CONDENSED STATEMENTS OF CONSOLIDATED CHANGES IN EQUITY (Unaudited) - USD ($) $ in Millions	Total	Series A Preferred Stock [Member]	Series B Preferred Stock [Member]	Series C Preferred Stock [Member]	Preferred Stock [Member]	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	CERC Corp [Member]	CERC Corp [Member] Common Stock [Member]	CERC Corp [Member] Additional Paid-in Capital [Member]	CERC Corp [Member] Retained Earnings [Member]	CERC Corp [Member] AOCI Attributable to Parent [Member]	Houston Electric [Member]	Houston Electric [Member] Common Stock [Member]	Houston Electric [Member] Additional Paid-in Capital [Member]	Houston Electric [Member] Retained Earnings [Member]	Houston Electric [Member] AOCI Attributable to Parent [Member]
Balance, beginning of period at Dec. 31, 2019						2,000,000
Balance, end of period at Mar. 31, 2020						2,000,000
Balance, beginning of period at Dec. 31, 2019							502,000,000					1,000					1,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuances related to benefit and investment plans							0
Balance, end of period at Mar. 31, 2020							502,000,000					1,000					1,000
Balance, beginning of period at Dec. 31, 2019						$ 1,740	$ 5	$ 6,080	$ 632	$ (98)		$ 0	$ 2,116	$ 515	$ 10		$ 0	$ 2,486	$ 780	$ (15)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuances related to benefit and investment plans							0	6
Net income (Loss)	$ (1,199)								(1,199)		$ 67			67		$ 33			33
Common Stock dividends declared (see Note 19)									(145)
Preferred Stock dividends declared (see Note 19)									(42)
Dividend to parent														(32)					(385)
Adoption of ASU 2016-13 | Accounting Standards Update 2016-13 [Member]									(7)					(5)
Other comprehensive income (loss)										(2)
Balance, end of period at Mar. 31, 2020	$ 6,970					$ 1,740	$ 5	6,086	(761)	(100)	2,671	$ 0	2,116	545	10	2,899	$ 0	2,486	428	(15)
Preferred Stock, par value		$ 0.01	$ 0.01	$ 0.01
Preferred Stock, Shares Authorized	20,000,000
Common stock, par value	$ 0.01
Common Stock, Shares Authorized	1,000,000,000
Preferred Stock, par value	$ 0.01
Preferred Stock, Shares Authorized	20,000,000
Common stock, par value	$ 0.01
Common Stock, Shares Authorized	1,000,000,000
Balance, beginning of period at Dec. 31, 2020	2,402,400	800,000	977,400	625,000	2,402,400	3,000,000
Balance, end of period at Mar. 31, 2021	2,402,400	800,000	977,400	625,000	2,402,400	3,000,000
Balance, beginning of period at Dec. 31, 2020	551,355,861						551,000,000					1,000					1,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuances related to benefit and investment plans							1,000,000
Balance, end of period at Mar. 31, 2021	551,865,588						552,000,000					1,000					1,000
Balance, beginning of period at Dec. 31, 2020	$ 8,348					$ 2,363	$ 6	6,914	(845)	(90)	2,567	$ 0	2,046	511	10	3,111	$ 0	2,548	563	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuances related to benefit and investment plans							0	2
Net income (Loss)	363								363		151			151		53			53
Common Stock dividends declared (see Note 19)									0
Preferred Stock dividends declared (see Note 19)									0
Dividend to parent														0					0
Adoption of ASU 2016-13 | Accounting Standards Update 2016-13 [Member]									0					0
Other comprehensive income (loss)										3
Balance, end of period at Mar. 31, 2021	$ 8,716					$ 2,363	$ 6	$ 6,916	$ (482)	$ (87)	$ 2,718	$ 0	$ 2,046	$ 662	$ 10	$ 3,164	$ 0	$ 2,548	$ 616	$ 0
Preferred Stock, par value	$ 0.01	$ 0.01	$ 0.01	$ 0.01
Preferred Stock, Shares Authorized	20,000,000
Common stock, par value	$ 0.01
Common Stock, Shares Authorized	1,000,000,000