ONE Gas (OGS) 10-K 18 Feb 16 2015 FY Annual report Financial data

Document And Entity Information

Document And Entity Information - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2015	Feb. 05, 2016	Jun. 30, 2015
Document Information [Line Items]
Entity Registrant Name	ONE Gas, Inc.
Entity Central Index Key	1,587,732
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$ 2.1
Entity Common Stock, Shares Outstanding		52,292,154
Document Fiscal Year Focus	2,015
Document Fiscal Period Focus	FY
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2015

STATEMENTS OF INCOME

STATEMENTS OF INCOME - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Gross Margin
Revenues	$ 1,547,692	$ 1,818,906	$ 1,689,952
Cost of natural gas	705,959	991,949	876,944
Net margin	841,733	826,957	813,008
Operating expenses
Operations and maintenance	414,476	420,686	393,072
Depreciation and amortization	133,023	125,722	144,758
General taxes	55,105	55,255	54,830
Total operating expenses	602,604	601,663	592,660
Operating income	239,129	225,294	220,348
Other income	263	1,625	6,165
Other expense	(2,813)	(2,949)	(3,680)
Interest expense	(44,570)	(45,842)	(61,366)
Income before income taxes	192,009	178,128	161,467
Income taxes	(72,979)	(68,338)	(62,272)
Net income	$ 119,030	$ 109,790	$ 99,195
Earnings per share
Basic	$ 2.26	$ 2.10	$ 1.90
Diluted	$ 2.24	$ 2.07	$ 1.90
Average shares (thousands)
Basic	52,578	52,364	52,319
Diluted	53,254	52,946	52,319
Dividends declared per share of stock	$ 1.20	$ 0.84	$ 0

STATEMENTS OF COMPREHENSIVE INC

STATEMENTS OF COMPREHENSIVE INCOME STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net income	$ 119,030	$ 109,790	$ 99,195
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Change in pension and other postretirement benefit plans liability, net of tax of $(483), $1,244, and $0, respectively	773	(1,781)	0
Other comprehensive loss	773	(1,781)	0
Comprehensive income	$ 119,803	$ 108,009	$ 99,195

STATEMENTS OF COMPREHENSIVE IN4

STATEMENTS OF COMPREHENSIVE INCOME (Parentheticals) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
STATEMENTS OF COMPREHENSIVE INCOME [Abstract]
Pension and other postretirement benefit plans, Tax	$ (483)	$ 1,244	$ 0

BALANCE SHEETS

BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Property, plant and equipment
Property, plant and equipment	$ 5,132,682	$ 4,850,201
Accumulated depreciation and amortization	1,620,771	1,556,481
Net property, plant and equipment	3,511,911	3,293,720
Current assets
Cash and cash equivalents	2,433	11,943
Accounts receivable, net	216,343	326,749
Materials and supplies	33,325	27,511
Income tax receivable	38,877	43,800
Natural gas in storage	142,153	185,300
Regulatory assets	32,925	50,193
Other current assets	16,789	22,005
Total current assets	482,845	667,501
Goodwill and other assets
Regulatory assets	435,863	478,723
Goodwill	157,953	157,953
Other assets	55,838	51,313
Total goodwill and other assets	649,654	687,989
Total assets	4,644,410	4,649,210
Equity and long-term debt
Common stock, $0.01 par value: authorized 250,000,000 shares; issued 52,598,005 shares and outstanding 52,259,224 at December 31, 2015; authorized 250,000,000 shares, issued and outstanding 52,083,859 shares at December 31, 2014	526	521
Paid-in capital	1,764,875	1,758,796
Retained earnings	95,046	39,894
Accumulated other comprehensive income (loss)	(4,401)	(5,174)
Treasury stock, at cost: 338,781 shares at December 31, 2015 and no shares at December 31, 2014	(14,491)	0
Total equity	1,841,555	1,794,037
Long-term debt, excluding current maturities	1,201,305	1,201,311
Total equity and long-term debt	3,042,860	2,995,348
Current liabilities
Current maturities of long-term debt	7	6
Notes payable	12,500	42,000
Accounts payable	107,482	159,064
Accrued interest	18,873	18,872
Accrued taxes other than income	37,249	44,742
Accrued liabilities	31,470	26,019
Customer deposits	60,325	60,003
Regulatory liabilities	24,615	32,467
Other current liabilities	11,700	9,260
Total current liabilities	304,221	392,433
Deferred credits and other liabilities [Abstract]
Deferred income taxes	951,785	894,585
Employee benefit obligations	272,309	287,779
Other deferred credits	73,235	79,065
Total deferred credits and other liabilities	$ 1,297,329	$ 1,261,429
Commitments and contingencies
Total liabilities and equity	$ 4,644,410	$ 4,649,210

BALANCE SHEETS BALANCE SHEETS P

BALANCE SHEETS BALANCE SHEETS Parenthetical - $ / shares	Dec. 31, 2015	Dec. 31, 2014
Common Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Common Stock, Shares Authorized	250,000,000	250,000,000
Common Stock, Shares, Issued	52,598,005	52,083,859
Common Stock, Shares, Outstanding	52,259,224	52,083,859
Treasury Stock, Shares	338,781	0

STATEMENTS OF CASH FLOWS

STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net income	$ 119,030	$ 109,790	$ 99,195
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	133,023	125,722	144,758
Deferred income taxes	63,789	49,935	62,205
Share-based compensation expense	9,187	7,613	0
Provision for doubtful accounts	4,520	7,195	5,460
Changes in assets and liabilities:
Accounts receivable	105,886	23,044	(102,142)
Materials and supplies	(5,814)	10,868	(1,668)
Income Tax Receivable	4,923	(43,800)	0
Natural gas in storage	43,147	(19,172)	(63,139)
Asset removal costs	(51,608)	(47,125)	(46,567)
Affiliate payable	0	0	(8,140)
Accounts payable	(59,635)	(6,881)	37,241
Accrued interest	1	18,743	(1)
Accrued taxes other than income	(7,493)	12,316	2,449
Accrued Liabilities	5,451	21,228	(5,443)
Customer deposits	322	2,643	(727)
Regulatory assets and liabilities	50,658	30,067	29,436
Employee benefit obligation	(15,033)	(10,102)	0
Other assets and liabilities	(6,147)	(45,421)	1,291
Cash provided by operating activities	394,207	246,663	154,208
Investing activities
Capital expenditures	(294,320)	(297,103)	(292,080)
Proceeds from sale of assets	0	0	1,327
Cash used in investing activities	(294,320)	(297,103)	(290,753)
Financing activities
Settlement of short-term notes payable to ONEOK, net	0	0	150,851
Borrowings on notes payable, net	(29,500)	42,000	0
Repurchase of common stock	(24,122)	0	0
Issuance of debt, net of discounts	0	1,199,994	0
Long-term debt financing costs	0	(11,087)	0
Cash payment to ONEOK upon separation	0	(1,130,000)	0
Issuance of common stock	7,051	2,001	0
Dividends paid	(62,826)	(43,696)	0
Repayment of long-term debt	0	0	(206)
Distributions to ONEOK	0	0	(14,969)
Cash provided by financing activities	(109,397)	59,212	135,676
Change in cash and cash equivalents	(9,510)	8,772	(869)
Cash and cash equivalents at beginning of period	11,943	3,171	4,040
Cash and cash equivalents at end of period	2,433	11,943	3,171
Supplemental cash flow information:
Cash paid for interest, net of amounts capitalized	42,980	21,066	0
Cash paid to ONEOK for interest, net of amounts capitalized	0	0	61,366
Cash (received) paid for income taxes, net	(5,423)	44,603	0
Cash paid to ONEOK for income taxes	$ 0	$ 0	$ 67

STATEMENT OF CHANGES IN EQUITY

STATEMENT OF CHANGES IN EQUITY - USD ($) $ in Thousands	Total	Retained Earnings [Member]	Owner's Net Investment [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Treasury Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]
Shares Issued, beginning balance at Dec. 31, 2012						0
Equity, beginning balance at Dec. 31, 2012	$ 1,154,797	$ 0	$ 1,154,797	$ 0	$ 0	$ 0	$ 0
Net income	99,195	0	99,195	0	0	0	0
Distributions to ONEOK	(14,969)	0	(14,969)	0	0	$ 0	0
Other comprehensive loss	0
Common stock issued, shares						100
Common stock issued, value	0	0	0	0	0	$ 0	0
Shares Issued, ending balance at Dec. 31, 2013						100
Equity, ending balance at Dec. 31, 2013	$ 1,239,023	0	1,239,023	0	0	$ 0	0
Common Stock, Dividends, Declared, Annualized Basis	$ 0.84
Net income	$ 109,790	84,214	25,576	0	0	0	0
Other comprehensive loss	(1,781)	0	0	(1,781)	0	0	0
Net transfers from ONEOK	481,086	0	484,479	(3,393)	0	0	0
Reclassification of Owner's investment to paid-in capital	0	0	(1,749,078)	0	0	$ 0	1,749,078
Net issuance of common stock at the separation, Shares						51,941,136
Issuance of common stock at the separation, value	0	0	0	0	0	$ 520	(520)
Common stock issued, shares						142,623
Common stock issued, value	9,615	0	0	0	0	$ 1	9,614
Common stock dividends - $1.20 and $0.84 per share	(43,696)	(44,320)	0	0	0	$ 0	624
Shares Issued, ending balance at Dec. 31, 2014						52,083,859
Equity, ending balance at Dec. 31, 2014	$ 1,794,037	39,894	0	(5,174)	0	$ 521	1,758,796
Common Stock, Dividends, Declared, Annualized Basis	$ 1.20
Net income	$ 119,030	119,030	0	0	0	0	0
Other comprehensive loss	773	0	0	773	0	0	0
Repurchase of common stock	(24,122)	0	0	0	(24,122)	$ 0	0
Common stock issued, shares						514,146
Common stock issued, value	14,663	0	0	0	9,631	$ 5	5,027
Common stock dividends - $1.20 and $0.84 per share	(62,826)	(63,878)	0	0	0	$ 0	1,052
Shares Issued, ending balance at Dec. 31, 2015						52,598,005
Equity, ending balance at Dec. 31, 2015	$ 1,841,555	$ 95,046	$ 0	$ (4,401)	$ (14,491)	$ 526	$ 1,764,875

SUMMARY OF SIGNIFICANT ACCOUNTI

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Notes)	12 Months Ended
	Dec. 31, 2015
Significant Accounting Policies [Line Items]
SIGNIFICANT ACCOUNTING POLICIES	1. SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Organization and Nature of Operations - Prior to January 31, 2014, ONE Gas was a wholly owned subsidiary of ONEOK and comprised its former natural gas distribution business. On January 8, 2014, ONEOK’s board of directors approved the distribution of all the shares of our common stock to holders of ONEOK common stock. On January 31, 2014, we became an independent, publicly traded company as a result of a distribution by ONEOK of our common stock to ONEOK’s shareholders. Our common stock began trading “regular-way” under the ticker symbol “OGS” on the NYSE on February 3, 2014. We provide natural gas distribution services to more than 2 million customers through our divisions in Oklahoma, Kansas and Texas through Oklahoma Natural Gas, Kansas Gas Service and Texas Gas Service, respectively. We serve residential, commercial, industrial and transportation customers in all three states. In addition, we also provide natural gas distribution services to wholesale and public authority customers. Basis of Presentation - Prior to our separation from ONEOK, our financial statements were derived from ONEOK’s financial statements, which included its natural gas distribution business as if we, for accounting purposes, had been a separate company for all periods presented. The assets and liabilities in the financial statements have been reflected on a historical basis. The financial statements for periods prior to the separation also include expense allocations for certain corporate functions historically performed by ONEOK, including allocations of general corporate expenses related to executive oversight, accounting, treasury, tax, legal, information technology and other services. We believe our assumptions underlying the financial statements, including the assumptions regarding the allocation of general corporate expenses from ONEOK, are reasonable. However, the financial statements may not include all of the actual expenses that would have been incurred by us and may not reflect our results of operations, financial position and cash flows had we been a separate publicly traded company during the periods presented prior to the separation. Because the operations of the natural gas distribution business within ONEOK were conducted through separate divisions, ONEOK’s net investment in us, excluding the long-term line of credit with ONEOK, is shown as owner’s net investment in lieu of equity in the financial statements prior to the separation. Transactions between ONEOK and us that were not part of the long-term line of credit with ONEOK or the short-term note payable to ONEOK have been identified in the Statements of Equity as a net transfer from ONEOK. All financial information presented after the separation represents the results of operations, financial position and cash flows of ONE Gas. Accordingly: • Our Statements of Income and Comprehensive Income for the year ended December 31, 2014 , consist of the results of ONE Gas for the eleven months ended December 31, 2014 , and the results of ONE Gas Predecessor for the one month ended January 31, 2014. Our Statements of Income and Comprehensive Income for the year ended December 31, 2013 , consist entirely of the results of ONE Gas Predecessor. Our net income for the period prior to January 31, 2014, was recorded to owner’s net investment. • Our Statement of Cash Flows for the year ended December 31, 2014 , consists of the results of ONE Gas for the eleven months ended December 31, 2014 , and the results of ONE Gas Predecessor for the one month ended January 31, 2014. Our Statement of Cash Flows for the year ended December 31, 2013 , consists entirely of the results of ONE Gas Predecessor. • Our Statement of Equity for the year ended December 31, 2014 , consists of both the activity for ONE Gas Predecessor prior to January 31, 2014, and the activity for ONE Gas completed in connection with, and subsequent to, the separation on January 31, 2014. Our Statement of Equity for the year ended December 31, 2013 , consists entirely of the results of ONE Gas Predecessor. The financial statements include the accounts of the natural gas distribution business as set forth in “Organization and Nature of Operations” above. All significant balances and transactions between our divisions have been eliminated. Use of Estimates - The preparation of our financial statements and related disclosures in accordance with GAAP requires us to make estimates and assumptions with respect to values or conditions that cannot be known with certainty that affect the reported amount of assets and liabilities, and the disclosure of contingent assets and liabilities at the date of the financial statements. These estimates and assumptions also affect the reported amounts of revenue and expenses during the reporting period. Items that may be estimated include, but are not limited to, the economic useful life of assets, fair value of assets and liabilities, provisions for doubtful accounts receivable, unbilled revenues for natural gas delivered but for which meters have not been read, natural gas purchased but for which no invoice has been received, provision for income taxes, including any deferred tax valuation allowances, the results of litigation and various other recorded or disclosed amounts. We evaluate these estimates on an ongoing basis using historical experience and other methods we consider reasonable based on the particular circumstances. Nevertheless, actual results may differ significantly from the estimates. Any effects on our financial position or results of operations from revisions to these estimates are recorded in the period when the facts that give rise to the revision become known. Fair Value Measurements - We define fair value as the price that would be received from the sale of an asset or the transfer of a liability in an orderly transaction between market participants at the measurement date. We use the market and income approaches to determine the fair value of our assets and liabilities and consider the markets in which the transactions are executed. We measure the fair value of a group of financial assets and liabilities consistent with how a market participant would price the net risk exposure at the measurement date. Fair Value Hierarchy - At each balance sheet date, we utilize a fair value hierarchy to classify fair value amounts recognized or disclosed in our financial statements based on the observability of inputs used to estimate such fair value. The levels of the hierarchy are described below: • Level 1 - Unadjusted quoted prices in active markets for identical assets or liabilities; • Level 2 - Significant observable pricing inputs other than quoted prices included within Level 1 that are, either directly or indirectly, observable as of the reporting date. Essentially, this represents inputs that are derived principally from or corroborated by observable market data; and • Level 3 - May include one or more unobservable inputs that are significant in establishing a fair value estimate. These unobservable inputs are developed based on the best information available and may include our own internal data. We recognize transfers into and out of the levels as of the end of each reporting period. Determining the appropriate classification of our fair value measurements within the fair value hierarchy requires management’s judgment regarding the degree to which market data is observable or corroborated by observable market data. We categorize derivatives for which fair value is determined using multiple inputs within a single level, based on the lowest level input that is significant to the fair value measurement in its entirety. See Note 8 for additional information regarding our fair value measurements. Cash and Cash Equivalents - Cash equivalents consist of highly liquid investments, which are readily convertible into cash and have original maturities of three months or less. Revenue Recognition - For regulated deliveries of natural gas, we read meters and bill customers on a monthly cycle. We recognize revenues upon the delivery of the natural gas commodity or services rendered to customers. The billing cycles for customers do not necessarily coincide with the accounting periods used for financial reporting purposes. Revenues are accrued for natural gas delivered and services rendered to customers, but not yet billed. Accrued unbilled revenue is based on a percentage estimate of amounts unbilled each month, which is dependent upon a number of factors, some of which require management’s judgment. These factors include customer consumption patterns and the impact of weather on usage. The amounts of accrued unbilled natural gas sales revenues at December 31, 2015 and 2014 , were $109.6 million and $141.7 million , respectively. Accounts Receivable - Accounts receivable represent valid claims against nonaffiliated customers for natural gas sold or services rendered, net of allowances for doubtful accounts. We assess the creditworthiness of our customers. Those customers who do not meet minimum standards are required to provide security, including deposits and other forms of collateral, when appropriate. With more than 2 million customers across three states, we are not exposed materially to a concentration of credit risk. We maintain an allowance for doubtful accounts based upon factors surrounding the credit risk of customers, historical trends, consideration of the current credit environment and other information. In Oklahoma, Kansas and most jurisdictions we serve in Texas, we are able to recover natural gas costs related to doubtful accounts through purchased-gas cost adjustment mechanisms. At December 31, 2015 and 2014 , our allowance for doubtful accounts was $3.5 million and $4.0 million , respectively. Inventories - Natural gas in storage is maintained on the basis of weighted-average cost. Natural gas inventories that are injected into storage are recorded in inventory based on actual purchase costs, including storage and transportation costs. Natural gas inventories that are withdrawn from storage are accounted for in our purchased-gas cost adjustment mechanisms at the weighted-average inventory cost. Materials and supplies inventories, which are included in other current assets on our Balance Sheets, are stated at the lower of weighted-average cost or net realizable value. Our materials and supplies inventories totaled $33.3 million and $27.5 million at December 31, 2015 and 2014 , respectively. Derivatives and Risk Management Activities - We record all derivative instruments at fair value, with the exception of normal purchases and normal sales that are expected to result in physical delivery. The accounting for changes in the fair value of a derivative instrument depends on whether it has been designated and qualifies as part of a hedging relationship and, if so, the reason for holding it, or if regulatory rulings require a different accounting treatment. If certain conditions are met, we may elect to designate a derivative instrument as a hedge of exposure to changes in fair values or cash flows. The table below summarizes the various ways in which we account for our derivative instruments and the impact on our financial statements: Recognition and Measurement Accounting Treatment Balance Sheet Income Statement Normal purchases and normal sales - Fair value not recorded - Change in fair value not recognized in earnings Mark-to-market - Recorded at fair value - Change in fair value recognized in, and recoverable through, the purchased-gas cost adjustment mechanisms We have not elected to designate any of our derivative instruments as hedges. Gains or losses associated with the fair value of commodity derivative instruments entered into by us are included in, and recoverable through, the purchased-gas cost adjustment mechanisms. See Note 8 for additional information regarding our fair value measurements and hedging activities using derivatives. Property, Plant and Equipment - Our properties are stated at cost, which includes direct construction costs such as direct labor, materials, burden and AFUDC. Generally, the cost of our property retired or sold, plus removal costs, less salvage, is charged to accumulated depreciation. Gains and losses from sales or retirement of an entire operating unit or system of our properties are recognized in income. Maintenance and repairs are charged directly to expense. AFUDC represents the cost of borrowed funds used to finance construction activities. We capitalize interest costs during the construction or upgrade of qualifying assets. Capitalized interest is recorded as a reduction to interest expense. Our properties are depreciated using the straight-line method over their estimated useful lives. Generally, we apply composite depreciation rates to functional groups of property having similar economic circumstances. We periodically conduct depreciation studies to assess the economic lives of our assets. These depreciation studies are completed as a part of our rate proceedings, and the changes in economic lives, if applicable, are implemented prospectively when the new rates are effective. Changes in the estimated economic lives of our property, plant and equipment could have a material effect on our financial position, results of operations or cash flows. Property, plant and equipment on our Balance Sheets includes construction work in process for capital projects that have not yet been placed in service and therefore are not being depreciated. Assets are transferred out of construction work in process when they are substantially complete and ready for their intended use. See Note 10 for additional information regarding our property, plant and equipment. Impairment of Goodwill and Long-Lived Assets - We assess our goodwill for impairment at least annually as of July 1. Total goodwill was $158.0 million at December 31, 2015 and 2014 , respectively. Our goodwill impairment analysis performed in 2015, 2014 and 2013 , utilized a qualitative assessment and did not result in any impairment indicators. Subsequent to July 1, 2015 , no event has occurred indicating that it is more likely that not that our fair value is less than our carrying value of our net assets. As part of our goodwill impairment test, we first assess qualitative factors (including macroeconomic conditions, industry and market considerations, cost factors and overall financial performance) to determine whether it is more likely than not that our fair value is less than our carrying amount. If further testing is necessary, we perform a two-step impairment test for goodwill. In the first step, an initial assessment is made by comparing our fair value with our book value, including goodwill. If the fair value is less than the book value, an impairment is indicated, and we must perform a second test to measure the amount of the impairment. In the second test, we calculate the implied fair value of the goodwill by deducting the fair value of all tangible and intangible net assets from the fair value determined in step one of the assessment. If the carrying value of the goodwill exceeds the implied fair value of the goodwill, we will record an impairment charge. To estimate our fair value, we use two generally accepted valuation approaches, an income approach and a market approach, using assumptions consistent with a market participant’s perspective. Under the income approach, we use anticipated cash flows over a period of years plus a terminal value and discount these amounts to their present value using appropriate discount rates. Under the market approach, we apply acquisition multiples to forecasted cash flows. The acquisition multiples used are consistent with historical asset transactions. The forecasted cash flows are based on average forecasted cash flows over a period of years. We assess our long-lived assets for impairment whenever events or changes in circumstances indicate that an asset’s carrying amount may not be recoverable. An impairment is indicated if the carrying amount of a long-lived asset exceeds the sum of the undiscounted future cash flows expected to result from the use and eventual disposition of the asset. If an impairment is indicated, we record an impairment loss equal to the difference between the carrying value and the fair value of the long-lived asset. We determined that there were no asset impairments in 2015, 2014 or 2013 . Regulation - We are subject to the rate regulation and accounting requirements of the OCC, KCC, RRC and various municipalities in Texas. We follow the accounting and reporting guidance for regulated operations. During the ratemaking process, regulatory authorities set the framework for what we can charge customers for our services and establish the manner that our costs are accounted for, including allowing us to defer recognition of certain costs and permitting recovery of the amounts through rates over time, as opposed to expensing such costs as incurred. Examples include weather normalization, unrecovered purchased-gas costs, pension and postemployment benefit costs and ad valorem taxes. This allows us to stabilize rates over time rather than passing such costs on to the customer for immediate recovery. Actions by regulatory authorities could have an effect on the amount recovered from rate payers. Any difference in the amount recoverable and the amount deferred is recorded as income or expense at the time of the regulatory action. A write-off of regulatory assets and costs not recovered may be required if all or a portion of the regulated operations have rates that are no longer: • established by independent regulators; • designed to recover the specific entity’s costs of providing regulated services; and • set at levels that will recover our costs when considering the demand and competition for our services. See Note 9 for additional information regarding our regulatory assets and liabilities disclosures. Pension and Other Postemployment Employee Benefits - We have defined benefit retirement plans covering eligible employees. We also sponsor welfare plans that provide other postemployment medical and life insurance benefits to eligible employees who retire with at least five years of service. To calculate the costs and liabilities related to our plans, we utilize an outside actuarial consultant, which uses statistical and other factors to anticipate future events. These factors include assumptions about the discount rate, expected return on plan assets, rate of future compensation increases, age and mortality and employment periods. In determining the projected benefit obligations and costs, assumptions can change from period to period and may result in material changes in the cost and liabilities we recognize. Prior to the separation, certain employees participated in pension and other postemployment employee benefit plans sponsored by ONEOK. We accounted for these plans as multiemployer benefit plans. Accordingly, we did not record an asset or liability to recognize the funded status of these plans. We recognized a liability only for any required contributions to those plans that were accrued and unpaid at the balance sheet date. The related pension and other postemployment expenses were allocated to us based on plan participants who directly supported our operations. These pension and other postemployment benefit costs included amounts associated with vested participants who are no longer employees. Prior to the separation, certain benefit costs associated with employees who directly supported our operations were determined based on a specific employee basis. We were also allocated benefit costs associated with employees of ONEOK that provided general corporate services. These amounts were charged to us by ONEOK as described in Note 2. Prior to the separation, we were not the plan sponsor for the ONEOK pension and other postemployment benefit plans. Accordingly, our balance sheets prior to the separation do not reflect any assets or liabilities related to these plans. See Note 12 for additional information regarding pension and other postemployment employee benefit plans. Income Taxes - Deferred income taxes are recorded for the difference between the financial statement and income tax basis of assets and liabilities and carryforward items, based on income tax laws and rates existing at the time the temporary differences are expected to reverse. The effect on deferred taxes of a change in tax rates is deferred and amortized for operations regulated by the OCC, KCC, RRC and various municipalities in Texas, if, as a result of an action by a regulator, it is probable that the effect of the change in tax rates will be recovered from or returned to customers through future rates. We continue to amortize previously deferred investment tax credits for ratemaking purposes over the periods prescribed by our regulators. A valuation allowance for deferred tax assets is recognized when it is more likely than not that some or all of the benefit from the deferred tax asset will not be realized. To assess that likelihood, we use estimates and judgment regarding our future taxable income, as well as the jurisdiction in which such taxable income is generated, to determine whether a valuation allowance is required. Such evidence can include our current financial position, our results of operations, both actual and forecasted, the reversal of deferred tax liabilities, as well as the current and forecasted business economics of our industry. We had no valuation allowance at December 31, 2015 and 2014 . We utilize a more-likely-than-not recognition threshold and measurement attribute for the financial statement recognition and measurement of a tax position that is taken or expected to be taken in a tax return. We reflect penalties and interest as part of income tax expense as they become applicable for tax provisions that do not meet the more-likely-than-not recognition threshold and measurement attribute. There were no material uncertain tax positions at December 31, 2015 and 2014 . See Note 13 for additional information regarding income taxes. Asset Retirement Obligations - Asset retirement obligations represent legal obligations associated with the retirement of long-lived assets that result from the acquisition, construction, development and/or normal use of the asset. Certain long-lived assets that comprise our natural gas distribution systems, primarily our pipeline assets, are subject to agreements or regulations that give rise to an asset retirement obligation for removal or other disposition costs associated with retiring the assets in place upon the discontinued use of the natural gas distribution system. We recognize the fair value of a liability for an asset retirement obligation in the period when it is incurred if a reasonable estimate of the fair value can be made. We are not able to estimate reasonably the fair value of the asset retirement obligations for portions of our assets because the settlement dates are indeterminable given our expected continued use of the assets with proper maintenance. We expect our natural gas distribution systems will continue in operation as long as natural gas supply and demand for natural gas distribution service exists. Based on the widespread use of natural gas for heating and cooking activities by residential and commercial customers in our service areas, management expects supply and demand to exist for the foreseeable future. In accordance with long-standing regulatory treatment, we collect through rates the estimated costs of removal on certain regulated properties through depreciation expense, with a corresponding credit to accumulated depreciation and amortization. These removal costs collected through our rates include costs attributable to legal and nonlegal removal obligations; however, the amounts collected that are in excess of these nonlegal asset-removal costs incurred are accounted for as a regulatory liability for financial reporting purposes. Historically, with the exception of the regulatory authority in Kansas, the regulatory authorities that have jurisdiction over our regulated operations have not required us to quantify or disclose this amount; rather, these costs are addressed prospectively in depreciation rates and are set in each general rate order. We have made an estimate of our regulatory liability using current rates since the last general rate order in each of our jurisdictions; however, for financial reporting purposes, significant uncertainty exists regarding the future disposition of this regulatory liability, pending, among other issues, clarification of regulatory intent. We continue to monitor the regulatory requirements, and the liability may be adjusted as more information is obtained. We record the estimated asset removal obligation in noncurrent liabilities in other deferred credits on our Balance Sheets. To the extent this estimated liability is adjusted, such amounts will be reclassified between accumulated depreciation and amortization and other deferred credits and therefore will not have an impact on earnings. Contingencies - Our accounting for contingencies covers a variety of business activities, including contingencies for legal and environmental exposures. We accrue these contingencies when our assessments indicate that it is probable that a liability has been incurred or an asset will not be recovered and an amount can be estimated reasonably. We expense legal fees as incurred and base our legal liability estimates on currently available facts and our estimates of the ultimate outcome or resolution. Accruals for estimated losses from environmental remediation obligations generally are recognized no later than the completion of a remediation feasibility study. Recoveries of environmental remediation costs from other parties are recorded as assets when their receipt is deemed probable. Actual results may differ from our estimates resulting in an impact, positive or negative, on earnings. See Note 14 for additional information regarding contingencies. Share-Based Payments - We expense the fair value of share-based payments net of estimated forfeitures. We estimate forfeiture rates based on historical forfeitures under our share-based payment plans. Prior to the separation, ONEOK charged us for compensation expense related to stock-based compensation awards granted to our employees that directly supported our operations. Share-based compensation was also a component of allocated amounts charged to us by ONEOK for general and administrative personnel providing services on our behalf. Earnings per share - Basic EPS is based on net income and is calculated based upon the daily weighted-average number of common shares outstanding during the periods presented. Also, this calculation includes fully vested stock awards that have not yet been issued as common stock. Diluted EPS includes the above, plus unvested stock awards granted under our compensation plans, but only to the extent these instruments dilute earnings per share. Segments - We operate in one reportable business segment: regulated public utilities that deliver natural gas to residential, commercial, industrial and transportation customers. We define reportable business segments as components of an organization for which discrete financial information is available and operating results are evaluated on a regular basis by the chief operating decision maker (CODM) in order to assess performance and allocate resources. Our CODM is our Chief Executive Officer (CEO). Characteristics of our organization that were relied upon in making this determination include the similar nature of services we provide, the functional alignment of our organizational structure, and the reports that are regularly reviewed by the CODM for the purpose of assessing performance and allocating resources. Our management is functionally aligned and centralized, with performance evaluated based upon results of the entire distribution business. Capital allocation decisions are driven by asset integrity management and operating efficiency, not geographic location. We evaluate performance based principally on operating income. Affiliate sales are recorded on the same basis as sales to unaffiliated customers and are discussed in further detail in Note 2. Net margin is comprised of total revenues less cost of natural gas. Cost of natural gas includes commodity purchases, fuel, storage and transportation costs and does not include an allocation of general operating costs or depreciation and amortization. In 2015 , 2014 and 2013 , we had no single external customer from which we received 10 percent or more of our gross revenues. Treasury Stock - We record treasury stock purchases at cost, which includes incremental direct transaction costs. Amounts are recorded as reductions in equity in our Balance Sheets. We record the reissuance of treasury stock at our weighted average cost of treasury shares recorded in equity in our Balance Sheets. Recently Issued Accounting Standards Update - In October 2015, the FASB issued ASU 2015-17, “Balance Sheet Classification of Deferred Taxes,” to simplify reporting of deferred taxes. The new guidance requires all deferred tax assets and liabilities, along with any related valuation allowance, be classified as noncurrent on the balance sheet. This guidance is required to be adopted for our interim and annual reports for periods beginning after December 15, 2016, but early adoption is permitted. We have adopted this guidance early to simplify our financial reporting process, have applied it prospectively for the period beginning October 1, 2015, and it did not have a material impact on our financial statements. Prior periods were not retrospectively adjusted. In August 2015, the FASB issued ASU 2015-15, “Interest-Imputation of Interest (Subtopic 835-30),” which specifically addresses the presentation and subsequent measurement of debt issuance costs associated with line of credit arrangements. We do not expect this issued guidance, which will be adopted concurrently with ASU 2015-03, to have a material impact on our financial statements. In April 2015, the FASB issued ASU 2015-03, “Interest-Imputation of Interest,” which 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. We do not expect this issued guidance, which is required to be adopted for our interim and annual reports for periods beginning after December 15, 2015, to have a material impact on our financial statements. In April 2015, the FASB issued ASU 2015-05, “Intangibles-Goodwill and Other-Internal-Use Software,” which helps entities evaluate the accounting for fees paid by a customer in a cloud computing arrangement. We do not expect this issued guidance, which is required to be adopted for our interim and annual reports for periods beginning after December 15, 2015, to have a material impact on our financial statements. In May 2014, the FASB issued ASU 2014-09, “Revenue from Contracts with Customers,” which clarifies and converges the revenue recognition principles under GAAP and IFRS. In July 2015, FASB delayed the effective date of ASU 2014-09 for one year. We are evaluating the impact of this recently issued guidance, which is required to be adopted for our interim and annual reports beginning with the first quarter 2018.

