Revenue Recognition Summary of Contract Assets and Liabilities (Details) $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($)
Change in Accounts Receivable [Roll Forward]
Opening balance as of December 31, 2019	$ 566
Closing balance as of March 31, 2020	612
Increase (Decrease) in Accounts Receivable on Contracts with Customers	46
Change in Other Accrued Unbilled Revenues [Roll Forward]
Opening balance as of December 31, 2019	469
Closing balance as of March 31, 2020	320
Increase (Decrease) in Unbilled Receivables	(149)
Change in Contract Asset [Roll Forward]
Opening balance as of December 31, 2019	6
Closing balance as of March 31, 2020	13
Increase (Decrease) in Contract with Customer, Asset	7
Change in Contract Liability [Roll Forward]
Opening balance as of December 31, 2019	30
Closing balance as of March 31, 2020	23
Increase (Decrease) in Contract with Customer, Liability	(7)
Contract with Customer, Liability, Revenue Recognized	25
Houston Electric [Member]
Change in Accounts Receivable [Roll Forward]
Opening balance as of December 31, 2019	210
Closing balance as of March 31, 2020	209
Increase (Decrease) in Accounts Receivable on Contracts with Customers	(1)
Change in Other Accrued Unbilled Revenues [Roll Forward]
Opening balance as of December 31, 2019	117
Closing balance as of March 31, 2020	92
Increase (Decrease) in Unbilled Receivables	(25)
Change in Contract Liability [Roll Forward]
Opening balance as of December 31, 2019	3
Closing balance as of March 31, 2020	8
Increase (Decrease) in Contract with Customer, Liability	5
Contract with Customer, Liability, Revenue Recognized	1
CERC Corp [Member]
Change in Accounts Receivable [Roll Forward]
Opening balance as of December 31, 2019	222
Closing balance as of March 31, 2020	265
Increase (Decrease) in Accounts Receivable on Contracts with Customers	43
Change in Other Accrued Unbilled Revenues [Roll Forward]
Opening balance as of December 31, 2019	249
Closing balance as of March 31, 2020	140
Increase (Decrease) in Unbilled Receivables	$ (109)