Reportable Business Segments Revenue by Products and Services (Details) - USD ($) $ in Millions	3 Months Ended										12 Months Ended
	Dec. 31, 2015	[1]	Sep. 30, 2015	[2]	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenue from External Customers	$ 1,087		$ 799		$ 824	$ 1,817	$ 1,689	$ 964	$ 1,183	$ 2,531	$ 4,527	$ 6,367	$ 5,522
Retail Gas Sales [Member]
Revenue from External Customers											3,725	5,049	4,150
Wholesale Gas Sales [Member]
Revenue from External Customers											657	1,159	913
Gas Transportation and Processing [Member]
Revenue from External Customers											26	38	345
Energy Products Or Services [Member]
Revenue from External Customers											$ 119	$ 121	$ 114

[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.