SEPARATION & RELATED-PARTY TRAN

SEPARATION & RELATED-PARTY TRANSACTIONS (Notes)	12 Months Ended
	Dec. 31, 2015
Separation & Related Party Transaction [Line Items]
Related Party Transactions Disclosure [Text Block]	2. SEPARATION & RELATED-PARTY TRANSACTIONS Distribution - On January 8, 2014, ONEOK’s board of directors approved the distribution of our common stock to holders of ONEOK common stock. In order for ONEOK to effect the distribution, we requested, and the SEC declared effective, our Registration Statement on Form 10 on January 10, 2014. ONEOK transferred all of the assets and liabilities primarily related to its natural gas distribution business to us. Assets and liabilities included accounts receivable and payable, natural gas in storage, regulatory assets and liabilities, pipeline and other natural gas distribution facilities, customer deposits, employee-related assets and liabilities, including amounts attributable to pension and other postemployment benefits, tax-related assets and liabilities and other assets and liabilities primarily associated with providing natural gas distribution service in Oklahoma, Kansas and Texas. Cash and certain corporate assets, such as office space in the corporate headquarters and certain IT hardware and software, were not transferred to us; however, a Transition Services Agreement between ONEOK and us provided access to such corporate assets as necessary to operate our business for a period of time to enable us to obtain the applicable corporate assets. Immediately prior to the contribution of the natural gas distribution business to us, ONEOK contributed to the capital of the natural gas distribution business all of the amounts outstanding on the natural gas distribution business’ short-term note payable to and long-term line of credit with ONEOK. We received approximately $1.19 billion of cash from a private placement of senior notes, which were later exchanged for registered notes, then used a portion of those proceeds to fund a cash payment of approximately $1.13 billion to ONEOK. Effective January 31, 2014, the number of our authorized shares increased to 250 million shares of common stock and 50 million of preferred stock. On January 31, 2014, ONEOK distributed one share of our common stock for every four shares of ONEOK common stock held by ONEOK shareholders of record as of the close of business on January 21, 2014, the record date of the distribution. At the close of business on January 31, 2014, we became an independent, publicly traded company as a result of the distribution. Reorganization Adjustments - We entered into the Separation and Distribution Agreement and several other agreements with ONEOK to effect the separation and provide a framework for our relationships with ONEOK after the distribution. These agreements govern the relationship between ONEOK and us subsequent to the completion of the distribution, and provide for the allocation among ONEOK and us of the assets, liabilities and obligations (including employee benefits and tax-related assets and liabilities) relating to the natural gas distribution business attributable to periods prior to, at and after the distribution. In accordance with the terms of the Separation and Distribution Agreement, ONEOK contributed the assets and liabilities of its natural gas distribution business to us. The noncash contributions below represent ONEOK assets and liabilities attributable to pension and other postemployment employee benefits, general corporate assets and liabilities and related deferred taxes not included previously in the ONE Gas Predecessor balance sheet, but the costs for which were included in ONE Gas Predecessor’s results of operations. The table below also includes the contribution of the short-term note payable to and long-term line of credit with ONEOK previously included in ONE Gas Predecessor balance sheets. The assets and liabilities below were recorded at historical cost as the reorganization was among entities under common control. Net transfers from ONEOK included: (Thousands of dollars) Property, plant and equipment, net $ 21,459 Regulatory assets, pension and other postemployment benefits 331,148 Other assets 80,700 Long-term line of credit with ONEOK 1,027,631 Short-term note payable to ONEOK 397,857 Pension and other postemployment benefits - liabilities (123,800 ) Other liabilities (34,404 ) Deferred taxes (86,112 ) Accumulated other comprehensive loss (3,393 ) Net contribution of assets (liabilities) $ 1,611,086 Less: Cash paid to ONEOK 1,130,000 Net transfers from ONEOK $ 481,086 Affiliate Transactions - Prior to our separation, we had certain transactions with ONEOK and its subsidiaries. We purchased a portion of our natural gas supply and natural gas transportation and storage services from ONEOK and its affiliates. These contracts were awarded through a competitive-bidding process, and the costs were recoverable through our purchased-gas cost adjustment mechanisms. Prior to our separation, the Statements of Income included expense allocations for certain corporate functions historically performed by ONEOK and allocated to its natural gas distribution business, including allocations of general corporate expenses related to executive oversight, accounting, treasury, tax, legal, information technology and facilities maintenance. Where costs were incurred specifically on our behalf, the costs were billed directly to us by ONEOK. In other situations, the costs were allocated to us through a variety of methods, depending upon the nature of the expenses. For example, a service that applied equally to all employees of ONEOK was allocated based upon the number of employees in each ONEOK affiliate. An expense benefiting us but having no direct basis for allocation was allocated by the modified Distrigas method, a method using a combination of ratios that include gross plant and investment, operating income and payroll expense. It is not practicable to determine what these general overhead costs would be on a stand-alone basis. These allocations included the following costs: Corporate Services - These represent costs for certain employees of ONEOK who provided general and administrative services on our behalf. These charges were either directly identifiable or allocated based upon usage factors for our operations. In addition, we received other allocated costs for our share of general corporate expenses of ONEOK, which were determined based on our relative use of the service or, if there was no direct basis for allocation, were allocated by the modified Distrigas method. All of these costs are reflected in operations and maintenance and depreciation expense in the Statements of Income. Benefit Plans and Incentives - These represent benefit costs and other incentives, including group health and welfare benefits, pension plans, other postemployment benefit plans and employee stock-based compensation plans. Costs associated with incentive and stock-based compensation plans were determined on a specific identification basis for certain employees who directly supported our operations. All other employee benefit costs historically were allocated using a percentage factor derived from a ratio of benefit costs to salary costs for ONEOK’s employees. These expenses are included in operations and maintenance expenses in the Statements of Income. Total compensation cost, which included costs for both employees who directly supported our operations and allocations for corporate services, charged to us by ONEOK related to share-based payment plans was $15.5 million during 2013. Compensation costs charged to us by ONEOK in 2014 were not material. See Note 11 for additional information regarding share-based payments. Total cost charged to us by ONEOK related to pension and other postemployment health and welfare plans was $52.1 million during 2013, which is net of amounts deferred through regulatory mechanisms of $1.8 million during 2013. Cost related to pension and other postemployment health and welfare plans which was charged to us by ONEOK in 2014 was not material. See Note 12 for additional information regarding employee benefit plans. Interest Expense - ONEOK utilized a centralized approach to cash management and the financing of its businesses. Cash receipts and cash expenditures for costs and expenses from our operations were transferred to or from ONEOK on a regular basis and recorded as increases or decreases in the balance due in short-term note payable to ONEOK under an unsecured promissory note we had in place with ONEOK. The amounts outstanding under the long-term line of credit with ONEOK and the short-term note payable to ONEOK accrued interest based on ONEOK’s weighted-average cost of long-term and short-term debt, respectively. The weighted average interest rate on amounts outstanding under the long-term line of credit with ONEOK was 5.79 percent in 2013. The interest rate on the revolver was reset each year based on ONEOK’s outstanding debt plus an adjustment of 50 basis points for ONEOK’s cost to administer the program. The weighted-average interest rate for the short-term notes payable to ONEOK was 0.92 percent for 2013. Principal under these notes payable beared interest based on ONEOK’s weighted-average cost of short-term debt, plus a utilization fee of 50 basis points, calculated monthly. The following table shows ONEOK’s and its subsidiaries’ transactions with us included in the Statements of Income for the periods indicated: Year Ended December 31, 2013 (Thousands of dollars) Cost of natural gas $ 226,582 Operations and maintenance Direct employee labor and benefit costs 177,526 Allocated employee labor and benefit costs 29,955 Charges for general and administrative services 36,078 Depreciation and amortization 6,940 Other (income)/expense, net (5,073 ) Interest expense 60,930 Total $ 532,938 Employee labor and benefit costs capitalized totaled $49.3 million for 2013. In addition, we recorded regulated utility revenue from ONEOK and its subsidiaries. This amount was immaterial for the period presented. The remaining related party transactions prior to the separation were not material in 2014.

CREDIT FACILITY AND SHORT-TERM

CREDIT FACILITY AND SHORT-TERM NOTES PAYABLE (Notes)	12 Months Ended
	Dec. 31, 2015
Short-term Debt [Line Items]
Short-term Debt [Text Block]	3. CREDIT FACILITY AND SHORT-TERM NOTES PAYABLE ONE Gas Credit Agreement - The ONE Gas Credit Agreement contains certain financial, operational and legal covenants. Among other things, these covenants include maintaining ONE Gas’ total debt-to-capital ratio of no more than 70 percent at the end of any calendar quarter. The ONE Gas Credit Agreement also contains customary affirmative and negative covenants, including covenants relating to liens, indebtedness of subsidiaries, investments, changes in the nature of business, fundamental changes, transactions with affiliates, burdensome agreements, and use of proceeds. In the event of a breach of certain covenants by ONE Gas, amounts outstanding under the ONE Gas Credit Agreement may become due and payable immediately. At December 31, 2015 , our total debt-to-capital ratio was 40 percent and we were in compliance with all covenants under the ONE Gas Credit Agreement. The ONE Gas Credit Agreement includes a $50 million sublimit for the issuance of standby letters of credit and also features an option to request an increase in the size of the facility to an aggregate of $1.2 billion from $700 million by either commitments from new lenders or increased commitments from existing lenders. Borrowings made under the facility are available for general corporate purposes. The ONE Gas Credit Agreement contains provisions for an applicable margin rate and an annual facility fee, both of which adjust with changes in our credit rating. Based on our current credit ratings, borrowings, if any, will accrue interest at LIBOR plus 79.5 basis points, and the annual facility fee is 8 basis points. We have a commercial paper program under which we may issue unsecured commercial paper up to a maximum amount of $700 million to fund short-term borrowing needs. The maturities of the commercial paper notes may vary but may not exceed 270 days from the date of issue. The commercial paper notes are sold generally at par less a discount representing an interest factor. The ONE Gas Credit Agreement is available to repay the commercial paper notes, if necessary. Amounts outstanding under the commercial paper program reduce the borrowing capacity under the ONE Gas Credit Agreement. At December 31, 2015, we had $12.5 million of commercial paper and $1.0 million in letters of credit issued under the ONE Gas Credit Agreement, with no borrowings and $686.5 million of remaining credit available under the ONE Gas Credit Agreement. The weighted-average interest rate on our commercial paper was 0.70 percent and 0.32 percent at December 31, 2015 and 2014, respectively.

LONG-TERM DEBT (Notes)

LONG-TERM DEBT (Notes)	12 Months Ended
	Dec. 31, 2015
Debt Instrument [Line Items]
Long-term Debt [Text Block]	4. LONG-TERM DEBT Senior notes issuance - In January 2014, we issued senior notes, consisting of $300 million of 2.07 percent senior notes due 2019 , $300 million of 3.61 percent senior notes due 2024 and $600 million of 4.658 percent senior notes due 2044 (collectively, our “Senior Notes”). The net proceeds were approximately $1.19 billion and were used to fund a one-time cash payment to ONEOK of approximately $1.13 billion as part of the separation. The remaining portion of the net proceeds was retained in order to provide sufficient financial flexibility and to support working capital requirements and capital expenditures. The indenture governing our Senior Notes includes an event of default upon the acceleration of other indebtedness of $100 million or more. Such events of default would entitle the trustee or the holders of 25 percent in the aggregate principal amount of the outstanding Senior Notes to declare those senior notes immediately due and payable in full. We may redeem our Senior Notes at par, plus accrued and unpaid interest to the redemption date, starting one month, three months, and six months, respectively, before their maturity dates. Prior to these dates, we may redeem these Senior Notes, in whole or in part, at a redemption price equal to the principal amount, plus accrued and unpaid interest and a make-whole premium. The redemption price will never be less than 100 percent of the principal amount of the respective note plus accrued and unpaid interest to the redemption date. Our Senior Notes are senior unsecured obligations, ranking equally in right of payment with all of our existing and future unsecured senior indebtedness.

EQUITY (Notes)

EQUITY (Notes)	12 Months Ended
	Dec. 31, 2015
Class of Stock [Line Items]
Stockholders' Equity Note Disclosure [Text Block]	5. EQUITY Preferred Stock - At December 31, 2015, we have 50 million , $0.01 par value, authorized shares of preferred stock available. We have not issued or established any classes or series of shares of preferred stock. Common Stock - At December 31, 2015 , we had approximately 197.4 million shares of authorized common stock available for issuance. Treasury Shares - We purchase treasury shares to be used to offset shares issued under our employee and non-employee director equity compensation and employee stock purchase plans. Our Board of Directors established an annual limit of $20 million of treasury stock purchases, exclusive of funds received through the dividend reinvestment and employee stock purchase plans. Stock purchases may be made in the open market or in private transactions at times, and in amounts that we deem appropriate. There is no guarantee as to the exact number of shares that we purchase, and we can terminate or limit the program at any time. We hold the purchased shares as treasury shares and account for them using the cost method. Dividends Declared - In January 2016, a dividend of $0.35 per share ( $1.40 per share on an annualized basis) was declared for shareholders of record on February 26, 2016, payable March 11, 2016.

ACCUMULATED OTHER COMPREHENSIVE

ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Notes)	12 Months Ended
	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Comprehensive Income (Loss) Note [Text Block]	6. ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) The following table sets forth the balance in accumulated other comprehensive income (loss) for the period indicated: Accumulated Other Comprehensive Income (Loss) (Thousands of dollars) January 1, 2014 $ — Transfers in upon separation (3,393 ) Pension and other postemployment benefit plans obligations Other comprehensive income (loss) before reclassification, net of tax of $1,442 (2,096 ) Amounts reclassified from accumulated other comprehensive income (loss), net of tax of $(198) 315 Other comprehensive income (loss) (1,781 ) December 31, 2014 (5,174 ) Pension and other postemployment benefit plans obligations Other comprehensive income (loss) before reclassification, net of tax of $(130) 209 Amounts reclassified from accumulated other comprehensive income (loss), net of tax of $(353) 564 Other comprehensive income (loss) 773 December 31, 2015 $ (4,401 ) The following table sets forth the effect of reclassifications from accumulated other comprehensive income (loss) on our Statements of Income for the period indicated: Details about Accumulated Other Comprehensive Income Year Ended December 31, Affected Line Item in the (Loss) Components 2015 2014 Statements of Income ( Thousands of dollars ) Pension and other postemployment benefit plan obligations (a) Amortization of net loss $ 47,494 $ 34,169 Amortization of unrecognized prior service cost (1,962 ) (1,211 ) 45,532 32,958 Regulatory adjustments (b) (44,615 ) (32,445 ) 917 513 Income before income taxes (353 ) (198 ) Income tax expense Total reclassifications for the period $ 564 $ 315 Net income (a) These components of accumulated other comprehensive income (loss) are included in the computation of net periodic benefit cost. See Note 12 for additional information regarding our net periodic benefit cost. (b) Regulatory adjustments represent pension and other postemployment benefit costs expected to be recovered through rates and are deferred as part of our regulatory assets. See Note 9 for additional information regarding our regulatory assets and liabilities.

