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Derivative Instruments and Hedging Activities - Offsetting Derivative Instruments and Credit Risk-Related Features (Details) - USD ($)
$ in Millions
Mar. 31, 2018
Dec. 31, 2017
Credit Risk-Related Contingent Features [Abstract]    
Aggregate fair value of derivative instruments in a net liability position with credit risk-related contingent features $ 101  
Aggregate fair value of collateral posted on these derivative instruments 10  
Aggregate fair value of additional collateral requirements in the event of a credit downgrade below investment grade 91  
Treasury Derivatives [Member]    
Assets [Abstract]    
Gross 176 $ 264
Derivative instruments - eligible for offset 78 107
Cash collateral received - eligible for offset 16 20
Net 82 137
Liabilities [Abstract]    
Gross 189 174
Derivative instruments - eligible for offset 78 107
Cash collateral pledged - eligible for offset 5 0
Net 106 67
LG And E And KU Energy LLC [Member]    
Credit Risk-Related Contingent Features [Abstract]    
Aggregate fair value of derivative instruments in a net liability position with credit risk-related contingent features 8  
Aggregate fair value of collateral posted on these derivative instruments 0  
Aggregate fair value of additional collateral requirements in the event of a credit downgrade below investment grade 8  
LG And E And KU Energy LLC [Member] | Treasury Derivatives [Member]    
Assets [Abstract]    
Gross 0 0
Derivative instruments - eligible for offset 0 0
Cash collateral received - eligible for offset 0 0
Net 0 0
Liabilities [Abstract]    
Gross 22 26
Derivative instruments - eligible for offset 0 0
Cash collateral pledged - eligible for offset 0 0
Net 22 26
Louisville Gas And Electric Co [Member]    
Credit Risk-Related Contingent Features [Abstract]    
Aggregate fair value of derivative instruments in a net liability position with credit risk-related contingent features 8  
Aggregate fair value of collateral posted on these derivative instruments 0  
Aggregate fair value of additional collateral requirements in the event of a credit downgrade below investment grade 8  
Louisville Gas And Electric Co [Member] | Treasury Derivatives [Member]    
Assets [Abstract]    
Gross 0 0
Derivative instruments - eligible for offset 0 0
Cash collateral received - eligible for offset 0 0
Net 0 0
Liabilities [Abstract]    
Gross 22 26
Derivative instruments - eligible for offset 0 0
Cash collateral pledged - eligible for offset 0 0
Net $ 22 $ 26