Debt Obligations (Current portion - Long-term Debt) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 2015	Dec. 31, 2014
Current portion - long-term debt	30.1us-gaap_LongTermDebtCurrent	20.1us-gaap_LongTermDebtCurrent
DP&L [Member]
Current portion - long-term debt	0.1	0.1
Pollution control series maturing in November 2040 - variable rates: 0.04% - 0.26% and 0.06% - 0.32% [Member]
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]
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%
First Mortgage Bonds Maturing in October 2013 - 5.125% [Member]
Current portion - long-term debt	30.0	20.0
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%
U.S. Government note maturing in February 2061 - 4.20% [Member]
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%, current	0.1	0.1
U.S. Government note maturing in February 2061 - 4.20% [Member] \| DP&L [Member]
Current portion - long-term debt	0.1	0.1
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]
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%
Senior Unsecured Notes at 6.50% maturing on October 15, 2016 [Member]
Debt instrument maturity year	Oct. 01, 2016
Debt instrument interest percentage	6.50%

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(1))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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- Definition

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

+ References

+ Details

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Namespace Prefix:	us-gaap_
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Period Type:	duration

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(2))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(2))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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- Definition

Amount of long-term debt, after unamortized discount or premium, scheduled to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19,20)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 20

-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19

-Article 5

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Carrying value as of the balance sheet date of the portion of long-term, collateralized debt obligations due within one year or the operating cycle, if longer. Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.20)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 20

-Article 5

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