EARNINGS PER SHARE (Notes)

EARNINGS PER SHARE (Notes)	12 Months Ended
	Dec. 31, 2015
EARNINGS PER SHARE OF COMMON STOCK, BASIC AND DILUTED [Line Items]
Earnings Per Share [Text Block]	7. EARNINGS PER SHARE The following tables set forth the computation of basic and diluted EPS from continuing operations for the periods indicated: Year Ended December 31, 2015 Income Shares Per Share Amount ( Thousands, except per share amounts ) Basic EPS Calculation Net income available for common stock $ 119,030 52,578 $ 2.26 Diluted EPS Calculation Effect of dilutive securities — 676 Net income available for common stock and common stock equivalents $ 119,030 53,254 $ 2.24 Year Ended December 31, 2014 Income Shares Per Share Amount ( Thousands, except per share amounts ) Basic EPS Calculation Net income available for common stock $ 109,790 52,364 $ 2.10 Diluted EPS Calculation Effect of dilutive securities — 582 Net income available for common stock and common stock equivalents $ 109,790 52,946 $ 2.07 Year Ended December 31, 2013 Income Shares Per Share Amount ( Thousands, except per share amounts ) Basic EPS Calculation Net income available for common stock $ 99,195 52,319 $ 1.90 Diluted EPS Calculation Effect of dilutive securities — — Net income available for common stock and common stock equivalents $ 99,195 52,319 $ 1.90 On January 31, 2014, 51,941,236 shares of our common stock were distributed to ONEOK shareholders in conjunction with the separation. For comparative purposes, and to provide a more meaningful calculation of weighted-average shares outstanding, we have assumed this amount and any shares associated with fully vested stock awards that have not been issued to be outstanding as of the beginning of each period prior to the separation presented in the calculation of weighted-average shares.

DERIVATIVE FINANCIAL INSTRUMENT

DERIVATIVE FINANCIAL INSTRUMENTS AND FAIR VALUE MEASUREMENTS (Notes)	12 Months Ended
	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value Disclosures	8. DERIVATIVE FINANCIAL INSTRUMENTS AND FAIR VALUE MEASUREMENTS Derivative Instruments - At December 31, 2015 , we held purchased natural gas call options for the heating season ending March 2016, with total notional amounts of 17.0 Bcf, for which we paid premiums of $5.8 million , and had a fair value of $0.4 million . At December 31, 2014 , we held purchased natural gas call options for the heating season ended March 2015, with total notional amounts of 16.0 Bcf, for which we paid premiums of $6.4 million , and had a fair value of $0.1 million . The premiums paid and any cash settlements received are recorded as part of our unrecovered purchased-gas costs in current regulatory assets as these contracts are included in, and recoverable through, the purchased-gas cost adjustment mechanisms. Additionally, changes in fair value associated with these contracts are deferred as part of our unrecovered purchased-gas costs in our Balance Sheets. Our natural gas call options are classified as Level 1 as fair value amounts are based on unadjusted quoted prices in active markets including NYMEX-settled prices. There were no transfers between levels for the periods presented. Other Financial Instruments - The approximate fair value of cash and cash equivalents, accounts receivable and accounts payable is equal to book value, due to the short-term nature of these items. Our cash and cash equivalents are comprised of bank and money market accounts, and are classified as Level 1. Short-term notes payable and commercial paper are due upon demand and, therefore, the carrying amounts approximate fair value and are classified as Level 1. The book value of our long-term debt, including current maturities, was $1.2 billion at both December 31, 2015 and 2014 . The estimated fair value of our long-term debt, including current maturities, was $1.2 billion and $1.3 billion at December 31, 2015 and 2014 , respectively. The estimated fair value of our Senior Notes was determined using quoted market prices, and are considered Level 2.

REGULATORY ASSETS AND LIABILITI

REGULATORY ASSETS AND LIABILITIES (Notes)	12 Months Ended
	Dec. 31, 2015
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]
Schedule of Regulatory Assets and Liabilities	9. REGULATORY ASSETS AND LIABILITIES The table below presents a summary of regulatory assets, net of amortization, and liabilities for the periods indicated: December 31, 2015 Remaining Recovery Period Current Noncurrent Total ( Thousands of dollars ) Under-recovered purchased-gas costs 1 year $ 13,336 $ — $ 13,336 Pension and other postemployment benefit costs See Note 12 15,670 425,175 440,845 Weather normalization 1 year 2,198 — 2,198 Reacquired debt costs 12 years 812 8,919 9,731 Other 1 to 23 years 909 1,769 2,678 Total regulatory assets, net of amortization 32,925 435,863 468,788 Accumulated removal costs (a) up to 50 years — (9,032 ) (9,032 ) Over-recovered purchased-gas costs 1 year (22,884 ) — (22,884 ) Ad valorem tax 1 year (1,731 ) — (1,731 ) Total regulatory liabilities (24,615 ) (9,032 ) (33,647 ) Net regulatory assets and liabilities $ 8,310 $ 426,831 $ 435,141 (a) Included in other deferred credits in our Balance Sheets. December 31, 2014 Remaining Recovery Period Current Noncurrent Total ( Thousands of dollars ) Under-recovered purchased-gas costs 1 year $ 28,712 $ — $ 28,712 Pension and other postemployment benefit costs See Note 12 18,108 466,684 484,792 Reacquired debt costs 13 years 812 9,730 10,542 Other 1 to 24 years 2,561 2,309 4,870 Total regulatory assets, net of amortization 50,193 478,723 528,916 Accumulated removal costs (a) up to 50 years — (15,451 ) (15,451 ) Weather normalization 1 year (16,516 ) — (16,516 ) Over-recovered purchased-gas costs 1 year (13,055 ) — (13,055 ) Ad valorem tax 1 year (2,896 ) — (2,896 ) Total regulatory liabilities (32,467 ) (15,451 ) (47,918 ) Net regulatory assets and liabilities $ 17,726 $ 463,272 $ 480,998 (a) Included in other deferred credits in our Balance Sheets. Regulatory assets on our Balance Sheets, as authorized by the various regulatory authorities, are probable of recovery. Base rates are designed to provide a recovery of cost during the period rates are in effect but do not generally provide for a return on investment for amounts we have deferred as regulatory assets. All of our regulatory assets recoverable through base rates are subject to review by the respective regulatory authorities during future rate proceedings. We are not aware of any evidence that these costs will not be recoverable through either rate riders or base rates, and we believe that we will be able to recover such costs, consistent with our historical recoveries. Purchased-gas costs represent the natural gas costs that have been over- or under-recovered from customers through the purchased-gas cost adjustment mechanisms, and includes natural gas utilized in our operations and premiums paid and any cash settlements received from our purchased natural gas call options. We amortize reacquired debt costs in accordance with the accounting guidelines prescribed by the OCC and KCC. In December 2013, the KCC approved a settlement agreement between ONEOK, the staff of the KCC, and the Citizens’ Utility Ratepayer Board that authorized the transfer of ONEOK’s Kansas Gas Service natural gas distribution assets to us. As a result, Kansas Gas Service expensed certain transition costs associated with ONEOK’s acquisition of Kansas Gas Service in 1997 that previously had been recorded as a regulatory asset and amortized and recovered in rates over a 40-year period. As such, we recorded a noncash charge to income of approximately $10.2 million before taxes during 2013 in depreciation and amortization. Weather normalization represents revenue over- or under-recovered through the weather normalization adjustment rider in Kansas. This amount is deferred as a regulatory asset or liability for a 12-month period. Kansas Gas Service then applies an adjustment to the customers’ bills for 12 months to refund the over-collected revenue or bill the under-collected revenue. Ad valorem tax represents an increase or decrease in Kansas Gas Service’s taxes above or below the amount approved in a rate case. This amount is deferred as a regulatory asset or liability for a 12-month period. Kansas Gas Service then applies an adjustment to the customers’ bills for 12 months to refund the over-collected revenue or bill the under-collected revenue. Recovery through rates resulted in amortization of regulatory assets of approximately $1.6 million and $6.4 million for the years ended December 31, 2015 and 2014 , respectively. Amortization of regulatory assets of approximately $32.0 million for the year ended December 31, 2013 , included amounts recovered through rates totaling $21.8 million and $10.2 million related to certain transition costs as described above. We collect, through our rates, the estimated costs of removal on certain regulated properties through depreciation expense, with a corresponding credit to accumulated depreciation and amortization. These removal costs are nonlegal obligations; however, the amounts collected that are in excess of these nonlegal asset-removal costs incurred are accounted for as a regulatory liability. We have made an estimate of our regulatory liability using current rates since the last general rate order in each of our jurisdictions. We record the estimated nonlegal asset removal obligation in noncurrent liabilities in other deferred credits on our Balance Sheets. In January 2016, as a result of our rate case in Oklahoma, we recorded a regulatory asset of $2.4 million to recover certain information technology costs incurred as a result of our separation from ONEOK in 2014, which will be recovered over four years.

PROPERTY, PLANT AND EQUIPMENT (

PROPERTY, PLANT AND EQUIPMENT (Notes)	12 Months Ended
	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
PROPERTY, PLANT AND EQUIPMENT	10. PROPERTY, PLANT AND EQUIPMENT The following table sets forth our property, plant and equipment by property type, for the periods indicated: December 31, December 31, 2015 2014 ( Thousands of dollars ) Natural gas distribution pipelines and related equipment $ 4,114,090 $ 3,909,881 Natural gas transmission pipelines and related equipment 462,654 450,810 General plant and other 498,906 418,157 Construction work in process 57,032 71,353 Property, plant and equipment 5,132,682 4,850,201 Accumulated depreciation and amortization (1,620,771 ) (1,556,481 ) Net property, plant and equipment $ 3,511,911 $ 3,293,720 We compute depreciation expense for distribution operations by applying composite, straight-line rates approved by various regulatory authorities. The average depreciation rates for our property are set forth in the following table for the periods indicated: Years Ended December 31, 2015 2014 2013 2.0% - 3.0% 2.0% - 3.0% 2.0% - 3.0% We recorded capitalized interest of $2.6 million , $2.5 million and $1.3 million for the years ended December 31, 2015, 2014 and 2013 , respectively. We incurred liabilities for construction work in process that had not been paid at December 31, 2015, 2014 and 2013 of $15.0 million , $7.0 million and $10.5 million , respectively. Such amounts are not included in capital expenditures on the Statements of Cash Flows. Amounts recorded for regulatory accounting purposes that were not reflected in our financial statements were not material for the years ended December 31, 2015 and 2014.

SHARE-BASED PAYMENTS (Notes)

SHARE-BASED PAYMENTS (Notes)	12 Months Ended
	Dec. 31, 2015
Share-based Payments [Line Items]
Disclosure of Compensation Related Costs, Share-based Payments	11. SHARE-BASED PAYMENTS The ONE Gas Equity Compensation Plan (ECP or ONE Gas Plan) provides for the granting of stock-based compensation, including incentive stock options, nonstatutory stock options, stock bonus awards, restricted stock awards, restricted stock unit awards, performance stock awards and performance unit awards to eligible employees and the granting of stock awards to nonemployee directors. We have reserved 2.8 million shares of common stock for issuance under the ECP. At December 31, 2015 , we had approximately 1.4 million shares available for issuance under the ECP, which reflect shares issued and estimated shares expected to be issued upon vesting of outstanding awards granted under the plan, less forfeitures. The plan allows for the deferral of awards granted in stock or cash, in accordance with Internal Revenue Code section 409A requirements. Prior to our separation, certain employees assigned to us in the separation participated in ONEOK’s share-based awards plans (ONEOK Plans). The ONEOK Plans provided for ONEOK common stock based awards to both employees and ONEOK’s nonemployee directors. The plans permitted the granting of various types of awards including, but not limited to, performance stock units and restricted stock units. Awards could be granted for no consideration other than prior and future services or based on certain financial performance targets. In connection with the separation, awards granted by ONEOK in 2012 and 2013 were cancelled and replaced with awards of ONE Gas shares. The number of restricted stock units held by a ONE Gas participant was multiplied by a ratio of 2.04 which was determined by the ONEOK volume-weighted average share price of $68.22 on January 31, 2014, and the ONE Gas volume-weighted average share price of $33.50 on February 3, 2014, rounded to the nearest whole share. The same ratio of 2.04 was used to convert the outstanding performance stock units awarded by ONEOK prior to the separation into awards for ONE Gas shares. A pre-distribution payout factor was applied to each grant based on ONEOK’s total shareholder return performance compared with its peer group for the number of days lapsed from the date of the grant to January 31, 2014, and these awards were frozen or “banked” and are not subject to an additional payout factor. The remaining units from each grant will continue to be at-risk based on our performance and the relative total shareholder return of our peer group. No incremental cost was recorded in our financial statements upon cancellation and replacement of the 2012 and 2013 restricted stock units and performance stock units because the previous awards were cancelled and replaced pursuant to anti-dilution provisions of the ONEOK Plans and the fair value of the awards immediately following the cancellation and replacement was not higher than the fair value of the awards immediately before the cancellation and replacement. We were charged by ONEOK for share-based compensation expense related to employees that directly supported our operations. ONEOK also charged us for the allocated costs of certain employees of ONEOK (including stock-based compensation) who provided general and administrative services on our behalf. Information included in this note is limited to share-based compensation associated with employees in 2014, and employees that directly supported our operations as part of ONEOK prior to our separation. See Note 2 for total costs charged to us by ONEOK. Compensation cost expensed for our share-based payment plans was $5.7 million , net of tax benefits of $3.5 million , for 2015, and $7.0 million , net of tax benefits of $4.4 million for 2014. Compensation cost charged to us for employees directly supporting our operations by ONEOK for 2013 totaled $9.7 million , respectively, which is net of $6.1 million of tax benefits. Restricted Stock Unit Awards - We have granted restricted stock unit awards to key employees that vest over a service period of generally three years and entitle the grantee to receive shares of our common stock. The awards granted that replaced awards granted by ONEOK in 2012 vested, and 2013 will vest, consistent with their original vesting dates in 2015 and 2016, respectively. Restricted stock unit awards granted in 2015 and 2014 and that replaced awards granted by ONEOK in 2013 accrue dividend equivalents in the form of additional restricted stock units prior to vesting. Restricted stock unit awards are measured at fair value as if they were vested and issued on the grant date, reduced by expected dividend payments for awards that do not accrue dividends and adjusted for estimated forfeitures. Compensation expense is recognized on a straight-line basis over the vesting period of the award. A forfeiture rate of 3 percent per year based on historical forfeitures under our share-based payment plans is used. Performance Stock Unit Awards - We have granted performance stock unit awards to key employees. The shares of common stock underlying the performance stock units vest at the expiration of a service period of generally three years if certain performance criteria are met by us as determined by the Executive Compensation Committee of the Board of Directors. The awards granted that replaced awards granted by ONEOK in 2012 vested, and 2013 will vest, consistent with their original vesting dates in 2015 and 2016, respectively, if certain performance criteria are met by us for the at-risk portion of the awards as described above. Upon vesting, a holder of performance stock units is entitled to receive a number of shares of common stock equal to a percentage (0 percent to 200 percent) of the performance stock units granted, based on our total shareholder return over the vesting period, compared with the total shareholder return of a peer group of other utilities over the same period. If paid, the outstanding performance stock unit awards entitle the grantee to receive shares of our common stock. The outstanding performance stock unit awards are equity awards with a market-based condition, which results in the compensation expense for these awards being recognized on a straight-line basis over the requisite service period, provided that the requisite service period is fulfilled, regardless of when, if ever, the market condition is satisfied. The new performance stock unit awards granted in 2015 and 2014 and the grants that replaced awards granted by ONEOK in 2013 accrue dividend equivalents in the form of additional performance stock units prior to vesting. The fair value of these performance stock units was estimated on the grant date based on a Monte Carlo model. The compensation expense on these awards will only be adjusted for changes in forfeitures. A forfeiture rate of 3 percent per year based on historical forfeitures under our and, prior to the separation, ONEOK’s share-based payment plans was used. Restricted Stock Unit Award Activity As of December 31, 2015 , there was $3.2 million of total unrecognized compensation costs related to the nonvested restricted stock unit awards, which is expected to be recognized over a weighted-average period of 1.8 years. The following tables set forth activity and various statistics for restricted stock unit awards outstanding under the respective plans for the period indicated: Number of Shares Weighted- Average Price Nonvested December 31, 2014 325,730 $ 23.47 Granted 75,880 $ 41.40 Vested (162,280 ) $ 18.32 Forfeited (8,072 ) $ 34.42 Nonvested December 31, 2015 231,258 $ 32.59 2015 2014 2013 Weighted-average grant date fair value (per share) $ 41.40 $ 33.19 $ 47.36 Fair value of shares granted (thousands of dollars) $ 3,141 $ 3,149 $ 1,323 Performance Stock Unit Award Activity As of December 31, 2015 , there was $4.7 million of total unrecognized compensation cost related to the nonvested performance stock unit awards, which is expected to be recognized over a weighted-average period of 1.7 years. The following tables set forth activity and various statistics related to our performance stock unit awards and the assumptions used by us, and ONEOK prior to 2014, in the valuations of the 2015, 2014 and 2013 grants at the grant date: Number of Units Weighted- Average Price Nonvested December 31, 2014 847,951 $ 17.62 Granted 100,860 $ 44.48 Vested (502,474 ) $ 14.33 Forfeited (7,087 ) $ 30.22 Nonvested December 31, 2015 439,250 $ 27.35 2015 2014 2013 Volatility 15.90% (a) 18.40% (a) 22.27% (b) Dividend yield 2.90% 3.37% 3.04% Risk-free interest rate 1.10% 0.67% 0.42% (a) - Volatility based on historical volatility over three years using daily stock price observations of our peer utilities. (b) - Volatility based on historical volatility over three years using daily ONEOK stock price observations. 2015 2014 2013 Weighted-average grant date fair value (per share) $ 44.48 $ 35.98 $ 52.30 Fair value of shares granted (thousands of dollars) $ 4,486 $ 4,462 $ 2,926 Employee Stock Purchase Plan We have reserved a total of 0.7 million shares of common stock for issuance under our Employee Stock Purchase Plan (the ESPP). Subject to certain exclusions, all employees who work at least 20 hours per week are eligible to participate in the ESPP. Employees can choose to have up to 10 percent of their annual base pay withheld to purchase our common stock, subject to terms and limitations of the plan. The purchase price of the stock is 85 percent of the lower of the average market price of our common stock on the grant date or exercise date. Approximately 40 percent and 36 percent of employees participated in the plan in 2015 and 2014, respectively, and purchased 51,092 shares at $36.15 in 2015 and 51,418 shares at $32.29 in 2014. Compensation expense, before taxes, was $1.3 million and $0.4 million in 2015 and 2014, respectively. All eligible employees of ONEOK were eligible to participate in a similar ESPP plan, but enrollment of our employees in that plan was terminated upon the separation. Compensation expense, before tax, charged to us by ONEOK for employees who directly supported our operations was $2.7 million for 2013. Employee Stock Award Program Under the program, each time the per-share closing price of our common stock on the NYSE closed for the first time at or above each $1.00 increment above its previous historical high closing price, we issued, for no monetary consideration, one share of our common stock to all eligible employees. The total number of shares of our common stock authorized for issuance under this program is 125,000 . Shares issued to employees under this program during 2015 and 2014 totaled 23,506 and 35,324 , and compensation expense, before taxes, related to the Employee Stock Award Program was $1.1 million and $2.5 million for 2015 and 2014, respectively. Compensation expense, before taxes, charged to us by ONEOK related to a similar program to ours that was administered by ONEOK for employees who directly supported our operations was $4.2 million for 2013.

