Regulatory Matters (Schedule of Regulatory Assets and Liabilities) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2012	Dec. 31, 2011
Total current regulatory assets	$ 15.2	$ 20.2
Total non-current regulatory assets	172.9	177.8
Total current regulatory liabilities		0.6
Total non-current regulatory liabilities	118.5	118.6
Estimated Costs of Removal - Regulated Property [Member]
Total non-current regulatory liabilities	112.5	112.4
Postretirement Benefit [Member]
Total non-current regulatory liabilities	6.0	6.2
Other Costs - Liabilities [Member]
Type of Recovery	C
Amortization Through	Ongoing
Total current regulatory liabilities		0.6
DP&L [Member]
Total current regulatory assets	12.7	17.7
Total non-current regulatory assets	172.9	177.8
Total non-current regulatory liabilities	118.5	118.6
DP&L [Member] | Estimated Costs of Removal - Regulated Property [Member]
Total non-current regulatory liabilities	112.5	112.4
DP&L [Member] | Postretirement Benefit [Member]
Total non-current regulatory liabilities	6.0	6.2
Deferred Recoverable Income Taxes [Member]
Type of Recovery	B/C	B/C
Amortization Through	Ongoing	Ongoing
Total non-current regulatory assets	23.3	24.1
Deferred Recoverable Income Taxes [Member] | DP&L [Member]
Type of Recovery		B/C
Amortization Through		Ongoing
Total non-current regulatory assets	23.3	24.1
Pension Benefits [Member]
Type of Recovery	C	C
Amortization Through	Ongoing	Ongoing
Total non-current regulatory assets	90.5	92.1
Pension Benefits [Member] | DP&L [Member]
Type of Recovery		C
Amortization Through		Ongoing
Total non-current regulatory assets	90.5	92.1
Unamortized Loss on Reacquired Debt [Member]
Type of Recovery	C	C
Amortization Through	Ongoing	Ongoing
Total non-current regulatory assets	12.6	13.0
Unamortized Loss on Reacquired Debt [Member] | DP&L [Member]
Type of Recovery		C
Amortization Through		Ongoing
Total non-current regulatory assets	12.6	13.0
Regional Transmission Organization Costs [Member]
Type of Recovery	D	D
Amortization Through	2014	2014
Total non-current regulatory assets	3.7	4.1
Regional Transmission Organization Costs [Member] | DP&L [Member]
Type of Recovery		D
Amortization Through		2014
Total non-current regulatory assets	3.7	4.1
TCRR, Transmission, Ancillary and Other PJM-related Costs [Member]
Type of Recovery	F	F
Amortization Through	Ongoing	Ongoing
Total current regulatory assets	2.8	4.7
TCRR, Transmission, Ancillary and Other PJM-related Costs [Member] | DP&L [Member]
Type of Recovery		F
Amortization Through		Ongoing
Total current regulatory assets	2.8	4.7
Deferred Storm Costs - 2008 [Member]
Type of Recovery	D	D
Total non-current regulatory assets	18.2	17.9
Deferred Storm Costs - 2008 [Member] | DP&L [Member]
Type of Recovery		D
Total non-current regulatory assets	18.2	17.9
Power Plant Emission Fees [Member]
Type of Recovery	C	C
Amortization Through	Ongoing	Ongoing
Total current regulatory assets	3.1	4.8
Power Plant Emission Fees [Member] | DP&L [Member]
Type of Recovery		C
Amortization Through		Ongoing
Total current regulatory assets	3.1	4.8
CCEM Smart Grid and Advanced Metering Infrastructure Costs [Member]
Type of Recovery	D	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	F
Amortization Through	Ongoing	Ongoing
Total non-current regulatory assets	6.9	8.8
CCEM Energy Efficiency Program Costs [Member] | DP&L [Member]
Type of Recovery		F
Amortization Through		Ongoing
Total non-current regulatory assets	6.9	8.8
Consumer Education Campaign
Type of Recovery	D	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	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	C
Amortization Through	Ongoing	Ongoing
Total current regulatory assets	9.3	10.7
Fuel and Purchased Power Recovery Costs [Member] | DP&L [Member]
Type of Recovery		C
Amortization Through		Ongoing
Total current regulatory assets	6.8	8.2
Other Costs - Assets [Member]
Total non-current regulatory assets	5.0	5.1
Other Costs - Assets [Member] | DP&L [Member]
Total non-current regulatory assets	$ 5.0	$ 5.1