Derivative Instruments and Hedging Activities - Gains and Losses (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Cash Flow Hedges [Member]
Amounts Included in Income, OCI or Regulatory Liabilities/Assets [Abstract]
Gain (Loss) Reclassified from AOCI into Income (Effective Portion)	$ 17	$ 1	$ 25	$ (29)
Gain (Loss) Recognized in Income on Derivative (Ineffective Portion and Amount Excluded from Effectiveness Testing)	0	0	0	(1)
Cash Flow Hedges [Member] \| Other Comprehensive Income (Loss) [Member]
Amounts Included in Income, OCI or Regulatory Liabilities/Assets [Abstract]
Derivative Gain (Loss) Recognized in OCI (Effective Portion)	27	1	26	(36)
Cash Flow Hedges [Member] \| Interest Rate Swaps [Member] \| Other Comprehensive Income (Loss) [Member]
Amounts Included in Income, OCI or Regulatory Liabilities/Assets [Abstract]
Derivative Gain (Loss) Recognized in OCI (Effective Portion)	0	0	0	(2)
Cash Flow Hedges [Member] \| Interest Rate Swaps [Member] \| Interest Expense [Member]
Amounts Included in Income, OCI or Regulatory Liabilities/Assets [Abstract]
Gain (Loss) Reclassified from AOCI into Income (Effective Portion)	(2)	(2)	(6)	(6)
Gain (Loss) Recognized in Income on Derivative (Ineffective Portion and Amount Excluded from Effectiveness Testing)	0	0	0	(1)
Cash Flow Hedges [Member] \| Cross Currency Swaps [Member] \| Other Comprehensive Income (Loss) [Member]
Amounts Included in Income, OCI or Regulatory Liabilities/Assets [Abstract]
Derivative Gain (Loss) Recognized in OCI (Effective Portion)	27	1	26	(34)
Cash Flow Hedges [Member] \| Cross Currency Swaps [Member] \| Interest Expense [Member]
Amounts Included in Income, OCI or Regulatory Liabilities/Assets [Abstract]
Gain (Loss) Reclassified from AOCI into Income (Effective Portion)	1	1	1	1
Gain (Loss) Recognized in Income on Derivative (Ineffective Portion and Amount Excluded from Effectiveness Testing)	0	0	0	0
Cash Flow Hedges [Member] \| Cross Currency Swaps [Member] \| Other Income (Expense) Net [Member]
Amounts Included in Income, OCI or Regulatory Liabilities/Assets [Abstract]
Gain (Loss) Reclassified from AOCI into Income (Effective Portion)	18	2	30	(24)
Gain (Loss) Recognized in Income on Derivative (Ineffective Portion and Amount Excluded from Effectiveness Testing)	0	0	0	0
Net Investment Hedges [Member] \| Foreign Currency Contracts [Member] \| Other Comprehensive Income (Loss) [Member]
Amounts Included in Income, OCI or Regulatory Liabilities/Assets [Abstract]
Derivative Gain (Loss) Recognized in OCI (Effective Portion)	0	1	11	1
Not Designated As Hedging Instruments [Member]
Amounts Included in Income, OCI or Regulatory Liabilities/Assets [Abstract]
Gain (loss) recognized in income on derivative	39	(82)	88	(241)
Not Designated As Hedging Instruments [Member] \| Foreign Currency Contracts [Member] \| Other Income (Expense) Net [Member]
Amounts Included in Income, OCI or Regulatory Liabilities/Assets [Abstract]
Gain (loss) recognized in income on derivative	40	(81)	92	(237)
Not Designated As Hedging Instruments [Member] \| Interest Rate Swaps [Member] \| Regulatory Assets Noncurrent [Member]
Amounts Included in Income, OCI or Regulatory Liabilities/Assets [Abstract]
Gain (loss) recognized as regulatory liabilities/assets	2	1	7	2
Not Designated As Hedging Instruments [Member] \| Interest Rate Swaps [Member] \| Interest Expense [Member]
Amounts Included in Income, OCI or Regulatory Liabilities/Assets [Abstract]
Gain (loss) recognized in income on derivative	(1)	(1)	(4)	(4)
LG And E And KU Energy LLC [Member] \| Not Designated As Hedging Instruments [Member] \| Interest Rate Swaps [Member] \| Regulatory Assets Noncurrent [Member]
Amounts Included in Income, OCI or Regulatory Liabilities/Assets [Abstract]
Gain (loss) recognized as regulatory liabilities/assets	2	1	7	2
LG And E And KU Energy LLC [Member] \| Not Designated As Hedging Instruments [Member] \| Interest Rate Swaps [Member] \| Interest Expense [Member]
Amounts Included in Income, OCI or Regulatory Liabilities/Assets [Abstract]
Gain (loss) recognized in income on derivative	(1)	(1)	(4)	(4)
Louisville Gas And Electric Co [Member] \| Not Designated As Hedging Instruments [Member] \| Interest Rate Swaps [Member] \| Regulatory Assets Noncurrent [Member]
Amounts Included in Income, OCI or Regulatory Liabilities/Assets [Abstract]
Gain (loss) recognized as regulatory liabilities/assets	2	1	7	2
Louisville Gas And Electric Co [Member] \| Not Designated As Hedging Instruments [Member] \| Interest Rate Swaps [Member] \| Interest Expense [Member]
Amounts Included in Income, OCI or Regulatory Liabilities/Assets [Abstract]
Gain (loss) recognized in income on derivative	$ (1)	$ (1)	$ (4)	$ (4)

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The amount of gain (loss) recognized as regulatory assets/liabilities during the period on derivative instruments designated as hedging instruments and not designated as hedging instruments for which regulatory treatment is being applied.

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Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

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The effective portion of net gain (loss) reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.

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The portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments representing (a) the amount of the hedge ineffectiveness and (b) the amount, if any, excluded from the assessment of hedge effectiveness.

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Amount before tax of increase (decrease) in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss).

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