Debt (Long-term Debt) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Unamortized deferred finance costs	$ (4.2)	$ (5.0)
Unamortized deferred finance costs	(10.4)	(11.1)
Unamortized debt discount and premiums, net	(0.6)	(0.7)
Total long-term debt at subsidary	755.3	754.5
Total long-term debt	1,921.9	1,993.3
Less: current portion	(507.0)	(572.8)
Long-term debt	1,414.9	1,420.5
THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument [Line Items]
Unamortized deferred finance costs	(5.4)	(6.2)
Unamortized debt discount and premiums, net	(3.5)	(3.6)
Unamortized debt discount	(0.1)	(0.2)
Total long-term debt	757.5	756.7
Less: current portion	(443.9)	(443.1)
Long-term debt	313.6	313.6
First Mortgage Bonds Maturing in September 2016 - 1.875% [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 445.0	445.0
Debt instrument maturity year	Sep. 01, 2016
Debt instrument interest percentage	1.875%
First Mortgage Bonds Maturing in September 2016 - 1.875% [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 445.0	445.0
Pollution Control Series Maturing in September 2036 - 4.80% [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 100.0	100.0
Debt instrument maturity year	Sep. 01, 2036
Debt instrument interest percentage	4.80%
Pollution Control Series Maturing in September 2036 - 4.80% [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 100.0	$ 100.0
Pollution Control Series Maturing in August 2020 - 1.13% - 1.14% [Member]
Debt Instrument [Line Items]
Debt instrument maturity year	Aug. 01, 2020
Debt instrument interest percentage minimum	1.29%	1.13%
Debt instrument interest percentage maximum	1.30%	1.17%
Pollution Control Series Maturing in August 2020 - 1.13% - 1.14% [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 200.0	$ 200.0
U.S. Government note maturing in February 2061 - 4.20% [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 18.0	18.1
Debt instrument maturity year	Feb. 01, 2061
Debt instrument interest percentage	4.20%
U.S. Government note maturing in February 2061 - 4.20% [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 18.0	18.1
Bank term loan due in July 2020 - rates from: 2.44% - 2.45% [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 125.0	$ 125.0
Debt instrument maturity year	Jul. 31, 2020
Debt instrument interest percentage minimum	2.67%	2.44%
Debt instrument interest percentage maximum	2.69%	2.67%
Senior unsecured due in October 2016 - 6.5% [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 57.0	$ 130.0
Debt instrument maturity year	Oct. 01, 2016
Debt instrument interest percentage	6.50%	6.50%
Senior unsecured due in October 2019 - 6.75% [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 200.0	$ 200.0
Debt instrument maturity year	Oct. 01, 2019
Debt instrument interest percentage	6.75%
Senior unsecured due in October 2021 - 7.25% [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 780.0	780.0
Debt instrument maturity year	Oct. 01, 2021
Debt instrument interest percentage	7.25%
Note to DPL Capital Trust II Maturing in September 2031 - 8.125% [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 15.6	$ 15.6
Debt instrument maturity year	Sep. 01, 2031
Debt instrument interest percentage	8.125%

Deferred Finance Costs, Net, Including Acquisition Adjustments

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Total Long-term Debt At Subsidiary With Purchase Accounting Adjustments

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Amount of long-term debt before deduction of unamortized discount or premium. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, with initial maturities beyond one year or the normal operating cycle, if longer.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Latest date the outstanding debt instruments are required to be repaid, in CCYY-MM-DD format.

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The amount of debt discount that was originally recognized at the issuance of the instrument that has yet to be amortized.

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The amount of debt discount (net of debt premium) that was originally recognized at the issuance of the instrument that has yet to be amortized.

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For an unclassified balance sheet, the carrying amount (net of accumulated amortization) as of the balance sheet date of capitalized costs associated with the issuance of debt instruments (for example, legal, accounting, underwriting, printing, and registration costs) that will be charged against earnings over the life of the debt instruments to which such costs pertain.

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Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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