Regulatory Assets and Liabilities (Schedule of Regulatory Assets and Liabilities) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Total current regulatory assets	$ 18.0	$ 21.1
Total non-current regulatory assets	180.9	185.5
Total current regulatory liabilities		0.1
Total non-current regulatory liabilities	118.8	117.3
Estimated Costs of Removal - Regulated Property [Member]
Total non-current regulatory liabilities	113.6	112.1
Postretirement Benefit [Member]
Total non-current regulatory liabilities	4.8	5.0
Other Costs - Liabilities [Member]
Total current regulatory liabilities		0.1
Total non-current regulatory liabilities	0.4	0.2
DP&L [Member]
Total current regulatory assets	16.6	18.3
Total non-current regulatory assets	180.9	185.5
Total current regulatory liabilities		0.1
Total non-current regulatory liabilities	118.8	117.3
DP&L [Member] | Estimated Costs of Removal - Regulated Property [Member]
Total non-current regulatory liabilities	113.6	112.1
DP&L [Member] | Postretirement Benefit [Member]
Total non-current regulatory liabilities	4.8	5.0
DP&L [Member] | Other Costs - Liabilities [Member]
Total current regulatory liabilities		0.1
Total non-current regulatory liabilities	0.4	0.2
Deferred Recoverable Income Taxes [Member]
Type of Recovery	B/C
Amortization Through	Ongoing
Total non-current regulatory assets	34.3	35.1
Deferred Recoverable Income Taxes [Member] | DP&L [Member]
Type of Recovery	B/C
Amortization Through	Ongoing
Total non-current regulatory assets	34.3	35.1
Pension Benefits [Member]
Type of Recovery	C
Amortization Through	Ongoing
Total non-current regulatory assets	87.3	88.9
Pension Benefits [Member] | DP&L [Member]
Type of Recovery	C
Amortization Through	Ongoing
Total non-current regulatory assets	87.3	88.9
Fuel and purchased power recovery costs [Member] | DP&L [Member]
Type of Recovery	C
Amortization Through	Ongoing
Total current regulatory assets	10.0	11.3
Unamortized Loss on Reacquired Debt [Member]
Type of Recovery	C
Amortization Through	Ongoing
Total non-current regulatory assets	11.7	11.9
Unamortized Loss on Reacquired Debt [Member] | DP&L [Member]
Type of Recovery	C
Amortization Through	Ongoing
Total non-current regulatory assets	11.7	11.9
Regional Transmission Organization Costs [Member]
Type of Recovery	D
Amortization Through	2014
Total non-current regulatory assets	2.2	2.6
Regional Transmission Organization Costs [Member] | DP&L [Member]
Type of Recovery	D
Amortization Through	2014
Total non-current regulatory assets	2.2	2.6
TCRR, Transmission, Ancillary and Other PJM-related Costs [Member]
Type of Recovery	F
Amortization Through	Ongoing
Total current regulatory assets	6.6	7.0
TCRR, Transmission, Ancillary and Other PJM-related Costs [Member] | DP&L [Member]
Type of Recovery	F
Amortization Through	Ongoing
Total current regulatory assets	6.6	7.0
Deferred Storm Costs [Member]
Type of Recovery	D
Total non-current regulatory assets	24.7	24.4
Deferred Storm Costs [Member] | DP&L [Member]
Type of Recovery	D
Total non-current regulatory assets	24.7	24.4
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]
Type of Recovery	D
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	3.4	5.2
CCEM Energy Efficiency Program Costs [Member] | DP&L [Member]
Type of Recovery	F
Amortization Through	Ongoing
Total non-current regulatory assets	3.4	5.2
Consumer Education Campaign
Type of Recovery	D
Total non-current regulatory assets	3.0	3.0
Consumer Education Campaign | DP&L [Member]
Type of Recovery	D
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]
Type of Recovery	D
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	11.4	14.1
Other Costs - Assets [Member]
Total non-current regulatory assets	4.6	4.7
Other Costs - Assets [Member] | DP&L [Member]
Total non-current regulatory assets	$ 4.6	$ 4.7