Derivative Instruments and Hedging Activities (Classification within the Condensed Consolidated Statements of Results of Operations or Balance Sheets of the Gains and Losses) (Details) (USD $) In Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Change in unrealized gain / (loss)	$ (29.9)	$ (2.1)	$ (41.1)	$ 0.8
Derivative, Gain (Loss) on Derivative, Net	6.0	(0.2)	8.2	(1.4)
Gain (Loss) on Derivative Instruments, Net, Pretax	(23.9)	(2.3)	(32.9)	(0.6)
Derivative Instruments, Gain (Loss) Recognized in Income, Net	(23.9)	(2.3)	(32.9)	(0.6)
DP&L [Member] | NYMEX Coal [Member]
Change in unrealized gain / (loss)	(27.9)	(3.8)	(41.6)	(1.0)
Derivative, Gain (Loss) on Derivative, Net	4.3	0.6	8.1
Gain (Loss) on Derivative Instruments, Net, Pretax	(23.6)	(3.2)	(33.5)	1.6
Derivative Instruments, Gain (Loss) Recognized in Income, Net	(23.6)	(3.2)	(33.5)	0.6
DP&L [Member] | NYMEX Coal [Member] | Partners Share of Gain Loss [Member]
Partner's share of gain (loss)	(13.8)	(1.6)	(21.2)	0.2
DP&L [Member] | NYMEX Coal [Member] | Regulatory Asset Liability [Member]
Regulatory (asset)/liability	(4.0)	(1.0)	(5.9)	(0.6)
DP&L [Member] | NYMEX Coal [Member] | Purchased Power [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net
DP&L [Member] | NYMEX Coal [Member] | Fuel [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	(5.8)	(0.6)	(6.4)	1.0
DP&L [Member] | NYMEX Coal [Member] | O&M [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net
DP&L [Member] | NYMEX Coal [Member] | Retail Revenue [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net
NYMEX Coal [Member]
Change in unrealized gain / (loss)	(27.9)	(3.8)	(41.6)	(1.0)
Derivative, Gain (Loss) on Derivative, Net	4.3	0.6	8.1	1.6
Gain (Loss) on Derivative Instruments, Net, Pretax	(23.6)	(3.2)	(33.5)	0.6
Derivative Instruments, Gain (Loss) Recognized in Income, Net	(23.6)	(3.2)	(33.5)	0.6
NYMEX Coal [Member] | Partners Share of Gain Loss [Member]
Partner's share of gain (loss)	(13.8)	(1.6)	(21.2)	0.2
NYMEX Coal [Member] | Regulatory Asset Liability [Member]
Regulatory (asset)/liability	(4.0)	(1.0)	(5.9)	(0.6)
NYMEX Coal [Member] | Purchased Power [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net
NYMEX Coal [Member] | Fuel [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	(5.8)	(0.6)	(6.4)	1.0
NYMEX Coal [Member] | O&M [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net
NYMEX Coal [Member] | Retail Revenue [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net
DP&L [Member] | Heating Oil [Member]
Change in unrealized gain / (loss)	(1.6)	1.3		1.5
Derivative, Gain (Loss) on Derivative, Net	0.5	(0.4)	1.5
Gain (Loss) on Derivative Instruments, Net, Pretax	(1.1)	0.9	1.5	(1.5)
Derivative Instruments, Gain (Loss) Recognized in Income, Net	(1.1)	0.9	1.5
DP&L [Member] | Heating Oil [Member] | Partners Share of Gain Loss [Member]
Partner's share of gain (loss)
DP&L [Member] | Heating Oil [Member] | Regulatory Asset Liability [Member]
Regulatory (asset)/liability	(0.6)	0.7	0.1	0.6
DP&L [Member] | Heating Oil [Member] | Purchased Power [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net
DP&L [Member] | Heating Oil [Member] | Fuel [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	(0.5)	0.2	1.3	(0.5)
DP&L [Member] | Heating Oil [Member] | O&M [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net			0.1	(0.1)
DP&L [Member] | Heating Oil [Member] | Retail Revenue [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net
Heating Oil [Member]
Change in unrealized gain / (loss)	(1.6)	1.3		1.5
Derivative, Gain (Loss) on Derivative, Net	0.5	(0.4)	1.5	(1.5)
Gain (Loss) on Derivative Instruments, Net, Pretax	(1.1)	0.9	1.5
Derivative Instruments, Gain (Loss) Recognized in Income, Net	(1.1)	0.9	1.5
Heating Oil [Member] | Partners Share of Gain Loss [Member]
Partner's share of gain (loss)
Heating Oil [Member] | Regulatory Asset Liability [Member]
Regulatory (asset)/liability	(0.6)	0.7	0.1	0.6
Heating Oil [Member] | Purchased Power [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net
Heating Oil [Member] | Fuel [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	(0.5)	0.2	1.3	(0.5)
Heating Oil [Member] | O&M [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net			0.1	(0.1)
Heating Oil [Member] | Retail Revenue [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net
DP&L [Member] | FTR's [Member]
Change in unrealized gain / (loss)	(0.1)	(0.1)	(0.1)	(0.4)
Derivative, Gain (Loss) on Derivative, Net		(0.4)	(0.6)
Gain (Loss) on Derivative Instruments, Net, Pretax	(0.1)	(0.5)	(0.7)	(1.4)
Derivative Instruments, Gain (Loss) Recognized in Income, Net	(0.1)	(0.5)	(0.7)	(1.8)
DP&L [Member] | FTR's [Member] | Partners Share of Gain Loss [Member]
Partner's share of gain (loss)
DP&L [Member] | FTR's [Member] | Regulatory Asset Liability [Member]
Regulatory (asset)/liability
DP&L [Member] | FTR's [Member] | Purchased Power [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	(0.1)	(0.5)	(0.7)	(1.8)
