Benefit Plans (Effect of Change in Health Care Cost Trend Rate) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($)
Service cost plus interest cost, One-percent increase	$ 0.1
Benefit obligation, One-percent increase	0.8
Benefit obligation, One-percent decrease	(0.7)
THE DAYTON POWER AND LIGHT COMPANY [Member]
Service cost plus interest cost, One-percent increase	0.1
Benefit obligation, One-percent increase	1.1
Benefit obligation, One-percent decrease	$ 0.7