Fair Value Measurements (Fair Value of Assets and Liabilities Measured on Recurring Basis) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Sep. 30, 2012 DP&L [Member]	Dec. 31, 2011 DP&L [Member]	Sep. 30, 2012 Estimate of Fair Value, Fair Value Disclosure [Member]	Dec. 31, 2011 Estimate of Fair Value, Fair Value Disclosure [Member]	Sep. 30, 2012 Estimate of Fair Value, Fair Value Disclosure [Member] DP&L [Member]	Dec. 31, 2011 Estimate of Fair Value, Fair Value Disclosure [Member] DP&L [Member]	Sep. 30, 2012 Level 1 [Member]	Dec. 31, 2011 Level 1 [Member]	Sep. 30, 2012 Level 1 [Member] DP&L [Member]	Dec. 31, 2011 Level 1 [Member] DP&L [Member]	Sep. 30, 2012 Level 2 [Member]	Dec. 31, 2011 Level 2 [Member]	Sep. 30, 2012 Level 2 [Member] DP&L [Member]	Dec. 31, 2011 Level 2 [Member] DP&L [Member]	Sep. 30, 2012 Level 3 [Member]	Sep. 30, 2012 Level 3 [Member] DP&L [Member]	Sep. 30, 2012 FTRs [Member] Estimate of Fair Value, Fair Value Disclosure [Member]	Dec. 31, 2011 FTRs [Member] Estimate of Fair Value, Fair Value Disclosure [Member]	Sep. 30, 2012 FTRs [Member] Estimate of Fair Value, Fair Value Disclosure [Member] DP&L [Member]	Dec. 31, 2011 FTRs [Member] Estimate of Fair Value, Fair Value Disclosure [Member] DP&L [Member]	Dec. 31, 2011 FTRs [Member] Level 2 [Member]	Dec. 31, 2011 FTRs [Member] Level 2 [Member] DP&L [Member]	Sep. 30, 2012 FTRs [Member] Level 3 [Member]	Sep. 30, 2012 FTRs [Member] Level 3 [Member] DP&L [Member]	Sep. 30, 2012 Futures [Member] Estimate of Fair Value, Fair Value Disclosure [Member]	Dec. 31, 2011 Futures [Member] Estimate of Fair Value, Fair Value Disclosure [Member]	Sep. 30, 2012 Futures [Member] Estimate of Fair Value, Fair Value Disclosure [Member] DP&L [Member]	Dec. 31, 2011 Futures [Member] Estimate of Fair Value, Fair Value Disclosure [Member] DP&L [Member]	Sep. 30, 2012 Futures [Member] Level 1 [Member]	Dec. 31, 2011 Futures [Member] Level 1 [Member]	Sep. 30, 2012 Futures [Member] Level 1 [Member] DP&L [Member]	Dec. 31, 2011 Futures [Member] Level 1 [Member] DP&L [Member]	Sep. 30, 2012 Forward NYMEX Coal Contracts [Member] Estimate of Fair Value, Fair Value Disclosure [Member]	Dec. 31, 2011 Forward NYMEX Coal Contracts [Member] Estimate of Fair Value, Fair Value Disclosure [Member]	Sep. 30, 2012 Forward NYMEX Coal Contracts [Member] Estimate of Fair Value, Fair Value Disclosure [Member] DP&L [Member]	Dec. 31, 2011 Forward NYMEX Coal Contracts [Member] Estimate of Fair Value, Fair Value Disclosure [Member] DP&L [Member]	Sep. 30, 2012 Forward NYMEX Coal Contracts [Member] Level 2 [Member]	Dec. 31, 2011 Forward NYMEX Coal Contracts [Member] Level 2 [Member]	Sep. 30, 2012 Forward NYMEX Coal Contracts [Member] Level 2 [Member] DP&L [Member]	Dec. 31, 2011 Forward NYMEX Coal Contracts [Member] Level 2 [Member] DP&L [Member]	Sep. 30, 2012 Debt [Member] Estimate of Fair Value, Fair Value Disclosure [Member]	Sep. 30, 2012 Debt [Member] Estimate of Fair Value, Fair Value Disclosure [Member] DP&L [Member]	Sep. 30, 2012 Debt [Member] Level 2 [Member]	Sep. 30, 2012 Debt [Member] Level 2 [Member] DP&L [Member]	Sep. 