ONEOK (OKE) 10-Q 2 May 18 2018 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2018	Apr. 23, 2018
Document Information [Line Items]
Entity Registrant Name	ONEOK INC /NEW/
Entity Central Index Key	1,039,684
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 Common Stock, Shares Outstanding		411,076,188
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q1
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2018

CONSOLIDATED STATEMENTS OF INCO

CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenues
Commodity sales	$ 2,820,004	$ 2,216,717
Services	282,073	532,894
Total revenues	3,102,077	2,749,611
Cost of sales and fuel (exclusive of items shown separately below)	2,368,026	2,143,843
Operations and maintenance	181,181	162,052
Depreciation and amortization	104,237	99,419
General taxes	29,023	27,153
(Gain) loss on sale of assets	(89)	7
Operating income	419,699	317,137
Equity in net earnings from investments (Note I)	40,187	39,564
Allowance for equity funds used during construction	230	13
Other income	738	4,341
Other expense	(3,309)	(3,467)
Interest expense (net of capitalized interest of $2,038, and $1,441, respectively)	(115,725)	(116,462)
Income before income taxes	341,820	241,126
Income taxes	(75,771)	(54,941)
Net income	266,049	186,185
Less: Net income attributable to noncontrolling interests	1,541	98,824
Net income attributable to ONEOK	264,508	87,361
Less: Preferred stock dividends	275	0
Net income available to common shareholders	$ 264,233	$ 87,361
Basic earnings per common share	$ 0.65	$ 0.41
Diluted earnings per common share	$ 0.64	$ 0.41
Average shares (thousands)
Basic	409,676	211,619
Diluted	412,173	213,602
Dividends declared per share of common stock	$ 0.770	$ 0.615

CONSOLIDATED STATEMENT OF INCOM

CONSOLIDATED STATEMENT OF INCOME (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Interest expense (net of capitalized interest)	$ 2,038	$ 1,441

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Net income	$ 266,049	$ 186,185
Other comprehensive income (loss), net of tax
Unrealized gains (losses) on derivatives, net of tax of $(10,312) and $(4,401), respectively	34,524	24,456
Realized (gains) losses on derivatives recognized in net income, net of tax of $(3,578) and $(3,365), respectively	11,976	17,283
Change in pension and postretirement benefit plan liability, net of tax of $(781) and $(1,360) respectively.	2,615	2,041
Other comprehensive income (loss) on investments in unconsolidated affiliates, net of tax of $(844) and $(58), respectively	2,824	325
Total other comprehensive income (loss), net of tax	51,939	44,105
Comprehensive income	317,988	230,290
Less: Comprehensive income attributable to noncontrolling interests	1,541	127,641
Comprehensive income attributable to ONEOK	$ 316,447	$ 102,649

CONSOLIDATED STATEMENTS OF COM5

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (PARANTHETICAL) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Unrealized Gains (Losses) on Derivatives, Tax	$ (10,312)	$ (4,401)
Realized (Gains) Losses on Derivatives in Net Income, Tax	(3,578)	(3,365)
Change in Pension and Postretirement Benefit Plan Liability, Tax	(781)	(1,360)
Other Comprehensive Income (Loss) on Investments in Unconsolidated Affiliates, Tax	$ (844)	$ (58)

