Fair Value Measurements (Fair Value of Assets and Liabilities Measured on Recurring Basis) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
DP&L [Member]
Total Master Trust Assets, Fair Value	$ 9.6	$ 9.7
Total Derivative Assets	20.8	15.1
Total Assets	30.4	24.8
Debt Instrument, Fair Value Disclosure	885.2	882.5
Total Derivative Liabilities	20.9	12.3
Total Liabilities	906.1	894.8
DP&L [Member] \| Forward Contract Power [Member]
Total Derivative Assets	20.5	15.1
Total Derivative Liabilities	20.6	11.2
DP&L [Member] \| Commodity Contract - FTR [Member]
Total Derivative Assets	0.3
Total Derivative Liabilities		0.6
DP&L [Member] \| Commodity Contract - Heating Oil [Member]
Total Derivative Liabilities	0.3	0.4
DP&L [Member] \| Natural Gas [Member]
Total Derivative Liabilities		0.1
Estimate of Fair Value, Fair Value Disclosure [Member]
Total Master Trust Assets, Fair Value	9.6	9.7
Total Derivative Assets	20.6	14.9
Total Assets	30.2	24.6
Total Derivative Liabilities	20.7	12.2
Total Liabilities	2,259.2	2,217.0
Estimate of Fair Value, Fair Value Disclosure [Member] \| Forward Contract Power [Member]
Total Derivative Assets	20.3	14.9
Total Derivative Liabilities	20.4	11.1
Estimate of Fair Value, Fair Value Disclosure [Member] \| Commodity Contract - FTR [Member]
Total Derivative Assets	0.3
Total Derivative Liabilities		0.6
Estimate of Fair Value, Fair Value Disclosure [Member] \| Commodity Contract - Heating Oil [Member]
Total Derivative Liabilities	0.3	0.4
Estimate of Fair Value, Fair Value Disclosure [Member] \| Natural Gas [Member]
Total Derivative Liabilities		0.1
Level 1 [Member]
Total Master Trust Assets, Fair Value	0.1	0.1
Total Assets	0.1	0.1
Total Derivative Liabilities	0.3	0.5
Total Liabilities	0.3	0.5
Level 1 [Member] \| Commodity Contract - Heating Oil [Member]
Total Derivative Liabilities	0.3	0.4
Level 1 [Member] \| Natural Gas [Member]
Total Derivative Liabilities		0.1
Level 1 [Member] \| DP&L [Member]
Total Master Trust Assets, Fair Value	0.1	0.1
Total Assets	0.1	0.1
Total Derivative Liabilities	0.3	0.5
Total Liabilities	0.3	0.5
Level 1 [Member] \| DP&L [Member] \| Commodity Contract - Heating Oil [Member]
Total Derivative Liabilities	0.3	0.4
Level 1 [Member] \| DP&L [Member] \| Natural Gas [Member]
Total Derivative Liabilities		0.1
Level 2 [Member]
Total Master Trust Assets, Fair Value	9.5	9.6
Total Derivative Assets	18.8	13.7
Total Assets	28.3	23.3
Total Derivative Liabilities	19.0	11.1
Total Liabilities	2,239.3	2,197.7
Level 2 [Member] \| Forward Contract Power [Member]
Total Derivative Assets	18.8	13.7
Total Derivative Liabilities	19.0	11.1
Level 2 [Member] \| DP&L [Member]
Total Master Trust Assets, Fair Value	9.5	9.6
Total Derivative Assets	19.0	13.9
Total Assets	28.5	23.5
Debt Instrument, Fair Value Disclosure	867.0	864.3
Total Derivative Liabilities	19.2	11.2
Total Liabilities	886.2	875.5
Level 2 [Member] \| DP&L [Member] \| Forward Contract Power [Member]
Total Derivative Assets	19.0	13.9
Total Derivative Liabilities	19.2	11.2
Level 3 [Member]
Total Derivative Assets	1.8	1.2
Total Assets	1.8	1.2
Total Derivative Liabilities	1.4	0.6
Total Liabilities	19.6	18.8
Level 3 [Member] \| Forward Contract Power [Member]
Total Derivative Assets	1.5	1.2
Total Derivative Liabilities	1.4
Level 3 [Member] \| Commodity Contract - FTR [Member]
Total Derivative Assets	0.3
Total Derivative Liabilities		0.6
Level 3 [Member] \| DP&L [Member]
Total Derivative Assets	1.8	1.2
Total Assets	1.8	1.2
Debt Instrument, Fair Value Disclosure	18.2	18.2
Total Derivative Liabilities	1.4	0.6
Total Liabilities	19.6	18.8
Level 3 [Member] \| DP&L [Member] \| Forward Contract Power [Member]
Total Derivative Assets	1.5	1.2
Total Derivative Liabilities	1.4
Level 3 [Member] \| DP&L [Member] \| Commodity Contract - FTR [Member]
Total Derivative Assets	0.3
Total Derivative Liabilities		0.6
Equity Securities [Member] \| DP&L [Member]
Total Master Trust Assets, Fair Value	3.8	3.7
Equity Securities [Member] \| Estimate of Fair Value, Fair Value Disclosure [Member]
Total Master Trust Assets, Fair Value	3.8	3.7
Equity Securities [Member] \| Level 2 [Member]
