Fair Value Measurements (Fair Value of Assets and Liabilities Measured on Recurring Basis) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
DP&L [Member]
Total Master Trust Assets, Fair Value	$ 10.0	$ 11.5
Total Derivative Assets	11.7	13.8
Total Assets	21.7	25.3
Debt Instrument, Fair Value Disclosure	884.7	859.6
Total Derivative Liabilities	28.0	10.6
Total Liabilities	912.7	870.2
DP&L [Member] | Forward Contract Power [Member]
Total Derivative Assets	11.7	13.4
Total Derivative Liabilities	26.9	10.6
DP&L [Member] | Commodity Contract - FTR [Member]
Total Derivative Assets		0.2
Total Derivative Liabilities	1.0
DP&L [Member] | Commodity Contract - Heating Oil [Member]
Total Derivative Assets		0.2
Total Derivative Liabilities	0.1
Estimate of Fair Value, Fair Value Disclosure [Member]
Total Master Trust Assets, Fair Value	10.0	11.5
Total Derivative Assets	11.2	13.8
Total Assets	21.2	25.3
Total Derivative Liabilities	28.0	10.6
Total Liabilities	2,373.9	2,345.2
Estimate of Fair Value, Fair Value Disclosure [Member] | Forward Contract Power [Member]
Total Derivative Assets	11.2	13.4
Total Derivative Liabilities	26.9	10.6
Estimate of Fair Value, Fair Value Disclosure [Member] | Commodity Contract - FTR [Member]
Total Derivative Assets		0.2
Total Derivative Liabilities	1.0
Estimate of Fair Value, Fair Value Disclosure [Member] | Commodity Contract - Heating Oil [Member]
Total Derivative Assets		0.2
Total Derivative Liabilities	0.1
Level 1 [Member]
Total Master Trust Assets, Fair Value	9.1	10.6
Total Derivative Assets		0.2
Total Assets	9.1	10.8
Total Derivative Liabilities	0.1
Total Liabilities	0.1
Level 1 [Member] | Commodity Contract - Heating Oil [Member]
Total Derivative Assets		0.2
Total Derivative Liabilities	0.1
Level 1 [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value	9.1	10.6
Total Derivative Assets		0.2
Total Assets	9.1	10.8
Total Derivative Liabilities	0.1
Total Liabilities	0.1
Level 1 [Member] | DP&L [Member] | Commodity Contract - Heating Oil [Member]
Total Derivative Assets		0.2
Total Derivative Liabilities	0.1
Level 2 [Member]
Total Master Trust Assets, Fair Value	0.9	0.9
Total Derivative Assets	11.2	13.4
Total Assets	12.1	14.3
Total Derivative Liabilities	26.9	10.6
Total Liabilities	2,354.5	2,326.7
Level 2 [Member] | Forward Contract Power [Member]
Total Derivative Assets	11.2	13.4
Total Derivative Liabilities	26.9	10.6
Level 2 [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value	0.9	0.9
Total Derivative Assets	11.7	13.4
Total Assets	12.6	14.3
Debt Instrument, Fair Value Disclosure	866.4	841.1
Total Derivative Liabilities	26.9	10.6
Total Liabilities	893.3	851.7
Level 2 [Member] | DP&L [Member] | Forward Contract Power [Member]
Total Derivative Assets	11.7	13.4
Total Derivative Liabilities	26.9	10.6
Level 3 [Member]
Total Derivative Assets		0.2
Total Assets		0.2
Total Derivative Liabilities	1.0
Total Liabilities	19.3	18.5
Level 3 [Member] | Commodity Contract - FTR [Member]
Total Derivative Assets		0.2
Total Derivative Liabilities	1.0
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	1.0
Total Liabilities	19.3	18.5
Level 3 [Member] | DP&L [Member] | Commodity Contract - FTR [Member]
Total Derivative Assets		0.2
Total Derivative Liabilities	1.0
Equity Securities [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value	3.6	4.4
Equity Securities [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Total Master Trust Assets, Fair Value	3.6	4.4
Equity Securities [Member] | Level 1 [Member]
Total Master Trust Assets, Fair Value	3.6	4.4
Equity Securities [Member] | Level 1 [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value	3.6	4.4
Equity Securities [Member] | Fair Value [Member]
Total Master Trust Assets, Fair Value	3.6	4.4
Debt Securities [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value	5.0	5.5
Debt Securities [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Total Master Trust Assets, Fair Value	5.0	5.5
Debt Securities [Member] | Level 1 [Member]
Total Master Trust Assets, Fair Value	5.0	5.5
Debt Securities [Member] | Level 1 [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value	5.0	5.5
Money Market Funds [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value	0.1	0.3
Money Market Funds [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Total Master Trust Assets, Fair Value	0.1	0.3
Money Market Funds [Member] | Level 1 [Member]
Total Master Trust Assets, Fair Value	0.1	0.3
Money Market Funds [Member] | Level 1 [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value	0.1	0.3
Money Market Funds [Member] | Fair Value [Member]
Total Master Trust Assets, Fair Value	0.1	0.3
Debt [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Debt Instrument, Fair Value Disclosure	2,345.9	2,334.6
Debt [Member] | Level 2 [Member]
Debt Instrument, Fair Value Disclosure	2,327.6	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	5.0	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