Regulatory Matters (Notes)	3 Months Ended
Regulatory Matters (Notes)	Mar. 31, 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 is seeking an increase to distribution revenues of $65.8 million per year. DP&L has 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. The PUCO has set the evidentiary hearing in this case for June 6, 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. This did not have a material impact to our financial statements during the three months ended March 31, 2018. Under the terms of the ESP, DPL will not make tax sharing payments and if DP&L's rates are reduced as a result of the TCJA, our cash flows could be adversely affected. At this time, we are unable to determine whether any of the above issues may have a material impact in the future on DP&L's business, financial condition, results of operations or cash flows. On March 15, 2018, the FERC initiated “show cause” proceedings against DP&L and numerous other utilities 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. DP&L intends to file new transmission rates in response to the show cause order. Because the filing will then be subject to review by the FERC and any interveners, DP&L is unable to determine the impact of the proceeding at this time.
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 is seeking an increase to distribution revenues of $65.8 million per year. DP&L has 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. The PUCO has set the evidentiary hearing in this case for June 6, 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. This did not have a material impact to our financial statements during the three months ended March 31, 2018. At this time, we are unable to determine whether any of the above issues may have a material impact in the future on DP&L's business, financial condition, results of operations or cash flows. On March 15, 2018, the FERC initiated “show cause” proceedings against DP&L and numerous other utilities 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. DP&L intends to file new transmission rates in response to the show cause order. Because the filing will then be subject to review by the FERC and any interveners, DP&L is unable to determine the impact of the proceeding at this time.