Fair Value (Fair Value of Assets and Liabilities Measured on Recurring Basis) (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Level 1 [Member]
Total Master Trust Assets, Fair Value	$ 0.3	$ 0.2
Total Derivative Assets	0.0	0.0
Total Assets	0.3	0.2
Total Derivative Liabilities	0.0	0.0
Total Liabilities	0.0	0.0
Level 1 [Member] \| Commodity Contract - FTR [Member]
Total Derivative Assets	0.0	0.0
Total Derivative Liabilities		0.0
Level 1 [Member] \| Forward Contract Power [Member]
Total Derivative Assets	0.0	0.0
Total Derivative Liabilities	0.0	0.0
Level 1 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.3	0.2
Total Derivative Assets	0.0	0.0
Total Assets	0.3	0.2
Total Derivative Liabilities	0.0	0.0
Total Liabilities	0.0	0.0
Level 1 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member] \| Commodity Contract - FTR [Member]
Total Derivative Assets	0.0	0.0
Total Derivative Liabilities		0.0
Level 1 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member] \| Forward Contract Power [Member]
Total Derivative Assets	0.0	0.0
Total Derivative Liabilities	0.0	0.0
Level 2 [Member]
Total Master Trust Assets, Fair Value	8.4	8.8
Total Derivative Assets	32.5	30.5
Total Assets	40.9	39.3
Total Derivative Liabilities	25.9	23.9
Total Liabilities	1,977.3	1,981.1
Level 2 [Member] \| Commodity Contract - FTR [Member]
Total Derivative Assets	0.0	0.0
Total Derivative Liabilities		0.0
Level 2 [Member] \| Forward Contract Power [Member]
Total Derivative Assets	32.5	30.5
Total Derivative Liabilities	25.9	23.9
Level 2 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	8.4	8.8
Total Derivative Assets	32.6	30.6
Total Assets	41.0	39.4
Total Derivative Liabilities	26.0	23.9
Total Liabilities	771.5	770.0
Level 2 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member] \| Commodity Contract - FTR [Member]
Total Derivative Assets	0.0	0.0
Total Derivative Liabilities		0.0
Level 2 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member] \| Forward Contract Power [Member]
Total Derivative Assets	32.6	30.6
Total Derivative Liabilities	26.0	23.9
Level 3 [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Total Derivative Assets	0.7	0.2
Total Assets	0.7	0.2
Total Derivative Liabilities	5.0	3.6
Total Liabilities	23.0	21.7
Level 3 [Member] \| Commodity Contract - FTR [Member]
Total Derivative Assets	0.1	0.2
Total Derivative Liabilities		0.5
Level 3 [Member] \| Forward Contract Power [Member]
Total Derivative Assets	0.6	0.0
Total Derivative Liabilities	5.0	3.1
Level 3 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Total Derivative Assets	0.7	0.2
Total Assets	0.7	0.2
Total Derivative Liabilities	5.0	3.6
Total Liabilities	23.0	21.7
Level 3 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member] \| Commodity Contract - FTR [Member]
Total Derivative Assets	0.1	0.2
Total Derivative Liabilities		0.5
Level 3 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member] \| Forward Contract Power [Member]
Total Derivative Assets	0.6	0.0
Total Derivative Liabilities	5.0	3.1
Fair Value [Member]
Total Master Trust Assets, Fair Value	8.7	9.0
Total Derivative Assets	33.2	30.7
Total Assets	41.9	39.7
Total Derivative Liabilities	30.9	27.5
Total Liabilities	2,000.3	2,002.8
Fair Value [Member] \| Commodity Contract - FTR [Member]
Total Derivative Assets	0.1	0.2
Total Derivative Liabilities		0.5
Fair Value [Member] \| Forward Contract Power [Member]
Total Derivative Assets	33.1	30.5
Total Derivative Liabilities	30.9	27.0
Fair Value [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	8.7	9.0
Total Derivative Assets	33.3	30.8
Total Assets	42.0	39.8
Total Derivative Liabilities	31.0	27.5
Total Liabilities	794.5	791.7
Fair Value [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member] \| Commodity Contract - FTR [Member]
Total Derivative Assets	0.1	0.2
Total Derivative Liabilities		0.5
Fair Value [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member] \| Forward Contract Power [Member]
Total Derivative Assets	33.2	30.6
Total Derivative Liabilities	31.0	27.0
Money Market Funds [Member] \| Level 1 [Member]
Total Master Trust Assets, Fair Value	0.3	0.2
Money Market Funds [Member] \| Level 1 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.3	0.2
Money Market Funds [Member] \| Level 2 [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Money Market Funds [Member] \| Level 2 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Money Market Funds [Member] \| Level 3 [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Money Market Funds [Member] \| Level 3 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Money Market Funds [Member] \| Fair Value [Member]
Total Master Trust Assets, Fair Value	0.3	0.2
Money Market Funds [Member] \| Fair Value [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.3	0.2
Equity Securities [Member] \| Level 1 [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Equity Securities [Member] \| Level 1 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Equity Securities [Member] \| Level 2 [Member]
