Summary of Significant Accounting Policies (Related Party Transactions) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Charges for services provided	$ 5.5		$ 27.8
Charges to the Service Company	0.2		0.2
Net Prepaid/Payables to the Service Company	9.4		9.4
DP&L [Member]
Charges for services provided	9.0		28.1
Premiums paid for insurance services provided by MVIC	(0.7)	(0.7)	(2.1)	(2.2)
Expense recoveries for services provided to DPLER	0.5	1.3	1.6	3.8
Deposits received from DPLER	20.1		20.1		19.2
DPLER [Member]
Sales to related party	125.6	123.8	376.6	336.0
Service Company [Member]
Net Prepaid/Payables to the Service Company	$ 9.4		$ 9.4