ONE Gas (OGS) 10-K 23 Feb 17 2016 FY Annual report Financial data

Document And Entity Information

Document And Entity Information - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2016	Feb. 10, 2017	Jun. 30, 2016
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			$ 3.2
Entity Common Stock, Shares Outstanding		52,283,788
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	FY
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2016

STATEMENTS OF INCOME

STATEMENTS OF INCOME - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Gross Margin
Revenues	$ 1,427,232	$ 1,547,692	$ 1,818,906
Cost of natural gas	541,797	705,959	991,949
Net margin	885,435	841,733	826,957
Operating expenses
Operations and maintenance	417,142	414,476	420,686
Depreciation and amortization	143,829	133,023	125,722
General taxes	55,344	55,105	55,255
Total operating expenses	616,315	602,604	601,663
Operating income	269,120	239,129	225,294
Other income	1,447	263	1,625
Other expense	(1,490)	(2,813)	(2,949)
Interest expense, net	(43,739)	(44,570)	(45,842)
Income before income taxes	225,338	192,009	178,128
Income taxes	(85,243)	(72,979)	(68,338)
Net income	140,095	119,030	109,790
Net Income (Loss) Available to Common Stockholders, Diluted	$ 140,095	$ 119,030	$ 109,790
Earnings per share
Basic	$ 2.67	$ 2.26	$ 2.10
Diluted	$ 2.65	$ 2.24	$ 2.07
Average shares (thousands)
Basic	52,453	52,578	52,364
Diluted	52,963	53,254	52,946
Dividends declared per share of stock	$ 1.40	$ 1.20	$ 0.84

STATEMENTS OF COMPREHENSIVE INC

STATEMENTS OF COMPREHENSIVE INCOME STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net income	$ 140,095	$ 119,030	$ 109,790
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Change in pension and other postretirement benefit plans liability, net of tax of $197, $(483), and $1,244, respectively	(314)	773	(1,781)
Other comprehensive loss	(314)	773	(1,781)
Comprehensive income	$ 139,781	$ 119,803	$ 108,009

STATEMENTS OF COMPREHENSIVE IN4

STATEMENTS OF COMPREHENSIVE INCOME (Parentheticals) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
STATEMENTS OF COMPREHENSIVE INCOME [Abstract]
Pension and other postretirement benefit plans, Tax	$ 197	$ (483)	$ 1,244

BALANCE SHEETS

BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Property, plant and equipment
Property, plant and equipment	$ 5,404,168	$ 5,132,682
Accumulated depreciation and amortization	1,672,548	1,620,771
Net property, plant and equipment	3,731,620	3,511,911
Current assets
Cash and cash equivalents	14,663	2,433
Accounts receivable, net	290,944	216,343
Materials and supplies	34,084	33,325
Income tax receivable	1,397	38,877
Natural gas in storage	125,432	142,153
Regulatory assets	83,146	32,925
Other current assets	19,257	16,789
Total current assets	568,923	482,845
Goodwill and other assets
Regulatory assets	440,522	435,863
Goodwill	157,953	157,953
Other assets	43,773	46,193
Total goodwill and other assets	642,248	640,009
Total assets	4,942,791	4,634,765
Equity and long-term debt
Common stock, $0.01 par value: authorized 250,000,000 shares; issued 52,598,005 shares and outstanding 52,283,260 shares at December 31, 2016; issued 52,598,005 shares and outstanding 52,259,224 shares at December 31, 2015	526	526
Paid-in capital	1,749,574	1,764,875
Retained earnings	161,021	95,046
Accumulated other comprehensive income (loss)	(4,715)	(4,401)
Treasury stock, at cost: 338,781 shares at December 31, 2015 and 314,745 shares at December 31, 2016	(18,126)	(14,491)
Total equity	1,888,280	1,841,555
Long-term debt, excluding current maturities, and net of issuance costs of $8,851 and $9,645, respectively	1,192,446	1,191,660
Total equity and long-term debt	3,080,726	3,033,215
Current liabilities
Current maturities of long-term debt	7	7
Notes payable	145,000	12,500
Accounts payable	131,988	107,482
Accrued interest	18,854	18,873
Accrued taxes other than income	42,571	37,249
Accrued liabilities	22,931	31,470
Customer deposits	61,209	60,325
Regulatory liabilities	11,922	24,615
Other current liabilities	9,451	11,700
Total current liabilities	443,933	304,221
Deferred credits and other liabilities [Abstract]
Deferred income taxes	1,038,568	951,785
Employee benefit obligations	303,507	272,309
Other deferred credits	76,057	73,235
Total deferred credits and other liabilities	1,418,132	1,297,329
Commitments and contingencies
Total liabilities and equity	$ 4,942,791	$ 4,634,765

BALANCE SHEETS BALANCE SHEETS P

BALANCE SHEETS BALANCE SHEETS Parenthetical - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
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	52,598,005
Common Stock, Shares, Outstanding	52,283,260	52,259,224
Treasury Stock, Shares	314,745	338,781
Debt Issuance Cost	$ 8,851	$ 9,645

STATEMENTS OF CASH FLOWS

STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net income	$ 140,095	$ 119,030	$ 109,790
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	143,829	133,023	125,722
Deferred income taxes	86,788	63,789	49,935
Share-based compensation expense	11,219	9,187	7,613
Provision for doubtful accounts	5,427	4,520	7,195
Changes in assets and liabilities:
Accounts receivable	(80,028)	105,886	23,044
Materials and supplies	(759)	(5,814)	10,868
Income Tax Receivable	37,480	4,923	(43,800)
Natural gas in storage	16,721	43,147	(19,172)
Asset removal costs	(53,430)	(51,608)	(47,125)
Accounts payable	27,596	(59,635)	(6,881)
Accrued interest	(19)	1	18,743
Accrued taxes other than income	5,322	(7,493)	12,316
Accrued Liabilities	(8,539)	5,451	21,228
Customer deposits	884	322	2,643
Regulatory assets and liabilities	(49,472)	50,658	30,067
Employee benefit obligation	(25,666)	(15,033)	(10,102)
Other assets and liabilities	24,119	(6,147)	(45,421)
Cash provided by operating activities	281,567	394,207	246,663
Investing activities
Capital expenditures	(309,071)	(294,320)	(297,103)
Other	492	0	0
Cash used in investing activities	(308,579)	(294,320)	(297,103)
Financing activities
Borrowings (repayment) on notes payable, net	132,500	(29,500)	42,000
Repurchase of common stock	(24,066)	(24,122)	0
Issuance of debt, net of discounts	0	0	1,199,994
Long-term debt financing costs	0	0	(11,087)
Cash payment to ONEOK upon separation	0	0	(1,130,000)
Issuance of common stock	4,017	7,051	2,001
Dividends paid	(73,209)	(62,826)	(43,696)
Cash provided by financing activities	39,242	(109,397)	59,212
Change in cash and cash equivalents	12,230	(9,510)	8,772
Cash and cash equivalents at beginning of period	2,433	11,943	3,171
Cash and cash equivalents at end of period	14,663	2,433	11,943
Supplemental cash flow information:
Cash paid for interest, net of amounts capitalized	42,129	42,980	21,066
Cash (received) paid for income taxes, net	$ (35,702)	$ (5,423)	$ 44,603

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]
Common Stock, Dividends, Declared, Annualized Basis	$ 0.84
Shares Issued, beginning balance at Dec. 31, 2013						100
Equity, beginning balance at Dec. 31, 2013	$ 1,239,023	$ 0	$ 1,239,023	$ 0	$ 0	$ 0	$ 0
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	(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	(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
Common Stock, Dividends, Declared, Annualized Basis	$ 1.40
Net income	$ 140,095	140,095	0	0	0	0	0
Other comprehensive loss	(314)	0	0	(314)	0	0	0
Repurchase of common stock	(24,066)	0	0	0	(24,066)	$ 0	0
Common stock issued, shares						0
Common stock issued, value	4,219	0	0	0	20,431	$ 0	(16,212)
Common stock dividends	(73,209)	(74,120)	0	0	0	$ 0	911
Shares Issued, ending balance at Dec. 31, 2016						52,598,005
Equity, ending balance at Dec. 31, 2016	$ 1,888,280	$ 161,021	$ 0	$ (4,715)	$ (18,126)	$ 526	$ 1,749,574

SUMMARY OF SIGNIFICANT ACCOUNTI

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Notes)	12 Months Ended
	Dec. 31, 2016
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 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. 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 the period prior to the separation also includes 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 period presented prior to the separation. 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 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 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. 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 7 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, 2016 and 2015 , were $143.2 million and $109.6 million , respectively. We collect and remit other taxes on behalf of governmental authorities, and we record these amounts in accrued taxes other than income in our Balance Sheets on a net basis. Cost of Natural Gas - Net margin is comprised of total revenues less cost of natural gas. Cost of natural gas includes commodity purchases, fuel, storage, transportation and other gas purchase costs recovered through our cost of natural gas regulatory mechanisms and does not include an allocation of general operating costs or depreciation and amortization. In addition, our cost of natural gas regulatory mechanisms provide a method of recovering natural gas costs on an ongoing basis without a profit. Therefore, although our revenues will fluctuate with the cost of gas that we purchase, net margin is not affected by fluctuations in the cost of natural gas. See Note 8 regulatory assets and liabilities for additional discussion of purchased gas cost recoveries. 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, 2016 and 2015 , our allowance for doubtful accounts was $4.2 million and $3.5 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 are stated at the lower of weighted-average cost or net realizable value. 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 formally 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 7 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 regulatory 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 9 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. Our goodwill impairment analysis performed in 2016, 2015 and 2014 , utilized a qualitative assessment and did not result in any impairment indicators. Subsequent to July 1, 2016 , no event has occurred indicating that it is more likely than 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 market 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 2016, 2015 or 2014 . 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 8 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. 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, 2016 and 2015 . 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, 2016 and 2015 . See Note 12 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 if the removal costs collected have exceeded our removal cost incurred; 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 13 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. 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, wholesale, public authority 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, operating efficiency, growth opportunities and government relocations, not geographic location or regulatory jurisdiction. In 2016 , 2015 and 2014 , 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 January 2017, the FASB issued ASU 2017-04, “Intangibles - Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment,” which simplifies how an entity is required to test goodwill for impairment by eliminating Step 2 of the goodwill test, where the measurement of a goodwill impairment loss was determined by comparing the implied fair value of a reporting unit’s goodwill with the carrying amount of that goodwill. Upon adoption, a goodwill impairment will be the amount by which a reporting unit’s carrying value exceeds its fair value, not to exceed the carrying amount of goodwill. This new guidance is required for our interim and annual reports for periods beginning after December 15, 2019, and early adoption is permitted. We do not expect this guidance to have a material impact on our financial statements and will adjust our goodwill testing procedures accordingly upon adoption. In March 2016, the FASB issued ASU 2016-09, “Improvements to Employee Share-Based Payment Accounting,” which includes various new aspects to simplify how share-based payments are accounted for and presented in the financial statements. The new standard modifies several aspects of the accounting and reporting for employee share-based payments and related tax accounting impacts, including the presentation in the statements of operations and cash flows. We will adopt this new guidance in the first quarter of 2017. Prospectively, we will record excess tax expenses or benefits in income tax expense. We will record a cumulative-effect increase of $11.0 million to retained earnings, with an offset to a deferred tax asset, as of the beginning of the reporting period in 2017 for excess tax benefits earned prior to January 1, 2017. We will continue our use of the estimation method to account for share unit awards forfeitures rather than actual forfeitures. We will adopt the classification of cash flows for changes in excess tax benefits prospectively in operating activities, and employer withholding shares for tax-withholding purposes for employees retrospectively in investing activities in our statement of cash flows. In February 2016, the FASB issued ASU 2016-02, “Leases (Topic 842),” which prescribes recognizing lease assets and liabilities on the balance sheet and includes disclosure of key information about leasing arrangements. A modified retrospective transition approach is required for leases existing at the time of adoption. We are evaluating our population of leases, analyzing lease agreements, and holding meetings with cross-divisional teams to determine the potential impact of this accounting standard on our financial position or results of operations and the transition approach we will utilize. This new guidance is required for our interim and annual reports for periods beginning after December 15, 2018, and early adoption is permitted. 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 adopted this guidance in the first quarter 2016, and it did not have an impact on our financial position or results of operations. 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 adopted this guidance in the first quarter of 2016, and have applied the changes retrospectively to all periods presented. We have presented such amounts as a direct deduction from the face amount of our long-term debt, rather than in other assets as a deferred charge in our Balance Sheets. Amortization of the debt issuance costs continues to be reported as interest expense in our Statements of Income. 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 adopted this guidance prospectively in the first quarter of 2016, and it did not have a material impact on our financial position or results of operations. 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 International Financial Reporting Standards. In July 2015, FASB delayed the effective date for one year. We have substantially completed evaluating all of our sources of revenue to determine the potential effect on our financial position, results of operations and cash flows. We continue to monitor accounting task forces and the FASB for additional implementation guidance related to: (1) the accounting for funds received from third parties to partially or fully reimburse the cost of construction of an asset; (2) the evaluation of collectability from customers

