Overview and Summary of Significant Accounting Policies (Narrative) (Details) (USD $)	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2011	Sep. 30, 2011	Sep. 30, 2011	Dec. 31, 2010
Service Area Square Miles		6,000
Service Area By County		24
Approximate number of retail customers		500,000
Number of coal fired power plants	8	8
Entity number of employees	1,528	1,528	1,528
Employees under a collective bargaining agreement which expires in October-2011		53.00%
Deferred SECA revenue	$ 14,100,000	$ 14,100,000	$ 14,100,000	$ 15,400,000
Reduction of depreciation expense net		4,800,000.00	7,200,000
Reduction in depreciation expense net of tax		$ 3,100,000.00	$ 4,700,000
Increase in diluted EPS		$ 0.03	$ 0.04
DP&L [Member]
Entity number of employees	1,497	1,497	1,497