EMPLOYEE BENEFIT PLANS (Notes)

EMPLOYEE BENEFIT PLANS (Notes)	12 Months Ended
	Dec. 31, 2015
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Pension and Other Postemployment Benefits Disclosure [Text Block]	12. EMPLOYEE BENEFIT PLANS Retirement and Other Postemployment Benefit Plans Prior to separation, certain employees participated in the Plans sponsored by ONEOK. We accounted for the Plans as multiemployer benefit plans. These defined benefit pension and other postemployment benefit costs included amounts associated with vested participants who are no longer employees. As described in Note 2, prior to 2014, ONEOK also charged us for the allocated cost of certain employees of ONEOK who provided general and administrative services on our behalf. ONEOK included an allocation of the benefit costs associated with these ONEOK employees based upon its allocation methodology, not necessarily specific to the employees providing general and administrative services on our behalf. Retirement Plans - We have a defined benefit pension plan covering nonbargaining-unit employees hired before January 1, 2005, and certain bargaining-unit employees hired before December 15, 2011. Nonbargaining unit employees hired after December 31, 2004; employees represented by Local No. 304 of the International Brotherhood of Electrical Workers (IBEW) hired on or after July 1, 2010; employees represented by the United Steelworkers hired on or after December 15, 2011; and employees who accepted a one-time opportunity to opt out of the defined benefit pension plan are covered by a profit-sharing plan. Certain employees of the Texas Gas Services division were entitled to benefits under a frozen cash-balance pension plan. In addition, we have a supplemental executive retirement plan for the benefit of certain officers. No new participants in the supplemental executive retirement plan have been approved since 2005, and it was formally closed to new participants as of January 1, 2014. We fund our defined benefit pension costs at a level needed to maintain or exceed the minimum funding levels required by the Employee Retirement Income Security Act of 1974, as amended, and the Pension Protection Act of 2006. Pension expense was $38.0 million and $27.1 million in 2015 and 2014, respectively, prior to regulatory deferrals. Pension expense charged to us by ONEOK for employees directly supporting our operations totaled $35.0 million for 2013, prior to regulatory deferrals. Other Postemployment Benefit Plans - We sponsor health and welfare plans that provide postemployment medical and life insurance benefits to certain employees who retire with at least five years of service. The postemployment medical plan is contributory based on hire date, age and years of service, with retiree contributions adjusted periodically, and contains other cost-sharing features such as deductibles and coinsurance. Other postemployment benefit expense was $5.0 million and $5.9 million in 2015 and 2014, respectively, prior to regulatory deferrals. Other postemployment benefit expense charged to us by ONEOK for employees directly supporting our operations totaled $12.3 million for 2013, prior to regulatory deferrals. Plan Amendments - In October 2015, plan amendments were approved to merge our frozen cash-balance defined benefit pension plan covering certain Texas Gas Service employees with our defined benefit pension plan covering certain eligible employees. In addition, we announced to eligible pre-65 participants in our postemployment medical plans a change from a self-insured postemployment medical plan to a plan providing participants an annual benefit that will allow them to select coverage on a healthcare exchange. As a result, we remeasured the respective plan assets and benefit obligations, effective October 1, 2015, which resulted in a reduction in benefit obligations of our postemployment benefit plan of $11.9 million . Net periodic benefit cost for the plans in 2015 was reduced by $3.4 million . Actuarial Assumptions - The following table sets forth the weighted-average assumptions used to determine benefit obligations for pension and postemployment benefits for the periods indicated: December 31, 2015 2014 Discount rate 4.75% 4.25% Compensation increase rate 3.35% - 3.40% 3.30% - 3.50% The following table sets forth the weighted-average assumptions used by us, and ONEOK prior to 2014, to determine the periodic benefit costs for the periods indicated: Nine Months Ended September 30, Three Months Ended December 31, Years Ended December 31, 2015 2015 2014 2013 Discount rate - pension plans 4.25% 4.75% 5.25% 4.25% Discount rate - other postemployment plans 4.25% 4.75% 5.00% 4.00% Expected long-term return on plan assets 7.75% 7.75% 7.75% 8.25% Compensation increase rate 3.30% - 3.50% 3.30% - 3.50% 3.35% - 3.50% 3.45% - 3.50% We determine our overall expected long-term rate of return on plan assets, based on our review of historical returns and economic growth models. At December 31, 2014, we updated our assumed mortality rates to incorporate the new set of mortality tables issued by the Society of Actuaries in October 2014. We determine our discount rates annually. We estimate our discount rate based upon a comparison of the expected cash flows associated with our future payments under our defined benefit pension and other postemployment obligations to a hypothetical bond portfolio created using high-quality bonds that closely match expected cash flows. Bond portfolios are developed by selecting a bond for each of the next 60 years based on the maturity dates of the bonds. Bonds selected to be included in the portfolios are only those rated by Moody’s as AA- or better and exclude callable bonds, bonds with less than a minimum issue size, yield outliers and other filtering criteria to remove unsuitable bonds. Regulatory Treatment - The OCC, KCC and regulatory authorities in Texas have approved the recovery of pension costs and other postemployment benefits costs through rates for Oklahoma Natural Gas, Kansas Gas Service and Texas Gas Service, respectively. The costs recovered through rates are based on current funding requirements and the net periodic benefit cost for defined benefit pension and other postemployment costs. Differences, if any, between the expense and the amount recovered through rates would be reflected in earnings, net of authorized deferrals. We historically have recovered defined benefit pension and other postemployment benefit costs through rates. We believe it is probable that regulators will continue to include the net periodic pension and other postemployment benefit costs in our cost of service. Obligations and Funded Status - In connection with the separation from ONEOK, we entered into an Employee Matters Agreement with ONEOK, which provides that our employees no longer participate in benefit plans sponsored or maintained by ONEOK as of the separation date. Effective January 1, 2014, the ONEOK defined benefit pension plans and other postemployment benefit plans transferred assets and obligations related to those employees transferring to ONE Gas and vested participants who are no longer employees to the new ONE Gas plans. As a result, we recorded sponsored pension and other postemployment plan obligations of approximately $1.1 billion , and sponsored defined benefit pension and other postemployment plan assets of approximately $1.0 billion , which are reflected below as our balances at the beginning of the period. Additionally, as a result of the transfer of unrecognized losses from ONEOK, our regulatory assets and deferred income taxes increased $331 million and $86 million , respectively. The following table sets forth our defined benefit pension and other postemployment benefit plans, benefit obligations and fair value of plan assets for the periods indicated: Pension Benefits Other Postemployment Benefits December 31, December 31, 2015 2014 2015 2014 Changes in Benefit Obligation (Thousands of dollars) Benefit obligation, beginning of period $ 1,028,171 $ 863,620 $ 257,688 $ 239,171 Service cost 13,660 11,620 3,257 3,468 Interest cost 43,542 43,791 10,628 11,605 Plan participants’ contributions — — 2,915 2,642 Actuarial loss (gain) (47,607 ) 159,275 (19,702 ) 14,998 Benefits paid (52,142 ) (50,135 ) (14,632 ) (14,196 ) Plan amendment — — (11,901 ) — Benefit obligation, end of period 985,624 1,028,171 228,253 257,688 Change in Plan Assets Fair value of plan assets, beginning of period 845,396 840,699 151,777 147,237 Actual return on plan assets (9,026 ) 53,907 1,335 6,912 Employer contributions 933 925 14,100 9,182 Plan participants’ contributions — — 2,915 2,642 Benefits paid (52,142 ) (50,135 ) (14,632 ) (14,196 ) Fair value of assets, end of period 785,161 845,396 155,495 151,777 Balance at December 31 $ (200,463 ) $ (182,775 ) $ (72,758 ) $ (105,911 ) Current liabilities $ (912 ) $ (907 ) $ — $ — Noncurrent liabilities (199,551 ) (181,868 ) (72,758 ) (105,911 ) Balance at December 31 $ (200,463 ) $ (182,775 ) $ (72,758 ) $ (105,911 ) The accumulated benefit obligation for our defined benefit pension plans was $934.3 million and $970.7 million at December 31, 2015 and 2014, respectively. There are no plan assets expected to be withdrawn and returned to us in 2016. Components of Net Periodic Benefit Cost - The following table sets forth the components of net periodic benefit cost for our defined benefit pension and other postemployment benefit plans for the period indicated: Pension Benefits Year Ended December 31, 2015 2014 (Thousands of dollars) Components of net periodic benefit cost Service cost $ 13,660 $ 11,620 Interest cost 43,542 43,791 Expected return on assets (61,769 ) (59,862 ) Amortization of unrecognized prior service cost 266 549 Amortization of net loss 42,226 30,200 Settlements 27 773 Net periodic benefit cost $ 37,952 $ 27,071 Other Postemployment Benefits Year Ended December 31, 2015 2014 (Thousands of dollars) Components of net periodic benefit cost Service cost $ 3,257 $ 3,468 Interest cost 10,628 11,605 Expected return on assets (11,892 ) (11,393 ) Amortization of unrecognized prior service cost (2,228 ) (1,760 ) Amortization of net loss 5,268 3,969 Net periodic benefit cost $ 5,033 $ 5,889 Other Comprehensive Income (Loss) - The following table sets forth the amounts recognized in other comprehensive income (loss) related to our defined benefit pension benefits for the period indicated: Pension Benefits Year Ended December 31, 2015 2014 (Thousands of dollars) Net gain (loss) arising during the period $ 339 $ (3,543 ) Amortization of loss 917 518 Deferred income taxes (483 ) 1,244 Total recognized in other comprehensive income (loss) $ 773 $ (1,781 ) There were no amounts recognized in other comprehensive income (loss) related to our other postemployment benefits for the periods presented. The tables below sets forth the amounts in accumulated other comprehensive income (loss) that had not yet been recognized as components of net periodic benefit expense for the periods indicated: Pension Benefits December 31, 2015 2014 (Thousands of dollars) Prior service credit (cost) $ — $ (266 ) Accumulated loss (407,798 ) (426,862 ) Accumulated other comprehensive loss before regulatory assets (407,798 ) (427,128 ) Regulatory asset for regulated entities 400,625 418,699 Accumulated other comprehensive loss after regulatory assets (7,173 ) (8,429 ) Deferred income taxes 2,772 3,255 Accumulated other comprehensive loss, net of tax $ (4,401 ) $ (5,174 ) Other Postemployment Benefits December 31, 2015 2014 (Thousands of dollars) Prior service credit (cost) $ 14,010 $ 4,337 Accumulated loss (50,447 ) (64,861 ) Accumulated other comprehensive loss before regulatory assets (36,437 ) (60,524 ) Regulatory asset for regulated entities 36,437 60,524 Accumulated other comprehensive loss after regulatory assets — — Deferred income taxes — — Accumulated other comprehensive loss, net of tax $ — $ — The following tables set forth the amounts recognized in either accumulated comprehensive income (loss) or regulatory assets expected to be recognized as components of net periodic benefit expense in the next fiscal year: Pension Benefits Other Postemployment Benefits Amounts to be recognized in 2016 (Thousands of dollars) Prior service credit (cost) $ — $ (3,633 ) Actuarial net loss $ 35,542 $ 4,608 Health Care Cost Trend Rates - The following table sets forth the assumed health care cost-trend rates for the periods indicated: 2015 2014 Health care cost-trend rate assumed for next year 4.00% - 7.50% 4.00% - 7.75% Rate to which the cost-trend rate is assumed to decline (the ultimate trend rate) 4.00% - 5.00% 4.00% - 5.00% Year that the rate reaches the ultimate trend rate 2022 2022 Assumed health care cost-trend rates have a significant effect on the amounts reported for our health care plans. A one percentage point change in assumed health care cost-trend rates would have the following effects: One Percentage One Percentage Point Increase Point Decrease (Thousands of dollars) Effect on total of service and interest cost $ 263 $ (266 ) Effect on other postemployment benefit obligation $ 3,655 $ (3,752 ) Plan Assets - Our investment strategy is to invest plan assets in accordance with sound investment practices that emphasize long-term fundamentals. The goal of this strategy is to maximize investment returns while managing risk in order to meet the plan’s current and projected financial obligations. To achieve this strategy, we have established a liability-driven investment strategy to change the allocations as the plan reaches certain funded status. The plan’s investments include a diverse blend of various domestic and international equities, investment-grade debt securities which mirror the cash flows of our liability, insurance contracts and alternative investments. The current target allocation for the assets of our defined benefit pension plan is as follows: U.S. large-cap equities 37.4 % Investment-grade bonds 30.0 % Developed foreign large-cap equities 10.6 % Alternative investments 7.7 % Mid-cap equities 5.6 % Emerging markets equities 5.0 % Small-cap equities 3.7 % Total 100 % As part of our risk management for the plans, minimums and maximums have been set for each of the asset classes listed above. All investment managers for the plan are subject to certain restrictions on the securities they purchase and, with the exception of indexing purposes, are prohibited from owning our stock. The following tables set forth our pension benefits and other postemployment benefits plan assets by fair value category as of the measurement date: Pension Benefits December 31, 2015 Asset Category Level 1 Level 2 Level 3 Total (Thousands of dollars) Investments: Equity securities (a) $ 405,935 $ 62,150 $ — $ 468,085 Government obligations — 44,651 — 44,651 Corporate obligations (b) — 139,396 — 139,396 Cash and money market funds (c) 5,429 10,279 — 15,708 Insurance contracts and group annuity contracts — — 56,465 56,465 Other investments (d) 2,884 — 57,972 60,856 Total assets $ 414,248 $ 256,476 $ 114,437 $ 785,161 (a) - This category represents securities of the various market sectors from diverse industries. (b) - This category represents bonds from diverse industries. (c) - This category is primarily money market funds. (d) - This category represents alternative investments such as hedge funds and other financial instruments. Pension Benefits December 31, 2014 Asset Category Level 1 Level 2 Level 3 Total (Thousands of dollars) Investments: Equity securities (a) $ 439,165 $ 66,766 $ — $ 505,931 Government obligations — 47,769 — 47,769 Corporate obligations (b) — 153,412 — 153,412 Cash and money market funds (c) 4,152 16,341 — 20,493 Insurance contracts and group annuity contracts — — 59,877 59,877 Other investments (d) — — 57,914 57,914 Total assets $ 443,317 $ 284,288 $ 117,791 $ 845,396 (a) - This category represents securities of the various market sectors from diverse industries. (b) - This category represents bonds from diverse industries. (c) - This category is primarily money market funds. (d) - This category represents alternative investments such as hedge funds. Other Postemployment Benefits December 31, 2015 Asset Category Level 1 Level 2 Level 3 Total (Thousands of dollars) Investments: Equity securities (a) $ 54,560 $ 7,498 $ — $ 62,058 Government obligations — 64 — 64 Corporate obligations (b) — 200 — 200 Cash and money market funds (c) 233 13,322 — 13,555 Insurance contracts and group annuity contracts — 79,531 — 79,531 Other investments (d) 4 — 83 87 Total assets $ 54,797 $ 100,615 $ 83 $ 155,495 (a) - This category represents securities of the various market sectors from diverse industries. (b) - This category represents bonds from diverse industries. (c) - This category is primarily money market funds. (d) - This category represents alternative investments such as hedge funds. Other Postemployment Benefits December 31, 2014 Asset Category Level 1 Level 2 Level 3 Total (Thousands of dollars) Investments: Equity securities (a) $ 49,553 $ 12,589 $ — $ 62,142 Government obligations — 78 — 78 Corporate obligations (b) — 251 — 251 Cash and money market funds (c) 964 5,894 — 6,858 Insurance contracts and group annuity contracts — 82,353 — 82,353 Other investments (d) — — 95 95 Total assets $ 50,517 $ 101,165 $ 95 $ 151,777 (a) - This category represents securities of the various market sectors from diverse industries. (b) - This category represents bonds from diverse industries. (c) - This category is primarily money market funds. (d) - This category represents alternative investments such as hedge funds. The following table sets forth the reconciliation of Level 3 fair value measurements of our pension plans for the periods indicated: Pension Benefits Insurance Contracts Other Investments Total (Thousands of dollars) January 1, 2014 $ 63,454 $ 73,590 $ 137,044 Net realized and unrealized gains (losses) 3,446 (15,676 ) (12,230 ) Settlements (7,023 ) — (7,023 ) December 31, 2014 $ 59,877 $ 57,914 $ 117,791 Net realized and unrealized gains 2,188 58 2,246 Settlements (5,600 ) — (5,600 ) December 31, 2015 $ 56,465 $ 57,972 $ 114,437 Contributions - During 2015, we contributed $0.9 million to our defined benefit pension plans and we contributed $14.1 million to our other postemployment benefit plans. In 2016, we expect to contribute $0.9 million to our defined benefit pension plans and expect to contribute $5.8 million to our other postemployment benefit plans. Pension and Other Postemployment Benefit Payments - Benefit payments for our defined benefit pension and other postemployment benefit plans for the period ended December 31, 2015 were $52.1 million and $14.6 million , respectively. The following table sets forth the pension benefits and other postemployment benefits payments expected to be paid in 2016-2025: Pension Benefits Other Postemployment Benefits to be paid in: (Thousands of dollars) 2016 $ 53,359 $ 14,116 2017 $ 54,710 $ 13,875 2018 $ 56,201 $ 14,435 2019 $ 57,238 $ 14,956 2020 $ 58,901 $ 15,406 2021 through 2025 $ 311,194 $ 81,175 The expected benefits to be paid are based on the same assumptions used to measure our benefit obligation at December 31, 2015, and include estimated future employee service. Other Employee Benefit Plans 401(k) Plan - We have a 401(k) Plan which covers all full-time employees, and employee contributions are discretionary. We match 100 percent of each participant’s eligible contribution up to 6 percent of each participant’s eligible compensation, subject to certain limits. Our contributions made to the plan were $10.2 million and $9.7 million 2015 and 2014, respectively. Prior to our separation, ONEOK maintained a similar 401(k) Plan and compensation expense charged to us for employees who directly supported our operations by ONEOK totaled $8.3 million in 2013 for ONEOK’s matching contributions to this plan. Profit-Sharing Plan - We have a profit-sharing plan for all employees that do not participate in our defined benefit pension plan. We plan to make a contribution to the profit-sharing plan each quarter equal to 1 percent of each participant’s eligible compensation during the quarter. Additional discretionary employer contributions may be made at the end of each year. Employee contributions are not allowed under the plan. Our contributions made to the plan were $6.5 million and $4.0 million in 2015 and 2014, respectively. ONEOK maintained a similar Profit-Sharing Plan and compensation expense associated with ONEOK’s contributions made to the plan for employees who directly supported our operations prior to the separation were $1.6 million in 2013. Employee Deferred Compensation Plan - Our Nonqualified Deferred Compensation Plan provides select employees with the option to defer portions of their compensation and provides nonqualified deferred compensation benefits that are not available due to limitations on employer and employee contributions to qualified defined contribution plans under the federal tax laws. Contributions made to the plan were not material in 2015 and 2014. ONEOK maintained a similar plan and contributions made to the plan for employees who directly supported our operations prior to the separation were not material in 2013.

INCOME TAXES (Notes)

INCOME TAXES (Notes)	12 Months Ended
	Dec. 31, 2015
Income tax [Line Items]
INCOME TAXES	13. INCOME TAXES The following table sets forth our provision for income taxes for the periods indicated: Years Ended December 31, 2015 2014 2013 ( Thousands of dollars ) Current income tax provision Federal $ 7,135 $ 17,006 $ — State 2,055 1,397 67 Total current income tax provision 9,190 18,403 67 Deferred income tax provision Federal 56,440 42,024 53,562 State 7,349 7,911 8,643 Total deferred income tax provision 63,789 49,935 62,205 Total provision for income taxes $ 72,979 $ 68,338 $ 62,272 The following table is a reconciliation of our income tax provision for the periods indicated: Years Ended December 31, 2015 2014 2013 ( Thousands of dollars ) Income before income taxes $ 192,009 $ 178,128 $ 161,467 Federal statutory income tax rate 35 % 35 % 35 % Provision for federal income taxes 67,203 62,345 56,513 State income taxes, net of federal tax benefit 6,114 6,051 5,661 Other, net (338 ) (58 ) 98 Total provision for income taxes $ 72,979 $ 68,338 $ 62,272 Prior to our separation from ONEOK, our operations were included in the consolidated federal and state income tax returns of ONEOK. Our income tax provision was calculated on a separate return basis. Accordingly, we recognized deferred tax assets and liabilities for the difference between the financial statement and income tax basis of assets and liabilities and carry-forward items, based on income tax laws and rates existing at the time the temporary differences are expected to reverse as if we had been a corporation for federal and state income tax purposes. In addition, ONEOK managed its tax position based upon the tax attributes of the consolidated group. Certain attributes may not be available to use if we had been operating as an independent company. The following table sets forth the tax effects of temporary differences that gave rise to significant portions of the deferred tax assets and liabilities for the periods indicated: December 31, 2015 2014 ( Thousands of dollars ) Deferred tax assets Employee benefits and other accrued liabilities $ 110,148 $ 128,715 Net operating loss — 8,144 Other 7,848 5,655 Total deferred tax assets 117,996 142,514 Deferred tax liabilities Excess of tax over book depreciation 897,667 820,853 Purchased-gas cost adjustment 3,999 16,177 Other regulatory assets and liabilities, net 168,115 193,159 Total deferred tax liabilities 1,069,781 1,030,189 Net deferred tax liabilities $ 951,785 $ 887,675 At December 31, 2015 and 2014, we had income taxes receivable of $38.9 million and $43.8 million , respectively. Prior to our separation from ONEOK, we were included in the ONEOK income tax returns for all applicable years. We file income tax returns in the United States federal jurisdiction as well as in the states where we have operations. In 2015, we filed our initial United States consolidated federal tax return for the period February 1, 2014 through December 31, 2014. We have adopted ASU 2015-17, “Balance Sheet Classification of Deferred Taxes,” early to simplify our financial reporting process and have applied it prospectively for the period beginning October 1, 2015. Prior periods were not retrospectively adjusted.

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Notes)	12 Months Ended
	Dec. 31, 2015
Commitments and Contingencies [Line Items]
COMMITMENTS AND CONTINGENCIES	14. COMMITMENTS AND CONTINGENCIES Commitments - Operating leases represent future minimum lease payments under noncancelable leases covering office space, facilities and information technology hardware and software. Rental expense was $5.0 million in each of 2015 and 2014 and $4.8 million in 2013. The following table sets forth our operating lease payments for the periods indicated: Operating Leases ( Millions of dollars ) 2016 $ 4.6 2017 4.5 2018 4.2 2019 3.5 2020 3.3 Thereafter 7.0 Total $ 27.1 Environmental Matters - We are subject to multiple historical, wildlife preservation and environmental laws and/or regulations, which affect many aspects of our present and future operations. Regulated activities include, but are not limited to, those involving air emissions, storm water and wastewater discharges, handling and disposal of solid and hazardous wastes, wetland preservation, hazardous materials transportation, and pipeline and facility construction. These laws and regulations require us to obtain and/or comply with a wide variety of environmental clearances, registrations, licenses, permits and other approvals. Failure to comply with these laws, regulations, licenses and permits may expose us to fines, penalties and/or interruptions in our operations that could be material to our results of operations. In addition, emission controls and/or other regulatory or permitting mandates under the Clean Air Act and other similar federal and state laws could require unexpected capital expenditures. We cannot assure that existing environmental statutes and regulations will not be revised or that new regulations will not be adopted or become applicable to us. Revised or additional statutes or regulations that result in increased compliance costs or additional operating restrictions could have a material adverse effect on our business, financial condition, results of operations and cash flows. We own or retain legal responsibility for the environmental conditions at 12 former manufactured natural gas sites in Kansas. These sites contain potentially harmful materials that are subject to control or remediation under various environmental laws and regulations. A consent agreement with the KDHE governs all work at these sites. The terms of the consent agreement allow us to investigate these sites and set remediation activities based upon the results of the investigations and risk analysis. Remediation involves typically the management of contaminated soils and may involve removal of structures and monitoring and/or remediation of groundwater. We have completed or addressed removal of the source of soil contamination at 11 of the 12 sites according to plans approved by KDHE. Regulatory closure has been achieved at three of the sites. We have begun site assessment at the remaining site where no active remediation has occurred. Our expenditures for environmental evaluation, mitigation, remediation and compliance to date have not been significant in relation to our financial position, results of operations or cash flows, and our expenditures related to environmental matters had no material effects on earnings or cash flows during 2015, 2014 and 2013 . A number of environmental issues may exist with respect to manufactured gas plants. With the trend toward stricter standards, greater regulation and more extensive permit requirements for the types of assets operated by us that are subject to environmental regulation, our environmental expenditures could increase in the future, and such expenditures may not be fully covered by insurance or recoverable in rates from our customers, and those costs may adversely affect our financial condition, results of operations and cash flows. Pipeline Safety - We are subject to PHMSA regulations, including integrity-management regulations. PHMSA regulations require pipeline companies operating high-pressure transmission pipelines to perform integrity assessments on pipeline segments that pass through densely populated areas or near specifically designated high-consequence areas. In January 2012, the Pipeline Safety, Regulatory Certainty and Job Creation Act was signed into law. The law increased maximum penalties for violating federal pipeline safety regulations and directs the DOT and Secretary of Transportation to conduct further review or studies on issues that may or may not be material to us. These issues include but are not limited to the following: • an evaluation of whether natural gas pipeline integrity-management requirements should be expanded beyond current high-consequence areas; • a verification of records for pipelines in class 3 and 4 locations and high-consequence areas to confirm maximum allowable operating pressures; and • a requirement to test previously untested pipelines operating above 30 percent yield strength in high-consequence areas. The potential capital and operating expenditures related to this legislation, the associated regulations or other new pipeline safety regulations are unknown. Legal Proceedings - We are a party to various litigation matters and claims that have arisen in the normal course of our operations. While the results of litigation and claims cannot be predicted with certainty, we believe the reasonably possible losses from such matters, individually and in the aggregate, are not material. Additionally, we believe the probable final outcome of such matters will not have a material adverse effect on our results of operations, financial position or cash flows.