CREDIT FACILITY AND SHORT-TERM

CREDIT FACILITY AND SHORT-TERM NOTES PAYABLE (Notes)	12 Months Ended
	Dec. 31, 2016
Short-term Debt [Line Items]
Short-term Debt [Text Block]	2. CREDIT FACILITY AND SHORT-TERM NOTES PAYABLE 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, 2016 , our total debt-to-capital ratio was 41 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, 2016 , we had $145.0 million of commercial paper and $1.5 million in letters of credit issued under the ONE Gas Credit Agreement, with no borrowings and $553.5 million of remaining credit available under the ONE Gas Credit Agreement. The weighted-average interest rate on our commercial paper was 0.95 percent and 0.70 percent at December 31, 2016 and 2015 , respectively.

LONG-TERM DEBT (Notes)

LONG-TERM DEBT (Notes)	12 Months Ended
	Dec. 31, 2016
Debt Instrument [Line Items]
Long-term Debt [Text Block]	3. LONG-TERM DEBT 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 . 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, 2016
Class of Stock [Line Items]
Stockholders' Equity Note Disclosure [Text Block]	4. EQUITY Preferred Stock - At December 31, 2016 , we had 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, 2016 , we had approximately 197.7 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. Dividends Declared - In January 2017, we declared a dividend of $0.42 per share ( $1.68 per share on an annualized basis) for shareholders of record on February 24, 2017, payable March 10, 2017.

ACCUMULATED OTHER COMPREHENSIVE

ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Notes)	12 Months Ended
	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Comprehensive Income (Loss) Note [Text Block]	5. 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, 2015 $ (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 ) Pension and other postemployment benefit plans obligations Other comprehensive income (loss) before reclassification, net of tax of $486 (776 ) Amounts reclassified from accumulated other comprehensive income (loss), net of tax of $(289) 462 Other comprehensive income (loss) (314 ) December 31, 2016 $ (4,715 ) 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 2016 2015 2014 Statements of Income ( Thousands of dollars ) Pension and other postemployment benefit plan obligations (a) Amortization of net loss $ 40,912 $ 47,494 $ 34,169 Amortization of unrecognized prior service cost (3,316 ) (1,962 ) (1,211 ) 37,596 45,532 32,958 Regulatory adjustments (b) (36,845 ) (44,615 ) (32,445 ) 751 917 513 Income before income taxes (289 ) (353 ) (198 ) Income tax expense Total reclassifications for the period $ 462 $ 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 11 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 8 for additional information regarding our regulatory assets and liabilities.

EARNINGS PER SHARE (Notes)

EARNINGS PER SHARE (Notes)	12 Months Ended
	Dec. 31, 2016
EARNINGS PER SHARE OF COMMON STOCK, BASIC AND DILUTED [Line Items]
Earnings Per Share [Text Block]	6. 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, 2016 Income Shares Per Share Amount ( Thousands, except per share amounts ) Basic EPS Calculation Net income available for common stock $ 140,095 52,453 $ 2.67 Diluted EPS Calculation Effect of dilutive securities — 510 Net income available for common stock and common stock equivalents $ 140,095 52,963 $ 2.65 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

DERIVATIVE FINANCIAL INSTRUMENT

DERIVATIVE FINANCIAL INSTRUMENTS AND FAIR VALUE MEASUREMENTS (Notes)	12 Months Ended
	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Fair Value Disclosures	7. DERIVATIVE FINANCIAL INSTRUMENTS AND FAIR VALUE MEASUREMENTS Derivative Instruments - At December 31, 2016 , we held purchased natural gas call options for the heating season ending March 2017 , with total notional amounts of 14.3 Bcf, for which we paid premiums of $5.4 million , and which had a fair value of $6.5 million . At December 31, 2015 , we held purchased natural gas call options for the heating season ended March 2016 , with total notional amounts of 17.0 Bcf, for which we paid premiums of $5.8 million , and which had a fair value of $0.4 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, 2016 and 2015 . The estimated fair value of our long-term debt, including current maturities, was $1.2 billion at both December 31, 2016 and 2015 . 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, 2016
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]
Schedule of Regulatory Assets and Liabilities	8. REGULATORY ASSETS AND LIABILITIES The table below presents a summary of regulatory assets, net of amortization, and liabilities for the periods indicated: December 31, 2016 Remaining Recovery Period Current Noncurrent Total ( Thousands of dollars ) Under-recovered purchased-gas costs 1 year $ 29,901 $ — $ 29,901 Pension and other postemployment benefit costs See Note 11 31,498 427,448 458,946 Weather normalization 1 year 17,661 — 17,661 Reacquired debt costs 11 years 812 8,108 8,920 Other 1 to 22 years 3,274 4,966 8,240 Total regulatory assets, net of amortization 83,146 440,522 523,668 Over-recovered purchased-gas costs 1 year (10,154 ) — (10,154 ) Ad-valorem tax 1 year (1,768 ) — (1,768 ) Total regulatory liabilities (11,922 ) — (11,922 ) Net regulatory assets and liabilities $ 71,224 $ 440,522 $ 511,746 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 11 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. 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. Weather normalization represents revenue over- or under-recovered through the WNA 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 $3.8 million , $1.6 million and $6.4 million for the years ended December 31, 2016, 2015 and 2014 , respectively. 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 if the removal costs collected have exceeded our removal costs incurred. 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, 2016
Property, Plant and Equipment [Line Items]
PROPERTY, PLANT AND EQUIPMENT	9. 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, 2016 2015 ( Thousands of dollars ) Natural gas distribution pipelines and related equipment $ 4,321,429 $ 4,114,090 Natural gas transmission pipelines and related equipment 481,953 462,654 General plant and other 530,459 498,906 Construction work in process 70,327 57,032 Property, plant and equipment 5,404,168 5,132,682 Accumulated depreciation and amortization (1,672,548 ) (1,620,771 ) Net property, plant and equipment $ 3,731,620 $ 3,511,911 We compute depreciation expense by applying composite, straight-line rates of 2.0 percent to 3.0 percent that were approved by various regulatory authorities. We recorded capitalized interest of $3.6 million , $2.6 million and $2.5 million for the years ended December 31, 2016, 2015 and 2014 , respectively. We incurred liabilities for construction work in process and asset removal costs that had not been paid at December 31, 2016, 2015 and 2014 of $11.9 million , $15.0 million and $7.0 million , respectively. Such amounts are not included in capital expenditures on the Statements of Cash Flows.

SHARE-BASED PAYMENTS (Notes)

SHARE-BASED PAYMENTS (Notes)	12 Months Ended
	Dec. 31, 2016
Share-based Payments [Line Items]
Disclosure of Compensation Related Costs, Share-based Payments	10. SHARE-BASED PAYMENTS The ONE Gas Equity Compensation Plan (ECP) 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, 2016 , we had approximately 1.1 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. Compensation cost expensed for our share-based payment plans was $7.0 million , net of tax benefits of $4.3 million , for 2016 , $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 . 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. Restricted stock unit awards granted 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. 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 performance stock unit awards granted 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 share-based payment plans was used. Restricted Stock Unit Award Activity As of December 31, 2016 , there was $2.8 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 1.7 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 Units Weighted- Average Price Nonvested December 31, 2015 231,258 $ 32.59 Granted 42,935 $ 58.30 Vested (77,033 ) $ 23.76 Forfeited (2,260 ) $ 38.04 Nonvested December 31, 2016 194,900 $ 41.68 2016 2015 2014 Weighted-average grant date fair value (per share) $ 58.30 $ 41.40 $ 33.19 Fair value of shares granted (thousands of dollars) $ 2,503 $ 3,141 $ 3,149 The fair value of restricted stock vested was $4.5 million and $6.5 million in 2016 and 2015, respectively. Performance Stock Unit Award Activity As of December 31, 2016 , there was $4.8 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 in the valuations of the 2016, 2015 and 2014 grants at the grant date: Number of Units Weighted- Average Price Nonvested December 31, 2015 439,250 $ 27.35 Granted 74,395 $ 64.06 Vested (221,882 ) $ 15.11 Forfeited (2,952 ) $ 41.44 Nonvested December 31, 2016 288,811 $ 46.06 2016 2015 2014 Volatility (a) 18.20% 15.90% 18.40% Dividend yield 2.40% 2.90% 3.37% Risk-free interest rate 0.91% 1.10% 0.67% (a) - Volatility based on historical volatility over three years using daily stock price observations of our peer utilities. 2016 2015 2014 Weighted-average grant date fair value (per share) $ 64.06 $ 44.48 $ 35.98 Fair value of shares granted (thousands of dollars) $ 4,766 $ 4,486 $ 4,462 The fair value of performance stock vested was $19.5 million and $23.5 million in 2016 and 2015, respectively. Employee Stock Purchase Plan We have reserved a total of 700 thousand 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 41 percent , 40 percent and 36 percent of employees participated in the plan in 2016, 2015 and 2014 , respectively, and purchased 83,431 shares at $54.51 in 2016 , 51,092 shares at $36.15 in 2015 , and 51,418 shares at $32.29 in 2014 . Compensation expense, before taxes, was $1.4 million , $1.3 million and $0.4 million in 2016, 2015 and 2014 , respectively. Employee Stock Award Program Under the Employee Stock Award Program, we issue, for no monetary consideration, one share of our common stock to all eligible employees when the per-share closing price of our common stock on the NYSE closes for the first time at or above each $1.00 increment above $34. 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 2016, 2015 and 2014 totaled 50,573 , 23,506 and 35,324 , respectively, leaving 15,603 shares for future awards. Compensation expense, before taxes, related to the Employee Stock Award Program was $3.0 million , $1.1 million and $2.5 million for 2016, 2015 and 2014 , respectively.

