Centerpoint Energy Resources 10-K 26 Feb 16 2015 FY Annual report Financial data

Document and Entity Information

Document and Entity Information Document - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Jun. 30, 2015
Document and Entity Information [Abstract]
Entity Registrant Name	CENTERPOINT ENERGY RESOURCES CORP
Entity Central Index Key	1,042,773
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Document Type	10-K
Document Period End Date	Dec. 31, 2015
Document Fiscal Year Focus	2,015
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding	1,000
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float		$ 0

STATEMENTS OF CONSOLIDATED INCO

STATEMENTS OF CONSOLIDATED INCOME - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenues	$ 4,527	$ 6,367	$ 5,522
Expenses:
Natural gas	3,102	4,921	3,908
Operation and maintenance	741	751	828
Depreciation and amortization	227	206	230
Taxes other than income taxes	144	154	155
Total	4,214	6,032	5,121
Operating Income	313	335	401
Other Income (Expense):
Interest and other finance charges	(137)	(141)	(154)
Equity in earnings (losses) of unconsolidated affiliates	(1,633)	308	188
Other, net	6	9	0
Total	(1,764)	176	34
Income (Loss) Before Income Taxes	(1,451)	511	435
Income tax expense (benefit)	(539)	188	371
Net Income (Loss)	$ (912)	$ 323	$ 64

STATEMENTS OF CONSOLIDATED COMP

STATEMENTS OF CONSOLIDATED COMPREHENSIVE INCOME - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ (912)	$ 323	$ 64
Other comprehensive income (loss), net of tax:
Adjustment to postretirement and other postemployment plans (net of tax of $6, $1 and $6)	8	(4)	6
Other comprehensive income (loss)	8	(4)	6
Comprehensive income (loss)	$ (904)	$ 319	$ 70

STATEMENTS OF CONSOLIDATED COM4

STATEMENTS OF CONSOLIDATED COMPREHENSIVE INCOME (PARENTHETICAL) (Parentheticals) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Tax, Portion Attributable to Parent	$ 6	$ (1)	$ 6

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions		Dec. 31, 2015	Dec. 31, 2014
ASSETS
Cash and cash equivalents		$ 0	$ 2
Accounts receivable, less bad debt reserve of $19 million and $23 million, respectively		350	595
Accrued unbilled revenue		183	262
Accounts and notes receivable — affiliated companies		8	18
Inventory		213	252
Non-trading derivative assets		89	99
Prepaid expenses and other current assets		61	90
Total current assets		904	1,318
Property, Plant and Equipment, Net		4,258	3,810
Other Assets:
Goodwill		840	840
Non-trading derivative assets		36	32
Notes receivable — affiliated companies		363	363
Investment in unconsolidated affiliates		2,594	4,521
Other		158	160
Total other assets		3,991	5,916
Total Assets		9,153	11,044
Current Liabilities:
Short-term borrowings	[1]	40	53
Current portion of long-term debt	[1]	325	0
Accounts payable		307	528
Accounts and notes payable — affiliated companies		39	228
Taxes accrued		63	67
Interest accrued		36	36
Customer deposits		80	80
Non-trading derivative liabilities		11	19
Other		158	137
Total current liabilities		1,059	1,148
Other Liabilities:
Deferred income taxes, net		1,774	2,251
Non-trading derivative liabilities		5	1
Benefit obligations		89	111
Regulatory liabilities		734	669
Other		210	194
Total other liabilities		2,812	3,226
Long-Term Debt		$ 2,028	$ 2,469
Commitments and Contingencies (Note 13)
Stockholder’s Equity		$ 3,254	$ 4,201
Total Liabilities And Stockholder’s Equity		$ 9,153	$ 11,044
[1]	Includes amounts due or exchangeable within one year of the date noted.

Balance Sheets Parenthetical (P

Balance Sheets Parenthetical (Parentheticals) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Balance Sheets Parenthetical [Abstract]
Allowance for Doubtful Accounts Receivable, Current	$ 19	$ 23

STATEMENTS OF CONSOLIDATED CASH

STATEMENTS OF CONSOLIDATED CASH FLOWS - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash Flows from Operating Activities:
Net income (loss)	$ (912)	$ 323	$ 64
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	227	206	230
Amortization of deferred financing costs	9	9	11
Deferred income taxes	(542)	178	357
Write-down of natural gas inventory	4	8	4
Equity in (earnings) losses of unconsolidated affiliates, net of distributions	1,779	(2)	(58)
Changes in other assets and liabilities:
Accounts receivable and unbilled revenues, net	347	7	(220)
Accounts receivable/payable–affiliated companies	9	1	(2)
Inventory	35	(81)	(10)
Taxes receivable	0	18	(18)
Accounts payable	(221)	17	110
Fuel cost recovery	43	(41)	108
Interest and taxes accrued	58	(3)	33
Non-trading derivatives, net	(6)	(34)	4
Margin deposits, net	(4)	(79)	16
Other current assets	13	8	3
Other current liabilities	(11)	(6)	5
Other assets	(6)	(11)	(18)
Other liabilities	(5)	11	6
Other, net	(1)	6	10
Net cash provided by operating activities	816	535	635
Cash Flows from Investing Activities:
Capital expenditures	(606)	(512)	(495)
Distributions from unconsolidated affiliates in excess of cumulative earnings	148	0	0
Investment in unconsolidated affiliates	0	(1)	0
Cash contribution to Enable	0	0	(38)
Other, net	6	0	(3)
Net cash used in investing activities	(452)	(513)	(536)
Cash Flows from Financing Activities:
Increase (decrease) in short-term borrowings, net	(13)	10	5
Proceeds from (payments of) commercial paper, net	(122)	223	118
Proceeds from long-term debt	0	0	1,050
Payments of long-term debt	0	0	(525)
Cash paid for debt exchange	0	0	(5)
Dividends to parent	(43)	(405)	0
Increase (decrease) in notes payable–affiliated companies	(188)	150	(741)
Other, net	0	1	(1)
Net cash used in financing activities	(366)	(21)	(99)
Net Increase (Decrease) in Cash and Cash Equivalents	(2)	1	0
Cash and Cash Equivalents at Beginning of the Year	2	1	1
Cash and Cash Equivalents at End of the Year	0	2	1
Cash Payments:
Interest, net of capitalized interest	125	128	148
Income taxes (refunds), net	6	(1)	(5)
Non-cash transactions:
Accounts payable related to capital expenditures	37	37	21
Formation of Enable	0	0	4,252
Exercise of SESH put to Enable	$ 1	$ 196	$ 0

STATEMENTS OF CONSOLIDATED STOC

STATEMENTS OF CONSOLIDATED STOCKHOLDER'S EQUITY - USD ($) $ in Millions	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Defined Benefit Plans Adjustment [Member]	Accumulated Other Comprehensive Loss [Member]
Balance (in shares) at Dec. 31, 2012		1,000
Balance at Dec. 31, 2012		$ 0	$ 2,416	$ 1,801
Adjustments to Additional Paid in Capital, Other			0
Net income (loss)	$ 64			64
Cash Dividends Paid to Parent Company				0
Balance at Dec. 31, 2013	4,286	$ 0	2,416	1,865	$ 5	$ 5
Balance (in shares) at Dec. 31, 2013		1,000
Adjustments to Additional Paid in Capital, Other			1
Net income (loss)	323			323
Cash Dividends Paid to Parent Company				(405)
Balance at Dec. 31, 2014	4,201	$ 0	2,417	1,783	1	1
Balance (in shares) at Dec. 31, 2014		1,000
Adjustments to Additional Paid in Capital, Other			0
Net income (loss)	(912)			(912)
Cash Dividends Paid to Parent Company				(43)
Balance at Dec. 31, 2015	$ 3,254	$ 0	$ 2,417	$ 828	$ 9	$ 9
Balance (in shares) at Dec. 31, 2015		1,000

Background

Background	12 Months Ended
	Dec. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Background and Basis of Presentation	Background CenterPoint Energy Resources Corp. (CERC Corp. and, together with its subsidiaries, CERC), which owns and operates natural gas distribution systems (NGD). A wholly-owned subsidiary of CERC Corp. offers variable and fixed-price physical natural gas supplies primarily to commercial and industrial customers and electric and gas utilities. As of December 31, 2015 , CERC Corp. also owned approximately 55.4% of the limited partner interests in Enable, which owns, operates and develops natural gas and crude oil infrastructure assets. CERC Corp. is an indirect, wholly-owned subsidiary of CenterPoint Energy, Inc. (CenterPoint Energy), a public utility holding company. For a description of CERC’s reportable business segments, see Note 15.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2015
Significant Accounting Policies [Abstract]
Significant Accounting Policies [Text Block]	Summary of Significant Accounting Policies (a) Use of Estimates The preparation of financial statements in conformity with generally accepted accounting principles requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. (b) Principles of Consolidation The accounts of CERC Corp. and its wholly-owned and majority owned subsidiaries are included in CERC’s consolidated financial statements. All intercompany transactions and balances are eliminated in consolidation. CERC uses the equity method of accounting for investments in entities in which CERC has an ownership interest between 20% and 50% and exercises significant influence. CERC also uses the equity method for investments in which it has ownership percentages greater than 50%, when it exercises significant influence, does not have control and is not considered the primary beneficiary, if applicable. In May 2013, CenterPoint Energy, OGE Energy Corp. (OGE) and affiliates of ArcLight Capital Partners, LLC (ArcLight), formed Enable as a private limited partnership. CenterPoint Energy has the ability to significantly influence the operating and financial policies of, but not solely control, Enable and, accordingly, recorded an equity method investment, at the historical costs of net assets contributed. Under the equity method, CERC adjusts its investment in Enable each period for contributions made, distributions received, CERC’s share of Enable’s comprehensive income and accretion of basis differences, as appropriate. CERC evaluates its equity method investments for impairment when events or changes in circumstances indicate there is a loss in value of the investment that is other than a temporary decline. CERC’s investment in Enable is considered to be a variable interest entity (VIE) because the power to direct the activities that most significantly impact Enable’s economic performance does not reside with the holders of equity investment at risk. However, CERC is not considered the primary beneficiary of Enable since it does not have the power to direct the activities of Enable that are considered most significant to the economic performance of Enable. As of December 31, 2015, CERC Corp. and OGE held approximately 55.4% and 26.3% , respectively, of the limited partner interests in Enable. Enable is controlled jointly by CERC Corp. and OGE, and each own 50% of the management rights in the general partner of Enable. As of December 31, 2015, CERC Corp. and OGE also own 40% and 60% , respectively, of the incentive distribution rights held by the general partner of Enable. Enable is expected to pay a minimum quarterly distribution of $0.2875 per unit on its outstanding units to the extent it has sufficient cash from operations after establishment of cash reserves and payment of fees and expenses, including payments to its general partner and its affiliates, within 45 days after the end of each quarter. If cash distributions to Enable’s unitholders exceed $0.330625 per unit in any quarter, the general partner will receive increasing percentages or incentive distributions rights, up to 50% , of the cash Enable distributes in excess of that amount. In certain circumstances the general partner of Enable will have the right to reset the minimum quarterly distribution and the target distribution levels at which the incentive distributions receive increasing percentages to higher levels based on Enable’s cash distributions at the time of the exercise of this reset election. Other investments, excluding marketable securities, are carried at cost. (c) Revenues CERC records revenue for natural gas sales and services under the accrual method and these revenues are recognized upon delivery to customers. Natural gas sales not billed by month-end are accrued based upon estimated purchased gas volumes, estimated lost and unaccounted for gas and currently effective tariff rates. (d) Long-lived Assets and Intangibles CERC records property, plant and equipment at historical cost. CERC expenses repair and maintenance costs as incurred. CERC periodically evaluates long-lived assets, including property, plant and equipment and specifically identifiable intangibles, when events or changes in circumstances indicate that the carrying value of these assets may not be recoverable. The determination of whether an impairment has occurred is based on an estimate of undiscounted cash flows attributable to the assets, compared to the carrying value of the assets. (e) Regulatory Assets and Liabilities CERC applies the guidance for accounting for regulated operations to the Natural Gas Distribution business segment. CERC’s rate-regulated subsidiaries may collect revenues subject to refund pending final determination in rate proceedings. In connection with such revenues, estimated rate refund liabilities are recorded which reflect management’s current judgment of the ultimate outcomes of the proceedings. CERC’s rate-regulated businesses recognize removal costs as a component of depreciation expense in accordance with regulatory treatment. As of December 31, 2015 and 2014 , these removal costs of $632 million and $605 million , respectively, are classified as regulatory liabilities in the Consolidated Balance Sheets. In addition, a portion of the amount of removal costs that relate to asset retirement obligations has been reclassified from a regulatory liability to an asset retirement liability in accordance with accounting guidance for asset retirement obligations. (f) Depreciation and Amortization Expense Depreciation and amortization is computed using the straight-line method based on economic lives or regulatory-mandated recovery periods. Amortization expense includes amortization of regulatory assets and other intangibles. (g) Capitalization of Interest and Allowance for Funds Used During Construction Interest and allowance for funds used during construction (AFUDC) are capitalized as a component of projects under construction and are amortized over the assets’ estimated useful lives once the assets are placed in service. AFUDC represents the composite interest cost of borrowed funds and a reasonable return on the equity funds used for construction for subsidiaries that apply the guidance for accounting for regulated operations. During 2015 , 2014 and 2013 , CERC capitalized interest and AFUDC of $2 million , $1 million and $1 million , respectively. (h) Income Taxes CERC is included in the consolidated income tax returns of CenterPoint Energy. CERC calculates its income tax provision on a separate return basis under a tax sharing agreement with CenterPoint Energy. CERC uses the asset and liability method of accounting for deferred income taxes in accordance with accounting guidance for income taxes. Deferred income tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases. A valuation allowance is established against deferred tax assets for which management believes realization is not considered to be more likely than not. Current federal and certain state income taxes are payable to or receivable from CenterPoint Energy. CERC recognizes interest and penalties as a component of income tax expense. (i) Accounts Receivable and Allowance for Doubtful Accounts Accounts receivable are recorded at the invoiced amount and do not bear interest. It is the policy of management to review the outstanding accounts receivable monthly, as well as the bad debt write-offs experienced in the past, and establish an allowance for doubtful accounts. Account balances are charged off against the allowance when management determines it is probable the receivable will not be recovered. The provision for doubtful accounts in CERC’s Statements of Consolidated Income for 2015 , 2014 and 2013 was $19 million , $20 million and $20 million , respectively. (j) Inventory Inventory consists principally of materials and supplies and natural gas. Materials and supplies are valued at the lower of average cost or market. Materials and supplies are recorded to inventory when purchased and subsequently charged to expense or capitalized to plant when installed. Natural gas inventories of CERC’s Energy Services business segment are valued at the lower of average cost or market. Natural gas inventories of CERC’s Natural Gas Distribution business segment are primarily valued at weighted average cost. During 2015 , 2014 and 2013 , CERC recorded $4 million , $8 million and $4 million , respectively, in write-downs of natural gas inventory to the lower of average cost or market. December 31, 2015 2014 (in millions) Materials and supplies $ 45 $ 41 Natural gas 168 211 Total inventory $ 213 $ 252 (k) Derivative Instruments CERC is exposed to various market risks. These risks arise from transactions entered into in the normal course of business. CERC utilizes derivative instruments such as physical forward contracts, swaps and options to mitigate the impact of changes in commodity prices and weather on its operating results and cash flows. Such derivatives are recognized in CERC’s Consolidated Balance Sheets at their fair value unless CERC elects the normal purchase and sales exemption for qualified physical transactions. A derivative may be designated as a normal purchase or normal sale if the intent is to physically receive or deliver the product for use or sale in the normal course of business. CenterPoint Energy has a Risk Oversight Committee composed of corporate and business segment officers that oversees commodity price, weather and credit risk activities, including CERC’s marketing, risk management services and hedging activities. The committee’s duties are to establish CERC’s commodity risk policies, allocate board-approved commercial risk limits, approve the use of new products and commodities, monitor positions and ensure compliance with CERC’s risk management policies and procedures and limits established by CenterPoint Energy’s board of directors. CERC’s policies prohibit the use of leveraged financial instruments. A leveraged financial instrument, for this purpose, is a transaction involving a derivative whose financial impact will be based on an amount other than the notional amount or volume of the instrument. (l) Environmental Costs CERC expenses or capitalizes environmental expenditures, as appropriate, depending on their future economic benefit. CERC expenses amounts that relate to an existing condition caused by past operations that do not have future economic benefit. CERC records undiscounted liabilities related to these future costs when environmental assessments and/or remediation activities are probable and the costs can be reasonably estimated. (m) Statements of Consolidated Cash Flows For purposes of reporting cash flows, CERC considers cash equivalents to be short-term, highly-liquid investments with maturities of three months or less from the date of purchase. CERC considers distributions received from equity method investments which do not exceed cumulative equity in earnings subsequent to the date of investment to be a return on investment and classifies these distributions as operating activities in the Statements of Consolidated Cash Flows. CERC considers distributions received from equity method investments in excess of cumulative equity in earnings subsequent to the date of investment to be a return of investment and classifies these distributions as investing activities in the Statements of Consolidated Cash Flows. (n) New Accounting Pronouncements In February 2015, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update No. 2015-02, Consolidation (Topic 810): Amendments to the Consolidation Analysis (ASU 2015-02). ASU 2015 -02 changes the analysis that reporting organizations must perform to evaluate whether they should consolidate certain legal entities, such as limited partnerships. The changes include, among others, modification of the evaluation of whether limited partnerships and similar legal entities are variable interest entities (VIEs) or voting interest entities and elimination of the presumption that a general partner should consolidate a limited partnership. ASU 2015-02 does not amend the related party guidance for situations in which power is shared between two or more entities that hold interests in a VIE. ASU 2015 -02 is effective for fiscal years, and interim periods within those years, beginning after December 15, 2015. CERC does not believe that ASU 2015-02 will have a material impact on its financial position, results of operations, cash flows and disclosures. In April 2015, the FASB issued Accounting Standards Update No. 2015-03, Interest-Imputation of Interest (Subtopic 835-30): Simplifying the Presentation of Debt Issuance Cost (ASU 2015-03) . ASU 2015-03 requires that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts. The recognition and measurement guidance for debt issuance costs are not affected by ASU 2015-03. CERC will adopt ASU 2015-03 retrospectively on January 1, 2016, which will result in a reduction of both other long-term assets and long-term debt on its Consolidated Balance Sheets. CERC had debt issuance costs of $15 million and $18 million included in other long-term assets on its Consolidated Balance Sheets as of December 31, 2015 and 2014, respectively. In April 2015, the FASB issued Accounting Standards Update No. 2015-05, Intangibles-Goodwill and Other-Internal-Use Software ( Subtopic 350-40 ) (ASU 2015-05). ASU 2015-05 provides guidance to customers about whether a cloud computing arrangement includes a software license. If a cloud computing arrangement includes a software license, the customer should account for the software license element of the arrangement consistent with the acquisition of other software licenses. If a cloud computing arrangement does not include a software license, the customer should account for the arrangement as a service contract. The guidance will not change a customer’s accounting for service contracts. ASU 2015-05 is effective for fiscal years, and interim periods within the fiscal years, beginning after December 15, 2015 and may be adopted either prospectively or retrospectively. CERC will adopt ASU 2015-05 on January 1, 2016. CERC does not believe that ASU 2015-05 will have a material impact on its financial position, results of operations, cash flows and disclosures. In May 2014, the FASB issued Accounting Standards Update No. 2014-09, Revenue from Contracts with Customers (Topic 606) (ASU 2014-09), which supersedes most current revenue recognition guidance. ASU 2014-09 provides a comprehensive new revenue recognition model that requires revenue to be recognized in a manner that depicts the transfer of goods or services to a customer at an amount that reflects the consideration expected to be received in exchange for those goods or services. ASU 2014-09 was initially effective for fiscal years, and interim periods within those years, beginning after December 15, 2016. Early adoption is not permitted, and entities have the option of using either a full retrospective or a modified retrospective adoption approach. In August 2015, the FASB issued Accounting Standard Update No. 2015-14, Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date , which delays the effective date of ASU 2014-09 by one year. CERC is currently evaluating the impact that ASU 2014-09 will have on its financial position, results of operations, cash flows and disclosures, and will adopt ASU 2014-09 on January 1, 2018 as permitted by the new guidance. In July 2015, the FASB issued Accounting Standards Update No. 2015-11, Inventory (Topic 330) Simplifying the Measurement of Inventory (ASU 2015-11). ASU 2015-11 changes the subsequent measurement guidance for inventory accounted for using methods other than the last in, first out (LIFO) and Retail Inventory methods. Companies will subsequently measure inventory at the lower of cost and net realizable value. Net realizable value is the estimated selling price in the ordinary course of business, less reasonably predictable costs of completion, disposal, and transportation. Subsequent measurement is unchanged for inventory measured using LIFO or the retail inventory method. ASU 2015-11 is effective for fiscal years, and interim periods within those years, beginning after December 15, 2016, with early adoption permitted. CERC does not believe that ASU 2015-11 will have a material impact on its financial position, results of operations, cash flows and disclosures. In November 2015, the FASB issued Accounting Standards Update No. 2015-17, Income Taxes (Topic 740): Balance Sheet Classification of Deferred Taxes (ASU 2015-17). ASU 2015-17 requires deferred tax liabilities and assets be classified as noncurrent in a classified statement of financial position. CERC adopted ASU 2015-17 retrospectively starting with fiscal year 2015. As such, certain prior period amounts have been reclassified to conform to the current presentation. In the Consolidated Balance Sheet as of December 31, 2014, CERC reclassified $1 million from current deferred income tax assets to reduce deferred income taxes within non-current liabilities. See Note 12 for additional information. Management believes that other recently issued standards, which are not yet effective, will not have a material impact on CenterPoint Energy’s consolidated financial position, results of operations or cash flows upon adoption. (o) Other Current Assets and Liabilities Included in other current assets on the Consolidated Balance Sheets at December 31, 2015 and 2014 were $31 million and $19 million , respectively, of margin deposits and $12 million and $45 million , respectively of under-recovered gas cost. Included in other current liabilities on the Consolidated Balance Sheets at December 31, 2015 and 2014 were $55 million and $37 million , respectively, of over-recovered gas cost.

Property, Plant and Equipment

Property, Plant and Equipment	12 Months Ended
	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment Disclosure [Text Block]	Property, Plant and Equipment (a) Property, Plant and Equipment Property, plant and equipment includes the following: Weighted Average Useful Lives December 31, (Years) 2015 2014 (in millions) Natural Gas Distribution 32 $ 5,762 $ 5,235 Energy Services 27 86 84 Other property 10 50 45 Total 5,898 5,364 Accumulated depreciation and amortization: Natural Gas Distribution 1,575 1,493 Energy Services 34 31 Other property 31 30 Total accumulated depreciation and amortization 1,640 1,554 Property, plant and equipment, net $ 4,258 $ 3,810 (b) Depreciation and Amortization The following table presents depreciation and amortization expense for 2015 , 2014 and 2013 : Year Ended December 31, 2015 2014 2013 (in millions) Depreciation expense $ 211 $ 195 $ 218 Amortization expense 16 11 12 Total depreciation and amortization expense $ 227 $ 206 $ 230 (c) Asset Retirement Obligations A reconciliation of the changes in the asset retirement obligation (ARO) liability is as follows: December 31, 2015 2014 (in millions) Beginning balance $ 139 $ 101 Accretion expense 5 4 Revisions in estimates of cash flows 12 34 Ending balance $ 156 $ 139 CERC recorded AROs associated with the removal of asbestos and asbestos-containing material in its buildings. CERC also recorded AROs relating to gas pipelines abandoned in place. The estimates of future liabilities were developed using historical information, and where available, quoted prices from outside contractors. The increase of $12 million in the ARO from the revision of estimate in 2015 is primarily attributable to a reduction in the estimated service lives of steel and plastic pipe. The decrease of $34 million in the ARO from the revision of estimate in 2014 is primarily attributable to a reduction in the estimated service lives of steel and plastic pipe. There were no material additions or settlements during the years ended December 31, 2015 or 2014 .

