Overview and Summary of Significant Accounting Policies (Narrative) (Details) (USD $)	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Service Area Square Miles	6,000
Service Area By County	24
Approximate number of retail customers	500,000
Approximate number of DPLER customers	$ 45,000
Number of coal fired power plants	8
Entity number of employees	1,494
Employees under a collective bargaining agreement which expires in October-2011	53.00%
Capitalized interest for unregulated generation propety	1,400,000	1,100,000
DP&L [Member]
Service Area Square Miles	6,000
Service Area By County	24
Approximate number of retail customers	500,000
Approximate number of DPLER customers	8
Entity number of employees	1,450
Employees under a collective bargaining agreement which expires in October-2011	53.00%
Capitalized interest for unregulated generation propety	$ 1,400,000