Regulatory Assets and Liabilities (Narrative) (Details)				12 Months Ended
	Mar. 08, 2017 USD ($) kWh	Jan. 30, 2017 USD ($)	Oct. 11, 2016 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Distribution Modernization Rider			$ 145,000,000
Distribution Modernization Rider Period			7 years
Regulatory Assets, Renewable Energy Recovery			$ 10,500,000
Energy Efficiency Rider Revenue				$ 20,100,000
Regulatory Assets				204,000,000	$ 194,300,000
Regulatory Liabilities				164,100,000	151,400,000
EERider shared savings incentive accrual, after tax				$ 4,500,000
Reconciliation rider as percent of costs in excess of base amount of Fuel, RPM, Alternative Energy and Competitive Bidding riders (percent)				10.00%
THE DAYTON POWER AND LIGHT COMPANY [Member]
Distribution Modernization Rider			$ 145,000,000
Distribution Modernization Rider Period			7 years
Regulatory Assets, Renewable Energy Recovery			$ 10,500,000
Energy Efficiency Rider Revenue				$ 20,100,000
Regulatory Assets				204,000,000	194,300,000
Regulatory Liabilities				164,100,000	$ 151,400,000
EERider shared savings incentive accrual, after tax				$ 4,500,000
Reconciliation rider as percent of costs in excess of base amount of Fuel, RPM, Alternative Energy and Competitive Bidding riders (percent)				10.00%
Subsequent Event [Member]
Distribution Modernization Rider		$ 90,000,000
Distribution Modernization Rider Period		5 years
Distribution Investment Rider		$ 35,000,000
Residential Customer KWh Usage | kWh	1,000
Monthly Bill Increase	$ 2.39
ESP 3 Settlement Time Period		6 years
Subsequent Event [Member] | THE DAYTON POWER AND LIGHT COMPANY [Member]
Distribution Modernization Rider		$ 90,000,000
Distribution Modernization Rider Period		5 years
Distribution Investment Rider		$ 35,000,000
Residential Customer KWh Usage | kWh	1,000
Monthly Bill Increase	$ 2.39
ESP 3 Settlement Time Period		6 years