Regulatory Assets and Liabilities (Schedule of Regulatory Assets and Liabilities) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Total current regulatory assets	$ 12.2	$ 21.1
Total non-current regulatory assets	172.4	185.5
Total current regulatory liabilities		0.1
Total non-current regulatory liabilities	118.0	117.3
Estimated Costs of Removal - Regulated Property [Member]
Total non-current regulatory liabilities	113.4	112.1
Postretirement Benefit [Member]
Total non-current regulatory liabilities	4.6	5.0
Other Costs - Liabilities [Member]
Total current regulatory liabilities		0.1
Total non-current regulatory liabilities		0.2
DP&L [Member]
Total current regulatory assets	10.8	18.3
Total non-current regulatory assets	172.4	185.5
Total current regulatory liabilities		0.1
Total non-current regulatory liabilities	118.0	117.3
DP&L [Member] | Estimated Costs of Removal - Regulated Property [Member]
Total non-current regulatory liabilities	113.4	112.1
DP&L [Member] | Postretirement Benefit [Member]
Total non-current regulatory liabilities	4.6	5.0
DP&L [Member] | Other Costs - Liabilities [Member]
Total current regulatory liabilities		0.1
Total non-current regulatory liabilities		0.2
Deferred Recoverable Income Taxes [Member]
Type of Recovery	B/C
Amortization Through	Ongoing
Total non-current regulatory assets	32.6	35.1
Deferred Recoverable Income Taxes [Member] | DP&L [Member]
Type of Recovery	B/C
Amortization Through	Ongoing
Total non-current regulatory assets	32.6	35.1
Pension Benefits [Member]
Type of Recovery	C
Amortization Through	Ongoing
Total non-current regulatory assets	84.0	88.9
Pension Benefits [Member] | DP&L [Member]
Type of Recovery	C
Amortization Through	Ongoing
Total non-current regulatory assets	84.0	88.9
Fuel and purchased power recovery costs [Member] | DP&L [Member]
Type of Recovery	C
Amortization Through	Ongoing
Total current regulatory assets	6.3	11.3
Unamortized Loss on Reacquired Debt [Member]
Type of Recovery	C
Amortization Through	Ongoing
Total non-current regulatory assets	11.2	11.9
Unamortized Loss on Reacquired Debt [Member] | DP&L [Member]
Type of Recovery	C
Amortization Through	Ongoing
Total non-current regulatory assets	11.2	11.9
Regional Transmission Organization Costs [Member]
Type of Recovery	D
Amortization Through	2014
Total non-current regulatory assets	1.5	2.6
Regional Transmission Organization Costs [Member] | DP&L [Member]
Type of Recovery	D
Amortization Through	2014
Total non-current regulatory assets	1.5	2.6
TCRR, Transmission, Ancillary and Other PJM-related Costs [Member]
Type of Recovery	F
Amortization Through	Ongoing
Total current regulatory assets	4.5	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	4.5	7.0
Deferred Storm Costs [Member]
Type of Recovery	D
Total non-current regulatory assets	25.3	24.4
Deferred Storm Costs [Member] | DP&L [Member]
Type of Recovery	D
Total non-current regulatory assets	25.3	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	0.8	5.2
CCEM Energy Efficiency Program Costs [Member] | DP&L [Member]
Type of Recovery	F
Amortization Through	Ongoing
Total non-current regulatory assets	0.8	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	7.7	14.1
Other Costs - Assets [Member]
Total non-current regulatory assets	4.3	4.7
Other Costs - Assets [Member] | DP&L [Member]
Total non-current regulatory assets	$ 4.3	$ 4.7