Revenue Recognition Disaggregation of Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Revenue from contracts	$ 7,350	$ 7,511	$ 6,282
Other (1)	68	53	(5)
Total revenues	7,418	7,564	6,277
Lease Income	6	6
Intersegment Eliminations [Member]
Disaggregation of Revenue [Line Items]
Total revenues	0	0	0
Reportable Subsegments [Member] | Electric
Disaggregation of Revenue [Line Items]
Revenue from contracts	3,451	3,507	3,235
Other (1)	19	12	(3)
Total revenues	3,470	3,519	3,232
Reportable Subsegments [Member] | Natural Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts	3,586	3,714	3,042
Other (1)	45	36	(11)
Total revenues	3,631	3,750	3,031
Reportable Subsegments [Member] | Corporate and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts	313	290	5
Other (1)	4	5	9
Total revenues	317	295	14
Houston Electric [Member]
Disaggregation of Revenue [Line Items]
Total revenues	2,911	2,990	3,234
Houston Electric [Member] | Reportable Subsegments [Member] | Electric Transmission & Distribution [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts	2,896	2,984	3,235
Other (1)	15	6	(1)
Total revenues	2,911	2,990	3,234
CERC Corp [Member]
Disaggregation of Revenue [Line Items]
Total revenues	2,763	3,018	3,031
Lease Income	2
CERC Corp [Member] | Reportable Subsegments [Member] | Natural Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts	2,714	2,979	3,042
Other (1)	49	39	(11)
Total revenues	$ 2,763	$ 3,018	$ 3,031