$ 79.0
Return on Equity SEET Threshold				9.85%
Due from PJM transmission settlement				$ 1.7		1.8	$ 40.8
PJM transmission enhancement repayment amount				$ 32.1
Tax rate after Tax Cuts and Jobs Act of 2017				21.00%
Refund of eligible excess ADIT and any related regulatory liability as required by the PUCO				$ 65.1
Refund of eligible excess ADIT and any related regulatory liability as required by the PUCO, including taxes				83.2
Reduction of Long-term regulatory liability related to deferred income taxes				23.4
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
Proposed annual increase in transmission rates to reflect effects on TCJA				$ 7.0
Proposed Increased Return on Equity SEET Threshold				9.99%
Subsidiaries [Member] | Vegetation Management and Other [Member]
Regulatory Assets, Noncurrent				$ 15.7
Subsidiaries [Member] | Undercollections to be collected [Member]
Regulatory Assets Type of Recovery				A/B
Regulatory Assets, Current				$ 26.8		19.1
Subsidiaries [Member] | Amounts being recovered through base rates [Member]
Regulatory Assets Type of Recovery				B
Regulatory Assets, Current				$ 0.7		0.6
Subsidiaries [Member] | Pension Costs [Member]
Regulatory Assets Type of Recovery				B
Regulatory Current Asset, End Date for Recovery				Ongoing
Regulatory Assets, Noncurrent				$ 94.4		83.9
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		29.1
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				Undetermined
Regulatory Assets, Noncurrent				$ 8.5		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				$ 7.1		10.0
Subsidiaries [Member] | Storm Costs [Member]
Regulatory Assets Type of Recovery				A
Regulatory Current Asset, End Date for Recovery				Undetermined
Regulatory Assets, Noncurrent				$ 11.5		5.1
Subsidiaries [Member] | Vegetation Management [Member]
Regulatory Assets Type of Recovery				A/B
Regulatory Current Asset, End Date for Recovery				Undetermined
Regulatory Assets, Noncurrent						12.7
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				$ 7.4		4.4
Subsidiaries [Member] | COVID-19 Deferral [Member]
Regulatory Assets, Noncurrent				$ 1.2
Postretirement Benefit Costs [Member]
Regulatory Liabilities Type of Recovery				B
Regulatory Liability, Amortization Through				Ongoing
Regulatory Liability, Noncurrent				$ 4.1		4.6
Postretirement Benefit Costs [Member] | Subsidiaries [Member]
Regulatory Liabilities Type of Recovery				B
Regulatory Liability, Amortization Through				Ongoing
Regulatory Liability, Noncurrent				$ 4.1		4.6
PJM transmission enhancement settlement repayment amount [Member]
Regulatory Liabilities Type of Recovery				A
Regulatory Liability, Noncurrent				$ 7.0		8.9
PJM transmission enhancement settlement repayment amount [Member] | Subsidiaries [Member]
Regulatory Liabilities Type of Recovery				A
Regulatory Liability, Noncurrent				$ 7.0		8.9
Deferred Income Tax Charge [Member]
Regulatory Liability, Amortization Through				Various
Regulatory Liability, Noncurrent				$ 61.2		73.6
Deferred Income Tax Charge [Member] | Subsidiaries [Member]
Regulatory Liability, Amortization Through				Various
Regulatory Liability, Noncurrent				$ 61.2		73.6
TCJA Regulatory Liability [Member] [Domain]
Regulatory Liabilities Type of Recovery				B
Regulatory Liability, Amortization Through				Ongoing
Regulatory Liability, Noncurrent				$ 7.2		12.9
TCJA Regulatory Liability [Member] [Domain] | Subsidiaries [Member]
Regulatory Liabilities Type of Recovery				B
Regulatory Liability, Amortization Through				Ongoing
Regulatory Liability, Noncurrent				$ 7.2		12.9
Removal Costs [Member]
Regulatory Liability, Amortization Through				Not Applicable
Regulatory Liability, Noncurrent				$ 138.8		143.6
Removal Costs [Member] | Subsidiaries [Member]
Regulatory Liability, Amortization Through				Not Applicable
Regulatory Liability, Noncurrent				$ 138.8		143.6
Overcollection of costs to be refunded [Member]
Regulatory Liabilities Type of Recovery				A/B
Regulatory Liability, Noncurrent				$ 18.0		27.9
Overcollection of costs to be refunded [Member] | Subsidiaries [Member]
Regulatory Liabilities Type of Recovery				A/B
Regulatory Liability, Noncurrent				$ 18.0		$ 27.9
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				7.0
Long-term [Member] | Subsidiaries [Member]
Due from PJM transmission settlement				7.0
Short-term [Member]
Due from PJM transmission settlement				1.7
Short-term [Member] | Subsidiaries [Member]
Due from PJM transmission settlement				$ 1.7