Regulatory Matters (Details) - USD ($) $ in Millions				6 Months Ended	12 Months Ended
	Jun. 18, 2018	May 31, 2018	Jan. 01, 2018	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Public Utilities, Requested Rate Increase (Decrease), Amount				$ 65.8
Public Utilities, Requested Rate Increase (Decrease), Percentage				4.00%
Requested revenue requirement based on stipulation agreement	$ 248.0
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	29.8
Period for refund of eligible excess ADIT and any related regulatory liability as required by PUCO			10 years
Due from PJM transmission settlement				$ 30.1		$ 0.0
PJM transmission settlement period		5 years
Recovery percentage of transmission charges and credits in DP&L's nonbypassable TCRR				100.00%
Subsidiaries [Member]
Public Utilities, Requested Rate Increase (Decrease), Amount				$ 65.8
Public Utilities, Requested Rate Increase (Decrease), Percentage				4.00%
Requested revenue requirement based on stipulation agreement	248.0
Public Utilities, Requested Rate Increase (Decrease), Amended, Amount	$ 29.8
Period for refund of eligible excess ADIT and any related regulatory liability as required by PUCO			10 years
Due from PJM transmission settlement						$ 0.0
PJM transmission settlement period		5 years
Recovery percentage of transmission charges and credits in DP&L's nonbypassable TCRR				100.00%
Subsequent Event [Member]
Proposed annual reduction in transmission rates to reflect effects of TCJA					$ 2.4
Subsequent Event [Member] | Subsidiaries [Member]
Proposed annual reduction in transmission rates to reflect effects of TCJA					$ 2.4
Long-term [Member]
Due from PJM transmission settlement				$ 42.9
Long-term [Member] | Subsidiaries [Member]
Due from PJM transmission settlement				43.0
Short-term [Member]
Due from PJM transmission settlement				30.1
Short-term [Member] | Subsidiaries [Member]
Due from PJM transmission settlement				$ 30.1