Unconsolidated Affiliate (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Percentage sale of units which trigger right of first refusal		5.00%
Equity Method Investment, Summarized Financial Information, Income Statement [Abstract]
CERC Corp.’s equity in earnings, net		$ 69	$ 72
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity [Abstract]
CERC Corp.’s equity method investment in Enable		$ 2,467		$ 2,472
Enable Midstream Partners [Member]
Equity method investment limited partner interest in Enable		54.00%
Distributions received from equity method investment		$ 74	74
Equity Method Investment, Summarized Financial Information, Income Statement [Abstract]
Operating revenues		748	666
Cost of sales, excluding depreciation and amortization		375	308
Operating income		139	140
Net income attributable to Enable		105	111
CERC Corp.’s interest		57	60
Basis difference amortization (1)	[1]	12	12
CERC Corp.’s equity in earnings, net		$ 69	72
Basis difference amortization period		31 years
Equity Method Investment, Summarized Financial Information, Assets and Liabilities [Abstract]
Current assets		$ 413		416
Non-current assets		11,274		11,177
Current liabilities		1,404		1,279
Non-current liabilities		2,664		2,660
Non-controlling interest		11		12
Preferred equity		362		362
Enable partners’ capital		7,246		7,280
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity [Abstract]
CERC’s ownership interest in Enable partners’ capital		3,913		3,935
CERC Corp.’s basis difference		(1,446)		(1,463)
CERC Corp.’s equity method investment in Enable		$ 2,467		2,472
OGE [Member]
Percentage sale of units which trigger right of first refusal		5.00%
Enable Midstream Partners [Member]
Limited partner interest in Enable		100.00%
Management rights ownership percentage		50.00%
Incentive distribution right		40.00%
Maximum incentive distribution right		50.00%
Enable Midstream Partners [Member] | OGE [Member]
Limited partner interest in Enable		25.60%
Management rights ownership percentage		50.00%
Incentive distribution right		60.00%
Enable Midstream Partners [Member] | Public unitholders [Member]
Limited partner interest in Enable		20.40%
Minimum [Member] | Enable Midstream Partners [Member]
Incentive distribution per unit		$ 0.2875
Maximum [Member] | Enable Midstream Partners [Member]
Incentive distribution per unit		$ 0.330625
Common Stock [Member] | Enable Midstream Partners [Member]
Enable equity method investment units held		233,856,623
Common Stock [Member] | Enable Midstream Partners [Member]
Enable units held		433,072,001
Common Stock [Member] | Enable Midstream Partners [Member] | OGE [Member]
Enable units held		110,982,805
Common Stock [Member] | Enable Midstream Partners [Member] | Public unitholders [Member]
Enable units held		88,232,573
Natural Gas Expenses [Member] | Enable Midstream Partners [Member]
Natural gas expenses, including transportation and storage costs		$ 37	33
Accounts payable for natural gas purchases from Enable		11		13
Transitional Service [Member] | Enable Midstream Partners [Member]
Reimbursement of transition services (1)	[2]	2	$ 2
Accounts receivable for amounts billed for transition services		$ 1		$ 1

[1] Equity in earnings of unconsolidated affiliate includes CERC Corp.’s share of Enable’s earnings adjusted for the amortization of the basis difference of CERC Corp.’s original investment in Enable and its underlying equity in Enable’s net assets. The basis difference is amortized over approximately 31 years, the average life of the assets to which the basis difference is attributed.

[2] Represents amounts billed under the Transition Agreements for certain support services provided to Enable. Actual transition services costs are recorded net of reimbursement.