Total Master Trust Assets, Fair Value	3.4	3.8
Equity Securities [Member] \| Level 2 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	3.4	3.8
Equity Securities [Member] \| Level 3 [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Equity Securities [Member] \| Level 3 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Equity Securities [Member] \| Fair Value [Member]
Total Master Trust Assets, Fair Value	3.4	3.8
Equity Securities [Member] \| Fair Value [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	3.4	3.8
Debt Securities [Member] \| Level 1 [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Debt Securities [Member] \| Level 1 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Debt Securities [Member] \| Level 2 [Member]
Total Master Trust Assets, Fair Value	4.5	4.3
Debt Securities [Member] \| Level 2 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	4.5	4.3
Debt Securities [Member] \| Level 3 [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Debt Securities [Member] \| Level 3 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Debt Securities [Member] \| Fair Value [Member]
Total Master Trust Assets, Fair Value	4.5	4.3
Debt Securities [Member] \| Fair Value [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	4.5	4.3
Hedge Funds [Member] \| Level 1 [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Hedge Funds [Member] \| Level 1 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Hedge Funds [Member] \| Level 2 [Member]
Total Master Trust Assets, Fair Value	0.2	0.4
Hedge Funds [Member] \| Level 2 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.2	0.4
Hedge Funds [Member] \| Level 3 [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Hedge Funds [Member] \| Level 3 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Hedge Funds [Member] \| Fair Value [Member]
Total Master Trust Assets, Fair Value	0.2	0.4
Hedge Funds [Member] \| Fair Value [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.2	0.4
Real Estate Funds [Member] \| Level 1 [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Real Estate Funds [Member] \| Level 1 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Real Estate Funds [Member] \| Level 2 [Member]
Total Master Trust Assets, Fair Value	0.3	0.3
Real Estate Funds [Member] \| Level 2 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.3	0.3
Real Estate Funds [Member] \| Level 3 [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Real Estate Funds [Member] \| Level 3 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.0	0.0
Real Estate Funds [Member] \| Fair Value [Member]
Total Master Trust Assets, Fair Value	0.3	0.3
Real Estate Funds [Member] \| Fair Value [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Total Master Trust Assets, Fair Value	0.3	0.3
Debt [Member] \| Level 1 [Member]
Debt	0.0	0.0
Debt [Member] \| Level 1 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt	0.0	0.0
Debt [Member] \| Level 2 [Member]
Debt	1,951.4	1,957.2
Debt [Member] \| Level 2 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt	745.5	746.1
Debt [Member] \| Level 3 [Member]
Debt	18.0	18.1
Debt [Member] \| Level 3 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt	18.0	18.1
Debt [Member] \| Fair Value [Member]
Debt	1,969.4	1,975.3
Debt [Member] \| Fair Value [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt	$ 763.5	$ 764.2

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)
-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

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- Definition

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

+ 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)
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-Publisher FASB
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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 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Fair value, after the effects of master netting arrangements, of a financial liability or 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 liabilities 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
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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 Trading Securities
-URI http://asc.fasb.org/extlink&oid=6526789

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-Publisher FASB
-Name Accounting Standards Codification
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-Publisher FASB
-Name Accounting Standards Codification
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-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 1
-Subparagraph a, f, g
-Article 7

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Fair value of financial and nonfinancial obligations.

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