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Variable Interest Entities (Narrative) (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended 12 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2014
Variable Interest Entities [Line Items]      
Asset impairment charges $ 0us-gaap_AssetImpairmentCharges $ 96us-gaap_AssetImpairmentCharges  
Cinergy Receivables [Member]      
Variable Interest Entities [Line Items]      
Minimum equity balance required by Cinergy Receivables 3duk_ReceivablesToMaintainMinimumEquityBalance
/ us-gaap_ConsolidationItemsAxis
= duk_CinergyReceivablesMember
   
Cinergy Receivables [Member] | Variable Interest Entity, Primary Beneficiary [Member]      
Variable Interest Entities [Line Items]      
Percent of proceeds received as cash 75.00%duk_Percentofproceedsreceivedascash
/ us-gaap_ConsolidationItemsAxis
= duk_CinergyReceivablesMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
   
Percent of proceeds received as subordinated note 25.00%duk_Percentofproceedsreceivedassubordinatednote
/ us-gaap_ConsolidationItemsAxis
= duk_CinergyReceivablesMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
   
Duke American Transmission Company [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]      
Variable Interest Entities [Line Items]      
Variable Interest Entity Ownership Interest 50.00%us-gaap_VariableInterestEntityOwnershipPercentage
/ us-gaap_ConsolidationItemsAxis
= duk_DukeAmericanTransmissionCompanyMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember
   
Atlantic Coast Pipeline [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]      
Variable Interest Entities [Line Items]      
Variable Interest Entity Ownership Interest 40.00%us-gaap_VariableInterestEntityOwnershipPercentage
/ us-gaap_ConsolidationItemsAxis
= duk_AtlanticCoastPipelineMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember
   
OVEC [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]      
Variable Interest Entities [Line Items]      
Variable Interest Entity Ownership Interest 9.00%us-gaap_VariableInterestEntityOwnershipPercentage
/ us-gaap_ConsolidationItemsAxis
= duk_OVECMember
/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis
= us-gaap_VariableInterestEntityNotPrimaryBeneficiaryMember
   
Duke Energy Ohio [Member]      
Variable Interest Entities [Line Items]      
Asset impairment charges   94us-gaap_AssetImpairmentCharges
/ dei_LegalEntityAxis
= duk_DukeEnergyOhioMember
 
Duke Energy Ohio [Member] | Cinergy Receivables [Member]      
Variable Interest Entities [Line Items]      
Fixed interest rate added to LIBOR to compute variable rate 1.00%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_ConsolidationItemsAxis
= duk_CinergyReceivablesMember
/ dei_LegalEntityAxis
= duk_DukeEnergyOhioMember
   
Duke Energy Ohio [Member] | Other VIEs [Member]      
Variable Interest Entities [Line Items]      
Asset impairment charges   $ 94us-gaap_AssetImpairmentCharges
/ us-gaap_ConsolidationItemsAxis
= duk_OtherViesMember
/ dei_LegalEntityAxis
= duk_DukeEnergyOhioMember
$ 94us-gaap_AssetImpairmentCharges
/ us-gaap_ConsolidationItemsAxis
= duk_OtherViesMember
/ dei_LegalEntityAxis
= duk_DukeEnergyOhioMember
Duke Energy Indiana [Member] | Cinergy Receivables [Member]      
Variable Interest Entities [Line Items]      
Fixed interest rate added to LIBOR to compute variable rate 1.00%us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
/ us-gaap_ConsolidationItemsAxis
= duk_CinergyReceivablesMember
/ dei_LegalEntityAxis
= duk_DukeEnergyIndianaMember