Debt (Long-term Debt Maturities) (Details) $ in Millions	Dec. 31, 2016 USD ($)
Debt Instrument [Line Items]
2016	$ 29.7
2017	29.6
2018	229.6
2019	254.6
2020	784.6
Thereafter	555.5
Total Maturities	1,883.6
Unamortized discounts and premiums, net	(6.1)
Total long-term debt	1,877.5
THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument [Line Items]
2016	4.7
2017	4.6
2018	4.6
2019	204.6
2020	4.5
Thereafter	540.0
Total Maturities	763.0
Unamortized discounts and premiums, net	(2.2)
Total long-term debt	$ 760.8