Income Taxes (Narrative) (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Entity Information [Line Items]
Effective income tax rates	3.40%	(71.50%)	18.60%	(34.20%)
Estimated annual effective income tax rate			30.80%	(42.30%)
THE DAYTON POWER AND LIGHT COMPANY [Member]
Entity Information [Line Items]
Effective income tax rates	4.90%	19.80%	24.80%	23.20%
Estimated annual effective income tax rate	0.00%	30.50%	29.00%	30.50%