Income Taxes - Components of Income Tax Expense (Benefit) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Deferred income tax expense (benefit):
Total deferred expense (benefit)	$ 213	$ (429)	$ 69
Total income tax expense (benefit)	110	80	30
Houston Electric
Current income tax expense (benefit):
Federal	22	76	84
State	22	19	20
Total current expense (benefit)	44	95	104
Deferred income tax expense (benefit):
Federal	31	(42)	(24)
State	1	0	0
Total deferred expense (benefit)	32	(42)	(24)
Total income tax expense (benefit)	76	53	80
CERC Corp
Deferred income tax expense (benefit):
Total deferred expense (benefit)	77	91	7
Total income tax expense (benefit)	51	97	(3)
Continuing Operations
Current income tax expense (benefit):
Federal	0	(36)	(6)
State	(28)	32	13
Total current expense (benefit)	(28)	(4)	7
Deferred income tax expense (benefit):
Federal	78	63	48
State	60	21	(25)
Total deferred expense (benefit)	138	84	23
Total income tax expense (benefit)	110	80	30
Continuing Operations | CERC Corp
Current income tax expense (benefit):
State	(26)	4	5
Total current expense (benefit)	(26)	4	5
Deferred income tax expense (benefit):
Federal	49	26	26
State	28	67	(34)
Total deferred expense (benefit)	77	93	(8)
Total income tax expense (benefit)	51	97	(3)
Discontinued Operations
Current income tax expense (benefit):
Federal	91	152	54
State	35	28	8
Total current expense (benefit)	126	180	62
Deferred income tax expense (benefit):
Federal	127	(422)	26
State	(52)	(91)	20
Total deferred expense (benefit)	75	(513)	46
Total income tax expense (benefit)	201	(333)	108
Discontinued Operations | CERC Corp
Current income tax expense (benefit):
State	0	0	2
Total current expense (benefit)	0	0	2
Deferred income tax expense (benefit):
Federal	0	0	13
State	0	(2)	2
Total deferred expense (benefit)	0	(2)	15
Total income tax expense (benefit)	$ 0	$ (2)	$ 17