Regulatory Assets and Liabilities (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Regulatory Assets	$ 194,300,000	$ 211,700,000
Regulatory Liabilities	151,400,000	128,500,000
EERider shared savings incentive accrual, after tax	$ 4,500,000	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]
Regulatory Assets	$ 194,300,000	211,700,000
Regulatory Liabilities	151,400,000	128,500,000
EERider shared savings incentive accrual, after tax	$ 4,500,000	$ 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%