QUARTERLY FINANCIAL DATA (UNAUD

QUARTERLY FINANCIAL DATA (UNAUDITED) (Notes)	12 Months Ended
	Dec. 31, 2015
Schedule of Quarterly Financial Information [Line Items]
QUARTERLY FINANCIAL DATA (UNAUDITED)	15. QUARTERLY FINANCIAL DATA (UNAUDITED) First Quarter Second Quarter Third Quarter Fourth Quarter Year Ended December 31, 2015 ( Thousands of dollars ) Revenues $ 676,531 $ 256,786 $ 225,226 $ 389,149 Net margin $ 262,978 $ 176,837 $ 170,502 $ 231,416 Operating income $ 109,005 $ 31,270 $ 24,951 $ 73,903 Net income $ 60,381 $ 12,076 $ 7,371 $ 39,202 Earnings per share Basic $ 1.15 $ 0.23 $ 0.14 $ 0.75 Diluted $ 1.13 $ 0.23 $ 0.14 $ 0.74 First Quarter Second Quarter Third Quarter Fourth Quarter Year Ended December 31, 2014 ( Thousands of dollars ) Revenues $ 766,178 $ 296,838 $ 241,522 $ 514,368 Net margin $ 259,836 $ 176,493 $ 166,452 $ 224,176 Operating income $ 109,353 $ 26,812 $ 19,119 $ 70,010 Net income $ 59,076 $ 9,454 $ 4,653 $ 36,607 Earnings per share Basic $ 1.13 $ 0.18 $ 0.09 $ 0.70 Diluted $ 1.13 $ 0.18 $ 0.09 $ 0.69

SUMMARY OF SIGNIFICANT ACCOUN24

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2015
Significant Accounting Policies [Line Items]
Basis of Accounting	Basis of Presentation - Prior to our separation from ONEOK, our financial statements were derived from ONEOK’s financial statements, which included its natural gas distribution business as if we, for accounting purposes, had been a separate company for all periods presented. The assets and liabilities in the financial statements have been reflected on a historical basis. The financial statements for periods prior to the separation also include expense allocations for certain corporate functions historically performed by ONEOK, including allocations of general corporate expenses related to executive oversight, accounting, treasury, tax, legal, information technology and other services. We believe our assumptions underlying the financial statements, including the assumptions regarding the allocation of general corporate expenses from ONEOK, are reasonable. However, the financial statements may not include all of the actual expenses that would have been incurred by us and may not reflect our results of operations, financial position and cash flows had we been a separate publicly traded company during the periods presented prior to the separation. Because the operations of the natural gas distribution business within ONEOK were conducted through separate divisions, ONEOK’s net investment in us, excluding the long-term line of credit with ONEOK, is shown as owner’s net investment in lieu of equity in the financial statements prior to the separation. Transactions between ONEOK and us that were not part of the long-term line of credit with ONEOK or the short-term note payable to ONEOK have been identified in the Statements of Equity as a net transfer from ONEOK. All financial information presented after the separation represents the results of operations, financial position and cash flows of ONE Gas. Accordingly: • Our Statements of Income and Comprehensive Income for the year ended December 31, 2014 , consist of the results of ONE Gas for the eleven months ended December 31, 2014 , and the results of ONE Gas Predecessor for the one month ended January 31, 2014. Our Statements of Income and Comprehensive Income for the year ended December 31, 2013 , consist entirely of the results of ONE Gas Predecessor. Our net income for the period prior to January 31, 2014, was recorded to owner’s net investment. • Our Statement of Cash Flows for the year ended December 31, 2014 , consists of the results of ONE Gas for the eleven months ended December 31, 2014 , and the results of ONE Gas Predecessor for the one month ended January 31, 2014. Our Statement of Cash Flows for the year ended December 31, 2013 , consists entirely of the results of ONE Gas Predecessor. • Our Statement of Equity for the year ended December 31, 2014 , consists of both the activity for ONE Gas Predecessor prior to January 31, 2014, and the activity for ONE Gas completed in connection with, and subsequent to, the separation on January 31, 2014. Our Statement of Equity for the year ended December 31, 2013 , consists entirely of the results of ONE Gas Predecessor. The financial statements include the accounts of the natural gas distribution business as set forth in “Organization and Nature of Operations” above. All significant balances and transactions between our divisions have been eliminated.
Use of Estimates	Use of Estimates - The preparation of our financial statements and related disclosures in accordance with GAAP requires us to make estimates and assumptions with respect to values or conditions that cannot be known with certainty that affect the reported amount of assets and liabilities, and the disclosure of contingent assets and liabilities at the date of the financial statements. These estimates and assumptions also affect the reported amounts of revenue and expenses during the reporting period. Items that may be estimated include, but are not limited to, the economic useful life of assets, fair value of assets and liabilities, provisions for doubtful accounts receivable, unbilled revenues for natural gas delivered but for which meters have not been read, natural gas purchased but for which no invoice has been received, provision for income taxes, including any deferred tax valuation allowances, the results of litigation and various other recorded or disclosed amounts. We evaluate these estimates on an ongoing basis using historical experience and other methods we consider reasonable based on the particular circumstances. Nevertheless, actual results may differ significantly from the estimates. Any effects on our financial position or results of operations from revisions to these estimates are recorded in the period when the facts that give rise to the revision become known.
Fair Value Measurement	Fair Value Measurements - We define fair value as the price that would be received from the sale of an asset or the transfer of a liability in an orderly transaction between market participants at the measurement date. We use the market and income approaches to determine the fair value of our assets and liabilities and consider the markets in which the transactions are executed. We measure the fair value of a group of financial assets and liabilities consistent with how a market participant would price the net risk exposure at the measurement date. Fair Value Hierarchy - At each balance sheet date, we utilize a fair value hierarchy to classify fair value amounts recognized or disclosed in our financial statements based on the observability of inputs used to estimate such fair value. The levels of the hierarchy are described below: • Level 1 - Unadjusted quoted prices in active markets for identical assets or liabilities; • Level 2 - Significant observable pricing inputs other than quoted prices included within Level 1 that are, either directly or indirectly, observable as of the reporting date. Essentially, this represents inputs that are derived principally from or corroborated by observable market data; and • Level 3 - May include one or more unobservable inputs that are significant in establishing a fair value estimate. These unobservable inputs are developed based on the best information available and may include our own internal data. We recognize transfers into and out of the levels as of the end of each reporting period. Determining the appropriate classification of our fair value measurements within the fair value hierarchy requires management’s judgment regarding the degree to which market data is observable or corroborated by observable market data. We categorize derivatives for which fair value is determined using multiple inputs within a single level, based on the lowest level input that is significant to the fair value measurement in its entirety. See Note 8 for additional information regarding our fair value measurements.
Cash and Cash Equivalents	Cash and Cash Equivalents - Cash equivalents consist of highly liquid investments, which are readily convertible into cash and have original maturities of three months or less.
Revenue Recognition	Revenue Recognition - For regulated deliveries of natural gas, we read meters and bill customers on a monthly cycle. We recognize revenues upon the delivery of the natural gas commodity or services rendered to customers. The billing cycles for customers do not necessarily coincide with the accounting periods used for financial reporting purposes. Revenues are accrued for natural gas delivered and services rendered to customers, but not yet billed. Accrued unbilled revenue is based on a percentage estimate of amounts unbilled each month, which is dependent upon a number of factors, some of which require management’s judgment. These factors include customer consumption patterns and the impact of weather on usage. The amounts of accrued unbilled natural gas sales revenues at December 31, 2015 and 2014 , were $109.6 million and $141.7 million , respectively.
Accounts Receivable	Accounts Receivable - Accounts receivable represent valid claims against nonaffiliated customers for natural gas sold or services rendered, net of allowances for doubtful accounts. We assess the creditworthiness of our customers. Those customers who do not meet minimum standards are required to provide security, including deposits and other forms of collateral, when appropriate. With more than 2 million customers across three states, we are not exposed materially to a concentration of credit risk. We maintain an allowance for doubtful accounts based upon factors surrounding the credit risk of customers, historical trends, consideration of the current credit environment and other information. In Oklahoma, Kansas and most jurisdictions we serve in Texas, we are able to recover natural gas costs related to doubtful accounts through purchased-gas cost adjustment mechanisms. At December 31, 2015 and 2014 , our allowance for doubtful accounts was $3.5 million and $4.0 million , respectively.
Inventories	Inventories - Natural gas in storage is maintained on the basis of weighted-average cost. Natural gas inventories that are injected into storage are recorded in inventory based on actual purchase costs, including storage and transportation costs. Natural gas inventories that are withdrawn from storage are accounted for in our purchased-gas cost adjustment mechanisms at the weighted-average inventory cost. Materials and supplies inventories, which are included in other current assets on our Balance Sheets, are stated at the lower of weighted-average cost or net realizable value. Our materials and supplies inventories totaled $33.3 million and $27.5 million at December 31, 2015 and 2014 , respectively.
Derivatives and Risk Management Activities	Derivatives and Risk Management Activities - We record all derivative instruments at fair value, with the exception of normal purchases and normal sales that are expected to result in physical delivery. The accounting for changes in the fair value of a derivative instrument depends on whether it has been designated and qualifies as part of a hedging relationship and, if so, the reason for holding it, or if regulatory rulings require a different accounting treatment. If certain conditions are met, we may elect to designate a derivative instrument as a hedge of exposure to changes in fair values or cash flows. The table below summarizes the various ways in which we account for our derivative instruments and the impact on our financial statements: Recognition and Measurement Accounting Treatment Balance Sheet Income Statement Normal purchases and normal sales - Fair value not recorded - Change in fair value not recognized in earnings Mark-to-market - Recorded at fair value - Change in fair value recognized in, and recoverable through, the purchased-gas cost adjustment mechanisms We have not elected to designate any of our derivative instruments as hedges. Gains or losses associated with the fair value of commodity derivative instruments entered into by us are included in, and recoverable through, the purchased-gas cost adjustment mechanisms. See Note 8 for additional information regarding our fair value measurements and hedging activities using derivatives.
Property, Plant and Equipment	Property, Plant and Equipment - Our properties are stated at cost, which includes direct construction costs such as direct labor, materials, burden and AFUDC. Generally, the cost of our property retired or sold, plus removal costs, less salvage, is charged to accumulated depreciation. Gains and losses from sales or retirement of an entire operating unit or system of our properties are recognized in income. Maintenance and repairs are charged directly to expense. AFUDC represents the cost of borrowed funds used to finance construction activities. We capitalize interest costs during the construction or upgrade of qualifying assets. Capitalized interest is recorded as a reduction to interest expense. Our properties are depreciated using the straight-line method over their estimated useful lives. Generally, we apply composite depreciation rates to functional groups of property having similar economic circumstances. We periodically conduct depreciation studies to assess the economic lives of our assets. These depreciation studies are completed as a part of our rate proceedings, and the changes in economic lives, if applicable, are implemented prospectively when the new rates are effective. Changes in the estimated economic lives of our property, plant and equipment could have a material effect on our financial position, results of operations or cash flows. Property, plant and equipment on our Balance Sheets includes construction work in process for capital projects that have not yet been placed in service and therefore are not being depreciated. Assets are transferred out of construction work in process when they are substantially complete and ready for their intended use. See Note 10 for additional information regarding our property, plant and equipment.
Impairment of Goodwill and Long-Lived Assets	Impairment of Goodwill and Long-Lived Assets - We assess our goodwill for impairment at least annually as of July 1. Total goodwill was $158.0 million at December 31, 2015 and 2014 , respectively. Our goodwill impairment analysis performed in 2015, 2014 and 2013 , utilized a qualitative assessment and did not result in any impairment indicators. Subsequent to July 1, 2015 , no event has occurred indicating that it is more likely that not that our fair value is less than our carrying value of our net assets. As part of our goodwill impairment test, we first assess qualitative factors (including macroeconomic conditions, industry and market considerations, cost factors and overall financial performance) to determine whether it is more likely than not that our fair value is less than our carrying amount. If further testing is necessary, we perform a two-step impairment test for goodwill. In the first step, an initial assessment is made by comparing our fair value with our book value, including goodwill. If the fair value is less than the book value, an impairment is indicated, and we must perform a second test to measure the amount of the impairment. In the second test, we calculate the implied fair value of the goodwill by deducting the fair value of all tangible and intangible net assets from the fair value determined in step one of the assessment. If the carrying value of the goodwill exceeds the implied fair value of the goodwill, we will record an impairment charge. To estimate our fair value, we use two generally accepted valuation approaches, an income approach and a market approach, using assumptions consistent with a market participant’s perspective. Under the income approach, we use anticipated cash flows over a period of years plus a terminal value and discount these amounts to their present value using appropriate discount rates. Under the market approach, we apply acquisition multiples to forecasted cash flows. The acquisition multiples used are consistent with historical asset transactions. The forecasted cash flows are based on average forecasted cash flows over a period of years. We assess our long-lived assets for impairment whenever events or changes in circumstances indicate that an asset’s carrying amount may not be recoverable. An impairment is indicated if the carrying amount of a long-lived asset exceeds the sum of the undiscounted future cash flows expected to result from the use and eventual disposition of the asset. If an impairment is indicated, we record an impairment loss equal to the difference between the carrying value and the fair value of the long-lived asset. We determined that there were no asset impairments in 2015, 2014 or 2013 .
Regulation	Regulation - We are subject to the rate regulation and accounting requirements of the OCC, KCC, RRC and various municipalities in Texas. We follow the accounting and reporting guidance for regulated operations. During the ratemaking process, regulatory authorities set the framework for what we can charge customers for our services and establish the manner that our costs are accounted for, including allowing us to defer recognition of certain costs and permitting recovery of the amounts through rates over time, as opposed to expensing such costs as incurred. Examples include weather normalization, unrecovered purchased-gas costs, pension and postemployment benefit costs and ad valorem taxes. This allows us to stabilize rates over time rather than passing such costs on to the customer for immediate recovery. Actions by regulatory authorities could have an effect on the amount recovered from rate payers. Any difference in the amount recoverable and the amount deferred is recorded as income or expense at the time of the regulatory action. A write-off of regulatory assets and costs not recovered may be required if all or a portion of the regulated operations have rates that are no longer: • established by independent regulators; • designed to recover the specific entity’s costs of providing regulated services; and • set at levels that will recover our costs when considering the demand and competition for our services. See Note 9 for additional information regarding our regulatory assets and liabilities disclosures.
Pension and Other Postretirement Plans	Pension and Other Postemployment Employee Benefits - We have defined benefit retirement plans covering eligible employees. We also sponsor welfare plans that provide other postemployment medical and life insurance benefits to eligible employees who retire with at least five years of service. To calculate the costs and liabilities related to our plans, we utilize an outside actuarial consultant, which uses statistical and other factors to anticipate future events. These factors include assumptions about the discount rate, expected return on plan assets, rate of future compensation increases, age and mortality and employment periods. In determining the projected benefit obligations and costs, assumptions can change from period to period and may result in material changes in the cost and liabilities we recognize. Prior to the separation, certain employees participated in pension and other postemployment employee benefit plans sponsored by ONEOK. We accounted for these plans as multiemployer benefit plans. Accordingly, we did not record an asset or liability to recognize the funded status of these plans. We recognized a liability only for any required contributions to those plans that were accrued and unpaid at the balance sheet date. The related pension and other postemployment expenses were allocated to us based on plan participants who directly supported our operations. These pension and other postemployment benefit costs included amounts associated with vested participants who are no longer employees. Prior to the separation, certain benefit costs associated with employees who directly supported our operations were determined based on a specific employee basis. We were also allocated benefit costs associated with employees of ONEOK that provided general corporate services. These amounts were charged to us by ONEOK as described in Note 2. Prior to the separation, we were not the plan sponsor for the ONEOK pension and other postemployment benefit plans. Accordingly, our balance sheets prior to the separation do not reflect any assets or liabilities related to these plans. See Note 12 for additional information regarding pension and other postemployment employee benefit plans.
Income Taxes	Income Taxes - Deferred income taxes are recorded for the difference between the financial statement and income tax basis of assets and liabilities and carryforward items, based on income tax laws and rates existing at the time the temporary differences are expected to reverse. The effect on deferred taxes of a change in tax rates is deferred and amortized for operations regulated by the OCC, KCC, RRC and various municipalities in Texas, if, as a result of an action by a regulator, it is probable that the effect of the change in tax rates will be recovered from or returned to customers through future rates. We continue to amortize previously deferred investment tax credits for ratemaking purposes over the periods prescribed by our regulators. A valuation allowance for deferred tax assets is recognized when it is more likely than not that some or all of the benefit from the deferred tax asset will not be realized. To assess that likelihood, we use estimates and judgment regarding our future taxable income, as well as the jurisdiction in which such taxable income is generated, to determine whether a valuation allowance is required. Such evidence can include our current financial position, our results of operations, both actual and forecasted, the reversal of deferred tax liabilities, as well as the current and forecasted business economics of our industry. We had no valuation allowance at December 31, 2015 and 2014 . We utilize a more-likely-than-not recognition threshold and measurement attribute for the financial statement recognition and measurement of a tax position that is taken or expected to be taken in a tax return. We reflect penalties and interest as part of income tax expense as they become applicable for tax provisions that do not meet the more-likely-than-not recognition threshold and measurement attribute. There were no material uncertain tax positions at December 31, 2015 and 2014 . See Note 13 for additional information regarding income taxes.
Asset Retirement Obligations	Asset Retirement Obligations - Asset retirement obligations represent legal obligations associated with the retirement of long-lived assets that result from the acquisition, construction, development and/or normal use of the asset. Certain long-lived assets that comprise our natural gas distribution systems, primarily our pipeline assets, are subject to agreements or regulations that give rise to an asset retirement obligation for removal or other disposition costs associated with retiring the assets in place upon the discontinued use of the natural gas distribution system. We recognize the fair value of a liability for an asset retirement obligation in the period when it is incurred if a reasonable estimate of the fair value can be made. We are not able to estimate reasonably the fair value of the asset retirement obligations for portions of our assets because the settlement dates are indeterminable given our expected continued use of the assets with proper maintenance. We expect our natural gas distribution systems will continue in operation as long as natural gas supply and demand for natural gas distribution service exists. Based on the widespread use of natural gas for heating and cooking activities by residential and commercial customers in our service areas, management expects supply and demand to exist for the foreseeable future. In accordance with long-standing regulatory treatment, we collect through rates the estimated costs of removal on certain regulated properties through depreciation expense, with a corresponding credit to accumulated depreciation and amortization. These removal costs collected through our rates include costs attributable to legal and nonlegal removal obligations; however, the amounts collected that are in excess of these nonlegal asset-removal costs incurred are accounted for as a regulatory liability for financial reporting purposes. Historically, with the exception of the regulatory authority in Kansas, the regulatory authorities that have jurisdiction over our regulated operations have not required us to quantify or disclose this amount; rather, these costs are addressed prospectively in depreciation rates and are set in each general rate order. We have made an estimate of our regulatory liability using current rates since the last general rate order in each of our jurisdictions; however, for financial reporting purposes, significant uncertainty exists regarding the future disposition of this regulatory liability, pending, among other issues, clarification of regulatory intent. We continue to monitor the regulatory requirements, and the liability may be adjusted as more information is obtained. We record the estimated asset removal obligation in noncurrent liabilities in other deferred credits on our Balance Sheets. To the extent this estimated liability is adjusted, such amounts will be reclassified between accumulated depreciation and amortization and other deferred credits and therefore will not have an impact on earnings.
Contingencies	Contingencies - Our accounting for contingencies covers a variety of business activities, including contingencies for legal and environmental exposures. We accrue these contingencies when our assessments indicate that it is probable that a liability has been incurred or an asset will not be recovered and an amount can be estimated reasonably. We expense legal fees as incurred and base our legal liability estimates on currently available facts and our estimates of the ultimate outcome or resolution. Accruals for estimated losses from environmental remediation obligations generally are recognized no later than the completion of a remediation feasibility study. Recoveries of environmental remediation costs from other parties are recorded as assets when their receipt is deemed probable. Actual results may differ from our estimates resulting in an impact, positive or negative, on earnings. See Note 14 for additional information regarding contingencies.
Share-Based Payments	Share-Based Payments - We expense the fair value of share-based payments net of estimated forfeitures. We estimate forfeiture rates based on historical forfeitures under our share-based payment plans. Prior to the separation, ONEOK charged us for compensation expense related to stock-based compensation awards granted to our employees that directly supported our operations. Share-based compensation was also a component of allocated amounts charged to us by ONEOK for general and administrative personnel providing services on our behalf.
Earnings Per Share	Earnings per share - Basic EPS is based on net income and is calculated based upon the daily weighted-average number of common shares outstanding during the periods presented. Also, this calculation includes fully vested stock awards that have not yet been issued as common stock. Diluted EPS includes the above, plus unvested stock awards granted under our compensation plans, but only to the extent these instruments dilute earnings per share.
Segments	Segments - We operate in one reportable business segment: regulated public utilities that deliver natural gas to residential, commercial, industrial and transportation customers. We define reportable business segments as components of an organization for which discrete financial information is available and operating results are evaluated on a regular basis by the chief operating decision maker (CODM) in order to assess performance and allocate resources. Our CODM is our Chief Executive Officer (CEO). Characteristics of our organization that were relied upon in making this determination include the similar nature of services we provide, the functional alignment of our organizational structure, and the reports that are regularly reviewed by the CODM for the purpose of assessing performance and allocating resources. Our management is functionally aligned and centralized, with performance evaluated based upon results of the entire distribution business. Capital allocation decisions are driven by asset integrity management and operating efficiency, not geographic location. We evaluate performance based principally on operating income. Affiliate sales are recorded on the same basis as sales to unaffiliated customers and are discussed in further detail in Note 2. Net margin is comprised of total revenues less cost of natural gas. Cost of natural gas includes commodity purchases, fuel, storage and transportation costs and does not include an allocation of general operating costs or depreciation and amortization. In 2015 , 2014 and 2013 , we had no single external customer from which we received 10 percent or more of our gross revenues.
Treasury Stock	Treasury Stock - We record treasury stock purchases at cost, which includes incremental direct transaction costs. Amounts are recorded as reductions in equity in our Balance Sheets. We record the reissuance of treasury stock at our weighted average cost of treasury shares recorded in equity in our Balance Sheets.
Recently Issues Accounting Standards Updates	Recently Issued Accounting Standards Update - In October 2015, the FASB issued ASU 2015-17, “Balance Sheet Classification of Deferred Taxes,” to simplify reporting of deferred taxes. The new guidance requires all deferred tax assets and liabilities, along with any related valuation allowance, be classified as noncurrent on the balance sheet. This guidance is required to be adopted for our interim and annual reports for periods beginning after December 15, 2016, but early adoption is permitted. We have adopted this guidance early to simplify our financial reporting process, have applied it prospectively for the period beginning October 1, 2015, and it did not have a material impact on our financial statements. Prior periods were not retrospectively adjusted. In August 2015, the FASB issued ASU 2015-15, “Interest-Imputation of Interest (Subtopic 835-30),” which specifically addresses the presentation and subsequent measurement of debt issuance costs associated with line of credit arrangements. We do not expect this issued guidance, which will be adopted concurrently with ASU 2015-03, to have a material impact on our financial statements. In April 2015, the FASB issued ASU 2015-03, “Interest-Imputation of Interest,” which 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. We do not expect this issued guidance, which is required to be adopted for our interim and annual reports for periods beginning after December 15, 2015, to have a material impact on our financial statements. In April 2015, the FASB issued ASU 2015-05, “Intangibles-Goodwill and Other-Internal-Use Software,” which helps entities evaluate the accounting for fees paid by a customer in a cloud computing arrangement. We do not expect this issued guidance, which is required to be adopted for our interim and annual reports for periods beginning after December 15, 2015, to have a material impact on our financial statements. In May 2014, the FASB issued ASU 2014-09, “Revenue from Contracts with Customers,” which clarifies and converges the revenue recognition principles under GAAP and IFRS. In July 2015, FASB delayed the effective date of ASU 2014-09 for one year. We are evaluating the impact of this recently issued guidance, which is required to be adopted for our interim and annual reports beginning with the first quarter 2018.

