Overview and Summary of Significant Accounting Policies (Narrative) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended	6 Months Ended	12 Months Ended
Jun. 30, 2011	Jun. 30, 2011	Jun. 30, 2011	Dec. 31, 2010
Service Area Square Miles		6,000
Service Area By County		24
Approximate number of retail customers		500,000
Number of coal fired power plants	8	8
Entity number of employees	1,535	1,535	1,535
Employees under a collective bargaining agreement which expires in October-2011		53.00%
Deferred SECA revenue	$ 14.1	$ 14.1	$ 14.1	$ 15.4
Reduction of depreciation expense net	2.4	4.8	9.6
Reduction in depreciation expense net of tax	$ 1.6	$ 3.1	$ 6.3
Increase in diluted EPS	$ 0.01	$ 0.02	$ 0.04
DP&L [Member]
Entity number of employees	1,503	1,503	1,503

Number of persons employed by the Entity

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Change In Accounting Estimate, per share amount

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Cumulative Effect Of Change In Accounting Principle Tabular Presentation By Financial Statement Line Item Adjustment Amount, net of tax

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Number Of Coal Fired Power Plants

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- Definition

This element represents the approximate number of retail customers that electricity is generated and distributed within the company's service territory.

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- Definition

Percentage Of Employees Under Collective Bargaining Agreement

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- Definition

Service area by county

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- Definition

Service area square miles

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- Definition

Effect of a change in accounting principle on a financial statement line item and any per share amounts affected for the prior period presented. The cumulative effect of the change on retained earnings or net assets in the statement of financial position, as of the beginning of the earliest period presented.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 154
-Paragraph 17
-Subparagraph b(2), b(3)
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6801783&loc=d3e22580-107794

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)(2)-(3)
-URI http://asc.fasb.org/extlink&oid=6801783&loc=d3e22499-107794

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Amount of deferred revenue as of balance sheet date. Deferred revenue represents collections of cash or other assets related to a revenue producing activity for which revenue has not yet been recognized. Generally, an entity records deferred revenue when it receives consideration from a customer before achieving certain criteria that must be met for revenue to be recognized in conformity with GAAP.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Staff Accounting Bulletin (SAB)
-Number Topic 13
-Section A

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 605
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB TOPIC 13.A.4(a).Q1 Response)
-URI http://asc.fasb.org/extlink&oid=6600647&loc=d3e214044-122780

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