Unconsolidated Affiliates (Details) - USD ($) $ / shares in Units, $ in Millions			12 Months Ended
		Nov. 22, 2016	Dec. 31, 2017	Dec. 31, 2016		Dec. 31, 2015	Aug. 30, 2017
Limited Partner Interest in Enable [Abstract]
Percentage of sales that trigger right of first refusal			5.00%
Distribution received from unconsolidated affiliates [Abstract]
Service agreement notice for termination at term end			90 days
Service agreement notice for termination at will number of days			180 days
Summarized unaudited consolidated income from Enable [Abstract]
CERC's equity in earnings (losses), net			$ 265	$ 208		$ (1,633)
Basis difference amortization period			31 years
Summarized unaudited consolidated balance sheet from Enable [Abstract]
Investment in unconsolidated affiliates			$ 2,472	$ 2,505
ArcLight [Member]
Limited Partner Interest in Enable [Abstract]
Units sold in public offering		1,424,281
OGE [Member]
Limited Partner Interest in Enable [Abstract]
Percentage of sales that trigger right of first refusal			5.00%
Enable Midstream Partners [Member]
Limited Partner Interest in Enable [Abstract]
Units sold in public offering		11,500,000
Transaction with Enable [Abstract]
Enable's common unit share price			$ 14.22	$ 15.73
Enable Midstream Partners [Member]
Limited Partner Interest in Enable [Abstract]
Limited partner interest in Enable			54.10%	54.10%	[1]	55.40%
Distribution received from unconsolidated affiliates [Abstract]
Distributions received from equity method investment			$ 297	$ 297		$ 294
Transaction with Enable [Abstract]
Impairment of equity method investment			$ 0	$ 0		1,225
Equity method investment carrying value per unit			$ 10.57	$ 10.71
Summarized unaudited consolidated income from Enable [Abstract]
Operating revenues			$ 2,803	$ 2,272		2,418
Cost of sales, excluding depreciation and amortization			1,381	1,017		1,097
Impairment of goodwill and other long-lived assets			0	9		1,134
Operating income (loss)			528	385		(712)
Net income (loss) attributable to Enable			400	290		(752)
CERC’s interest			216	160		(416)
Basis difference amortization (1)	[2]		49	48		8
Impairment of CERC’s equity method investment in Enable			0	0		(1,225)
CERC's equity in earnings (losses), net	[3]		265	208		(1,633)
Impairment charges						1,846
Share of impairment charges Enable recorded for goodwill and long-lived assets						621
Equity in earnings (losses) of unconsolidated affiliates, excluding impairment charge						213
Summarized unaudited consolidated balance sheet from Enable [Abstract]
Current assets			416	396
Non-current assets			11,177	10,816
Current liabilities			1,279	362
Non-current liabilities			2,660	3,056
Non-controlling interest			12	12
Preferred equity			362	362
Enable partners’ capital			7,280	7,420
CERC’s ownership interest in Enable partners’ capital			3,935	4,067
CERC’s basis difference			(1,463)	(1,562)
Investment in unconsolidated affiliates			2,472	2,505
Enable Midstream Partners [Member]
Transaction with Enable [Abstract]
Interest income related to notes receivable from Enable			$ 0	$ 1		$ 8
Common Stock [Member] | Enable Midstream Partners [Member]
Limited Partner Interest in Enable [Abstract]
Enable units held	[4]		233,856,623
Enable Midstream Partners [Member]
Limited Partner Interest in Enable [Abstract]
Management rights ownership percentage			50.00%
Distribution received from unconsolidated affiliates [Abstract]
Incentive distribution right			40.00%
Maximum incentive distribution right			50.00%
Enable Midstream Partners [Member] | OGE [Member]
Limited Partner Interest in Enable [Abstract]
Limited partner interest in Enable			25.70%	25.70%		26.30%
Management rights ownership percentage			50.00%
Distribution received from unconsolidated affiliates [Abstract]
Incentive distribution right			60.00%
Enable Midstream Partners [Member] | Common Stock [Member] | OGE [Member]
Limited Partner Interest in Enable [Abstract]
Enable units held			110,982,805
Enable Midstream Partners [Member] | Subordinated Units [Member]
Limited Partner Interest in Enable [Abstract]
Enable units held							139,704,916
Minimum [Member] | Enable Midstream Partners [Member]
Distribution received from unconsolidated affiliates [Abstract]
Incentive distribution per unit			$ 0.2875
Maximum [Member] | Enable Midstream Partners [Member]
Distribution received from unconsolidated affiliates [Abstract]
Incentive distribution per unit			$ 0.330625
Transitional Service [Member] | Enable Midstream Partners [Member]
Transaction with Enable [Abstract]
Reimbursement of transition services (1)	[5]		$ 4	$ 7		$ 16
Accounts receivable for amounts billed for transition services			1	1
Natural Gas Expenses [Member] | Enable Midstream Partners [Member]
Transaction with Enable [Abstract]
Natural gas expenses, including transportation and storage costs			115	110		$ 117
Accounts payable for natural gas purchases from Enable			$ 13	$ 10

[1] In November 2016, Enable completed a public offering of 11,500,000 common units of which 1,424,281 were sold by ArcLight Capital Partners, LLC. The common units issued and sold by Enable resulted in dilution of both CERC Corp.’s and OGE’s limited partner interest in Enable.

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

[3] These amounts include impairment charges totaling $1,846 million composed of CERC’s impairment of its equity method investment in Enable of $1,225 million and CERC’s share, $621 million, of impairment charges Enable recorded for goodwill and long-lived assets for the year ended December 31, 2015. This impairment is offset by $213 million of earnings for the year ended December 31, 2015.

[4] The 139,704,916 subordinated units previously owned by CERC Corp. converted into common units of Enable on a one-for-one basis, on August 30, 2017, at the end of the subordination period, as set forth in Enable’s Fourth Amended and Restated Agreement of Limited Partnership. Upon conversion, holders of common units resulting from the conversion of subordinated units have all the rights and obligations of unitholders holding all other common units, including the right to receive distributions pro rata made with respect to common units.

[5] Represents amounts billed under the Transition Agreements, including the costs of seconded employees. Substantially all of the seconded employees became employees of Enable effective January 1, 2015. Actual transition services costs are recorded net of reimbursement.