Leases (Details) $ in Millions	3 Months Ended
	Mar. 31, 2022 USD ($) MW	Mar. 31, 2021 USD ($)	Dec. 31, 2021 USD ($) MW
Lease, Cost [Abstract]
Operating lease cost	$ 2	$ 2
Short-term lease cost	46	10
Variable lease cost	(1)	0
Total lease cost	47	12
Operating Leases, Lease Income [Abstract]
Operating lease income	1	2
Variable lease income	0	0
Total lease income	1	2
Assets and Liabilities, Lessee [Abstract]
Operating ROU assets	16		$ 22
Finance ROU assets	344		179
Total leased assets	360		201
Current operating lease liability	4		6
Non-current operating lease liability	12		17
Total leased liabilities	$ 16		$ 23
Weighted-average remaining lease term (in years) - operating leases	5 years 2 months 12 days		6 years 2 months 12 days
Weighted-average discount rate - operating leases (as a percent)	3.20%		3.10%
Weighted-average remaining lease term (in years) - finance leases	7 years 3 months 18 days		7 years 6 months
Weighted-average discount rate - finance leases (as a percent)	2.21%		2.21%
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 current liabilities		Other current liabilities
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Other non-current liabilities		Other non-current liabilities
Operating Lease Liabilities, Payments Due [Abstract]
Remainder of 2022	$ 4
2023	4
2024	3
2025	2
2026	2
2027 and beyond	3
Total lease payments	18
Less: Interest	2
Present value of lease liabilities	16		$ 23
Lessor, Operating Lease, Payments, Fiscal Year Maturity [Abstract]
Finance lease, not yet commenced, amount	$ 347
Lease not yet commenced, amount of megawatts | MW	252
Remainder of 2022	$ 5
2023	5
2024	5
2025	5
2026	6
2027	6
2028 and beyond	136
Total lease payments to be received	168
Other Information Related to Leases [Abstract]
Operating cash flows from operating leases included in the measurement of lease liabilities	2	2
Financing cash flows from finance leases included in the measurement of lease liabilities	171	0
Houston Electric
Lease Disclosure [Line Items]
Expenses associated with short-term lease	$ 51		$ 20
Additional MW of mobile generation | MW	128
Cash payment	$ 171
Number of megawatts of mobile generation | MW	505
Number of megawatts of mobile generation, amount delivered | MW	253		125
Lease, Cost [Abstract]
Operating lease cost	$ 0	0
Short-term lease cost	46	10
Variable lease cost	(1)	0
Total lease cost	45	10
Operating Leases, Lease Income [Abstract]
Operating lease income	0	0
Variable lease income	0	0
Total lease income	0	0
Assets and Liabilities, Lessee [Abstract]
Operating ROU assets	1		$ 1
Finance ROU assets	343		179
Total leased assets	344		180
Current operating lease liability	0		1
Non-current operating lease liability	1		0
Total leased liabilities	$ 1		$ 1
Weighted-average remaining lease term (in years) - operating leases	4 years 3 months 18 days		4 years 1 month 6 days
Weighted-average discount rate - operating leases (as a percent)	3.00%		2.86%
Weighted-average remaining lease term (in years) - finance leases	7 years 3 months 18 days		7 years 6 months
Weighted-average discount rate - finance leases (as a percent)	2.21%		2.21%
Operating Lease Liabilities, Payments Due [Abstract]
Remainder of 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]
Remainder of 2022	1
2023	0
2024	0
2025	0
2026	0
2027	0
2028 and beyond	0
Total lease payments to be received	1
Other Information Related to Leases [Abstract]
Operating cash flows from operating leases included in the measurement of lease liabilities	0	0
Financing cash flows from finance leases included in the measurement of lease liabilities	171	0
CERC Corp
Lease, Cost [Abstract]
Operating lease cost	1	1
Short-term lease cost	0	0
Variable lease cost	0	0
Total lease cost	1	1
Operating Leases, Lease Income [Abstract]
Operating lease income	1	1
Variable lease income	0	0
Total lease income	1	1
Assets and Liabilities, Lessee [Abstract]
Operating ROU assets	7		12
Finance ROU assets	0		0
Total leased assets	7		12
Current operating lease liability	2		2
Non-current operating lease liability	5		11
Total leased liabilities	$ 7		$ 13
Weighted-average remaining lease term (in years) - operating leases	4 years 6 months		6 years 6 months
Weighted-average discount rate - operating leases (as a percent)	3.52%		3.20%
Operating Lease Liabilities, Payments Due [Abstract]
Remainder of 2022	$ 1
2023	2
2024	2
2025	1
2026	1
2027 and beyond	1
Total lease payments	8
Less: Interest	1
Present value of lease liabilities	7		$ 13
Lessor, Operating Lease, Payments, Fiscal Year Maturity [Abstract]
Remainder of 2022	3
2023	3
2024	3
2025	3
2026	4
2027	4
2028 and beyond	132
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	1	1
Financing cash flows from finance leases included in the measurement of lease liabilities	$ 0	$ 0