Summary of Significant Accounting Policies (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013 sqmi employee	Mar. 31, 2012
Service Area Square Miles	6,000
Service Area By County	24
Approximate number of retail customers	514,000
Approximate number of DPLER customers	247,000
Entity number of employees	1,475
Number of coal fired power plants	8
Employees under a collective bargaining agreement which expires in October-2011	53.00%
Capitalized interest for unregulated generation propety	$ 0.3	$ 1.4
DP&L [Member]
Service Area Square Miles	6,000
Service Area By County	24
Approximate number of retail customers	514,000
Entity number of employees	1,412
Number of coal fired power plants	8
Employees under a collective bargaining agreement which expires in October-2011	55.00%
Capitalized interest for unregulated generation propety	$ 0.3	$ 1.4