Pension and Postretirement Benefits (Net Periodic Benefit Cost (Income)) (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Contributions by employer			$ 0	$ 0
Pension [Member]
Service cost	$ 1,800,000	$ 1,500,000	3,600,000	3,000,000
Interest cost	4,300,000	4,400,000	8,600,000	8,800,000
Expected return on assets	(5,600,000)	(5,600,000)	(11,300,000)	(11,400,000)
Prior service cost	500,000	300,000	1,000,000	700,000
Actuarial loss / (gain)	1,400,000	800,000	2,900,000	1,700,000
Net periodic benefit cost	2,400,000	1,400,000	4,800,000	2,800,000
Postretirement [Member]
Service cost	0	0	0	100,000
Interest cost	100,000	200,000	300,000	400,000
Expected return on assets	0	0	0	(100,000)
Prior service cost	0	0	0	0
Actuarial loss / (gain)	(100,000)	(200,000)	(200,000)	(300,000)
Net periodic benefit cost	0	0	100,000	100,000
THE DAYTON POWER AND LIGHT COMPANY [Member]
Contributions by employer			0	0
THE DAYTON POWER AND LIGHT COMPANY [Member] | Pension [Member]
Service cost	1,700,000	1,400,000	3,500,000	2,900,000
Interest cost	4,300,000	4,300,000	8,600,000	8,700,000
Expected return on assets	(5,500,000)	(5,600,000)	(11,200,000)	(11,300,000)
Prior service cost	800,000	700,000	1,600,000	1,400,000
Actuarial loss / (gain)	2,400,000	1,600,000	4,800,000	3,200,000
Net periodic benefit cost	3,700,000	2,400,000	7,300,000	4,900,000
THE DAYTON POWER AND LIGHT COMPANY [Member] | Postretirement [Member]
Service cost	0	100,000	0	100,000
Interest cost	200,000	200,000	400,000	400,000
Expected return on assets	0	(100,000)	0	(100,000)
Prior service cost	0	0	0	0
Actuarial loss / (gain)	(100,000)	(100,000)	(300,000)	(300,000)
Net periodic benefit cost	$ 100,000	$ 100,000	$ 100,000	$ 100,000