Related Party Transactions (Houston Electric and CERC) (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Related Party Transaction [Line Items]
Capital distribution to parent associated with the Internal Spin				$ 0	$ 0
Houston Electric [Member]
Related Party Transaction [Line Items]
Interest income (expense) (1)	[1]	$ 1	$ 1	1	3
Cash dividends paid to parent		60	45	123	87
Cash contribution from parent		0	0	0	0
Capital distribution to parent associated with the Internal Spin		0	0	0	0
Houston Electric [Member] | Operation and maintenance expense [Member]
Related Party Transaction [Line Items]
Net affiliate service charges (billings)		(3)	(1)	(8)	(6)
Houston Electric [Member] | CenterPoint Energy [Member] | Operation and maintenance expense [Member]
Related Party Transaction [Line Items]
Corporate service charges		47	41	138	127
CERC Corp [Member]
Related Party Transaction [Line Items]
Interest income (expense) (1)	[1]	(2)	0	(4)	0
Cash dividends paid to parent		75	89	286	337
Cash contribution from parent		600	0	600	38
Capital distribution to parent associated with the Internal Spin		1,460	0	1,460	0
CERC Corp [Member] | Operation and maintenance expense [Member]
Related Party Transaction [Line Items]
Net affiliate service charges (billings)		3	1	8	6
CERC Corp [Member] | CenterPoint Energy [Member] | Operation and maintenance expense [Member]
Related Party Transaction [Line Items]
Corporate service charges		$ 36	$ 30	$ 105	$ 93
Investments [Member] | Houston Electric [Member]
Related Party Transaction [Line Items]
Weighted average interest rate		2.45%		2.45%		1.90%
Investments [Member] | CERC Corp [Member]
Related Party Transaction [Line Items]
Weighted average interest rate		2.45%		2.45%		1.90%
Accounts and notes receivable (payable) - affiliate companies [Member] | Houston Electric [Member]
Related Party Transaction [Line Items]
Money pool investments (borrowings) (1)	[2]	$ (75)		$ (75)		$ (60)
Accounts and notes receivable (payable) - affiliate companies [Member] | CERC Corp [Member]
Related Party Transaction [Line Items]
Money pool investments (borrowings) (1)	[2]	$ 0		$ 0		$ (570)

[1] Interest income is included in Other, net and interest expense is included in Interest and other finance charges on the Condensed Statements of Consolidated Income.

[2] Included in Accounts and notes receivable (payable)–affiliated companies in the Condensed Consolidated Balance Sheets.