Debt Obligations (Long-term Debt) (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
Jun. 30, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Unamortized debt discount / premiums, net	$ (0.6)	$ (0.7)
Total long-term debt at subsidary	760.3	874.7
Total long-term debt	2,010.3	2,139.6
THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument [Line Items]
Unamortized debt discount / premiums, net	(2.7)	(2.8)
Unamortized debt discount	(0.3)	(0.5)
Total long-term debt	762.7	877.0
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 January 2028 - 4.70% [Member]
Debt Instrument [Line Items]
Long-term debt, gross		35.3
Debt instrument maturity year	Jan. 01, 2028
Debt instrument interest percentage	4.70%
Pollution Control Series Maturing in January 2028 - 4.70% [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 0.0	35.3
Pollution Control Series Maturing in January 2034 - 4.80% [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 100.0	179.1
Debt instrument maturity year	Jan. 01, 2034
Debt instrument interest percentage	4.80%
Pollution Control Series Maturing in January 2034 - 4.80% [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 100.0	179.1
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 November 2040 - rates: 0.02% - 0.12% and 0.04% - 0.15% [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 100.0	$ 100.0
Debt instrument maturity year	Nov. 01, 2040
Debt instrument interest percentage minimum	0.02%	0.04%
Debt instrument interest percentage maximum	0.12%	0.15%
Pollution control series maturing in November 2040 - rates: 0.02% - 0.12% and 0.04% - 0.15% [Member] \| THE DAYTON POWER AND LIGHT COMPANY [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 100.0	$ 100.0
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%
Debt instrument interest percentage minimum
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 May 2018 - rates from: 2.41% - 2.44% and 2.42% - 2.45% [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 125.0	$ 140.0
Debt instrument maturity year	May 01, 2018
Debt instrument interest percentage minimum	2.41%	2.42%
Debt instrument interest percentage maximum	2.44%	2.45%
Senior unsecured due in October 2016 - 6.5% [Member]
Debt Instrument [Line Items]
Long-term debt, gross	$ 130.0	$ 130.0
Debt instrument maturity year	Oct. 01, 2016
Debt instrument interest percentage	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%

Total Long-term Debt At Subsidary 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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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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