Generation Separation (Policies)	12 Months Ended
Generation Separation (Policies)	Dec. 31, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued Operations, Policy [Policy Text Block]	Discontinued operations reporting occurs only when the disposal of a business or a group of businesses represents a strategic shift that has (or will have) a major effect on our operations and financial results. We report financial results for discontinued operations separately from continuing operations to distinguish the financial impact of disposal transactions from ongoing operations. Prior period amounts in the statement of operations and balance sheet are retrospectively revised to reflect the businesses determined to be discontinued operations. The cash flows of businesses that are determined to be discontinued operations are included within the relevant categories within operating, investing and financing activities on the face of the Statements of Cash Flows. Transactions between the businesses determined to be discontinued operations and businesses that are expected to continue to exist after the disposal are not eliminated to appropriately reflect the continuing operations and balances held-for-sale. The results of discontinued operations include any gain or loss recognized on closing or adjustment of the carrying amount to fair value. See Note 16 – Discontinued Operations for further information.
THE DAYTON POWER AND LIGHT COMPANY [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued Operations, Policy [Policy Text Block]	Discontinued operations reporting occurs only when the disposal of a business or a group of businesses represents a strategic shift that has (or will have) a major effect on our operations and financial results. We report financial results for discontinued operations separately from continuing operations to distinguish the financial impact of disposal transactions from ongoing operations. Prior period amounts in the statement of operations and balance sheet are retrospectively revised to reflect the businesses determined to be discontinued operations. The cash flows of businesses that are determined to be discontinued operations are included within the relevant categories within operating, investing and financing activities on the face of the Statements of Cash Flows. Transactions between the businesses determined to be discontinued operations and businesses that are expected to continue to exist after the disposal are not eliminated to appropriately reflect the continuing operations and balances held-for-sale. The results of discontinued operations include any gain or loss recognized on closing or adjustment of the carrying amount to fair value. See Note 13 – Generation Separation for further information. Generation Separation With the transfer of DP&L's generation assets to an affiliate (see Note 13 – Generation Separation), DP&L's generation business is presented as a discontinued operation and the operating activities have been reclassified to "Discontinued operations" in the Statements of Operations for the years ended December 31, 2017, 2016 and 2015 and in the footnotes to the financial statements. The assets and liabilities related to the discontinued operations have been reclassified to held-for-sale in the balance sheet as of December 31, 2016. The PUCO authorized DP&L to maintain long-term debt of $750 million or 75% of its rate base, whichever is greater, until January 1, 2018, or to file an application to explain why it would not achieve those metrics. Accordingly, $750.0 million of debt and the pro rata interest expense associated with that debt were allocated to continuing operations. All remaining debt and interest expense were included in discontinued operations above. The interest expense included in discontinued operations was $0.2 million, $0.5 million and $2.9 million for the years ended December 31, 2017, 2016 and 2015, respectively.