Regulatory Matters (Details) - USD ($) $ in Millions		9 Months Ended
Regulatory Matters (Details) - USD ($) $ in Millions	Nov. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Distribution Investment Rider	$ 120.8
Return on Equity SEET Threshold		9.85%
Cash Contribution from Parent Company			$ 150.0
Transmission System Refund		$ 4.5
Schedule of Regulatory Assets and Liabilities [Text Block]		Regulatory Matters Smart Grid and Comprehensive Settlement On October 23, 2020, AES Ohio entered into a Stipulation and Recommendation (settlement) with the staff of the PUCO and various customers, and organizations representing customers of AES Ohio and certain other parties with respect to, among other matters, AES Ohio's applications pending at the PUCO for (i) approval of AES Ohio's plan to modernize its distribution grid (the Smart Grid Plan), (ii) findings that AES Ohio passed the SEET for 2018 and 2019, and (iii) findings that AES Ohio's current ESP 1 satisfies the SEET and the more favorable in the aggregate (MFA) regulatory test. A hearing was held in January 2021 for consideration of this settlement and on June 16, 2021, the PUCO issued their opinion and order accepting the stipulation as filed. Applications for rehearing of the PUCO's orders relating to the comprehensive settlement were filed on July 16, 2021 and remain pending. Consistent with AES’ earlier statement of intent and based on recent discussions with AES, with the PUCO’s issuance of their opinion and order, DPL and AES Ohio expect that AES will make cash contributions of $150.0 million in 2021 to enable Smart Grid investment. Decoupling On January 23, 2020 AES Ohio filed with the PUCO requesting approval to defer its decoupling costs consistent with the methodology approved in its Distribution Rate Case. If approved, deferral would be effective December 18, 2019 and going forward would reduce impacts of weather, energy efficiency programs and economic changes in customer demand. An evidentiary hearing was held on this matter on May 4, 2021. Distribution Rate Case On November 30, 2020, AES Ohio filed a new Distribution Rate Case with the PUCO. This rate case proposes a revenue increase of $120.8 million per year and incorporates the DIR investments that were planned and approved in the last rate case but not yet included in distribution rates, other distribution investments since September 2015 and investments necessitated by the tornados that occurred on Memorial Day in 2019. The rate case also includes a proposal for increased tree-trimming expenses and certain customer demand-side management programs and recovery of prior-approved regulatory assets for tree trimming, uncollectible expenses and rate case expense. This case is pending a commission order. On July 26, 2021, the PUCO staff filed its Staff Report of Investigation in the distribution rate case. Settlement negotiations are currently ongoing, and the hearing is set to begin on December 7, 2021. FERC Proceedings On March 3, 2020, AES Ohio filed an application before the FERC to change its transmission rate from a stated rate to a formula rate, which was accepted by the FERC and made effective as of May 3, 2020, subject to further proceedings and potential refunds. An uncontested settlement was filed December 10, 2020 and approved April 15, 2021. Among other things, the settlement established new depreciation rates for our transmission assets and an authorized return on equity of 9.85%, and started an amortization process to return excess deferred taxes created by the TCJA. Because the approved settlement rates were lower than the proposed rates that went into effect, AES Ohio has accrued and/or paid refunds of approximately $4.5 million to users of the transmission system in the second quarter and third quarters of 2021 through credits on PJM bills.
Subsidiaries [Member]
Distribution Investment Rider	$ 120.8
Return on Equity SEET Threshold		9.85%
Transmission System Refund		$ 4.5
Schedule of Regulatory Assets and Liabilities [Text Block]		Regulatory Matters Smart Grid and Comprehensive Settlement On October 23, 2020, AES Ohio entered into a Stipulation and Recommendation (settlement) with the staff of the PUCO and various customers, and organizations representing customers of AES Ohio and certain other parties with respect to, among other matters, AES Ohio's applications pending at the PUCO for (i) approval of AES Ohio's plan to modernize its distribution grid (the Smart Grid Plan), (ii) findings that AES Ohio passed the SEET for 2018 and 2019, and (iii) findings that AES Ohio's current ESP 1 satisfies the SEET and the more favorable in the aggregate (MFA) regulatory test. A hearing was held in January 2021 for consideration of this settlement and on June 16, 2021, the PUCO issued their opinion and order accepting the stipulation as filed. Applications for rehearing of the PUCO's orders relating to the comprehensive settlement were filed on July 16, 2021 and remain pending. Consistent with AES’ earlier statement of intent and based on recent discussions with AES, with the PUCO’s issuance of their opinion and order, DPL and AES Ohio expect that AES will make cash contributions of $150.0 million in 2021 to enable Smart Grid investment. Decoupling On January 23, 2020 AES Ohio filed with the PUCO requesting approval to defer its decoupling costs consistent with the methodology approved in its Distribution Rate Case. If approved, deferral would be effective December 18, 2019 and going forward would reduce impacts of weather, energy efficiency programs and economic changes in customer demand. An evidentiary hearing was held on this matter on May 4, 2021. Distribution Rate Case On November 30, 2020, AES Ohio filed a new Distribution Rate Case with the PUCO. This rate case proposes a revenue increase of $120.8 million per year and incorporates the DIR investments that were planned and approved in the last rate case but not yet included in distribution rates, other distribution investments since September 2015 and investments necessitated by the tornados that occurred on Memorial Day in 2019. The rate case also includes a proposal for increased tree-trimming expenses and certain customer demand-side management programs and recovery of prior-approved regulatory assets for tree trimming, uncollectible expenses and rate case expense. This case is pending a commission order. On July 26, 2021, the PUCO staff filed its Staff Report of Investigation in the distribution rate case. Settlement negotiations are currently ongoing, and the hearing is set to begin on December 7, 2021. FERC Proceedings On March 3, 2020, AES Ohio filed an application before the FERC to change its transmission rate from a stated rate to a formula rate, which was accepted by the FERC and made effective as of May 3, 2020, subject to further proceedings and potential refunds. An uncontested settlement was filed December 10, 2020 and approved April 15, 2021. Among other things, the settlement established new depreciation rates for our transmission assets and an authorized return on equity of 9.85%, and started an amortization process to return excess deferred taxes created by the TCJA. Because the approved settlement rates were lower than the proposed rates that went into effect, AES Ohio has accrued and/or paid refunds of approximately $4.5 million to users of the transmission system in the second quarter and third quarters of 2021 through credits on PJM bills.
Forecast [Member]
Cash Contribution from Parent Company		$ 150.0
Forecast [Member] \| Subsidiaries [Member]
Cash Contribution from Parent Company		$ 150.0