Reportable Business Segments Revenue by Products and Services (Details) - USD ($) $ in Millions	3 Months Ended										12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	[1]	Sep. 30, 2015	[2]	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenue from External Customers	$ 1,349	$ 978	$ 807	$ 1,320	$ 1,087		$ 799		$ 824	$ 1,817	$ 4,454	$ 4,527	$ 6,367
Retail Gas Sales [Member]
Revenue from External Customers											3,329	3,725	5,049
Wholesale Gas Sales [Member]
Revenue from External Customers											977	657	1,159
Gas Transportation and Processing [Member]
Revenue from External Customers											23	26	38
Energy Products Or Services [Member]
Revenue from External Customers											$ 125	$ 119	$ 121

[1] CERC recognized $984 million ($620 million after tax) in impairment charges related to Enable during the three months ended December 31, 2015.

[2] CERC recognized $862 million ($537 million after tax) in impairment charges related to Enable during the three months ended September 30, 2015.