Fair Value Measurements (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015
Debt maturity date, earliest	2019
Debt maturity date, latest	2061
Unrealized gains and immaterial losses on Master Trust assets in AOCI	$ 1.0	$ 0.7
Unrealized gains and immaterial losses on Master Trust assets in AOCI, after tax	$ 0.6	0.5
Percent of inputs to the fair value of derivative instruments from quoted market prices	95.00%
Gross additions to our existing landfill and asbestos AROs	$ 72.9	39.0
Gross additions to our existing landfill and asbestos AROs, after tax	47.4	25.4
Increase (Decrease) in Asset Retirement Obligations	40.3
Increase (Decrease) in Asset Retirement Obligations after tax	(26.2)
Available-for-sale Securities, Gross Realized Gains (Losses), Sale Proceeds	2.6
AvailableForSaleSecuritiesGross Realized Gains Losses Sale Proceeds Net of Tax	1.7
THE DAYTON POWER AND LIGHT COMPANY [Member]
Unrealized gains and immaterial losses on Master Trust assets in AOCI	1.1	0.8
Unrealized gains and immaterial losses on Master Trust assets in AOCI, after tax	$ 0.7	0.5
Percent of inputs to the fair value of derivative instruments from quoted market prices	95.00%
Gross additions to our existing landfill and asbestos AROs	$ 73.1	39.2
Gross additions to our existing landfill and asbestos AROs, after tax	47.5	$ 25.5
Increase (Decrease) in Asset Retirement Obligations	40.3
Increase (Decrease) in Asset Retirement Obligations after tax	(26.2)
Available-for-sale Securities, Gross Realized Gains (Losses), Sale Proceeds	2.6
AvailableForSaleSecuritiesGross Realized Gains Losses Sale Proceeds Net of Tax	1.7
Stuart and Killen [Member]
Gross additions to our existing landfill and asbestos AROs	67.9
Gross additions to our existing landfill and asbestos AROs, after tax	44.1
Stuart and Killen [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Gross additions to our existing landfill and asbestos AROs	67.9
Gross additions to our existing landfill and asbestos AROs, after tax	$ 44.1

Realized gains and losses from sale of available for sale securities, net of tax.

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Amount of ARO costs incurred after tax

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The increase (decrease) during the reporting period in the carrying amount after tax

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Long Term Debt Range Adjusted To Fair Value At Merger End

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Long Term Debt Range Adjusted To Fair Value at Merger Start

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Percentage Of Inputs To The Fair Value Of Derivative Instruments From Quoted Market Prices

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The change in unrealized holding gain (loss), net of tax, on available-for-sale securities included in a separate component of shareholders' equity during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
-Paragraph 9
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The total amount of proceeds received for the sale of securities, categorized neither as held-to-maturity nor trading securities, during the reporting period.

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Amount of asset retirement obligations (ARO) costs incurred (whether capitalized or charged to expense) during the period.

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-Name Accounting Standards Codification
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The increase (decrease) during the reporting period in the carrying amount of asset retirement obligations.

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Amount before tax and reclassification adjustments of unrealized holding gain (loss) on available-for-sale securities.

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-Name Accounting Standards Codification
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