SEPARATION & RELATED-PARTY TR25

SEPARATION & RELATED-PARTY TRANSACTIONS (Tables)	12 Months Ended
	Dec. 31, 2015
Separation & Related Party Transaction [Line Items]
NET TRANSFERS FROM ONEOK [Table Text Block]	Net transfers from ONEOK included: (Thousands of dollars) Property, plant and equipment, net $ 21,459 Regulatory assets, pension and other postemployment benefits 331,148 Other assets 80,700 Long-term line of credit with ONEOK 1,027,631 Short-term note payable to ONEOK 397,857 Pension and other postemployment benefits - liabilities (123,800 ) Other liabilities (34,404 ) Deferred taxes (86,112 ) Accumulated other comprehensive loss (3,393 ) Net contribution of assets (liabilities) $ 1,611,086 Less: Cash paid to ONEOK 1,130,000 Net transfers from ONEOK $ 481,086
Schedule of Related Party Transactions	The following table shows ONEOK’s and its subsidiaries’ transactions with us included in the Statements of Income for the periods indicated: Year Ended December 31, 2013 (Thousands of dollars) Cost of natural gas $ 226,582 Operations and maintenance Direct employee labor and benefit costs 177,526 Allocated employee labor and benefit costs 29,955 Charges for general and administrative services 36,078 Depreciation and amortization 6,940 Other (income)/expense, net (5,073 ) Interest expense 60,930 Total $ 532,938

ACCUMULATED OTHER COMPREHENSI26

ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Tables)	12 Months Ended
	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]	The following table sets forth the balance in accumulated other comprehensive income (loss) for the period indicated: Accumulated Other Comprehensive Income (Loss) (Thousands of dollars) January 1, 2014 $ — Transfers in upon separation (3,393 ) Pension and other postemployment benefit plans obligations Other comprehensive income (loss) before reclassification, net of tax of $1,442 (2,096 ) Amounts reclassified from accumulated other comprehensive income (loss), net of tax of $(198) 315 Other comprehensive income (loss) (1,781 ) December 31, 2014 (5,174 ) Pension and other postemployment benefit plans obligations Other comprehensive income (loss) before reclassification, net of tax of $(130) 209 Amounts reclassified from accumulated other comprehensive income (loss), net of tax of $(353) 564 Other comprehensive income (loss) 773 December 31, 2015 $ (4,401 )
Reclassification out of Accumulated Other Comprehensive Income [Table Text Block]	The following table sets forth the effect of reclassifications from accumulated other comprehensive income (loss) on our Statements of Income for the period indicated: Details about Accumulated Other Comprehensive Income Year Ended December 31, Affected Line Item in the (Loss) Components 2015 2014 Statements of Income ( Thousands of dollars ) Pension and other postemployment benefit plan obligations (a) Amortization of net loss $ 47,494 $ 34,169 Amortization of unrecognized prior service cost (1,962 ) (1,211 ) 45,532 32,958 Regulatory adjustments (b) (44,615 ) (32,445 ) 917 513 Income before income taxes (353 ) (198 ) Income tax expense Total reclassifications for the period $ 564 $ 315 Net income (a) These components of accumulated other comprehensive income (loss) are included in the computation of net periodic benefit cost. See Note 12 for additional information regarding our net periodic benefit cost. (b) Regulatory adjustments represent pension and other postemployment benefit costs expected to be recovered through rates and are deferred as part of our regulatory assets. See Note 9 for additional information regarding our regulatory assets and liabilities.

EARNINGS PER SHARE (Tables)

EARNINGS PER SHARE (Tables)	12 Months Ended
	Dec. 31, 2015
EARNINGS PER SHARE OF COMMON STOCK, BASIC AND DILUTED [Line Items]
Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]	The following tables set forth the computation of basic and diluted EPS from continuing operations for the periods indicated: Year Ended December 31, 2015 Income Shares Per Share Amount ( Thousands, except per share amounts ) Basic EPS Calculation Net income available for common stock $ 119,030 52,578 $ 2.26 Diluted EPS Calculation Effect of dilutive securities — 676 Net income available for common stock and common stock equivalents $ 119,030 53,254 $ 2.24 Year Ended December 31, 2014 Income Shares Per Share Amount ( Thousands, except per share amounts ) Basic EPS Calculation Net income available for common stock $ 109,790 52,364 $ 2.10 Diluted EPS Calculation Effect of dilutive securities — 582 Net income available for common stock and common stock equivalents $ 109,790 52,946 $ 2.07 Year Ended December 31, 2013 Income Shares Per Share Amount ( Thousands, except per share amounts ) Basic EPS Calculation Net income available for common stock $ 99,195 52,319 $ 1.90 Diluted EPS Calculation Effect of dilutive securities — — Net income available for common stock and common stock equivalents $ 99,195 52,319 $ 1.90

REGULATORY ASSETS AND LIABILI28

REGULATORY ASSETS AND LIABILITIES (Tables)	12 Months Ended
	Dec. 31, 2015
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]
SCHEDULE OF REGULATED ASSETS AND LIABILITIES	The table below presents a summary of regulatory assets, net of amortization, and liabilities for the periods indicated: December 31, 2015 Remaining Recovery Period Current Noncurrent Total ( Thousands of dollars ) Under-recovered purchased-gas costs 1 year $ 13,336 $ — $ 13,336 Pension and other postemployment benefit costs See Note 12 15,670 425,175 440,845 Weather normalization 1 year 2,198 — 2,198 Reacquired debt costs 12 years 812 8,919 9,731 Other 1 to 23 years 909 1,769 2,678 Total regulatory assets, net of amortization 32,925 435,863 468,788 Accumulated removal costs (a) up to 50 years — (9,032 ) (9,032 ) Over-recovered purchased-gas costs 1 year (22,884 ) — (22,884 ) Ad valorem tax 1 year (1,731 ) — (1,731 ) Total regulatory liabilities (24,615 ) (9,032 ) (33,647 ) Net regulatory assets and liabilities $ 8,310 $ 426,831 $ 435,141 (a) Included in other deferred credits in our Balance Sheets. December 31, 2014 Remaining Recovery Period Current Noncurrent Total ( Thousands of dollars ) Under-recovered purchased-gas costs 1 year $ 28,712 $ — $ 28,712 Pension and other postemployment benefit costs See Note 12 18,108 466,684 484,792 Reacquired debt costs 13 years 812 9,730 10,542 Other 1 to 24 years 2,561 2,309 4,870 Total regulatory assets, net of amortization 50,193 478,723 528,916 Accumulated removal costs (a) up to 50 years — (15,451 ) (15,451 ) Weather normalization 1 year (16,516 ) — (16,516 ) Over-recovered purchased-gas costs 1 year (13,055 ) — (13,055 ) Ad valorem tax 1 year (2,896 ) — (2,896 ) Total regulatory liabilities (32,467 ) (15,451 ) (47,918 ) Net regulatory assets and liabilities $ 17,726 $ 463,272 $ 480,998 (a) Included in other deferred credits in our Balance Sheets.

PROPERTY, PLANT AND EQUIPMENT29

PROPERTY, PLANT AND EQUIPMENT (Tables) - Regulated [Member]	12 Months Ended
	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment by Property Type	The following table sets forth our property, plant and equipment by property type, for the periods indicated: December 31, December 31, 2015 2014 ( Thousands of dollars ) Natural gas distribution pipelines and related equipment $ 4,114,090 $ 3,909,881 Natural gas transmission pipelines and related equipment 462,654 450,810 General plant and other 498,906 418,157 Construction work in process 57,032 71,353 Property, plant and equipment 5,132,682 4,850,201 Accumulated depreciation and amortization (1,620,771 ) (1,556,481 ) Net property, plant and equipment $ 3,511,911 $ 3,293,720
Average Depreciation Rates for Regulated Property	We compute depreciation expense for distribution operations by applying composite, straight-line rates approved by various regulatory authorities. The average depreciation rates for our property are set forth in the following table for the periods indicated: Years Ended December 31, 2015 2014 2013 2.0% - 3.0% 2.0% - 3.0% 2.0% - 3.0%

SHARE-BASED PAYMENTS (Tables)

SHARE-BASED PAYMENTS (Tables)	12 Months Ended
	Dec. 31, 2015
Share-based Payments [Line Items]
Schedule of Share-based Compensation, Restricted Stock Units Activity	The following tables set forth activity and various statistics for restricted stock unit awards outstanding under the respective plans for the period indicated: Number of Shares Weighted- Average Price Nonvested December 31, 2014 325,730 $ 23.47 Granted 75,880 $ 41.40 Vested (162,280 ) $ 18.32 Forfeited (8,072 ) $ 34.42 Nonvested December 31, 2015 231,258 $ 32.59 2015 2014 2013 Weighted-average grant date fair value (per share) $ 41.40 $ 33.19 $ 47.36 Fair value of shares granted (thousands of dollars) $ 3,141 $ 3,149 $ 1,323
Schedule of Nonvested Performance-based Units Activity	The following tables set forth activity and various statistics related to our performance stock unit awards and the assumptions used by us, and ONEOK prior to 2014, in the valuations of the 2015, 2014 and 2013 grants at the grant date: Number of Units Weighted- Average Price Nonvested December 31, 2014 847,951 $ 17.62 Granted 100,860 $ 44.48 Vested (502,474 ) $ 14.33 Forfeited (7,087 ) $ 30.22 Nonvested December 31, 2015 439,250 $ 27.35 2015 2014 2013 Volatility 15.90% (a) 18.40% (a) 22.27% (b) Dividend yield 2.90% 3.37% 3.04% Risk-free interest rate 1.10% 0.67% 0.42% (a) - Volatility based on historical volatility over three years using daily stock price observations of our peer utilities. (b) - Volatility based on historical volatility over three years using daily ONEOK stock price observations. 2015 2014 2013 Weighted-average grant date fair value (per share) $ 44.48 $ 35.98 $ 52.30 Fair value of shares granted (thousands of dollars) $ 4,486 $ 4,462 $ 2,926

EMPLOYEE BENEFIT PLANS (Tables)

EMPLOYEE BENEFIT PLANS (Tables)	12 Months Ended
	Dec. 31, 2015
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Schedule of Assumptions Used [Table Text Block]	Actuarial Assumptions - The following table sets forth the weighted-average assumptions used to determine benefit obligations for pension and postemployment benefits for the periods indicated: December 31, 2015 2014 Discount rate 4.75% 4.25% Compensation increase rate 3.35% - 3.40% 3.30% - 3.50% The following table sets forth the weighted-average assumptions used by us, and ONEOK prior to 2014, to determine the periodic benefit costs for the periods indicated: Nine Months Ended September 30, Three Months Ended December 31, Years Ended December 31, 2015 2015 2014 2013 Discount rate - pension plans 4.25% 4.75% 5.25% 4.25% Discount rate - other postemployment plans 4.25% 4.75% 5.00% 4.00% Expected long-term return on plan assets 7.75% 7.75% 7.75% 8.25% Compensation increase rate 3.30% - 3.50% 3.30% - 3.50% 3.35% - 3.50% 3.45% - 3.50%
Schedule of Defined Benefit Plans Disclosures [Table Text Block]	The following table sets forth our defined benefit pension and other postemployment benefit plans, benefit obligations and fair value of plan assets for the periods indicated: Pension Benefits Other Postemployment Benefits December 31, December 31, 2015 2014 2015 2014 Changes in Benefit Obligation (Thousands of dollars) Benefit obligation, beginning of period $ 1,028,171 $ 863,620 $ 257,688 $ 239,171 Service cost 13,660 11,620 3,257 3,468 Interest cost 43,542 43,791 10,628 11,605 Plan participants’ contributions — — 2,915 2,642 Actuarial loss (gain) (47,607 ) 159,275 (19,702 ) 14,998 Benefits paid (52,142 ) (50,135 ) (14,632 ) (14,196 ) Plan amendment — — (11,901 ) — Benefit obligation, end of period 985,624 1,028,171 228,253 257,688 Change in Plan Assets Fair value of plan assets, beginning of period 845,396 840,699 151,777 147,237 Actual return on plan assets (9,026 ) 53,907 1,335 6,912 Employer contributions 933 925 14,100 9,182 Plan participants’ contributions — — 2,915 2,642 Benefits paid (52,142 ) (50,135 ) (14,632 ) (14,196 ) Fair value of assets, end of period 785,161 845,396 155,495 151,777 Balance at December 31 $ (200,463 ) $ (182,775 ) $ (72,758 ) $ (105,911 ) Current liabilities $ (912 ) $ (907 ) $ — $ — Noncurrent liabilities (199,551 ) (181,868 ) (72,758 ) (105,911 ) Balance at December 31 $ (200,463 ) $ (182,775 ) $ (72,758 ) $ (105,911 )
Schedule of Net Benefit Costs [Table Text Block]	Components of Net Periodic Benefit Cost - The following table sets forth the components of net periodic benefit cost for our defined benefit pension and other postemployment benefit plans for the period indicated: Pension Benefits Year Ended December 31, 2015 2014 (Thousands of dollars) Components of net periodic benefit cost Service cost $ 13,660 $ 11,620 Interest cost 43,542 43,791 Expected return on assets (61,769 ) (59,862 ) Amortization of unrecognized prior service cost 266 549 Amortization of net loss 42,226 30,200 Settlements 27 773 Net periodic benefit cost $ 37,952 $ 27,071 Other Postemployment Benefits Year Ended December 31, 2015 2014 (Thousands of dollars) Components of net periodic benefit cost Service cost $ 3,257 $ 3,468 Interest cost 10,628 11,605 Expected return on assets (11,892 ) (11,393 ) Amortization of unrecognized prior service cost (2,228 ) (1,760 ) Amortization of net loss 5,268 3,969 Net periodic benefit cost $ 5,033 $ 5,889
Schedule of Amounts Recognized in Other Comprehensive Income (Loss) [Table Text Block]	Other Comprehensive Income (Loss) - The following table sets forth the amounts recognized in other comprehensive income (loss) related to our defined benefit pension benefits for the period indicated: Pension Benefits Year Ended December 31, 2015 2014 (Thousands of dollars) Net gain (loss) arising during the period $ 339 $ (3,543 ) Amortization of loss 917 518 Deferred income taxes (483 ) 1,244 Total recognized in other comprehensive income (loss) $ 773 $ (1,781 )
Schedule of Net Periodic Benefit Cost Not yet Recognized [Table Text Block]	The tables below sets forth the amounts in accumulated other comprehensive income (loss) that had not yet been recognized as components of net periodic benefit expense for the periods indicated: Pension Benefits December 31, 2015 2014 (Thousands of dollars) Prior service credit (cost) $ — $ (266 ) Accumulated loss (407,798 ) (426,862 ) Accumulated other comprehensive loss before regulatory assets (407,798 ) (427,128 ) Regulatory asset for regulated entities 400,625 418,699 Accumulated other comprehensive loss after regulatory assets (7,173 ) (8,429 ) Deferred income taxes 2,772 3,255 Accumulated other comprehensive loss, net of tax $ (4,401 ) $ (5,174 ) Other Postemployment Benefits December 31, 2015 2014 (Thousands of dollars) Prior service credit (cost) $ 14,010 $ 4,337 Accumulated loss (50,447 ) (64,861 ) Accumulated other comprehensive loss before regulatory assets (36,437 ) (60,524 ) Regulatory asset for regulated entities 36,437 60,524 Accumulated other comprehensive loss after regulatory assets — — Deferred income taxes — — Accumulated other comprehensive loss, net of tax $ — $ —
Schedule of Amounts in Accumulated Other Comprehensive Income (Loss) to be Recognized over Next Fiscal Year [Table Text Block]	The following tables set forth the amounts recognized in either accumulated comprehensive income (loss) or regulatory assets expected to be recognized as components of net periodic benefit expense in the next fiscal year: Pension Benefits Other Postemployment Benefits Amounts to be recognized in 2016 (Thousands of dollars) Prior service credit (cost) $ — $ (3,633 ) Actuarial net loss $ 35,542 $ 4,608
Schedule of Health Care Cost Trend Rates [Table Text Block]	Health Care Cost Trend Rates - The following table sets forth the assumed health care cost-trend rates for the periods indicated: 2015 2014 Health care cost-trend rate assumed for next year 4.00% - 7.50% 4.00% - 7.75% Rate to which the cost-trend rate is assumed to decline (the ultimate trend rate) 4.00% - 5.00% 4.00% - 5.00% Year that the rate reaches the ultimate trend rate 2022 2022
Schedule of Effect of One-Percentage-Point Change in Assumed Health Care Cost Trend Rates [Table Text Block]	Assumed health care cost-trend rates have a significant effect on the amounts reported for our health care plans. A one percentage point change in assumed health care cost-trend rates would have the following effects: One Percentage One Percentage Point Increase Point Decrease (Thousands of dollars) Effect on total of service and interest cost $ 263 $ (266 ) Effect on other postemployment benefit obligation $ 3,655 $ (3,752 )
Schedule of Allocation of Plan Assets [Table Text Block]	Plan Assets - Our investment strategy is to invest plan assets in accordance with sound investment practices that emphasize long-term fundamentals. The goal of this strategy is to maximize investment returns while managing risk in order to meet the plan’s current and projected financial obligations. To achieve this strategy, we have established a liability-driven investment strategy to change the allocations as the plan reaches certain funded status. The plan’s investments include a diverse blend of various domestic and international equities, investment-grade debt securities which mirror the cash flows of our liability, insurance contracts and alternative investments. The current target allocation for the assets of our defined benefit pension plan is as follows: U.S. large-cap equities 37.4 % Investment-grade bonds 30.0 % Developed foreign large-cap equities 10.6 % Alternative investments 7.7 % Mid-cap equities 5.6 % Emerging markets equities 5.0 % Small-cap equities 3.7 % Total 100 % As part of our risk management for the plans, minimums and maximums have been set for each of the asset classes listed above. All investment managers for the plan are subject to certain restrictions on the securities they purchase and, with the exception of indexing purposes, are prohibited from owning our stock. The following tables set forth our pension benefits and other postemployment benefits plan assets by fair value category as of the measurement date: Pension Benefits December 31, 2015 Asset Category Level 1 Level 2 Level 3 Total (Thousands of dollars) Investments: Equity securities (a) $ 405,935 $ 62,150 $ — $ 468,085 Government obligations — 44,651 — 44,651 Corporate obligations (b) — 139,396 — 139,396 Cash and money market funds (c) 5,429 10,279 — 15,708 Insurance contracts and group annuity contracts — — 56,465 56,465 Other investments (d) 2,884 — 57,972 60,856 Total assets $ 414,248 $ 256,476 $ 114,437 $ 785,161 (a) - This category represents securities of the various market sectors from diverse industries. (b) - This category represents bonds from diverse industries. (c) - This category is primarily money market funds. (d) - This category represents alternative investments such as hedge funds and other financial instruments. Pension Benefits December 31, 2014 Asset Category Level 1 Level 2 Level 3 Total (Thousands of dollars) Investments: Equity securities (a) $ 439,165 $ 66,766 $ — $ 505,931 Government obligations — 47,769 — 47,769 Corporate obligations (b) — 153,412 — 153,412 Cash and money market funds (c) 4,152 16,341 — 20,493 Insurance contracts and group annuity contracts — — 59,877 59,877 Other investments (d) — — 57,914 57,914 Total assets $ 443,317 $ 284,288 $ 117,791 $ 845,396 (a) - This category represents securities of the various market sectors from diverse industries. (b) - This category represents bonds from diverse industries. (c) - This category is primarily money market funds. (d) - This category represents alternative investments such as hedge funds. Other Postemployment Benefits December 31, 2015 Asset Category Level 1 Level 2 Level 3 Total (Thousands of dollars) Investments: Equity securities (a) $ 54,560 $ 7,498 $ — $ 62,058 Government obligations — 64 — 64 Corporate obligations (b) — 200 — 200 Cash and money market funds (c) 233 13,322 — 13,555 Insurance contracts and group annuity contracts — 79,531 — 79,531 Other investments (d) 4 — 83 87 Total assets $ 54,797 $ 100,615 $ 83 $ 155,495 (a) - This category represents securities of the various market sectors from diverse industries. (b) - This category represents bonds from diverse industries. (c) - This category is primarily money market funds. (d) - This category represents alternative investments such as hedge funds. Other Postemployment Benefits December 31, 2014 Asset Category Level 1 Level 2 Level 3 Total (Thousands of dollars) Investments: Equity securities (a) $ 49,553 $ 12,589 $ — $ 62,142 Government obligations — 78 — 78 Corporate obligations (b) — 251 — 251 Cash and money market funds (c) 964 5,894 — 6,858 Insurance contracts and group annuity contracts — 82,353 — 82,353 Other investments (d) — — 95 95 Total assets $ 50,517 $ 101,165 $ 95 $ 151,777 (a) - This category represents securities of the various market sectors from diverse industries. (b) - This category represents bonds from diverse industries. (c) - This category is primarily money market funds. (d) - This category represents alternative investments such as hedge funds.
Schedule of Effect of Significant Unobservable Inputs, Changes in Plan Assets [Table Text Block]	The following table sets forth the reconciliation of Level 3 fair value measurements of our pension plans for the periods indicated: Pension Benefits Insurance Contracts Other Investments Total (Thousands of dollars) January 1, 2014 $ 63,454 $ 73,590 $ 137,044 Net realized and unrealized gains (losses) 3,446 (15,676 ) (12,230 ) Settlements (7,023 ) — (7,023 ) December 31, 2014 $ 59,877 $ 57,914 $ 117,791 Net realized and unrealized gains 2,188 58 2,246 Settlements (5,600 ) — (5,600 ) December 31, 2015 $ 56,465 $ 57,972 $ 114,437
Schedule of Expected Benefit Payments [Table Text Block]	The following table sets forth the pension benefits and other postemployment benefits payments expected to be paid in 2016-2025: Pension Benefits Other Postemployment Benefits to be paid in: (Thousands of dollars) 2016 $ 53,359 $ 14,116 2017 $ 54,710 $ 13,875 2018 $ 56,201 $ 14,435 2019 $ 57,238 $ 14,956 2020 $ 58,901 $ 15,406 2021 through 2025 $ 311,194 $ 81,175

INCOME TAXES (Tables)

INCOME TAXES (Tables)	12 Months Ended
	Dec. 31, 2015
Income tax [Line Items]
Reconciliation of Income Tax Provision	The following table sets forth our provision for income taxes for the periods indicated: Years Ended December 31, 2015 2014 2013 ( Thousands of dollars ) Current income tax provision Federal $ 7,135 $ 17,006 $ — State 2,055 1,397 67 Total current income tax provision 9,190 18,403 67 Deferred income tax provision Federal 56,440 42,024 53,562 State 7,349 7,911 8,643 Total deferred income tax provision 63,789 49,935 62,205 Total provision for income taxes $ 72,979 $ 68,338 $ 62,272
Schedule of Effective Income Tax Rate Reconciliation	The following table is a reconciliation of our income tax provision for the periods indicated: Years Ended December 31, 2015 2014 2013 ( Thousands of dollars ) Income before income taxes $ 192,009 $ 178,128 $ 161,467 Federal statutory income tax rate 35 % 35 % 35 % Provision for federal income taxes 67,203 62,345 56,513 State income taxes, net of federal tax benefit 6,114 6,051 5,661 Other, net (338 ) (58 ) 98 Total provision for income taxes $ 72,979 $ 68,338 $ 62,272
Schedule of Deferred Tax Assets and Liabilities	The following table sets forth the tax effects of temporary differences that gave rise to significant portions of the deferred tax assets and liabilities for the periods indicated: December 31, 2015 2014 ( Thousands of dollars ) Deferred tax assets Employee benefits and other accrued liabilities $ 110,148 $ 128,715 Net operating loss — 8,144 Other 7,848 5,655 Total deferred tax assets 117,996 142,514 Deferred tax liabilities Excess of tax over book depreciation 897,667 820,853 Purchased-gas cost adjustment 3,999 16,177 Other regulatory assets and liabilities, net 168,115 193,159 Total deferred tax liabilities 1,069,781 1,030,189 Net deferred tax liabilities $ 951,785 $ 887,675

