Fair Value Measurements (Fair Value of Assets and Liabilities Measured on Recurring Basis) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
DP&L [Member]
Total Master Trust Assets, Fair Value	$ 10.2	$ 11.5
Total Derivative Assets	16.6	13.8
Total Assets	26.8	25.3
Debt Instrument, Fair Value Disclosure	887.5	859.6
Total Derivative Liabilities	35.6	10.6
Total Liabilities	923.1	870.2
DP&L [Member] | Forward Contract Power [Member]
Total Derivative Assets	16.5	13.4
Total Derivative Liabilities	34.3	10.6
DP&L [Member] | Commodity Contract - FTR [Member]
Total Derivative Assets		0.2
Total Derivative Liabilities	1.3
DP&L [Member] | Commodity Contract - Heating Oil [Member]
Total Derivative Assets	0.1	0.2
Estimate of Fair Value, Fair Value Disclosure [Member]
Total Master Trust Assets, Fair Value	10.2	11.5
Total Derivative Assets	16.0	13.8
Total Assets	26.2	25.3
Total Derivative Liabilities	35.5	10.6
Total Liabilities	2,459.8	2,345.2
Estimate of Fair Value, Fair Value Disclosure [Member] | Forward Contract Power [Member]
Total Derivative Assets	15.9	13.4
Estimate of Fair Value, Fair Value Disclosure [Member] | Commodity Contract - FTR [Member]
Total Derivative Assets		0.2
Total Derivative Liabilities	1.3	10.6
Estimate of Fair Value, Fair Value Disclosure [Member] | Commodity Contract - Heating Oil [Member]
Total Derivative Assets	0.1	0.2
Estimate of Fair Value, Fair Value Disclosure [Member] | Interest Rate Contract [Member]
Total Derivative Liabilities	34.2
Level 1 [Member]
Total Master Trust Assets, Fair Value	9.3	10.6
Total Derivative Assets	0.1	0.2
Total Assets	9.4	10.8
Level 1 [Member] | Commodity Contract - Heating Oil [Member]
Total Derivative Assets	0.1	0.2
Level 1 [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value	9.3	10.6
Total Derivative Assets	0.1	0.2
Total Assets	9.4	10.8
Level 1 [Member] | DP&L [Member] | Commodity Contract - Heating Oil [Member]
Total Derivative Assets	0.1	0.2
Level 2 [Member]
Total Master Trust Assets, Fair Value	0.9	0.9
Total Derivative Assets	15.9	13.4
Total Assets	16.8	14.3
Total Derivative Liabilities	34.2	10.6
Total Liabilities	2,440.2	2,326.7
Level 2 [Member] | Forward Contract Power [Member]
Total Derivative Assets	15.9	13.4
Level 2 [Member] | Commodity Contract - FTR [Member]
Total Derivative Liabilities		10.6
Level 2 [Member] | Interest Rate Contract [Member]
Total Derivative Liabilities	34.2
Level 2 [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value	0.9	0.9
Total Derivative Assets	16.5	13.4
Total Assets	17.4	14.3
Debt Instrument, Fair Value Disclosure	869.2	841.1
Total Derivative Liabilities	34.3	10.6
Total Liabilities	903.5	851.7
Level 2 [Member] | DP&L [Member] | Forward Contract Power [Member]
Total Derivative Assets	16.5	13.4
Total Derivative Liabilities	34.3	10.6
Level 3 [Member]
Total Derivative Assets		0.2
Total Assets		0.2
Total Derivative Liabilities	1.3
Total Liabilities	19.6	18.5
Level 3 [Member] | Commodity Contract - FTR [Member]
Total Derivative Assets		0.2
Total Derivative Liabilities	1.3
Level 3 [Member] | DP&L [Member]
Total Derivative Assets		0.2
Total Assets		0.2
Debt Instrument, Fair Value Disclosure	18.3	18.5
Total Derivative Liabilities	1.3
Total Liabilities	19.6	18.5
Level 3 [Member] | DP&L [Member] | Commodity Contract - FTR [Member]
Total Derivative Assets		0.2
Total Derivative Liabilities	1.3
Equity Securities [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value	3.9	4.4
Equity Securities [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Total Master Trust Assets, Fair Value	3.9	4.4
Equity Securities [Member] | Level 1 [Member]
Total Master Trust Assets, Fair Value	3.9	4.4
Equity Securities [Member] | Level 1 [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value	3.9	4.4
Equity Securities [Member] | Fair Value [Member]
Total Master Trust Assets, Fair Value	3.9	4.4
Debt Securities [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value	4.8	5.5
Debt Securities [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Total Master Trust Assets, Fair Value	4.8	5.5
Debt Securities [Member] | Level 1 [Member]
Total Master Trust Assets, Fair Value	4.8	5.5
Debt Securities [Member] | Level 1 [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value	4.8	5.5
Money Market Funds [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value	0.2	0.3
Money Market Funds [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Total Master Trust Assets, Fair Value	0.2	0.3
Money Market Funds [Member] | Level 1 [Member]
Total Master Trust Assets, Fair Value	0.2	0.3
Money Market Funds [Member] | Level 1 [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value	0.2	0.3
Money Market Funds [Member] | Fair Value [Member]
Total Master Trust Assets, Fair Value	0.2	0.3
Debt [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Debt Instrument, Fair Value Disclosure	2,424.3	2,334.6
Debt [Member] | Level 2 [Member]
Debt Instrument, Fair Value Disclosure	2,406.0	2,316.1
Debt [Member] | Level 3 [Member]
Debt Instrument, Fair Value Disclosure	18.3	18.5
Debt [Member] | Fair Value [Member]
Total Master Trust Assets, Fair Value	4.8	5.5
Hedge Funds [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value	0.9	0.9
Hedge Funds [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Total Master Trust Assets, Fair Value	0.9	0.9
Hedge Funds [Member] | Level 2 [Member]
Total Master Trust Assets, Fair Value	0.9	0.9
Hedge Funds [Member] | Level 2 [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value	0.9	0.9
Hedge Funds [Member] | Fair Value [Member]
Total Master Trust Assets, Fair Value	0.9	0.9
Real Estate Funds [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value	0.4	0.4
Real Estate Funds [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Total Master Trust Assets, Fair Value	0.4	0.4
Real Estate Funds [Member] | Level 1 [Member]
Total Master Trust Assets, Fair Value	0.4	0.4
Real Estate Funds [Member] | Level 1 [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value	0.4	0.4
Real Estate Funds [Member] | Fair Value [Member]
Total Master Trust Assets, Fair Value	$ 0.4	$ 0.4