Related Party Transactions (Houston Electric and CERC) (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Houston Electric [Member]
Related Party Transaction [Line Items]
Interest income (expense) (1)	[1]	$ 0	$ 5	$ 0	$ 14
Cash dividends paid to parent		52	60	457	100
Cash contribution from parent		0	0	0	590
Capital Distribution to Parent		0	0	0	0
Property, plant and equipment from parent	[2]	35	0	35	0
Houston Electric [Member] | Operation and maintenance expense [Member]
Related Party Transaction [Line Items]
Net affiliate service charges (billings)		(4)	(3)	(14)	(7)
Houston Electric [Member] | CenterPoint Energy [Member] | Operation and maintenance expense [Member]
Related Party Transaction [Line Items]
Corporate service charges		48	38	142	132
CERC Corp [Member]
Related Party Transaction [Line Items]
Interest income (expense) (1)	[1]	0	1	0	3
Cash dividends paid to parent		8	16	80	119
Cash contribution from parent		0	0	0	0
Capital Distribution to Parent		0	0	286	0
Property, plant and equipment from parent	[2]	23	0	23	0
CERC Corp [Member] | Operation and maintenance expense [Member]
Related Party Transaction [Line Items]
Net affiliate service charges (billings)		4	3	14	7
CERC Corp [Member] | CenterPoint Energy [Member] | Operation and maintenance expense [Member]
Related Party Transaction [Line Items]
Corporate service charges		$ 52	$ 31	$ 156	$ 106
Investments [Member] | Houston Electric [Member]
Related Party Transaction [Line Items]
Weighted average interest rate		0.19%		0.19%		1.98%
Investments [Member] | CERC Corp [Member]
Related Party Transaction [Line Items]
Weighted average interest rate		0.19%		0.19%		1.98%
Accounts and notes receivable (payable) - affiliate companies [Member] | Houston Electric [Member]
Related Party Transaction [Line Items]
Money pool investments (borrowings) (1)	[3]	$ 25		$ 25		$ 481
Accounts and notes receivable (payable) - affiliate companies [Member] | CERC Corp [Member]
Related Party Transaction [Line Items]
Money pool investments (borrowings) (1)	[3]	$ 0		$ 0		$ 0

[1] Interest income is included in Other income (expense), net and interest expense is included in Interest and other finance charges on Houston Electric’s and CERC’s respective Condensed Statements of Consolidated Income.

[2] Property, plant and equipment purchased from CenterPoint Energy at its net carrying value on the date of purchase.

[3] Included in Accounts and notes receivable (payable)–affiliated companies on Houston Electric’s and CERC’s respective Condensed Consolidated Balance Sheets.