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current assets
Cash and cash equivalents	$ 17,474	$ 37,193
Accounts receivable, net	844,218	1,202,951
Materials and supplies	98,695	90,301
Natural gas and natural gas liquids in storage	185,298	342,293
Commodity imbalances	38,993	38,712
Other current assets	106,067	53,008
Total current assets	1,290,745	1,764,458
Property, plant and equipment
Property, plant and equipment	15,838,443	15,559,667
Accumulated depreciation and amortization	2,960,254	2,861,541
Net property, plant and equipment	12,878,189	12,698,126
Investments and other assets
Investments in unconsolidated affiliates	997,380	1,003,156
Goodwill and intangible assets	990,485	993,460
Deferred income taxes	116,120	205,907
Other assets	159,428	180,830
Total investments and other assets	2,263,413	2,383,353
Total assets	16,432,347	16,845,937
Current liabilities
Current maturities of long-term debt (Note D)	932,650	432,650
Short-term borrowings (Note D)	0	614,673
Accounts payable	773,054	1,140,571
Commodity imbalances	124,687	164,161
Accrued interest	97,525	135,309
Other current liabilities	122,922	179,971
Total current liabilities	2,050,838	2,667,335
Long-term debt, excluding current maturities (Note D)	7,091,751	8,091,629
Deferred income taxes	53,805	52,697
Other deferred credits	366,701	348,924
Total deferred credits and other liabilities	420,506	401,621
Commitments and contingencies (Note J)
Equity (Note E)
Preferred stock, $0.01 par value: issued 20,000 shares at March 31, 2018 and December 31, 2017	0	0
Common stock, $0.01 par value:authorized 1,200,000,000 shares, issued 445,016,234 shares and outstanding411,073,529 shares at March 31, 2018; issued 423,166,234 shares and outstanding 388,703,543 shares at December 31, 2017	4,450	4,232
Paid-in Capital	7,735,173	6,588,878
Accumulated other comprehensive loss (Note F)	(174,692)	(188,530)
Retained Earnings	0	0
Treasury stock, at cost: 33,942,705 shares at March 31, 2018, and 34,462,691 shares at December 31, 2017	(863,485)	(876,713)
Total ONEOK Shareholders' Equity	6,701,446	5,527,867
Noncontrolling interests in consolidated subsidiaries	167,806	157,485
Total equity	6,869,252	5,685,352
Total liabilities and equity	$ 16,432,347	$ 16,845,937

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Mar. 31, 2018	Dec. 31, 2017
Equity (Note E)
Common stock, shares, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares, authorized (in shares)	1,200,000,000	1,200,000,000
Common stock, shares, issued (in shares)	445,016,234	423,166,234
Common stock, shares, outstanding (in shares)	411,073,529	388,703,543
Treasury stock, shares (in shares)	33,942,705	34,462,691
Preferred stock, shares, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares, issued (in shares)	20,000	20,000

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating activities
Net income	$ 266,049	$ 186,185
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	104,237	99,419
Equity in net earnings from investments	(40,187)	(39,564)
Distributions received from unconsolidated affiliates	41,095	39,520
Deferred income taxes	74,890	53,397
Share-based compensation expense	7,203	5,907
Pension and postretirement benefit expense, net of contributions	(8,393)	(5,018)
Allowance for equity funds used during construction	(230)	(13)
(Gain) loss on sale of assets	(89)	7
Changes in assets and liabilities:
Accounts receivable	358,733	137,586
Natural gas and natural gas liquids in storage	149,825	(53,305)
Accounts payable	(361,008)	(122,843)
Commodity imbalances, net	(39,755)	1,888
Settlement of exit activities liabilities	(1,580)	(4,119)
Accrued interest	(37,784)	(22,363)
Risk-management assets and liabilities	34,387	45,977
Other assets and liabilities, net	(52,072)	(53,571)
Cash provided by operating activities	495,321	269,090
Investing activities
Capital expenditures (less allowance for equity funds used during construction)	(264,467)	(112,737)
Contributions to unconsolidated affiliates	(147)	(4,422)
Distributions received from unconsolidated affiliates in excess of cumulative earnings	8,721	7,400
Proceeds from sale of assets	241	296
Cash used in investing activities	(255,652)	(109,463)
Financing activities
Dividends paid	(316,408)	(129,842)
Distributions to noncontrolling interests	(1,500)	(136,680)
Borrowing (repayment) of short-term borrowings, net	(614,673)	180,452
Repayment of long-term debt	(501,913)	(1,951)
Issuance of common stock	1,182,117	3,722
Other, net	(7,011)	(13,395)
Cash used in financing activities	(259,388)	(97,694)
Change in cash and cash equivalents	(19,719)	61,933
Cash and cash equivalents at beginning of period	37,193	248,875
Cash and cash equivalents at end of period	$ 17,474	$ 310,808

