Reportable Segments Revenues by Products and Services (Details) - USD ($) $ in Millions	3 Months Ended												12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018		Sep. 30, 2018		Jun. 30, 2018		Mar. 31, 2018		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues by Products and Services:
Revenues	$ 3,230	$ 2,742	$ 2,798	$ 3,531	$ 3,036		$ 2,212		$ 2,186		$ 3,155		$ 12,301	$ 10,589	$ 9,614
Electric Delivery [Member]
Revenues by Products and Services:
Revenues													3,019	3,232	2,997
Retail Electric Sales [Member]
Revenues by Products and Services:
Revenues													486
Wholesale Electric Sales [Member]
Revenues by Products and Services:
Revenues													14
Retail Gas Sales [Member]
Revenues by Products and Services:
Revenues													4,802	4,161	3,634
Wholesale Gas Sales [Member]
Revenues by Products and Services:
Revenues													2,312	3,008	2,811
Gas Transportation and Processing [Member]
Revenues by Products and Services:
Revenues													33	32	29
Infrastructure Services [Member]
Revenues by Products and Services:
Revenues													1,186
Energy Products and Services [Member]
Revenues by Products and Services:
Revenues													449	156	143
Houston Electric [Member]
Revenues by Products and Services:
Revenues	680	859	765	686	728		897		854		755		2,990	3,234	2,998
Houston Electric [Member] | Electric Delivery [Member]
Revenues by Products and Services:
Revenues													2,990	3,234	2,998
Houston Electric [Member] | Retail Gas Sales [Member]
Revenues by Products and Services:
Revenues													0	0	0
Houston Electric [Member] | Wholesale Gas Sales [Member]
Revenues by Products and Services:
Revenues													0	0	0
Houston Electric [Member] | Gas Transportation and Processing [Member]
Revenues by Products and Services:
Revenues													0	0	0
Houston Electric [Member] | Energy Products and Services [Member]
Revenues by Products and Services:
Revenues													0	0	0
CERC Corp [Member]
Revenues by Products and Services:
Revenues	$ 1,734	$ 1,126	$ 1,342	$ 2,368	$ 2,303	[1]	$ 1,312	[1]	$ 1,328	[1]	$ 2,400	[1]	6,570	7,343	6,603
CERC Corp [Member] | Electric Delivery [Member]
Revenues by Products and Services:
Revenues													0	0	0
CERC Corp [Member] | Retail Gas Sales [Member]
Revenues by Products and Services:
Revenues													4,070	4,161	3,634
CERC Corp [Member] | Wholesale Gas Sales [Member]
Revenues by Products and Services:
Revenues													2,313	3,008	2,811
CERC Corp [Member] | Gas Transportation and Processing [Member]
Revenues by Products and Services:
Revenues													33	32	29
CERC Corp [Member] | Energy Products and Services [Member]
Revenues by Products and Services:
Revenues													$ 154	$ 142	$ 129

[1] Amounts have been recast to reflect discontinued operations in all periods presented.