EMPLOYEE BENEFIT PLANS (Notes)

EMPLOYEE BENEFIT PLANS (Notes)	12 Months Ended
	Dec. 31, 2016
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Pension and Other Postemployment Benefits Disclosure [Text Block]	11. EMPLOYEE BENEFIT PLANS Retirement and Other Postemployment Benefit Plans 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 Service division are 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 $32.0 million , $38.0 million and $27.1 million in 2016, 2015 and 2014 , respectively. 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 $2.6 million , $5.0 million and $5.9 million in 2016, 2015 and 2014 , respectively, prior to regulatory deferrals. Plan Amendments - In October 2015, we announced to certain 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 would allow them to select coverage on a healthcare exchange beginning January 1, 2017. As a result, we remeasured the respective plan assets and liabilities, which resulted in a reduction in benefit obligations of our postemployment benefit plan of $11.9 million in the fourth quarter of 2015. In September 2016, due to uncertain market conditions with health insurance exchange providers, we elected not to move the eligible pre-65 participants in our postemployment medical plans to a healthcare exchange. As a result, we remeasured the respective plan assets and benefit obligations, effective September 30, 2016. In the fourth quarter of 2016, we further amended our other postemployment medical plan to allow certain participants access to reimbursable retirement accounts. The net impact of these plan amendments in 2016 was a $483 thousand increase in our other postemployment benefit plan obligation. 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, 2016 2015 Discount rate - pension plans 4.30% 4.75% Discount rate - other postemployment plans 4.20% 4.75% Compensation increase rate 3.25% - 3.40% 3.35% - 3.40% The following table sets forth the weighted-average assumptions used by us to determine the periodic benefit costs for the periods indicated: Nine Months Ended September 30, Three Months Ended December 31, Years Ended December 31, 2016 2016 2015 2014 Discount rate - pension plans 4.75% 4.75% 4.25%/4.75% (a) 5.25% Discount rate - other postemployment plans 4.75% 3.75% 4.25%/4.75% (a) 5.00% Expected long-term return on plan assets - pension plans 7.75% 7.75% 7.75% 7.75% Expected long-term return on plan assets - other postemployment plans 8.00% 7.75% 7.75% 7.75% Compensation increase rate 3.35% - 3.40% 3.35% - 3.40% 3.30% - 3.50% 3.35% - 3.50% (a) Discount rate for the nine months ended September 30, 2015, and three months ended December 31, 2015, respectively. 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, 2016, we updated our assumed mortality rates to incorporate the new set of mortality tables issued by the Society of Actuaries in October 2016. 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 - 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, 2016 2015 2016 2015 Changes in Benefit Obligation (Thousands of dollars) Benefit obligation, beginning of period $ 985,624 $ 1,028,171 $ 228,253 $ 257,688 Service cost 12,055 13,660 2,675 3,257 Interest cost 45,550 43,542 10,235 10,628 Plan participants’ contributions — — 3,043 2,915 Actuarial loss (gain) 25,886 (47,607 ) 14,309 (19,702 ) Benefits paid (71,066 ) (52,142 ) (15,450 ) (14,632 ) Plan amendment — — 483 (11,901 ) Settlements (31,518 ) — — — Benefit obligation, end of period 966,531 985,624 243,548 228,253 Change in Plan Assets Fair value of plan assets, beginning of period 785,161 845,396 155,495 151,777 Actual return on plan assets 48,768 (9,026 ) 9,733 1,335 Employer contributions 12,441 933 13,225 14,100 Plan participants’ contributions — — 3,043 2,915 Benefits paid (71,066 ) (52,142 ) (15,450 ) (14,632 ) Settlements (35,718 ) — — — Fair value of assets, end of period 739,586 785,161 166,046 155,495 Balance at December 31 $ (226,945 ) $ (200,463 ) $ (77,502 ) $ (72,758 ) Current liabilities $ (941 ) $ (912 ) $ — $ — Noncurrent liabilities (226,004 ) (199,551 ) (77,502 ) (72,758 ) Balance at December 31 $ (226,945 ) $ (200,463 ) $ (77,502 ) $ (72,758 ) In the fourth quarter of 2016, we settled a portion of our benefit obligation with the purchase of annuities. Benefits paid reflects $18.1 million of lump sum payments to certain terminated vested participants. The accumulated benefit obligation for our defined benefit pension plans was $912.4 million and $934.3 million at December 31, 2016 and 2015 , respectively. There are no plan assets expected to be withdrawn and returned to us in 2017 . Components of Net Periodic Benefit Cost - The following tables set 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, 2016 2015 2014 (Thousands of dollars) Components of net periodic benefit cost Service cost $ 12,055 $ 13,660 $ 11,620 Interest cost 45,550 43,542 43,791 Expected return on assets (61,183 ) (61,769 ) (59,862 ) Amortization of unrecognized prior service cost — 266 549 Amortization of net loss 35,543 42,226 30,200 Settlements — 27 773 Net periodic benefit cost $ 31,965 $ 37,952 $ 27,071 Other Postemployment Benefits Year Ended December 31, 2016 2015 2014 (Thousands of dollars) Components of net periodic benefit cost Service cost $ 2,675 $ 3,257 $ 3,468 Interest cost 10,235 10,628 11,605 Expected return on assets (12,370 ) (11,892 ) (11,393 ) Amortization of unrecognized prior service cost (3,316 ) (2,228 ) (1,760 ) Amortization of net loss 5,369 5,268 3,969 Net periodic benefit cost $ 2,593 $ 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, 2016 2015 2014 (Thousands of dollars) Net gain (loss) arising during the period $ (1,262 ) $ 339 $ (3,543 ) Amortization of loss 751 917 518 Deferred income taxes 197 (483 ) 1,244 Total recognized in other comprehensive income (loss) $ (314 ) $ 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 set 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, 2016 2015 (Thousands of dollars) Prior service credit (cost) $ — $ — Accumulated loss (414,757 ) (407,798 ) Accumulated other comprehensive loss before regulatory assets (414,757 ) (407,798 ) Regulatory asset for regulated entities 407,073 400,625 Accumulated other comprehensive loss after regulatory assets (7,684 ) (7,173 ) Deferred income taxes 2,969 2,772 Accumulated other comprehensive loss, net of tax $ (4,715 ) $ (4,401 ) Other Postemployment Benefits December 31, 2016 2015 (Thousands of dollars) Prior service credit (cost) $ 10,211 $ 14,010 Accumulated loss (62,084 ) (50,447 ) Accumulated other comprehensive loss before regulatory assets (51,873 ) (36,437 ) Regulatory asset for regulated entities 51,873 36,437 Accumulated other comprehensive loss after regulatory assets — — Deferred income taxes — — Accumulated other comprehensive loss, net of tax $ — $ — The following table sets 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 2017 (Thousands of dollars) Prior service credit (cost) $ — $ (4,597 ) Actuarial net loss $ 36,107 $ 6,484 Health Care Cost Trend Rates - The following table sets forth the assumed health care cost-trend rates for the periods indicated: 2016 2015 Health care cost-trend rate assumed for next year 7.25% 4.00% - 7.50% Rate to which the cost-trend rate is assumed to decline (the ultimate trend rate) 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 $ 233 $ (232 ) Effect on other postemployment benefit obligation $ 3,937 $ (3,991 ) 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 current target allocation for the assets of our other postemployment benefits plan is 30 percent fixed income securities and 70 percent equity securities. 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, 2016 Asset Category Level 1 Level 2 Level 3 Total (Thousands of dollars) Investments: Equity securities (a) $ 371,655 $ 58,987 $ — $ 430,642 Government obligations — 47,445 — 47,445 Corporate obligations (b) — 129,036 — 129,036 Cash and money market funds (c) 13,786 16,114 — 29,900 Insurance contracts and group annuity contracts — — 45,140 45,140 Other investments (d) — 71 57,352 57,423 Total assets $ 385,441 $ 251,653 $ 102,492 $ 739,586 (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, 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. Other Postemployment Benefits December 31, 2016 Asset Category Level 1 Level 2 Level 3 Total (Thousands of dollars) Investments: Equity securities (a) $ 39,817 $ 7,323 $ — $ 47,140 Government obligations — 75 — 75 Corporate obligations (b) — 19,948 — 19,948 Cash and money market funds (c) 74 16,989 — 17,063 Insurance contracts and group annuity contracts — 81,820 — 81,820 Total assets $ 39,891 $ 126,155 $ — $ 166,046 (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. 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. 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, 2015 $ 59,877 $ 57,914 $ 117,791 Net realized and unrealized gains (losses) 2,188 58 2,246 Settlements (5,600 ) — (5,600 ) December 31, 2015 $ 56,465 $ 57,972 $ 114,437 Net realized and unrealized gains (losses) 4,518 (620 ) 3,898 Sales and settlements (15,843 ) — (15,843 ) December 31, 2016 $ 45,140 $ 57,352 $ 102,492 Contributions - During 2016 , we contributed $12.4 million to our defined benefit pension plans and we contributed $13.2 million to our other postemployment benefit plans. In 2017 , we expect to contribute $1.0 million to our defined benefit pension plans and expect to contribute $3.1 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, 2016 were $71.1 million and $15.5 million , respectively. The following table sets forth the pension benefits and other postemployment benefits payments expected to be paid in 2017-2026: Pension Benefits Other Postemployment Benefits to be paid in: (Thousands of dollars) 2017 $ 51,539 $ 16,165 2018 $ 52,660 $ 16,815 2019 $ 53,450 $ 17,073 2020 $ 54,812 $ 17,379 2021 $ 56,033 $ 17,401 2022 through 2026 $ 294,519 $ 86,559 The expected benefits to be paid are based on the same assumptions used to measure our benefit obligation at December 31, 2016 , 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 eligible compensation, subject to certain limits. Our contributions made to the plan were $10.8 million , $10.2 million and $9.7 million in 2016, 2015 and 2014 , respectively. 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 $6.0 million , $6.5 million and $4.0 million in 2016, 2015 and 2014 , respectively. 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 2016, 2015 and 2014 .

