Income Taxes (Narrative) (Details)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Entity Information [Line Items]
Effective income tax rates	37.90%	21.40%
Estimated annual effective income tax rate	37.60%	20.60%
THE DAYTON POWER AND LIGHT COMPANY [Member]
Entity Information [Line Items]
Effective income tax rates	34.40%	26.90%
Estimated annual effective income tax rate	33.80%	27.00%