Total Master Trust Assets, Fair Value	3.8	3.7
Equity Securities [Member] \| Level 2 [Member] \| DP&L [Member]
Total Master Trust Assets, Fair Value	3.8	3.7
Equity Securities [Member] \| Fair Value [Member]
Total Master Trust Assets, Fair Value	3.8	3.7
Debt Securities [Member] \| DP&L [Member]
Total Master Trust Assets, Fair Value	4.6	4.7
Debt Securities [Member] \| Estimate of Fair Value, Fair Value Disclosure [Member]
Total Master Trust Assets, Fair Value	4.6	4.7
Debt Securities [Member] \| Level 2 [Member]
Total Master Trust Assets, Fair Value	4.6	4.7
Debt Securities [Member] \| Level 2 [Member] \| DP&L [Member]
Total Master Trust Assets, Fair Value	4.6	4.7
Money Market Funds [Member] \| DP&L [Member]
Total Master Trust Assets, Fair Value	0.1	0.1
Money Market Funds [Member] \| Estimate of Fair Value, Fair Value Disclosure [Member]
Total Master Trust Assets, Fair Value	0.1	0.1
Money Market Funds [Member] \| Level 1 [Member]
Total Master Trust Assets, Fair Value	0.1	0.1
Money Market Funds [Member] \| Level 1 [Member] \| DP&L [Member]
Total Master Trust Assets, Fair Value	0.1	0.1
Money Market Funds [Member] \| Fair Value [Member]
Total Master Trust Assets, Fair Value	0.1	0.1
Debt [Member] \| Estimate of Fair Value, Fair Value Disclosure [Member]
Debt Instrument, Fair Value Disclosure	2,238.5	2,204.8
Debt [Member] \| Level 2 [Member]
Debt Instrument, Fair Value Disclosure	2,220.3	2,186.6
Debt [Member] \| Level 3 [Member]
Debt Instrument, Fair Value Disclosure	18.2	18.2
Debt [Member] \| Fair Value [Member]
Total Master Trust Assets, Fair Value	4.6	4.7
Hedge Funds [Member] \| DP&L [Member]
Total Master Trust Assets, Fair Value	0.7	0.8
Hedge Funds [Member] \| Estimate of Fair Value, Fair Value Disclosure [Member]
Total Master Trust Assets, Fair Value	0.7	0.8
Hedge Funds [Member] \| Level 2 [Member]
Total Master Trust Assets, Fair Value	0.7	0.8
Hedge Funds [Member] \| Level 2 [Member] \| DP&L [Member]
Total Master Trust Assets, Fair Value	0.7	0.8
Hedge Funds [Member] \| Fair Value [Member]
Total Master Trust Assets, Fair Value	0.7	0.8
Real Estate Funds [Member] \| DP&L [Member]
Total Master Trust Assets, Fair Value	0.4	0.4
Real Estate Funds [Member] \| Estimate of Fair Value, Fair Value Disclosure [Member]
Total Master Trust Assets, Fair Value	0.4	0.4
Real Estate Funds [Member] \| Level 2 [Member]
Total Master Trust Assets, Fair Value	0.4	0.4
Real Estate Funds [Member] \| Level 2 [Member] \| DP&L [Member]
Total Master Trust Assets, Fair Value	0.4	0.4
Real Estate Funds [Member] \| Fair Value [Member]
Total Master Trust Assets, Fair Value	$ 0.4	$ 0.4

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)

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Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 10

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13433-108611

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

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-Name Accounting Standards Codification

-Topic 815

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-Section 45

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

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

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-Name Accounting Standards Codification

-Topic 210

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-Topic 210

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- Definition

Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Available-for-Sale Securities

-URI http://asc.fasb.org/extlink&oid=6505594

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Trading Securities

-URI http://asc.fasb.org/extlink&oid=6526789

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

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-Section 25

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Subparagraph a, f, g

-Article 7

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 35

-Paragraph 1

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Fair value of financial and nonfinancial obligations.

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