Regulatory Matters (Schedule of Regulatory Assets and Liabilities) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Total current regulatory assets	$ 21.8	$ 20.8
Total non-current regulatory assets	181.3	193.2
Total current regulatory liabilities		0.5
Total non-current regulatory liabilities	117.5	118.6
Estimated Costs of Removal - Regulated Property [Member]
Total non-current regulatory liabilities	111.6	112.4
Postretirement Benefit [Member]
Total non-current regulatory liabilities	5.6	6.2
Other Costs - Liabilities [Member]
Total current regulatory liabilities		0.5
Total non-current regulatory liabilities	0.3
DP&L [Member]
Total current regulatory assets	18.9	17.7
Total non-current regulatory assets	181.3	177.8
Total non-current regulatory liabilities	117.5	118.6
DP&L [Member] | Estimated Costs of Removal - Regulated Property [Member]
Total non-current regulatory liabilities	111.6	112.4
DP&L [Member] | Postretirement Benefit [Member]
Total non-current regulatory liabilities	5.6	6.2
DP&L [Member] | Other Costs - Liabilities [Member]
Total non-current regulatory liabilities	0.3
Deferred Recoverable Income Taxes [Member]
Type of Recovery	B/C
Amortization Through	Ongoing
Total non-current regulatory assets	37.0	39.5
Deferred Recoverable Income Taxes [Member] | DP&L [Member]
Total non-current regulatory assets	37.0	24.1
Pension Benefits [Member]
Type of Recovery	C
Amortization Through	Ongoing
Total non-current regulatory assets	87.1	92.1
Pension Benefits [Member] | DP&L [Member]
Total non-current regulatory assets	87.1	92.1
Unamortized Loss on Reacquired Debt [Member]
Type of Recovery	C
Amortization Through	Ongoing
Total non-current regulatory assets	12.2	13.0
Unamortized Loss on Reacquired Debt [Member] | DP&L [Member]
Total non-current regulatory assets	12.2	13.0
Regional Transmission Organization Costs [Member]
Type of Recovery	D
Amortization Through	2014
Total non-current regulatory assets	3.0	4.1
Regional Transmission Organization Costs [Member] | DP&L [Member]
Type of Recovery	D
Amortization Through	2014
Total non-current regulatory assets	3.0	4.1
TCRR, Transmission, Ancillary and Other PJM-related Costs [Member]
Type of Recovery	F
Amortization Through	Ongoing
Total current regulatory assets	6.3	4.7
TCRR, Transmission, Ancillary and Other PJM-related Costs [Member] | DP&L [Member]
Total current regulatory assets	6.3	4.7
Deferred Storm Costs - 2008 [Member]
Type of Recovery	D
Total non-current regulatory assets	18.7	17.9
Deferred Storm Costs - 2008 [Member] | DP&L [Member]
Total non-current regulatory assets	18.7	17.9
Power Plant Emission Fees [Member]
Type of Recovery	C
Amortization Through	Ongoing
Total current regulatory assets	(0.3)	4.8
Power Plant Emission Fees [Member] | DP&L [Member]
Total current regulatory assets	(0.3)	4.8
CCEM Smart Grid and Advanced Metering Infrastructure Costs [Member]
Type of Recovery	D
Total non-current regulatory assets	6.6	6.6
CCEM Smart Grid and Advanced Metering Infrastructure Costs [Member] | DP&L [Member]
Total non-current regulatory assets	6.6	6.6
CCEM Energy Efficiency Program Costs [Member]
Type of Recovery	F
Amortization Through	Ongoing
Total non-current regulatory assets	5.9	8.8
CCEM Energy Efficiency Program Costs [Member] | DP&L [Member]
Total non-current regulatory assets	5.9	8.8
Consumer Education Campaign
Type of Recovery	D
Total non-current regulatory assets	3.0	3.0
Consumer Education Campaign | DP&L [Member]
Total non-current regulatory assets	3.0	3.0
Retail Settlement System Costs [Member]
Type of Recovery	D
Total non-current regulatory assets	3.1	3.1
Retail Settlement System Costs [Member] | DP&L [Member]
Total non-current regulatory assets	3.1	3.1
Fuel and Purchased Power Recovery Costs [Member]
Type of Recovery	C
Amortization Through	Ongoing
Total current regulatory assets	15.8	11.3
Fuel and Purchased Power Recovery Costs [Member] | DP&L [Member]
Total current regulatory assets	12.9	8.2
Other Costs - Assets [Member]
Total non-current regulatory assets	4.7	5.1
Other Costs - Assets [Member] | DP&L [Member]
Total non-current regulatory assets	$ 4.7	$ 5.1