Revenue Recognition Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Revenue from contracts	$ 2,541	$ 2,141
Other (1)	6	26
Revenues	2,547	2,167
Lease Income	2	1
Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts	833	767
Other (1)	(3)	0
Revenues	830	767
Natural Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts	1,655	1,296
Other (1)	8	25
Revenues	1,663	1,321
Corporate and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts	53	78
Other (1)	1	1
Revenues	54	79
Houston Electric [Member]
Disaggregation of Revenue [Line Items]
Revenues	684	634
Houston Electric [Member] | Houston Electric T&D [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts	687	638
Other (1)	(3)	(4)
Revenues	684	634
CERC Corp [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,177	1,011
CERC Corp [Member] | Natural Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts	1,172	984
Other (1)	5	27
Revenues	$ 1,177	$ 1,011