Debt (Narrative) (Details)			6 Months Ended		12 Months Ended
	Aug. 07, 2017 USD ($)	Jun. 23, 2017 USD ($)	Jun. 30, 2017 USD ($) fiscal_quarter debt_covenant	Jun. 30, 2016 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2016 USD ($)
Debt Instrument [Line Items]
Retirement of long-term debt			$ 22,800,000	$ 75,400,000
Total Debt to Total Capitalization Ratio			0.52
THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument [Line Items]
Retirement of long-term debt			$ 10,300,000	$ 0
Total Debt to Total Capitalization Ratio			0.52
Four Point Eight Zero Percentage Of Bonds Maturing In September Two Thousand Thirty Six [Member]
Debt Instrument [Line Items]
Extinguishment of Debt, Amount		$ 8,100,000
Long-term Debt, Gross			$ 91,900,000			$ 100,000,000
Debt instrument interest percentage			4.80%
Four Point Eight Zero Percentage Of Bonds Maturing In September Two Thousand Thirty Six [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument [Line Items]
Extinguishment of Debt, Amount		$ 8,100,000
Long-term Debt, Gross			$ 91,900,000			100,000,000
Debt instrument interest percentage			4.80%
Term Loan Maturing 2022 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 442,800,000			445,000,000
Term Loan Maturing 2022 [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			$ 442,800,000			$ 445,000,000
Revolving Credit Agreement and Standby Letters of Credit [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument [Line Items]
Number of financial covenants | debt_covenant			2
Number of prior quarters included in EBITDA to interest calculation | fiscal_quarter			4
DPL Revolving Credit Agreement and Term Loan Maturing July 2020 [Member]
Debt Instrument [Line Items]
Number of financial covenants | debt_covenant			2
Number of prior quarters included in EBITDA to interest calculation | fiscal_quarter			4
Number of prior quarters included in debt to EBITDA ratio | fiscal_quarter			4
Subsequent Event [Member]
Debt Instrument [Line Items]
Long Term Indebtedness, Less than or Equal to					$ 750,000,000.0
Subsequent Event [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument [Line Items]
Long Term Indebtedness, Less than or Equal to					$ 750,000,000.0
Subsequent Event [Member] | Four Point Eight Zero Percentage Of Bonds Maturing In September Two Thousand Thirty Six [Member]
Debt Instrument [Line Items]
Extinguishment of Debt, Amount	$ 21,900,000
Long-term Debt, Gross	70,000,000
Subsequent Event [Member] | Four Point Eight Zero Percentage Of Bonds Maturing In September Two Thousand Thirty Six [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument [Line Items]
Extinguishment of Debt, Amount	21,900,000
Long-term Debt, Gross	$ 70,000,000