INCOME TAXES (Notes)

INCOME TAXES (Notes)	12 Months Ended
	Dec. 31, 2016
Income tax [Line Items]
INCOME TAXES	12. INCOME TAXES The following table sets forth our provision for income taxes for the periods indicated: Years Ended December 31, 2016 2015 2014 ( Thousands of dollars ) Current income tax provision Federal $ (2,016 ) $ 7,135 $ 17,006 State 471 2,055 1,397 Total current income tax provision (1,545 ) 9,190 18,403 Deferred income tax provision Federal 76,247 56,440 42,024 State 10,541 7,349 7,911 Total deferred income tax provision 86,788 63,789 49,935 Total provision for income taxes $ 85,243 $ 72,979 $ 68,338 The following table is a reconciliation of our income tax provision for the periods indicated: Years Ended December 31, 2016 2015 2014 ( Thousands of dollars ) Income before income taxes $ 225,338 $ 192,009 $ 178,128 Federal statutory income tax rate 35 % 35 % 35 % Provision for federal income taxes 78,868 67,203 62,345 State income taxes, net of federal tax benefit 7,158 6,114 6,051 Other, net (783 ) (338 ) (58 ) Total provision for income taxes $ 85,243 $ 72,979 $ 68,338 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, 2016 2015 ( Thousands of dollars ) Deferred tax assets Employee benefits and other accrued liabilities $ 123,333 $ 110,148 Net operating loss 23,094 — Other 5,716 7,848 Total deferred tax assets 152,143 117,996 Deferred tax liabilities Excess of tax over book depreciation 990,682 897,667 Purchased-gas cost adjustment 13,822 3,999 Other regulatory assets and liabilities, net 186,207 168,115 Total deferred tax liabilities 1,190,711 1,069,781 Net deferred tax liabilities $ 1,038,568 $ 951,785 As of December 31, 2016, we have federal and state income tax net operating loss (NOL) carryforwards of $63.0 million and $21.0 million , respectively, which will expire at various dates from 2024 through 2036. We believe that it is more likely than not that the tax benefits of the NOL carryforwards will be utilized prior to their expirations; therefore, no valuation allowance is necessary. Deferred tax assets related to tax benefits of employee share-based compensation have been reduced for performance share units and restricted share units that vested in periods in which we were in an NOL position. This vesting resulted in tax deductions in excess of previously recorded benefits based on the performance share unit and restricted share unit value at the time of grant. Although these additional tax benefits are reflected in NOL carryforwards in the tax return, the additional tax benefit is not recognized until the deduction reduces taxes payable. A portion of the tax benefit does not reduce our current taxes payable due to NOL carryforwards; accordingly, these tax benefits are not reflected in our NOLs in deferred tax assets. Cumulative tax benefits included in NOL carryforwards but not reflected in deferred tax assets were $11.0 million as of December 31, 2016. We have filed our consolidated federal and state tax returns for years 2014 and 2015.

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Notes)	12 Months Ended
	Dec. 31, 2016
Commitments and Contingencies [Line Items]
COMMITMENTS AND CONTINGENCIES	13. 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 $8.6 million in 2016 and $5.0 million in each of 2015 and 2014. The following table sets forth our operating lease payments for the periods indicated: Operating Leases ( Millions of dollars ) 2017 $ 5.6 2018 5.2 2019 4.4 2020 3.6 2021 3.2 Thereafter 4.4 Total $ 26.4 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 require us to investigate these sites and set remediation activities based upon the results of the investigations and risk analysis. Remediation typically involves 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, and continue to monitor groundwater at eight of the 12 sites according to plans approved by the KDHE. Regulatory closure has been achieved at three of the sites, subject to any future regulatory remediation requirements that may require additional costs. During 2016, we completed a site assessment at the twelfth site where no active soil remediation has occurred. We have submitted a work plan to the KDHE for approval to remove contaminated soil at this site. Costs associated with the remediation at this site are not expected to be material to our results of operations or financial position. With regard to one of our other former manufactured natural gas sites, recent results from periodic monitoring and a 2016 interim site investigation indicated elevated levels of potentially harmful materials at the site. In response to the results of the interim site investigation, during the fourth quarter of 2016, potential investigation and remediation alternatives were developed. We have estimated the potential costs associated with additional investigation and remediation to be in the range of $4.0 million to $7.0 million . Additional testing and work plan development will be conducted in 2017 to determine a remediation work plan to present to the KDHE for approval and could impact our estimates of the cost of remediation at this site. A single reliable estimate of the remediation costs is not feasible due to the amount of uncertainty in the ultimate remediation approach that will be utilized. Accordingly, in the fourth quarter of 2016, we recorded a reserve of $4.0 million for this site. 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 2016, 2015 and 2014. A number of environmental issues may exist with respect to manufactured gas plants that are unknown to us. Accordingly, future costs are dependent on the final determination and regulatory approval of any remedial actions, the complexity of the site, level of remediation required, changing technology and governmental regulations, and to the extent not recovered by insurance or recoverable in rates from our customers, could be material to our financial condition, results of operations or cash flows. 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 recovered by insurance or recoverable in rates from our customers, and those costs may adversely affect our financial condition, results of operations and cash flows. We do not expect expenditures for these matters to have a material adverse effect on our financial condition, results of operations or 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 the 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. In April 2016, PHMSA published a NPRM, the Safety of Gas Transmission & Gathering Lines Rule, in the Federal Register to revise pipeline safety regulations applicable to the safety of onshore natural gas transmission and gathering pipelines. Proposals include changes to pipeline integrity management requirements and other safety-related requirements. The NPRM comment period ended July 7, 2016, and comments are under review by PHMSA. The potential capital and operating expenditures associated with the NPRM are currently being evaluated and could be significant depending on the final regulations. 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, 2016
Schedule of Quarterly Financial Information [Line Items]
QUARTERLY FINANCIAL DATA (UNAUDITED)	14. QUARTERLY FINANCIAL DATA (UNAUDITED) First Quarter Second Quarter Third Quarter Fourth Quarter Year Ended December 31, 2016 ( Thousands of dollars ) Revenues $ 508,364 $ 245,923 $ 232,191 $ 440,754 Operating income $ 116,073 $ 43,621 $ 30,892 $ 78,534 Net income $ 64,743 $ 20,300 $ 12,737 $ 42,315 Earnings per share Basic $ 1.23 $ 0.39 $ 0.24 $ 0.81 Diluted $ 1.22 $ 0.38 $ 0.24 $ 0.80 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 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

SUMMARY OF SIGNIFICANT ACCOUN23

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2016
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 the period prior to the separation also includes 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 period presented prior to the separation. 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 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 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. 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 7 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, 2016 and 2015 , were $143.2 million and $109.6 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, 2016 and 2015 , our allowance for doubtful accounts was $4.2 million and $3.5 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 are stated at the lower of weighted-average cost or net realizable value.
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 formally 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 7 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 regulatory 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 9 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. Our goodwill impairment analysis performed in 2016, 2015 and 2014 , utilized a qualitative assessment and did not result in any impairment indicators. Subsequent to July 1, 2016 , no event has occurred indicating that it is more likely than 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 market 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 2016, 2015 or 2014 .
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 8 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.
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, 2016 and 2015 . 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, 2016 and 2015 . See Note 12 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 if the removal costs collected have exceeded our removal cost incurred; 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 13 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.
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, wholesale, public authority 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, operating efficiency, growth opportunities and government relocations, not geographic location or regulatory jurisdiction. In 2016 , 2015 and 2014 , 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 January 2017, the FASB issued ASU 2017-04, “Intangibles - Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment,” which simplifies how an entity is required to test goodwill for impairment by eliminating Step 2 of the goodwill test, where the measurement of a goodwill impairment loss was determined by comparing the implied fair value of a reporting unit’s goodwill with the carrying amount of that goodwill. Upon adoption, a goodwill impairment will be the amount by which a reporting unit’s carrying value exceeds its fair value, not to exceed the carrying amount of goodwill. This new guidance is required for our interim and annual reports for periods beginning after December 15, 2019, and early adoption is permitted. We do not expect this guidance to have a material impact on our financial statements and will adjust our goodwill testing procedures accordingly upon adoption. In March 2016, the FASB issued ASU 2016-09, “Improvements to Employee Share-Based Payment Accounting,” which includes various new aspects to simplify how share-based payments are accounted for and presented in the financial statements. The new standard modifies several aspects of the accounting and reporting for employee share-based payments and related tax accounting impacts, including the presentation in the statements of operations and cash flows. We will adopt this new guidance in the first quarter of 2017. Prospectively, we will record excess tax expenses or benefits in income tax expense. We will record a cumulative-effect increase of $11.0 million to retained earnings, with an offset to a deferred tax asset, as of the beginning of the reporting period in 2017 for excess tax benefits earned prior to January 1, 2017. We will continue our use of the estimation method to account for share unit awards forfeitures rather than actual forfeitures. We will adopt the classification of cash flows for changes in excess tax benefits prospectively in operating activities, and employer withholding shares for tax-withholding purposes for employees retrospectively in investing activities in our statement of cash flows. In February 2016, the FASB issued ASU 2016-02, “Leases (Topic 842),” which prescribes recognizing lease assets and liabilities on the balance sheet and includes disclosure of key information about leasing arrangements. A modified retrospective transition approach is required for leases existing at the time of adoption. We are evaluating our population of leases, analyzing lease agreements, and holding meetings with cross-divisional teams to determine the potential impact of this accounting standard on our financial position or results of operations and the transition approach we will utilize. This new guidance is required for our interim and annual reports for periods beginning after December 15, 2018, and early adoption is permitted. 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 adopted this guidance in the first quarter 2016, and it did not have an impact on our financial position or results of operations. 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 adopted this guidance in the first quarter of 2016, and have applied the changes retrospectively to all periods presented. We have presented such amounts as a direct deduction from the face amount of our long-term debt, rather than in other assets as a deferred charge in our Balance Sheets. Amortization of the debt issuance costs continues to be reported as interest expense in our Statements of Income. 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 adopted this guidance prospectively in the first quarter of 2016, and it did not have a material impact on our financial position or results of operations. 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 International Financial Reporting Standards. In July 2015, FASB delayed the effective date for one year. We have substantially completed evaluating all of our sources of revenue to determine the potential effect on our financial position, results of operations and cash flows. We continue to monitor accounting task forces and the FASB for additional implementation guidance related to: (1) the accounting for funds received from third parties to partially or fully reimburse the cost of construction of an asset; (2) the evaluation of collectability from customers if a utility has regulatory mechanisms to help assure recovery of uncollected accounts from ratepayers; and (3) the accounting for alternative revenue programs, such as performance-based ratemaking, that may impact the final conclusions of our evaluation. Until these items are resolved, we cannot determine the effect the new guidance will have on our financial position, results of operations, cash flows, business processes or the transition method we will utilize to adopt the new guidance. We are required to adopt this new guidance for our interim and annual reports beginning with the first quarter 2018.

ACCUMULATED OTHER COMPREHENSI24

ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Tables)	12 Months Ended
	Dec. 31, 2016
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, 2015 $ (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 ) Pension and other postemployment benefit plans obligations Other comprehensive income (loss) before reclassification, net of tax of $486 (776 ) Amounts reclassified from accumulated other comprehensive income (loss), net of tax of $(289) 462 Other comprehensive income (loss) (314 ) December 31, 2016 $ (4,715 )
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 2016 2015 2014 Statements of Income ( Thousands of dollars ) Pension and other postemployment benefit plan obligations (a) Amortization of net loss $ 40,912 $ 47,494 $ 34,169 Amortization of unrecognized prior service cost (3,316 ) (1,962 ) (1,211 ) 37,596 45,532 32,958 Regulatory adjustments (b) (36,845 ) (44,615 ) (32,445 ) 751 917 513 Income before income taxes (289 ) (353 ) (198 ) Income tax expense Total reclassifications for the period $ 462 $ 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 11 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 8 for additional information regarding our regulatory assets and liabilities.