CONSOLIDATED STATEMENT OF CHANG

CONSOLIDATED STATEMENT OF CHANGES IN EQUITY - USD ($) $ in Thousands	Total	Common Stock	Preferred Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Treasury Stock	Noncontrolling Interests in Consolidated Subsidiaries
Cumulative effect adjustment for adoption of ASUs	$ 73,368	$ 0	$ 0	$ 0	$ 0	$ 73,368	$ 0	$ 0
Shares, issued, beginning balance at Dec. 31, 2016		245,811,180	0
Total equity, beginning balance at Dec. 31, 2016	3,428,915	$ 2,458	$ 0	1,234,314	(154,350)	0	(893,677)	3,240,170
Net income	186,185	0	0	0	0	87,361	0	98,824
Other comprehensive income (loss) (Note F)	44,105	0	0	0	15,288	0	0	28,817
Common Stock Issued	3,201	$ 0	0	(2,506)	0	0	5,707	0
Stock Issued During Period, Shares, Other		0
Common stock dividends	(129,842)	$ 0	0	0	0	(129,842)	0	0
Distributions to Noncontrolling Interests	(136,680)	0	0	0	0	0	0	(136,680)
Other	261	$ 0	$ 0	261	0	0	0	0
Shares, issued, ending balance at Mar. 31, 2017		245,811,180	0
Total equity, ending balance at Mar. 31, 2017	3,469,513	$ 2,458	$ 0	1,232,069	(139,062)	30,887	(887,970)	3,231,131
Cumulative effect adjustment for adoption of ASUs	1,719	$ 0	$ 0	0	(38,101)	39,803	0	17
Shares, issued, beginning balance at Dec. 31, 2017		423,166,234	20,000
Total equity, beginning balance at Dec. 31, 2017	5,685,352	$ 4,232	$ 0	6,588,878	(188,530)	0	(876,713)	157,485
Net income	266,049	0	0	0	0	264,508	0	1,541
Other comprehensive income (loss) (Note F)	51,939	0	0	0	51,939	0	0	0
Common Stock Issued	1,182,693	$ 218	0	1,169,247	0	0	13,228	0
Stock Issued During Period, Shares, Other		21,850,000
Common stock dividends	(316,271)	$ 0	0	(11,960)	0	(304,311)	0	0
Preferred stock dividends	(275)	0	0	(275)	0	0	0	0
Distributions to Noncontrolling Interests	(1,500)	0	0	0	0	0	0	(1,500)
Contributions from noncontrolling interests	10,263	0	0	0	0	0	0	10,263
Other	(10,717)	$ 0	$ 0	(10,717)	0	0	0	0
Shares, issued, ending balance at Mar. 31, 2018		445,016,234	20,000
Total equity, ending balance at Mar. 31, 2018	$ 6,869,252	$ 4,450	$ 0	$ 7,735,173	$ (174,692)	$ 0	$ (863,485)	$ 167,806

CONSOLIDATED STATEMENT OF CHA10

CONSOLIDATED STATEMENT OF CHANGES IN EQUITY CONSOLIDATED STATEMENT OF CHANGES IN EQUITY Parenthetical - $ / shares	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Stockholders' Equity [Abstract]
Dividends paid (in dollars per share)	$ 0.770	$ 0.615

