Revenue Recognition and Allowance for Credit Losses - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Disaggregation of Revenue [Line Items]
Revenue from contracts	$ 1,959	$ 1,715	$ 4,747	$ 4,256
Other	(15)	27	(40)	33
Total revenues	1,944	1,742	4,707	4,289
Lease income	3	2	4	4
Houston Electric
Disaggregation of Revenue [Line Items]
Revenue from contracts	892	791	1,648	1,478
Other	(11)	(5)	(21)	(8)
Total revenues	881	786	1,627	1,470
CERC
Disaggregation of Revenue [Line Items]
Revenue from contracts	805	701	2,590	2,291
Other	(9)	20	(30)	25
Total revenues	796	721	2,560	2,316
Electric
Disaggregation of Revenue [Line Items]
Revenue from contracts	1,060	933	1,958	1,766
Other	(7)	4	(12)	1
Total revenues	1,053	937	1,946	1,767
Natural Gas
Disaggregation of Revenue [Line Items]
Revenue from contracts	827	718	2,672	2,373
Other	(9)	22	(30)	30
Total revenues	818	740	2,642	2,403
Corporate and Other
Disaggregation of Revenue [Line Items]
Revenue from contracts	72	64	117	117
Other	1	1	2	2
Total revenues	$ 73	$ 65	$ 119	$ 119