Debt Obligations (Long-term Debt) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 2015	Dec. 31, 2014
Total long-term debt at subsidary	$ 874.7	$ 874.7
Unamortized debt discount	(0.7)	(0.7)
Total long-term debt	2,129.6us-gaap_LongTermDebt	2,139.6us-gaap_LongTermDebt
DP&L [Member]
Unamortized debt discount	(0.4)	(0.5)
Total long-term debt	877.1	877.0
THE DAYTON POWER AND LIGHT COMPANY [Member]
Unamortized debt discount	(2.8)	(2.8)
First Mortgage Bonds Maturing in October 2013 - 5.125% [Member]
Debt instrument maturity year	May 01, 2018
Debt instrument interest percentage minimum	2.41%	2.42%
Debt instrument interest percentage maximum	2.43%	2.45%
First Mortgage Bonds Maturing in September 2016
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 \| DP&L [Member]
Long-term debt, gross	445.0	445.0
Debt instrument maturity year	Sep. 01, 2016
Debt instrument interest percentage	1.875%
Pollution Control Series Maturing in January 2028 - 4.70% [Member]
Long-term debt, gross	35.3	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] \| DP&L [Member]
Long-term debt, gross	35.3	35.3
Debt instrument maturity year	Jan. 01, 2028
Debt instrument interest percentage	4.70%
Pollution Control Series Maturing in January 2034 - 4.80% [Member]
Long-term debt, gross	179.1	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] \| DP&L [Member]
Long-term debt, gross	179.1	179.1
Debt instrument maturity year	Jan. 01, 2034
Debt instrument interest percentage	4.80%
Pollution Control Series Maturing in September 2036 - 4.80% [Member]
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] \| DP&L [Member]
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 November 2040 - variable rates: 0.04% - 0.26% and 0.06% - 0.32% [Member]
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	0.05%	0.15%
Pollution control series maturing in November 2040 - variable rates: 0.04% - 0.26% and 0.06% - 0.32% [Member] \| DP&L [Member]
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	0.05%	0.15%
U.S. Government note maturing in February 2061 - 4.20% [Member]
Long-term debt, gross	(18.1)	(18.1)
Debt instrument maturity year	Feb. 01, 2061
Debt instrument interest percentage	4.20%
Debt instrument interest percentage minimum	4.20%
U.S. Government note maturing in February 2061 - 4.20% [Member] \| DP&L [Member]
Long-term debt, gross	18.1	18.1
Debt instrument maturity year	Feb. 01, 2061
Debt instrument interest percentage	4.20%
Debt instrument interest percentage minimum	4.20%
Bank Term Loan maturing in May 2018 [Member]
Long-term debt, gross	130.0	140.0
Debt instrument maturity year	May 01, 2018
Debt instrument interest percentage minimum	2.41%	2.42%
Debt instrument interest percentage maximum	2.43%	2.45%
Note to DPL Capital Trust II Maturing in September 2031 - 8.125% [Member]
Long-term debt, gross	15.6	15.6
Debt instrument maturity year	Sep. 01, 2031
Debt instrument interest percentage	8.125%
Senior Unsecured Notes at 6.50% maturing on October 15, 2016 [Member]
Long-term debt, gross	130.0	130.0
Debt instrument maturity year	Oct. 01, 2016
Debt instrument interest percentage	6.50%
Senior Unsecured Notes at 6.80% maturing on October 2019 [Member]
Long-term debt, gross	200.0	200.0
Debt instrument maturity year	Oct. 01, 2019
Debt instrument interest percentage	6.75%
Ten Year Senior Unsecured Notes at 7.25% maturing at October 15, 2021 [Member]
Long-term debt, gross	$ 780.0	$ 780.0
Debt instrument maturity year	Oct. 01, 2021
Debt instrument interest percentage	7.25%

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

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Maximum contractual interest rate for funds borrowed, under the debt agreement.

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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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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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