Ownership of Coal-fired Facilities (Narrative) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
Sep. 30, 2011
Undivided ownership interests	7
Construction Work in Process	$ 42.0
DP&L [Member] \| DP&L Investment [Member]
Construction Work in Process	$ 42.0

The period end amount of construction work in progress at a jointly owned electricity generation plant.

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

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 10

-Section C

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 980

-SubTopic 360

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 10.C)

-URI http://asc.fasb.org/extlink&oid=6500719&loc=d3e659983-123033

Name:	us-gaap_JointlyOwnedUtilityPlantOwnershipAmountOfConstructionWorkInProgress
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant