CONDENSED STATEMENTS OF CONSOLIDATED CHANGES IN EQUITY - USD ($) $ in Millions	Total	Common Stock [Member]	Series A Preferred Stock [Member]	Series B Preferred Stock [Member]	Series C Preferred Stock [Member]	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Retained Earnings [Member] Series A Preferred Stock [Member]	Retained Earnings [Member] Series B Preferred Stock [Member]	Retained Earnings [Member] Series C Preferred Stock [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, 2018						2,000,000
Balance, end of period at Sep. 30, 2019						2,000,000
Balance, beginning of period at Dec. 31, 2018							501,000,000								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 Sep. 30, 2019							502,000,000								1,000					1,000
Balance, beginning of period at Dec. 31, 2018						$ 1,740	$ 5	$ 6,072	$ 349				$ (108)		$ 0	$ 2,015	$ 423	$ 5		$ 0	$ 1,896	$ 800	$ (14)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other																0
Issuance of stock, shares		0				0
Issuances of stock, net of issuance costs		$ 0				$ 0		0
Issuances related to benefit and investment plans							0	0
Recognition of beneficial conversion feature	$ 0							0						$ 0					$ 0
Contribution From Parent																0					590
Net income (Loss)	634								634					159			159		312			312
Common Stock dividends declared (see Note 19)		$ (433)							(289)
Preferred Stock dividends declared (see Note 19)			$ (50)	$ (51)						$ (24)	$ (34)	$ 0
Amortization of Beneficial Conversion Feature	0								0					0					0
Dividend to parent																	(119)					(100)
Adoption of ASU 2016-13 | Accounting Standards Update 2016-13 [Member]									0								0
Other comprehensive income (loss)													1										(1)
Balance, end of period at Sep. 30, 2019	8,346					$ 1,740	$ 5	6,072	636				(107)	2,483	$ 0	2,015	463	5	3,483	$ 0	2,486	1,012	(15)
Balance, beginning of period at Jun. 30, 2019						2,000,000
Balance, end of period at Sep. 30, 2019						2,000,000
Balance, beginning of period at Jun. 30, 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 Sep. 30, 2019							502,000,000								1,000					1,000
Balance, beginning of period at Jun. 30, 2019						$ 1,740	$ 5	6,065	552				(105)		$ 0	2,015	486	5		$ 0	2,486	887	(15)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other																0
Issuance of stock, shares		0				0
Issuances of stock, net of issuance costs		$ 0				$ 0		0
Issuances related to benefit and investment plans							0	7
Recognition of beneficial conversion feature								0
Contribution From Parent																0					0
Net income (Loss)	270								270					(7)			(7)		185			185
Common Stock dividends declared (see Note 19)									(145)
Preferred Stock dividends declared (see Note 19)										(24)	(17)	0
Amortization of Beneficial Conversion Feature	0								0
Dividend to parent																	(16)					(60)
Adoption of ASU 2016-13 | Accounting Standards Update 2016-13 [Member]									0								0
Other comprehensive income (loss)													(2)										0
Balance, end of period at Sep. 30, 2019	$ 8,346					$ 1,740	$ 5	6,072	636				(107)	2,483	$ 0	2,015	463	5	3,483	$ 0	2,486	1,012	(15)
Preferred stock par value (in dollars per share)			$ 0.01	$ 0.01	$ 0.01
Preferred Stock, Shares Authorized	20,000,000
Common Stock, Par or Stated Value Per Share	$ 0.01
Common Stock, Shares Authorized	1,000,000,000
Preferred stock par value (in dollars per share)			$ 0.01	$ 0.01	$ 0.01
Common Stock, Par or Stated Value Per Share	$ 0.01
Common Stock, Shares Authorized	1,000,000,000
Balance, beginning of period at Dec. 31, 2019			800,000	977,500	725,000	2,000,000
Balance, end of period at Sep. 30, 2020			800,000	977,500	725,000	3,000,000
Balance, beginning of period at Dec. 31, 2019	502,242,061						502,000,000								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 Sep. 30, 2020	544,819,895						545,000,000								1,000					1,000
Balance, beginning of period at Dec. 31, 2019	$ 8,359					$ 1,740	$ 5	6,080	632				(98)	2,641	$ 0	2,116	515	10	3,251	$ 0	2,486	780	(15)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other																(1)
Issuance of stock, shares		42,000,000				1,000,000
Issuances of stock, net of issuance costs		$ 0				$ 716		672
Issuances related to benefit and investment plans							0	21
Recognition of beneficial conversion feature	(32)							(32)						0					0
Contribution From Parent																286					0
Net income (Loss)	(973)								(973)					76			76		277			277
Common Stock dividends declared (see Note 19)		$ (309)							(309)
Preferred Stock dividends declared (see Note 19)			$ (49)	$ (51)	$ (14)					(49)	(51)	(14)
Amortization of Beneficial Conversion Feature	(25)								(25)					0					0
Dividend to parent																	(80)					(457)
Adoption of ASU 2016-13 | Accounting Standards Update 2016-13 [Member]									(7)								5
Other comprehensive income (loss)													16										15
Balance, end of period at Sep. 30, 2020	$ 8,388					$ 2,456	$ 5	6,805	(796)				(82)	2,345	$ 0	1,829	506	10	3,086	$ 0	2,486	600	0
Balance, beginning of period at Jun. 30, 2020						3,000,000
Balance, end of period at Sep. 30, 2020			800,000	977,500	725,000	3,000,000
Balance, beginning of period at Jun. 30, 2020							545,000,000								1,000					1,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuances related to benefit and investment plans							0
Balance, end of period at Sep. 30, 2020	544,819,895						545,000,000								1,000					1,000
Balance, beginning of period at Jun. 30, 2020						$ 2,441	$ 5	6,801	(771)				(84)		$ 0	1,829	518	10		$ 0	2,486	495	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other																0
Issuance of stock, shares		0				0
Issuances of stock, net of issuance costs		$ 0				$ 15		(1)
Issuances related to benefit and investment plans							0	5
Recognition of beneficial conversion feature								0
Contribution From Parent																0					0
Net income (Loss)	$ 121								121					(4)			(4)		157			157
Common Stock dividends declared (see Note 19)									(82)
Preferred Stock dividends declared (see Note 19)										$ (24)	$ (17)	$ (7)
Amortization of Beneficial Conversion Feature	(16)								(16)
Dividend to parent																	(8)					(52)
Adoption of ASU 2016-13 | Accounting Standards Update 2016-13 [Member]									0								0
Other comprehensive income (loss)													2										0
Balance, end of period at Sep. 30, 2020	$ 8,388					$ 2,456	$ 5	$ 6,805	$ (796)				$ (82)	$ 2,345	$ 0	$ 1,829	$ 506	$ 10	$ 3,086	$ 0	$ 2,486	$ 600	$ 0
Preferred stock par value (in dollars per share)			$ 0.01	$ 0.01	$ 0.01
Preferred Stock, Shares Authorized	20,000,000
Common Stock, Par or Stated Value Per Share	$ 0.01
Common Stock, Shares Authorized	1,000,000,000