Financing Activities - Long-term Debt and ATM Program (Details) shares in Thousands, £ in Millions, $ in Millions	1 Months Ended			3 Months Ended
	May 31, 2018 USD ($)	Mar. 31, 2018 USD ($)	Mar. 31, 2018 GBP (£)	Mar. 31, 2018 USD ($) shares	Mar. 31, 2017 USD ($)	Mar. 31, 2018 GBP (£)	Feb. 28, 2018 USD ($)
At-the-Market Stock Offering Program (Numeric) [Abstract]
Net proceeds from issuance of common stock				$ 100	$ 73
WPD South Wales PLC [Member] | Index Linked Senior Unsecured Notes [Member]
Long-term Debt (Numeric) [Abstract]
Principal amount | £						£ 30
Stated interest rate		0.01%		0.01%		0.01%
Proceeds from debt, net of issuance costs | £			£ 31
Maturity date		Dec. 31, 2036	Dec. 31, 2036
Proceeds from debt, including premium net of debt issuance costs		$ 44
LGE [Member] | Senior Debt Obligations [Member] | Pollution Control Revenue Bonds, 2001 Series A [Member] | Remarketed [Member]
Long-term Debt (Numeric) [Abstract]
Principal amount		$ 28		$ 28
Stated interest rate		2.30%		2.30%		2.30%
Maturity date		Dec. 31, 2026	Dec. 31, 2026
Repurchase date of debt instruments		Sep. 01, 2021	Sep. 01, 2021
LGE [Member] | Senior Debt Obligations [Member] | Pollution Control Revenue Bonds, 2001 Series B [Member] | Remarketed [Member] | Subsequent Event [Member]
Long-term Debt (Numeric) [Abstract]
Principal amount	$ 35
Stated interest rate	2.55%
Maturity date	Dec. 31, 2027
Repurchase date of debt instruments	May 03, 2021
LGE [Member] | Senior Debt Obligations [Member] | Jefferson County Pollution Control Revenue Bonds, 2001 Series B [Member] | Remarketed [Member] | Subsequent Event [Member]
Long-term Debt (Numeric) [Abstract]
Principal amount	$ 35
Stated interest rate	2.55%
Maturity date	Dec. 31, 2027
Repurchase date of debt instruments	May 03, 2021
LG And E And KU Energy LLC [Member] | LGE [Member] | Senior Debt Obligations [Member] | Pollution Control Revenue Bonds, 2001 Series A [Member] | Remarketed [Member]
Long-term Debt (Numeric) [Abstract]
Principal amount		$ 28		$ 28
Stated interest rate		2.30%		2.30%		2.30%
Maturity date		Dec. 31, 2026	Dec. 31, 2026
Repurchase date of debt instruments		Sep. 01, 2021	Sep. 01, 2021
LG And E And KU Energy LLC [Member] | LGE [Member] | Senior Debt Obligations [Member] | Pollution Control Revenue Bonds, 2001 Series B [Member] | Remarketed [Member] | Subsequent Event [Member]
Long-term Debt (Numeric) [Abstract]
Principal amount	$ 35
Stated interest rate	2.55%
Maturity date	Dec. 31, 2027
Repurchase date of debt instruments	May 03, 2021
LG And E And KU Energy LLC [Member] | LGE [Member] | Senior Debt Obligations [Member] | Jefferson County Pollution Control Revenue Bonds, 2001 Series B [Member] | Remarketed [Member] | Subsequent Event [Member]
Long-term Debt (Numeric) [Abstract]
Principal amount	$ 35
Stated interest rate	2.55%
Maturity date	Dec. 31, 2027
Repurchase date of debt instruments	May 03, 2021
LG And E And KU Energy LLC [Member] | Affiliated Entity [Member] | Note Payable [Member] | Subsequent Event [Member]
Long-term Debt (Numeric) [Abstract]
Stated interest rate	4.00%
Maturity date	May 31, 2028
Notes Payable, Noncurrent	$ 250
Louisville Gas And Electric Co [Member] | Senior Debt Obligations [Member] | Pollution Control Revenue Bonds, 2001 Series A [Member]
Long-term Debt (Numeric) [Abstract]
Principal amount		$ 28		$ 28
Stated interest rate		2.30%		2.30%		2.30%
Maturity date		Dec. 31, 2026	Dec. 31, 2026
Repurchase date of debt instruments		Sep. 01, 2021	Sep. 01, 2021
Louisville Gas And Electric Co [Member] | Senior Debt Obligations [Member] | Pollution Control Revenue Bonds, 2001 Series B [Member] | Remarketed [Member] | Subsequent Event [Member]
Long-term Debt (Numeric) [Abstract]
Principal amount	$ 35
Stated interest rate	2.55%
Maturity date	Dec. 31, 2027
Repurchase date of debt instruments	May 03, 2021
Louisville Gas And Electric Co [Member] | Senior Debt Obligations [Member] | Jefferson County Pollution Control Revenue Bonds, 2001 Series B [Member] | Remarketed [Member] | Subsequent Event [Member]
Long-term Debt (Numeric) [Abstract]
Principal amount	$ 35
Stated interest rate	2.55%
Maturity date	Dec. 31, 2027
Repurchase date of debt instruments	May 03, 2021
At The Market Stock Offering Program [Member]
At-the-Market Stock Offering Program (Numeric) [Abstract]
Aggregate sales price of common stock based on two separate equity distribution agreements							$ 1,000
Stock Issued During Period, Shares, New Issues | shares				3,000
Net proceeds from issuance of common stock				$ 85