Goodwill

Goodwill	12 Months Ended
	Dec. 31, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill Disclosure [Text Block]	Goodwill Goodwill by reportable business segment as of both December 31, 2015 and 2014 are as follows: (in millions) Natural Gas Distribution $ 746 Energy Services (1) 83 Other 11 Total $ 840 (1) Amounts presented are net of accumulated goodwill impairment charge of $252 million . CERC performs goodwill impairment tests at least annually and evaluates goodwill when events or changes in circumstances indicate that its carrying value may not be recoverable. The impairment evaluation for goodwill is performed by using a two-step process. In the first step, the fair value of each reporting unit is compared with the carrying amount of the reporting unit, including goodwill. The estimated fair value of the reporting unit is generally determined on the basis of discounted cash flows. If the estimated fair value of the reporting unit is less than the carrying amount of the reporting unit, then a second step must be completed to determine the amount of the goodwill impairment that should be recorded. In the second step, the implied fair value of the reporting unit’s goodwill is determined by allocating the reporting unit’s fair value to all of its assets and liabilities other than goodwill (including any unrecognized intangible assets) in a manner similar to a purchase price allocation. The resulting implied fair value of the goodwill that results from the application of this second step is then compared to the carrying amount of the goodwill and an impairment charge is recorded for the difference. CERC performed its annual goodwill impairment test in the third quarter of each of 2015 and 2014 and determined, based on the results of the first step, that no goodwill impairment charge was required for any reportable segment. Other intangibles were not material as of December 31, 2015 and 2014.

Regulatory Matters

Regulatory Matters	12 Months Ended
	Dec. 31, 2015
Regulatory Matters [Abstract]
Regulatory Matters	Regulatory Accounting The following is a list of regulatory assets/liabilities reflected on CERC’s Consolidated Balance Sheets as of December 31, 2015 and 2014 : December 31, 2015 2014 (in millions) Regulatory assets in other long-term assets (1) (2) $ 105 $ 103 Regulatory liabilities (734 ) (669 ) Net $ (629 ) $ (566 ) (1) Regulatory assets that are not earning a return were not material at December 31, 2015 or 2014 . (2) NGD’s actuarially determined pension and other postemployment expense in excess of the amount being recovered through rates is being deferred for rate making purposes. Deferred pension and other postemployment expenses of $5 million as of December 31, 2015 were not earning a return.

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2015
Compensation and Retirement Disclosure [Abstract]
Employee Benefit Plans	Employee Benefit Plans (a) Pension Plans Substantially all of CERC’s employees participate in CenterPoint Energy’s qualified non-contributory defined benefit pension plan. Under the cash balance formula, participants accumulate a retirement benefit based upon 5% of eligible earnings and accrued interest. CenterPoint Energy’s funding policy is to review amounts annually in accordance with applicable regulations in order to achieve adequate funding of projected benefit obligations. Pension expense is allocated to CERC based on covered employees. This calculation is intended to allocate pension costs in the same manner as a separate employer plan. Assets of the plan are not segregated or restricted by CenterPoint Energy’s participating subsidiaries. CERC recognized pension expense of $24 million , $27 million and $29 million for the years ended December 31, 2015 , 2014 and 2013 , respectively. In addition to the plan, CERC participates in CenterPoint Energy’s non-qualified benefit restoration plans, which allow participants to receive the benefits to which they would have been entitled under CenterPoint Energy’s non-contributory pension plan except for federally mandated limits on qualified plan benefits or on the level of compensation on which qualified plan benefits may be calculated. The expense associated with the non-qualified pension plan was $2 million for each of the years ended December 31, 2015 , 2014 and 2013 , respectively. (b) Savings Plan CERC participates in CenterPoint Energy’s qualified savings plan, which includes a cash or deferred arrangement under Section 401(k) of the Internal Revenue Code of 1986, as amended. Under the plan, participating employees may contribute a portion of their compensation, on a pre-tax or after-tax basis, generally up to a maximum of 50% of eligible compensation. CERC matches 100% of the first 6% of each employee’s compensation contributed. The matching contributions are fully vested at all times. Participating employees may elect to invest all (prior to January 1, 2016) or a portion of their contributions to the plan in CenterPoint Energy common stock, to have dividends reinvested in additional shares or to receive dividend payments in cash on any investment in CenterPoint Energy common stock, and to transfer all or part of their investment in CenterPoint Energy common stock to other investment options offered by the plan. Effective January 1, 2016 the savings plan was amended to limit the percentage of future contributions that could be invested in CenterPoint Energy common stock to 25% and to prohibit transfers of account balances where the transfer would result in more than 25% of a participant’s total account balance invested in CenterPoint Energy common stock. The savings plan has significant holdings of CenterPoint Energy common stock. As of December 31, 2015, 16,942,974 shares of CenterPoint Energy’s common stock were held by the savings plan, which represented approximately 17% of its investments. Given the concentration of the investments in CenterPoint Energy’s common stock, the savings plan and its participants have market risk related to this investment. CenterPoint Energy allocates to CERC the savings plan benefit expense related to CERC’s employees. Savings plan benefit expense was $14 million , $20 million and $19 million for the years ended December 31, 2015 , 2014 and 2013 , respectively. (c) Postretirement Benefits CERC’s employees participate in CenterPoint Energy’s plans, which provide certain healthcare and life insurance benefits for retired employees on both a contributory and non-contributory basis. Employees become eligible for these benefits if they have met certain age and service requirements at retirement, as defined in the plans. Under plan amendments effective in early 1999, healthcare benefits for future retirees were changed to limit employer contributions for medical coverage. Such benefit costs are accrued over the active service period of employees. CERC is required to fund a portion of its obligations in accordance with rate orders. All other obligations are funded on a pay-as-you-go basis. The net postretirement benefit cost includes the following components: Year Ended December 31, 2015 2014 2013 (in millions) Service cost — benefits earned during the period $ 1 $ 1 $ 1 Interest cost on accumulated benefit obligation 5 5 5 Expected return on plan assets (1 ) (1 ) (1 ) Amortization of prior service cost 1 1 1 Amortization of net loss 1 1 2 Net postretirement benefit cost $ 7 $ 7 $ 8 CERC used the following assumptions to determine net postretirement benefit costs: Year Ended December 31, 2015 2014 2013 Discount rate 3.90 % 4.75 % 3.90 % Expected return on plan assets 4.05 % 3.10 % 3.10 % In determining net periodic benefits cost, CERC uses fair value, as of the beginning of the year, as its basis for determining expected return on plan assets. Following are reconciliations of CERC’s beginning and ending balances of its postretirement benefit plan’s benefit obligation, plan assets and funded status for 2015 and 2014 . The measurement dates for plan assets and obligations were December 31, 2015 and 2014 . December 31, 2015 2014 (in millions, except for actuarial assumptions) Change in Benefit Obligation Accumulated benefit obligation, beginning of year $ 126 $ 116 Service cost 1 1 Interest cost 5 5 Benefits paid (12 ) (13 ) Participant contributions 4 4 Medicare reimbursement 1 2 Plan amendment (5 ) 1 Curtailment — (2 ) Actuarial (gain) loss (19 ) 12 Accumulated benefit obligation, end of year $ 101 $ 126 Change in Plan Assets Plan assets, beginning of year $ 26 $ 26 Benefits paid (12 ) (13 ) Employer contributions 7 8 Participant contributions 4 4 Actual investment return — 1 Plan assets, end of year $ 25 $ 26 Amounts Recognized in Balance Sheets Current liabilities-other $ (6 ) $ (7 ) Other liabilities-benefit obligations (70 ) (93 ) Net liability, end of year $ (76 ) $ (100 ) Actuarial Assumptions Discount rate 4.35 % 3.90 % Expected long-term return on assets 3.95 % 4.00 % Healthcare cost trend rate assumed for the next year - Pre 65 6.00 % 7.25 % Healthcare cost trend rate assumed for the next year - Post 65 5.50 % 8.50 % Prescription cost trend rate assumed for the next year 11.00 % 6.50 % Rate to which the cost trend rate is assumed to decline (ultimate trend rate) 5.00 % 5.00 % Year that the healthcare rate reaches the ultimate trend rate 2024 2024 Year that the prescription drug rate reaches the ultimate trend rate 2024 2024 The discount rate assumption was determined by matching the projected cash flows of CenterPoint Energy’s plans against a hypothetical yield curve of high-quality corporate bonds represented by a series of annualized individual discount rates from one-half to 99 years . The expected rate of return assumption was developed using the targeted asset allocation of CenterPoint Energy’s plans and the expected return for each asset class, based on the long-term capital market assumptions, adjusted for investment fees and diversification effects, in addition to expected inflation. For measurement purposes, medical costs are assumed to increase to 6.00% and 5.50% for the pre-65 and post-65 retirees during 2016 , respectively, and the prescription cost is assumed to increase 11.00% during 2016 , after which these rates decrease until reaching the ultimate trend rate of 5.00% in 2024. CERC’s changes in accumulated comprehensive income (loss) related to postretirement and other postemployment plans are as follows: Year Ended December 31, 2015 2014 (in millions) Beginning Balance $ 1 $ 5 Other comprehensive income (loss) before reclassifications (1) 13 (5 ) Amounts reclassified from accumulated other comprehensive income: Actuarial gains (2) 1 — Total reclassifications from accumulated other comprehensive income 1 — Tax expense (6 ) 1 Net current period other comprehensive income (loss) 8 (4 ) Ending Balance $ 9 $ 1 (1) Total other comprehensive income related to the re-measurement of pension, postretirement and other postemployment plans. (2) These accumulated other comprehensive components are included in the computation of net periodic cost. Amounts recognized in accumulated other comprehensive (income) loss consist of the following: December 31, 2015 2014 (in millions) Unrecognized actuarial loss $ 3 $ 13 Unrecognized prior service cost (credit) (1 ) 2 Total recognized in accumulated other comprehensive loss 2 15 Less: deferred tax benefit (1) (11 ) (16 ) Net amount recognized in accumulated other comprehensive income $ (9 ) $ (1 ) (1) CERC’s postretirement benefit obligation is reduced by the impact of previously non-taxable government subsidies under the Medicare Prescription Drug Act. Because the subsidies were non-taxable, the temporary difference used in measuring the deferred tax impact was determined on the unrecognized losses excluding such subsidies. The changes in plan assets and benefit obligations recognized in other comprehensive loss during 2015 are as follows: Postretirement Benefits (in millions) Net loss $ 10 Amortization of prior service cost 3 Total recognized in other comprehensive loss $ 13 The total expense recognized in net periodic costs and other comprehensive gains was $2 million for postretirement benefits for the year ended December 31, 2015 . CERC does not expect to recognize any amounts in accumulated other comprehensive loss as components of net periodic benefit cost during 2016 . Assumed healthcare cost trend rates have a significant effect on the reported amounts for CERC’s postretirement benefit plans. A 1% change in the assumed healthcare cost trend rate would have the following effects: 1% Increase 1% Decrease (in millions) Effect on the postretirement benefit obligation $ 2 $ 2 Effect on the total of service and interest cost — — In managing the investments associated with the postretirement benefit plan, CERC’s objective is to preserve and enhance the value of plan assets while maintaining an acceptable level of volatility. These objectives are expected to be achieved through an investment strategy that manages liquidity requirements while maintaining a long-term horizon in making investment decisions and efficient and effective management of plan assets. As part of the investment strategy discussed above, CERC maintained the following asset allocation ranges for its postretirement benefit plan as of December 31, 2015 : U.S. equity 15–25% International equity 2–12% Fixed income 68–78% Cash 0–2% The fair values of CERC’s postretirement plan assets at December 31, 2015 and 2014 , by asset category are as follows: Fair Value Measurements as of December 31, 2015 Total Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) (in millions) Mutual funds (1) $ 25 $ 25 $ — $ — Total $ 25 $ 25 $ — $ — (1) 70% of the amount invested in mutual funds was in fixed income securities; 23% was in U.S. equities and 7% was in international equities. Fair Value Measurements as of December 31, 2014 Total Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) (in millions) Mutual funds (1) $ 26 $ 26 $ — $ — Total $ 26 $ 26 $ — $ — (1) 70% of the amount invested in mutual funds was in fixed income securities; 23% was in U.S. equities and 7% was in international equities. CERC expects to contribute $6 million to its postretirement benefits plan in 2016 . The following benefit payments are expected to be made by the postretirement benefit plan: Postretirement Benefit Plan Benefit Payments Medicare Subsidy Receipts (in millions) 2016 $ 10 $ (2 ) 2017 10 (2 ) 2018 10 (2 ) 2019 11 (2 ) 2020 11 (3 ) 2021-2025 56 (17 ) (d) Postemployment Benefits CERC participates in CenterPoint Energy’s plan that provides postemployment benefits for former or inactive employees, their beneficiaries and covered dependents, after employment but before retirement (primarily healthcare and life insurance benefits for participants in the long-term disability plan). CERC recorded postemployment benefit expense of $4 million , $2 million and $1 million for the years ended December 31, 2015 , 2014 and 2013 , respectively. Amounts relating to postemployment benefits included in Benefit Obligations in the accompanying Consolidated Balance Sheets as of December 31, 2015 and 2014 , were $14 million and $12 million , respectively. (e) Other Non-Qualified Plans CERC participates in CenterPoint Energy’s deferred compensation plans that provide benefits payable to directors, officers and certain key employees or their designated beneficiaries at specified future dates, upon termination, retirement or death. Benefit payments are made from the general assets of CERC. During 2015 , 2014 and 2013 , the benefit expense relating to these plans was less than $1 million each year. Amounts relating to deferred compensation plans included in Benefit Obligations in the accompanying Consolidated Balance Sheets as of both December 31, 2015 and 2014 were $3 million . (f) Other Employee Matters As of December 31, 2015 , approximately 34% of CERC’s employees were covered by collective bargaining agreements. Two collective bargaining agreements with Professional Employees International Union Local 12, which collectively cover approximately 4% of CERC’s employees, are scheduled to expire in March and May of 2016. CERC believes it has good relationships with these bargaining units and expects to negotiate new agreements in 2016.

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2015
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions CERC participates in a “money pool” through which it can borrow or invest on a short-term basis. Funding needs are aggregated and external borrowing or investing is based on the net cash position. The net funding requirements of the money pool are expected to be met with borrowings under CenterPoint Energy’s revolving credit facility or the sale of CenterPoint Energy’s commercial paper. CERC had money pool borrowings of $-0- and $188 million as of December 31, 2015 and 2014 , respectively, which are included in accounts and notes payable — affiliated companies in the Consolidated Balance Sheets. For the years ended December 31, 2015, 2014 and 2013, CERC had affiliate related net interest income (expense) of less than $(1) million , less than $1 million and $(2) million , respectively. CenterPoint Energy provides some corporate services to CERC. The costs of services have been charged directly to CERC using methods that management believes are reasonable. These methods include negotiated usage rates, dedicated asset assignment and proportionate corporate formulas based on operating expenses, assets, gross margin, employees and a composite of assets, gross margin and employees. CenterPoint Houston provides a number of services to CERC. These services are billed at actual cost, either directly or as an allocation, and include fleet services, shop services, geographic services, surveying and right-of-way, radio communications, data circuit management and field operations. Additionally, CERC provides certain services to CenterPoint Houston. These services are billed at actual cost, either directly or as an allocation and include line locating and other miscellaneous services. These charges are not necessarily indicative of what would have been incurred had CERC not been an affiliate of CenterPoint Energy. Amounts charged to and from CERC for these services were as follows and are included primarily in operation and maintenance expenses: Year Ended December 31, 2015 2014 2013 (in millions) Corporate service charges $ 118 $ 115 $ 105 Charges from CenterPoint Houston for services provided 18 17 21 Billings to CenterPoint Houston for services provided (6 ) (5 ) (9 ) $ 130 $ 127 $ 117 Dividends of $43 million and $405 million were paid to the parent in 2015 and 2014 . No dividends were paid to the parent in 2013 . See Note 10 for related party transactions with Enable.

