Benefit Plans (Net Periodic Benefit Cost (Income)) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Contributions by employer		$ 0
Pension [Member]
Contributions by employer	$ 5,000,000	0
Service cost	1,400,000	1,800,000
Interest cost	3,700,000	4,300,000
Expected return on assets	(5,700,000)	(5,700,000)
Prior service cost	500,000	500,000
Actuarial loss / (gain)	1,000,000	1,500,000
Net periodic benefit cost	900,000	2,400,000
Postretirement [Member]
Service cost	0	0
Interest cost	100,000	200,000
Expected return on assets	0	0
Prior service cost	0	0
Actuarial loss / (gain)	(100,000)	(100,000)
Net periodic benefit cost	0	100,000
THE DAYTON POWER AND LIGHT COMPANY [Member]
Contributions by employer		0
THE DAYTON POWER AND LIGHT COMPANY [Member] | Pension [Member]
Contributions by employer	5,000,000	0
Service cost	1,400,000	1,800,000
Interest cost	3,700,000	4,300,000
Expected return on assets	(5,700,000)	(5,700,000)
Prior service cost	800,000	800,000
Actuarial loss / (gain)	1,800,000	2,400,000
Net periodic benefit cost	2,000,000	3,600,000
THE DAYTON POWER AND LIGHT COMPANY [Member] | Postretirement [Member]
Service cost	0	0
Interest cost	100,000	200,000
Expected return on assets	0	0
Prior service cost	0	0
Actuarial loss / (gain)	(100,000)	(200,000)
Net periodic benefit cost	$ 0	$ 0