Revenue Recognition and Allowance for Credit Losses - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Disaggregation of Revenue [Line Items]
Revenue from contracts	$ 2,788	$ 2,541
Other	(25)	6
Operating revenues	2,763	2,547
Lease income	1	2
Electric
Disaggregation of Revenue [Line Items]
Revenue from contracts	898	833
Other	(5)	(3)
Operating revenues	893	830
Natural Gas
Disaggregation of Revenue [Line Items]
Revenue from contracts	1,845	1,655
Other	(21)	8
Operating revenues	1,824	1,663
Corporate and Other
Disaggregation of Revenue [Line Items]
Revenue from contracts	45	53
Other	1	1
Operating revenues	46	54
Houston Electric
Disaggregation of Revenue [Line Items]
Revenue from contracts	756	687
Other	(10)	(3)
Operating revenues	746	684
CERC Corp
Disaggregation of Revenue [Line Items]
Revenue from contracts	1,409	1,172
Other	(24)	5
Operating revenues	$ 1,385	$ 1,177