CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Accounts receivable, less allowance for credit losses	$ 780	$ 676
Allowance for credit losses	65	52
Accrued Unbilled Revenues, Allowance for Credit Losses, Current	$ 4	$ 5
Preferred Stock [Abstract]
Preferred Stock, par value	$ 0.01	$ 0.01
Preferred Stock, Shares Authorized	20,000,000	20,000,000
Preferred stock outstanding (in shares)	2,402,400	2,402,400
Preferred stock aggregate liquidation preference	$ 2,402	$ 2,402
Common Stock [Abstract]
Common stock, par value	$ 0.01	$ 0.01
Common Stock, Shares Authorized	1,000,000,000	1,000,000,000
Common Stock, Shares, Outstanding	551,865,588	551,355,861
Houston Electric [Member]
Accounts receivable, less allowance for credit losses	$ 263	$ 268
Allowance for credit losses	1	1
CERC Corp [Member]
Accounts receivable, less allowance for credit losses	349	233
Allowance for credit losses	56	45
Accrued Unbilled Revenues, Allowance for Credit Losses, Current	3	4
Variable Interest Entity, Primary Beneficiary [Member]
Accounts receivable, less allowance for credit losses	24	23
Variable Interest Entity, Primary Beneficiary [Member] | Houston Electric [Member]
Accounts receivable, less allowance for credit losses	$ 24	$ 23