SUMMARY OF SIGNIFICANT ACCOUNTI

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Notes)	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Significant Accounting Policies [Text Block]	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Our accompanying unaudited consolidated financial statements have been prepared pursuant to the rules and regulations of the SEC. These statements have been prepared in accordance with GAAP and reflect all adjustments that, in our opinion, are necessary for a fair statement of the results for the interim periods presented. All such adjustments are of a normal recurring nature. The 2017 year-end Consolidated Balance Sheet data was derived from our audited financial statements but does not include all disclosures required by GAAP. Certain reclassifications have been made in the prior-year financial statements to conform to the current year presentation. These unaudited consolidated financial statements should be read in conjunction with our audited consolidated financial statements in our Annual Report. Merger Transaction - On June 30, 2017, we completed the acquisition of all of the outstanding common units of ONEOK Partners that we did not already own at a fixed exchange ratio of 0.985 of a share of our common stock for each ONEOK Partners common unit. We issued 168.9 million shares of our common stock to third-party common unitholders of ONEOK Partners in exchange for all of the 171.5 million outstanding common units of ONEOK Partners that we previously did not own. As a result of the completion of the Merger Transaction, common units of ONEOK Partners are no longer publicly traded. Prior to June 30, 2017, we and our subsidiaries owned all of the general partner interest, which included incentive distribution rights, and a portion of the limited partner interest, which together represented a 41.2 percent ownership interest in ONEOK Partners. The earnings of ONEOK Partners that are attributed to its units held by the public until June 30, 2017, are reported as “Net income attributable to noncontrolling interest” in our accompanying Consolidated Statements of Income. Our general partner incentive distribution rights effectively terminated at the closing of the Merger Transaction. Our significant accounting policies are consistent with those disclosed in Note A of the Notes to Consolidated Financial Statements in our Annual Report, except as described below for accounting standards adopted this quarter. Recently Issued Accounting Standards Update - Changes to GAAP are established by the Financial Accounting Standards Board (FASB) in the form of ASUs to the FASB Accounting Standards Codification. We consider the applicability and impact of all ASUs. ASUs not listed below were assessed and determined to be either not applicable or clarifications of ASUs listed below. We also exclude ASUs not yet adopted that were disclosed in our Annual Report to not materially impact us. The following tables provide a brief description of recent accounting pronouncements and our analysis of the effects on our financial statements: Standard Description Date of Adoption Effect on the Financial Statements or Other Significant Matters Standards that were adopted ASU 2014-09, “Revenue from Contracts with Customers (Topic 606)” The standard outlines the principles an entity must apply to measure and recognize revenue for entities that enter into contracts to provide goods or services to their customers. The core principle is that an entity should recognize revenue at an amount that reflects the consideration to which the entity expects to be entitled in exchange for transferring goods or services to a customer. The amendment also requires more extensive disaggregated revenue disclosures in interim and annual financial statements. First quarter 2018 We adopted this standard on January 1, 2018, using the modified retrospective method. We recognized the cumulative effect of adopting the new revenue standard as an increase to beginning retained earnings of $1.7 million. Results for reporting periods beginning after January 1, 2018, are presented under the new standard, while prior periods are not adjusted and continue to be reported under the accounting standards in effect for those periods. The adoption of Topic 606 was not material to our net income; however, a significant portion of amounts historically presented as services revenues are now presented as a reduction to cost of sales and fuel. See Note K for discussion of these changes and additional disclosures. Standard Description Date of Adoption Effect on the Financial Statements or Other Significant Matters Standards that were adopted ( continued ) ASU 2016-01, “Financial Instruments-Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities” The standard requires all equity