Goodwill Impairment (Narrative) (USD $) In Millions, unless otherwise specified	3 Months Ended			9 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Goodwill Allocated to DP&L Reporting Unit		$ 2,400.0		$ 2,400.0
Goodwill Impairment		1,850.0		1,850.0
Range of Goodwill Impairment Minimum	1,700.0
Range of Goodwill Impairment Maximum	2,000.0
Effective Income Tax Rate, Continuing Operations		(1.20%)	29.90%	(2.30%)	32.90%
Parent Company [Member]
Goodwill Impairment		$ 1,850.0		$ 1,850.0
DP&L [Member]
Effective Income Tax Rate, Continuing Operations		(138.30%)	29.60%	40.30%	32.00%