Leases (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022 USD ($) MW	Jun. 30, 2021 USD ($)	Jun. 30, 2022 USD ($) MW	Jun. 30, 2021 USD ($)	Dec. 31, 2021 USD ($) MW
Lease, Cost [Abstract]
Operating lease cost	$ 2	$ 2	$ 2	$ 4
Short-term lease cost	37	25	84	35
Variable lease cost	0	0	0	0
Total lease cost	39	27	86	39
Operating Leases, Lease Income [Abstract]
Operating lease income	1	1	3	3
Variable lease income	1	1	1	1
Total lease income	2	2	4	4
Assets and Liabilities, Lessee [Abstract]
Operating ROU assets	15		15		$ 22
Finance ROU assets	332		332		179
Total leased assets	347		347		201
Current operating lease liability	4		4		6
Non-current operating lease liability	11		11		17
Total leased liabilities	$ 15		$ 15		$ 23
Weighted-average remaining lease term (in years) - operating leases	5 years 1 month 6 days		5 years 1 month 6 days		6 years 2 months 12 days
Weighted-average discount rate - operating leases (as a percent)	3.13%		3.13%		3.10%
Weighted-average remaining lease term (in years) - finance leases	7 years		7 years		7 years 6 months
Weighted-average discount rate - finance leases (as a percent)	2.21%		2.21%		2.21%
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	Other non-current assets		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		Property, Plant and Equipment, Net
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	Other current liabilities		Other current liabilities		Other current liabilities
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Other non-current liabilities		Other non-current liabilities		Other non-current liabilities
Operating Lease Liabilities, Payments Due [Abstract]
Remainder of 2022	$ 3		$ 3
2023	4		4
2024	4		4
2025	2		2
2026	2		2
2027 and beyond	2		2
Total lease payments	17		17
Less: Interest	2		2
Present value of lease liabilities	15		15		$ 23
Lessor, Operating Lease, Payments, Fiscal Year Maturity [Abstract]
Finance lease, not yet commenced, amount	$ 347		$ 347
Lease not yet commenced, amount of megawatts | MW	252		252
Remainder of 2022	$ 3		$ 3
2023	6		6
2024	6		6
2025	6		6
2026	7		7
2027	6		6
2028 and beyond	136		136
Total lease payments to be received	170		170
Other Information Related to Leases [Abstract]
Operating cash flows from operating leases included in the measurement of lease liabilities	1	2	3	3
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	$ 72		$ 72		$ 20
Additional MW of mobile generation | MW	128		128
Cash payment	$ 171
Number of megawatts of mobile generation | MW	505		505
Number of megawatts of mobile generation, amount delivered | MW	253		253		125
Lease, Cost [Abstract]
Operating lease cost	$ 0	0	$ 0	0
Short-term lease cost	37	25	83	35
Variable lease cost	0	0	0	0
Total lease cost	37	25	83	35
Operating Leases, Lease Income [Abstract]
Operating lease income	0	0	0	0
Variable lease income	0	0	0	0
Total lease income	0	0	0	0
Assets and Liabilities, Lessee [Abstract]
Operating ROU assets	1		1		$ 1
Finance ROU assets	332		332		179
Total leased assets	333		333		180
Current operating lease liability	0		0		1
Non-current operating lease liability	1		1		0
Total leased liabilities	$ 1		$ 1		$ 1
Weighted-average remaining lease term (in years) - operating leases	4 years 8 months 12 days		4 years 8 months 12 days		4 years 1 month 6 days
Weighted-average discount rate - operating leases (as a percent)	3.20%		3.20%		2.86%
Weighted-average remaining lease term (in years) - finance leases	7 years		7 years		7 years 6 months
Weighted-average discount rate - finance leases (as a percent)	2.21%		2.21%		2.21%
Operating Lease Liabilities, Payments Due [Abstract]
Remainder of 2022	$ 1		$ 1
2023	0		0
2024	0		0
2025	0		0
2026	0		0
2027 and beyond	0		0
Total lease payments	1		1
Less: Interest	0		0
Present value of lease liabilities	1		1		$ 1
Lessor, Operating Lease, Payments, Fiscal Year Maturity [Abstract]
Remainder of 2022	0		0
2023	1		1
2024	1		1
2025	1		1
2026	0		0
2027	0		0
2028 and beyond	0		0
Total lease payments to be received	3		3
Other Information Related to Leases [Abstract]
Operating cash flows from operating leases included in the measurement of lease liabilities	0	0	0	0
Financing cash flows from finance leases included in the measurement of lease liabilities			171	0
CERC
Lease, Cost [Abstract]
Operating lease cost	0	1	1	2
Short-term lease cost	0	0	0	0
Variable lease cost	0	0	0	0
Total lease cost	0	1	1	2
Operating Leases, Lease Income [Abstract]
Operating lease income	1	0	1	1
Variable lease income	0	0	0	0
Total lease income	1	0	1	1
Assets and Liabilities, Lessee [Abstract]
Operating ROU assets	7		7		12
Finance ROU assets	0		0		0
Total leased assets	7		7		12
Current operating lease liability	2		2		2
Non-current operating lease liability	5		5		11
Total leased liabilities	$ 7		$ 7		$ 13
Weighted-average remaining lease term (in years) - operating leases	4 years 3 months 18 days		4 years 3 months 18 days		6 years 6 months
Weighted-average discount rate - operating leases (as a percent)	3.54%		3.54%		3.20%
Weighted-average discount rate - finance leases (as a percent)	0.00%		0.00%		0.00%
Operating Lease Liabilities, Payments Due [Abstract]
Remainder of 2022	$ 1		$ 1
2023	2		2
2024	2		2
2025	1		1
2026	1		1
2027 and beyond	0		0
Total lease payments	7		7
Less: Interest	0		0
Present value of lease liabilities	7		7		$ 13
Lessor, Operating Lease, Payments, Fiscal Year Maturity [Abstract]
Remainder of 2022	2		2
2023	3		3
2024	3		3
2025	3		3
2026	4		4
2027	4		4
2028 and beyond	132		132
Total lease payments to be received	151		151
Other Information Related to Leases [Abstract]
Operating cash flows from operating leases included in the measurement of lease liabilities	$ 0	$ 1	1	2
Financing cash flows from finance leases included in the measurement of lease liabilities			$ 0	$ 0