EARNINGS PER SHARE (Tables)

EARNINGS PER SHARE (Tables)	12 Months Ended
	Dec. 31, 2016
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, 2016 Income Shares Per Share Amount ( Thousands, except per share amounts ) Basic EPS Calculation Net income available for common stock $ 140,095 52,453 $ 2.67 Diluted EPS Calculation Effect of dilutive securities — 510 Net income available for common stock and common stock equivalents $ 140,095 52,963 $ 2.65 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

REGULATORY ASSETS AND LIABILI26

REGULATORY ASSETS AND LIABILITIES (Tables)	12 Months Ended
	Dec. 31, 2016
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, 2016 Remaining Recovery Period Current Noncurrent Total ( Thousands of dollars ) Under-recovered purchased-gas costs 1 year $ 29,901 $ — $ 29,901 Pension and other postemployment benefit costs See Note 11 31,498 427,448 458,946 Weather normalization 1 year 17,661 — 17,661 Reacquired debt costs 11 years 812 8,108 8,920 Other 1 to 22 years 3,274 4,966 8,240 Total regulatory assets, net of amortization 83,146 440,522 523,668 Over-recovered purchased-gas costs 1 year (10,154 ) — (10,154 ) Ad-valorem tax 1 year (1,768 ) — (1,768 ) Total regulatory liabilities (11,922 ) — (11,922 ) Net regulatory assets and liabilities $ 71,224 $ 440,522 $ 511,746 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 11 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.

PROPERTY, PLANT AND EQUIPMENT27

PROPERTY, PLANT AND EQUIPMENT (Tables)	12 Months Ended
	Dec. 31, 2016
Regulated [Member]
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, 2016 2015 ( Thousands of dollars ) Natural gas distribution pipelines and related equipment $ 4,321,429 $ 4,114,090 Natural gas transmission pipelines and related equipment 481,953 462,654 General plant and other 530,459 498,906 Construction work in process 70,327 57,032 Property, plant and equipment 5,404,168 5,132,682 Accumulated depreciation and amortization (1,672,548 ) (1,620,771 ) Net property, plant and equipment $ 3,731,620 $ 3,511,911

SHARE-BASED PAYMENTS (Tables)

SHARE-BASED PAYMENTS (Tables)	12 Months Ended
	Dec. 31, 2016
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 Units Weighted- Average Price Nonvested December 31, 2015 231,258 $ 32.59 Granted 42,935 $ 58.30 Vested (77,033 ) $ 23.76 Forfeited (2,260 ) $ 38.04 Nonvested December 31, 2016 194,900 $ 41.68 2016 2015 2014 Weighted-average grant date fair value (per share) $ 58.30 $ 41.40 $ 33.19 Fair value of shares granted (thousands of dollars) $ 2,503 $ 3,141 $ 3,149
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 in the valuations of the 2016, 2015 and 2014 grants at the grant date: Number of Units Weighted- Average Price Nonvested December 31, 2015 439,250 $ 27.35 Granted 74,395 $ 64.06 Vested (221,882 ) $ 15.11 Forfeited (2,952 ) $ 41.44 Nonvested December 31, 2016 288,811 $ 46.06 2016 2015 2014 Volatility (a) 18.20% 15.90% 18.40% Dividend yield 2.40% 2.90% 3.37% Risk-free interest rate 0.91% 1.10% 0.67% (a) - Volatility based on historical volatility over three years using daily stock price observations of our peer utilities. 2016 2015 2014 Weighted-average grant date fair value (per share) $ 64.06 $ 44.48 $ 35.98 Fair value of shares granted (thousands of dollars) $ 4,766 $ 4,486 $ 4,462

EMPLOYEE BENEFIT PLANS (Tables)

EMPLOYEE BENEFIT PLANS (Tables)	12 Months Ended
	Dec. 31, 2016
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, 2016 2015 Discount rate - pension plans 4.30% 4.75% Discount rate - other postemployment plans 4.20% 4.75% Compensation increase rate 3.25% - 3.40% 3.35% - 3.40% The following table sets forth the weighted-average assumptions used by us to determine the periodic benefit costs for the periods indicated: Nine Months Ended September 30, Three Months Ended December 31, Years Ended December 31, 2016 2016 2015 2014 Discount rate - pension plans 4.75% 4.75% 4.25%/4.75% (a) 5.25% Discount rate - other postemployment plans 4.75% 3.75% 4.25%/4.75% (a) 5.00% Expected long-term return on plan assets - pension plans 7.75% 7.75% 7.75% 7.75% Expected long-term return on plan assets - other postemployment plans 8.00% 7.75% 7.75% 7.75% Compensation increase rate 3.35% - 3.40% 3.35% - 3.40% 3.30% - 3.50% 3.35% - 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, 2016 2015 2016 2015 Changes in Benefit Obligation (Thousands of dollars) Benefit obligation, beginning of period $ 985,624 $ 1,028,171 $ 228,253 $ 257,688 Service cost 12,055 13,660 2,675 3,257 Interest cost 45,550 43,542 10,235 10,628 Plan participants’ contributions — — 3,043 2,915 Actuarial loss (gain) 25,886 (47,607 ) 14,309 (19,702 ) Benefits paid (71,066 ) (52,142 ) (15,450 ) (14,632 ) Plan amendment — — 483 (11,901 ) Settlements (31,518 ) — — — Benefit obligation, end of period 966,531 985,624 243,548 228,253 Change in Plan Assets Fair value of plan assets, beginning of period 785,161 845,396 155,495 151,777 Actual return on plan assets 48,768 (9,026 ) 9,733 1,335 Employer contributions 12,441 933 13,225 14,100 Plan participants’ contributions — — 3,043 2,915 Benefits paid (71,066 ) (52,142 ) (15,450 ) (14,632 ) Settlements (35,718 ) — — — Fair value of assets, end of period 739,586 785,161 166,046 155,495 Balance at December 31 $ (226,945 ) $ (200,463 ) $ (77,502 ) $ (72,758 ) Current liabilities $ (941 ) $ (912 ) $ — $ — Noncurrent liabilities (226,004 ) (199,551 ) (77,502 ) (72,758 ) Balance at December 31 $ (226,945 ) $ (200,463 ) $ (77,502 ) $ (72,758 )
Schedule of Net Benefit Costs [Table Text Block]	Components of Net Periodic Benefit Cost - The following tables set 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, 2016 2015 2014 (Thousands of dollars) Components of net periodic benefit cost Service cost $ 12,055 $ 13,660 $ 11,620 Interest cost 45,550 43,542 43,791 Expected return on assets (61,183 ) (61,769 ) (59,862 ) Amortization of unrecognized prior service cost — 266 549 Amortization of net loss 35,543 42,226 30,200 Settlements — 27 773 Net periodic benefit cost $ 31,965 $ 37,952 $ 27,071 Other Postemployment Benefits Year Ended December 31, 2016 2015 2014 (Thousands of dollars) Components of net periodic benefit cost Service cost $ 2,675 $ 3,257 $ 3,468 Interest cost 10,235 10,628 11,605 Expected return on assets (12,370 ) (11,892 ) (11,393 ) Amortization of unrecognized prior service cost (3,316 ) (2,228 ) (1,760 ) Amortization of net loss 5,369 5,268 3,969 Net periodic benefit cost $ 2,593 $ 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, 2016 2015 2014 (Thousands of dollars) Net gain (loss) arising during the period $ (1,262 ) $ 339 $ (3,543 ) Amortization of loss 751 917 518 Deferred income taxes 197 (483 ) 1,244 Total recognized in other comprehensive income (loss) $ (314 ) $ 773 $ (1,781 )
Schedule of Net Periodic Benefit Cost Not yet Recognized [Table Text Block]	The tables below set 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, 2016 2015 (Thousands of dollars) Prior service credit (cost) $ — $ — Accumulated loss (414,757 ) (407,798 ) Accumulated other comprehensive loss before regulatory assets (414,757 ) (407,798 ) Regulatory asset for regulated entities 407,073 400,625 Accumulated other comprehensive loss after regulatory assets (7,684 ) (7,173 ) Deferred income taxes 2,969 2,772 Accumulated other comprehensive loss, net of tax $ (4,715 ) $ (4,401 ) Other Postemployment Benefits December 31, 2016 2015 (Thousands of dollars) Prior service credit (cost) $ 10,211 $ 14,010 Accumulated loss (62,084 ) (50,447 ) Accumulated other comprehensive loss before regulatory assets (51,873 ) (36,437 ) Regulatory asset for regulated entities 51,873 36,437 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 table sets 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 2017 (Thousands of dollars) Prior service credit (cost) $ — $ (4,597 ) Actuarial net loss $ 36,107 $ 6,484
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: 2016 2015 Health care cost-trend rate assumed for next year 7.25% 4.00% - 7.50% Rate to which the cost-trend rate is assumed to decline (the ultimate trend rate) 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 $ 233 $ (232 ) Effect on other postemployment benefit obligation $ 3,937 $ (3,991 )
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 current target allocation for the assets of our other postemployment benefits plan is 30 percent fixed income securities and 70 percent equity securities. 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, 2016 Asset Category Level 1 Level 2 Level 3 Total (Thousands of dollars) Investments: Equity securities (a) $ 371,655 $ 58,987 $ — $ 430,642 Government obligations — 47,445 — 47,445 Corporate obligations (b) — 129,036 — 129,036 Cash and money market funds (c) 13,786 16,114 — 29,900 Insurance contracts and group annuity contracts — — 45,140 45,140 Other investments (d) — 71 57,352 57,423 Total assets $ 385,441 $ 251,653 $ 102,492 $ 739,586 (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, 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. Other Postemployment Benefits December 31, 2016 Asset Category Level 1 Level 2 Level 3 Total (Thousands of dollars) Investments: Equity securities (a) $ 39,817 $ 7,323 $ — $ 47,140 Government obligations — 75 — 75 Corporate obligations (b) — 19,948 — 19,948 Cash and money market funds (c) 74 16,989 — 17,063 Insurance contracts and group annuity contracts — 81,820 — 81,820 Total assets $ 39,891 $ 126,155 $ — $ 166,046 (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. 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.
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, 2015 $ 59,877 $ 57,914 $ 117,791 Net realized and unrealized gains (losses) 2,188 58 2,246 Settlements (5,600 ) — (5,600 ) December 31, 2015 $ 56,465 $ 57,972 $ 114,437 Net realized and unrealized gains (losses) 4,518 (620 ) 3,898 Sales and settlements (15,843 ) — (15,843 ) December 31, 2016 $ 45,140 $ 57,352 $ 102,492
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 2017-2026: Pension Benefits Other Postemployment Benefits to be paid in: (Thousands of dollars) 2017 $ 51,539 $ 16,165 2018 $ 52,660 $ 16,815 2019 $ 53,450 $ 17,073 2020 $ 54,812 $ 17,379 2021 $ 56,033 $ 17,401 2022 through 2026 $ 294,519 $ 86,559

INCOME TAXES (Tables)

INCOME TAXES (Tables)	12 Months Ended
	Dec. 31, 2016
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, 2016 2015 2014 ( Thousands of dollars ) Current income tax provision Federal $ (2,016 ) $ 7,135 $ 17,006 State 471 2,055 1,397 Total current income tax provision (1,545 ) 9,190 18,403 Deferred income tax provision Federal 76,247 56,440 42,024 State 10,541 7,349 7,911 Total deferred income tax provision 86,788 63,789 49,935 Total provision for income taxes $ 85,243 $ 72,979 $ 68,338
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, 2016 2015 2014 ( Thousands of dollars ) Income before income taxes $ 225,338 $ 192,009 $ 178,128 Federal statutory income tax rate 35 % 35 % 35 % Provision for federal income taxes 78,868 67,203 62,345 State income taxes, net of federal tax benefit 7,158 6,114 6,051 Other, net (783 ) (338 ) (58 ) Total provision for income taxes $ 85,243 $ 72,979 $ 68,338
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, 2016 2015 ( Thousands of dollars ) Deferred tax assets Employee benefits and other accrued liabilities $ 123,333 $ 110,148 Net operating loss 23,094 — Other 5,716 7,848 Total deferred tax assets 152,143 117,996 Deferred tax liabilities Excess of tax over book depreciation 990,682 897,667 Purchased-gas cost adjustment 13,822 3,999 Other regulatory assets and liabilities, net 186,207 168,115 Total deferred tax liabilities 1,190,711 1,069,781 Net deferred tax liabilities $ 1,038,568 $ 951,785

