Equity (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Jun. 28, 2021	May 07, 2021	Apr. 27, 2021	Apr. 16, 2021	Apr. 05, 2021	Dec. 31, 2020
Class of Stock [Line Items]
Preferred stock, outstanding (in shares)	1,775,903		1,775,903							2,402,400
Preferred stock	$ 1,739		$ 1,739							$ 2,363
Preferred Stock Dividends and Other Adjustments [Abstract]
Preferred stock dividend requirement	30	$ 37	59	$ 66
Amortization of beneficial conversion feature	0	9	0	9
Total income allocated to preferred shareholders	30	46	59	75
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	(87)	(100)	(90)	(98)
Other comprehensive income (loss) from unconsolidated affiliates	1	0	2	(3)
Prior service cost (2)	0	1	0	1
Actuarial losses	2	1	4	3
Reclassification of net deferred loss from cash flow hedges (3)	0	19	0	19
Tax expense	(1)	(5)	(1)	(6)
Net current period other comprehensive income	2	16	5	14
Ending Balance	$ (85)	$ (84)	$ (85)	$ (84)
Common Stock
Class of Stock [Line Items]
Dividends declared per share	$ 0.1600	$ 0.1500	$ 0.1600	$ 0.4400
Common Stock dividends paid per share	0.1600	0.1500	0.1600	0.4400
Series A Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends declared	0	0	0	30.6250
Preferred stock dividends paid per share	0	$ 0	0	$ 30.6250
Preferred Stock, Liquidation Preference Per Share	$ 1,000		$ 1,000
Preferred stock, outstanding (in shares)	800,000		800,000							800,000
Preferred stock	$ 790		$ 790							$ 790
Preferred Stock Dividends and Other Adjustments [Abstract]
Preferred stock dividend requirement	$ 13	$ 13	$ 25	$ 25
Series B Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends declared	$ 17.5000	$ 17.5000	$ 17.5000	$ 35.0000
Preferred stock dividends paid per share	17.5000	$ 17.5000	17.5000	$ 35.0000
Preferred Stock, Liquidation Preference Per Share	$ 1,000		$ 1,000
Preferred stock, outstanding (in shares)	975,903		975,903							977,400
Preferred stock	$ 949		$ 949							$ 950
Preferred stock to be converted to common stock (in shares)					7		1,490
Shares of common stock issued (in shares)					214		45,653
Preferred Stock Dividends and Other Adjustments [Abstract]
Preferred stock dividend requirement	$ 17	$ 17	$ 34	$ 34
Series C Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends declared	$ 0	$ 0.1500	$ 0	$ 0.1500
Preferred stock dividends paid per share	0	$ 0.1500	0	$ 0.1500
Preferred Stock, Liquidation Preference Per Share	$ 1,000		$ 1,000
Preferred stock, outstanding (in shares)	0		0							625,000
Preferred stock	$ 0		$ 0							$ 623
Preferred stock to be converted to common stock (in shares)						187,500		37,500	400,000
Shares of common stock issued (in shares)						12,246,897		2,449,379	26,126,714
Preferred Stock Dividends and Other Adjustments [Abstract]
Preferred stock dividend requirement	$ 0	$ 7	$ 0	$ 7
Preferred Stock
Class of Stock [Line Items]
Preferred stock, outstanding (in shares)	1,775,903		1,775,903							2,402,400
Preferred stock	$ 1,739		$ 1,739							$ 2,363
Houston Electric
Preferred Stock Dividends and Other Adjustments [Abstract]
Amortization of beneficial conversion feature			0	0
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	0	(15)	0	(15)
Other comprehensive income (loss) from unconsolidated affiliates	0	0	0	0
Prior service cost (2)	0	0	0	0
Actuarial losses	0	0	0	0
Reclassification of net deferred loss from cash flow hedges (3)	0	19	0	19
Tax expense	0	(4)	0	(4)
Net current period other comprehensive income	0	15	0	15
Ending Balance	0	0	0	0
CERC Corp
Preferred Stock Dividends and Other Adjustments [Abstract]
Amortization of beneficial conversion feature			0	0
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning Balance	10	10	10	10
Other comprehensive income (loss) from unconsolidated affiliates	0	0	0	0
Prior service cost (2)	0	0	0	0
Actuarial losses	0	0	0	0
Reclassification of net deferred loss from cash flow hedges (3)	0	0	0	0
Tax expense	0	0	0	0
Net current period other comprehensive income	0	0	0	0
Ending Balance	$ 10	$ 10	$ 10	$ 10