30, 2012 Debt [Member] Level 3 [Member]	Sep. 30, 2012 Debt [Member] Level 3 [Member] DP&L [Member]	Sep. 30, 2012 Forward Contract Power [Member] Estimate of Fair Value, Fair Value Disclosure [Member]	Dec. 31, 2011 Forward Contract Power [Member] Estimate of Fair Value, Fair Value Disclosure [Member]	Sep. 30, 2012 Forward Contract Power [Member] Estimate of Fair Value, Fair Value Disclosure [Member] DP&L [Member]	Dec. 31, 2011 Forward Contract Power [Member] Estimate of Fair Value, Fair Value Disclosure [Member] DP&L [Member]	Sep. 30, 2012 Forward Contract Power [Member] Level 2 [Member]	Dec. 31, 2011 Forward Contract Power [Member] Level 2 [Member]	Sep. 30, 2012 Forward Contract Power [Member] Level 2 [Member] DP&L [Member]	Dec. 31, 2011 Forward Contract Power [Member] Level 2 [Member] DP&L [Member]	Sep. 30, 2012 Equity Securities [Member] DP&L [Member]	Dec. 31, 2011 Equity Securities [Member] DP&L [Member]	Sep. 30, 2012 Equity Securities [Member] Estimate of Fair Value, Fair Value Disclosure [Member]	Dec. 31, 2011 Equity Securities [Member] Estimate of Fair Value, Fair Value Disclosure [Member]	Sep. 30, 2012 Equity Securities [Member] Estimate of Fair Value, Fair Value Disclosure [Member] DP&L [Member]	Dec. 31, 2011 Equity Securities [Member] Estimate of Fair Value, Fair Value Disclosure [Member] DP&L [Member]	Sep. 30, 2012 Equity Securities [Member] Level 2 [Member]	Dec. 31, 2011 Equity Securities [Member] Level 2 [Member]	Sep. 30, 2012 Equity Securities [Member] Level 2 [Member] DP&L [Member]	Dec. 31, 2011 Equity Securities [Member] Level 2 [Member] DP&L [Member]	Sep. 30, 2012 Equity Securities [Member] Fair Value [Member]	Dec. 31, 2011 Equity Securities [Member] Fair Value [Member]	Sep. 30, 2012 Debt Securities [Member] DP&L [Member]	Dec. 31, 2011 Debt Securities [Member] DP&L [Member]	Sep. 30, 2012 Debt Securities [Member] Estimate of Fair Value, Fair Value Disclosure [Member]	Dec. 31, 2011 Debt Securities [Member] Estimate of Fair Value, Fair Value Disclosure [Member]	Sep. 30, 2012 Debt Securities [Member] Estimate of Fair Value, Fair Value Disclosure [Member] DP&L [Member]	Dec. 31, 2011 Debt Securities [Member] Estimate of Fair Value, Fair Value Disclosure [Member] DP&L [Member]	Sep. 30, 2012 Debt Securities [Member] Level 2 [Member]	Dec. 31, 2011 Debt Securities [Member] Level 2 [Member]	Sep. 30, 2012 Debt Securities [Member] Level 2 [Member] DP&L [Member]	Dec. 31, 2011 Debt Securities [Member] Level 2 [Member] DP&L [Member]	Sep. 30, 2012 Debt Securities [Member] Fair Value [Member]	Dec. 31, 2011 Debt Securities [Member] Fair Value [Member]	Sep. 30, 2012 Money Market Funds [Member] DP&L [Member]	Dec. 31, 2011 Money Market Funds [Member] DP&L [Member]	Sep. 30, 2012 Money Market Funds [Member] Estimate of Fair Value, Fair Value Disclosure [Member]	Dec. 31, 2011 Money Market Funds [Member] Estimate of Fair Value, Fair Value Disclosure [Member]	Sep. 30, 2012 Money Market Funds [Member] Estimate of Fair Value, Fair Value Disclosure [Member] DP&L [Member]	Dec. 31, 2011 Money Market Funds [Member] Estimate of Fair Value, Fair Value