Derivative Instruments and Hedging Activities - Fair Values (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Designated As Hedging Instruments [Member]
Fair Values by Balance Sheet Location [Abstract]
Asset value	$ 123	$ 101
Liability value	0	0
Designated As Hedging Instruments [Member] | Current Assets [Member]
Fair Values by Balance Sheet Location [Abstract]
Asset value	5	4
Designated As Hedging Instruments [Member] | Current Assets [Member] | Interest Rate Swaps [Member]
Fair Values by Balance Sheet Location [Abstract]
Asset value	0	0
Designated As Hedging Instruments [Member] | Current Assets [Member] | Cross Currency Swaps [Member]
Fair Values by Balance Sheet Location [Abstract]
Asset value	5	4
Designated As Hedging Instruments [Member] | Current Assets [Member] | Foreign Currency Contracts [Member]
Fair Values by Balance Sheet Location [Abstract]
Asset value	0	0
Designated As Hedging Instruments [Member] | Noncurrent Assets [Member]
Fair Values by Balance Sheet Location [Abstract]
Asset value	118	97
Designated As Hedging Instruments [Member] | Noncurrent Assets [Member] | Interest Rate Swaps [Member]
Fair Values by Balance Sheet Location [Abstract]
Asset value	0	0
Designated As Hedging Instruments [Member] | Noncurrent Assets [Member] | Cross Currency Swaps [Member]
Fair Values by Balance Sheet Location [Abstract]
Asset value	118	97
Designated As Hedging Instruments [Member] | Noncurrent Assets [Member] | Foreign Currency Contracts [Member]
Fair Values by Balance Sheet Location [Abstract]
Asset value	0	0
Designated As Hedging Instruments [Member] | Current Liabilities [Member]
Fair Values by Balance Sheet Location [Abstract]
Liability value	0	0
Designated As Hedging Instruments [Member] | Current Liabilities [Member] | Interest Rate Swaps [Member]
Fair Values by Balance Sheet Location [Abstract]
Liability value	0	0
Designated As Hedging Instruments [Member] | Current Liabilities [Member] | Cross Currency Swaps [Member]
Fair Values by Balance Sheet Location [Abstract]
Liability value	0	0
Designated As Hedging Instruments [Member] | Current Liabilities [Member] | Foreign Currency Contracts [Member]
Fair Values by Balance Sheet Location [Abstract]
Liability value	0	0
Designated As Hedging Instruments [Member] | Noncurrent Liabilities [Member]
Fair Values by Balance Sheet Location [Abstract]
Liability value	0	0
Designated As Hedging Instruments [Member] | Noncurrent Liabilities [Member] | Interest Rate Swaps [Member]
Fair Values by Balance Sheet Location [Abstract]
Liability value	0	0
Designated As Hedging Instruments [Member] | Noncurrent Liabilities [Member] | Cross Currency Swaps [Member]
Fair Values by Balance Sheet Location [Abstract]
Liability value	0	0
Designated As Hedging Instruments [Member] | Noncurrent Liabilities [Member] | Foreign Currency Contracts [Member]
Fair Values by Balance Sheet Location [Abstract]
Liability value	0	0
Not Designated As Hedging Instruments [Member]
Fair Values by Balance Sheet Location [Abstract]
Asset value	174	163
Liability value	49	174
Not Designated As Hedging Instruments [Member] | Current Assets [Member]
Fair Values by Balance Sheet Location [Abstract]
Asset value	86	45
Not Designated As Hedging Instruments [Member] | Current Assets [Member] | Interest Rate Swaps [Member]
Fair Values by Balance Sheet Location [Abstract]
Asset value	0	0
Not Designated As Hedging Instruments [Member] | Current Assets [Member] | Cross Currency Swaps [Member]
Fair Values by Balance Sheet Location [Abstract]
Asset value	0	0
Not Designated As Hedging Instruments [Member] | Current Assets [Member] | Foreign Currency Contracts [Member]
Fair Values by Balance Sheet Location [Abstract]
Asset value	86	45
Not Designated As Hedging Instruments [Member] | Noncurrent Assets [Member]
Fair Values by Balance Sheet Location [Abstract]
Asset value	88	118
Not Designated As Hedging Instruments [Member] | Noncurrent Assets [Member] | Interest Rate Swaps [Member]
Fair Values by Balance Sheet Location [Abstract]
Asset value	0	0
Not Designated As Hedging Instruments [Member] | Noncurrent Assets [Member] | Cross Currency Swaps [Member]
Fair Values by Balance Sheet Location [Abstract]
Asset value	0	0
Not Designated As Hedging Instruments [Member] | Noncurrent Assets [Member] | Foreign Currency Contracts [Member]
Fair Values by Balance Sheet Location [Abstract]
Asset value	88	118
Not Designated As Hedging Instruments [Member] | Current Liabilities [Member]
Fair Values by Balance Sheet Location [Abstract]
Liability value	26	71
Not Designated As Hedging Instruments [Member] | Current Liabilities [Member] | Interest Rate Swaps [Member]
Fair Values by Balance Sheet Location [Abstract]
