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Summary of Significant Accounting Policies (Related Party Transactions) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
DP&L [Member]      
Charges for Services Provided $ 30.5us-gaap_RelatedPartyTransactionExpensesFromTransactionsWithRelatedParty
/ dei_LegalEntityAxis
= dpl_DpLMember
   
Charges to the Service Company 0.1us-gaap_RelatedPartyTransactionOtherRevenuesFromTransactionsWithRelatedParty
/ dei_LegalEntityAxis
= dpl_DpLMember
   
Net prepaid/payable to the Service Company (4.7)us-gaap_AccountsPayableRelatedPartiesCurrent
/ dei_LegalEntityAxis
= dpl_DpLMember
   
Expense recoveries for services provided to DPLER 2.2dpl_RelatedPartyTransactionExpenseRecoveries
/ dei_LegalEntityAxis
= dpl_DpLMember
5.2dpl_RelatedPartyTransactionExpenseRecoveries
/ dei_LegalEntityAxis
= dpl_DpLMember
4.0dpl_RelatedPartyTransactionExpenseRecoveries
/ dei_LegalEntityAxis
= dpl_DpLMember
Deposits received from DPLER 20.1us-gaap_RelatedPartyDepositLiabilities
/ dei_LegalEntityAxis
= dpl_DpLMember
19.2us-gaap_RelatedPartyDepositLiabilities
/ dei_LegalEntityAxis
= dpl_DpLMember
20.2us-gaap_RelatedPartyDepositLiabilities
/ dei_LegalEntityAxis
= dpl_DpLMember
Premiums paid for Insurance Services provided by MVIC (2.9)us-gaap_RelatedPartyTransactionSellingGeneralAndAdministrativeExpensesFromTransactionsWithRelatedParty
/ dei_LegalEntityAxis
= dpl_DpLMember
(2.9)us-gaap_RelatedPartyTransactionSellingGeneralAndAdministrativeExpensesFromTransactionsWithRelatedParty
/ dei_LegalEntityAxis
= dpl_DpLMember
(2.6)us-gaap_RelatedPartyTransactionSellingGeneralAndAdministrativeExpensesFromTransactionsWithRelatedParty
/ dei_LegalEntityAxis
= dpl_DpLMember
DPLER [Member]      
Sales to related party 487.1us-gaap_RevenueFromRelatedParties
/ dei_LegalEntityAxis
= dpl_DpleAndDplerMember
453.9us-gaap_RevenueFromRelatedParties
/ dei_LegalEntityAxis
= dpl_DpleAndDplerMember
390.8us-gaap_RevenueFromRelatedParties
/ dei_LegalEntityAxis
= dpl_DpleAndDplerMember
Service Company [Member]      
Charges for Services Provided 35.8us-gaap_RelatedPartyTransactionExpensesFromTransactionsWithRelatedParty
/ dei_LegalEntityAxis
= dpl_ServiceCompanyMember
   
Charges to the Service Company 0.1us-gaap_RelatedPartyTransactionOtherRevenuesFromTransactionsWithRelatedParty
/ dei_LegalEntityAxis
= dpl_ServiceCompanyMember
   
Net prepaid/payable to the Service Company $ (4.7)us-gaap_AccountsPayableRelatedPartiesCurrent
/ dei_LegalEntityAxis
= dpl_ServiceCompanyMember