Debt Obligations (Long-term Debt) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended			9 Months Ended		9 Months Ended		9 Months Ended		9 Months Ended		6 Months Ended	9 Months Ended	12 Months Ended	9 Months Ended					3 Months Ended
	Sep. 30, 2011	Mar. 01, 2011	Dec. 31, 2010	Sep. 30, 2011 DP&L [Member] First Mortgage Bonds Maturing in October 2013 - 5.125% [Member]	Dec. 31, 2010 DP&L [Member] First Mortgage Bonds Maturing in October 2013 - 5.125% [Member]	Sep. 30, 2011 DP&L [Member] Pollution Control Series Maturing in January 2028 - 4.70% [Member]	Dec. 31, 2010 DP&L [Member] Pollution Control Series Maturing in January 2028 - 4.70% [Member]	Sep. 30, 2011 DP&L [Member] Pollution Control Series Maturing in January 2034 - 4.80% [Member]	Dec. 31, 2010 DP&L [Member] Pollution Control Series Maturing in January 2034 - 4.80% [Member]	Sep. 30, 2011 DP&L [Member] Pollution Control Series Maturing in September 2036 - 4.80% [Member]	Dec. 31, 2010 DP&L [Member] Pollution Control Series Maturing in September 2036 - 4.80% [Member]	Jun. 30, 2011 DP&L [Member] Pollution control series maturing in November 2040 - variable rates: 0.23% - 0.29% and 0.16% - 0.36% [Member]	Sep. 30, 2011 DP&L [Member] Pollution control series maturing in November 2040 - variable rates: 0.23% - 0.29% and 0.16% - 0.36% [Member]	Dec. 31, 2010 DP&L [Member] Pollution control series maturing in November 2040 - variable rates: 0.23% - 0.29% and 0.16% - 0.36% [Member]	Sep. 30, 2011 DP&L [Member] U.S. Government note maturing in February 2061 - 4.20% [Member]	Sep. 30, 2011 Bank Term Loan - variable rates: 1.48% - 1.49% [Member]		Sep. 30, 2011 Note to DPL Capital Trust II Maturing in September 2031 - 8.125% [Member]	Dec. 31, 2010 Note to DPL Capital Trust II Maturing in September 2031 - 8.125% [Member]	Sep. 30, 2011 DP&L [Member]	Dec. 31, 2010 DP&L [Member]
Total long-term debt, gross	$ 1,223.6		$ 1,026.6	$ 470.0	$ 470.0	$ 35.3	$ 35.3	$ 179.1	$ 179.1	$ 100.0	$ 100.0		$ 100.0	$ 100.0	$ 0.1	$ 300.0	[1]	$ 20.6	$ 142.6	$ 902.9	$ 884.4
Obligation for capital lease																				0.5	0.1
Unamortized debt discount																				(0.4)	(0.5)
Total long-term debt																				$ 903.0	$ 884.0
Debt instrument maturity year	2061			October 2013		January 2028		January 2034		September 2036		November 2040 -			February 2061			September 2031		2026
Debt instrument interest percentage		4.20%		5.125%		4.70%		4.80%		4.80%					4.20%			8.125%
Debt instrument interest percentage minimum													0.06%	0.16%		1.48%
Debt instrument interest percentage maximum													0.29%	0.36%		1.49%

[1] Range of interest rates since the loan was drawn in August 2011.