Liability value	4	4
Not Designated As Hedging Instruments [Member] | Current Liabilities [Member] | Cross Currency Swaps [Member]
Fair Values by Balance Sheet Location [Abstract]
Liability value	0	0
Not Designated As Hedging Instruments [Member] | Current Liabilities [Member] | Foreign Currency Contracts [Member]
Fair Values by Balance Sheet Location [Abstract]
Liability value	22	67
Not Designated As Hedging Instruments [Member] | Noncurrent Liabilities [Member]
Fair Values by Balance Sheet Location [Abstract]
Liability value	23	103
Not Designated As Hedging Instruments [Member] | Noncurrent Liabilities [Member] | Interest Rate Swaps [Member]
Fair Values by Balance Sheet Location [Abstract]
Liability value	15	22
Not Designated As Hedging Instruments [Member] | Noncurrent Liabilities [Member] | Cross Currency Swaps [Member]
Fair Values by Balance Sheet Location [Abstract]
Liability value	0	0
Not Designated As Hedging Instruments [Member] | Noncurrent Liabilities [Member] | Foreign Currency Contracts [Member]
Fair Values by Balance Sheet Location [Abstract]
Liability value	8	81
LG And E And KU Energy LLC [Member] | Not Designated As Hedging Instruments [Member]
Fair Values by Balance Sheet Location [Abstract]
Asset value	0	0
Liability value	19	26
LG And E And KU Energy LLC [Member] | Not Designated As Hedging Instruments [Member] | Current Assets [Member]
Fair Values by Balance Sheet Location [Abstract]
Asset value	0	0
LG And E And KU Energy LLC [Member] | Not Designated As Hedging Instruments [Member] | Current Assets [Member] | Interest Rate Swaps [Member]
Fair Values by Balance Sheet Location [Abstract]
Asset value	0	0
LG And E And KU Energy LLC [Member] | Not Designated As Hedging Instruments [Member] | Noncurrent Assets [Member]
Fair Values by Balance Sheet Location [Abstract]
Asset value	0	0
LG And E And KU Energy LLC [Member] | Not Designated As Hedging Instruments [Member] | Noncurrent Assets [Member] | Interest Rate Swaps [Member]
Fair Values by Balance Sheet Location [Abstract]
Asset value	0	0
LG And E And KU Energy LLC [Member] | Not Designated As Hedging Instruments [Member] | Current Liabilities [Member]
Fair Values by Balance Sheet Location [Abstract]
Liability value	4	4
LG And E And KU Energy LLC [Member] | Not Designated As Hedging Instruments [Member] | Current Liabilities [Member] | Interest Rate Swaps [Member]
Fair Values by Balance Sheet Location [Abstract]
Liability value	4	4
LG And E And KU Energy LLC [Member] | Not Designated As Hedging Instruments [Member] | Noncurrent Liabilities [Member]
Fair Values by Balance Sheet Location [Abstract]
Liability value	15	22
LG And E And KU Energy LLC [Member] | Not Designated As Hedging Instruments [Member] | Noncurrent Liabilities [Member] | Interest Rate Swaps [Member]
Fair Values by Balance Sheet Location [Abstract]
Liability value	15	22
Louisville Gas And Electric Co [Member] | Not Designated As Hedging Instruments [Member]
Fair Values by Balance Sheet Location [Abstract]
Asset value	0	0
Liability value	19	26
Louisville Gas And Electric Co [Member] | Not Designated As Hedging Instruments [Member] | Current Assets [Member]
Fair Values by Balance Sheet Location [Abstract]
Asset value	0	0
Louisville Gas And Electric Co [Member] | Not Designated As Hedging Instruments [Member] | Current Assets [Member] | Interest Rate Swaps [Member]
Fair Values by Balance Sheet Location [Abstract]
Asset value	0	0
Louisville Gas And Electric Co [Member] | Not Designated As Hedging Instruments [Member] | Noncurrent Assets [Member]
Fair Values by Balance Sheet Location [Abstract]
Asset value	0	0
Louisville Gas And Electric Co [Member] | Not Designated As Hedging Instruments [Member] | Noncurrent Assets [Member] | Interest Rate Swaps [Member]
Fair Values by Balance Sheet Location [Abstract]
Asset value	0	0
Louisville Gas And Electric Co [Member] | Not Designated As Hedging Instruments [Member] | Current Liabilities [Member]
Fair Values by Balance Sheet Location [Abstract]
Liability value	4	4
Louisville Gas And Electric Co [Member] | Not Designated As Hedging Instruments [Member] | Current Liabilities [Member] | Interest Rate Swaps [Member]
Fair Values by Balance Sheet Location [Abstract]
Liability value	4	4
Louisville Gas And Electric Co [Member] | Not Designated As Hedging Instruments [Member] | Noncurrent Liabilities [Member]
Fair Values by Balance Sheet Location [Abstract]
Liability value	15	22
Louisville Gas And Electric Co [Member] | Not Designated As Hedging Instruments [Member] | Noncurrent Liabilities [Member] | Interest Rate Swaps [Member]
Fair Values by Balance Sheet Location [Abstract]
Liability value	$ 15	$ 22