Stock-Based Incentive Compensation Plans and Employee Benefit Plans Pension and Postretirement Benefits (Details) - USD ($) $ in Millions			12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Amounts recognized in balance sheets
Other liabilities-benefit obligations	$ (750)		$ (680)	$ (750)
Interest crediting rate	3.25%		2.25%	3.25%
Changes in plan assets and benefit obligations recognized in other comprehensive income
Amortization of net loss			$ (7)	$ (8)
Prior service cost (2)			0	(1)
Other Postretirement Benefits Plan [Member]
Components of net periodic costs [Abstract]
Service cost (1)			2	3	$ 2
Interest cost (2)			11	15	13
Expected return on plan assets (2)			(5)	(5)	(5)
Amortization of prior service cost (2)			(4)	(5)	(5)
Net periodic cost (credit)			$ 4	$ 8	$ 5
Assumptions used to determine net periodic benefit (income) cost
Discount rate			3.25%	3.20%	3.60%
Expected return on plan assets	3.20%	3.95%	3.95%	4.60%	4.55%
Change in benefit obligation [Roll Forward]
Benefit obligation, beginning of year			$ 356	$ 331
Plan obligations assumed in Merger			0	37
Service cost (1)			2	3	$ 2
Interest cost (2)			11	15	13
Participant contributions			6	8
Benefits paid			(22)	(26)
Plan amendment			0	9
Actuarial (gain) loss (1)			13	(21)
Benefit obligation, end of year	$ 356	$ 331	366	356	331
Change in plan assets [Rollforward]
Fair value of plan assets, beginning of year			128	114
Employer contributions			10	17
Participant contributions			6	8
Benefits paid			(22)	(26)
Actual investment return			12	15
Fair value of plan assets, end of year	128	$ 114	134	128	$ 114
Funded status of plan
Funded status, end of year	(228)		(232)	(228)
Amounts recognized in balance sheets
Current liabilities-other	(8)		(9)	(8)
Other liabilities-benefit obligations	(220)		(223)	(220)
Net liability, end of year	$ (228)		$ (232)	$ (228)
Discount rate (2)	3.25%		2.50%	3.25%
Expected return on plan assets (3)	3.20%	3.95%	3.95%	4.60%	4.55%
Prescription drug cost trend rate assumed for the next year - Pre-65			7.50%	8.00%
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate)	4.50%		4.50%	4.50%
Amounts recognized in accumulated other comprehensive loss
Unrecognized actuarial loss (gain)	$ (16)		$ (14)	$ (16)
Unrecognized prior service cost	7		7	7
Net amount recognized in accumulated other comprehensive loss (gain)	$ (9)		(7)	(9)
Changes in plan assets and benefit obligations recognized in other comprehensive income
Net loss (gain)			2
Amortization of net loss			0
Prior service cost (2)			0
Total recognized in comprehensive income			2
Total expense recognized in net periodic cost and other comprehensive income			6
Pension Plan [Member]
Components of net periodic costs [Abstract]
Service cost (1)			43	40
Interest cost (2)			75	96
Net periodic cost (credit)			$ 49	$ 93	$ 61
Assumptions used to determine net periodic benefit (income) cost
Discount rate			3.20%	4.35%	3.65%
Expected return on plan assets	5.00%	5.75%	5.75%	6.00%	6.00%
Rate of increase in compensation levels			4.95%	4.60%	4.45%
Change in benefit obligation [Roll Forward]
Benefit obligation, beginning of year			$ 2,453	$ 2,013
Plan obligations assumed in Merger			0	332
Service cost (1)			43	40
Interest cost (2)			75	96
Benefits paid			(207)	(244)
Plan amendment			0	1
Actuarial (gain) loss (1)			143	216
Curtailment			0	(1)
Benefit obligation, end of year	$ 2,453	$ 2,013	2,507	2,453	$ 2,013
Change in plan assets [Rollforward]
Fair value of plan assets, beginning of year			2,005	1,516
Plan assets assumed in Merger			0	286
Employer contributions			86	109
Benefits paid			(207)	(244)
Actual investment return			251	338
Fair value of plan assets, end of year	2,005	$ 1,516	2,135	2,005	$ 1,516
Funded status of plan
Funded status, end of year	(448)		(372)	(448)
Amounts recognized in balance sheets
Current liabilities-other	(8)		(8)	(8)
Other liabilities-benefit obligations	(440)		(364)	(440)
Net liability, end of year	$ (448)		$ (372)	$ (448)
Discount rate (2)	3.20%	4.35%	2.45%	3.20%	4.35%
Expected return on plan assets (3)	5.00%	5.75%	5.75%	6.00%	6.00%
Rate of increase in compensation levels	4.95%		5.05%	4.95%
