Derivative Instruments and Hedging Activities (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Fair value of commodity derivative instruments	$ 27.5
Collateral Already Posted, Aggregate Fair Value	8.0
Derivative Liability, Fair Value, Amount Offset Against Collateral	17.9
Collateral if debt were to fall below investment grade	1.6
THE DAYTON POWER AND LIGHT COMPANY [Member]
Fair value of commodity derivative instruments	27.5
Collateral Already Posted, Aggregate Fair Value	8.0
Derivative Liability, Fair Value, Amount Offset Against Collateral	17.9
Collateral if debt were to fall below investment grade	$ 1.6
Short-term Derivative Positions [Member]
Derivative Asset, Current		$ 11.1
Amount No Longer Considered Derivative		$ 0.1

Amount of derivative gain previously accounted for as MTM but now being accounted for as NPNS

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The aggregate fair value of additional assets that would be required to be posted as collateral for derivative instruments with credit-risk-related contingent features if the credit-risk-related contingent features were triggered at the end of the reporting period.

+ References

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The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

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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, expected to be settled within one year or normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value, before 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 elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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Fair value, after effects of master netting arrangements, of 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 offset against the right to receive collateral. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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