Revenue Recognition Summary of Contract Assets and Liabilities (Details) $ in Millions	9 Months Ended
Sep. 30, 2020 USD ($)
Change in Accounts Receivable [Roll Forward]
Opening balance as of December 31, 2019	$ 566
Closing balance as of September 30, 2020	568
Increase (Decrease) in Accounts Receivable on Contracts with Customers	2
Change in Other Accrued Unbilled Revenues [Roll Forward]
Opening balance as of December 31, 2019	469
Closing balance as of September 30, 2020	285
Increase (Decrease) in Unbilled Receivables	(184)
Change in Contract Asset [Roll Forward]
Opening balance as of December 31, 2019	6
Closing balance as of September 30, 2020	22
Increase (Decrease) in Contract with Customer, Asset	16
Change in Contract Liability [Roll Forward]
Opening balance as of December 31, 2019	30
Closing balance as of September 30, 2020	20
Increase (Decrease) in Contract with Customer, Liability	(10)
Contract with Customer, Liability, Revenue Recognized	29
Houston Electric [Member]
Change in Accounts Receivable [Roll Forward]
Opening balance as of December 31, 2019	210
Closing balance as of September 30, 2020	321
Increase (Decrease) in Accounts Receivable on Contracts with Customers	111
Change in Other Accrued Unbilled Revenues [Roll Forward]
Opening balance as of December 31, 2019	117
Closing balance as of September 30, 2020	124
Increase (Decrease) in Unbilled Receivables	7
Change in Contract Liability [Roll Forward]
Opening balance as of December 31, 2019	3
Closing balance as of September 30, 2020	4
Increase (Decrease) in Contract with Customer, Liability	1
Contract with Customer, Liability, Revenue Recognized	3
CERC Corp [Member]
Change in Accounts Receivable [Roll Forward]
Opening balance as of December 31, 2019	222
Closing balance as of September 30, 2020	123
Increase (Decrease) in Accounts Receivable on Contracts with Customers	(99)
Change in Other Accrued Unbilled Revenues [Roll Forward]
Opening balance as of December 31, 2019	249
Closing balance as of September 30, 2020	91
Increase (Decrease) in Unbilled Receivables	$ (158)

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Amount, after allowance for credit loss, of right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time, classified as current.

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Unbilled amounts due for services rendered or to be rendered, actions taken or to be taken, or a promise to refrain from taking certain actions in accordance with the terms of a legally binding agreement between the entity and, at a minimum, one other party. An example would be amounts associated with contracts or programs where the recognized revenue for performance thereunder exceeds the amounts billed under the terms thereof as of the date of the balance sheet.

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