DP&L [Member] | FTR's [Member] | Fuel [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net
DP&L [Member] | FTR's [Member] | O&M [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net
DP&L [Member] | FTR's [Member] | Retail Revenue [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net
FTR's [Member]
Change in unrealized gain / (loss)	(0.1)	(0.1)	(0.1)	(0.4)
Derivative, Gain (Loss) on Derivative, Net		(0.4)	(0.6)	(1.4)
Gain (Loss) on Derivative Instruments, Net, Pretax	(0.1)	(0.5)	(0.7)	(1.8)
Derivative Instruments, Gain (Loss) Recognized in Income, Net	(0.1)	(0.5)	(0.7)	(1.8)
FTR's [Member] | Partners Share of Gain Loss [Member]
Partner's share of gain (loss)
FTR's [Member] | Regulatory Asset Liability [Member]
Regulatory (asset)/liability
FTR's [Member] | Purchased Power [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	(0.1)	(0.5)	(0.7)	(1.8)
FTR's [Member] | Fuel [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net
FTR's [Member] | O&M [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net
FTR's [Member] | Retail Revenue [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net
DP&L [Member] | Forward Power Contracts [Member]
Change in unrealized gain / (loss)	0.3	0.5		0.7
Derivative, Gain (Loss) on Derivative, Net	(0.3)		(0.8)
Gain (Loss) on Derivative Instruments, Net, Pretax		0.5	(0.8)	(0.1)
Derivative Instruments, Gain (Loss) Recognized in Income, Net		0.5	(0.8)	0.6
DP&L [Member] | Forward Power Contracts [Member] | Partners Share of Gain Loss [Member]
Partner's share of gain (loss)
DP&L [Member] | Forward Power Contracts [Member] | Regulatory Asset Liability [Member]
Regulatory (asset)/liability
DP&L [Member] | Forward Power Contracts [Member] | Wholesale Revenue [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net				(0.1)
DP&L [Member] | Forward Power Contracts [Member] | Purchased Power [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	0.1	0.5	(0.6)	0.7
DP&L [Member] | Forward Power Contracts [Member] | Fuel [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net
DP&L [Member] | Forward Power Contracts [Member] | O&M [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net
DP&L [Member] | Forward Power Contracts [Member] | Retail Revenue [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	(0.1)		(0.2)
Forward Power Contracts [Member]
Change in unrealized gain / (loss)	(0.3)	0.5	0.6	0.7
Derivative, Gain (Loss) on Derivative, Net	1.2		(0.8)	(0.1)
Gain (Loss) on Derivative Instruments, Net, Pretax	0.9	0.5	(0.2)	0.6
Derivative Instruments, Gain (Loss) Recognized in Income, Net	0.9	0.5	(0.2)	0.6
Forward Power Contracts [Member] | Partners Share of Gain Loss [Member]
Partner's share of gain (loss)
Forward Power Contracts [Member] | Regulatory Asset Liability [Member]
Regulatory (asset)/liability
Forward Power Contracts [Member] | Wholesale Revenue [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net				(0.1)
Forward Power Contracts [Member] | Purchased Power [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	2.5	0.5	6.1	0.7
Forward Power Contracts [Member] | Fuel [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net
Forward Power Contracts [Member] | O&M [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net
Forward Power Contracts [Member] | Retail Revenue [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	(1.6)		(6.3)
DP&L [Member] | Partners Share of Gain Loss [Member]
Partner's share of gain (loss)	(13.8)	(1.6)	(21.2)	0.2
Partners Share of Gain Loss [Member]
Partner's share of gain (loss)	(13.8)	(1.6)	(21.2)	0.2
DP&L [Member] | Regulatory Asset Liability [Member]
Regulatory (asset)/liability	(4.6)	(0.3)	(5.8)
Regulatory Asset Liability [Member]
Regulatory (asset)/liability	(4.6)	(0.3)	(5.8)
DP&L [Member] | Wholesale Revenue [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net				(0.1)
Wholesale Revenue [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net				(0.1)
DP&L [Member] | Purchased Power [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net			(1.3)	(1.1)
Purchased Power [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	2.4		5.4	(1.1)
DP&L [Member] | Fuel [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	(6.3)	(0.4)	(5.1)	0.5
Fuel [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	(6.3)	(0.4)	(5.1)	0.5
DP&L [Member] | O&M [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net			0.1	(0.1)
O&M [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net			0.1	(0.1)
DP&L [Member] | Retail Revenue [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	(0.1)		(0.2)
Retail Revenue [Member]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	(1.6)		(6.3)
DP&L [Member]
Change in unrealized gain / (loss)	(29.3)	(2.1)	(41.7)	0.8
Derivative, Gain (Loss) on Derivative, Net	4.5	(0.2)	8.2
Gain (Loss) on Derivative Instruments, Net, Pretax	(24.8)	(2.3)	(33.5)	(1.4)
Derivative Instruments, Gain (Loss) Recognized in Income, Net	$ (24.8)	$ (2.3)	$ (33.5)	$ (0.6)