Fair Value Measurements (Fair Value of Assets and Liabilities Measured on Recurring Basis) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Total Master Trust Assets, Fair Value	$ 11.5	[1]	$ 10.6	[1]
Total Derivative Assets	13.8	[1]	6.5	[1]
Total Assets	25.3	[1]	17.1	[1]
Debt Instrument, Fair Value Disclosure	2,334.6	[1]
Total Derivative Liabilities	10.6	[1]	42.7	[1]
Total Liabilities	2,345.2	[1]	2,749.8	[1]
Forward Contract Power [Member]
Total Derivative Assets	13.4	[1]	6.3	[1]
Total Derivative Liabilities	10.6	[1]	13.1	[1]
Commodity Contract - FTR [Member]
Total Derivative Assets	0.2	[1]
Total Derivative Liabilities			0.1	[1]
Commodity Contract - Heating Oil [Member]
Total Derivative Assets	0.2	[1]	0.2	[1]
Interest Rate Contract [Member]
Total Derivative Liabilities			29.5	[1]
DP&L [Member]
Total Master Trust Assets, Fair Value	11.5		10.6
Estimate of Fair Value, Fair Value Disclosure [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value	11.5	[1]	10.6	[1]
Total Derivative Assets	13.8	[1]	7.5	[1]
Total Assets	25.3	[1]	18.1	[1]
Debt Instrument, Fair Value Disclosure	859.6	[1]	926.9	[1]
Total Derivative Liabilities	10.6	[1]	11.7	[1]
Total Liabilities	870.2	[1]	938.6	[1]
Estimate of Fair Value, Fair Value Disclosure [Member] | DP&L [Member] | Forward Contract Power [Member]
Total Derivative Assets	13.4	[1]	7.3	[1]
Total Derivative Liabilities	10.6	[1]	11.6	[1]
Estimate of Fair Value, Fair Value Disclosure [Member] | DP&L [Member] | Commodity Contract - FTR [Member]
Total Derivative Assets	0.2	[1]
Estimate of Fair Value, Fair Value Disclosure [Member] | DP&L [Member] | Commodity Contract - Heating Oil [Member]
Total Derivative Assets	0.2	[1]	0.2	[1]
Estimate of Fair Value, Fair Value Disclosure [Member] | DP&L [Member] | NYMEX Coal Contract [Member]
Total Derivative Liabilities			0.1	[1]
Level 1 [Member]
Total Master Trust Assets, Fair Value	0.3		0.2
Total Derivative Assets	0.2		0.2
Total Assets	0.5		0.4
Level 1 [Member] | Commodity Contract - Heating Oil [Member]
Total Derivative Assets	0.2		0.2
Level 1 [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value	0.3		0.2
Total Derivative Assets	0.2		0.2
Total Assets	0.5		0.4
Level 1 [Member] | DP&L [Member] | Commodity Contract - Heating Oil [Member]
Total Derivative Assets	0.2		0.2
Level 2 [Member]
Total Master Trust Assets, Fair Value	11.2		10.4
Total Derivative Assets	13.4		6.3
Total Assets	24.6		16.7
Debt Instrument, Fair Value Disclosure	2,316.1
Total Derivative Liabilities	10.6		42.6
Total Liabilities	2,326.7		2,730.8
Level 2 [Member] | Forward Contract Power [Member]
Total Derivative Assets	13.4		6.3
Total Derivative Liabilities	10.6		13.1
Level 2 [Member] | Interest Rate Contract [Member]
Total Derivative Liabilities			29.5
Level 2 [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value	11.2		10.4
Total Derivative Assets	13.4		7.3
Total Assets	24.6		17.7
Debt Instrument, Fair Value Disclosure	841.1		908.0
Total Derivative Liabilities	10.6		11.6
Total Liabilities	851.7		919.6
Level 2 [Member] | DP&L [Member] | Forward Contract Power [Member]
Total Derivative Assets	13.4		7.3
Total Derivative Liabilities	10.6		11.6
Level 3 [Member]
Total Derivative Assets	0.2
Total Assets	0.2
Debt Instrument, Fair Value Disclosure	18.5
Total Derivative Liabilities			0.1
Total Liabilities	18.5		19.0
Level 3 [Member] | Commodity Contract - FTR [Member]
Total Derivative Assets	0.2
Total Derivative Liabilities			0.1
Level 3 [Member] | DP&L [Member]
Total Derivative Assets	0.2
Total Assets	0.2
Debt Instrument, Fair Value Disclosure	18.5		18.9
Total Derivative Liabilities			0.1
Total Liabilities	18.5		19.0
Level 3 [Member] | DP&L [Member] | Commodity Contract - FTR [Member]
Total Derivative Assets	0.2
Level 3 [Member] | DP&L [Member] | NYMEX Coal Contract [Member]
Total Derivative Liabilities			0.1
Equity Securities [Member]
Total Master Trust Assets, Fair Value	4.4	[1]	5.1	[1]
Equity Securities [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value	4.4		5.1
Equity Securities [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value	4.4	[1]	5.1	[1]
Equity Securities [Member] | Level 2 [Member]
Total Master Trust Assets, Fair Value	4.4		5.1
Equity Securities [Member] | Level 2 [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value	4.4		5.1
Debt Securities [Member]
Total Master Trust Assets, Fair Value	5.5	[1]	5.0	[1]
Debt Securities [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value	5.5		5.0
Debt Securities [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value	5.5	[1]	5.0	[1]
Debt Securities [Member] | Level 2 [Member]
Total Master Trust Assets, Fair Value	5.5		5.0
Debt Securities [Member] | Level 2 [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value	5.5		5.0
Money Market Funds [Member]
Total Master Trust Assets, Fair Value	0.3	[1]	0.2	[1]
Money Market Funds [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value	0.3		0.2
Money Market Funds [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value	0.3	[1]	0.2	[1]
Money Market Funds [Member] | Level 1 [Member]
Total Master Trust Assets, Fair Value	0.3		0.2
Money Market Funds [Member] | Level 1 [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value	0.3		0.2
Hedge Funds, Multi-strategy [Member]
Total Master Trust Assets, Fair Value			0.3	[1]
Hedge Funds, Multi-strategy [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value			0.3	[1]
Hedge Funds, Multi-strategy [Member] | Level 2 [Member]
Total Master Trust Assets, Fair Value			0.3
Hedge Funds, Multi-strategy [Member] | Level 2 [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value			0.3
Debt [Member]
Debt Instrument, Fair Value Disclosure			2,707.1	[1]
Debt [Member] | Level 2 [Member]
Debt Instrument, Fair Value Disclosure			2,688.2
Debt [Member] | Level 3 [Member]
Debt Instrument, Fair Value Disclosure			18.9
Hedge Funds [Member]
Total Master Trust Assets, Fair Value	0.9	[1]
Hedge Funds [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value	0.9
Hedge Funds [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value	0.9	[1]
Hedge Funds [Member] | Level 2 [Member]
Total Master Trust Assets, Fair Value	0.9
Hedge Funds [Member] | Level 2 [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value	0.9
Real Estate Funds [Member]
Total Master Trust Assets, Fair Value	0.4	[1]	0.3
Real Estate Funds [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value	0.4		0.3
Real Estate Funds [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value	0.4	[1]
Real Estate Funds [Member] | Level 2 [Member]
Total Master Trust Assets, Fair Value	0.4
Real Estate Funds [Member] | Level 2 [Member] | DP&L [Member]
Total Master Trust Assets, Fair Value	$ 0.4

[1] (a)Includes credit valuation adjustment