Disclosure [Member] DP&L [Member]	Sep. 30, 2012 Money Market Funds [Member] Level 1 [Member]	Sep. 30, 2012 Money Market Funds [Member] Level 1 [Member] DP&L [Member]	Dec. 31, 2011 Money Market Funds [Member] Level 2 [Member]	Dec. 31, 2011 Money Market Funds [Member] Level 2 [Member] DP&L [Member]	Sep. 30, 2012 Money Market Funds [Member] Fair Value [Member]	Dec. 31, 2011 Money Market Funds [Member] Fair Value [Member]	Sep. 30, 2012 Hedge Funds, Multi-strategy [Member] Estimate of Fair Value, Fair Value Disclosure [Member]	Dec. 31, 2011 Hedge Funds, Multi-strategy [Member] Estimate of Fair Value, Fair Value Disclosure [Member]	Sep. 30, 2012 Hedge Funds, Multi-strategy [Member] Estimate of Fair Value, Fair Value Disclosure [Member] DP&L [Member]	Sep. 30, 2012 Hedge Funds, Multi-strategy [Member] Level 2 [Member]	Dec. 31, 2011 Hedge Funds, Multi-strategy [Member] Level 2 [Member]	Sep. 30, 2012 Hedge Funds, Multi-strategy [Member] Level 2 [Member] DP&L [Member]	Sep. 30, 2012 Hedge Funds, Multi-strategy [Member] Fair Value [Member]	Dec. 31, 2011 Hedge Funds, Multi-strategy [Member] Fair Value [Member]	Sep. 30, 2012 Multi Strategy Fund [Member] DP&L [Member]	Dec. 31, 2011 Multi Strategy Fund [Member] DP&L [Member]	Dec. 31, 2011 Multi Strategy Fund [Member] Estimate of Fair Value, Fair Value Disclosure [Member] DP&L [Member]	Dec. 31, 2011 Multi Strategy Fund [Member] Level 2 [Member] DP&L [Member]	Sep. 30, 2012 Interest Rate Swap [Member] Estimate of Fair Value, Fair Value Disclosure [Member]	Dec. 31, 2011 Interest Rate Swap [Member] Estimate of Fair Value, Fair Value Disclosure [Member]	Sep. 30, 2012 Interest Rate Swap [Member] Level 2 [Member]	Dec. 31, 2011 Interest Rate Swap [Member] Level 2 [Member]
Total Master Trust Assets, Fair Value		$ 11.2	$ 10.3			$ 11.2	$ 10.3			$ 0.2				$ 11.0	$ 10.3																																									$ 5.2	$ 4.4	$ 5.2	$ 4.4	$ 5.2	$ 4.4	$ 5.2	$ 4.4	$ 5.2	$ 4.4	$ 5.2	$ 4.4	$ 5.5	$ 5.5	$ 5.5	$ 5.5	$ 5.5	$ 5.5	$ 5.5	$ 5.5	$ 5.5	$ 5.5	$ 5.5	$ 5.5	$ 0.2	$ 0.2	$ 0.2	$ 0.2	$ 0.2	$ 0.2	$ 0.2	$ 0.2	$ 0.2	$ 0.2	$ 0.2	$ 0.2	$ 0.3	$ 0.2	$ 0.3	$ 0.3	$ 0.2	$ 0.3	$ 0.3	$ 0.2	$ 0.3	$ 0.2	$ 0.2	$ 0.2
Total Derivative Assets				17.3	19.2	5.5	6.0	0.4	1.8	0.4	1.8	16.8	17.4	5.0	17.4	0.1	0.1	0.1	0.1	0.1	0.1	0.1	0.1	0.1	0.1	0.4	1.8	0.4	1.8	0.4	1.8	0.4	1.8															16.8	17.3	5.0	4.1	16.8	17.3	5.0	17.3
Total Assets				11.2	10.3			0.2				11.0	10.3
Total Assets				28.5	29.5	16.7	16.3	0.6	1.8	0.6	1.8	27.8	27.7	16.0	27.7	0.1	0.1
Debt Instrument, Fair Value Disclosure																																										(2,769.4)	(934.5)	(2,750.4)	(915.5)	(19.0)	(19.0)
Total Derivative Liabilities				(57.9)	(60.3)	(19.8)	(19.5)					(57.8)	(60.3)	(19.7)	(27.8)	(0.1)	(0.1)	(0.1)		(0.1)				(0.1)	(0.1)									(1.1)	(14.5)	(1.1)	(14.5)	(1.1)	(14.5)	(1.1)	(14.5)							(21.0)	(13.3)	(18.6)	(5.0)	(21.0)	(13.3)	(18.6)	(13.3)																																																	(35.7)	(32.5)	(35.7)	(32.5)
Total Liabilities				$ (2,827.3)	$ (60.3)	$ (954.3)	$ (19.5)					$ (2,808.2)	$ (60.3)	$ (935.2)	$ (27.8)	$ (19.1)	$ (19.1)
Acquisition cost per share	$ 30.00