Leases (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($) MW	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Lease, Cost [Abstract]
Operating lease cost	$ 8	$ 9
Short-term lease cost	119	14
Total lease cost	127	23
Operating Leases, Lease Income [Abstract]
Operating lease income	6	5
Variable lease income	1	1
Total lease income	7	6
Assets and Liabilities, Lessee [Abstract]
Operating ROU assets	22	31
Finance ROU assets	179	0
Total leased assets	201	31
Current operating lease liability	6	6
Non-current operating lease liability	17	26
Total leased liabilities	$ 23	$ 32
Weighted-average remaining lease term (in years) - operating leases	6 years 2 months 12 days	6 years
Weighted-average discount rate - operating leases (as a percent)	3.10%	3.14%
Weighted-average remaining lease term (in years) - finance leases	7 years 6 months
Weighted-average discount rate - finance leases (as a percent)	2.21%	0.00%
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Other non-current assets	Other non-current assets
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Property, Plant and Equipment, net	Property, Plant and Equipment, net
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	Other	Other
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Other	Other
Operating Lease Liabilities, Payments Due [Abstract]
2022	$ 6
2023	5
2024	3
2025	3
2026	3
2027 and beyond	5
Total lease payments	25
Less: Interest	2
Present value of lease liabilities	23	$ 32
Lessor, Operating Lease, Payments, Fiscal Year Maturity [Abstract]
Finance lease, not yet commenced, amount	$ 496
Lease not yet commenced, amount of megawatts | MW	380
2022	$ 5
2023	5
2024	5
2025	6
2026	6
2027 and beyond	142
Total lease payments to be received	169
Other Information Related to Leases [Abstract]
Operating cash flows from operating leases included in the measurement of lease liabilities	6
Financing cash flows from finance leases included in the measurement of lease liabilities	179	0	$ 0
Houston Electric
Lease Disclosure [Line Items]
Expenses associated with short-term lease	20
Recovery of deferred costs sought	$ 200
Number of megawatts of mobile generation | MW	505
Number of megawatts of mobile generation delivered | MW	125
Right to terminate, lease costs refunded (as a percent)	75.00%
Lease, Cost [Abstract]
Operating lease cost	$ 1	0
Short-term lease cost	118	12
Total lease cost	119	12
Operating Leases, Lease Income [Abstract]
Operating lease income	1	0
Variable lease income	0	0
Total lease income	1	0
Assets and Liabilities, Lessee [Abstract]
Operating ROU assets	1	1
Finance ROU assets	179	0
Total leased assets	180	1
Current operating lease liability	1	0
Non-current operating lease liability	0	1
Total leased liabilities	$ 1	$ 1
Weighted-average remaining lease term (in years) - operating leases	4 years 1 month 6 days	4 years
Weighted-average discount rate - operating leases (as a percent)	2.86%	2.59%
Weighted-average remaining lease term (in years) - finance leases	7 years 6 months
Weighted-average discount rate - finance leases (as a percent)	2.21%	0.00%
Operating Lease Liabilities, Payments Due [Abstract]
2022	$ 1
2023	0
2024	0
2025	0
2026	0
2027 and beyond	0
Total lease payments	1
Less: Interest	0
Present value of lease liabilities	1	$ 1
Lessor, Operating Lease, Payments, Fiscal Year Maturity [Abstract]
2022	0
2023	0
2024	0
2025	0
2026	0
2027 and beyond	0
Total lease payments to be received	0
Other Information Related to Leases [Abstract]
Operating cash flows from operating leases included in the measurement of lease liabilities	1
Financing cash flows from finance leases included in the measurement of lease liabilities	179	0	$ 0
CERC Corp
Lease, Cost [Abstract]
Operating lease cost	4	5
Short-term lease cost	0	0
Total lease cost	4	5
Operating Leases, Lease Income [Abstract]
Operating lease income	3	2
Variable lease income	0	0
Total lease income	3	2
Assets and Liabilities, Lessee [Abstract]
Operating ROU assets	12	19
Finance ROU assets	0	0
Total leased assets	12	19
Current operating lease liability	2	3
Non-current operating lease liability	11	18
Total leased liabilities	$ 13	$ 21
Weighted-average remaining lease term (in years) - operating leases	6 years 6 months	7 years 6 months
Weighted-average discount rate - operating leases (as a percent)	3.20%	3.36%
Weighted-average discount rate - finance leases (as a percent)	0.00%	0.00%
Operating Lease Liabilities, Payments Due [Abstract]
2022	$ 3
2023	2
2024	2
2025	2
2026	2
2027 and beyond	3
Total lease payments	14
Less: Interest	1
Present value of lease liabilities	13	$ 21
Lessor, Operating Lease, Payments, Fiscal Year Maturity [Abstract]
2022	3
2023	3
2024	3
2025	3
2026	4
2027 and beyond	136
Total lease payments to be received	152
Other Information Related to Leases [Abstract]
Operating cash flows from operating leases included in the measurement of lease liabilities	3
Financing cash flows from finance leases included in the measurement of lease liabilities	$ 0