Ownership of Coal-fired Facilities (Narrative) (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
Jun. 30, 2012
Undivided ownership interests	7
Construction work in process	$ 71.0
Property Plant and Equipment Purchase Accounting Adjustment	114.1
DP&L [Member]
Undivided ownership interests	7
Construction work in process	71.0
Number Of Generating Facilities	18
Property Plant and Equipment Purchase Accounting Adjustment	114.1
DP&L Investment [Member]
Construction work in process	71.0
DP&L Investment [Member] \| DP&L [Member]
Construction work in process	$ 71.0

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 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

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

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 10

-Section C

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