Regulatory Matters (Notes)	6 Months Ended
Regulatory Matters (Notes)	Jun. 30, 2018
Schedule of Regulatory Assets and Liabilities [Text Block]	Regulatory Matters On November 30, 2015, DP&L filed a distribution rate case using a 12-month test year of June 1, 2015 to May 31, 2016 to measure revenue and expenses and a date certain of September 30, 2015 to measure its asset base. DP&L sought an increase to distribution revenues of $65.8 million per year. DP&L asked for recovery of certain regulatory assets as well as two new riders that would allow DP&L to recover certain costs on an ongoing basis. It has proposed a modified rate design, which would increase the monthly customer charge, in an effort to decouple distribution revenues from electric sales. If approved as filed, the rates are expected to increase a typical residential customer bill approximately 4% based on rates in effect at the time of the filing. On March 12, 2018, the PUCO Staff filed its Staff Report of Investigation in the distribution rate case. In response, DP&L submitted objections and supplemental testimony on April 11, 2018. On June 18, 2018, DP&L entered into a stipulation and recommendation with various intervening parties and the Staff of the PUCO with respect to the pending distribution rate case filing. If this stipulation is approved, it would establish a revenue requirement of $248.0 million for DP&L's electric service base distribution rates which reflects an increase to distribution revenues of $29.8 million per year. The evidentiary hearing on the stipulation was completed on July 24, 2018. An order in this proceeding is expected to be issued by the PUCO in the fourth quarter of 2018. Impact of tax reform On January 10, 2018, the PUCO initiated a proceeding to consider the impacts of the TCJA to determine the appropriate course of action to pass benefits resulting from the legislation on to ratepayers. The PUCO also directed Ohio utilities to record deferred liabilities for the estimated reduction in federal income tax resulting from the TCJA beginning January 1, 2018. Under the terms of the stipulation in the distribution rate case mentioned above, DP&L agreed to file an application at the PUCO to refund eligible excess accumulated deferred income taxes (excess ADIT) and any related regulatory liability over a 10-year period. Excess ADIT related to depreciation life and method differences will be returned to customers in accordance with federal tax law and related regulations. On March 15, 2018, the FERC initiated “show cause” proceedings against numerous utilities, including DP&L, that had stated transmission rates, directing each utility to file either revised transmission rates to reflect the effects of the TCJA or to show cause why no changes in transmission rates were appropriate. On May 8, 2018, DP&L filed to adjust its FERC jurisdictional transmission rates to reflect this impact. The filing is currently under review by the FERC and DP&L is unable to predict whether the proposed rates will be accepted as filed or if they may be further modified. As proposed, the decrease is approximately $2.4 million annually. DP&L has recorded a reduction to revenues and regulatory liabilities for the estimated impact. PJM transmission enhancement settlement On May 31, 2018, the FERC issued an Order on Contested Settlement regarding the cost allocation method for existing and new transmission facilities contained in the PJM Interconnection’s Open Access Transmission Tariff. The FERC order approved the settlement which will have the impact of reducing DP&L’s transmission costs through PJM beginning in August 2018, including credits to reimburse DP&L for amounts overcharged in prior years. The precise amount of the reduced charges is unknown, but DP&L has recorded a receivable of $42.9 million ($30.1 million is short-term) for the estimated credits we will receive from PJM over the next five years. All of the transmission charges and credits impacted by this FERC order are items that are included for 100% recovery in DP&L’s nonbypassable TCRR. Accordingly, DP&L has also established offsetting regulatory liabilities. While this development will have a temporary cash flow benefit to DP&L, there is no impact to operating income or net income as all credits will be passed to DP&L’s customers through the TCRR.
Subsidiaries [Member]
Schedule of Regulatory Assets and Liabilities [Text Block]	Regulatory Matters On November 30, 2015, DP&L filed a distribution rate case using a 12-month test year of June 1, 2015 to May 31, 2016 to measure revenue and expenses and a date certain of September 30, 2015 to measure its asset base. DP&L sought an increase to distribution revenues of $65.8 million per year. DP&L asked for recovery of certain regulatory assets as well as two new riders that would allow DP&L to recover certain costs on an ongoing basis. It has proposed a modified rate design, which would increase the monthly customer charge, in an effort to decouple distribution revenues from electric sales. If approved as filed, the rates are expected to increase a typical residential customer bill approximately 4% based on rates in effect at the time of the filing. On March 12, 2018, the PUCO Staff filed its Staff Report of Investigation in the distribution rate case. In response, DP&L submitted objections and supplemental testimony on April 11, 2018. On June 18, 2018, DP&L entered into a stipulation and recommendation with various intervening parties and the Staff of the PUCO with respect to the pending distribution rate case filing. If this stipulation is approved, it would establish a revenue requirement of $248.0 million for DP&L's electric service base distribution rates which reflects an increase to distribution revenues of $29.8 million per year. The evidentiary hearing on the stipulation was completed on July 24, 2018. An order in this proceeding is expected to be issued by the PUCO in the fourth quarter of 2018. Impact of tax reform On January 10, 2018, the PUCO initiated a proceeding to consider the impacts of the TCJA to determine the appropriate course of action to pass benefits resulting from the legislation on to ratepayers. The PUCO also directed Ohio utilities to record deferred liabilities for the estimated reduction in federal income tax resulting from the TCJA beginning January 1, 2018. Under the terms of the stipulation in the distribution rate case mentioned above, DP&L agreed to file an application at the PUCO to refund eligible excess accumulated deferred income taxes (excess ADIT) and any related regulatory liability over a 10-year period. Excess ADIT related to depreciation life and method differences will be returned to customers in accordance with federal tax law and related regulations. On March 15, 2018, the FERC initiated “show cause” proceedings against numerous utilities, including DP&L, that had stated transmission rates, directing each utility to file either revised transmission rates to reflect the effects of the TCJA or to show cause why no changes in transmission rates were appropriate. On May 8, 2018, DP&L filed to adjust its FERC jurisdictional transmission rates to reflect this impact. The filing is currently under review by the FERC and DP&L is unable to predict whether the proposed rates will be accepted as filed or if they may be further modified. As proposed, the decrease is approximately $2.4 million annually. DP&L has recorded a reduction to revenues and regulatory liabilities for the estimated impact. PJM transmission enhancement settlement On May 31, 2018, the FERC issued an Order on Contested Settlement regarding the cost allocation method for existing and new transmission facilities contained in the PJM Interconnection’s Open Access Transmission Tariff. The FERC order approved the settlement which will have the impact of reducing DP&L’s transmission costs through PJM beginning in August 2018, including credits to reimburse DP&L for amounts overcharged in prior years. The precise amount of the reduced charges is unknown, but DP&L has recorded a receivable of $43.0 million ($30.1 million is short-term) for the estimated credits we will receive from PJM over the next five years. All of the transmission charges and credits impacted by this FERC order are items that are included for 100% recovery in DP&L’s nonbypassable TCRR. Accordingly, DP&L has also established offsetting regulatory liabilities. While this development will have a temporary cash flow benefit to DP&L, there is no impact to operating income or net income as all credits will be passed to DP&L’s customers through the TCRR.