COMMITMENTS AND CONTINGENCIES31

COMMITMENTS AND CONTINGENCIES (Tables)	12 Months Ended
	Dec. 31, 2016
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 ) 2017 $ 5.6 2018 5.2 2019 4.4 2020 3.6 2021 3.2 Thereafter 4.4 Total $ 26.4

QUARTERLY FINANCIAL DATA (UNA32

QUARTERLY FINANCIAL DATA (UNAUDITED) (Tables)	12 Months Ended
	Dec. 31, 2016
Schedule of Quarterly Financial Information [Line Items]
Quarterly Financial Data	First Quarter Second Quarter Third Quarter Fourth Quarter Year Ended December 31, 2016 ( Thousands of dollars ) Revenues $ 508,364 $ 245,923 $ 232,191 $ 440,754 Operating income $ 116,073 $ 43,621 $ 30,892 $ 78,534 Net income $ 64,743 $ 20,300 $ 12,737 $ 42,315 Earnings per share Basic $ 1.23 $ 0.39 $ 0.24 $ 0.81 Diluted $ 1.22 $ 0.38 $ 0.24 $ 0.80 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 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

SUMMARY OF SIGNIFICANT ACCOUN33

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) $ in Thousands, number in Millions	12 Months Ended
	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)
Significant Accounting Policies [Line Items]
Operating Loss Carryforwards, Tax Benefit	$ 11,000
Unbilled Receivables, Current	$ 143,200	$ 109,600
Number of natural gas distribution services customers	2
Allowance for Doubtful Accounts Receivable, Current	$ 4,200	3,500
Materials, Supplies, and Other	34,084	33,325
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

CREDIT FACILITY AND SHORT-TER34

CREDIT FACILITY AND SHORT-TERM NOTES PAYABLE (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Line of Credit Facility [Line Items]
Ratio of Indebtedness to Net Capital	0.41
Commercial paper maximum borrowing capacity	$ 700,000
Commercial Paper	145,000	$ 12,500
Letters of Credit Outstanding, Amount	1,500
Short-term Debt	0
Line of Credit Facility, Remaining Borrowing Capacity	$ 553,500
Short-term Debt, Weighted Average Interest Rate	0.95%	0.70%
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	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Cash Payment to ONEOK Upon Separation	$ 0	$ 0	$ 1,130,000
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, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Dividends declared per share of stock		$ 1.40	$ 1.20	$ 0.84
Preferred Stock, Shares Authorized		50
Preferred Stock, Par or Stated Value Per Share		$ 0.01
Common stock authorized and available for issuance		197.7
Stock Repurchase Program, Authorized Amount		$ 20
Common Stock, Dividends, Declared, Annualized Basis		$ 1.40	$ 1.20	$ 0.84
Dividend Declared [Member]
Common Stock, Dividends, Per Share, Declared	$ 0.42
Common Stock, Dividends, Declared, Annualized Basis	$ 1.68

ACCUMULATED OTHER COMPREHENSI37

ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Pension and other postretirement benefit plans, Tax	$ 486	$ (130)
Accumulated Other Comprehensive Income (Loss), beginning balance	(4,401)	(5,174)
Pension and other postretirement benefit plans obligations [Abstract]
Other comprehensive income (loss), before reclassification, net of tax	(776)	209
Amounts reclassified from accumulated other comprehensive income (loss), net of tax	462	564
Other comprehensive loss	(314)	773	$ (1,781)
Accumulated Other Comprehensive Income (Loss), ending balance	(4,715)	(4,401)	(5,174)
Pension and other postretirement benefit plans obligations [Abstract]
Amortization of net loss	40,912	47,494	34,169
Amortization of unrecognized prior service cost	(3,316)	(1,962)	(1,211)
Other comprehensive income (loss) reclassification adjustment, before tax and regulatory adjustments	37,596	45,532	32,958
Other comprehensive income (loss) reclassification - regulatory adjustments	(36,845)	(44,615)	(32,445)
Other comprehensive income (loss) reclassification adjustment, before tax	751	917	513
Other comprehensive income (loss) reclassification adjustment, Tax	(289)	(353)	(198)
Other comprehensive income (loss) reclassification adjustment, net of tax	$ 462	$ 564	$ 315

EARNINGS PER SHARE (Details)

EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
EARNINGS PER SHARE OF COMMON STOCK, BASIC AND DILUTED [Line Items]
Net income	$ 42,315	$ 12,737	$ 20,300	$ 64,743	$ 39,202	$ 7,371	$ 12,076	$ 60,381	$ 140,095	$ 119,030	$ 109,790
Weighted Average Number of Shares Outstanding, Basic									52,453,000	52,578,000	52,364,000
Earnings Per Share, Basic	$ 0.81	$ 0.24	$ 0.39	$ 1.23	$ 0.75	$ 0.14	$ 0.23	$ 1.15	$ 2.67	$ 2.26	$ 2.10
Dilutive Securities, Effect on Basic Earnings Per Share									$ 0	$ 0	$ 0
Weighted Average Number Diluted Shares Outstanding Adjustment									510,000	676,000	582,000
Net Income (Loss) Available to Common Stockholders, Diluted									$ 140,095	$ 119,030	$ 109,790
Weighted Average Number of Shares Outstanding, Diluted									52,963,000	53,254,000	52,946,000
Earnings Per Share, Diluted	$ 0.80	$ 0.24	$ 0.38	$ 1.22	$ 0.74	$ 0.14	$ 0.23	$ 1.13	$ 2.65	$ 2.24	$ 2.07
Common Stock, Shares, Issued	52,598,005				52,598,005				52,598,005	52,598,005

DERIVATIVE FINANCIAL INSTRUME39

DERIVATIVE FINANCIAL INSTRUMENTS AND FAIR VALUE MEASUREMENTS (Details)	12 Months Ended
	Dec. 31, 2016USD ($)MMcf	Dec. 31, 2015USD ($)MMcf
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative, Nonmonetary Notional Amount | MMcf	14,300	17,000
Premiums recorded in other current assets on natural gas contracts held	$ 5,400,000	$ 5,800,000
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	6,500,000	400,000
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Long-term Debt, Fair Value	$ 1,200,000,000	$ 1,200,000,000

REGULATORY ASSETS AND LIABILI40

REGULATORY ASSETS AND LIABILITIES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Jan. 31, 2016
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]
Regulatory Assets, Current	$ 83,146	$ 32,925
Regulatory Assets, Noncurrent	440,522	435,863
Regulatory Liability, Current	(11,922)	(24,615)
Net regulatory assets and liabilities, current	71,224	8,310
Net regulatory assets and liabilities, noncurrent	440,522	426,831
Net Regulatory Assets	511,746	435,141
Amortization of Rate Deferral	$ 3,800	$ 1,600	$ 6,400
Accumulated removal costs [Member]
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]
Regulatory Asset, Amortization Period		up to 50 years
Regulatory Liability, Current		$ 0
Regulatory Liability, Noncurrent		(9,032)
Regulatory Liabilities		$ (9,032)
Weather normalization [Member]
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]
Regulatory Asset, Amortization Period	1 year	1 year
Regulatory Assets, Current	$ 17,661	$ 2,198
Regulatory Assets, Noncurrent	0	0
Regulatory Assets	$ 17,661	$ 2,198
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	$ (10,154)	$ (22,884)
Regulatory Liability, Noncurrent	0	0
Regulatory Liabilities	$ (10,154)	$ (22,884)
Ad valorem tax [Member]
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]
Regulatory Asset, Amortization Period	1 year	1 year
Regulatory Liability, Current	$ (1,768)	$ (1,731)
Regulatory Liability, Noncurrent	0	0
Regulatory Liabilities	(1,768)	(1,731)
Total regulated liabilities [Member]
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]
Regulatory Liability, Current	(11,922)	(24,615)
Regulatory Liability, Noncurrent	0	(9,032)
Regulatory Liabilities	$ (11,922)	$ (33,647)
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	$ 29,901	$ 13,336
Regulatory Assets, Noncurrent	0	0
Regulatory Assets	$ 29,901	$ 13,336
Pension and postretirement benefit costs [Member]
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]
Regulatory Asset, Amortization Period	See Note 11	See Note 11
Regulatory Assets, Current	$ 31,498	$ 15,670
Regulatory Assets, Noncurrent	427,448	425,175
Regulatory Assets	$ 458,946	$ 440,845
Reacquired debt costs [Member]
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]
Regulatory Asset, Amortization Period	11 years	12 years
Regulatory Assets, Current	$ 812	$ 812
Regulatory Assets, Noncurrent	8,108	8,919
Regulatory Assets	$ 8,920	$ 9,731
Other regulatory assets [Member]
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]
Regulatory Asset, Amortization Period	1 to 22 years	1 to 23 years
Regulatory Assets, Current	$ 3,274	$ 909
Regulatory Assets, Noncurrent	4,966	1,769
Regulatory Assets	8,240	2,678
Total regulatory assets, net of amortization [Member]
SCHEDULE OF REGULATED ASSETS AND LIABILITIES [Line Items]
Regulatory Assets, Current	83,146	32,925
Regulatory Assets, Noncurrent	440,522	435,863
Regulatory Assets	$ 523,668	$ 468,788
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 EQUIPMENT41

PROPERTY, PLANT AND EQUIPMENT (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Property, plant and equipment	$ 5,404,168	$ 5,132,682
Accumulated depreciation and amortization	(1,672,548)	(1,620,771)
Net property, plant and equipment	3,731,620	3,511,911
Regulated [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	5,404,168	5,132,682
Accumulated depreciation and amortization	(1,672,548)	(1,620,771)
Net property, plant and equipment	$ 3,731,620	$ 3,511,911
Average depreciation rates, minimum	2.00%	2.00%	2.00%
Average depreciation rates, maximum	3.00%	3.00%	3.00%
Interest costs capitalized	$ 3,600	$ 2,600	$ 2,500
Construction work in process expenditures incurred but not yet paid	11,900	15,000	$ 7,000
Natural gas distribution pipelines and related equipment | Regulated [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	4,321,429	4,114,090
Natural gas transmission pipelines and related equipment | Regulated [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	481,953	462,654
General plant and other | Regulated [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	530,459	498,906
Construction work in process | Regulated [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment	$ 70,327	$ 57,032

SHARE-BASED PAYMENTS (Details)