Derivative Instruments

Derivative Instruments	12 Months Ended
	Dec. 31, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments	Derivative Instruments CERC is exposed to various market risks. These risks arise from transactions entered into in the normal course of business. CERC utilizes derivative instruments such as physical forward contracts, swaps and options to mitigate the impact of changes in commodity prices and weather on its operating results and cash flows. (a) Non-Trading Activities Derivative Instruments. CERC enters into certain derivative instruments to manage physical commodity price risk and does not engage in proprietary or speculative commodity trading. These financial instruments do not qualify or are not designated as cash flow or fair value hedges. Weather Hedges. CERC has weather normalization or other rate mechanisms that mitigate the impact of weather on NGD in Arkansas, Louisiana, Mississippi, Minnesota and Oklahoma. NGD in Texas does not have such mechanisms, although fixed customer charges are historically higher in Texas compared to NGD’s other jurisdictions. As a result, fluctuations from normal weather may have a positive or negative effect on NGD’s results in Texas. CERC has historically entered into heating-degree day swaps for certain NGD jurisdictions to mitigate the effect of fluctuations from normal weather on its results of operations and cash flows for the winter heating season, which contained a bilateral dollar cap of $16 million in both 2013–2014 and 2014–2015. However, NGD did not enter into heating-degree day swaps for the 2015–2016 winter season as a result of NGD’s Minnesota division implementing a full decoupling pilot in July 2015. The swaps are based on 10 -year normal weather. During the years ended December 31, 2015 , 2014 and 2013 , CERC recognized losses of $4 million , $10 million and $16 million , respectively, related to these swaps. Weather hedge gains and losses are included in revenues in the Statements of Consolidated Income. (b) Derivative Fair Values and Income Statement Impacts The following tables present information about CERC’s derivative instruments and hedging activities. The first four tables provide a balance sheet overview of CERC’s Derivative Assets and Liabilities as of December 31, 2015 and 2014 , while the last table provides a breakdown of the related income statement impacts for the years ending December 31, 2015 and 2014 . Fair Value of Derivative Instruments December 31, 2015 Total derivatives not designated as hedging instruments Balance Sheet Location Derivative Assets Fair Value Derivative Liabilities Fair Value (in millions) Natural gas derivatives (1) (2) (3) Current Assets: Non-trading derivative assets $ 90 $ 2 Natural gas derivatives (1) (2) (3) Other Assets: Non-trading derivative assets 36 — Natural gas derivatives (1) (2) (3) Current Liabilities: Non-trading derivative liabilities 10 60 Natural gas derivatives (1) (2) (3) Other Liabilities: Non-trading derivative liabilities 4 25 Total $ 140 $ 87 (1) The fair value shown for natural gas contracts is comprised of derivative gross volumes totaling 767 billion cubic feet (Bcf) or a net 112 Bcf long position. Of the net long position, basis swaps constitute 133 Bcf. (2) Natural gas contracts are presented on a net basis in the Consolidated Balance Sheets. Natural gas contracts are subject to master netting arrangements. This netting applies to all undisputed amounts due or past due and causes derivative assets (liabilities) to be ultimately presented net in a liability (asset) account within the Consolidated Balance Sheets. The net of total non-trading derivative assets and liabilities was a $109 million asset as shown on CERC’s Consolidated Balance Sheets (and as detailed in the table below), and was comprised of the natural gas contracts derivative assets and liabilities separately shown above offset by collateral netting of $56 million . (3) Derivative Assets and Derivative Liabilities include no material amounts related to physical forward transactions with Enable. Offsetting of Natural Gas Derivative Assets and Liabilities December 31, 2015 Gross Amounts Recognized (1) Gross Amounts Offset in the Consolidated Balance Sheets Net Amount Presented in the Consolidated Balance Sheets (2) (in millions) Current Assets: Non-trading derivative assets $ 100 $ (11 ) $ 89 Other Assets: Non-trading derivative assets 40 (4 ) 36 Current Liabilities: Non-trading derivative liabilities (62 ) 51 (11 ) Other Liabilities: Non-trading derivative liabilities (25 ) 20 (5 ) Total $ 53 $ 56 $ 109 (1) Gross amounts recognized include some derivative assets and liabilities that are not subject to master netting arrangements. (2) The derivative assets and liabilities on the Consolidated Balance Sheets exclude accounts receivable or accounts payable that, should they exist, could be used as offsets to these balances in the event of a default. Fair Value of Derivative Instruments December 31, 2014 Total derivatives not designated as hedging instruments Balance Sheet Location Derivative Assets Fair Value Derivative Liabilities Fair Value (in millions) Natural gas derivatives (1) (2) (3) Current Assets: Non-trading derivative assets $ 101 $ 1 Natural gas derivatives (1) (2) (3) Other Assets: Non-trading derivative assets 32 — Natural gas derivatives (1) (2) (3) Current Liabilities: Non-trading derivative liabilities 14 83 Natural gas derivatives (1) (2) (3) Other Liabilities: Non-trading derivative liabilities 2 18 Total $ 149 $ 102 (1) The fair value shown for natural gas contracts is comprised of derivative gross volumes totaling 804 Bcf or a net 60 Bcf long position. Of the net long position, basis swaps constitute 127 Bcf. (2) Natural gas contracts are presented on a net basis in the Consolidated Balance Sheets. Natural gas contracts are subject to master netting arrangements. This netting applies to all undisputed amounts due or past due and causes derivative assets (liabilities) to be ultimately presented net in a liability (asset) account within the Consolidated Balance Sheets. The net of total non-trading derivative assets and liabilities was a $111 million asset as shown on CERC’s Consolidated Balance Sheets (and as detailed in the table below), and was comprised of the natural gas contracts derivative assets and liabilities separately shown above, offset by collateral netting of $64 million . (3) Derivative Assets and Derivative Liabilities include no material amounts related to physical forward transactions with Enable. Offsetting of Natural Gas Derivative Assets and Liabilities December 31, 2014 Gross Amounts Recognized (1) Gross Amounts Offset in the Consolidated Balance Sheets Net Amount Presented in the Consolidated Balance Sheets (2) (in millions) Current Assets: Non-trading derivative assets $ 115 $ (16 ) $ 99 Other Assets: Non-trading derivative assets 34 (2 ) 32 Current Liabilities: Non-trading derivative liabilities (84 ) 65 (19 ) Other Liabilities: Non-trading derivative liabilities (18 ) 17 (1 ) Total $ 47 $ 64 $ 111 (1) Gross amounts recognized include some derivative assets and liabilities that are not subject to master netting arrangements. (2) The derivative assets and liabilities on the Consolidated Balance Sheets exclude accounts receivable or accounts payable that, should they exist, could be used as offsets to these balances in the event of a default. For CERC’s price stabilization activities of the Natural Gas Distribution business segment, the settled costs of derivatives are ultimately recovered through purchased gas adjustments. Accordingly, the net unrealized gains and losses associated with these contracts are recorded as net regulatory assets. Realized and unrealized gains and losses on other derivatives are recognized in the Statements of Consolidated Income as revenue for retail sales derivative contracts and as natural gas expense for financial natural gas derivatives and non-retail related physical natural gas derivatives. Income Statement Impact of Derivative Activity Year Ended December 31, Total derivatives not designated as hedging instruments Income Statement Location 2015 2014 2013 (in millions) Natural gas derivatives Gains (Losses) in Revenue $ 134 $ 35 $ 11 Natural gas derivatives (1) Gains (Losses) in Expense: Natural Gas (105 ) 11 10 Total $ 29 $ 46 $ 21 (1) The Gains (Losses) in Expense: Natural Gas includes $-0- and $2 million during the years ended December 31, 2015 and 2014 , respectively, related to physical forwards purchased from Enable. (c) Credit Risk Contingent Features CERC enters into financial derivative contracts containing material adverse change provisions. These provisions could require CERC to post additional collateral if the Standard & Poor’s Ratings Services or Moody’s Investors Service, Inc. credit ratings of CERC are downgraded. The total fair value of the derivative instruments that contain credit risk contingent features that are in a net liability position at December 31, 2015 and 2014 was $3 million and $2 million , respectively. CERC posted no assets as collateral towards derivative instruments that contain credit risk contingent features at either December 31, 2015 or 2014 . If all derivative contracts (in a net liability position) containing credit risk contingent features were triggered at both December 31, 2015 and 2014 , $2 million of additional assets would be required to be posted as collateral. (d) Credit Quality of Counterparties In addition to the risk associated with price movements, credit risk is also inherent in CERC’s non-trading derivative activities. Credit risk relates to the risk of loss resulting from non-performance of contractual obligations by a counterparty. The following table shows the composition of counterparties to the non-trading derivative assets of CERC as of December 31, 2015 and 2014 : December 31, 2015 December 31, 2014 Investment Grade(1) Total Investment Grade(1) Total (in millions) Energy marketers $ 4 $ 10 $ 2 $ 4 Financial institutions — — — — End users (2) 2 115 2 127 Total $ 6 $ 125 $ 4 $ 131 (1) “Investment grade” is primarily determined using publicly available credit ratings, and considers credit support (including parent company guarantees) and collateral (including cash and standby letters of credit). For unrated counterparties, CERC determines a synthetic credit rating by performing financial statement analysis, and considers contractual rights and restrictions and collateral. (2) End users are comprised primarily of customers who have contracted to fix the price of a portion of their physical gas requirements for future periods.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2015
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements Assets and liabilities that are recorded at fair value in the Consolidated Balance Sheets are categorized based upon the level of judgment associated with the inputs used to measure their value. Hierarchical levels, as defined below and directly related to the amount of subjectivity associated with the inputs to fair valuations of these assets and liabilities, are as follows: Level 1: Inputs are unadjusted quoted prices in active markets for identical assets or liabilities at the measurement date. The types of assets carried at Level 1 fair value generally are exchange-traded derivatives and equity securities. Level 2: Inputs, other than quoted prices included in Level 1, are observable for the asset or liability, either directly or indirectly. Level 2 inputs include quoted prices for similar instruments in active markets, and inputs other than quoted prices that are observable for the asset or liability. Fair value assets and liabilities that are generally included in this category are derivatives with fair values based on inputs from actively quoted markets. A market approach is utilized to value CERC’s Level 2 assets or liabilities. Level 3: Inputs are unobservable for the asset or liability, and include situations where there is little, if any, market activity for the asset or liability. Unobservable inputs reflect CERC’s judgments about the assumptions market participants would use in pricing the asset or liability since limited market data exists. CERC develops these inputs based on the best information available, including CERC’s own data. A market approach is utilized to value CERC’s Level 3 assets or liabilities. At December 31, 2015 , CERC’s Level 3 assets and liabilities are comprised of physical forward contracts and options. Level 3 physical forward contracts are valued using a discounted cash flow model which includes illiquid forward price curve locations (ranging from $1.36 to $3.29 per one million British thermal units (Btu)) as an unobservable input. Level 3 options are valued through Black-Scholes (including forward start) option models which include option volatilities (ranging from 0 to 82% ) as an unobservable input. CERC’s Level 3 derivative assets and liabilities consist of both long and short positions (forwards and options) and their fair value is sensitive to forward prices and volatilities. If forward prices decrease, CERC’s long forwards lose value whereas its short forwards gain in value. If volatility decreases, CERC’s long options lose value whereas its short options gain in value. CERC determines the appropriate level for each financial asset and liability on a quarterly basis and recognizes transfers between levels at the end of the reporting period. For the year ended December 31, 2015 , there were no transfers between Level 1 and 2. CERC also recognizes purchases of Level 3 financial assets and liabilities at their fair market value at the end of the reporting period. The following tables present information about CERC’s assets and liabilities (including derivatives that are presented net) measured at fair value on a recurring basis as of December 31, 2015 and 2014 , and indicate the fair value hierarchy of the valuation techniques utilized by CERC to determine such fair value. Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Netting Adjustments (1) Balance as of December 31, 2015 (in millions) Assets Corporate equities $ 2 $ — $ — $ — $ 2 Investments, including money market funds 11 — — — 11 Natural gas derivatives (2) 4 115 21 (15 ) 125 Total assets $ 17 $ 115 $ 21 $ (15 ) $ 138 Liabilities Natural gas derivatives (2) $ 13 $ 65 $ 9 $ (71 ) $ 16 Total liabilities $ 13 $ 65 $ 9 $ (71 ) $ 16 (1) Amounts represent the impact of legally enforceable master netting arrangements that allow CERC to settle positive and negative positions and also include cash collateral of $56 million posted with the same counterparties. (2) Natural gas derivatives include no material amounts related to physical forward transactions with Enable. Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Netting Adjustments (1) Balance as of December 31, 2014 (in millions) Assets Corporate equities $ 2 $ — $ — $ — $ 2 Investments, including money market funds 11 — — — 11 Natural gas derivatives (2) 7 122 20 (18 ) 131 Total assets $ 20 $ 122 $ 20 $ (18 ) $ 144 Liabilities Natural gas derivatives $ 22 $ 77 $ 3 $ (82 ) $ 20 Total liabilities $ 22 $ 77 $ 3 $ (82 ) $ 20 (1) Amounts represent the impact of legally enforceable master netting arrangements that allow CERC to settle positive and negative positions and also include cash collateral of $64 million posted with the same counterparties. (2) Natural gas derivatives include no material amounts related to physical forward transactions with Enable. The following tables present additional information about assets or liabilities, including derivatives that are measured at fair value on a recurring basis for which CERC has utilized Level 3 inputs to determine fair value: Fair Value Measurements Using Significant Unobservable Inputs (Level 3) Derivative assets and liabilities, net Year Ended December 31, 2015 2014 2013 (in millions) Beginning balance $ 17 $ 3 $ 2 Total gains 7 14 3 Total settlements (12 ) 1 (3 ) Transfers out of Level 3 (1 ) — — Transfers into Level 3 1 (1 ) 1 Ending balance (1) $ 12 $ 17 $ 3 The amount of total gains for the period included in earnings attributable to the change in unrealized gains or losses relating to assets still held at the reporting date $ 6 $ 16 $ 2 (1) During 2015, 2014 and 2013, CenterPoint Energy did not have significant Level 3 purchases or sales. Items Measured at Fair Value on a Nonrecurring Basis Based on the sustained low Enable common unit price and further declines in such price during the three months ended September 30, 2015 and December 31, 2015, respectively, as well as the market outlook for continued depressed crude oil and natural gas prices impacting the midstream oil and gas industry, CenterPoint Energy determined in connection with its preparation of financial statements for the three months ended September 30, 2015 and December 31, 2015, respectively, that an other than temporary decrease in the value of its investment in Enable had occurred. The impairment analyses compared the estimated fair value of CenterPoint Energy’s investment in Enable to its carrying value. The fair value of the investment was determined using multiple valuation methodologies under both the market and income approaches. Both of these approaches incorporate significant estimates and assumptions, including: Market Approach • volume weighted average quoted price of Enable’s common units; • recent market transactions of comparable companies; and • EBITDA to total enterprise multiples for comparable companies. Income Approach • Enable’s forecasted cash distributions; • projected cash flows of incentive distribution rights; • forecasted growth rate of Enable’s cash distributions; and • determination of the cost of equity, including market risk premiums. Weighting of the different approaches Significant unobservable inputs used include the growth rate applied to the projected cash distributions beyond 2020 and the discount rate used to determine the present value of the estimated future cash flows. CERC based its assumptions on projected financial information that CERC believes is reasonable; however, actual results may differ materially from those projections. Based on the significant unobservable estimates and assumptions required, CenterPoint Energy concluded that the fair value estimate should be classified as a Level 3 measurement within the fair value hierarchy. As a result of the analysis, CERC recorded other than temporary impairments on its investment in Enable of $250 million and $975 million during the three months ended September 30, 2015 and December 31, 2015, respectively. See Note 10 for further discussion of the impairment. As of December 31, 2014, there were no significant assets or liabilities measured at fair value on a nonrecurring basis. Estimated Fair Value of Financial Instruments The fair values of cash and cash equivalents and short-term borrowings are estimated to be approximately equivalent to carrying amounts and have been excluded from the table below. Non-trading derivative assets and liabilities are stated at fair value and are excluded from the table below. The fair value of each debt instrument is determined by multiplying the principal amount of each debt instrument by the market price. These assets and liabilities, which are not measured at fair value in the Condensed Consolidated Balance Sheets but for which the fair value is disclosed, would be classified as Level 1 or Level 2 in the fair value hierarchy. December 31, 2015 December 31, 2014 Carrying Amount Fair Value Carrying Amount Fair Value (in millions) Financial assets: Notes receivable - affiliated companies $ 363 $ 356 $ 363 $ 362 Financial liabilities: Long-term debt $ 2,353 $ 2,551 $ 2,469 $ 2,772

Unconsolidated Affiliates (Note

Unconsolidated Affiliates (Notes)	12 Months Ended
	Dec. 31, 2015
Equity Method Investments and Joint Ventures [Abstract]
Equity Method Investments and Joint Ventures Disclosure [Text Block]	Unconsolidated Affiliates On May 1, 2013 (the Closing Date) CERC Corp., OGE Energy Corp. (OGE) and ArcLight Capital Partners, LLC (ArcLight) closed on the formation of Enable, and CERC recorded an equity method investment in Enable at the historical cost of the contributed net assets. See Note 2 for further information on the formation of Enable. CERC’s maximum exposure to loss related to Enable, a VIE in which CERC is not the primary beneficiary, is limited to its equity investment as presented in the Consolidated Balance Sheet as of December 31, 2015 , CERC Corp.’s guarantee of collection of Enable’s $1.1 billion senior notes due 2019 and 2024 (Guaranteed Senior Notes) and other guarantees discussed in Note 13, and outstanding current accounts receivable from Enable. As of December 31, 2015, certain of the entities contributed to Enable by CERC Corp. were obligated on approximately $363 million of notes owed to a wholly-owned subsidiary of CERC Corp., which bore interest at an annual rate of 2.10% to 2.45% . Enable redeemed such notes scheduled to mature in 2017 in connection with the private placement discussed further in Note 16. CERC recorded interest income of $8 million during both the year ended December 31, 2015 and 2014 , and had interest receivable from Enable of $4 million as of both December 31, 2015 and 2014 , on its notes receivable from Enable. Effective on the Closing Date, CenterPoint Energy and Enable entered into a Services Agreement, Employee Transition Agreement, Transitional Seconding Agreement and other agreements (Transition Agreements). Under the Services Agreement, CERC agreed to provide certain support services to Enable such as accounting, legal, risk management and treasury functions for an initial term ending on April 30, 2016, after which such services continue on a year-to-year basis unless terminated by Enable with at least 90 days’ notice. CERC expects to provide certain services to Enable following the completion of the initial term. CERC provided seconded employees to Enable to support its operations for a term ending on December 31, 2014. Enable, at its discretion, had the right to select and offer employment to seconded employees from CERC. During the fourth quarter of 2014, Enable notified CERC that it selected seconded employees and provided employment offers to substantially all of the seconded employees from CERC. Substantially all of the seconded employees became employees of Enable effective January 1, 2015. See Note 6 for additional information. On April 16, 2014, Enable completed its initial public offering (IPO) of 28,750,000 common units, at a price of $20.00 per unit, which included 3,750,000 common units sold by ArcLight pursuant to an over-allotment option that was fully exercised by the underwriters. Enable received $464 million in net proceeds from the sale of the units, after deducting underwriting fees, structuring fees and other offering costs. In connection with Enable’s IPO, a portion of CERC’s common units were converted into subordinated units, as discussed further below. Subsequent to the IPO, Enable continues to be controlled jointly by CERC and OGE. As a result of Enable’s IPO, CERC’s limited partner interest in Enable was reduced from approximately 58.3% to approximately 54.7% . CERC accounted for the dilution of its investment in Enable as a result of Enable’s IPO as a failed partial sale of in-substance real estate. CERC did not receive any cash from Enable’s IPO and, as such, CERC did not recognize a gain or loss. CERC’s basis difference in Enable was reduced for the impact of the Enable IPO. In accordance with the Enable formation agreements, CERC had certain put rights, and Enable had certain call rights, exercisable with respect to the 25.05% interest in Southeast Supply Header, LLC (SESH) retained by CERC on the Closing Date, under which CERC would contribute its retained interest in SESH, in exchange for a specified number of limited partner common units in Enable and a cash payment, payable either from CERC to Enable or from Enable to CERC, to the extent of changes in the value of SESH subject to certain restrictions. Specifically, the rights were exercisable with respect to (1) a 24.95% interest in SESH, which closed on May 30, 2014 and (2) a 0.1% interest in SESH, which closed on June 30, 2015. CERC billed Enable for reimbursement of transition services, including the costs of seconded employees, $16 million and $163 million during the years ended December 31, 2015 and 2014 , respectively, under the Transition Agreements. Actual transition services costs are recorded net of reimbursements received from Enable. CERC had accounts receivable from Enable of $3 million and $28 million as of December 31, 2015 and 2014 , respectively, for amounts billed for transition services, including the cost of seconded employees. CERC incurred natural gas expenses, including transportation and storage costs, of $117 million and $130 million during the year ended December 31, 2015 and 2014 , respectively, for transactions with Enable. CERC had accounts payable to Enable of $11 million and $23 million at December 31, 2015 and 2014 , respectively, from such transactions. As of December 31, 2015 , CERC held an approximate 55.4% limited partner interest in Enable consisting of 94,151,707 common units and 139,704,916 subordinated units. As of December 31, 2015, CERC and OGE each own a 50% management interest in the general partner of Enable and a 40% and 60% interest, respectively, in the incentive distribution rights held by the general partner. CERC recognized a loss of $1,633 million from its investment in Enable as of December 31, 2015 . This loss included impairment charges totaling $1,846 million composed of CERC’s impairment of its investment in Enable of $1,225 million and CERC’s share, $621 million , of impairment charges Enable recorded for goodwill and long-lived assets. CERC evaluates its equity method investments for impairment when factors indicate that a decrease in the value of its investment has occurred and the carrying amount of its investment may not be recoverable. An impairment loss, based on the excess of the carrying value over estimated fair value of the investment, is recognized in earnings when an impairment is deemed to be other than temporary. Considerable judgment is used in determining if an impairment loss is other than temporary and the amount of any impairment. Based on the sustained low Enable common unit price and further declines in such price during the three months ended September 30, 2015 and December 31, 2015, respectively, as well as the market outlook for continued depressed crude oil and natural gas prices impacting the midstream oil and gas industry, CERC determined in connection with its preparation of financial statements for the three months ended September 30, 2015 and December 31, 2015, that an other than temporary decrease in the value of its investment in Enable had occurred. CERC wrote down the value of its investment in Enable to its estimated fair value which resulted in impairment charges of $250 million as of September 30, 2015 and $975 million as of December 31, 2015. Both the income approach and market approach were utilized to estimate the fair value of CERC’s total investment in Enable, which includes the limited partner common and subordinated units, general partner interest and incentive distribution rights held by CERC. The determination of fair value considered a number of relevant factors including Enable’s common unit price and forecasted results, recent comparable transactions and the limited float of Enable’s publicly traded common units. See Note 9 for further discussion of the determination of fair value of CERC’s investment in Enable. Investment in Unconsolidated Affiliates: Year Ended December 31, 2015 2014 (in millions) Enable $ 2,594 $ 4,520 SESH (1) — 1 Total $ 2,594 $ 4,521 (1) CERC disposed of its remaining interest in SESH on June 30, 2015. Equity in Earnings (Losses) of Unconsolidated Affiliates, net: Year Ended December 31, 2015 2014 2013 (in millions) Enable $ (1,633 ) $ 303 $ 173 SESH (1) — 5 15 Total $ (1,633 ) $ 308 $ 188 (1) CERC contributed a 24.95% interest in SESH to Enable on May 30, 2014 and its remaining interest in SESH to Enable on June 30, 2015. Summarized consolidated income (loss) information for Enable is as follows: Year Ended December 31, 2015 2014 2013 (in millions) Operating revenues $ 2,418 $ 3,367 $ 2,123 Cost of sales, excluding depreciation and amortization 1,097 1,914 1,241 Impairment of goodwill and other long-lived assets 1,134 8 12 Operating income (loss) (712 ) 586 322 Net income (loss) attributable to Enable (752 ) 530 289 Reconciliation of Equity in Earnings (Losses), net: CERC’s interest $ (416 ) $ 298 $ 168 Basis difference amortization (1) 8 5 5 Impairment of CERC’s equity method investment in Enable (1,225 ) — — CERC’s equity in earnings (losses), net (2) $ (1,633 ) $ 303 $ 173 (1) 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 33 years, the average life of the assets to which the basis difference is attributed. (2) These amounts include CERC’s share of Enable’s impairment of goodwill and long-lived assets and the impairment of CERC’s equity method investment in Enable totaling $1,846 million during the year ended December 31, 2015 . This impairment is offset by $213 million of earnings for the year ended December 31, 2015 . Summarized consolidated balance sheet information for Enable is as follows: December 31, 2015 2014 (in millions) Current assets $ 381 $ 438 Non-current assets 10,857 11,399 Current liabilities 615 671 Non-current liabilities 3,092 2,343 Non-controlling interest 12 31 Enable partners’ capital 7,519 8,792 Reconciliation of Investment in Enable: CERC’s ownership interest in Enable partners’ capital $ 4,163 $ 4,869 CERC’s basis difference (1,569 ) (349 ) CERC’s investment in Enable $ 2,594 $ 4,520 Distributions Received from Unconsolidated Affiliates: Year Ended December 31, 2015 2014 2013 (in millions) Enable $ 294 $ 298 $ 106 SESH (1) — 7 23 Total $ 294 $ 305 $ 129 (1) CERC contributed a 24.95% interest in SESH to Enable on each of May 1, 2013 and May 30, 2014 and its remaining interest in SESH to Enable on June 30, 2015.

