Loss recognized as a result of the initial and subsequent write-down of a long-lived asset's carrying amount to fair value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
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The aggregate amount of write-downs for impairments recognized during the period for long lived assets held for use (including those held for disposal by means other than sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 958
-SubTopic 225
-Section 45
-Paragraph 11
-Subparagraph (a)
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Impairment
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
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-Section 45
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-Section 50
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Fair value portion of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

+ References

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-Name Accounting Standards Codification
-Topic 820
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Fixed-asset Impairment Fixed-asset Impairment (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Impairment of Long-Lived Assets Held-for-use	$ 0.0	$ 235.5	$ 66.4	$ 235.5
Stuart [Member]
Impairment of Long-Lived Assets Held-for-use			39.1
Impaired Assets to be Disposed of by Method Other than Sale, Amount of Impairment Loss			9.8
Killen [Member]
Impairment of Long-Lived Assets Held-for-use			27.3	230.8
Impaired Assets to be Disposed of by Method Other than Sale, Amount of Impairment Loss			6.4
Peaking Generating Facilities [Member]
Impairment of Long-Lived Assets Held-for-use				4.7
THE DAYTON POWER AND LIGHT COMPANY [Member]
Impairment of Long-Lived Assets Held-for-use	0.0	857.1	66.3	857.1
THE DAYTON POWER AND LIGHT COMPANY [Member] \| Stuart [Member]
Impairment of Long-Lived Assets Held-for-use			39.0	292.0
Impaired Assets to be Disposed of by Method Other than Sale, Amount of Impairment Loss			9.8
THE DAYTON POWER AND LIGHT COMPANY [Member] \| Killen [Member]
Impairment of Long-Lived Assets Held-for-use			27.3	246.2
Impaired Assets to be Disposed of by Method Other than Sale, Amount of Impairment Loss			6.4
THE DAYTON POWER AND LIGHT COMPANY [Member] \| Zimmer [Member]
Impairment of Long-Lived Assets Held-for-use				318.9
Level 3 [Member] \| Stuart [Member]
Property, Plant, and Equipment, Fair Value Disclosure	3.3		3.3
Level 3 [Member] \| Killen [Member]
Property, Plant, and Equipment, Fair Value Disclosure	7.9	84.3	7.9	84.3
Level 3 [Member] \| Peaking Generating Facilities [Member]
Property, Plant, and Equipment, Fair Value Disclosure		5.2		5.2
Level 3 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member] \| Stuart [Member]
Property, Plant, and Equipment, Fair Value Disclosure	3.3	164.4	3.3	164.4
Level 3 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member] \| Killen [Member]
Property, Plant, and Equipment, Fair Value Disclosure	$ 7.9	84.3	$ 7.9	84.3
Level 3 [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member] \| Zimmer [Member]
Property, Plant, and Equipment, Fair Value Disclosure		$ 111.0		$ 111.0