investments, other than those accounted for using the equity method of accounting or those that result in consolidation of the investee, to be measured at fair value with changes in fair value recognized in net income, eliminates the available-for-sale classification for equity securities with readily determinable fair values and eliminates the cost method for equity investments without readily determinable fair values. First quarter 2018 We do not have any equity investments classified as available-for-sale or accounted for using the cost method, therefore, the impact of adopting of this standard was not material. ASU 2016-15, “Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments” The standard clarifies the classification of certain cash receipts and cash payments on the statement of cash flows where diversity in practice has been identified. First quarter 2018 The impact of adopting this standard was not material. ASU 2017-07, “Compensation - Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost” The standard requires the service cost component of net benefit cost to be reported in the same line item or items as other compensation costs from services rendered by the pertinent employees during the period. The other components of net benefit cost are required to be presented in the income statement separately from the service cost component and outside a subtotal of income from operations. First quarter 2018 We adopted this standard on January 1, 2018, and utilized the practical expedient to estimate the impact on the prior comparative period information presented. Immaterial reclassifications have been made to prior comparative period information to reflect the current period presentation. Prior to adoption, we expensed all components of the net periodic benefit costs for our pension and postretirement benefit plans in operations and maintenance expense. We now record only the service component of the net periodic benefit costs in operations and maintenance expense, with the remainder being recorded in other expense. There was no change to net income from the adoption of this standard. ASU 2017-12, “Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities The standard more closely aligns hedge accounting with companies’ existing risk-management strategies by expanding the strategies eligible for hedge accounting, relaxing the timing requirements of hedge documentation and effectiveness assessments, permitting in certain cases, the use of qualitative assessments on an ongoing basis to assess hedge effectiveness, and requiring new disclosures and presentation. First quarter 2018 We adopted this standard in the first quarter 2018 and recorded an immaterial cumulative-effect adjustment to the opening balance of retained earnings and other comprehensive income to eliminate the separate measurement of hedge ineffectiveness. See Note C for changes to disclosures due to adopting this standard. ASU 2018-02, “Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income” This standard allows a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act. First quarter 2018 We adopted this standard in the first quarter 2018 and recorded a $38.1 million adjustment to retained earnings and accumulated other comprehensive income to eliminate the stranded tax effects resulting from the Tax Cuts and Jobs Act. Standard Description Date of Adoption Effect on the Financial Statements or Other Significant Matters Standards that are not yet adopted ASU 2016-02, “Leases (Topic 842)” The standard requires the recognition of lease assets and lease liabilities by lessees for those leases classified as operating leases under previous GAAP. It also requires qualitative disclosures along with specific quantitative disclosures by lessees and lessors to meet the objective of enabling users of financial statements to assess the amount, timing and uncertainty of cash flows arising from leases. First quarter 2019 We are evaluating our current leases and other contracts that may be considered leases under the new standard and the impact on our internal controls, accounting policies and financial statements and disclosures. Our evaluation process includes creating a database of our existing leases and identifying a central group to track and account for lease activity, which is ongoing. We are developing internal controls to ensure the completeness and accuracy of the data. Due to this ongoing work, we cannot yet determine the quantitative impact, but adoption of the standard will result in the recognition of right of use assets and lease liabilities not previously recorded that will be presented on our Consolidated Balance Sheet under Topic 842 and will require disclosure in our footnotes. We are also monitoring recent exposure drafts and clarifications issued by the FASB.

