Revenue Recognition and Allowance for Credit Losses - Summary of Contract Assets and Liabilities (Details) $ in Millions	3 Months Ended
	Mar. 31, 2022 USD ($)
Accounts Receivable
Opening balance as of December 31, 2021	$ 627
Closing balance as of March 31, 2022	876
Increase (decrease) in accounts receivable	249
Other Accrued Unbilled Revenues
Opening balance as of December 31, 2021	513
Closing balance as of March 31, 2022	432
Increase (decrease) in other accrued unbilled revenues	(81)
Contract Assets
Opening balance as of December 31, 2021	15
Closing balance as of March 31, 2022	16
Increase (decrease) in contract assets	1
Contract Liabilities
Opening balance as of December 31, 2021	16
Closing balance as of March 31, 2022	27
Increase (decrease) in contract liabilities	11
Revenue recognized included in the opening contract liability for the period	10
Houston Electric
Accounts Receivable
Opening balance as of December 31, 2021	225
Closing balance as of March 31, 2022	247
Increase (decrease) in accounts receivable	22
Other Accrued Unbilled Revenues
Opening balance as of December 31, 2021	127
Closing balance as of March 31, 2022	95
Increase (decrease) in other accrued unbilled revenues	(32)
Contract Liabilities
Opening balance as of December 31, 2021	4
Closing balance as of March 31, 2022	8
Increase (decrease) in contract liabilities	4
Revenue recognized included in the opening contract liability for the period	1
CERC Corp
Accounts Receivable
Opening balance as of December 31, 2021	223
Closing balance as of March 31, 2022	408
Increase (decrease) in accounts receivable	185
Other Accrued Unbilled Revenues
Opening balance as of December 31, 2021	247
Closing balance as of March 31, 2022	209
Increase (decrease) in other accrued unbilled revenues	$ (38)