Short-term Borrowings and Long-

Short-term Borrowings and Long-term Debt	12 Months Ended
	Dec. 31, 2015
Debt Disclosure [Abstract]
Short-term Borrowings and Long-term Debt	Short-term Borrowings and Long-term Debt December 31, 2015 December 31, 2014 Long-Term Current (1) Long-Term Current (1) (in millions) Short-term borrowings: Inventory financing $ — $ 40 $ — $ 53 Total short-term borrowings — 40 — 53 Long-term debt: Senior notes 4.50% to 6.625% due 2016 to 2041 1,843 325 2,168 — Commercial paper (2) 219 — 341 — Unamortized discount and premium (34 ) — (40 ) — Total long-term debt 2,028 325 2,469 — Total debt $ 2,028 $ 365 $ 2,469 $ 53 (1) Includes amounts due or exchangeable within one year of the date noted. (2) Classified as long-term debt because the termination date of the facility that backstops the commercial paper is more than one year from the date noted. CERC’s short-term borrowings from the money pool are not reflected in the table above. For information regarding CERC’s money poor borrowings, please see Note 7. (a) Short-term Borrowings Inventory Financing . NGD has asset management agreements associated with its utility distribution service in Arkansas, north Louisiana and Oklahoma that extend through 2019. Pursuant to the provisions of the agreements, NGD sells natural gas and agrees to repurchase an equivalent amount of natural gas during the winter heating seasons at the same cost, plus a financing charge. These transactions are accounted for as a financing and had an associated principal obligation of $40 million and $53 million as of December 31, 2015 and 2014 , respectively. (b) Long-term Debt Revolving Credit Facility. As of December 31, 2015 and 2014 , CERC had the following revolving credit facility and utilization of such facility: December 31, 2015 December 31, 2014 Size of Loans Letters Commercial Loans Letters Commercial (in millions) $ 600 $ — $ 2 $ 219 (1) $ — $ — $ 341 (1) (1) Weighted average interest rate was 0.81% and 0.68% as of December 31, 2015 and 2014, respectively. CERC Corp.’s $600 million revolving credit facility, which is scheduled to terminate on September 9, 2019, can be drawn at the London Interbank Offered Rate plus 1.50% based on CERC Corp.’s current credit ratings. The revolving credit facility contains a financial covenant which limits CERC’s consolidated debt to an amount not to exceed 65% of CERC’s consolidated capitalization. As of December 31, 2015, CERC’s debt to capital ratio, as defined in its credit facility agreement, was 33.9% . CERC Corp. was in compliance with all financial covenants in its revolving credit facility as of December 31, 2015 . Maturities. CERC’s consolidated maturities of long-term debt are $325 million in 2016, $250 million in 2017, $300 million in 2018, $219 million in 2019 and $-0- in 2020.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2015
Income Taxes [Abstract]
Income Taxes	Income Taxes The components of CERC’s income tax expense (benefit) were as follows: Year Ended December 31, 2015 2014 2013 (in millions) Current income tax expense: Federal $ — $ — $ 5 State 3 10 9 Total current expense 3 10 14 Deferred income tax expense (benefit): Federal (488 ) 171 350 State (54 ) 7 7 Total deferred expense (benefit) (542 ) 178 357 Total income tax expense (benefit) $ (539 ) $ 188 $ 371 A reconciliation of income tax expense (benefit) using the federal statutory income tax rate to the actual income tax expense and resulting effective income tax rate is as follows: Year Ended December 31, 2015 2014 2013 (in millions) Income (loss) before income taxes $ (1,451 ) $ 511 $ 435 Federal statutory income tax rate 35 % 35 % 35 % Expected federal income tax expense (benefit) (508 ) 179 152 Increase (decrease) in tax expense resulting from: State income tax expense, net of federal income tax (33 ) 11 23 Decrease in settled and uncertain income tax positions — — (2 ) Tax effect related to the formation of Enable Midstream Partnership — — 198 Other, net 2 (2 ) — Total (31 ) 9 219 Total income tax expense (benefit) $ (539 ) $ 188 $ 371 Effective tax rate 37.1 % 36.8 % 85.3 % In 2013, CERC recorded a deferred tax expense of $225 million at the formation of Enable related to the book-to-tax basis difference for contributed non-tax deductible goodwill and recognized a tax benefit of $27 million associated with the remeasurement of state deferred taxes at formation. In addition, CERC recognized a tax benefit of $2 million based on the settlement with the Internal Revenue Service (IRS) of outstanding tax claims for the 2002 and 2003 tax years. The tax effects of temporary differences that give rise to significant portions of deferred tax assets and liabilities were as follows: December 31, 2015 2014 (in millions) Deferred tax assets: Benefits and compensation $ 39 $ 48 Loss and credit carryforwards 388 326 Asset retirement obligations 59 52 Other 39 28 Valuation allowance (2 ) (2 ) Total deferred tax assets 523 452 Deferred tax liabilities: Property, plant, and equipment 929 803 Investment in unconsolidated affiliates 1,277 1,788 Regulatory assets/liabilities, net — 13 Other 91 99 Total deferred tax liabilities 2,297 2,703 Net deferred tax liabilities $ 1,774 $ 2,251 Effective December 31, 2015, all deferred taxes for 2014 and 2015 are classified as noncurrent. See Note 2. CERC is included in the consolidated income tax returns of CenterPoint Energy. CERC calculates its income tax provision on a separate return basis under a tax sharing agreement with CenterPoint Energy. Tax Attribute Carryforwards and Valuation Allowance. CERC has $946 million of federal net operating loss carryforwards which expire between 2031 and 2035 , $23 million of federal capital loss carryforwards which expire between 2018 and 2019 , and $1 million of charitable contribution carryforwards which expire between 2018 and 2020 . CERC has $905 million of state net operating loss carryforwards which expire between 2016 and 2035 , $7 million of state tax credits which do not expire, and $244 million of state capital loss carryforwards which expire in 2017 . Management has established a valuation allowance of $2 million net of federal tax on certain state net operating losses and the full amount of the state capital loss carryforwards. The valuation allowance was established based upon management’s evaluation that certain state carryforwards may not be fully realized. Uncertain Income Tax Positions . The following table reconciles the beginning and ending balance of CERC’s unrecognized tax benefits (expenses): December 31, 2015 2014 2013 (in millions) Balance, beginning of year $ — $ — $ (20 ) Tax Positions related to prior years: Reductions — — (2 ) Tax Positions related to current year: Settlements — — 22 Balance, end of year $ — $ — $ — CERC reported no uncertain tax liability as of December 31, 2015 and expects no significant change to the uncertain tax liability over the next twelve months ending December 31, 2016. CERC recognizes interest and penalties as a component of income tax expense. CERC recognized $4 million of income tax expense related to interest on tax positions during 2013. Tax Audits and Settlements. CenterPoint Energy’s tax years through 2013 have been audited and settled with the IRS. For 2014 and 2015, CenterPoint Energy is a participant in the IRS’s Compliance Assurance Process. CenterPoint Energy has considered the effects of these examinations in its accrual for settled issues and liability for uncertain income tax positions (if any) as of December 31, 2015.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies (a) Natural Gas Supply Commitments Natural gas supply commitments include natural gas contracts related to CERC’s Natural Gas Distribution and Energy Services business segments, which have various quantity requirements and durations, that are not classified as non-trading derivative assets and liabilities in CERC’s Consolidated Balance Sheets as of December 31, 2015 and 2014 as these contracts meet an exception as “normal purchases contracts” or do not meet the definition of a derivative. Natural gas supply commitments also include natural gas transportation contracts that do not meet the definition of a derivative. As of December 31, 2015 , minimum payment obligations for natural gas supply commitments are approximately $478 million in 2016, $457 million in 2017, $405 million in 2018, $217 million in 2019, $90 million in 2020 and $38 million after 2020. (b) Asset Management Agreements NGD has asset management agreements (AMAs) associated with its utility distribution service in Arkansas, Louisiana, Mississippi, Oklahoma and Texas. Generally, these AMAs are contracts between NGD and an asset manager that are intended to transfer the working capital obligation and maximize the utilization of the assets. In these AMAs, NGD agreed to release transportation and storage capacity to other parties to manage gas storage, supply and delivery arrangements for NGD and to use the released capacity for other purposes when it is not needed for NGD. NGD is compensated by the asset manager through payments made over the life of the AMAs based in part on the results of the asset optimization. NGD has an obligation to purchase its winter storage requirements that have been released to the asset manager under these AMAs. The AMAs have varying terms, the longest of which expires in 2019. (c) Lease Commitments The following table sets forth information concerning CERC’s obligations under non-cancelable long-term operating leases as of December 31, 2015 , which primarily consist of rental agreements for building space, data processing equipment, compression equipment and rights-of-way: (in millions) 2016 $ 5 2017 3 2018 3 2019 3 2020 2 2021 and beyond 7 Total $ 23 Total lease expense for all operating leases was $8 million , $9 million and $20 million during 2015 , 2014 and 2013 , respectively. (d) Legal, Environmental and Other Regulatory Matters Legal Matters Gas Market Manipulation Cases . CenterPoint Energy, CenterPoint Energy Houston Electric, LLC or their predecessor, Reliant Energy, Incorporated (Reliant Energy), and certain of their former subsidiaries have been named as defendants in certain lawsuits described below. Under a master separation agreement between CenterPoint Energy and a former subsidiary, Reliant Resources, Inc. (RRI), CenterPoint Energy and its subsidiaries are entitled to be indemnified by RRI and its successors for any losses, including certain attorneys’ fees and other costs, arising out of these lawsuits. In May 2009, RRI sold its Texas retail business to a subsidiary of NRG and RRI changed its name to RRI Energy, Inc. In December 2010, Mirant Corporation merged with and became a wholly-owned subsidiary of RRI, and RRI changed its name to GenOn Energy, Inc. (GenOn). In December 2012, NRG acquired GenOn through a merger in which GenOn became a wholly-owned subsidiary of NRG. None of the sale of the retail business, the merger with Mirant Corporation, or the acquisition of GenOn by NRG alters RRI’s (now GenOn’s) contractual obligations to indemnify CenterPoint Energy and its subsidiaries, including CenterPoint Houston, for certain liabilities, including their indemnification obligations regarding the gas market manipulation litigation, nor does it affect the terms of existing guarantee arrangements for certain GenOn gas transportation contracts discussed below. A large number of lawsuits were filed against numerous gas market participants in a number of federal and western state courts in connection with the operation of the natural gas markets in 2000–2002. CenterPoint Energy and its affiliates have since been released or dismissed from all but one such case. CenterPoint Energy Services, Inc. (CES), a subsidiary of CERC Corp., is a defendant in a case now pending in federal court in Nevada alleging a conspiracy to inflate Wisconsin natural gas prices in 2000–2002. In July 2011, the court issued an order dismissing the plaintiffs’ claims against other defendants in the case, each of whom had demonstrated Federal Energy Regulatory Commission jurisdictional sales for resale during the relevant period, based on federal preemption, and stayed the remainder of the case pending outcome of the appeals. The plaintiffs appealed this ruling to the U.S. Court of Appeals for the Ninth Circuit, which reversed the trial court’s dismissal of the plaintiffs’ claims. On April 21, 2015, the U.S. Supreme Court affirmed the Ninth Circuit’s ruling and remanded the case to the district court for further proceedings, which are now underway. CenterPoint Energy and CES intend to continue vigorously defending against the plaintiffs’ claims. CERC does not expect the ultimate outcome of this matter to have a material adverse effect on its financial condition, results of operations or cash flows. Environmental Matters Manufactured Gas Plant Sites. CERC and its predecessors operated manufactured gas plants (MGPs) in the past. With respect to certain Minnesota MGP sites, CERC has completed state-ordered remediation and continues state-ordered monitoring and water treatment. As of December 31, 2015 , CERC had a recorded liability of $7 million for continued monitoring and any future remediation required by regulators in Minnesota. The estimated range of possible remediation costs for the sites for which CERC believes it may have responsibility was $5 million to $29 million based on remediation continuing for 30 to 50 years. The cost estimates are based on studies of a site or industry average costs for remediation of sites of similar size. The actual remediation costs will depend on the number of sites to be remediated, the participation of other potentially responsible parties (PRPs), if any, and the remediation methods used. In addition to the Minnesota sites, the Environmental Protection Agency and other regulators have investigated MGP sites that were owned or operated by CERC or may have been owned by one of its former affiliates. CERC does not expect the ultimate outcome of these matters to have a material adverse effect on its financial condition, results of operations or cash flows. Asbestos. Some facilities owned by CERC’s predecessors contain or have contained asbestos insulation and other asbestos-containing materials. CERC or its predecessor companies have been named, along with numerous others, as a defendant in lawsuits filed by a number of individuals who claim injury due to exposure to asbestos. Some of the claimants have worked at locations owned by CERC, but most existing claims relate to facilities previously owned by CERC’s subsidiaries. CERC anticipates that additional claims like those received may be asserted in the future. Although their ultimate outcome cannot be predicted at this time, CERC intends to continue vigorously contesting claims that it does not consider to have merit and, based on its experience to date, does not expect these matters, either individually or in the aggregate, to have a material adverse effect on its financial condition, results of operations or cash flows. Other Environmental. From time to time, CERC identifies the presence of environmental contaminants on property where it conducts or has conducted operations. Other such sites involving contaminants may be identified in the future. CERC has and expects to continue to remediate identified sites consistent with its legal obligations. From time to time, CERC has received notices from regulatory authorities or others regarding its status as a PRP in connection with sites found to require remediation due to the presence of environmental contaminants. In addition, CERC has been named from time to time as a defendant in litigation related to such sites. Although the ultimate outcome of such matters cannot be predicted at this time, CERC does not expect, based on its experience to date, these matters, either individually or in the aggregate, to have a material adverse effect on its financial condition, results of operations or cash flows. Other Proceedings CERC is involved in other legal, environmental, tax and regulatory proceedings before various courts, regulatory commissions and governmental agencies regarding matters arising in the ordinary course of business. From time to time, CERC is also a defendant in legal proceedings with respect to claims brought by various plaintiffs against broad groups of participants in the energy industry. Some of these proceedings involve substantial amounts. CERC regularly analyzes current information and, as necessary, provides accruals for probable and reasonably estimable liabilities on the eventual disposition of these matters. CERC does not expect the disposition of these matters to have a material adverse effect on its financial condition, results of operations or cash flows. (e) Guarantees Prior to the distribution of CenterPoint Energy’s ownership in RRI to its shareholders, CERC had guaranteed certain contractual obligations of what became RRI’s trading subsidiary. When the companies separated, RRI agreed to secure CERC against obligations under the guarantees RRI had been unable to extinguish by the time of separation. Pursuant to such agreement, as amended in December 2007, RRI (now GenOn) agreed to provide to CERC cash or letters of credit as security against CERC’s obligations under its remaining guarantees for demand charges under certain gas transportation agreements if and to the extent changes in market conditions expose CERC to a risk of loss on those guarantees based on an annual calculation, with any required collateral to be posted each December. The undiscounted maximum potential payout of the demand charges under these transportation contracts, which will be in effect until 2018, was approximately $27 million as of December 31, 2015 . Based on market conditions in the fourth quarter of 2015 at the time the most recent annual calculation was made under the agreement, GenOn was not obligated to post any security. If GenOn should fail to perform the contractual obligations, CERC could have to honor its guarantee and, in such event, any collateral then provided as security may be insufficient to satisfy CERC’s obligations. CERC Corp. has also provided a guarantee of collection of $1.1 billion of Enable’s Guaranteed Senior Notes. This guarantee is subordinated to all senior debt of CERC Corp. and is subject to automatic release on May 1, 2016. The fair value of these guarantees is not material.

Unaudited Quarterly Information

Unaudited Quarterly Information	12 Months Ended
	Dec. 31, 2015
Unaudited Quarterly Information [Abstract]
Quarterly Financial Information [Text Block]	Unaudited Quarterly Information Summarized quarterly financial data is as follows: Year Ended December 31, 2015 First Quarter Second Quarter Third Quarter (1) Fourth Quarter (2) (in millions) Revenues $ 1,817 $ 824 $ 799 $ 1,087 Operating income 160 27 18 108 Net income (loss) 109 22 (508 ) (535 ) Year Ended December 31, 2014 First Quarter Second Quarter Third Quarter Fourth Quarter (in millions) Revenues $ 2,531 $ 1,183 $ 964 $ 1,689 Operating income (loss) 188 39 (3 ) 111 Net income 152 48 28 95 (1) CERC recognized $862 million ( $537 million after tax) in impairment charges related to Enable during the three months ended September 30, 2015. (2) CERC recognized $984 million ( $620 million after tax) in impairment charges related to Enable during the three months ended December 31, 2015.

Reportable Business Segments

Reportable Business Segments	12 Months Ended
	Dec. 31, 2015
Segment Reporting [Abstract]
Reportable Business Segments	Reportable Business Segments Because CERC is an indirect, wholly-owned subsidiary of CenterPoint Energy, CERC’s determination of reportable business segments considers the strategic operating units under which CenterPoint Energy manages sales, allocates resources and assesses performance of various products and services to wholesale or retail customers in differing regulatory environments. CERC uses operating income as the measure of profit or loss for its business segments. CERC’s reportable business segments include the following: Natural Gas Distribution, Energy Services, Midstream Investments and Other Operations. Natural Gas Distribution consists of intrastate natural gas sales to, and natural gas transportation and distribution for, residential, commercial, industrial and institutional customers. Energy Services represents CERC’s non-rate regulated gas sales and services operations. Midstream Investments consists of CERC’s investment in Enable. The Other Operations business segment includes unallocated corporate costs and inter-segment eliminations. Prior to May 1, 2013, CERC also reported an Interstate Pipelines business segment, which included CERC’s interstate natural gas pipeline operations, and a Field Services business segment, which included CERC’s non-rate regulated natural gas gathering, processing and treating operations. The formation of Enable closed on May 1, 2013. Enable now owns substantially all of CERC’s former Interstate Pipelines and Field Services business segments. As a result, effective May 1, 2013, CERC reports equity earnings associated with its interest in Enable under its Midstream Investments segment, and no longer has Interstate Pipelines and Field Services reporting segments prospectively. Financial data for business segments and products and services are as follows: Revenues from External Customers Inter-segment Revenues Depreciation and Amortization Operating Income (Loss) Total Assets Expenditures for Long- Lived Assets (in millions) As of and for the year ended December 31, 2015: Natural Gas Distribution $ 2,603 $ 29 $ 222 $ 273 $ 5,657 $ 601 Energy Services 1,924 33 5 42 857 5 Midstream Investments (1) — — — — 2,594 — Other — — — (2 ) 789 — Reconciling Eliminations — (62 ) — — (744 ) — Consolidated $ 4,527 $ — $ 227 $ 313 $ 9,153 $ 606 As of and for the year ended December 31, 2014: Natural Gas Distribution $ 3,271 $ 30 $ 201 $ 287 $ 5,464 $ 525 Energy Services 3,095 84 5 52 978 3 Midstream Investments (1) — — — — 4,521 — Other 1 — — (4 ) 1,045 — Reconciling Eliminations — (114 ) — — (964 ) — Consolidated $ 6,367 $ — $ 206 $ 335 $ 11,044 $ 528 As of and for the year ended December 31, 2013: Natural Gas Distribution $ 2,837 $ 26 $ 185 $ 263 $ 4,976 $ 430 Energy Services 2,374 27 5 13 895 3 Interstate Pipelines (2) (3) 133 53 20 72 — 29 Field Services (3) 178 18 20 73 — 16 Midstream Investments (1) — — — — 4,518 — Other — — — (20 ) 1,139 — Reconciling Eliminations — (124 ) — — (996 ) — Consolidated $ 5,522 $ — $ 230 $ 401 $ 10,532 $ 478 (1) Midstream Investments’ equity earnings (losses) are as follows: Year Ended December 31, 2015 2014 2013 (in millions) Enable (1) $ (1,633 ) $ 303 $ 173 SESH — 5 8 Total $ (1,633 ) $ 308 $ 181 (1) These amounts include CERC’s share of Enable’s impairment of goodwill and long-lived assets and the impairment of CERC’s equity method investment in Enable totaling $1,846 million during the year ended December 31, 2015 . This impairment is offset by $213 million of earnings for the year ended December 31, 2015 . Midstream Investments’ total assets are as follows: December 31, December 31, (in millions) Enable $ 2,594 $ 4,520 SESH — 1 Total $ 2,594 $ 4,521 (2) Interstate Pipelines recorded equity income of $7 million in the year ended December 31, 2013 from its interest in SESH, a jointly-owned pipeline. These amounts are included in Equity in earnings of unconsolidated affiliates under the Other Income (Expense) caption. As discussed above, effective May 1, 2013, CenterPoint Energy reports equity earnings associated with its interest in Enable and equity earnings associated with its interest in SESH under its Midstream Investments segment, and no longer has an Interstate Pipelines reporting segment prospectively. (3) Results reflected in the year ended December 31, 2013 represent only January 2013 through April 2013. Year Ended December 31, Revenues by Products and Services: 2015 2014 2013 (in millions) Retail gas sales $ 3,725 $ 5,049 $ 4,150 Wholesale gas sales 657 1,159 913 Gas transportation and processing 26 38 345 Energy products and services 119 121 114 Total $ 4,527 $ 6,367 $ 5,522

Subsequent Events (Notes)

Subsequent Events (Notes)	12 Months Ended
	Dec. 31, 2015
Subsequent Events [Abstract]
Subsequent Events [Text Block]	Subsequent Events On January 22, 2016 , Enable declared a quarterly cash distribution of $0.318 per unit on all of its outstanding common and subordinated units for the quarter ended December 31, 2015. Accordingly, CERC Corp. expects to receive a cash distribution of approximately $74 million from Enable in the first quarter of 2016 to be made with respect to CERC Corp.’s limited partner interest in Enable for the fourth quarter of 2015. On January 28, 2016, CenterPoint Energy entered into a purchase agreement with Enable pursuant to which it agreed to purchase in a private placement (Private Placement) an aggregate of 14,520,000 10% Series A Fixed-to-Floating Non-Cumulative Redeemable Perpetual Preferred Units representing limited partner interests in Enable (Series A Preferred Units) for a cash purchase price of $25.00 per Series A Preferred Unit. The Private Placement closed on February 18, 2016. In connection with the Private Placement, Enable redeemed approximately $363 million of notes scheduled to mature in 2017 payable to a wholly-owned subsidiary of CERC Corp. CERC Corp. made a dividend to CenterPoint Energy of $363 million and CenterPoint Energy used the dividend for its investment in the Series A Preferred Units. On January 29, 2016, CES announced an agreement to acquire the retail commercial and industrial businesses of Continuum Energy Services , a Tulsa and Houston-based company, for $77.5 million plus working capital. The transaction is conditioned upon the receipt of certain third party consents and approvals. CERC expects the transaction to close by the end of the first quarter of 2016.