FAIR VALUE MEASUREMENTS (Notes)

FAIR VALUE MEASUREMENTS (Notes)	3 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	FAIR VALUE MEASUREMENTS Determining Fair Value - 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 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. While many of the contracts in our derivative portfolio are executed in liquid markets where price transparency exists, some contracts are executed in markets for which market prices may exist, but the market may be relatively inactive. This results in limited price transparency that requires management’s judgment and assumptions to estimate fair values. For certain transactions, we utilize modeling techniques using NYMEX-settled pricing data and implied forward LIBOR curves. Inputs into our fair value estimates include commodity-exchange prices, over-the-counter quotes, historical correlations of pricing data, data obtained from third-party pricing services and LIBOR and other liquid money-market instrument rates. We validate our valuation inputs with third-party information and settlement prices from other sources, where available. In addition, as prescribed by the income approach, we compute the fair value of our derivative portfolio by discounting the projected future cash flows from our derivative assets and liabilities to present value using interest-rate yields to calculate present-value discount factors derived from LIBOR, Eurodollar futures and the LIBOR interest-rate swaps market. We also take into consideration the potential impact on market prices of liquidating positions in an orderly manner over a reasonable period of time under current market conditions. We consider current market data in evaluating counterparties’, as well as our own, nonperformance risk, net of collateral, by using specific and sector bond yields and monitoring the credit default swap markets. Although we use our best estimates to determine the fair value of the derivative contracts we have executed, the ultimate market prices realized could differ from our estimates, and the differences could be material. The fair value of our forward-starting interest-rate swaps are determined using financial models that incorporate the implied forward LIBOR yield curve for the same period as the future interest-rate swap settlements. 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 - fair value measurements are based on unadjusted quoted prices for identical securities in active markets, including NYMEX-settled prices. These balances are comprised predominantly of exchange-traded derivative contracts for natural gas and crude oil. • Level 2 - fair value measurements are based on significant observable pricing inputs, such as NYMEX-settled prices for natural gas and crude oil, and financial models that utilize implied forward LIBOR yield curves for interest-rate swaps. • Level 3 - fair value measurements are based on inputs that may include one or more unobservable inputs, including internally developed natural gas basis and NGL price curves that incorporate observable and unobservable market data from broker quotes, third-party pricing services, market volatilities derived from the most recent NYMEX close spot prices and forward LIBOR curves, and adjustments for the credit risk of our counterparties. We corroborate the data on which our fair value estimates are based using our market knowledge of recent transactions, analysis of historical correlations and validation with independent broker quotes. These balances categorized as Level 3 are composed of derivatives for natural gas and NGLs. We do not believe that our Level 3 fair value estimates have a material impact on our results of operations, as the majority of our derivatives are accounted for as hedges. 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. Recurring Fair Value Measurements - The following tables set forth our recurring fair value measurements for the periods indicated: March 31, 2018 Level 1 Level 2 Level 3 Total - Gross Netting (a) Total - Net ( Thousands of dollars ) Derivative assets Commodity contracts Financial contracts $ 3,180 $ — $ 20,065 $ 23,245 $ (23,245 ) $ — Physical contracts — — 40 40 — 40 Interest-rate contracts — 83,513 — 83,513 — 83,513 Total derivative assets $ 3,180 $ 83,513 $ 20,105 $ 106,798 $ (23,245 ) $ 83,553 Derivative liabilities Commodity contracts Financial contracts $ (8,121 ) $ — $ (15,799 ) $ (23,920 ) $ 23,920 $ — Physical