Revenue Recognition - Disaggregation of Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Revenue from contracts	$ 8,256	$ 7,350	$ 7,511
Other	96	68	53
Total revenues	8,352	7,418	7,564
Lease Income	7	6	6
Electric
Disaggregation of Revenue [Line Items]
Revenue from contracts	3,726	3,451	3,507
Other	37	19	12
Total revenues	3,763	3,470	3,519
Natural Gas
Disaggregation of Revenue [Line Items]
Revenue from contracts	4,281	3,586	3,714
Other	55	45	36
Total revenues	4,336	3,631	3,750
Corporate and Other
Disaggregation of Revenue [Line Items]
Revenue from contracts	249	313	290
Other	4	4	5
Total revenues	253	317	295
Houston Electric
Disaggregation of Revenue [Line Items]
Revenue from contracts	3,117	2,896	2,984
Other	17	15	6
Total revenues	3,134	2,911	2,990
CERC Corp
Disaggregation of Revenue [Line Items]
Revenue from contracts	3,210	2,714	2,979
Other	38	49	39
Total revenues	3,248	2,763	3,018
Lease Income	$ 3	$ 2	$ 1