Summary of Significant Accoun25

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2015
Significant Accounting Policies [Abstract]
Use Of Estimates	Use of Estimates The preparation of financial statements in conformity with generally accepted accounting principles requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities at the date of the financial statements, and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
Principles of Consolidation	Principles of Consolidation The accounts of CERC Corp. and its wholly-owned and majority owned subsidiaries are included in CERC’s consolidated financial statements. All intercompany transactions and balances are eliminated in consolidation. CERC uses the equity method of accounting for investments in entities in which CERC has an ownership interest between 20% and 50% and exercises significant influence. CERC also uses the equity method for investments in which it has ownership percentages greater than 50%, when it exercises significant influence, does not have control and is not considered the primary beneficiary, if applicable. In May 2013, CenterPoint Energy, OGE Energy Corp. (OGE) and affiliates of ArcLight Capital Partners, LLC (ArcLight), formed Enable as a private limited partnership. CenterPoint Energy has the ability to significantly influence the operating and financial policies of, but not solely control, Enable and, accordingly, recorded an equity method investment, at the historical costs of net assets contributed. Under the equity method, CERC adjusts its investment in Enable each period for contributions made, distributions received, CERC’s share of Enable’s comprehensive income and accretion of basis differences, as appropriate. CERC evaluates its equity method investments for impairment when events or changes in circumstances indicate there is a loss in value of the investment that is other than a temporary decline. CERC’s investment in Enable is considered to be a variable interest entity (VIE) because the power to direct the activities that most significantly impact Enable’s economic performance does not reside with the holders of equity investment at risk. However, CERC is not considered the primary beneficiary of Enable since it does not have the power to direct the activities of Enable that are considered most significant to the economic performance of Enable. As of December 31, 2015, CERC Corp. and OGE held approximately 55.4% and 26.3% , respectively, of the limited partner interests in Enable. Enable is controlled jointly by CERC Corp. and OGE, and each own 50% of the management rights in the general partner of Enable. As of December 31, 2015, CERC Corp. and OGE also own 40% and 60% , respectively, of the incentive distribution rights held by the general partner of Enable. Enable is expected to pay a minimum quarterly distribution of $0.2875 per unit on its outstanding units to the extent it has sufficient cash from operations after establishment of cash reserves and payment of fees and expenses, including payments to its general partner and its affiliates, within 45 days after the end of each quarter. If cash distributions to Enable’s unitholders exceed $0.330625 per unit in any quarter, the general partner will receive increasing percentages or incentive distributions rights, up to 50% , of the cash Enable distributes in excess of that amount. In certain circumstances the general partner of Enable will have the right to reset the minimum quarterly distribution and the target distribution levels at which the incentive distributions receive increasing percentages to higher levels based on Enable’s cash distributions at the time of the exercise of this reset election. Other investments, excluding marketable securities, are carried at cost.
Revenues	Revenues CERC records revenue for natural gas sales and services under the accrual method and these revenues are recognized upon delivery to customers. Natural gas sales not billed by month-end are accrued based upon estimated purchased gas volumes, estimated lost and unaccounted for gas and currently effective tariff rates.
Long-lived Assets and Intangibles	Long-lived Assets and Intangibles CERC records property, plant and equipment at historical cost. CERC expenses repair and maintenance costs as incurred. CERC periodically evaluates long-lived assets, including property, plant and equipment and specifically identifiable intangibles, when events or changes in circumstances indicate that the carrying value of these assets may not be recoverable. The determination of whether an impairment has occurred is based on an estimate of undiscounted cash flows attributable to the assets, compared to the carrying value of the assets.
Regulatory Assets and Liabilities	Regulatory Assets and Liabilities CERC applies the guidance for accounting for regulated operations to the Natural Gas Distribution business segment. CERC’s rate-regulated subsidiaries may collect revenues subject to refund pending final determination in rate proceedings. In connection with such revenues, estimated rate refund liabilities are recorded which reflect management’s current judgment of the ultimate outcomes of the proceedings. CERC’s rate-regulated businesses recognize removal costs as a component of depreciation expense in accordance with regulatory treatment. As of December 31, 2015 and 2014 , these removal costs of $632 million and $605 million , respectively, are classified as regulatory liabilities in the Consolidated Balance Sheets. In addition, a portion of the amount of removal costs that relate to asset retirement obligations has been reclassified from a regulatory liability to an asset retirement liability in accordance with accounting guidance for asset retirement obligations.
Depreciation and Amortization Expense	Depreciation and Amortization Expense Depreciation and amortization is computed using the straight-line method based on economic lives or regulatory-mandated recovery periods. Amortization expense includes amortization of regulatory assets and other intangibles.
Capitalization of Interest and Allowance for Funds Used During Construction	Capitalization of Interest and Allowance for Funds Used During Construction Interest and allowance for funds used during construction (AFUDC) are capitalized as a component of projects under construction and are amortized over the assets’ estimated useful lives once the assets are placed in service. AFUDC represents the composite interest cost of borrowed funds and a reasonable return on the equity funds used for construction for subsidiaries that apply the guidance for accounting for regulated operations. During 2015 , 2014 and 2013 , CERC capitalized interest and AFUDC of $2 million , $1 million and $1 million , respectively.
Income Taxes	Income Taxes CERC is included in the consolidated income tax returns of CenterPoint Energy. CERC calculates its income tax provision on a separate return basis under a tax sharing agreement with CenterPoint Energy. CERC uses the asset and liability method of accounting for deferred income taxes in accordance with accounting guidance for income taxes. Deferred income tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases. A valuation allowance is established against deferred tax assets for which management believes realization is not considered to be more likely than not. Current federal and certain state income taxes are payable to or receivable from CenterPoint Energy. CERC recognizes interest and penalties as a component of income tax expense.
Accounts Receivable and Allowance for Doubtful Accounts	Accounts Receivable and Allowance for Doubtful Accounts Accounts receivable are recorded at the invoiced amount and do not bear interest. It is the policy of management to review the outstanding accounts receivable monthly, as well as the bad debt write-offs experienced in the past, and establish an allowance for doubtful accounts. Account balances are charged off against the allowance when management determines it is probable the receivable will not be recovered. The provision for doubtful accounts in CERC’s Statements of Consolidated Income for 2015 , 2014 and 2013 was $19 million , $20 million and $20 million , respectively.
Inventory	Inventory Inventory consists principally of materials and supplies and natural gas. Materials and supplies are valued at the lower of average cost or market. Materials and supplies are recorded to inventory when purchased and subsequently charged to expense or capitalized to plant when installed. Natural gas inventories of CERC’s Energy Services business segment are valued at the lower of average cost or market. Natural gas inventories of CERC’s Natural Gas Distribution business segment are primarily valued at weighted average cost. During 2015 , 2014 and 2013 , CERC recorded $4 million , $8 million and $4 million , respectively, in write-downs of natural gas inventory to the lower of average cost or market.
Derivative Instruments	Derivative Instruments CERC is exposed to various market risks. These risks arise from transactions entered into in the normal course of business. CERC utilizes derivative instruments such as physical forward contracts, swaps and options to mitigate the impact of changes in commodity prices and weather on its operating results and cash flows. Such derivatives are recognized in CERC’s Consolidated Balance Sheets at their fair value unless CERC elects the normal purchase and sales exemption for qualified physical transactions. A derivative may be designated as a normal purchase or normal sale if the intent is to physically receive or deliver the product for use or sale in the normal course of business. CenterPoint Energy has a Risk Oversight Committee composed of corporate and business segment officers that oversees commodity price, weather and credit risk activities, including CERC’s marketing, risk management services and hedging activities. The committee’s duties are to establish CERC’s commodity risk policies, allocate board-approved commercial risk limits, approve the use of new products and commodities, monitor positions and ensure compliance with CERC’s risk management policies and procedures and limits established by CenterPoint Energy’s board of directors. CERC’s policies prohibit the use of leveraged financial instruments. A leveraged financial instrument, for this purpose, is a transaction involving a derivative whose financial impact will be based on an amount other than the notional amount or volume of the instrument.
Environmental Costs	Environmental Costs CERC expenses or capitalizes environmental expenditures, as appropriate, depending on their future economic benefit. CERC expenses amounts that relate to an existing condition caused by past operations that do not have future economic benefit. CERC records undiscounted liabilities related to these future costs when environmental assessments and/or remediation activities are probable and the costs can be reasonably estimated.
Statement of Consolidated Cash Flows	Statements of Consolidated Cash Flows For purposes of reporting cash flows, CERC considers cash equivalents to be short-term, highly-liquid investments with maturities of three months or less from the date of purchase. CERC considers distributions received from equity method investments which do not exceed cumulative equity in earnings subsequent to the date of investment to be a return on investment and classifies these distributions as operating activities in the Statements of Consolidated Cash Flows. CERC considers distributions received from equity method investments in excess of cumulative equity in earnings subsequent to the date of investment to be a return of investment and classifies these distributions as investing activities in the Statements of Consolidated Cash Flows.
New Accounting Pronouncements	New Accounting Pronouncements In February 2015, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update No. 2015-02, Consolidation (Topic 810): Amendments to the Consolidation Analysis (ASU 2015-02). ASU 2015 -02 changes the analysis that reporting organizations must perform to evaluate whether they should consolidate certain legal entities, such as limited partnerships. The changes include, among others, modification of the evaluation of whether limited partnerships and similar legal entities are variable interest entities (VIEs) or voting interest entities and elimination of the presumption that a general partner should consolidate a limited partnership. ASU 2015-02 does not amend the related party guidance for situations in which power is shared between two or more entities that hold interests in a VIE. ASU 2015 -02 is effective for fiscal years, and interim periods within those years, beginning after December 15, 2015. CERC does not believe that ASU 2015-02 will have a material impact on its financial position, results of operations, cash flows and disclosures. In April 2015, the FASB issued Accounting Standards Update No. 2015-03, Interest-Imputation of Interest (Subtopic 835-30): Simplifying the Presentation of Debt Issuance Cost (ASU 2015-03) . ASU 2015-03 requires that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability, consistent with debt discounts. The recognition and measurement guidance for debt issuance costs are not affected by ASU 2015-03. CERC will adopt ASU 2015-03 retrospectively on January 1, 2016, which will result in a reduction of both other long-term assets and long-term debt on its Consolidated Balance Sheets. CERC had debt issuance costs of $15 million and $18 million included in other long-term assets on its Consolidated Balance Sheets as of December 31, 2015 and 2014, respectively. In April 2015, the FASB issued Accounting Standards Update No. 2015-05, Intangibles-Goodwill and Other-Internal-Use Software ( Subtopic 350-40 ) (ASU 2015-05). ASU 2015-05 provides guidance to customers about whether a cloud computing arrangement includes a software license. If a cloud computing arrangement includes a software license, the customer should account for the software license element of the arrangement consistent with the acquisition of other software licenses. If a cloud computing arrangement does not include a software license, the customer should account for the arrangement as a service contract. The guidance will not change a customer’s accounting for service contracts. ASU 2015-05 is effective for fiscal years, and interim periods within the fiscal years, beginning after December 15, 2015 and may be adopted either prospectively or retrospectively. CERC will adopt ASU 2015-05 on January 1, 2016. CERC does not believe that ASU 2015-05 will have a material impact on its financial position, results of operations, cash flows and disclosures. In May 2014, the FASB issued Accounting Standards Update No. 2014-09, Revenue from Contracts with Customers (Topic 606) (ASU 2014-09), which supersedes most current revenue recognition guidance. ASU 2014-09 provides a comprehensive new revenue recognition model that requires revenue to be recognized in a manner that depicts the transfer of goods or services to a customer at an amount that reflects the consideration expected to be received in exchange for those goods or services. ASU 2014-09 was initially effective for fiscal years, and interim periods within those years, beginning after December 15, 2016. Early adoption is not permitted, and entities have the option of using either a full retrospective or a modified retrospective adoption approach. In August 2015, the FASB issued Accounting Standard Update No. 2015-14, Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date , which delays the effective date of ASU 2014-09 by one year. CERC is currently evaluating the impact that ASU 2014-09 will have on its financial position, results of operations, cash flows and disclosures, and will adopt ASU 2014-09 on January 1, 2018 as permitted by the new guidance. In July 2015, the FASB issued Accounting Standards Update No. 2015-11, Inventory (Topic 330) Simplifying the Measurement of Inventory (ASU 2015-11). ASU 2015-11 changes the subsequent measurement guidance for inventory accounted for using methods other than the last in, first out (LIFO) and Retail Inventory methods. Companies will subsequently measure inventory at the lower of cost and net realizable value. Net realizable value is the estimated selling price in the ordinary course of business, less reasonably predictable costs of completion, disposal, and transportation. Subsequent measurement is unchanged for inventory measured using LIFO or the retail inventory method. ASU 2015-11 is effective for fiscal years, and interim periods within those years, beginning after December 15, 2016, with early adoption permitted. CERC does not believe that ASU 2015-11 will have a material impact on its financial position, results of operations, cash flows and disclosures. In November 2015, the FASB issued Accounting Standards Update No. 2015-17, Income Taxes (Topic 740): Balance Sheet Classification of Deferred Taxes (ASU 2015-17). ASU 2015-17 requires deferred tax liabilities and assets be classified as noncurrent in a classified statement of financial position. CERC adopted ASU 2015-17 retrospectively starting with fiscal year 2015. As such, certain prior period amounts have been reclassified to conform to the current presentation. In the Consolidated Balance Sheet as of December 31, 2014, CERC reclassified $1 million from current deferred income tax assets to reduce deferred income taxes within non-current liabilities. See Note 12 for additional information. Management believes that other recently issued standards, which are not yet effective, will not have a material impact on CenterPoint Energy’s consolidated financial position, results of operations or cash flows upon adoption.
Other Current Assets and Liabilities	Other Current Assets and Liabilities Included in other current assets on the Consolidated Balance Sheets at December 31, 2015 and 2014 were $31 million and $19 million , respectively, of margin deposits and $12 million and $45 million , respectively of under-recovered gas cost. Included in other current liabilities on the Consolidated Balance Sheets at December 31, 2015 and 2014 were $55 million and $37 million , respectively, of over-recovered gas cost.

Summary of Significant Accoun26

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2015
Significant Accounting Policies [Abstract]
Schedule of Inventory [Table Text Block]	December 31, 2015 2014 (in millions) Materials and supplies $ 45 $ 41 Natural gas 168 211 Total inventory $ 213 $ 252

Property, Plant and Equipment (

Property, Plant and Equipment (Tables)	12 Months Ended
	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	Property, plant and equipment includes the following: Weighted Average Useful Lives December 31, (Years) 2015 2014 (in millions) Natural Gas Distribution 32 $ 5,762 $ 5,235 Energy Services 27 86 84 Other property 10 50 45 Total 5,898 5,364 Accumulated depreciation and amortization: Natural Gas Distribution 1,575 1,493 Energy Services 34 31 Other property 31 30 Total accumulated depreciation and amortization 1,640 1,554 Property, plant and equipment, net $ 4,258 $ 3,810
Depreciation And Amortization [Table Text Block]	The following table presents depreciation and amortization expense for 2015 , 2014 and 2013 : Year Ended December 31, 2015 2014 2013 (in millions) Depreciation expense $ 211 $ 195 $ 218 Amortization expense 16 11 12 Total depreciation and amortization expense $ 227 $ 206 $ 230
Asset Retirement Obligations	A reconciliation of the changes in the asset retirement obligation (ARO) liability is as follows: December 31, 2015 2014 (in millions) Beginning balance $ 139 $ 101 Accretion expense 5 4 Revisions in estimates of cash flows 12 34 Ending balance $ 156 $ 139

Goodwill (Tables)

Goodwill (Tables)	12 Months Ended
	Dec. 31, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill	Goodwill by reportable business segment as of both December 31, 2015 and 2014 are as follows: (in millions) Natural Gas Distribution $ 746 Energy Services (1) 83 Other 11 Total $ 840 (1) Amounts presented are net of accumulated goodwill impairment charge of $252 million .

Regulatory Matters (Tables)

Regulatory Matters (Tables)	12 Months Ended
	Dec. 31, 2015
Regulatory Matters [Abstract]
Schedule of Regulatory Assets and Liabilities	The following is a list of regulatory assets/liabilities reflected on CERC’s Consolidated Balance Sheets as of December 31, 2015 and 2014 : December 31, 2015 2014 (in millions) Regulatory assets in other long-term assets (1) (2) $ 105 $ 103 Regulatory liabilities (734 ) (669 ) Net $ (629 ) $ (566 ) (1) Regulatory assets that are not earning a return were not material at December 31, 2015 or 2014 . (2) NGD’s actuarially determined pension and other postemployment expense in excess of the amount being recovered through rates is being deferred for rate making purposes. Deferred pension and other postemployment expenses of $5 million as of December 31, 2015 were not earning a return.

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2015
Compensation and Retirement Disclosure [Abstract]
Schedule of Defined Benefit Plans Disclosures [Table Text Block]	As part of the investment strategy discussed above, CERC maintained the following asset allocation ranges for its postretirement benefit plan as of December 31, 2015 : U.S. equity 15–25% International equity 2–12% Fixed income 68–78% Cash 0–2% Following are reconciliations of CERC’s beginning and ending balances of its postretirement benefit plan’s benefit obligation, plan assets and funded status for 2015 and 2014 . The measurement dates for plan assets and obligations were December 31, 2015 and 2014 . December 31, 2015 2014 (in millions, except for actuarial assumptions) Change in Benefit Obligation Accumulated benefit obligation, beginning of year $ 126 $ 116 Service cost 1 1 Interest cost 5 5 Benefits paid (12 ) (13 ) Participant contributions 4 4 Medicare reimbursement 1 2 Plan amendment (5 ) 1 Curtailment — (2 ) Actuarial (gain) loss (19 ) 12 Accumulated benefit obligation, end of year $ 101 $ 126 Change in Plan Assets Plan assets, beginning of year $ 26 $ 26 Benefits paid (12 ) (13 ) Employer contributions 7 8 Participant contributions 4 4 Actual investment return — 1 Plan assets, end of year $ 25 $ 26 Amounts Recognized in Balance Sheets Current liabilities-other $ (6 ) $ (7 ) Other liabilities-benefit obligations (70 ) (93 ) Net liability, end of year $ (76 ) $ (100 ) Actuarial Assumptions Discount rate 4.35 % 3.90 % Expected long-term return on assets 3.95 % 4.00 % Healthcare cost trend rate assumed for the next year - Pre 65 6.00 % 7.25 % Healthcare cost trend rate assumed for the next year - Post 65 5.50 % 8.50 % Prescription cost trend rate assumed for the next year 11.00 % 6.50 % Rate to which the cost trend rate is assumed to decline (ultimate trend rate) 5.00 % 5.00 % Year that the healthcare rate reaches the ultimate trend rate 2024 2024 Year that the prescription drug rate reaches the ultimate trend rate 2024 2024 CERC’s changes in accumulated comprehensive income (loss) related to postretirement and other postemployment plans are as follows: Year Ended December 31, 2015 2014 (in millions) Beginning Balance $ 1 $ 5 Other comprehensive income (loss) before reclassifications (1) 13 (5 ) Amounts reclassified from accumulated other comprehensive income: Actuarial gains (2) 1 — Total reclassifications from accumulated other comprehensive income 1 — Tax expense (6 ) 1 Net current period other comprehensive income (loss) 8 (4 ) Ending Balance $ 9 $ 1 (1) Total other comprehensive income related to the re-measurement of pension, postretirement and other postemployment plans. (2) These accumulated other comprehensive components are included in the computation of net periodic cost. Amounts recognized in accumulated other comprehensive (income) loss consist of the following: December 31, 2015 2014 (in millions) Unrecognized actuarial loss $ 3 $ 13 Unrecognized prior service cost (credit) (1 ) 2 Total recognized in accumulated other comprehensive loss 2 15 Less: deferred tax benefit (1) (11 ) (16 ) Net amount recognized in accumulated other comprehensive income $ (9 ) $ (1 ) (1) CERC’s postretirement benefit obligation is reduced by the impact of previously non-taxable government subsidies under the Medicare Prescription Drug Act. Because the subsidies were non-taxable, the temporary difference used in measuring the deferred tax impact was determined on the unrecognized losses excluding such subsidies. The changes in plan assets and benefit obligations recognized in other comprehensive loss during 2015 are as follows: Postretirement Benefits (in millions) Net loss $ 10 Amortization of prior service cost 3 Total recognized in other comprehensive loss $ 13 The following benefit payments are expected to be made by the postretirement benefit plan: Postretirement Benefit Plan Benefit Payments Medicare Subsidy Receipts (in millions) 2016 $ 10 $ (2 ) 2017 10 (2 ) 2018 10 (2 ) 2019 11 (2 ) 2020 11 (3 ) 2021-2025 56 (17 ) The net postretirement benefit cost includes the following components: Year Ended December 31, 2015 2014 2013 (in millions) Service cost — benefits earned during the period $ 1 $ 1 $ 1 Interest cost on accumulated benefit obligation 5 5 5 Expected return on plan assets (1 ) (1 ) (1 ) Amortization of prior service cost 1 1 1 Amortization of net loss 1 1 2 Net postretirement benefit cost $ 7 $ 7 $ 8 CERC used the following assumptions to determine net postretirement benefit costs: Year Ended December 31, 2015 2014 2013 Discount rate 3.90 % 4.75 % 3.90 % Expected return on plan assets 4.05 % 3.10 % 3.10 %
Defined Benefit Plan Schedule Of Effect Of One Percentage Point Change In Assumed Health Care Cost Trend Rates Text Block	Assumed healthcare cost trend rates have a significant effect on the reported amounts for CERC’s postretirement benefit plans. A 1% change in the assumed healthcare cost trend rate would have the following effects: 1% Increase 1% Decrease (in millions) Effect on the postretirement benefit obligation $ 2 $ 2 Effect on the total of service and interest cost — —
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Text Block]	The fair values of CERC’s postretirement plan assets at December 31, 2015 and 2014 , by asset category are as follows: Fair Value Measurements as of December 31, 2015 Total Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) (in millions) Mutual funds (1) $ 25 $ 25 $ — $ — Total $ 25 $ 25 $ — $ — (1) 70% of the amount invested in mutual funds was in fixed income securities; 23% was in U.S. equities and 7% was in international equities. Fair Value Measurements as of December 31, 2014 Total Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) (in millions) Mutual funds (1) $ 26 $ 26 $ — $ — Total $ 26 $ 26 $ — $ — (1) 70% of the amount invested in mutual funds was in fixed income securities; 23% was in U.S. equities and 7% was in international equities.

Related Party Transactions Rela

Related Party Transactions Related Party Transaction (Tables)	12 Months Ended
	Dec. 31, 2015
Related Party Transaction [Line Items]
Schedule of Related Party Transactions [Table Text Block]	CenterPoint Energy provides some corporate services to CERC. The costs of services have been charged directly to CERC using methods that management believes are reasonable. These methods include negotiated usage rates, dedicated asset assignment and proportionate corporate formulas based on operating expenses, assets, gross margin, employees and a composite of assets, gross margin and employees. CenterPoint Houston provides a number of services to CERC. These services are billed at actual cost, either directly or as an allocation, and include fleet services, shop services, geographic services, surveying and right-of-way, radio communications, data circuit management and field operations. Additionally, CERC provides certain services to CenterPoint Houston. These services are billed at actual cost, either directly or as an allocation and include line locating and other miscellaneous services. These charges are not necessarily indicative of what would have been incurred had CERC not been an affiliate of CenterPoint Energy. Amounts charged to and from CERC for these services were as follows and are included primarily in operation and maintenance expenses: Year Ended December 31, 2015 2014 2013 (in millions) Corporate service charges $ 118 $ 115 $ 105 Charges from CenterPoint Houston for services provided 18 17 21 Billings to CenterPoint Houston for services provided (6 ) (5 ) (9 ) $ 130 $ 127 $ 117

Derivative Instruments (Tables)

