Pension and Postretirement Benefits (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2010	Dec. 31, 2010 Management Employees [Member]	Feb. 28, 2011 DP&L [Member]	Sep. 30, 2010 DP&L [Member]
Defined benefit plan employee vested percentage	100.00%	100.00%
Defined benefit plan employee vested minimum period	5
Contribution to the defined benefit plan			$ 40.0	$ 40.0