Derivative Instruments and Hedging Activities - Fair Values (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Designated As Hedging Instruments [Member]
Fair Values by Balance Sheet Location [Abstract]
Asset value	$ 161	$ 188
Liability value	2	0
Designated As Hedging Instruments [Member] | Current Assets [Member]
Fair Values by Balance Sheet Location [Abstract]
Asset value	29	32
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	28	32
Designated As Hedging Instruments [Member] | Current Assets [Member] | Foreign Currency Contracts [Member]
Fair Values by Balance Sheet Location [Abstract]
Asset value	1	0
Designated As Hedging Instruments [Member] | Noncurrent Assets [Member]
Fair Values by Balance Sheet Location [Abstract]
Asset value	132	156
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	132	156
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	2	0
Designated As Hedging Instruments [Member] | Current Liabilities [Member] | Interest Rate Swaps [Member]
Fair Values by Balance Sheet Location [Abstract]
Liability value	2	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	163	211
Liability value	196	58
Not Designated As Hedging Instruments [Member] | Current Assets [Member]
Fair Values by Balance Sheet Location [Abstract]
Asset value	28	31
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	28	31
Not Designated As Hedging Instruments [Member] | Noncurrent Assets [Member]
Fair Values by Balance Sheet Location [Abstract]
Asset value	135	180
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	135	180
Not Designated As Hedging Instruments [Member] | Current Liabilities [Member]
Fair Values by Balance Sheet Location [Abstract]
Liability value	91	25
Not Designated As Hedging Instruments [Member] | Current Liabilities [Member] | Interest Rate Swaps [Member]
Fair Values by Balance Sheet Location [Abstract]
Liability value	5	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	86	21
Not Designated As Hedging Instruments [Member] | Noncurrent Liabilities [Member]
Fair Values by Balance Sheet Location [Abstract]
Liability value	105	33
Not Designated As Hedging Instruments [Member] | Noncurrent Liabilities [Member] | Interest Rate Swaps [Member]
Fair Values by Balance Sheet Location [Abstract]
Liability value	24	27
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	81	6
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	29	31
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	5	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	5	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	24	27
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	24	27
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	29	31
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	5	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	5	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	24	27
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	$ 24	$ 27