Related Party Transactions (Houston Electric and CERC) (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Houston Electric [Member]
Related Party Transaction [Line Items]
Interest income (expense) (1)	[1]	$ 3	$ 0
Cash dividends paid to parent		24	32
Cash contribution from parent		590	0
Houston Electric [Member] | Operation and maintenance expense [Member]
Related Party Transaction [Line Items]
Net affiliate service charges (billings)		(2)	(2)
Houston Electric [Member] | CenterPoint Energy [Member] | Operation and maintenance expense [Member]
Related Party Transaction [Line Items]
Corporate service charges		52	44
CERC Corp [Member]
Related Party Transaction [Line Items]
Interest income (expense) (1)	[1]	1	(2)
Cash dividends paid to parent		20	86
Cash contribution from parent		0	0
CERC Corp [Member] | Operation and maintenance expense [Member]
Related Party Transaction [Line Items]
Net affiliate service charges (billings)		2	2
CERC Corp [Member] | CenterPoint Energy [Member] | Operation and maintenance expense [Member]
Related Party Transaction [Line Items]
Corporate service charges		$ 43	$ 34
Investments [Member] | Houston Electric [Member]
Related Party Transaction [Line Items]
Weighted average interest rate		2.87%		2.42%
Investments [Member] | CERC Corp [Member]
Related Party Transaction [Line Items]
Weighted average interest rate		2.87%		2.42%
Accounts and notes receivable (payable) - affiliate companies [Member] | Houston Electric [Member]
Related Party Transaction [Line Items]
Money pool investments (borrowings) (1)	[2]	$ 979		$ (1)
Accounts and notes receivable (payable) - affiliate companies [Member] | CERC Corp [Member]
Related Party Transaction [Line Items]
Money pool investments (borrowings) (1)	[2]	$ 220		$ 114

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