Interest crediting rate	3.25%		2.25%	3.25%
Amounts recognized in accumulated other comprehensive loss
Unrecognized actuarial loss (gain)	$ 105		$ 109	$ 105
Unrecognized prior service cost	0		0	0
Net amount recognized in accumulated other comprehensive loss (gain)	105		109	105
Changes in plan assets and benefit obligations recognized in other comprehensive income
Net loss (gain)			11
Amortization of net loss			(7)
Prior service cost (2)			0
Total recognized in comprehensive income			4
Total expense recognized in net periodic cost and other comprehensive income			53
Pension benefits that have accumulated benefit obligations in excess of plan assets
Accumulated benefit obligation	2,352		2,427	2,352
Projected benefit obligation	2,385		2,440	2,385
Fair value of plan assets	2,005		2,135	2,005
Accumulated benefit obligation for all defined benefit pension plans	2,420		2,495	2,420
Non-qualified Pension Plan [Member]
Change in plan assets [Rollforward]
Employer contributions			10
Pension benefits that have accumulated benefit obligations in excess of plan assets
Accumulated benefit obligation	68		68	68
Projected benefit obligation	68		68	68
Fair value of plan assets	$ 0		$ 0	$ 0
Minimum [Member] | Other Postretirement Benefits Plan [Member]
Amounts recognized in balance sheets
Health care cost trend rate assumed for the next year	5.50%		5.25%	5.50%
Year that the cost trend rates reach the ultimate trend rate			2028	2028
Maximum [Member] | Other Postretirement Benefits Plan [Member]
Amounts recognized in balance sheets
Health care cost trend rate assumed for the next year	5.75%		19.70%	5.75%
Year that the cost trend rates reach the ultimate trend rate			2029	2029
Common Stock [Member] | CenterPoint Energy [Member]
Pension benefits that have accumulated benefit obligations in excess of plan assets
Number of Common stock held by the savings plan (in shares)			10,150,958
CERC Corp [Member]
Amounts recognized in balance sheets
Other liabilities-benefit obligations	$ (80)		$ (83)	$ (80)
Changes in plan assets and benefit obligations recognized in other comprehensive income
Amortization of net loss			0	0
Prior service cost (2)			(1)	0
CERC Corp [Member] | Other Postretirement Benefits Plan [Member]
Components of net periodic costs [Abstract]
Service cost (1)			1	1	$ 1
Interest cost (2)			3	5	4
Expected return on plan assets (2)			(1)	(1)	(1)
Amortization of prior service cost (2)			1	1	1
Net periodic cost (credit)			$ 4	$ 6	$ 5
Assumptions used to determine net periodic benefit (income) cost
Discount rate			3.25%	3.20%	3.60%
Expected return on plan assets	2.85%	3.35%	3.35%	4.15%	3.85%
Change in benefit obligation [Roll Forward]
Benefit obligation, beginning of year			$ 102	$ 110
Plan obligations assumed in Merger			0	0
Service cost (1)			1	1	$ 1
Interest cost (2)			3	5	4
Participant contributions			2	4
Benefits paid			(6)	(8)
Plan amendment			0	5
Actuarial (gain) loss (1)			3	15
Benefit obligation, end of year	$ 102	$ 110	105	102	110
Change in plan assets [Rollforward]
Fair value of plan assets, beginning of year			27	25
Employer contributions			3	3
Participant contributions			2	4
Benefits paid			(6)	(8)
Actual investment return			2	3
Fair value of plan assets, end of year	27	$ 25	28	27	$ 25
Funded status of plan
Funded status, end of year	(75)		(77)	(75)
Amounts recognized in balance sheets
Current liabilities-other	(3)		(3)	(3)
Other liabilities-benefit obligations	(72)		(74)	(72)
Net liability, end of year	$ (75)		$ (77)	$ (75)
Discount rate (2)	3.25%		2.50%	3.25%
Expected return on plan assets (3)	2.85%	3.35%	3.35%	4.15%	3.85%
Prescription drug cost trend rate assumed for the next year - Pre-65			7.50%	8.00%
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate)	4.50%		4.50%	4.50%
Amounts recognized in accumulated other comprehensive loss
Unrecognized actuarial loss (gain)	$ (12)		$ (12)	$ (12)
Unrecognized prior service cost	7		7	7
Net amount recognized in accumulated other comprehensive loss (gain)	$ (5)		(5)	$ (5)
Changes in plan assets and benefit obligations recognized in other comprehensive income