Derivative Instruments (Tables)	12 Months Ended
	Dec. 31, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of Derivative Instruments in Statement of Financial Position, Fair Value	The following tables present information about CERC’s derivative instruments and hedging activities. The first four tables provide a balance sheet overview of CERC’s Derivative Assets and Liabilities as of December 31, 2015 and 2014 , while the last table provides a breakdown of the related income statement impacts for the years ending December 31, 2015 and 2014 . Fair Value of Derivative Instruments December 31, 2015 Total derivatives not designated as hedging instruments Balance Sheet Location Derivative Assets Fair Value Derivative Liabilities Fair Value (in millions) Natural gas derivatives (1) (2) (3) Current Assets: Non-trading derivative assets $ 90 $ 2 Natural gas derivatives (1) (2) (3) Other Assets: Non-trading derivative assets 36 — Natural gas derivatives (1) (2) (3) Current Liabilities: Non-trading derivative liabilities 10 60 Natural gas derivatives (1) (2) (3) Other Liabilities: Non-trading derivative liabilities 4 25 Total $ 140 $ 87 (1) The fair value shown for natural gas contracts is comprised of derivative gross volumes totaling 767 billion cubic feet (Bcf) or a net 112 Bcf long position. Of the net long position, basis swaps constitute 133 Bcf. (2) Natural gas contracts are presented on a net basis in the Consolidated Balance Sheets. Natural gas contracts are subject to master netting arrangements. This netting applies to all undisputed amounts due or past due and causes derivative assets (liabilities) to be ultimately presented net in a liability (asset) account within the Consolidated Balance Sheets. The net of total non-trading derivative assets and liabilities was a $109 million asset as shown on CERC’s Consolidated Balance Sheets (and as detailed in the table below), and was comprised of the natural gas contracts derivative assets and liabilities separately shown above offset by collateral netting of $56 million . (3) Derivative Assets and Derivative Liabilities include no material amounts related to physical forward transactions with Enable. Offsetting of Natural Gas Derivative Assets and Liabilities December 31, 2015 Gross Amounts Recognized (1) Gross Amounts Offset in the Consolidated Balance Sheets Net Amount Presented in the Consolidated Balance Sheets (2) (in millions) Current Assets: Non-trading derivative assets $ 100 $ (11 ) $ 89 Other Assets: Non-trading derivative assets 40 (4 ) 36 Current Liabilities: Non-trading derivative liabilities (62 ) 51 (11 ) Other Liabilities: Non-trading derivative liabilities (25 ) 20 (5 ) Total $ 53 $ 56 $ 109 (1) Gross amounts recognized include some derivative assets and liabilities that are not subject to master netting arrangements. (2) The derivative assets and liabilities on the Consolidated Balance Sheets exclude accounts receivable or accounts payable that, should they exist, could be used as offsets to these balances in the event of a default. Fair Value of Derivative Instruments December 31, 2014 Total derivatives not designated as hedging instruments Balance Sheet Location Derivative Assets Fair Value Derivative Liabilities Fair Value (in millions) Natural gas derivatives (1) (2) (3) Current Assets: Non-trading derivative assets $ 101 $ 1 Natural gas derivatives (1) (2) (3) Other Assets: Non-trading derivative assets 32 — Natural gas derivatives (1) (2) (3) Current Liabilities: Non-trading derivative liabilities 14 83 Natural gas derivatives (1) (2) (3) Other Liabilities: Non-trading derivative liabilities 2 18 Total $ 149 $ 102 (1) The fair value shown for natural gas contracts is comprised of derivative gross volumes totaling 804 Bcf or a net 60 Bcf long position. Of the net long position, basis swaps constitute 127 Bcf. (2) Natural gas contracts are presented on a net basis in the Consolidated Balance Sheets. Natural gas contracts are subject to master netting arrangements. This netting applies to all undisputed amounts due or past due and causes derivative assets (liabilities) to be ultimately presented net in a liability (asset) account within the Consolidated Balance Sheets. The net of total non-trading derivative assets and liabilities was a $111 million asset as shown on CERC’s Consolidated Balance Sheets (and as detailed in the table below), and was comprised of the natural gas contracts derivative assets and liabilities separately shown above, offset by collateral netting of $64 million . (3) Derivative Assets and Derivative Liabilities include no material amounts related to physical forward transactions with Enable. Offsetting of Natural Gas Derivative Assets and Liabilities December 31, 2014 Gross Amounts Recognized (1) Gross Amounts Offset in the Consolidated Balance Sheets Net Amount Presented in the Consolidated Balance Sheets (2) (in millions) Current Assets: Non-trading derivative assets $ 115 $ (16 ) $ 99 Other Assets: Non-trading derivative assets 34 (2 ) 32 Current Liabilities: Non-trading derivative liabilities (84 ) 65 (19 ) Other Liabilities: Non-trading derivative liabilities (18 ) 17 (1 ) Total $ 47 $ 64 $ 111 (1) Gross amounts recognized include some derivative assets and liabilities that are not subject to master netting arrangements. (2) The derivative assets and liabilities on the Consolidated Balance Sheets exclude accounts receivable or accounts payable that, should they exist, could be used as offsets to these balances in the event of a default.
Schedule of Derivative Instruments, Gain (Loss) in Statement of Financial Performance	For CERC’s price stabilization activities of the Natural Gas Distribution business segment, the settled costs of derivatives are ultimately recovered through purchased gas adjustments. Accordingly, the net unrealized gains and losses associated with these contracts are recorded as net regulatory assets. Realized and unrealized gains and losses on other derivatives are recognized in the Statements of Consolidated Income as revenue for retail sales derivative contracts and as natural gas expense for financial natural gas derivatives and non-retail related physical natural gas derivatives. Income Statement Impact of Derivative Activity Year Ended December 31, Total derivatives not designated as hedging instruments Income Statement Location 2015 2014 2013 (in millions) Natural gas derivatives Gains (Losses) in Revenue $ 134 $ 35 $ 11 Natural gas derivatives (1) Gains (Losses) in Expense: Natural Gas (105 ) 11 10 Total $ 29 $ 46 $ 21 (1) The Gains (Losses) in Expense: Natural Gas includes $-0- and $2 million during the years ended December 31, 2015 and 2014 , respectively, related to physical forwards purchased from Enable.
Credit Quality Of Counterparties	In addition to the risk associated with price movements, credit risk is also inherent in CERC’s non-trading derivative activities. Credit risk relates to the risk of loss resulting from non-performance of contractual obligations by a counterparty. The following table shows the composition of counterparties to the non-trading derivative assets of CERC as of December 31, 2015 and 2014 : December 31, 2015 December 31, 2014 Investment Grade(1) Total Investment Grade(1) Total (in millions) Energy marketers $ 4 $ 10 $ 2 $ 4 Financial institutions — — — — End users (2) 2 115 2 127 Total $ 6 $ 125 $ 4 $ 131 (1) “Investment grade” is primarily determined using publicly available credit ratings, and considers credit support (including parent company guarantees) and collateral (including cash and standby letters of credit). For unrated counterparties, CERC determines a synthetic credit rating by performing financial statement analysis, and considers contractual rights and restrictions and collateral. (2) End users are comprised primarily of customers who have contracted to fix the price of a portion of their physical gas requirements for future periods.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2015
Fair Value Disclosures [Abstract]
Fair Value, Assets Measured on Recurring Basis [Table Text Block]	The following tables present information about CERC’s assets and liabilities (including derivatives that are presented net) measured at fair value on a recurring basis as of December 31, 2015 and 2014 , and indicate the fair value hierarchy of the valuation techniques utilized by CERC to determine such fair value. Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Netting Adjustments (1) Balance as of December 31, 2015 (in millions) Assets Corporate equities $ 2 $ — $ — $ — $ 2 Investments, including money market funds 11 — — — 11 Natural gas derivatives (2) 4 115 21 (15 ) 125 Total assets $ 17 $ 115 $ 21 $ (15 ) $ 138 Liabilities Natural gas derivatives (2) $ 13 $ 65 $ 9 $ (71 ) $ 16 Total liabilities $ 13 $ 65 $ 9 $ (71 ) $ 16 (1) Amounts represent the impact of legally enforceable master netting arrangements that allow CERC to settle positive and negative positions and also include cash collateral of $56 million posted with the same counterparties. (2) Natural gas derivatives include no material amounts related to physical forward transactions with Enable. Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Netting Adjustments (1) Balance as of December 31, 2014 (in millions) Assets Corporate equities $ 2 $ — $ — $ — $ 2 Investments, including money market funds 11 — — — 11 Natural gas derivatives (2) 7 122 20 (18 ) 131 Total assets $ 20 $ 122 $ 20 $ (18 ) $ 144 Liabilities Natural gas derivatives $ 22 $ 77 $ 3 $ (82 ) $ 20 Total liabilities $ 22 $ 77 $ 3 $ (82 ) $ 20 (1) Amounts represent the impact of legally enforceable master netting arrangements that allow CERC to settle positive and negative positions and also include cash collateral of $64 million posted with the same counterparties. (2) Natural gas derivatives include no material amounts related to physical forward transactions with Enable.
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block]	The following tables present additional information about assets or liabilities, including derivatives that are measured at fair value on a recurring basis for which CERC has utilized Level 3 inputs to determine fair value: Fair Value Measurements Using Significant Unobservable Inputs (Level 3) Derivative assets and liabilities, net Year Ended December 31, 2015 2014 2013 (in millions) Beginning balance $ 17 $ 3 $ 2 Total gains 7 14 3 Total settlements (12 ) 1 (3 ) Transfers out of Level 3 (1 ) — — Transfers into Level 3 1 (1 ) 1 Ending balance (1) $ 12 $ 17 $ 3 The amount of total gains for the period included in earnings attributable to the change in unrealized gains or losses relating to assets still held at the reporting date $ 6 $ 16 $ 2 (1) During 2015, 2014 and 2013, CenterPoint Energy did not have significant Level 3 purchases or sales.
Fair Value, by Balance Sheet Grouping [Table Text Block]	December 31, 2015 December 31, 2014 Carrying Amount Fair Value Carrying Amount Fair Value (in millions) Financial assets: Notes receivable - affiliated companies $ 363 $ 356 $ 363 $ 362 Financial liabilities: Long-term debt $ 2,353 $ 2,551 $ 2,469 $ 2,772

Unconsolidated Affiliates (Tabl

Unconsolidated Affiliates (Tables)	12 Months Ended
	Dec. 31, 2015
Equity Method Investments and Joint Ventures [Abstract]
Equity Method Investments [Table Text Block]	Investment in Unconsolidated Affiliates: Year Ended December 31, 2015 2014 (in millions) Enable $ 2,594 $ 4,520 SESH (1) — 1 Total $ 2,594 $ 4,521 (1) CERC disposed of its remaining interest in SESH on June 30, 2015. Equity in Earnings (Losses) of Unconsolidated Affiliates, net: Year Ended December 31, 2015 2014 2013 (in millions) Enable $ (1,633 ) $ 303 $ 173 SESH (1) — 5 15 Total $ (1,633 ) $ 308 $ 188 (1) CERC contributed a 24.95% interest in SESH to Enable on May 30, 2014 and its remaining interest in SESH to Enable on June 30, 2015. Summarized consolidated income (loss) information for Enable is as follows: Year Ended December 31, 2015 2014 2013 (in millions) Operating revenues $ 2,418 $ 3,367 $ 2,123 Cost of sales, excluding depreciation and amortization 1,097 1,914 1,241 Impairment of goodwill and other long-lived assets 1,134 8 12 Operating income (loss) (712 ) 586 322 Net income (loss) attributable to Enable (752 ) 530 289 Reconciliation of Equity in Earnings (Losses), net: CERC’s interest $ (416 ) $ 298 $ 168 Basis difference amortization (1) 8 5 5 Impairment of CERC’s equity method investment in Enable (1,225 ) — — CERC’s equity in earnings (losses), net (2) $ (1,633 ) $ 303 $ 173 (1) 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 33 years, the average life of the assets to which the basis difference is attributed. (2) These amounts include CERC’s share of Enable’s impairment of goodwill and long-lived assets and the impairment of CERC’s equity method investment in Enable totaling $1,846 million during the year ended December 31, 2015 . This impairment is offset by $213 million of earnings for the year ended December 31, 2015 . Summarized consolidated balance sheet information for Enable is as follows: December 31, 2015 2014 (in millions) Current assets $ 381 $ 438 Non-current assets 10,857 11,399 Current liabilities 615 671 Non-current liabilities 3,092 2,343 Non-controlling interest 12 31 Enable partners’ capital 7,519 8,792 Reconciliation of Investment in Enable: CERC’s ownership interest in Enable partners’ capital $ 4,163 $ 4,869 CERC’s basis difference (1,569 ) (349 ) CERC’s investment in Enable $ 2,594 $ 4,520 Distributions Received from Unconsolidated Affiliates: Year Ended December 31, 2015 2014 2013 (in millions) Enable $ 294 $ 298 $ 106 SESH (1) — 7 23 Total $ 294 $ 305 $ 129 (1) CERC contributed a 24.95% interest in SESH to Enable on each of May 1, 2013 and May 30, 2014 and its remaining interest in SESH to Enable on June 30, 2015.

Short-term Borrowings and Lon35

Short-term Borrowings and Long-term Debt (Tables)	12 Months Ended
	Dec. 31, 2015
Debt Disclosure [Abstract]
Schedule of Debt [Table Text Block]	December 31, 2015 December 31, 2014 Long-Term Current (1) Long-Term Current (1) (in millions) Short-term borrowings: Inventory financing $ — $ 40 $ — $ 53 Total short-term borrowings — 40 — 53 Long-term debt: Senior notes 4.50% to 6.625% due 2016 to 2041 1,843 325 2,168 — Commercial paper (2) 219 — 341 — Unamortized discount and premium (34 ) — (40 ) — Total long-term debt 2,028 325 2,469 — Total debt $ 2,028 $ 365 $ 2,469 $ 53 (1) Includes amounts due or exchangeable within one year of the date noted. (2) Classified as long-term debt because the termination date of the facility that backstops the commercial paper is more than one year from the date noted.
Schedule of Line of Credit Facilities [Table Text Block]	As of December 31, 2015 and 2014 , CERC had the following revolving credit facility and utilization of such facility: December 31, 2015 December 31, 2014 Size of Loans Letters Commercial Loans Letters Commercial (in millions) $ 600 $ — $ 2 $ 219 (1) $ — $ — $ 341 (1) (1) Weighted average interest rate was 0.81% and 0.68% as of December 31, 2015 and 2014, respectively.

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2015
Income Taxes [Abstract]
Income Tax Expense Disclosure	The components of CERC’s income tax expense (benefit) were as follows: Year Ended December 31, 2015 2014 2013 (in millions) Current income tax expense: Federal $ — $ — $ 5 State 3 10 9 Total current expense 3 10 14 Deferred income tax expense (benefit): Federal (488 ) 171 350 State (54 ) 7 7 Total deferred expense (benefit) (542 ) 178 357 Total income tax expense (benefit) $ (539 ) $ 188 $ 371
Reconciliation Of Expected Federal Income Tax Expense To Actual	A reconciliation of income tax expense (benefit) using the federal statutory income tax rate to the actual income tax expense and resulting effective income tax rate is as follows: Year Ended December 31, 2015 2014 2013 (in millions) Income (loss) before income taxes $ (1,451 ) $ 511 $ 435 Federal statutory income tax rate 35 % 35 % 35 % Expected federal income tax expense (benefit) (508 ) 179 152 Increase (decrease) in tax expense resulting from: State income tax expense, net of federal income tax (33 ) 11 23 Decrease in settled and uncertain income tax positions — — (2 ) Tax effect related to the formation of Enable Midstream Partnership — — 198 Other, net 2 (2 ) — Total (31 ) 9 219 Total income tax expense (benefit) $ (539 ) $ 188 $ 371 Effective tax rate 37.1 % 36.8 % 85.3 %
Income Tax Asset Liability Disclosure	The tax effects of temporary differences that give rise to significant portions of deferred tax assets and liabilities were as follows: December 31, 2015 2014 (in millions) Deferred tax assets: Benefits and compensation $ 39 $ 48 Loss and credit carryforwards 388 326 Asset retirement obligations 59 52 Other 39 28 Valuation allowance (2 ) (2 ) Total deferred tax assets 523 452 Deferred tax liabilities: Property, plant, and equipment 929 803 Investment in unconsolidated affiliates 1,277 1,788 Regulatory assets/liabilities, net — 13 Other 91 99 Total deferred tax liabilities 2,297 2,703 Net deferred tax liabilities $ 1,774 $ 2,251
Uncertain Income Tax Positions	Uncertain Income Tax Positions . The following table reconciles the beginning and ending balance of CERC’s unrecognized tax benefits (expenses): December 31, 2015 2014 2013 (in millions) Balance, beginning of year $ — $ — $ (20 ) Tax Positions related to prior years: Reductions — — (2 ) Tax Positions related to current year: Settlements — — 22 Balance, end of year $ — $ — $ —

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Operating Leases of Lessee Disclosure [Table Text Block]	The following table sets forth information concerning CERC’s obligations under non-cancelable long-term operating leases as of December 31, 2015 , which primarily consist of rental agreements for building space, data processing equipment, compression equipment and rights-of-way: (in millions) 2016 $ 5 2017 3 2018 3 2019 3 2020 2 2021 and beyond 7 Total $ 23

Unaudited Quarterly Informati38

Unaudited Quarterly Information (Tables)	12 Months Ended
	Dec. 31, 2015
Unaudited Quarterly Information [Abstract]
Quarterly financial data	Summarized quarterly financial data is as follows: Year Ended December 31, 2015 First Quarter Second Quarter Third Quarter (1) Fourth Quarter (2) (in millions) Revenues $ 1,817 $ 824 $ 799 $ 1,087 Operating income 160 27 18 108 Net income (loss) 109 22 (508 ) (535 ) Year Ended December 31, 2014 First Quarter Second Quarter Third Quarter Fourth Quarter (in millions) Revenues $ 2,531 $ 1,183 $ 964 $ 1,689 Operating income (loss) 188 39 (3 ) 111 Net income 152 48 28 95 (1) CERC recognized $862 million ( $537 million after tax) in impairment charges related to Enable during the three months ended September 30, 2015. (2) CERC recognized $984 million ( $620 million after tax) in impairment charges related to Enable during the three months ended December 31, 2015.

Reportable Business Segments (T

Reportable Business Segments (Tables)	12 Months Ended
	Dec. 31, 2015
Segment Reporting [Abstract]
Schedule of Segment Reporting Information, by Segment [Table Text Block]	Financial data for business segments and products and services are as follows: Revenues from External Customers Inter-segment Revenues Depreciation and Amortization Operating Income (Loss) Total Assets Expenditures for Long- Lived Assets (in millions) As of and for the year ended December 31, 2015: Natural Gas Distribution $ 2,603 $ 29 $ 222 $ 273 $ 5,657 $ 601 Energy Services 1,924 33 5 42 857 5 Midstream Investments (1) — — — — 2,594 — Other — — — (2 ) 789 — Reconciling Eliminations — (62 ) — — (744 ) — Consolidated $ 4,527 $ — $ 227 $ 313 $ 9,153 $ 606 As of and for the year ended December 31, 2014: Natural Gas Distribution $ 3,271 $ 30 $ 201 $ 287 $ 5,464 $ 525 Energy Services 3,095 84 5 52 978 3 Midstream Investments (1) — — — — 4,521 — Other 1 — — (4 ) 1,045 — Reconciling Eliminations — (114 ) — — (964 ) — Consolidated $ 6,367 $ — $ 206 $ 335 $ 11,044 $ 528 As of and for the year ended December 31, 2013: Natural Gas Distribution $ 2,837 $ 26 $ 185 $ 263 $ 4,976 $ 430 Energy Services 2,374 27 5 13 895 3 Interstate Pipelines (2) (3) 133 53 20 72 — 29 Field Services (3) 178 18 20 73 — 16 Midstream Investments (1) — — — — 4,518 — Other — — — (20 ) 1,139 — Reconciling Eliminations — (124 ) — — (996 ) — Consolidated $ 5,522 $ — $ 230 $ 401 $ 10,532 $ 478 (1) Midstream Investments’ equity earnings (losses) are as follows: Year Ended December 31, 2015 2014 2013 (in millions) Enable (1) $ (1,633 ) $ 303 $ 173 SESH — 5 8 Total $ (1,633 ) $ 308 $ 181 (1) These amounts include CERC’s share of Enable’s impairment of goodwill and long-lived assets and the impairment of CERC’s equity method investment in Enable totaling $1,846 million during the year ended December 31, 2015 . This impairment is offset by $213 million of earnings for the year ended December 31, 2015 . Midstream Investments’ total assets are as follows: December 31, December 31, (in millions) Enable $ 2,594 $ 4,520 SESH — 1 Total $ 2,594 $ 4,521 (2) Interstate Pipelines recorded equity income of $7 million in the year ended December 31, 2013 from its interest in SESH, a jointly-owned pipeline. These amounts are included in Equity in earnings of unconsolidated affiliates under the Other Income (Expense) caption. As discussed above, effective May 1, 2013, CenterPoint Energy reports equity earnings associated with its interest in Enable and equity earnings associated with its interest in SESH under its Midstream Investments segment, and no longer has an Interstate Pipelines reporting segment prospectively. (3) Results reflected in the year ended December 31, 2013 represent only January 2013 through April 2013.
Revenue from External Customers by Products and Services [Table Text Block]	Year Ended December 31, Revenues by Products and Services: 2015 2014 2013 (in millions) Retail gas sales $ 3,725 $ 5,049 $ 4,150 Wholesale gas sales 657 1,159 913 Gas transportation and processing 26 38 345 Energy products and services 119 121 114 Total $ 4,527 $ 6,367 $ 5,522
Midstream Investments [Table Text Block]	Midstream Investments’ equity earnings (losses) are as follows: Year Ended December 31, 2015 2014 2013 (in millions) Enable (1) $ (1,633 ) $ 303 $ 173 SESH — 5 8 Total $ (1,633 ) $ 308 $ 181 (1) These amounts include CERC’s share of Enable’s impairment of goodwill and long-lived assets and the impairment of CERC’s equity method investment in Enable totaling $1,846 million during the year ended December 31, 2015 . This impairment is offset by $213 million of earnings for the year ended December 31, 2015 . Midstream Investments’ total assets are as follows: December 31, December 31, (in millions) Enable $ 2,594 $ 4,520 SESH — 1 Total $ 2,594 $ 4,521

Schedule II Valuation and Quali

Schedule II Valuation and Qualifying Accounts (Tables)	12 Months Ended
	Dec. 31, 2015
Valuation and Qualifying Accounts Disclosure [Line Items]
Schedule of Valuation and Qualifying Accounts Disclosure [Text Block]	CENTERPOINT ENERGY RESOURCES CORP. AND SUBSIDIARIES (An Indirect, Wholly-Owned Subsidiary of CenterPoint Energy, Inc.) SCHEDULE II — VALUATION AND QUALIFYING ACCOUNTS For the Three Years Ended December 31, 2015 Column A Column B Column C Column D Column E Description Balance at Beginning of Period Additions Deductions From Reserves (1) Balance at End of Period Charged to Income Charged to Other Accounts (in millions) Year Ended December 31, 2015: Accumulated provisions: Uncollectible accounts receivable $ 23 $ 19 $ (2 ) $ 21 $ 19 Deferred tax asset valuation allowance 2 — — — 2 Year Ended December 31, 2014: Accumulated provisions: Uncollectible accounts receivable $ 25 $ 20 $ 1 $ 23 $ 23 Deferred tax asset valuation allowance 2 — — — 2 Year Ended December 31, 2013: Accumulated provisions: Uncollectible accounts receivable $ 23 $ 20 $ — $ 18 $ 25 Deferred tax asset valuation allowance 2 — — — 2 (1) Deductions from reserves represent losses or expenses for which the respective reserves were created. In the case of the uncollectible accounts reserve, such deductions are net of recoveries of amounts previously written off.

Background (Details)

Background (Details)	Dec. 31, 2015	May. 30, 2014	Mar. 31, 2014
Enable Midstream Partners [Member]
Equity Method Investment, Ownership Percentage	55.40%	54.70%	58.30%

Summary of Significant Accoun42

Summary of Significant Accounting Policies (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Summary of Accounting Policies [Line Items]
Regulatory liabilities	$ 734	$ 669
Capitalized Interest Costs, Including Allowance for Funds Used During Construction	2	1	$ 1
Provision for doubtful accounts	19	20	20
Write-down of natural gas inventory	4	8	$ 4
Inventory	213	252
Deferred Tax Asset, Reclassified to Noncurrent Deferred Tax Liability		1
Margin deposits	31	19
Under Recovered Gas Costs	12	45
Over Recovered Gas Costs	$ 55	37
Enable Midstream Partners [Member]
Summary of Accounting Policies [Line Items]
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage	55.40%
Management Rights Ownership Percentage	50.00%
Incentive Distribution Right	40.00%
Incentive Distribution Right, Maximum	50.00%
Enable Midstream Partners [Member] | OGE [Member]
Summary of Accounting Policies [Line Items]
Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage	26.30%
Management Rights Ownership Percentage	50.00%
Incentive Distribution Right	60.00%
Minimum [Member] | Enable Midstream Partners [Member]
Summary of Accounting Policies [Line Items]
Incentive Distribution, Distribution Per Unit	$ 0.2875
Maximum [Member] | Enable Midstream Partners [Member]
Summary of Accounting Policies [Line Items]
Incentive Distribution, Distribution Per Unit	$ 0.330625
Removal Costs [Member]
Summary of Accounting Policies [Line Items]
Regulatory liabilities	$ 632	605
Materials And Supplies [Member]
Summary of Accounting Policies [Line Items]
Inventory	45	41
Public Utilities, Inventory, Natural Gas [Member]
Summary of Accounting Policies [Line Items]
Inventory	168	211
Other Noncurrent Assets [Member]
Summary of Accounting Policies [Line Items]
Unamortized Debt Issuance Expense	$ 15	$ 18

Property, Plant and Equipment43

Property, Plant and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 5,898	$ 5,364
Accumulated depreciation and amortization	1,640	1,554
Property, Plant and Equipment, Net	4,258	3,810
Depreciation expense	211	195	$ 218
Amortization expense	16	11	12
Total depreciation and amortization expense	227	206	230
Beginning balance	139	101
Accretion expense	5	4
Revisions in estimates of cash flows	12	34
Ending balance	156	139	$ 101
Natural Gas Distribution [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	5,762	5,235
Accumulated depreciation and amortization	$ 1,575	1,493
Natural Gas Distribution [Member] | Weighted Average [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	32 years
Energy Services [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 86	84
Accumulated depreciation and amortization	$ 34	31
Energy Services [Member] | Weighted Average [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	27 years
Other property [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 50	45
Accumulated depreciation and amortization	$ 31	$ 30
Other property [Member] | Weighted Average [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	10 years

Goodwill (Details)

Goodwill (Details) - USD ($) $ in Millions		Dec. 31, 2015	Dec. 31, 2014
Goodwill [Line Items]
Goodwill		$ 840	$ 840
Natural Gas Distribution [Member]
Goodwill [Line Items]
Goodwill		746	746
Energy Services [Member]
Goodwill [Line Items]
Goodwill	[1]	83	83
Accumulated Goodwill Impairment Charge		252	252
Corporate and Other [Member]
Goodwill [Line Items]
Goodwill		$ 11	$ 11
[1]	Amounts presented are net of accumulated goodwill impairment charge of $252 million.

Regulatory Matters (Details)

Regulatory Matters (Details) - USD ($) $ in Millions		Dec. 31, 2015	Dec. 31, 2014
Schedule Of Regulatory Assets And Liabilities [Line Items]
Regulatory assets in other long-term assets (1) (2)	[1],[2]	$ 105	$ 103
Regulatory liabilities		(734)	(669)
Net Regulatory Assets (Liabilities)		(629)	$ (566)
Pension and Other Postretirement Plans Costs [Member]
Schedule Of Regulatory Assets And Liabilities [Line Items]
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided		$ 5
[1]	NGD’s actuarially determined pension and other postemployment expense in excess of the amount being recovered through rates is being deferred for rate making purposes. Deferred pension and other postemployment expenses of $5 million as of December 31, 2015 were not earning a return.
[2]	Regulatory assets that are not earning a return were not material at December 31, 2015 or 2014.