contracts — — (1,208 ) (1,208 ) — (1,208 ) Interest-rate contracts — (11,169 ) — (11,169 ) — (11,169 ) Total derivative liabilities $ (8,121 ) $ (11,169 ) $ (17,007 ) $ (36,297 ) $ 23,920 $ (12,377 ) (a) - Derivative assets and liabilities are presented in our Consolidated Balance Sheets on a net basis. We net derivative assets and liabilities when a legally enforceable master-netting arrangement exists between the counterparty to a derivative contract and us. At March 31, 2018 , we held no cash and posted $18.5 million of cash with various counterparties, including $0.7 million of cash collateral that is offsetting derivative net liability positions under master-netting arrangements in the table above. The remaining $17.8 million of cash collateral in excess of derivative net liability positions is included in other current assets in our Consolidated Balance Sheets. December 31, 2017 Level 1 Level 2 Level 3 Total - Gross Netting (a) Total - Net ( Thousands of dollars ) Derivative assets Commodity contracts Financial contracts $ 4,252 $ — $ 20,203 $ 24,455 $ (24,455 ) $ — Interest rate contracts — 49,960 — 49,960 — 49,960 Total derivative assets $ 4,252 $ 49,960 $ 20,203 $ 74,415 $ (24,455 ) $ 49,960 Derivative liabilities Commodity contracts Financial contracts $ (5,708 ) $ — $ (48,260 ) $ (53,968 ) $ 53,936 $ (32 ) Physical contracts — — (4,781 ) (4,781 ) — (4,781 ) Total derivative liabilities $ (5,708 ) $ — $ (53,041 ) $ (58,749 ) $ 53,936 $ (4,813 ) (a) - Derivative assets and liabilities are presented in our Consolidated Balance Sheets on a net basis. We net derivative assets and liabilities when a legally enforceable master-netting arrangement exists between the counterparty to a derivative contract and us. At December 31, 2017 , we held no cash and posted $49.7 million of cash with various counterparties, including $29.5 million of cash collateral that is offsetting derivative net liability positions under master-netting arrangements in the table above. The remaining $20.2 million of cash collateral in excess of derivative net liability positions is included in other current assets in our Consolidated Balance Sheets. The following table sets forth a reconciliation of our Level 3 fair value measurements for the periods indicated: Three Months Ended March 31, Derivative Assets (Liabilities) 2018 2017 ( Thousands of dollars ) Net assets (liabilities) at beginning of period $ (32,838 ) $ (23,319 ) Total realized/unrealized gains (losses): Included in earnings (a) (85 ) 913 Included in other comprehensive income (loss) 36,021 21,634 Net assets (liabilities) at end of period $ 3,098 $ (772 ) (a) - Included in commodity sales revenues in our Consolidated Statements of Income. Realized/unrealized gains (losses) include the realization of our derivative contracts through maturity. During the three months ended March 31, 2018 and 2017 , gains or losses included in earnings attributable to the change in unrealized gains or losses relating to assets and liabilities still held at the end of each reporting period were not material. We recognize transfers into and out of the levels in the fair value hierarc hy as of the end of each reporting period. During the three months ended March 31, 2018 and 2017 , there were no tra ns fers between levels. Other Financial Instruments - The approximate fair value of cash and cash equivalents, accounts receivable, accounts payable and short-term borrowings is equal to book value due to the short-term nature of these items. Our cash and cash equivalents are composed of bank and money market accounts and are classified as Level 1. Our short-term borrowings are classified as Level 2 since the estimated fair value of the short-term borrowings can be determined using information available in the commercial paper market. The estimated fair value of our consolidated long-term debt, including current maturities, was $8.7 billion and $9.3 billion at March 31, 2018 , and December 31, 2017 , respectively. The book value of our consolidated long-term debt, including current maturities, was $8.0 billion and $8.5 billion at March 31, 2018 , and December 31, 2017 , respectively. The estimated fair value of the aggregate of our and ONEOK Partners’ senior notes outstanding was determined using quoted market prices for similar issues with similar terms and maturities. The estimated fair value of our consolidated long-term debt is classified as Level 2.