COMMITMENTS AND CONTINGENCIES33

COMMITMENTS AND CONTINGENCIES (Tables)	12 Months Ended
	Dec. 31, 2015
Commitments and Contingencies [Line Items]
Future Minimum Rental Payments for Operating Leases	The following table sets forth our operating lease payments for the periods indicated: Operating Leases ( Millions of dollars ) 2016 $ 4.6 2017 4.5 2018 4.2 2019 3.5 2020 3.3 Thereafter 7.0 Total $ 27.1

QUARTERLY FINANCIAL DATA (UNA34

QUARTERLY FINANCIAL DATA (UNAUDITED) (Tables)	12 Months Ended
	Dec. 31, 2015
Schedule of Quarterly Financial Information [Line Items]
Quarterly Financial Data	First Quarter Second Quarter Third Quarter Fourth Quarter Year Ended December 31, 2015 ( Thousands of dollars ) Revenues $ 676,531 $ 256,786 $ 225,226 $ 389,149 Net margin $ 262,978 $ 176,837 $ 170,502 $ 231,416 Operating income $ 109,005 $ 31,270 $ 24,951 $ 73,903 Net income $ 60,381 $ 12,076 $ 7,371 $ 39,202 Earnings per share Basic $ 1.15 $ 0.23 $ 0.14 $ 0.75 Diluted $ 1.13 $ 0.23 $ 0.14 $ 0.74 First Quarter Second Quarter Third Quarter Fourth Quarter Year Ended December 31, 2014 ( Thousands of dollars ) Revenues $ 766,178 $ 296,838 $ 241,522 $ 514,368 Net margin $ 259,836 $ 176,493 $ 166,452 $ 224,176 Operating income $ 109,353 $ 26,812 $ 19,119 $ 70,010 Net income $ 59,076 $ 9,454 $ 4,653 $ 36,607 Earnings per share Basic $ 1.13 $ 0.18 $ 0.09 $ 0.70 Diluted $ 1.13 $ 0.18 $ 0.09 $ 0.69

SUMMARY OF SIGNIFICANT ACCOUN35

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) $ in Thousands, number in Millions	12 Months Ended
	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)
Significant Accounting Policies [Line Items]
Unbilled Receivables, Current	$ 109,600	$ 141,700
Number of natural gas distribution services customers	2
Allowance for Doubtful Accounts Receivable, Current	$ 3,500	4,000
Materials, Supplies, and Other	33,325	27,511
Goodwill	157,953	157,953
Goodwill, Impairment Loss	0	0	$ 0
Asset Impairment Charges	0	0	$ 0
Deferred Tax Assets, Valuation Allowance	0	0
Liability for Uncertain Tax Positions, Current	$ 0	$ 0
Segment Reporting, Disclosure of Major Customers	0	0	0

SEPARATION & RELATED-PARTY TR36

SEPARATION & RELATED-PARTY TRANSACTIONS (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Separation & Related Party Transaction [Line Items]
Proceeds from Issuance of Private Placement	$ 1,190,000
Cash Payment to ONEOK Upon Separation	$ 1,130,000	$ 0	$ 1,130,000	$ 0
Common Stock, Shares Authorized	250,000,000	250,000,000	250,000,000
Preferred Stock, Shares Authorized	50,000,000	50,000,000
Operations and maintenance [Abstract]
Plant, property and equipment, net	$ 21,459
Regulatory assets, pension and other post-retirements benefits	331,148
Other assets transferred	80,700
Long-term line of credit with ONEOK	1,027,631
Short-term note payable to ONEOK	397,857
Pension and other postretirement benefits - liabilities	(123,800)
Other liabilities transferred	(34,404)
Deferred taxes	(86,112)
Accumulated other comprehensive loss	(3,393)
Net contribution of assets (liabilities)	1,611,086
Less: Cash paid to ONEOK	1,130,000
Net transfers from ONEOK upon separation	$ 481,086
ONEOK, Inc. [Member]
Separation & Related Party Transaction [Line Items]
Total share-based compensation cost charged to us by ONEOK				15,500
Pension and postretirement health and life insurance plans costs charged to us by ONEOK, net				52,100
Amount of pension and postretirement health and life insurance costs deferred through regulatory mechanisms				1,800
Expense [Abstract]
Cost of natural gas				226,582
Operations and maintenance [Abstract]
Direct employee labor and benefits costs				177,526
Allocated employee labor and benefit costs				29,955
Charges for general and administrative services				36,078
Depreciation and amortization				6,940
Other (income)/expense, net				(5,073)
Interest expense				60,930
Total expenses				532,938
Employee labor and benefit costs capitalized				$ 49,300
Short-term note payable to ONEOK [Member] | ONEOK, Inc. [Member]
Operations and maintenance [Abstract]
Weighted-average interest rate				0.92%
Note Payable, Interest Rate Description				Principal under this note payable bears interest based on ONEOK’s weighted-average cost of short-term debt, plus a utilization fee of 50 basis points, calculated monthly.
Long-term line of credit with ONEOK [Member] | ONEOK, Inc. [Member]
Operations and maintenance [Abstract]
Weighted-average interest rate				5.79%
Line of Credit Facility, Interest Rate Description				The interest rate on the revolver was reset each year based on ONEOK’s outstanding debt plus an adjustment of 50 basis points for ONEOK’s cost to administer the program.

CREDIT FACILITY AND SHORT-TER37

CREDIT FACILITY AND SHORT-TERM NOTES PAYABLE (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)
Line of Credit Facility [Line Items]
Ratio of Indebtedness to Net Capital	0.4
Commercial paper maximum borrowing capacity	$ 700,000
Commercial Paper	12,500	$ 42,000
Letters of Credit Outstanding, Amount	1,000
Line of Credit Facility, Remaining Borrowing Capacity	$ 686,500
Short-term Debt, Weighted Average Interest Rate	0.70%	0.32%
Line of Credit [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Covenant Description	The ONE Gas Credit Agreement contains certain financial, operational and legal covenants. Among other things, these covenants include maintaining ONE Gas’ total debt-to-capital ratio of no more than 70 percent at the end of any calendar quarter. The ONE Gas Credit Agreement also contains customary affirmative and negative covenants, including covenants relating to liens, indebtedness of subsidiaries, investments, changes in the nature of business, fundamental changes, transactions with affiliates, burdensome agreements, and use of proceeds. In the event of a breach of certain covenants by ONE Gas, amounts outstanding under the ONE Gas Credit Agreement may become due and payable immediately.
Line of credit facility sublimit	$ 50,000
Line Of Credit Facility Option To Increase Borrowing Capacity	1,200,000
Line of Credit Facility, Maximum Borrowing Capacity	$ 700,000
Line of Credit Facility, Interest Rate Description	Borrowings, if any, will accrue interest at LIBOR plus 79.5 basis points.
Line of Credit Facility, Commitment Fee Description	The annual facility fee is 8 basis points.

LONG-TERM DEBT (Details)

LONG-TERM DEBT (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Proceeds from Issuance of Private Placement	$ 1,190,000
Cash Payment to ONEOK Upon Separation	$ 1,130,000	$ 0	$ 1,130,000	$ 0
Note Payable Due 2019 [Member]
Debt Instrument [Line Items]
Debt Instrument, Covenant Description	The indenture governing our Senior Notes includes an event of default upon the acceleration of other indebtedness of $100 million or more. Such events of default would entitle the trustee or the holders of 25 percent in the aggregate principal amount of the outstanding Senior Notes to declare those senior notes immediately due and payable in full.
Long-term Debt, Gross		$ 300,000
Debt Instrument, Interest Rate, Stated Percentage		2.07%
Debt Instrument, Call Feature	We may redeem our Senior Notes at par, plus accrued and unpaid interest to the redemption date, starting one month, three months, and six months, respectively, before their maturity dates. Prior to these dates, we may redeem these Senior Notes, in whole or in part, at a redemption price equal to the principal amount, plus accrued and unpaid interest and a make-whole premium. The redemption price will never be less than 100 percent of the principal amount of the respective note plus accrued and unpaid interest to the redemption date. Our Senior Notes are senior unsecured obligations, ranking equally in right of payment with all of our existing and future unsecured senior indebtedness.
Note Payable Due 2024 [Member]
Debt Instrument [Line Items]
Debt Instrument, Covenant Description	The indenture governing our Senior Notes includes an event of default upon the acceleration of other indebtedness of $100 million or more. Such events of default would entitle the trustee or the holders of 25 percent in the aggregate principal amount of the outstanding Senior Notes to declare those senior notes immediately due and payable in full.
Long-term Debt, Gross		$ 300,000
Debt Instrument, Interest Rate, Stated Percentage		3.61%
Debt Instrument, Call Feature		We may redeem our Senior Notes at par, plus accrued and unpaid interest to the redemption date, starting one month, three months, and six months, respectively, before their maturity dates. Prior to these dates, we may redeem these Senior Notes, in whole or in part, at a redemption price equal to the principal amount, plus accrued and unpaid interest and a make-whole premium. The redemption price will never be less than 100 percent of the principal amount of the respective note plus accrued and unpaid interest to the redemption date. Our Senior Notes are senior unsecured obligations, ranking equally in right of payment with all of our existing and future unsecured senior indebtedness.
Notes Payable Due 2044 [Member]
Debt Instrument [Line Items]
Debt Instrument, Covenant Description	The indenture governing our Senior Notes includes an event of default upon the acceleration of other indebtedness of $100 million or more. Such events of default would entitle the trustee or the holders of 25 percent in the aggregate principal amount of the outstanding Senior Notes to declare those senior notes immediately due and payable in full.
Long-term Debt, Gross		$ 600,000
Debt Instrument, Interest Rate, Stated Percentage		4.658%
Debt Instrument, Call Feature		We may redeem our Senior Notes at par, plus accrued and unpaid interest to the redemption date, starting one month, three months, and six months, respectively, before their maturity dates. Prior to these dates, we may redeem these Senior Notes, in whole or in part, at a redemption price equal to the principal amount, plus accrued and unpaid interest and a make-whole premium. The redemption price will never be less than 100 percent of the principal amount of the respective note plus accrued and unpaid interest to the redemption date. Our Senior Notes are senior unsecured obligations, ranking equally in right of payment with all of our existing and future unsecured senior indebtedness.

EQUITY (Details)

EQUITY (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Jan. 31, 2014
Dividends declared per share of stock		$ 1.20	$ 0.84	$ 0
Preferred Stock, Shares Authorized		50			50
Preferred Stock, Par or Stated Value Per Share		$ 0.01
Common stock authorized and available for issuance		197.4
Stock Repurchase Program, Authorized Amount		$ 20
Common Stock, Dividends, Declared, Annualized Basis		$ 1.20	$ 0.84
Dividend Declared [Member]
Common Stock, Dividends, Per Share, Declared	$ 0.35
Common Stock, Dividends, Declared, Annualized Basis	$ 1.40

ACCUMULATED OTHER COMPREHENSI40

ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pension and other postretirement benefit plans, Tax		$ (130)	$ 1,442
Accumulated Other Comprehensive Income (Loss), beginning balance	$ 0	(5,174)	0
Transfers in upon separation	$ 3,393
Pension and other postretirement benefit plans obligations [Abstract]
Other comprehensive income (loss), before reclassification, net of tax of $(130)		209	(2,096)
Amounts reclassified from accumulated other comprehensive income (loss), net of tax of $(353)		564	315
Other comprehensive loss		773	(1,781)	$ 0
Accumulated Other Comprehensive Income (Loss), ending balance		(4,401)	(5,174)	$ 0
Pension and other postretirement benefit plans obligations [Abstract]
Amortization of net loss		47,494	34,169
Amortization of unrecognized prior service cost		(1,962)	(1,211)
Other comprehensive income (loss) reclassification adjustment, before tax and regulatory adjustments		45,532	32,958
Other comprehensive income (loss) reclassification - regulatory adjustments		(44,615)	(32,445)
Other comprehensive income (loss) reclassification adjustment, before tax		917	513
Other comprehensive income (loss) reclassification adjustment, Tax		(353)	(198)
Other comprehensive income (loss) reclassification adjustment, net of tax		$ 564	$ 315

EARNINGS PER SHARE (Details)

EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	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	Jan. 31, 2014
EARNINGS PER SHARE OF COMMON STOCK, BASIC AND DILUTED [Line Items]
Net income	$ 39,202	$ 7,371	$ 12,076	$ 60,381	$ 36,607	$ 4,653	$ 9,454	$ 59,076	$ 119,030	$ 109,790	$ 99,195
Weighted Average Number of Shares Outstanding, Basic									52,578,000	52,364,000	52,319,000
Earnings Per Share, Basic	$ 0.75	$ 0.14	$ 0.23	$ 1.15	$ 0.70	$ 0.09	$ 0.18	$ 1.13	$ 2.26	$ 2.10	$ 1.90
Dilutive Securities, Effect on Basic Earnings Per Share									$ 0	$ 0	$ 0
Weighted Average Number Diluted Shares Outstanding Adjustment									676,000	582,000	0
Net Income (Loss) Available to Common Stockholders, Diluted									$ 119,030	$ 109,790	$ 99,195
Weighted Average Number of Shares Outstanding, Diluted									53,254,000	52,946,000	52,319,000
Earnings Per Share, Diluted	$ 0.74	$ 0.14	$ 0.23	$ 1.13	$ 0.69	$ 0.09	$ 0.18	$ 1.13	$ 2.24	$ 2.07	$ 1.90
Common Stock, Shares, Issued	52,598,005				52,083,859				52,598,005	52,083,859		51,941,236

DERIVATIVE FINANCIAL INSTRUME42

DERIVATIVE FINANCIAL INSTRUMENTS AND FAIR VALUE MEASUREMENTS (Details)	12 Months Ended
	Dec. 31, 2015USD ($)MMcf	Dec. 31, 2014USD ($)MMcf
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative, Nonmonetary Notional Amount | MMcf	17,000	16,000
Premiums recorded in other current assets on natural gas contracts held	$ 5,800,000	$ 6,400,000
Fair Value Assets, Transfers between Levels	0	0
Long-term Debt	1,200,000,000	1,200,000,000
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair value of natural gas call options held	400,000	100,000
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Long-term Debt, Fair Value	$ 1,200,000,000	$ 1,300,000,000

REGULATORY ASSETS AND LIABILI43

REGULATORY ASSETS AND LIABILITIES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Jan. 31, 2016
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]
Regulatory Assets, Current		$ 32,925	$ 50,193
Regulatory Assets, Noncurrent		435,863	478,723
Regulatory Liability, Current		(24,615)	(32,467)
Net regulatory assets and liabilities, current		8,310	17,726
Net regulatory assets and liabilities, noncurrent		426,831	463,272
Net Regulatory Assets		435,141	480,998
Amortization of Rate Deferral		$ 1,600	$ 6,400	$ 21,800
Amortization of Regulatory Asset				32,000
Accumulated removal costs [Member]
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]
Regulatory Asset, Amortization Period		up to 50 years	up to 50 years
Regulatory Liability, Current		$ 0	$ 0
Regulatory Liability, Noncurrent		(9,032)	(15,451)
Regulatory Liabilities		$ (9,032)	$ (15,451)
Weather normalization [Member]
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]
Regulatory Asset, Amortization Period		1 year	1 year
Regulatory Assets, Current		$ 2,198
Regulatory Assets, Noncurrent		0
Regulatory Assets		$ 2,198
Regulatory Liability, Current			$ (16,516)
Regulatory Liability, Noncurrent			0
Regulatory Liabilities			$ (16,516)
Over-recovered purchased-gas costs [Member]
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]
Regulatory Asset, Amortization Period		1 year	1 year
Regulatory Liability, Current		$ (22,884)	$ (13,055)
Regulatory Liability, Noncurrent		0	0
Regulatory Liabilities		$ (22,884)	$ (13,055)
Ad valorem tax [Member]
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]
Regulatory Asset, Amortization Period		1 year	1 year
Regulatory Liability, Current		$ (1,731)	$ (2,896)
Regulatory Liability, Noncurrent		0	0
Regulatory Liabilities		(1,731)	(2,896)
Total regulated liabilities [Member]
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]
Regulatory Liability, Current		(24,615)	(32,467)
Regulatory Liability, Noncurrent		(9,032)	(15,451)
Regulatory Liabilities		$ (33,647)	$ (47,918)
Under-recovered purchased-gas costs [Member]
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]
Regulatory Asset, Amortization Period		1 year	1 year
Regulatory Assets, Current		$ 13,336	$ 28,712
Regulatory Assets, Noncurrent		0	0
Regulatory Assets		$ 13,336	$ 28,712
Pension and postretirement benefit costs [Member]
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]
Regulatory Asset, Amortization Period		See Note 12	See Note 12
Regulatory Assets, Current		$ 15,670	$ 18,108
Regulatory Assets, Noncurrent		425,175	466,684
Regulatory Assets		$ 440,845	$ 484,792
Reacquired debt costs [Member]
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]
Regulatory Asset, Amortization Period		12 years	13 years
Regulatory Assets, Current		$ 812	$ 812
Regulatory Assets, Noncurrent		8,919	9,730
Regulatory Assets		$ 9,731	$ 10,542
Other regulatory assets [Member]
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]
Regulatory Asset, Amortization Period		1 to 23 years	1 to 24 years
Regulatory Assets, Current		$ 909	$ 2,561
Regulatory Assets, Noncurrent		1,769	2,309
Regulatory Assets		2,678	4,870
Total regulatory assets, net of amortization [Member]
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]
Regulatory Assets, Current		32,925	50,193
Regulatory Assets, Noncurrent		435,863	478,723
Regulatory Assets		$ 468,788	$ 528,916
Natural Gas Transition Cost [Member]
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]
Amortization of Regulatory Asset				$ 10,200
Subsequent Event [Member] | Information Technology Costs [Member]
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]
Regulatory Asset, Amortization Period	4
Regulatory Assets, Noncurrent					$ 2,400

PROPERTY, PLANT AND EQUIPMENT44

PROPERTY, PLANT AND EQUIPMENT (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Line Items]
Property, plant and equipment	$ 5,132,682	$ 4,850,201
Accumulated depreciation and amortization	(1,620,771)	(1,556,481)
Net property, plant and equipment	3,511,911	3,293,720
Regulated [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	5,132,682	4,850,201
Accumulated depreciation and amortization	(1,620,771)	(1,556,481)
Net property, plant and equipment	$ 3,511,911	$ 3,293,720
Average depreciation rates, minimum	2.00%	2.00%	2.00%
Average depreciation rates, maximum	3.00%	3.00%	3.00%
Interest costs capitalized	$ 2,600	$ 2,500	$ 1,300
Construction work in process expenditures incurred but not yet paid	15,000	7,000	$ 10,500
Natural gas distribution pipelines and related equipment | Regulated [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	4,114,090	3,909,881
Natural gas transmission pipelines and related equipment | Regulated [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	462,654	450,810
General plant and other | Regulated [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	498,906	418,157
Construction work in process | Regulated [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	$ 57,032	$ 71,353

SHARE-BASED PAYMENTS (Details)

SHARE-BASED PAYMENTS (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Feb. 03, 2014	Jan. 31, 2014
Share-based Payments [Line Items]
Common Stock, Capital Shares Reserved for Future Issuance	2,800,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	1,400,000
Share Price					$ 68.22
Volume-weighted average share price of ONE Gas stock on February 3, 2014				$ 33.50
Share-based compensation expense, net of tax	$ 5,700	$ 7,000	$ 9,700
Share-based compensation, tax benefit	3,500	4,400	6,100
Employee Stock Award Program Compensation Expense	$ 9,187	$ 7,613	$ 0
Employee Stock Purchase Plan [Member]
Share-based Payments [Line Items]
Description	Subject to certain exclusions, all employees who work at least 20 hours per week are eligible to participate in the ESPP.  Employees can choose to have up to 10 percent of their annual base pay withheld to purchase our common stock, subject to terms and limitations of the plan. The purchase price of the stock is 85 percent of the lower of the average market price of our common stock on the grant date or exercise date.
Employee Stock Award Program [Member]
Share-based Payments [Line Items]
Description	Under the program, each time the per-share closing price of our common stock on the NYSE closed for the first time at or above each $1.00 increment above its previous historical high closing price, we issued, for no monetary consideration, one share of our common stock to all eligible employees.
Restricted Stock Units (RSUs) [Member]
Share-based Payments [Line Items]
Share-based awards conversion ratio upon separation					2.04%
Award vesting period	3 years
Forfeiture rate maximum (in hundredths)	3.00%
Total compensation cost not yet recognized	$ 3,200
Total compensation cost not yet recognized, period for recognition	1 year 9 months 18 days
Nonvested beginning balance (in units)	325,730
Nonvested beginning balance (in dollars per unit)	$ 23.47
Granted (in units)	75,880
Weighted -average grant date fair value (per unit)	$ 41.40	$ 33.19	$ 47.36
Vested (in units)	(162,280)
Vested (in dollars per unit)	$ 18.32
Forfeited (in units)	(8,072)
Forfeited (in dollars per unit)	$ 34.42
Nonvested ending balance (in units)	231,258	325,730
Nonvested ending balance (in dollars per unit)	$ 32.59	$ 23.47
Fair value of shares granted (thousands of dollars)	$ 3,141	$ 3,149	$ 1,323
Performance Unit Awards [Member]
Share-based Payments [Line Items]
Share-based awards conversion ratio upon separation					2.04%
Award vesting period	3 years
Forfeiture rate maximum (in hundredths)	3.00%
Total compensation cost not yet recognized	$ 4,700
Total compensation cost not yet recognized, period for recognition	1 year 8 months 12 days
Nonvested beginning balance (in units)	847,951
Nonvested beginning balance (in dollars per unit)	$ 17.62
Granted (in units)	100,860
Weighted -average grant date fair value (per unit)	$ 44.48	$ 35.98	$ 52.30
Vested (in units)	(502,474)
Vested (in dollars per unit)	$ 14.33
Forfeited (in units)	(7,087)
Forfeited (in dollars per unit)	$ 30.22
Nonvested ending balance (in units)	439,250	847,951
Nonvested ending balance (in dollars per unit)	$ 27.35	$ 17.62
Fair value of shares granted (thousands of dollars)	$ 4,486	$ 4,462	$ 2,926
Expected volatility rate	15.90%	18.40%	22.27%
Expected dividend yield	2.90%	3.37%	3.04%
Risk-free interest rate	1.10%	0.67%	0.42%
Employee Stock Purchase Plan [Member]
Share-based Payments [Line Items]
Common Stock, Capital Shares Reserved for Future Issuance	700,000
Maximum allowable percentage of annual base pay withheld to purchase common stock	10.00%
Purchase price percentage of the lower of its grant date or exercise date market price (in hundredths)	85.00%
Percent of employees who participated in the Employee Stock Purchase Plan	40.00%	36.00%
Shares sold under employee stock purchase plan	51,092	51,418
Share price of shares sold under Employee Stock Purchase Plan in dollars per share	$ 36.15	$ 32.29
Employee Stock Purchase Plan Compensation Expense	$ 1,300	$ 400	$ 2,700
Employee Stock Award Program [Member]
Share-based Payments [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	125,000
Shares issued to employees under the Employee Stock Award Program	23,506	35,324
Employee Stock Award Program Compensation Expense	$ 1,100	$ 2,500	$ 4,200