Employee Benefit Plans Pension

Employee Benefit Plans Pension and Postretirement Benefits (Details) - USD ($) $ in Millions		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2015	Dec. 31, 2014
Pension and Savings Plan
New percentage of eligible earnings used to determine retirement benefits							5.00%
Pension Expense				$ 24	$ 27	$ 29
Non Qualified Pension Plan Benefit Expense				$ 2	2	2
Maximum Percentage Of Employee Compensation Eligible For Contribution To Savings Plan				50.00%
Description Of Company Match Under Savings Plan				100.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay				6.00%
Defined Contribution Plan, Cost Recognized				$ 14	20	19
Amounts Recognized in Balance Sheets
Other liabilities-benefit obligations							$ (89)	$ (111)
Amounts reclassified from accumulated other comprehensive income: [Abstract]
Tax expense				(6)	1	(6)
Net current period other comprehensive income (loss)				8	(4)	6
Other Pension Plan, Postretirement or Supplemental Plans [Member]
Amounts reclassified from accumulated other comprehensive income: [Abstract]
Beginning Balance				(1)	(5)
Other comprehensive income (loss) before reclassifications (1)	[1]			13	(5)
Actuarial gains (2)	[2]			1	0
Total reclassifications from accumulated other comprehensive income				1	0
Tax expense				(6)	1
Net current period other comprehensive income (loss)				8	(4)
Ending Balance		$ (9)	$ (1)	(9)	(1)	(5)
Amounts recognized in accumulated other comprehensive loss
Unrecognized actuarial loss							3	13
Unrecognized prior service cost (credit)							(1)	2
Total recognized in accumulated other comprehensive loss							2	15
Less: deferred tax benefit (1)	[3]						(11)	(16)
Net amount recognized in accumulated other comprehensive income		$ (9)	$ (1)	(1)	(5)	(5)	(9)	(1)
Other Postretirement Benefit Plans, Defined Benefit [Member]
Components of net periodic benefit cost
Service cost — benefits earned during the period				1	1	1
Interest cost on accumulated benefit obligation				5	5	5
Expected return on plan assets				(1)	(1)	(1)
Amortization of prior service cost				1	1	1
Amortization of net loss				1	1	2
Net postretirement benefit cost				$ 7	$ 7	$ 8
Assumptions used to determine net postretirement benefit costs
Discount rate				3.90%	4.75%	3.90%
Expected return on plan assets		3.95%	4.00%	4.05%	3.10%	3.10%
Change in Benefit Obligation [Roll Forward]
Accumulated benefit obligation, beginning of year				$ 126	$ 116
Service cost — benefits earned during the period				1	1	$ 1
Interest cost on accumulated benefit obligation				5	5	5
Benefits paid				(12)	(13)
Participant contributions				4	4
Medicare reimbursement				1	2
Plan amendment				(5)	1
Curtailment				0	(2)
Actuarial (gain) loss				(19)	12
Accumulated benefit obligation, end of year		$ 101	$ 126	101	126	116
Change in Plan Assets [Roll Forward]
Plan assets, beginning of year				26	26
Benefits paid				(12)	(13)
Employer contributions				7	8
Participant contributions				4	4
Actual investment return				0	1
Plan assets, end of year		$ 25	$ 26	$ 25	$ 26	$ 26
Amounts Recognized in Balance Sheets
Current liabilities-other							(6)	(7)
Other liabilities-benefit obligations							(70)	(93)
Net liability, end of year							$ (76)	$ (100)
Discount rate							4.35%	3.90%
Expected return on plan assets		3.95%	4.00%	4.05%	3.10%	3.10%
Prescription cost trend rate assumed for the next year				11.00%	6.50%
Rate to which the cost trend rate is assumed to decline (ultimate trend rate)				5.00%	5.00%
Annualized individual discount rates based on time period, minimum				6 months
Annualized individual discount rates based on time period, maximum				99 years
Changes in plan assets and benefit obligations recognized in other comprehensive income
Net loss				$ 10
Amortization of prior service cost				3
Total recognized in other comprehensive loss				13
Total expense (benefit) recognized in net periodic cost and other comprehensive income				(2)
Effect of a one-percentage point change in assumed healthcare cost trend rates
Effect of One Percentage Point Increase on Postretirement Benefit Obligation				2
Effect of One Percentage Point Increase on Total of Service and Interest Cost				0
Effect of One Percentage Point Decrease on Postretirement Benefit Obligation				2
Effect of One Percentage Point Decrease on Total of Service and Interest Cost				$ 0
Minimum [Member] | Other Postretirement Benefit Plans, Defined Benefit [Member]
Amounts Recognized in Balance Sheets
Healthcare cost trend rate assumed for the next year				6.00%	7.25%
Maximum [Member] | Other Postretirement Benefit Plans, Defined Benefit [Member]
Amounts Recognized in Balance Sheets
Healthcare cost trend rate assumed for the next year				5.50%	8.50%
Health Care [Member] | Other Postretirement Benefit Plans, Defined Benefit [Member]
Amounts Recognized in Balance Sheets
Year that the healthcare rate reaches the ultimate trend rate							2,024	2,024
Prescription Drug [Member] | Other Postretirement Benefit Plans, Defined Benefit [Member]
Amounts Recognized in Balance Sheets
Year that the healthcare rate reaches the ultimate trend rate							2,024	2,024
Common Stock [Member] | CenterPoint Energy [Member]
Pension and Savings Plan
Defined contribution plan, Maximum percentage allowed in company stock				25.00%
Number Of Shares In Common Stock Held By Savings Plan							16,942,974
Percentage of investment in common stocks							17.00%
[1]	Total other comprehensive income related to the re-measurement of pension, postretirement and other postemployment plans.
[2]	These accumulated other comprehensive components are included in the computation of net periodic cost.
[3]	CERC’s postretirement benefit obligation is reduced by the impact of previously non-taxable government subsidies under the Medicare Prescription Drug Act. Because the subsidies were non-taxable, the temporary difference used in measuring the deferred tax impact was determined on the unrecognized losses excluding such subsidies.

Employee Benefit Plans Plan Ass

Employee Benefit Plans Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]
Estimated contributions next fiscal year	$ 6
Postemployment Benefits
Postemployment benefit income (expense)	4		$ 2		$ 1
Postemployment Benefits Liability, Noncurrent	14		12
Benefit expense related to deferred compensation plans	1		1		1
Other Postretirement Benefit Plans, Defined Benefit [Member]
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]
Fair Value of Plan Assets	25		26		$ 26
Expected Future Benefit Payments, Fiscal Year Maturity
Benefit Payments - 2016	10
Benefit Payments - 2017	10
Benefit Payments - 2018	10
Benefit Payments - 2019	11
Benefit Payments - 2020	11
Benefit Payments - 2021-2025	56
Medicare Subsidy Receipts - 2016	(2)
Medicare Subsidy Receipts - 2017	(2)
Medicare Subsidy Receipts - 2018	(2)
Medicare Subsidy Receipts - 2019	(2)
Medicare Subsidy Receipts - 2020	(3)
Medicare Subsidy Receipts - 2021-2025	$ (17)
Other Postretirement Benefit Plans, Defined Benefit [Member] | U.S. Equity [Member]
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations Range Minimum	15.00%
Defined Benefit Plan, Target Plan Asset Allocations Range Maximum	25.00%
Other Postretirement Benefit Plans, Defined Benefit [Member] | International Equity [Member]
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations Range Minimum	2.00%
Defined Benefit Plan, Target Plan Asset Allocations Range Maximum	12.00%
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fixed Income [Member]
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations Range Minimum	68.00%
Defined Benefit Plan, Target Plan Asset Allocations Range Maximum	78.00%
Other Postretirement Benefit Plans, Defined Benefit [Member] | Cash and Cash Equivalents [Member]
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations Range Minimum	0.00%
Defined Benefit Plan, Target Plan Asset Allocations Range Maximum	2.00%
Other Postretirement Benefit Plans, Defined Benefit [Member] | Equity Funds [Member]
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]
Fair Value of Plan Assets	$ 25	[1]	26	[2]
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member]
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]
Fair Value of Plan Assets	25		26
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Equity Funds [Member]
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]
Fair Value of Plan Assets	25	[1]	26	[2]
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member]
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]
Fair Value of Plan Assets	0		0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Equity Funds [Member]
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]
Fair Value of Plan Assets	0	[1]	0	[2]
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member]
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]
Fair Value of Plan Assets	0		0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Equity Funds [Member]
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]
Fair Value of Plan Assets	$ 0	[1]	$ 0	[2]
International Equity [Member] | Equity Funds [Member]
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]
Defined Benefit Plan, Actual Plan Asset Allocations	7.00%		7.00%
Fixed Income Funds [Member] | Equity Funds [Member]
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]
Defined Benefit Plan, Actual Plan Asset Allocations	70.00%		70.00%
U.S. Equity [Member] | Equity Funds [Member]
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]
Defined Benefit Plan, Actual Plan Asset Allocations	23.00%		23.00%
Benefit Obligation [Member]
Postemployment Benefits
Deferred Compensation Liability, Classified, Noncurrent	$ 3		$ 3
[1]	70% of the amount invested in mutual funds was in fixed income securities; 23% was in U.S. equities and 7% was in international equities.
[2]	70% of the amount invested in mutual funds was in fixed income securities; 23% was in U.S. equities and 7% was in international equities.

Employee Benefit Plans Other Em

Employee Benefit Plans Other Employee Matters (Details) - Employees Subject To Collective Bargaining Agreements [Member] - Labor Force Concentration Risk [Member]	12 Months Ended
	Dec. 31, 2015
Number of Employees, Total [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	34.00%
Workforce Subject to Collective Bargaining Arrangements Expiring within One Year [Member]
Concentration Risk [Line Items]
Concentration Risk, Percentage	4.00%

Related Party Transactions (Det

Related Party Transactions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Related Party Transaction [Line Items]
Money Pool Borrowings	$ 0	$ 188
Net interest income (expense) related to affiliate borrowings	(1)	1	$ (2)
Related Party Transaction, Amounts of Transaction	130	127	117
Dividends paid to parent	43	405	0
Operation And Maintenance Expense Member | CenterPoint Energy [Member]
Related Party Transaction [Line Items]
Corporate services charge	118	115	105
Operation And Maintenance Expense Member | CenterPoint Houston [Member]
Related Party Transaction [Line Items]
Corporate services charge	18	17	21
Related Party Transaction, Other Revenues from Transactions with Related Party	$ (6)	$ (5)	$ (9)

Derivative Instruments (Details

Derivative Instruments (Details) $ in Millions		12 Months Ended
		Dec. 31, 2015USD ($)Bcf		Dec. 31, 2014USD ($)Bcf		Dec. 31, 2013USD ($)
Weather Hedges Term		10 years
Derivative Asset, Fair Value, Gross Asset		$ 140		$ 149
Derivative Liability, Fair Value, Gross Liability		87		102
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net		29		46		$ 21
Total fair value of derivative instruments that contain credit risk contingent features that are in a net liability position		3		2
Aggregate fair value of assets already posted as collateral		0		0
Credit risk contingent feature assets		2		2
Credit Risk Derivative Assets, at Fair Value		$ 125		$ 131
Energy Related Derivative [Member]
Derivative, Nonmonetary Notional Amount, Volume | Bcf		767		804
Derivative Assets (Liabilities), at Fair Value, Net	[1]	$ 109		$ 111
Collateral Netting		56		64
Derivative, Fair Value, Net	[2]	53		47
Derivative, fair value, offsets, net		56		64
Current Assets [Member] | Energy Related Derivative [Member]
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	[2]	100		115
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset		(11)		(16)
Derivative Asset	[1]	89		99
Other Noncurrent Assets [Member] | Energy Related Derivative [Member]
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	[2]	40		34
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset		(4)		(2)
Derivative Asset	[1]	36		32
Current Liabilities [Member] | Energy Related Derivative [Member]
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	[2]	(62)		(84)
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset		51		65
Derivative Liability	[1]	(11)		(19)
Other Noncurrent Liabilities [Member] | Energy Related Derivative [Member]
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement	[2]	(25)		(18)
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset		20		17
Derivative Liability	[1]	(5)		(1)
Gains (Losses) in Revenue [Member] | Weather Hedge Swaps [Member]
Derivative, Gain (Loss) on Derivative, Net		(4)		(10)		(16)
Gains (Losses) in Revenue [Member] | Energy Related Derivative [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net		134		35		11
Gains (Losses) in Expense: Natural Gas [Member] | Energy Related Derivative [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net	[3]	(105)		11		$ 10
Not Designated as Hedging Instrument [Member] | Current Assets [Member] | Energy Related Derivative [Member]
Derivative Asset, Fair Value, Gross Asset	[4]	90	[5],[6]	101	[7],[8]
Derivative Liability, Fair Value, Gross Liability	[4]	2	[5],[6]	1	[7],[8]
Not Designated as Hedging Instrument [Member] | Other Noncurrent Assets [Member] | Energy Related Derivative [Member]
Derivative Asset, Fair Value, Gross Asset	[4]	36	[5],[6]	32	[7],[8]
Derivative Liability, Fair Value, Gross Liability	[4]	0	[5],[6]	0	[7],[8]
Not Designated as Hedging Instrument [Member] | Current Liabilities [Member] | Energy Related Derivative [Member]
Derivative Asset, Fair Value, Gross Asset	[4]	10	[5],[6]	14	[7],[8]
Derivative Liability, Fair Value, Gross Liability	[4]	60	[5],[6]	83	[7],[8]
Not Designated as Hedging Instrument [Member] | Other Noncurrent Liabilities [Member] | Energy Related Derivative [Member]
Derivative Asset, Fair Value, Gross Asset	[4]	4	[5],[6]	2	[7],[8]
Derivative Liability, Fair Value, Gross Liability	[4]	$ 25	[5],[6]	$ 18	[7],[8]
Long [Member] | Energy Related Derivative [Member]
Derivative, Nonmonetary Notional Amount, Volume | Bcf		112		60
Swap [Member] | Long [Member] | Energy Related Derivative [Member]
Derivative, Nonmonetary Notional Amount, Volume | Bcf		133		127
Retail End Users [Member]
Credit Risk Derivative Assets, at Fair Value	[9]	$ 115		$ 127
Financial Institutions [Member]
Credit Risk Derivative Assets, at Fair Value		0		0
Energy Marketers [Member]
Credit Risk Derivative Assets, at Fair Value		10		4
2014To2015 [Member]
Weather Hedge, Bilateral Cap Amount		16
2013To2014 [Member]
Weather Hedge, Bilateral Cap Amount		16
Enable Midstream Partners [Member] | Forward Contracts [Member] | Gains (Losses) in Expense: Natural Gas [Member] | Energy Related Derivative [Member]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net		0		2
External Credit Rating, Investment Grade [Member]
Credit Risk Derivative Assets, at Fair Value	[10]	6		4
External Credit Rating, Investment Grade [Member] | Retail End Users [Member]
Credit Risk Derivative Assets, at Fair Value	[9],[10]	2		2
External Credit Rating, Investment Grade [Member] | Financial Institutions [Member]
Credit Risk Derivative Assets, at Fair Value	[10]	0		0
External Credit Rating, Investment Grade [Member] | Energy Marketers [Member]
Credit Risk Derivative Assets, at Fair Value	[10]	$ 4		$ 2
[1]	The derivative assets and liabilities on the Consolidated Balance Sheets exclude accounts receivable or accounts payable that, should they exist, could be used as offsets to these balances in the event of a default.
[2]	Gross amounts recognized include some derivative assets and liabilities that are not subject to master netting arrangements.
[3]	The Gains (Losses) in Expense: Natural Gas includes $-0- and $2 million during the years ended December 31, 2015 and 2014, respectively, related to physical forwards purchased from Enable.
[4]	Derivative Assets and Derivative Liabilities include no material amounts related to physical forward transactions with Enable.
[5]	Natural gas contracts are presented on a net basis in the Consolidated Balance Sheets. Natural gas contracts are subject to master netting arrangements. This netting applies to all undisputed amounts due or past due and causes derivative assets (liabilities) to be ultimately presented net in a liability (asset) account within the Consolidated Balance Sheets. The net of total non-trading derivative assets and liabilities was a $109 million asset as shown on CERC’s Consolidated Balance Sheets (and as detailed in the table below), and was comprised of the natural gas contracts derivative assets and liabilities separately shown above offset by collateral netting of $56 million.
[6]	The fair value shown for natural gas contracts is comprised of derivative gross volumes totaling 767 billion cubic feet (Bcf) or a net 112 Bcf long position. Of the net long position, basis swaps constitute 133 Bcf.
[7]	Natural gas contracts are presented on a net basis in the Consolidated Balance Sheets. Natural gas contracts are subject to master netting arrangements. This netting applies to all undisputed amounts due or past due and causes derivative assets (liabilities) to be ultimately presented net in a liability (asset) account within the Consolidated Balance Sheets. The net of total non-trading derivative assets and liabilities was a $111 million asset as shown on CERC’s Consolidated Balance Sheets (and as detailed in the table below), and was comprised of the natural gas contracts derivative assets and liabilities separately shown above, offset by collateral netting of $64 million.
[8]	The fair value shown for natural gas contracts is comprised of derivative gross volumes totaling 804 Bcf or a net 60 Bcf long position. Of the net long position, basis swaps constitute 127 Bcf.
[9]	End users are comprised primarily of customers who have contracted to fix the price of a portion of their physical gas requirements for future periods.
[10]	“Investment grade” is primarily determined using publicly available credit ratings, and considers credit support (including parent company guarantees) and collateral (including cash and standby letters of credit). For unrated counterparties, CERC determines a synthetic credit rating by performing financial statement analysis, and considers contractual rights and restrictions and collateral.

Fair Value Measurements (Detail

Fair Value Measurements (Details)		3 Months Ended			12 Months Ended
		Dec. 31, 2015USD ($)		Sep. 30, 2015USD ($)	Dec. 31, 2015USD ($)		Dec. 31, 2014USD ($)		Dec. 31, 2013USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Assets, Level 1 to Level 2 Transfers, Amount		$ 0			$ 0
Fair Value, Liabilities, Level 1 to Level 2 Transfers, Amount		0			0
Fair Value, Assets, Level 2 to Level 1 Transfers, Amount		0			0
Fair Value, Liabilities, Level 2 to Level 1 Transfers, Amount		0			0
Assets
Derivative Asset, Fair Value, Gross Liability		(15,000,000)	[1]		(15,000,000)	[1]	$ (18,000,000)	[2]
Total assets		138,000,000			138,000,000		144,000,000
Liabilities
Derivative Liability, Fair Value, Gross Asset		(71,000,000)	[1]		(71,000,000)	[1]	(82,000,000)	[2]
Total liabilities		16,000,000			16,000,000		20,000,000
Cash collateral posted with counterparties		56,000,000			56,000,000		64,000,000
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation Calculation Roll Forward
Beginning balance					17,000,000	[3]	3,000,000	[3]	$ 2,000,000
Total gains					7,000,000		14,000,000		3,000,000
Total settlements					(12,000,000)		1,000,000		(3,000,000)
Transfers out of Level 3					(1,000,000)		0		0
Transfers into Level 3					1,000,000		(1,000,000)		1,000,000
Ending balance (1)	[3]	12,000,000			12,000,000		17,000,000		3,000,000
The amount of total gains for the period included in earnings attributable to the change in unrealized gains or losses relating to assets still held at the reporting date					6,000,000		16,000,000		2,000,000
Carrying Amount [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation Calculation Roll Forward
Notes receivable - affiliated companies		363,000,000			363,000,000		363,000,000
Long-term debt		2,353,000,000			2,353,000,000		2,469,000,000
Fair Value [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation Calculation Roll Forward
Notes receivable - affiliated companies		356,000,000			356,000,000		362,000,000
Long-term debt		2,551,000,000			2,551,000,000		2,772,000,000
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets
Total assets		17,000,000			17,000,000		20,000,000
Liabilities
Total liabilities		13,000,000			13,000,000		22,000,000
Significant Other Observable Inputs (Level 2) [Member]
Assets
Total assets		115,000,000			115,000,000		122,000,000
Liabilities
Total liabilities		65,000,000			65,000,000		77,000,000
Significant Unobservable Inputs (Level 3) [Member]
Assets
Total assets		21,000,000			21,000,000		20,000,000
Liabilities
Total liabilities		9,000,000			$ 9,000,000		3,000,000
Options Held [Member] | Maximum [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Option volatilities low range					82.00%
Options Held [Member] | Minimum [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Option volatilities low range					0.00%
Forward Contracts [Member] | Maximum [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Illiquid forward price low range					3.29
Forward Contracts [Member] | Minimum [Member] | Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Illiquid forward price low range					1.36
Fair Value, Measurements, Recurring [Member]
Assets
Corporate equities		2,000,000			$ 2,000,000		2,000,000
Investments, including money market funds		11,000,000			11,000,000		11,000,000
Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets
Corporate equities		2,000,000			2,000,000		2,000,000
Investments, including money market funds		11,000,000			11,000,000		11,000,000
Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets
Corporate equities		0			0		0
Investments, including money market funds		0			0		0
Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets
Corporate equities		0			0		0
Investments, including money market funds		0			0		0
Energy Related Derivative [Member] | Fair Value, Measurements, Recurring [Member]
Assets
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	[4]	(15,000,000)	[1]		(15,000,000)	[1]	(18,000,000)	[2]
Natural gas derivatives (2)	[4]	125,000,000			125,000,000		131,000,000
Liabilities
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset		(71,000,000)	[1],[4]		(71,000,000)	[1],[4]	(82,000,000)	[2]
Natural gas derivatives (2)		16,000,000	[4]		16,000,000	[4]	20,000,000
Energy Related Derivative [Member] | Fair Value, Measurements, Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	[4]	4,000,000			4,000,000		7,000,000
Liabilities
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement		13,000,000	[4]		13,000,000	[4]	22,000,000
Energy Related Derivative [Member] | Fair Value, Measurements, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Assets
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	[4]	115,000,000			115,000,000		122,000,000
Liabilities
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement		65,000,000	[4]		65,000,000	[4]	77,000,000
Energy Related Derivative [Member] | Fair Value, Measurements, Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
Assets
Derivative Asset, Fair Value, Gross Asset Including Not Subject to Master Netting Arrangement	[4]	21,000,000			21,000,000		20,000,000
Liabilities
Derivative Liability, Fair Value, Gross Liability Including Not Subject to Master Netting Arrangement		9,000,000	[4]		9,000,000	[4]	3,000,000
Enable Midstream Partners [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation Calculation Roll Forward
Equity Method Investment, Other than Temporary Impairment		$ 975,000,000		$ 250,000,000	$ 1,225,000,000		$ 0		$ 0
[1]	Amounts represent the impact of legally enforceable master netting arrangements that allow CERC to settle positive and negative positions and also include cash collateral of $56 million posted with the same counterparties.
[2]	Amounts represent the impact of legally enforceable master netting arrangements that allow CERC to settle positive and negative positions and also include cash collateral of $64 million posted with the same counterparties.
[3]	During 2015, 2014 and 2013, CenterPoint Energy did not have significant Level 3 purchases or sales.
[4]	Natural gas derivatives include no material amounts related to physical forward transactions with Enable.

