Debt Obligations (Long-term Debt) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Total long-term debt at subsidary	$ 874.6	$ 874.6
Unamortized debt discount	(0.5)	(0.7)
Total long-term debt	2,154.3	2,284.2
DP&L [Member]
Unamortized debt discount	(0.5)	(0.7)
Total long-term debt	877.0	876.9
First Mortgage Bonds Maturing in October 2013 - 5.125% [Member]
Debt instrument maturity year	May 01, 2018
Debt instrument interest percentage minimum	2.41%	2.42%
Debt instrument interest percentage maximum	2.42%	2.45%
First Mortgage Bonds Maturing in September 2016
Long-term debt, gross	445.0	445.0
Debt instrument maturity year	Sep. 01, 2016
Debt instrument interest percentage	1.875%
First Mortgage Bonds Maturing in September 2016 | DP&L [Member]
Long-term debt, gross	445.0	445.0
Debt instrument maturity year	Sep. 01, 2016
Debt instrument interest percentage	1.875%
Pollution Control Series Maturing in January 2028 - 4.70% [Member]
Long-term debt, gross	36.0	36.0
Debt instrument maturity year	Jan. 01, 2028
Debt instrument interest percentage	4.70%
Pollution Control Series Maturing in January 2028 - 4.70% [Member] | DP&L [Member]
Long-term debt, gross	35.3	35.3
Debt instrument maturity year	Jan. 01, 2028
Debt instrument interest percentage	4.70%
Pollution Control Series Maturing in January 2034 - 4.80% [Member]
Long-term debt, gross	179.6	179.6
Debt instrument maturity year	Jan. 01, 2034
Debt instrument interest percentage	4.80%
Pollution Control Series Maturing in January 2034 - 4.80% [Member] | DP&L [Member]
Long-term debt, gross	179.1	179.1
Debt instrument maturity year	Jan. 01, 2034
Debt instrument interest percentage	4.80%
Pollution Control Series Maturing in September 2036 - 4.80% [Member]
Long-term debt, gross	96.4	96.4
Debt instrument maturity year	Sep. 01, 2036
Debt instrument interest percentage	4.80%
Pollution Control Series Maturing in September 2036 - 4.80% [Member] | DP&L [Member]
Long-term debt, gross	100.0	100.0
Debt instrument maturity year	Sep. 01, 2036
Debt instrument interest percentage	4.80%
Pollution control series maturing in November 2040 - variable rates: 0.04% - 0.26% and 0.06% - 0.32% [Member]
Long-term debt, gross	100.0	100.0
Debt instrument maturity year	Nov. 01, 2040
Debt instrument interest percentage minimum	0.04%	0.05%
Debt instrument interest percentage maximum	0.15%	0.24%
Pollution control series maturing in November 2040 - variable rates: 0.04% - 0.26% and 0.06% - 0.32% [Member] | DP&L [Member]
Long-term debt, gross	100.0	100.0
Debt instrument maturity year	Nov. 01, 2040
Debt instrument interest percentage minimum	0.04%	0.05%
Debt instrument interest percentage maximum	0.15%	0.24%
U.S. Government note maturing in February 2061 - 4.20% [Member]
Long-term debt, gross	(18.1)	(18.3)
Debt instrument maturity year	Feb. 01, 2061
Debt instrument interest percentage	4.20%
Debt instrument interest percentage minimum	4.20%
U.S. Government note maturing in February 2061 - 4.20% [Member] | DP&L [Member]
Long-term debt, gross	18.1	18.2
Debt instrument maturity year	Feb. 01, 2061
Debt instrument interest percentage	4.20%
Debt instrument interest percentage minimum	4.20%
Bank Term Loan maturing in May 2018 [Member]
Long-term debt, gross	150.0	180.0
Debt instrument maturity year	May 01, 2018
Debt instrument interest percentage minimum	2.41%	2.42%
Debt instrument interest percentage maximum	2.42%	2.45%
Note to DPL Capital Trust II Maturing in September 2031 - 8.125% [Member]
Long-term debt, gross	19.7	19.6
Debt instrument maturity year	Sep. 01, 2031
Debt instrument interest percentage	8.125%
Senior Unsecured Notes at 6.50% maturing on October 15, 2016 [Member]
Long-term debt, gross	330.0	430.0
Debt instrument maturity year	Oct. 01, 2016
Debt instrument interest percentage	6.50%
Ten Year Senior Unsecured Notes at 7.25% maturing at October 15, 2021 [Member]
Long-term debt, gross	$ 780.0	$ 780.0
Debt instrument maturity year	Oct. 01, 2021
Debt instrument interest percentage	7.25%