SHARE-BASED PAYMENTS (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 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	1,100,000
Share-based compensation expense, net of tax	$ 7,000	$ 5,700	$ 7,000
Share-based compensation, tax benefit	$ 4,300	3,500	4,400
Shares remaining	15,603
Employee Stock Award Program Compensation Expense	$ 11,219	9,187	$ 7,613
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]
Award vesting period	3 years
Forfeiture rate maximum (in hundredths)	3.00%
Total compensation cost not yet recognized	$ 2,800
Total compensation cost not yet recognized, period for recognition	1 year 8 months 18 days
Fair value of vested shares	$ 4,500	$ 6,500
Nonvested beginning balance (in units)	231,258
Nonvested beginning balance (in dollars per unit)	$ 32.59
Granted (in units)	42,935
Weighted -average grant date fair value (per unit)	$ 58.30	$ 41.40	$ 33.19
Vested (in units)	(77,033)
Vested (in dollars per unit)	$ 23.76
Forfeited (in units)	(2,260)
Forfeited (in dollars per unit)	$ 38.04
Nonvested ending balance (in units)	194,900	231,258
Nonvested ending balance (in dollars per unit)	$ 41.68	$ 32.59
Fair value of shares granted (thousands of dollars)	$ 2,503	$ 3,141	$ 3,149
Performance Unit Awards [Member]
Share-based Payments [Line Items]
Award vesting period	3 years
Forfeiture rate maximum (in hundredths)	3.00%
Total compensation cost not yet recognized	$ 4,800
Total compensation cost not yet recognized, period for recognition	1 year 8 months 12 days
Fair value of vested shares	$ 19,500	$ 23,500
Nonvested beginning balance (in units)	439,250
Nonvested beginning balance (in dollars per unit)	$ 27.35
Granted (in units)	74,395
Weighted -average grant date fair value (per unit)	$ 64.06	$ 44.48	$ 35.98
Vested (in units)	(221,882)
Vested (in dollars per unit)	$ 15.11
Forfeited (in units)	(2,952)
Forfeited (in dollars per unit)	$ 41.44
Nonvested ending balance (in units)	288,811	439,250
Nonvested ending balance (in dollars per unit)	$ 46.06	$ 27.35
Fair value of shares granted (thousands of dollars)	$ 4,766	$ 4,486	$ 4,462
Expected volatility rate	18.20%	15.90%	18.40%
Expected dividend yield	2.40%	2.90%	3.37%
Risk-free interest rate	0.91%	1.10%	0.67%
Description	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.
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	41.00%	40.00%	36.00%
Shares sold under employee stock purchase plan	83,431	51,092	51,418
Share price of shares sold under Employee Stock Purchase Plan in dollars per share	$ 54.51	$ 36.15	$ 32.29
Employee Stock Purchase Plan Compensation Expense	$ 1,400	$ 1,300	$ 400
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	50,573	23,506	35,324
Employee Stock Award Program Compensation Expense	$ 3,000	$ 1,100	$ 2,500

EMPLOYEE BENEFIT PLANS (Details

EMPLOYEE BENEFIT PLANS (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan Assumptions Used To Determine Benefit Obligations Rate of Compensation Increase, Minimum	3.25%		3.25%	3.35%
Defined Benefit Plan Assumptions Used To Determine Benefit Obligations Rate of Compensation Increase, Maximum	3.40%		3.40%	3.40%
Compensation increase rate - minimum	3.35%	3.35%		3.30%	3.35%
Compensation increase rate- maximum	3.40%	3.40%		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.
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefits paid	$ (18,100)
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Benefits paid	(18,100)
Noncurrent liabilities	(303,507)		$ (303,507)	$ (272,309)
Benefits paid	$ (18,100)
Assets expected to be withdrawn or returned			0
Amortization of unrecognized prior service cost			$ (3,316)	(1,962)	$ (1,211)
Amortization of loss			40,912	47,494	34,169
Total recognized in other comprehensive income (loss)			(314)	$ 773	(1,781)
Amount recognized in other comprehensive income			$ 0
Health care cost-trend rate assumed for next year			7.25%
Rate to which the cost-trend rate is assumed to decline (the ultimate trend rate)			5.00%
Year that the rate reaches the ultimate trend rate	2,022		2,022	2,022
Target asset allocation			100.00%
US Large-Cap Equity [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Target asset allocation			37.40%
Investment-grade bonds [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Target asset allocation			30.00%
Developed foreign large-cap equities [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Target asset allocation			10.60%
Alternative investments [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Target asset allocation			7.70%
Mid-cap equities [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Target asset allocation			5.60%
Emerging market equities [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Target asset allocation			5.00%
Small-cap equities [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Target asset allocation			3.70%
Equity Securities [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Target Allocation Percentage			.7
Fixed Income Funds [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Target Allocation Percentage			.3
Pension Plan [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost			$ 31,965	$ 37,952	$ 27,071
Plan amendment			$ 0	$ 0
Discount rate	4.30%		4.30%	4.75%
Weighted average discount rate	4.75%	4.75%			5.25%
Expected long-term return on plan assets	7.75%	7.75%		7.75%	7.75%
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation, beginning of period		$ 985,624	$ 985,624	$ 1,028,171
Service cost			12,055	13,660	$ 11,620
Interest cost			45,550	43,542	43,791
Plan participants' contributions			0	0
Actuarial loss (gain)			25,886	(47,607)
Plan amendment			0	0
Benefits paid			(71,066)	(52,142)
Settlements			(31,518)	0
Benefit obligation, end of period	$ 966,531		966,531	985,624	1,028,171
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period		785,161	785,161	845,396
Actual return on plan assets			48,768	(9,026)
Employer contributions			12,441	933
Plan participants' contributions			0	0
Benefits paid			(71,066)	(52,142)
Settlements			(35,718)	0
Fair value of plan assets, end of period	739,586		739,586	785,161	845,396
Balance at December 31	(226,945)		(226,945)	(200,463)
Current liabilities	(941)		(941)	(912)
Noncurrent liabilities	(226,004)		(226,004)	(199,551)
Balance at December 31	(226,945)		(226,945)	(200,463)
Benefits paid			(71,066)	(52,142)
Accumulated benefit obligation	912,400		912,400	934,300
Service cost			12,055	13,660	11,620
Interest cost			45,550	43,542	43,791
Expected return on assets			(61,183)	(61,769)	(59,862)
Amortization of unrecognized prior service cost			0	266	549
Amortization of loss			35,543	42,226	30,200
Settlements			0	27	773
Net periodic benefit cost			31,965	37,952	27,071
Net loss arising during the period			(1,262)	339	(3,543)
Amortization of loss			751	917	518
Deferred income taxes			197	(483)	1,244
Total recognized in other comprehensive income (loss)			314	(773)	1,781
Prior service credit (cost)	0		0	0
Accumulated loss	(414,757)		(414,757)	(407,798)
Accumulated other comprehensive loss before regulatory assets	(414,757)		(414,757)	(407,798)
Regulatory asset for regulated entities	407,073		407,073	400,625
Accumulated other comprehensive loss after regulatory assets	(7,684)		(7,684)	(7,173)
Deferred income taxes	2,969		2,969	2,772
Accumulated other comprehensive loss, net of tax	(4,715)		(4,715)	(4,401)
Prior service credit (cost) expected to be recognized in following fiscal year	0		0
Actuarial net loss, to be recognized in 2017	36,107		36,107
Effect of a one percentage point change on total of service and interest cost - increase			233
Effect of a one percentage point change on other postemployment benefit obligation - increase			3,937
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Level 3 fair value measurement, January 1		114,437	114,437	117,791
Net realized and unrealized gains (losses)			3,898	2,246
Settlements			(15,843)	(5,600)
Level 3 fair value measurement, December 31	102,492		102,492	114,437	117,791
Employer contributions			12,441	933
Expected employer contributions in 2017			1,000
2,017	51,539		51,539
2,018	52,660		52,660
2,019	53,450		53,450
2,020	54,812		54,812
2,021	56,033		56,033
2022 through 2027	294,519		294,519
Pension Plan [Member] | Equity Securities [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period		468,085	468,085
Fair value of plan assets, end of period	430,642		430,642	468,085
Pension Plan [Member] | Government Obligations [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period		44,651	44,651
Fair value of plan assets, end of period	47,445		47,445	44,651
Pension Plan [Member] | Corporate Obligations [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period		139,396	139,396
Fair value of plan assets, end of period	129,036		129,036	139,396
Pension Plan [Member] | Cash and Money Market Funds [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period		15,708	15,708
Fair value of plan assets, end of period	29,900		29,900	15,708
Pension Plan [Member] | Insurance contracts and group annuity contracts [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period		56,465	56,465
Fair value of plan assets, end of period	45,140		45,140	56,465
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Level 3 fair value measurement, January 1		56,465	56,465	59,877
Net realized and unrealized gains (losses)			4,518	2,188
Settlements			(15,843)	(5,600)
Level 3 fair value measurement, December 31	45,140		45,140	56,465	59,877
Pension Plan [Member] | Other Investments [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period		60,856	60,856
Fair value of plan assets, end of period	57,423		57,423	60,856
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Level 3 fair value measurement, January 1		57,972	57,972	57,914
Net realized and unrealized gains (losses)			(620)	58
Settlements			0	0
Level 3 fair value measurement, December 31	57,352		57,352	57,972	57,914
Pension Plan [Member] | Level 1 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period		414,248	414,248
Fair value of plan assets, end of period	385,441		385,441	414,248
Pension Plan [Member] | Level 1 [Member] | Equity Securities [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period		405,935	405,935
Fair value of plan assets, end of period	371,655		371,655	405,935
Pension Plan [Member] | Level 1 [Member] | Government Obligations [Member]
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
Pension Plan [Member] | Level 1 [Member] | Corporate Obligations [Member]
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
Pension Plan [Member] | Level 1 [Member] | Cash and Money Market Funds [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period		5,429	5,429
Fair value of plan assets, end of period	13,786		13,786	5,429
Pension Plan [Member] | Level 1 [Member] | Insurance contracts and group annuity contracts [Member]
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
Pension Plan [Member] | Level 1 [Member] | Other Investments [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period		2,884	2,884
Fair value of plan assets, end of period	0		0	2,884
Pension Plan [Member] | Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period		256,476	256,476
Fair value of plan assets, end of period	251,653		251,653	256,476
Pension Plan [Member] | Level 2 [Member] | Equity Securities [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period		62,150	62,150
Fair value of plan assets, end of period	58,987		58,987	62,150
Pension Plan [Member] | Level 2 [Member] | Government Obligations [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period		44,651	44,651
Fair value of plan assets, end of period	47,445		47,445	44,651
Pension Plan [Member] | Level 2 [Member] | Corporate Obligations [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period		139,396	139,396
Fair value of plan assets, end of period	129,036		129,036	139,396
Pension Plan [Member] | Level 2 [Member] | Cash and Money Market Funds [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period		10,279	10,279
Fair value of plan assets, end of period	16,114		16,114	10,279
Pension Plan [Member] | Level 2 [Member] | Insurance contracts and group annuity contracts [Member]
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
Pension Plan [Member] | Level 2 [Member] | Other Investments [Member]
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	71		71	0
Pension Plan [Member] | Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period		114,437	114,437
Fair value of plan assets, end of period	102,492		102,492	114,437
Pension Plan [Member] | Level 3 [Member] | Equity Securities [Member]
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
Pension Plan [Member] | Level 3 [Member] | Government Obligations [Member]
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
Pension Plan [Member] | Level 3 [Member] | Corporate Obligations [Member]
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
Pension Plan [Member] | Level 3 [Member] | Cash and Money Market Funds [Member]
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
Pension Plan [Member] | Level 3 [Member] | Insurance contracts and group annuity contracts [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period		56,465	56,465
Fair value of plan assets, end of period	45,140		45,140	56,465
Pension Plan [Member] | Level 3 [Member] | Other Investments [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period		$ 57,972	57,972
Fair value of plan assets, end of period	$ 57,352		57,352	57,972
Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Net periodic benefit cost			$ 2,593	5,033	$ 5,889
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
Plan amendment			$ 483	$ 11,901
Discount rate	4.20%		4.20%	4.75%
Weighted average discount rate	3.75%	4.75%			5.00%
Expected long-term return on plan assets	7.75%	8.00%		7.75%	7.75%
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation, beginning of period		$ 228,253	$ 228,253	$ 257,688
Service cost			2,675	3,257	$ 3,468
Interest cost			10,235	10,628	11,605
Plan participants' contributions			3,043	2,915
Actuarial loss (gain)			14,309	(19,702)
Plan amendment			483	11,901
Benefits paid			(15,450)	(14,632)
Settlements			0	0
Benefit obligation, end of period	$ 243,548		243,548	228,253	257,688
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period		155,495	155,495	151,777
Actual return on plan assets			9,733	1,335
Employer contributions			13,225	14,100
Plan participants' contributions			3,043	2,915
Benefits paid			(15,450)	(14,632)
Settlements			0	0
Fair value of plan assets, end of period	166,046		166,046	155,495	151,777
Balance at December 31	(77,502)		(77,502)	(72,758)
Current liabilities	0		0	0
Noncurrent liabilities	(77,502)		(77,502)	(72,758)
Balance at December 31	(77,502)		(77,502)	(72,758)
Benefits paid			(15,450)	(14,632)
Service cost			2,675	3,257	3,468
Interest cost			10,235	10,628	11,605
Expected return on assets			(12,370)	(11,892)	(11,393)
Amortization of unrecognized prior service cost			(3,316)	(2,228)	(1,760)
Amortization of loss			5,369	5,268	3,969
Net periodic benefit cost			2,593	5,033	5,889
Amortization of loss				0
Prior service credit (cost)	10,211		10,211	14,010
Accumulated loss	(62,084)		(62,084)	(50,447)
Accumulated other comprehensive loss before regulatory assets	(51,873)		(51,873)	(36,437)
Regulatory asset for regulated entities	51,873		51,873	36,437
Accumulated other comprehensive loss after regulatory assets	0		0	0
Deferred income taxes	0		0	0
Accumulated other comprehensive loss, net of tax	0		0	0
Prior service credit (cost) expected to be recognized in following fiscal year	(4,597)		(4,597)
Actuarial net loss, to be recognized in 2017	6,484		6,484
Effect of a one percentage point change on total of service and interest cost - decrease			(232)
Effect of a one percentage point change on other postemployment benefit obligation - decrease			(3,991)
Defined Benefit Plan, Change in Fair Value of Plan Assets, Level 3 Reconciliation [Roll Forward]
Employer contributions			13,225	14,100
Expected employer contributions in 2017			3,100
2,017	16,165		16,165
2,018	16,815		16,815
2,019	17,073		17,073
2,020	17,379		17,379
2,021	17,401		17,401
2022 through 2027	86,559		86,559
Other Postretirement Benefit Plan [Member] | Equity Securities [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period		62,058	62,058
Fair value of plan assets, end of period	47,140		47,140	62,058
Other Postretirement Benefit Plan [Member] | Government Obligations [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period		64	64
Fair value of plan assets, end of period	75		75	64
Other Postretirement Benefit Plan [Member] | Corporate Obligations [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period		200	200
Fair value of plan assets, end of period	19,948		19,948	200
Other Postretirement Benefit Plan [Member] | Cash and Money Market Funds [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period		13,555	13,555
Fair value of plan assets, end of period	17,063		17,063	13,555
Other Postretirement Benefit Plan [Member] | Insurance contracts and group annuity contracts [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period		79,531	79,531
Fair value of plan assets, end of period	81,820		81,820	79,531
Other Postretirement Benefit Plan [Member] | Other Investments [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period		87	87
Fair value of plan assets, end of period				87
Other Postretirement Benefit Plan [Member] | Level 1 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period		54,797	54,797
Fair value of plan assets, end of period	39,891		39,891	54,797
Other Postretirement Benefit Plan [Member] | Level 1 [Member] | Equity Securities [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period		54,560	54,560
Fair value of plan assets, end of period	39,817		39,817	54,560
Other Postretirement Benefit Plan [Member] | Level 1 [Member] | Government Obligations [Member]
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 Postretirement Benefit Plan [Member] | Level 1 [Member] | Corporate Obligations [Member]
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 Postretirement Benefit Plan [Member] | Level 1 [Member] | Cash and Money Market Funds [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period		233	233
Fair value of plan assets, end of period	74		74	233
Other Postretirement Benefit Plan [Member] | Level 1 [Member] | Insurance contracts and group annuity contracts [Member]
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 Postretirement Benefit Plan [Member] | Level 1 [Member] | Other Investments [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period		4	4
Fair value of plan assets, end of period				4
Other Postretirement Benefit Plan [Member] | Level 2 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period		100,615	100,615
Fair value of plan assets, end of period	126,155		126,155	100,615
Other Postretirement Benefit Plan [Member] | Level 2 [Member] | Equity Securities [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period		7,498	7,498
Fair value of plan assets, end of period	7,323		7,323	7,498
Other Postretirement Benefit Plan [Member] | Level 2 [Member] | Government Obligations [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period		64	64
Fair value of plan assets, end of period	75		75	64
Other Postretirement Benefit Plan [Member] | Level 2 [Member] | Corporate Obligations [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period		200	200
Fair value of plan assets, end of period	19,948		19,948	200
Other Postretirement Benefit Plan [Member] | Level 2 [Member] | Cash and Money Market Funds [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period		13,322	13,322
Fair value of plan assets, end of period	16,989		16,989	13,322
Other Postretirement Benefit Plan [Member] | Level 2 [Member] | Insurance contracts and group annuity contracts [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period		79,531	79,531
Fair value of plan assets, end of period	81,820		81,820	79,531
Other Postretirement Benefit Plan [Member] | Level 2 [Member] | Other Investments [Member]
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
Other Postretirement Benefit Plan [Member] | Level 3 [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period		83	83
Fair value of plan assets, end of period	0		0	83
Other Postretirement Benefit Plan [Member] | Level 3 [Member] | Equity Securities [Member]
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 Postretirement Benefit Plan [Member] | Level 3 [Member] | Government Obligations [Member]
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 Postretirement Benefit Plan [Member] | Level 3 [Member] | Corporate Obligations [Member]
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 Postretirement Benefit Plan [Member] | Level 3 [Member] | Cash and Money Market Funds [Member]
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 Postretirement Benefit Plan [Member] | Level 3 [Member] | Insurance contracts and group annuity contracts [Member]
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 Postretirement Benefit Plan [Member] | Level 3 [Member] | Other Investments [Member]
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets, beginning of period		$ 83	$ 83
Fair value of plan assets, end of period				$ 83
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%
Rate to which the cost-trend rate is assumed to decline (the ultimate trend rate)				5.00%
Maximum [Member] | Pension Plan [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Weighted average discount rate				4.75%
Maximum [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Weighted average discount rate				4.75%
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%
Rate to which the cost-trend rate is assumed to decline (the ultimate trend rate)				4.00%
Minimum [Member] | Pension Plan [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Weighted average discount rate				4.25%
Minimum [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plans and Other Postemployment Benefit Plans Table Text Block [Line Items]
Weighted average discount rate				4.25%
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			$ 10,800	$ 10,200
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.					9,700
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			$ 6,000	$ 6,500
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.					$ 4,000

