Fair Value Measurements (Narrative) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 2012	Dec. 31, 2011
Acquisition cost per share		$ 30
Debt maturities minimum period	2013
Debt maturities maximum period	2061
Unrealized gains / (losses) on financial instruments, Amount before tax	$ 0.6
Percent of inputs to the fair value of derivative instruments from quoted market prices	99.00%
Money market funds	100.0	125.0
DP&L [Member]
Acquisition cost per share		$ 30
Debt maturities minimum period	2013
Debt maturities maximum period	2061
Available-for-sale Securities, Change in Net Unrealized Holding Gain (Loss) before Taxes	1.5	1.0
Available-for-sale Securities, Change in Net Unrealized Holding Gain (Loss), Net of Tax	$ 1.0	$ 0.7
Percent of inputs to the fair value of derivative instruments from quoted market prices	99.00%
Debt Obligation on 4.9% Equity Ownership [Member] \| DP&L [Member]
Debt maturities minimum period	2013
Debt maturities maximum period	2026
First Mortgage Bonds Maturing in October 2013 - 5.125% [Member]
Debt maturities maximum period	October 2013
First Mortgage Bonds Maturing in October 2013 - 5.125% [Member] \| DP&L [Member]
Debt maturities maximum period	October 2013
Pollution Control Series Maturing in January 2028 - 4.70% [Member]
Debt maturities maximum period	January 2028
Pollution Control Series Maturing in January 2028 - 4.70% [Member] \| DP&L [Member]
Debt maturities maximum period	January 2028
Pollution Control Series Maturing in January 2034 - 4.80% [Member]
Debt maturities maximum period	January 2034
Pollution Control Series Maturing in January 2034 - 4.80% [Member] \| DP&L [Member]
Debt maturities maximum period	January 2034
Pollution Control Series Maturing in September 2036 - 4.80% [Member]
Debt maturities maximum period	September 2036
Pollution Control Series Maturing in September 2036 - 4.80% [Member] \| DP&L [Member]
Debt maturities maximum period	September 2036
Pollution control series maturing in November 2040 - variable rates: 0.04% - 0.20% and 0.06% - 0.32% [Member]
Debt maturities maximum period	November 2040 -
Pollution control series maturing in November 2040 - variable rates: 0.04% - 0.20% and 0.06% - 0.32% [Member] \| DP&L [Member]
Debt maturities maximum period	November 2040
U.S. Government note maturing in February 2061 - 4.20% [Member]
Debt maturities maximum period	February 2061
U.S. Government note maturing in February 2061 - 4.20% [Member] \| DP&L [Member]
Debt maturities maximum period	February 2061
Note to DPL Capital Trust II Maturing in September 2031 - 8.125% [Member]
Debt maturities maximum period	September 2031
Five Year Senior Unsecured Notes at 6.50% maturing on October 15, 2016 [Member]
Debt maturities maximum period	October 2016
Ten Year Senior Unsecured Notes at 7.25% maturing at October 15, 2021 [Member]
Debt maturities maximum period	October 2021

When presenting a range of maturity dates, the latest date when the outstanding debt instruments are required to be repaid. May be presented in a variety of ways (for example: year only, month and year, day, month and year, and number of years).

+ References+ Details

When presenting a range of maturity dates, the earliest date when the outstanding debt instruments are required to be repaid. May be presented in a variety of ways (for example: year only, month and year, day, month and year, and number of years).

+ References+ Details

- Definition

Investment in short-term money-market instruments (such as commercial paper, banker's acceptances, repurchase agreements, government securities, certificates of deposit, and so forth) which are highly liquid (that is, readily convertible to known amounts of cash) and so near their maturity that they present an insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify as cash equivalents by definition. Original maturity means an original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

+ References+ Details

- Definition

Gross appreciation or the gross loss in value of the total of unsold available-for-sale securities during the period being reported (except when designated as a fair value hedge).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 11

-URI http://asc.fasb.org/extlink&oid=6920043&loc=d3e637-108580

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 13

-URI http://asc.fasb.org/extlink&oid=6920043&loc=d3e653-108580

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 13

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 55

-Paragraph 2

-Subparagraph (e)

-URI http://asc.fasb.org/extlink&oid=6920433&loc=d3e998-108581

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 130

-Paragraph 24

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 130

-Paragraph 17

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Accounting Research Bulletin (ARB)

-Number 51

-Paragraph 38

-Subparagraph c(3)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details