Unconsolidated Affiliates (Deta

Unconsolidated Affiliates (Details) - USD ($) $ / shares in Units, $ in Millions		Apr. 16, 2014	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Jun. 30, 2015	May. 30, 2014	Mar. 31, 2014	May. 01, 2013
Accounts and notes receivable — affiliated companies			$ 8		$ 8	$ 18
Service Agreement Notice For Termination At Term End					90 days
Equity Method Investment, Contributed Ownership Percentage											24.95%
Basis Difference, Amortization Period					33 years
Equity in earnings (losses) of unconsolidated affiliates					$ (1,633)	308	$ 188
Investment in unconsolidated affiliates			2,594		2,594	4,521
Summarized unaudited consolidated balance sheet from Enable [Abstract]
Investment in unconsolidated affiliates			2,594		2,594	4,521
Distribution received from unconsolidated affiliates [Abstract]
Proceeds from Equity Method Investment, Dividends or Distributions					294	305	129
Southeast Supply Header LLC [Member]
Equity Method Investment, Ownership Percentage										25.05%
Equity Method Investment, Contributed Ownership Percentage								0.10%	24.95%
Equity in earnings (losses) of unconsolidated affiliates	[1]				0	5	15
Investment in unconsolidated affiliates	[2]		0		0	1
Summarized unaudited consolidated balance sheet from Enable [Abstract]
Investment in unconsolidated affiliates	[2]		$ 0		0	1
Distribution received from unconsolidated affiliates [Abstract]
Proceeds from Equity Method Investment, Dividends or Distributions	[1]				$ 0	7	23
Enable Midstream Partners [Member]
Partners' Capital Account, Units, Sold in Public Offering		28,750,000
Share Price		$ 20
Proceeds from Issuance Initial Public Offering		$ 464
Equity Method Investment, Ownership Percentage			55.40%		55.40%				54.70%	58.30%
Equity in earnings (losses) of unconsolidated affiliates					$ (1,633)	303	173
Impairment Charges			$ 984	$ 862
Equity Method Investment, Other than Temporary Impairment			975	250	1,225	0	0
Goodwill And Long-LIved Assets Impairment Charges, Entity's Share					621
Investment in unconsolidated affiliates			2,594		2,594	4,520
Summarized unaudited consolidated income from Enable [Abstract]
Operating revenues					2,418	3,367	2,123
Cost of sales, excluding depreciation and amortization					1,097	1,914	1,241
Impairment of goodwill and other long-lived assets					1,134	8	12
Operating income (loss)					(712)	586	322
Net income (loss) attributable to Enable					(752)	530	289
Equity Method Investment, Gross Equity In Earnings (Losses)					(416)	298	168
Basis difference amortization (1)	[3]				8	5	5
Equity Method Investment, Other than Temporary Impairment			(975)	$ (250)	(1,225)	0	0
CERC’s equity in earnings (losses), net (2)	[4]				(1,633)	303	173
Income (Loss) From Equity Method Investment, Excluding Impairment Charge					213
Summarized unaudited consolidated balance sheet from Enable [Abstract]
Current assets			381		381	438
Non-current assets			10,857		10,857	11,399
Current liabilities			615		615	671
Non-current liabilities			3,092		3,092	2,343
Non-controlling interest			12		12	31
Enable partners’ capital			7,519		7,519	8,792
CERC’s ownership interest in Enable partners’ capital			4,163		4,163	4,869
CERC’s basis difference			(1,569)		(1,569)	(349)
Investment in unconsolidated affiliates			2,594		2,594	4,520
Distribution received from unconsolidated affiliates [Abstract]
Proceeds from Equity Method Investment, Dividends or Distributions					294	298	$ 106
Enable Midstream Partners [Member] | ArcLight [Member]
Partners' Capital Account, Units, Sold in Public Offering		3,750,000
Enable Midstream Partners [Member] | CERC Corp [Member]
Impairment Charges					1,846
Enable Guaranteed Senior Notes [Member]
Guarantor Obligations, Maximum Exposure, Undiscounted			1,100		1,100
Enable Midstream Partners [Member]
Notes receivable — affiliated companies			363		$ 363
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Minimum					2.10%
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Maximum					2.45%
Interest Income, Related Party					$ 8	8
Accounts and notes receivable — affiliated companies			4		4	4
Enable Midstream Partners [Member] | Enable Guaranteed Senior Notes [Member]
Guarantor Obligations, Maximum Exposure, Undiscounted			1,100		1,100
Transitional Service [Member] | Enable Midstream Partners [Member]
Reimbursement Revenue					16	163
Accounts Receivable, Related Parties			$ 3		$ 3	28
Common Stock [Member] | Enable Midstream Partners [Member]
Equity Method Investment, Ownership, Shares			94,151,707		94,151,707
Subordinated Units [Member] | Enable Midstream Partners [Member]
Equity Method Investment, Ownership, Shares			139,704,916		139,704,916
Natural Gas Expenses [Member] | Enable Midstream Partners [Member]
Affiliate Costs					$ 117	130
Accounts Payable, Related Parties, Current			$ 11		$ 11	$ 23
Enable Midstream Partners [Member]
Management Rights Ownership Percentage					50.00%
Enable Midstream Partners [Member] | OGE [Member]
Management Rights Ownership Percentage					50.00%
Incentive Distribution Right, Percentage					60.00%
Enable Midstream Partners [Member] | CERC Corp [Member]
Management Rights Ownership Percentage					50.00%
Incentive Distribution Right, Percentage					40.00%
[1]	CERC contributed a 24.95% interest in SESH to Enable on May 30, 2014 and its remaining interest in SESH to Enable on June 30, 2015.
[2]	CERC disposed of its remaining interest in SESH on June 30, 2015.
[3]	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 33 years, the average life of the assets to which the basis difference is attributed.
[4]	These amounts include CERC’s share of Enable’s impairment of goodwill and long-lived assets and the impairment of CERC’s equity method investment in Enable totaling $1,846 million during the year ended December 31, 2015. This impairment is offset by $213 million of earnings for the year ended December 31, 2015.

Short-term Borrowings and Lon53

Short-term Borrowings and Long-term Debt (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Short-term Debt	[1]	$ 40	$ 53
Debt Instrument, Unamortized Discount (Premium), Net		(34)	(40)
Long-term Debt, Excluding Current Maturities		2,028	2,469
Long-term Debt, Current Maturities	[1]	325	0
Debt, Current	[1]	365	53
Size of Facility		600	600
Long-term Debt, Maturities in 2016		325
Long-term Debt, Maturities in 2017		250
Long-term Debt, Maturities in 2018		300
Long-term Debt, Maturities in 2019		219
Long-term Debt, Maturities in 2020		0
Inventory financing [Member]
Debt Instrument [Line Items]
Short-term Debt	[1]	$ 40	53
Senior Notes 4.50% to 6.625% due 2016 to 2041
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Minimum		4.50%
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Maximum		6.625%
Long-term Debt, Gross, Noncurrent		$ 1,843	2,168
Long-term Debt, Gross, Current	[1]	325	0
Commercial Paper [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross, Noncurrent	[2]	219	341
Long-term Debt, Gross, Current	[1],[2]	$ 0	0
Line of Credit [Member]
Debt Instrument [Line Items]
Percentage on limitation of debt to total capitalization under covenant (in hundredths)		65.00%
Ratio of Indebtedness to Net Capital		0.339
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Loans		$ 0	0
Letter of Credit [Member]
Debt Instrument [Line Items]
Loans		2	0
Commercial Paper [Member]
Debt Instrument [Line Items]
Loans	[3]	$ 219	$ 341
Debt, Weighted Average Interest Rate		0.81%	0.68%
London Interbank Offered Rate (LIBOR) [Member] | Line of Credit [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Interest Rate Description		1.50%
[1]	Includes amounts due or exchangeable within one year of the date noted.
[2]	Classified as long-term debt because the termination date of the facility that backstops the commercial paper is more than one year from the date noted.
[3]	Weighted average interest rate was 0.81% and 0.68% as of December 31, 2015 and 2014, respectively.

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Current income tax expense:
Federal	$ 0	$ 0	$ 5
State	3	10	9
Total current expense	3	10	14
Deferred income tax expense (benefit):
Federal	(488)	171	350
State	(54)	7	7
Total deferred expense (benefit)	(542)	178	357
Total income tax expense (benefit)	(539)	188	371
Income tax reconciliation
Income (loss) before income taxes	$ (1,451)	$ 511	$ 435
Federal statutory income tax rate	35.00%	35.00%	35.00%
Expected federal income tax expense (benefit)	$ (508)	$ 179	$ 152
Increase (decrease) in tax expense resulting from:
State income tax expense, net of federal income tax	(33)	11	23
Decrease in settled and uncertain income tax positions	0	0	(2)
Tax effect related to the formation of Enable Midstream Partnership	0	0	198
Other, net	2	(2)	0
Total	(31)	9	219
Total income tax expense (benefit)	$ (539)	$ 188	$ 371
Effective tax rate	37.10%	36.80%	85.30%
Deferred Tax Liabilities, Goodwill and Intangible Assets			$ 225
Tax Adjustments, Settlements, and Unusual Provisions			(2)
Deferred tax assets:
Benefits and compensation	$ 39	$ 48
Loss and credit carryforwards	388	326
Asset retirement obligations	59	52
Other	39	28
Valuation allowance	(2)	(2)
Total deferred tax assets	523	452
Deferred tax liabilities:
Deferred Tax Liabilities, Property, Plant and Equipment	929	803
Investment in unconsolidated affiliates	1,277	1,788
Regulatory assets/liabilities, net	0	13
Other	91	99
Total deferred tax liabilities	2,297	2,703
Net deferred tax liabilities	1,774	2,251
Reconciliation of Unrecognized Tax Benefits (Expenses) [Roll Forward]
Balance, beginning of year		0	(20)
Tax Positions related to prior years:
Reductions			(2)
Tax Positions related to current year:
Settlements			22
Balance, end of year			0
Income Tax Expense Benefit Related To Interest On Income Tax Positions		$ 4
Federal [Member]
Deferred tax liabilities:
Federal net operating loss carryforwards	946
State capital loss carryforwards, valuation allowance net of federal tax	2
State and Local Jurisdiction [Member]
Deferred tax liabilities:
Federal net operating loss carryforwards	905
Tax Credit Carryforward, Amount	7
Capital Loss Carryforward [Member] | Federal [Member]
Deferred tax liabilities:
Tax Credit Carryforward, Amount	23
Capital Loss Carryforward [Member] | State and Local Jurisdiction [Member]
Deferred tax liabilities:
Tax Credit Carryforward, Amount	244
Charitable Contribution Carryforward [Member] | Federal [Member]
Deferred tax liabilities:
Tax Credit Carryforward, Amount	$ 1
Enable Midstream Partners [Member]
Deferred income tax expense (benefit):
Total deferred expense (benefit)			$ (27)
Latest Tax Year [Member] | Federal [Member]
Deferred tax liabilities:
Operating Loss Carryforwards, Expiration Dates	Dec. 31, 2035
Latest Tax Year [Member] | State and Local Jurisdiction [Member]
Deferred tax liabilities:
Operating Loss Carryforwards, Expiration Dates	Dec. 31, 2035
Latest Tax Year [Member] | Capital Loss Carryforward [Member] | Federal [Member]
Deferred tax liabilities:
Other Tax Carryforward, Expiration Dates	Dec. 31, 2019
Latest Tax Year [Member] | Capital Loss Carryforward [Member] | State and Local Jurisdiction [Member]
Deferred tax liabilities:
Other Tax Carryforward, Expiration Dates	Dec. 31, 2017
Latest Tax Year [Member] | Charitable Contribution Carryforward [Member] | Federal [Member]
Deferred tax liabilities:
Other Tax Carryforward, Expiration Dates	Dec. 31, 2020
Earliest Tax Year [Member] | Federal [Member]
Deferred tax liabilities:
Operating Loss Carryforwards, Expiration Dates	Dec. 31, 2031
Earliest Tax Year [Member] | State and Local Jurisdiction [Member]
Deferred tax liabilities:
Operating Loss Carryforwards, Expiration Dates	Dec. 31, 2016
Earliest Tax Year [Member] | Capital Loss Carryforward [Member] | Federal [Member]
Deferred tax liabilities:
Other Tax Carryforward, Expiration Dates	Dec. 31, 2018
Earliest Tax Year [Member] | Charitable Contribution Carryforward [Member] | Federal [Member]
Deferred tax liabilities:
Other Tax Carryforward, Expiration Dates	Dec. 31, 2018

Commitments and Contingencies55

Commitments and Contingencies (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2,016	$ 5
2,017	3
2,018	3
2,019	3
2,020	2
2021 and beyond	7
Total	23
Total lease expense for all operating leases	8	$ 9	$ 20
GenOn Demand Charges Transportation Contracts [Member]
Legal, Environmental and Other Regulatory Matters [Abstract]
Guarantor Obligations, Maximum Exposure, Undiscounted	27
Enable Guaranteed Senior Notes [Member]
Legal, Environmental and Other Regulatory Matters [Abstract]
Guarantor Obligations, Maximum Exposure, Undiscounted	1,100
Minnesota Service Territory [Member]
Legal, Environmental and Other Regulatory Matters [Abstract]
Accrual for Environmental Loss Contingencies	7
Minnesota Service Territory [Member] | Minimum [Member]
Legal, Environmental and Other Regulatory Matters [Abstract]
Site Contingency Loss Exposure	$ 5
Site Contingency, Years to Resolve Contingency	30 years
Minnesota Service Territory [Member] | Maximum [Member]
Legal, Environmental and Other Regulatory Matters [Abstract]
Site Contingency Loss Exposure	$ 29
Site Contingency, Years to Resolve Contingency	50 years
Gas Market Manipulation Cases [Member]
Legal, Environmental and Other Regulatory Matters [Abstract]
Loss Contingency, Pending Claims, Number	1
Natural Gas Supply Commitments [Member]
Long-term Purchase Commitment [Line Items]
2,016	$ 478
2,017	457
2,018	405
2,019	217
2,020	90
After 2,020	$ 38

Unaudited Quarterly Informati56

Unaudited Quarterly Information (Details) - USD ($) $ in Millions	3 Months Ended										12 Months Ended
	Dec. 31, 2015		Sep. 30, 2015		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
Revenues	$ 1,087	[1]	$ 799	[2]	$ 824	$ 1,817	$ 1,689	$ 964	$ 1,183	$ 2,531	$ 4,527	$ 6,367	$ 5,522
Operating Income (Loss)	108	[1]	18	[2]	27	160	111	(3)	39	188	313	335	401
Net Income (Loss)	(535)	[1]	(508)	[2]	$ 22	$ 109	$ 95	$ 28	$ 48	$ 152	$ (912)	$ 323	$ 64
Enable Midstream Partners [Member]
Impairment Charges	984		862
Impairment Charge, net of tax	$ 620		$ 537
[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.

Reportable Business Segments (D

Reportable Business Segments (Details) - USD ($) $ in Millions		3 Months Ended										12 Months Ended
		Dec. 31, 2015		Sep. 30, 2015		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
Segment Reporting Information [Line Items]
Revenue from External Customers		$ 1,087	[1]	$ 799	[2]	$ 824	$ 1,817	$ 1,689	$ 964	$ 1,183	$ 2,531	$ 4,527	$ 6,367	$ 5,522
Depreciation and Amortization												227	206	230
Operating Income (Loss)		108	[1]	18	[2]	$ 27	$ 160	111	$ (3)	$ 39	$ 188	313	335	401
Assets		9,153						11,044				9,153	11,044	10,532
Capital Expenditures for Long-Lived Assets												606	528	478
Equity income												(1,633)	308	188
Investment in unconsolidated affiliate		2,594						4,521				2,594	4,521
Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Revenue from External Customers												2,603	3,271	2,837
Depreciation and Amortization												222	201	185
Operating Income (Loss)												273	287	263
Capital Expenditures for Long-Lived Assets												601	525	430
Energy Services [Member]
Segment Reporting Information [Line Items]
Revenue from External Customers												1,924	3,095	2,374
Depreciation and Amortization												5	5	5
Operating Income (Loss)												42	52	13
Capital Expenditures for Long-Lived Assets												5	3	3
Interstate Pipelines [Member]
Segment Reporting Information [Line Items]
Revenue from External Customers	[3],[4]													133
Depreciation and Amortization	[3],[4]													20
Operating Income (Loss)	[3],[4]													72
Capital Expenditures for Long-Lived Assets	[3],[4]													29
Field Services [Member]
Segment Reporting Information [Line Items]
Revenue from External Customers	[4]													178
Depreciation and Amortization	[4]													20
Operating Income (Loss)	[4]													73
Capital Expenditures for Long-Lived Assets	[4]													16
Midstream Investments [Member]
Segment Reporting Information [Line Items]
Revenue from External Customers	[5]											0	0	0
Depreciation and Amortization	[5]											0	0	0
Operating Income (Loss)	[5]											0	0	0
Capital Expenditures for Long-Lived Assets	[5]											0	0	0
Equity income												(1,633)	308	181
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Revenue from External Customers												0	1	0
Depreciation and Amortization												0	0	0
Operating Income (Loss)												(2)	(4)	(20)
Capital Expenditures for Long-Lived Assets												0	0	0
Operating Segments [Member] | Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Assets		5,657						5,464				5,657	5,464	4,976
Operating Segments [Member] | Energy Services [Member]
Segment Reporting Information [Line Items]
Assets		857						978				857	978	895
Operating Segments [Member] | Interstate Pipelines [Member]
Segment Reporting Information [Line Items]
Assets	[3],[4]													0
Operating Segments [Member] | Field Services [Member]
Segment Reporting Information [Line Items]
Assets	[4]													0
Operating Segments [Member] | Midstream Investments [Member]
Segment Reporting Information [Line Items]
Assets	[5]	2,594						4,521				2,594	4,521	4,518
Operating Segments [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Assets		789						1,045				789	1,045	1,139
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue from External Customers												(62)	(114)	(124)
Assets		(744)						(964)				(744)	(964)	(996)
Intersegment Eliminations [Member] | Natural Gas Distribution [Member]
Segment Reporting Information [Line Items]
Revenue from External Customers												(29)	(30)	(26)
Intersegment Eliminations [Member] | Energy Services [Member]
Segment Reporting Information [Line Items]
Revenue from External Customers												(33)	(84)	(27)
Intersegment Eliminations [Member] | Interstate Pipelines [Member]
Segment Reporting Information [Line Items]
Revenue from External Customers	[3],[4]													(53)
Intersegment Eliminations [Member] | Field Services [Member]
Segment Reporting Information [Line Items]
Revenue from External Customers	[4]													(18)
Intersegment Eliminations [Member] | Midstream Investments [Member]
Segment Reporting Information [Line Items]
Revenue from External Customers	[5]											0	0	0
Intersegment Eliminations [Member] | Corporate and Other [Member]
Segment Reporting Information [Line Items]
Revenue from External Customers												0	0	0
Enable Midstream Partners [Member]
Segment Reporting Information [Line Items]
Equity income												(1,633)	303	173
Impairment Charges		984		$ 862
Income (Loss) From Equity Method Investment, Excluding Impairment Charge												213
Investment in unconsolidated affiliate		2,594						4,520				2,594	4,520
Enable Midstream Partners [Member] | Midstream Investments [Member]
Segment Reporting Information [Line Items]
Equity income	[6]											(1,633)	303	173
Enable Midstream Partners [Member] | CERC Corp [Member]
Segment Reporting Information [Line Items]
Impairment Charges												1,846
Southeast Supply Header LLC [Member]
Segment Reporting Information [Line Items]
Equity income	[7]											0	5	15
Investment in unconsolidated affiliate	[8]	$ 0						$ 1				0	1
Southeast Supply Header LLC [Member] | Interstate Pipelines [Member]
Segment Reporting Information [Line Items]
Equity income														7
Southeast Supply Header LLC [Member] | Midstream Investments [Member]
Segment Reporting Information [Line Items]
Equity income												$ 0	$ 5	$ 8
[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.
[3]	Interstate Pipelines recorded equity income of $7 million in the year ended December 31, 2013 from its interest in SESH, a jointly-owned pipeline. These amounts are included in Equity in earnings of unconsolidated affiliates under the Other Income (Expense) caption. As discussed above, effective May 1, 2013, CenterPoint Energy reports equity earnings associated with its interest in Enable and equity earnings associated with its interest in SESH under its Midstream Investments segment, and no longer has an Interstate Pipelines reporting segment prospectively.
[4]	Results reflected in the year ended December 31, 2013 represent only January 2013 through April 2013.
[5]	Midstream Investments’ equity earnings (losses) are as follows: Year Ended December 31, 2015 2014 2013 (in millions)Enable (1) $(1,633) $303 $173SESH — 5 8 Total $(1,633) $308 $181(1)These amounts include CERC’s share of Enable’s impairment of goodwill and long-lived assets and the impairment of CERC’s equity method investment in Enable totaling $1,846 million during the year ended December 31, 2015. This impairment is offset by $213 million of earnings for the year ended December 31, 2015.Midstream Investments’ total assets are as follows: December 31, 2015 December 31, 2014 (in millions)Enable $2,594 $4,520SESH — 1 Total $2,594 $4,521
[6]	These amounts include CERC’s share of Enable’s impairment of goodwill and long-lived assets and the impairment of CERC’s equity method investment in Enable totaling $1,846 million during the year ended December 31, 2015. This impairment is offset by $213 million of earnings for the year ended December 31, 2015.
[7]	CERC contributed a 24.95% interest in SESH to Enable on May 30, 2014 and its remaining interest in SESH to Enable on June 30, 2015.
[8]	CERC disposed of its remaining interest in SESH on June 30, 2015.

Reportable Business Segments Re

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.

Subsequent Events (Details)

Subsequent Events (Details) - USD ($) $ / shares in Units, $ in Millions	Jan. 29, 2016	Jan. 28, 2016	Jan. 22, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Subsequent Event [Line Items]
Proceeds from Equity Method Investment, Dividends or Distributions				$ 294	$ 305	$ 129
Dividends paid to parent				43	405	0
Subsequent Event [Member]
Subsequent Event [Line Items]
Dividends paid to parent		$ 363
Business Acquisition, Name of Acquired Entity	Continuum Energy Services
Amount to be paid to acquire Continuum	$ 77.5
Enable Midstream Partners [Member]
Subsequent Event [Line Items]
Proceeds from Equity Method Investment, Dividends or Distributions				$ 294	$ 298	$ 106
Enable Midstream Partners [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Dividends Payable, Date Declared			Jan. 22, 2016
Common Stock, Dividends, Per Share, Declared			$ 0.318
Proceeds from Equity Method Investment, Dividends or Distributions			$ 74
Series A Preferred Stock [Member] | Enable Midstream Partners [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Number of Series A Preferred Units Purchased		14,520,000
Interest Rate on Series A Preferred Units		10.00%
Purchase Price Per Unit of Series A Preferred		$ 25
Enable Midstream Partners [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Amount of Debt Redeemed by Enable		$ 363

Schedule II Valuation and Qua60

Schedule II Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Allowance for Trade Receivables [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period		$ 23	$ 25	$ 23
Charged To Income		19	20	20
Addition to Other Accounts		(2)
Charged to Other Accounts			1	0
Deductions From Reserves	[1]	21	23	18
Balance at End of Period		19	23	25
Valuation Allowance of Deferred Tax Assets [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period		2	2	2
Charged To Income		0	0	0
Charged to Other Accounts		0	0	0
Deductions From Reserves	[1]	0	0	0
Balance at End of Period		$ 2	$ 2	$ 2
[1]	Deductions from reserves represent losses or expenses for which the respective reserves were created. In the case of the uncollectible accounts reserve, such deductions are net of recoveries of amounts previously written off.