Short-term Borrowings and Long-term Debt - Debt Transactions (Details) $ in Millions	1 Months Ended	12 Months Ended
	Feb. 28, 2021 USD ($) day	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Debt Instrument [Line Items]
Proceeds from long-term debt		$ 4,493	$ 799	$ 2,916
CERC Corp
Debt Instrument [Line Items]
Proceeds from long-term debt		1,699	500	0
CERC Corp | Bridge Loan
Debt Instrument [Line Items]
Financing commitments	$ 1,700
Financing commitment term | day	364
Houston Electric
Debt Instrument [Line Items]
Proceeds from long-term debt		1,096	$ 299	$ 696
Senior Notes | CERC Corp
Debt Instrument [Line Items]
Principal amount of debt issued		1,700
General Mortgage Bonds | Houston Electric
Debt Instrument [Line Items]
Principal amount of debt issued		1,100
Senior Note and GMBs
Debt Instrument [Line Items]
Principal amount of debt issued		4,500
CERC Senior notes .70% due 2023 | Senior Notes | CERC Corp
Debt Instrument [Line Items]
Principal amount of debt issued		$ 700
Debt instrument interest rate (as a percent)		0.70%
CERC Senior Notes Floating Rate due 2023 | Senior Notes | CERC Corp
Debt Instrument [Line Items]
Principal amount of debt issued		$ 1,000
CERC Senior Notes Floating Rate due 2023 | Senior Notes | CERC Corp | London Interbank Offered Rate (LIBOR)
Debt Instrument [Line Items]
Basis spread on LIBOR (as a percent)		0.50%
General Mortgage Bonds Due 2031 | General Mortgage Bonds | Houston Electric
Debt Instrument [Line Items]
Principal amount of debt issued		$ 400
Debt instrument interest rate (as a percent)		2.35%
General Mortgage Bonds Due 2051 | General Mortgage Bonds | Houston Electric
Debt Instrument [Line Items]
Principal amount of debt issued		$ 700
Debt instrument interest rate (as a percent)		3.35%
CNP Senior Note 1.45% due 2026 | Senior Notes
Debt Instrument [Line Items]
Principal amount of debt issued		$ 500
Debt instrument interest rate (as a percent)		1.45%
CNP Senior Note 2.65% due 2031 | Senior Notes
Debt Instrument [Line Items]
Principal amount of debt issued		$ 500
Debt instrument interest rate (as a percent)		2.65%
CNP Floating Senior Note | Senior Notes
Debt Instrument [Line Items]
Principal amount of debt issued		$ 700
CNP Floating Senior Note | Senior Notes | Secured Overnight Financing Rate
Debt Instrument [Line Items]
Basis spread on LIBOR (as a percent)		0.65%
CERC Senior notes .70% and Floating Rate due 2023 | Senior Notes | CERC Corp
Debt Instrument [Line Items]
Proceeds from long-term debt	$ 1,690
General Mortgage Bonds Due 2031 and 2051 | General Mortgage Bonds | Houston Electric
Debt Instrument [Line Items]
Proceeds from long-term debt		$ 1,080
CNP Senior Notes 1.45%, 2.65%, and Floating | Senior Notes
Debt Instrument [Line Items]
Proceeds from long-term debt		$ 1,690