INCOME TAXES (Details)

INCOME TAXES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Deferred Tax Assets, Operating Loss Carryforwards, Domestic	$ 63,000
Operating Loss Carryforwards, Tax Benefit	11,000
Deferred Tax Assets, Operating Loss Carryforwards, State and Local	21,000
Income taxes receivable	1,397	$ 38,877
Current income tax provision (benefit)
Federal	(2,016)	7,135	$ 17,006
State	471	2,055	1,397
Total current income tax provision (benefit)	(1,545)	9,190	18,403
Deferred income tax provision
Federal	76,247	56,440	42,024
State	10,541	7,349	7,911
Total deferred income tax provision	86,788	63,789	49,935
Income Tax Reconciliation [Abstract]
Income before income taxes	$ 225,338	$ 192,009	$ 178,128
Federal statutory income tax rate	35.00%	35.00%	35.00%
Provision for federal income taxes	$ 78,868	$ 67,203	$ 62,345
State income taxes, net of federal benefit	7,158	6,114	6,051
Other, net	(783)	(338)	(58)
Income tax provision	85,243	72,979	$ 68,338
Deferred tax assets
Deferred tax assets, employee benefits and other accrued liabilities	123,333	110,148
Net operating loss	23,094	0
Other	5,716	7,848
Total deferred tax assets	152,143	117,996
Deferred tax liabilities
Excess of tax over book depreciation	990,682	897,667
Purchased-gas cost adjustment	13,822	3,999
Other regulatory assets and liabilities, net	186,207	168,115
Total deferred tax liabilities	1,190,711	1,069,781
Net deferred tax liabilities	$ 1,038,568	$ 951,785
Minimum [Member]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2024
Maximum [Member]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2036

COMMITMENTS AND CONTINGENCIES -

COMMITMENTS AND CONTINGENCIES - Part 1 (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating Leased Assets [Line Items]
Operating Leases, Rent Expense	$ 8.6	$ 5	$ 5
Operating Leases, Future Minimum Payments Due [Abstract]
2,017	5.6
2,018	5.2
2,019	4.4
2,020	3.6
2,021	3.2
Thereafter	4.4
Total	$ 26.4

COMMITMENTS AND CONTINGENCIES46

COMMITMENTS AND CONTINGENCIES - Part 2 (Details)	12 Months Ended
	Dec. 31, 2016
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 with ongoing groundwater monitoring	8
Number Of Sites Soil Remediation Is Completed Or Near Completion	11
Number of sites where regulatory closure has been achieved	3
Environmental Reserve Estimate Range, Low	4
Environmental Reserve Estimate Range, High	7
Environmental Reserve Estimate, Actual	4
Percentage yield of high consequence pipeline areas	30.00%

QUARTERLY FINANCIAL DATA (UNA47

QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Quarterly Financial Information [Line Items]
Revenues	$ 440,754	$ 232,191	$ 245,923	$ 508,364	$ 389,149	$ 225,226	$ 256,786	$ 676,531	$ 1,427,232	$ 1,547,692	$ 1,818,906
Net margin									885,435	841,733	826,957
Operating income	78,534	30,892	43,621	116,073	73,903	24,951	31,270	109,005	269,120	239,129	225,294
Net income	$ 42,315	$ 12,737	$ 20,300	$ 64,743	$ 39,202	$ 7,371	$ 12,076	$ 60,381	$ 140,095	$ 119,030	$ 109,790
Basic	$ 0.81	$ 0.24	$ 0.39	$ 1.23	$ 0.75	$ 0.14	$ 0.23	$ 1.15	$ 2.67	$ 2.26	$ 2.10
Diluted	$ 0.80	$ 0.24	$ 0.38	$ 1.22	$ 0.74	$ 0.14	$ 0.23	$ 1.13	$ 2.65	$ 2.24	$ 2.07