Reportable Segments Revenues by Products and Services (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues by Products and Services:
Revenues	$ 3,036	$ 2,212	$ 2,186	$ 3,155	$ 2,638	$ 2,098	$ 2,143	$ 2,735	$ 10,589	$ 9,614	$ 7,528
Electric Delivery [Member]
Revenues by Products and Services:
Revenues									3,232	2,997	3,060
Retail Gas Sales [Member]
Revenues by Products and Services:
Revenues									4,161	3,634	3,329
Wholesale Gas Sales [Member]
Revenues by Products and Services:
Revenues									3,008	2,811	977
Gas Transportation and Processing [Member]
Revenues by Products and Services:
Revenues									32	29	23
Energy Products Or Services [Member]
Revenues by Products and Services:
Revenues									156	143	139
Houston Electric [Member]
Revenues by Products and Services:
Revenues	$ 728	$ 897	$ 854	$ 755	$ 765	$ 843	$ 752	$ 638	3,234	2,998	3,059
Houston Electric [Member] | Electric Delivery [Member]
Revenues by Products and Services:
Revenues									3,234	2,998	3,059
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 Or Services [Member]
Revenues by Products and Services:
Revenues									0	0	0
CERC Corp [Member]
Revenues by Products and Services:
Revenues									7,343	6,603	4,454
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									4,161	3,634	3,329
CERC Corp [Member] | Wholesale Gas Sales [Member]
Revenues by Products and Services:
Revenues									3,008	2,811	977
CERC Corp [Member] | Gas Transportation and Processing [Member]
Revenues by Products and Services:
Revenues									32	29	23
CERC Corp [Member] | Energy Products Or Services [Member]
Revenues by Products and Services:
Revenues									$ 142	$ 129	$ 125