Net loss (gain)			0
Amortization of net loss			0
Prior service cost (2)			0
Total recognized in comprehensive income			0
Total expense recognized in net periodic cost and other comprehensive income			4
CERC Corp [Member] | Non-qualified Pension Plan [Member]
Change in plan assets [Rollforward]
Employer contributions			$ 0
CERC Corp [Member] | Minimum [Member] | Other Postretirement Benefits Plan [Member]
Amounts recognized in balance sheets
Health care cost trend rate assumed for the next year	5.50%		5.25%	5.50%
Year that the cost trend rates reach the ultimate trend rate			2028	2028
CERC Corp [Member] | Maximum [Member] | Other Postretirement Benefits Plan [Member]
Amounts recognized in balance sheets
Health care cost trend rate assumed for the next year	5.75%		19.70%	5.75%
Year that the cost trend rates reach the ultimate trend rate			2029	2029
Houston Electric [Member]
Amounts recognized in balance sheets
Other liabilities-benefit obligations	$ (75)		$ (75)	$ (75)
Changes in plan assets and benefit obligations recognized in other comprehensive income
Amortization of net loss			0	0
Prior service cost (2)			0	0
Houston Electric [Member] | Other Postretirement Benefits Plan [Member]
Components of net periodic costs [Abstract]
Service cost (1)			0	1	$ 0
Interest cost (2)			5	7	8
Expected return on plan assets (2)			(4)	(4)	(4)
Amortization of prior service cost (2)			(5)	(6)	(5)
Net periodic cost (credit)			$ (4)	$ (2)	$ (1)
Assumptions used to determine net periodic benefit (income) cost
Discount rate			3.25%	3.20%	3.60%
Expected return on plan assets	3.30%	4.05%	4.05%	4.70%	4.75%
Change in benefit obligation [Roll Forward]
Benefit obligation, beginning of year			$ 162	$ 166
Plan obligations assumed in Merger			0	0
Service cost (1)			0	1	$ 0
Interest cost (2)			5	7	8
Participant contributions			2	2
Benefits paid			(10)	(13)
Plan amendment			0	3
Actuarial (gain) loss (1)			9	(4)
Benefit obligation, end of year	$ 162	$ 166	168	162	166
Change in plan assets [Rollforward]
Fair value of plan assets, beginning of year			101	89
Employer contributions			3	10
Participant contributions			2	2
Benefits paid			(10)	(13)
Actual investment return			10	13
Fair value of plan assets, end of year	101	$ 89	106	101	$ 89
Funded status of plan
Funded status, end of year	(61)		(62)	(61)
Amounts recognized in balance sheets
Current liabilities-other	0		0	0
Other liabilities-benefit obligations	(61)		(62)	(61)
Net liability, end of year	$ (61)		$ (62)	$ (61)
Discount rate (2)	3.25%		2.50%	3.25%
Expected return on plan assets (3)	3.30%	4.05%	4.05%	4.70%	4.75%
Prescription drug cost trend rate assumed for the next year - Pre-65			7.50%	8.00%
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate)	4.50%		4.50%	4.50%
Houston Electric [Member] | Non-qualified Pension Plan [Member]
Change in plan assets [Rollforward]
Employer contributions			$ 0
Houston Electric [Member] | Minimum [Member] | Other Postretirement Benefits Plan [Member]
Amounts recognized in balance sheets
Health care cost trend rate assumed for the next year	5.50%		5.25%	5.50%
Year that the cost trend rates reach the ultimate trend rate			2028	2028
Houston Electric [Member] | Maximum [Member] | Other Postretirement Benefits Plan [Member]
Amounts recognized in balance sheets
Health care cost trend rate assumed for the next year	5.75%		19.70%	5.75%
Year that the cost trend rates reach the ultimate trend rate			2029	2029
Operation And Maintenance Expense [Member] | Pension Plan [Member]
Components of net periodic costs [Abstract]
Service cost (1)			$ 43	$ 40	$ 37
Change in benefit obligation [Roll Forward]
Service cost (1)			43	40	37
Other Nonoperating Income (Expense) [Member] | Pension Plan [Member]
Components of net periodic costs [Abstract]
Interest cost (2)			75	96	79
Expected return on plan assets (2)			(112)	(105)	(107)
Amortization of prior service cost (2)			0	9	9
Amortization of net loss (2)			41	52	43
Settlement cost (2) (3)			2	2	0
Curtailment gain (2) (4)			0	(1)	0
Change in benefit obligation [Roll Forward]
Interest cost (2)			$ 75	$ 96	$ 79