Fair Value Measurements (Narrative) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Acquisition cost per share		$ 30.00
Long Term Debt Range Adjusted To Fair Value at Merger Start	2013
Long Term Debt Range Adjusted To Fair Value At Merger End	2061
Unrealized gain	$ 0.8
Unrealized gain after tax	0.5
Percent of inputs to the fair value of derivative instruments from quoted market prices	99.00%
Money market funds	125.0	125.0
DP&L [Member]
Long Term Debt Range Adjusted To Fair Value at Merger Start	2013
Long Term Debt Range Adjusted To Fair Value At Merger End	2061
Unrealized gain	1.7	1.0
Unrealized gain after tax	$ 1.1	$ 0.7
Percent of inputs to the fair value of derivative instruments from quoted market prices	99.00%
First Mortgage Bonds Maturing in October 2013 - 5.125% [Member]
Debt maturities maximum period	Oct. 01, 2013
First Mortgage Bonds Maturing in October 2013 - 5.125% [Member] | DP&L [Member]
Debt maturities maximum period	Oct. 01, 2013
Pollution Control Series Maturing in January 2028 - 4.70% [Member]
Debt maturities maximum period	Jan. 01, 2028
Pollution Control Series Maturing in January 2028 - 4.70% [Member] | DP&L [Member]
Debt maturities maximum period	Jan. 01, 2028
Pollution Control Series Maturing in January 2034 - 4.80% [Member]
Debt maturities maximum period	Jan. 01, 2034
Pollution Control Series Maturing in January 2034 - 4.80% [Member] | DP&L [Member]
Debt maturities maximum period	Jan. 01, 2034
Pollution Control Series Maturing in September 2036 - 4.80% [Member]
Debt maturities maximum period	Sep. 01, 2036
Pollution Control Series Maturing in September 2036 - 4.80% [Member] | DP&L [Member]
Debt maturities maximum period	Sep. 01, 2036
Pollution control series maturing in November 2040 - variable rates: 0.04% - 0.26% and 0.06% - 0.32% [Member]
Debt maturities maximum period	Nov. 01, 2040
Pollution control series maturing in November 2040 - variable rates: 0.04% - 0.26% and 0.06% - 0.32% [Member] | DP&L [Member]
Debt maturities maximum period	Nov. 01, 2040
U.S. Government note maturing in February 2061 - 4.20% [Member]
Debt maturities maximum period	Feb. 01, 2061
U.S. Government note maturing in February 2061 - 4.20% [Member] | DP&L [Member]
Debt maturities maximum period	Feb. 01, 2061
Note to DPL Capital Trust II Maturing in September 2031 - 8.125% [Member]
Debt maturities maximum period	Sep. 01, 2031
Five Year Senior Unsecured Notes at 6.50% maturing on October 15, 2016 [Member]
Debt maturities maximum period	Oct. 01, 2016
Ten Year Senior Unsecured Notes at 7.25% maturing at October 15, 2021 [Member]
Debt maturities maximum period	Oct. 01, 2021