EMPLOYEE BENEFIT PLANS (Details

EMPLOYEE BENEFIT PLANS (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended	9 Months Ended	12 Months Ended
	Jan. 31, 2014	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Jan. 01, 2014
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Change in net periodic benefit cost							$ 3,400
Defined Benefit Plan Assumptions Used To Determine Benefit Obligations Rate of Compensation Increase, Minimum							3.35%	3.30%
Defined Benefit Plan Assumptions Used To Determine Benefit Obligations Rate of Compensation Increase, Maximum							3.40%	3.50%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate							4.75%	4.25%
Expected long-term return on plan assets		7.75%	7.75%		7.75%	8.25%
Compensation increase rate - minimum		3.30%	3.30%		3.35%	3.45%
Compensation increase rate- maximum		3.50%	3.50%		3.50%	3.50%
Description of basis used to determine overall expected long-term rate of return on plan assets				We determine our overall expected long-term rate of return on plan assets, based on our review of historical returns and economic growth models. As of December 31, 2014, we updated our assumed mortality rates to incorporate the new set of mortality tables issued by the Society of Actuaries in October 2014. We determine our discount rates annually.  We estimate our discount rate based upon a comparison of the expected cash flows associated with our future payments under our defined benefit pension and other postemployment obligations to a hypothetical bond portfolio created using high-quality bonds that closely match expected cash flows.  Bond portfolios are developed by selecting a bond for each of the next 60 years based on the maturity dates of the bonds.  Bonds selected to be included in the portfolios are only those rated by Moody’s as AA- or better and exclude callable bonds, bonds with less than a minimum issue size, yield outliers and other filtering criteria to remove unsuitable bonds.
Benefit obligation									$ 1,100,000
Fair value of plan assets									$ 1,000,000
Increase in regulatory assets as a result of the transfer of unrecognized losses from ONEOK	$ 331,000
Increase in deferred income taxes as a result of the transfer of unrecognized losses from ONEOK	86,000
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Noncurrent liabilities							$ (272,309)	$ (287,779)
Defined Benefit Plan, Amount and Timing of Assets Expected to be Returned to Employer During Following 12 Month Period				0
Amortization of unrecognized prior service cost				$ (1,962)	$ (1,211)
Amortization of loss				47,494	34,169
Total recognized in other comprehensive income (loss)				$ (773)	$ 1,781	$ 0
Year that the rate reaches the ultimate trend rate							2,022	2,022
Defined Benefit Plan, Target Plan Asset Allocations				100.00%
Maximum [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Health care cost-trend rate assumed for next year				7.50%	7.75%
Rate to which the cost-trend rate is assumed to decline (the ultimate trend rate)				5.00%	5.00%
Minimum [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Health care cost-trend rate assumed for next year				4.00%	4.00%
Rate to which the cost-trend rate is assumed to decline (the ultimate trend rate)				4.00%	4.00%
ONEOK Profit-Sharing Plan [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Expense charged to us by ONEOK, Inc.						1,600
ONE Gas 401(k) Plan [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Percent of employee contributions matched of eligible compensation (in hundredths)				100.00%
Maximum percentage of each participants eligible compensation subject to certain limits matching (in hundredths)				6.00%
Contributions made to 401(k) plan				$ 10,200	$ 9,700
ONEOK 401(k) Plan [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Expense charged to us by ONEOK, Inc.						8,300
ONE Gas Profit-Sharing Plan [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Profit sharing contribution percentage				1.00%
Contributions made to profit-sharing plan				$ 6,500	4,000
US Large-Cap Equity [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Defined Benefit Plan, Target Plan Asset Allocations				37.40%
Investment-grade bonds [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Defined Benefit Plan, Target Plan Asset Allocations				30.00%
Developed foreign large-cap equities [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Defined Benefit Plan, Target Plan Asset Allocations				10.60%
Alternative investments [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Defined Benefit Plan, Target Plan Asset Allocations				7.70%
Mid-cap equities [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Defined Benefit Plan, Target Plan Asset Allocations				5.60%
Emerging market equities [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Defined Benefit Plan, Target Plan Asset Allocations				5.00%
Small-cap equities [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Defined Benefit Plan, Target Plan Asset Allocations				3.70%
Pension Plan [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost				$ 37,952	$ 27,071	$ 35,000
Discount rate		4.75%	4.25%		5.25%	4.25%
Benefit obligation	863,620	$ 985,624	$ 1,028,171	1,028,171	$ 863,620	$ 863,620	$ 985,624	$ 1,028,171
Fair value of plan assets	840,699	785,161	845,396	845,396	840,699	840,699	785,161	845,396
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation, beginning of period	863,620		1,028,171	1,028,171	863,620
Service cost				13,660	11,620
Plan participants' contributions				0	0
Actuarial loss				(47,607)	159,275
Benefits paid				(52,142)	(50,135)
Plan amendment				0	0
Benefit obligation, end of period		985,624		985,624	1,028,171	863,620
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period	840,699		845,396	845,396	840,699
Actual return on plan assets				(9,026)	53,907
Employer contributions				933	925
Plan participants' contributions				0	0
Fair value of plan assets, end of period		785,161		785,161	845,396	840,699
Balance at December 31							(200,463)	(182,775)
Current liabilities							(912)	(907)
Noncurrent liabilities							(199,551)	(181,868)
Balance at December 31							(200,463)	(182,775)
Accumulated benefit obligation for defined benefit pension plans							934,300	970,700
Service cost				13,660	11,620
Interest cost				43,542	43,791
Expected return on assets				(61,769)	(59,862)
Amortization of unrecognized prior service cost				266	549
Amortization of loss				42,226	30,200
Settlements				27	773
Net periodic benefit cost				37,952	27,071	35,000
Net loss arising during the period				339	(3,543)
Amortization of loss				917	518
Deferred income taxes				(483)	1,244
Total recognized in other comprehensive income (loss)				773	(1,781)
Prior service credit (cost)							0	(266)
Accumulated loss							(407,798)	(426,862)
Accumulated other comprehensive loss before regulatory assets							(407,798)	(427,128)
Regulatory asset for regulated entities							400,625	418,699
Accumulated other comprehensive loss after regulatory assets							(7,173)	(8,429)
Deferred income taxes							2,772	3,255
Accumulated other comprehensive loss, net of tax							(4,401)	(5,174)
Prior service credit (cost) expected to be recognized in following fiscal year							0
Actuarial net loss, to be recognized in 2016							35,542
Effect of a one percentage point change on total of service and interest cost - increase				263
Effect of a one percentage point change on other postemployment benefit obligation - increase				3,655
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Level 3 fair value measurement, January 1	137,044		117,791	117,791	137,044
Net realized and unrealized gains (losses)				2,246	(12,230)
Settlements				(5,600)	(7,023)
Level 3 fair value measurement, December 31		114,437		114,437	117,791	137,044
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year				900
2,016							53,359
2,017							54,710
2,018							56,201
2,019							57,238
2,020							58,901
2021 through 2025							311,194
Pension Plan [Member] | Level 1 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		414,248	443,317	443,317	443,317		414,248	443,317
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			443,317	443,317
Fair value of plan assets, end of period		414,248		414,248	443,317
Pension Plan [Member] | Level 2 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		256,476	284,288	284,288	284,288		256,476	284,288
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			284,288	284,288
Fair value of plan assets, end of period		256,476		256,476	284,288
Pension Plan [Member] | Level 3 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		114,437	117,791	117,791	117,791		114,437	117,791
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			$ 117,791	117,791
Fair value of plan assets, end of period		$ 114,437		114,437	117,791
Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost				$ 5,033	$ 5,889	$ 12,300
Minimum number of years of service for certain employees to be eligible to participate in shared welfare plans that provide postemployment medical and life insurance benefits				5
Discount rate		4.75%	4.25%		5.00%	4.00%
Benefit obligation	239,171	$ 228,253	$ 257,688	$ 257,688	$ 239,171	$ 239,171	228,253	257,688
Fair value of plan assets	147,237	155,495	151,777	151,777	147,237	147,237	155,495	151,777
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation, beginning of period	239,171		257,688	257,688	239,171
Service cost				3,257	3,468
Plan participants' contributions				2,915	2,642
Actuarial loss				(19,702)	14,998
Benefits paid				(14,632)	(14,196)
Plan amendment				(11,901)	0
Benefit obligation, end of period		228,253		228,253	257,688	239,171
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period	147,237		151,777	151,777	147,237
Actual return on plan assets				1,335	6,912
Employer contributions				14,100	9,182
Plan participants' contributions				2,915	2,642
Fair value of plan assets, end of period		155,495		155,495	151,777	147,237
Balance at December 31							(72,758)	(105,911)
Current liabilities							0	0
Noncurrent liabilities							(72,758)	(105,911)
Balance at December 31							(72,758)	(105,911)
Service cost				3,257	3,468
Interest cost				10,628	11,605
Expected return on assets				(11,892)	(11,393)
Amortization of unrecognized prior service cost				(2,228)	(1,760)
Amortization of loss				5,268	3,969
Net periodic benefit cost				5,033	5,889	12,300
Amortization of loss				0	0
Prior service credit (cost)							14,010	4,337
Accumulated loss							(50,447)	(64,861)
Accumulated other comprehensive loss before regulatory assets							(36,437)	(60,524)
Regulatory asset for regulated entities							36,437	60,524
Accumulated other comprehensive loss after regulatory assets							0	0
Deferred income taxes							0	0
Accumulated other comprehensive loss, net of tax							0	0
Prior service credit (cost) expected to be recognized in following fiscal year							(3,633)
Actuarial net loss, to be recognized in 2016							4,608
Effect of a one percentage point change on total of service and interest cost - decrease				(266)
Effect of a one percentage point change on other postemployment benefit obligation - decrease				(3,752)
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year				5,800
2,016							14,116
2,017							13,875
2,018							14,435
2,019							14,956
2,020							15,406
2021 through 2025							81,175
Other Postretirement Benefit Plan [Member] | Level 1 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		54,797	50,517	50,517	50,517		54,797	50,517
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			50,517	50,517
Fair value of plan assets, end of period		54,797		54,797	50,517
Other Postretirement Benefit Plan [Member] | Level 2 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		100,615	101,165	101,165	101,165		100,615	101,165
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			101,165	101,165
Fair value of plan assets, end of period		100,615		100,615	101,165
Other Postretirement Benefit Plan [Member] | Level 3 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		83	95	95	95		83	95
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			95	95
Fair value of plan assets, end of period		83		83	95
Equity Securities [Member] | Pension Plan [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		468,085	505,931	505,931	505,931		468,085	505,931
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			505,931	505,931
Fair value of plan assets, end of period		468,085		468,085	505,931
Equity Securities [Member] | Pension Plan [Member] | Level 1 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		405,935	439,165	439,165	439,165		405,935	439,165
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			439,165	439,165
Fair value of plan assets, end of period		405,935		405,935	439,165
Equity Securities [Member] | Pension Plan [Member] | Level 2 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		62,150	66,766	66,766	66,766		62,150	66,766
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			66,766	66,766
Fair value of plan assets, end of period		62,150		62,150	66,766
Equity Securities [Member] | Pension Plan [Member] | Level 3 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		0	0	0	0		0	0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			0	0
Fair value of plan assets, end of period		0		0	0
Equity Securities [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		62,058	62,142	62,142	62,142		62,058	62,142
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			62,142	62,142
Fair value of plan assets, end of period		62,058		62,058	62,142
Equity Securities [Member] | Other Postretirement Benefit Plan [Member] | Level 1 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		54,560	49,553	49,553	49,553		54,560	49,553
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			49,553	49,553
Fair value of plan assets, end of period		54,560		54,560	49,553
Equity Securities [Member] | Other Postretirement Benefit Plan [Member] | Level 2 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		7,498	12,589	12,589	12,589		7,498	12,589
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			12,589	12,589
Fair value of plan assets, end of period		7,498		7,498	12,589
Equity Securities [Member] | Other Postretirement Benefit Plan [Member] | Level 3 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		0	0	0	0		0	0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			0	0
Fair value of plan assets, end of period		0		0	0
Cash and Money Market Funds [Member] | Pension Plan [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		15,708	20,493	20,493	20,493		15,708	20,493
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			20,493	20,493
Fair value of plan assets, end of period		15,708		15,708	20,493
Cash and Money Market Funds [Member] | Pension Plan [Member] | Level 1 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		5,429	4,152	4,152	4,152		5,429	4,152
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			4,152	4,152
Fair value of plan assets, end of period		5,429		5,429	4,152
Cash and Money Market Funds [Member] | Pension Plan [Member] | Level 2 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		10,279	16,341	16,341	16,341		10,279	16,341
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			16,341	16,341
Fair value of plan assets, end of period		10,279		10,279	16,341
Cash and Money Market Funds [Member] | Pension Plan [Member] | Level 3 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		0	0	0	0		0	0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			0	0
Fair value of plan assets, end of period		0		0	0
Cash and Money Market Funds [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		13,555	6,858	6,858	6,858		13,555	6,858
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			6,858	6,858
Fair value of plan assets, end of period		13,555		13,555	6,858
Cash and Money Market Funds [Member] | Other Postretirement Benefit Plan [Member] | Level 1 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		233	964	964	964		233	964
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			964	964
Fair value of plan assets, end of period		233		233	964
Cash and Money Market Funds [Member] | Other Postretirement Benefit Plan [Member] | Level 2 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		13,322	5,894	5,894	5,894		13,322	5,894
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			5,894	5,894
Fair value of plan assets, end of period		13,322		13,322	5,894
Cash and Money Market Funds [Member] | Other Postretirement Benefit Plan [Member] | Level 3 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		0	0	0	0		0	0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			0	0
Fair value of plan assets, end of period		0		0	0
Government Obligations [Member] | Pension Plan [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		44,651	47,769	47,769	47,769		44,651	47,769
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			47,769	47,769
Fair value of plan assets, end of period		44,651		44,651	47,769
Government Obligations [Member] | Pension Plan [Member] | Level 1 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		0	0	0	0		0	0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			0	0
Fair value of plan assets, end of period		0		0	0
Government Obligations [Member] | Pension Plan [Member] | Level 2 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		44,651	47,769	47,769	47,769		44,651	47,769
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			47,769	47,769
Fair value of plan assets, end of period		44,651		44,651	47,769
Government Obligations [Member] | Pension Plan [Member] | Level 3 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		0	0	0	0		0	0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			0	0
Fair value of plan assets, end of period		0		0	0
Government Obligations [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		64	78	78	78		64	78
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			78	78
Fair value of plan assets, end of period		64		64	78
Government Obligations [Member] | Other Postretirement Benefit Plan [Member] | Level 1 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		0	0	0	0		0	0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			0	0
Fair value of plan assets, end of period		0		0	0
Government Obligations [Member] | Other Postretirement Benefit Plan [Member] | Level 2 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		64	78	78	78		64	78
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			78	78
Fair value of plan assets, end of period		64		64	78
Government Obligations [Member] | Other Postretirement Benefit Plan [Member] | Level 3 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		0	0	0	0		0	0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			0	0
Fair value of plan assets, end of period		0		0	0
Corporate Obligations [Member] | Pension Plan [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		139,396	153,412	153,412	153,412		139,396	153,412
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			153,412	153,412
Fair value of plan assets, end of period		139,396		139,396	153,412
Corporate Obligations [Member] | Pension Plan [Member] | Level 1 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		0	0	0	0		0	0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			0	0
Fair value of plan assets, end of period		0		0	0
Corporate Obligations [Member] | Pension Plan [Member] | Level 2 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		139,396	153,412	153,412	153,412		139,396	153,412
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			153,412	153,412
Fair value of plan assets, end of period		139,396		139,396	153,412
Corporate Obligations [Member] | Pension Plan [Member] | Level 3 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		0	0	0	0		0	0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			0	0
Fair value of plan assets, end of period		0		0	0
Corporate Obligations [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		200	251	251	251		200	251
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			251	251
Fair value of plan assets, end of period		200		200	251
Corporate Obligations [Member] | Other Postretirement Benefit Plan [Member] | Level 1 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		0	0	0	0		0	0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			0	0
Fair value of plan assets, end of period		0		0	0
Corporate Obligations [Member] | Other Postretirement Benefit Plan [Member] | Level 2 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		200	251	251	251		200	251
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			251	251
Fair value of plan assets, end of period		200		200	251
Corporate Obligations [Member] | Other Postretirement Benefit Plan [Member] | Level 3 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		0	0	0	0		0	0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			0	0
Fair value of plan assets, end of period		0		0	0
Insurance contracts and group annuity contracts [Member] | Pension Plan [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		56,465	59,877	59,877	59,877		56,465	59,877
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			59,877	59,877
Fair value of plan assets, end of period		56,465		56,465	59,877
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Level 3 fair value measurement, January 1	63,454		59,877	59,877	63,454
Net realized and unrealized gains (losses)				2,188	3,446
Settlements				(5,600)	(7,023)
Level 3 fair value measurement, December 31		56,465		56,465	59,877	63,454
Insurance contracts and group annuity contracts [Member] | Pension Plan [Member] | Level 1 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		0	0	0	0		0	0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			0	0
Fair value of plan assets, end of period		0		0	0
Insurance contracts and group annuity contracts [Member] | Pension Plan [Member] | Level 2 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		0	0	0	0		0	0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			0	0
Fair value of plan assets, end of period		0		0	0
Insurance contracts and group annuity contracts [Member] | Pension Plan [Member] | Level 3 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		56,465	59,877	59,877	59,877		56,465	59,877
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			59,877	59,877
Fair value of plan assets, end of period		56,465		56,465	59,877
Insurance contracts and group annuity contracts [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		79,531	82,353	82,353	82,353		79,531	82,353
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			82,353	82,353
Fair value of plan assets, end of period		79,531		79,531	82,353
Insurance contracts and group annuity contracts [Member] | Other Postretirement Benefit Plan [Member] | Level 1 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		0	0	0	0		0	0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			0	0
Fair value of plan assets, end of period		0		0	0
Insurance contracts and group annuity contracts [Member] | Other Postretirement Benefit Plan [Member] | Level 2 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		79,531	82,353	82,353	82,353		79,531	82,353
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			82,353	82,353
Fair value of plan assets, end of period		79,531		79,531	82,353
Insurance contracts and group annuity contracts [Member] | Other Postretirement Benefit Plan [Member] | Level 3 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		0	0	0	0		0	0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			0	0
Fair value of plan assets, end of period		0		0	0
Other Investments [Member] | Pension Plan [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		60,856	57,914	57,914	57,914		60,856	57,914
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			57,914	57,914
Fair value of plan assets, end of period		60,856		60,856	57,914
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Level 3 fair value measurement, January 1	$ 73,590		57,914	57,914	73,590
Net realized and unrealized gains (losses)				58	(15,676)
Settlements				0	0
Level 3 fair value measurement, December 31		57,972		57,972	57,914	$ 73,590
Other Investments [Member] | Pension Plan [Member] | Level 1 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		2,884	0	0	0		2,884	0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			0	0
Fair value of plan assets, end of period		2,884		2,884	0
Other Investments [Member] | Pension Plan [Member] | Level 2 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		0	0	0	0		0	0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			0	0
Fair value of plan assets, end of period		0		0	0
Other Investments [Member] | Pension Plan [Member] | Level 3 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		57,972	57,914	57,914	57,914		57,972	57,914
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			57,914	57,914
Fair value of plan assets, end of period		57,972		57,972	57,914
Other Investments [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		87	95	95	95		87	95
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			95	95
Fair value of plan assets, end of period		87		87	95
Other Investments [Member] | Other Postretirement Benefit Plan [Member] | Level 1 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		4	0	0	0		4	0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			0	0
Fair value of plan assets, end of period		4		4	0
Other Investments [Member] | Other Postretirement Benefit Plan [Member] | Level 2 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		0	0	0	0		0	0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			0	0
Fair value of plan assets, end of period		0		0	0
Other Investments [Member] | Other Postretirement Benefit Plan [Member] | Level 3 [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Fair value of plan assets		83	95	95	95		$ 83	$ 95
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period			$ 95	95
Fair value of plan assets, end of period		$ 83		$ 83	$ 95

INCOME TAXES (Details)

INCOME TAXES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income taxes receivable	$ 38,877	$ 43,800
Current income tax provision (benefit)
Federal	7,135	17,006	$ 0
State	2,055	1,397	67
Total current income tax provision (benefit)	9,190	18,403	67
Deferred income tax provision
Federal	56,440	42,024	53,562
State	7,349	7,911	8,643
Total deferred income tax provision	63,789	49,935	62,205
Income Tax Reconciliation [Abstract]
Income before income taxes	$ 192,009	$ 178,128	$ 161,467
Federal statutory income tax rate	35.00%	35.00%	35.00%
Provision for federal income taxes	$ 67,203	$ 62,345	$ 56,513
State income taxes, net of federal benefit	6,114	6,051	5,661
Other, net	(338)	(58)	98
Income tax provision	72,979	68,338	$ 62,272
Deferred tax assets
Deferred tax assets, employee benefits and other accrued liabilities	110,148	128,715
Net operating loss	0	8,144
Other	7,848	5,655
Total deferred tax assets	117,996	142,514
Deferred tax liabilities
Excess of tax over book depreciation	897,667	820,853
Purchased-gas cost adjustment	3,999	16,177
Other regulatory assets and liabilities, net	168,115	193,159
Total deferred tax liabilities	1,069,781	1,030,189
Net deferred tax liabilities	$ 951,785	$ 887,675

COMMITMENTS AND CONTINGENCIES -

COMMITMENTS AND CONTINGENCIES - Part 1 (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating Leased Assets [Line Items]
Operating Leases, Rent Expense	$ 5	$ 5	$ 4.8
Operating Leases, Future Minimum Payments Due [Abstract]
2,016	4.6
2,017	4.5
2,018	4.2
2,019	3.5
2,020	3.3
Thereafter	7
Total	$ 27.1

COMMITMENTS AND CONTINGENCIES49

COMMITMENTS AND CONTINGENCIES - Part 2 (Details)	Dec. 31, 2015
Commitments and Contingencies [Line Items]
Number Of Former Manufactured Gas Sites Where We Own Or Retain Legal Responsibility For Environmental Conditions	12
Number Of Sites Soil Remediation Is Completed Or Near Completion	11
Number of sites where regulatory closure has been achieved	3
Percentage yield of high consequence pipeline areas	30.00%

QUARTERLY FINANCIAL DATA (UNA50

QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Thousands	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
Schedule of Quarterly Financial Information [Line Items]
Revenues	$ 389,149	$ 225,226	$ 256,786	$ 676,531	$ 514,368	$ 241,522	$ 296,838	$ 766,178	$ 1,547,692	$ 1,818,906	$ 1,689,952
Net margin	231,416	170,502	176,837	262,978	224,176	166,452	176,493	259,836	841,733	826,957	813,008
Operating income	73,903	24,951	31,270	109,005	70,010	19,119	26,812	109,353	239,129	225,294	220,348
Net income	$ 39,202	$ 7,371	$ 12,076	$ 60,381	$ 36,607	$ 4,653	$ 9,454	$ 59,076	$ 119,030	$ 109,790	$ 99,195
Basic	$ 0.75	$ 0.14	$ 0.23	$ 1.15	$ 0.70	$ 0.09	$ 0.18	$ 1.13	$ 2.26	$ 2.10	$ 1.90
Diluted	$ 0.74	$ 0.14	$ 0.23	$ 1.13	$ 0.69	$ 0.09	$ 0.18	$ 1.13	$ 2.24	$ 2.07	$ 1.90