RISK MANAGEMENT AND HEDGING ACT

RISK MANAGEMENT AND HEDGING ACTIVITIES USING DERIVATIVES (Notes)	3 Months Ended
	Mar. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
RISK MANAGEMENT AND HEDGING ACTIVITIES USING DERIVATIVES	RISK-MANAGEMENT AND HEDGING ACTIVITIES USING DERIVATIVES Risk-Management Activities - We are sensitive to changes in natural gas, crude oil and NGL prices, principally as a result of contractual terms under which these commodities are processed, purchased and sold. We are also subject to the risk of interest-rate fluctuation in the normal course of business. We use physical-forward purchases and sales and financial derivatives to secure a certain price for a portion of our natural gas, condensate and NGL products; to reduce our exposure to commodity price and interest-rate fluctuations; and to achieve more predictable cash flows. We follow established policies and procedures to assess risk and approve, monitor and report our risk-management activities. We have not used these instruments for trading purposes. Commodity price risk - Commodity price risk refers to the risk of loss in cash flows and future earnings arising from adverse changes in the price of natural gas, NGLs and condensate. We use the following commodity derivative instruments to reduce the near-term commodity price risk associated with a portion of the forecasted sales of these commodities: • Futures contracts - Standardized contracts to purchase or sell natural gas and crude oil for future delivery or settlement under the provisions of exchange regulations; • Forward contracts - Nonstandardized commitments between two parties to purchase or sell natural gas, crude oil or NGLs for future physical delivery. These contracts are typically nontransferable and can only be canceled with the consent of both parties; • Swaps - Exchange of one or more payments based on the value of one or more commodities. These instruments transfer the financial risk associated with a future change in value between the counterparties of the transaction, without also conveying ownership interest in the asset or liability; and • Options - Contractual agreements that give the holder the right, but not the obligation, to buy or sell a fixed quantity of a commodity at a fixed price within a specified period of time. Options may either be standardized and exchange-traded or customized and nonexchange-traded. We may also use other instruments including collars to mitigate commodity price risk. A collar is a combination of a purchased put option and a sold call option, which places a floor and a ceiling price for commodity sales being hedged. In our Natural Gas Gathering and Processing segment, we are exposed to commodity price risk as a result of retaining a portion of the commodity sales proceeds associated with our POP with fee contracts. Under certain POP with fee contracts, our fees and POP percentage may increase or decrease if production volumes, delivery pressures or commodity prices change relative to specified thresholds. We also are exposed to basis risk between the various production and market locations where we buy and sell commodities. As part of our hedging strategy, we use the previously described commodity derivative financial instruments and physical-forward contracts to reduce the impact of price fluctuations related to natural gas, NGLs and condensate. In our Natural Gas Liquids segment, we are primarily exposed to commodity price risk resulting from the relative values of the various NGL products to each other, the value of NGLs in storage and the relative value of NGLs to natural gas. We are also exposed to location price differential risk as a result of the relative value of NGL purchases at one location and sales at another location, primarily related to our optimization and marketing businesses. We utilize physical-forward contracts and commodity derivative financial instruments to reduce the impact of price fluctuations related to NGLs. In our Natural Gas Pipelines segment, we are exposed to commodity price risk because our intrastate and interstate natural gas pipelines retain natural gas from our customers for operations or as part of our fee for services provided. When the amount of natural gas consumed in operations by these pipelines differs from the amount provided by our customers, our pipelines must buy or sell natural gas, or store or use natural gas from inventory, which can expose this segment to commodity price risk depending on the regulatory treatment for this activity. To the extent that commodity price risk in our Natural Gas Pipelines segment is not mitigated by fuel cost-recovery mechanisms, we may use physical-forward sales or purchases to reduce the impact of price fluctuations related to natural gas. At March 31, 2018 , and December 31, 2017 , there were no financial derivative instruments with respect to our natural gas pipeline operations. Interest-rate risk - We manage interest-rate risk through the use of fixed-rate debt, floating-rate debt and interest-rate swaps. Interest-rate swaps are agreements to exchange interest payments at some future point based on specified notional amounts. In January 2018, we settled the remaining $500 million of our interest-rate swaps used to hedge our LIBOR-based interest payments. In March 2018, we entered into forward-starting interest-rate swaps with notional amounts totaling $750 million to hedge the variability of interest payments on a portion of our forecasted debt issuances that may result from changes in the benchmark interest rate before the debt is issued. At March 31, 2018 , and December 31, 2017 , we had forward-starting interest-rate swaps with notional amounts totaling $2.0 billion and $1.3 billion , respectively, to hedge the variability of interest payments on a portion of our forecasted debt issuances. At December 31, 2017 , we had interest-rate swaps with a notional amount totaling $500 million to hedge the variability of our LIBOR-based interest payments. All of our interest-rate swaps are designated as cash flow hedges. Accounting Treatment - Our accounting treatment of derivative instruments is consistent with that disclosed in Note A of the Notes to Consolidated Financial Statements in our Annual Report, updated for the adoption of ASU 2017-12. Fair Values of Derivative Instruments - See Note B for a discussion of the inputs associated with our fair value measurements. The following table sets forth the fair values of our derivative instruments presented on a gross basis for the periods indicated: March 31, 2018 December 31, 2017 Location in our Consolidated Balance Sheets Assets (Liabilities) Assets (Liabilities) ( Thousands of dollars ) Derivatives designated as hedging instruments Commodity contracts Financial contracts Other current assets/other current liabilities $ 16,719 $ (19,764 ) $ 16,978 $ (42,819 ) Other assets/other deferred credits 3,061 (747 ) — (3,838 ) Physical contracts Other current assets/other current liabilities 40 (1,208 ) — (4,781 ) Interest-rate contracts Other current assets 59,502 — 1,330 — Other assets/other deferred credits 24,011 (11,169 ) 48,630 — Total derivatives designated as hedging instruments 103,333 (32,888 ) 66,938 (51,438 ) Derivatives not designated as hedging instruments Commodity contracts Financial contracts Other current assets/other current liabilities 3,465 (3,409 ) 7,477 (7,311 ) Total derivatives not designated as hedging instruments 3,465 (3,409 ) 7,477 (7,311 ) Total derivatives $ 106,798 $ (36,297 ) $ 74,415 $ (58,749 ) Notional Quantities for Derivative Instruments - The following table sets forth the notional quantities for derivative instruments held for the periods indicated: March 31, 2018 December 31, 2017 Contract Type Purchased/ Payor Sold/ Receiver Purchased/ Payor Sold/ Receiver Derivatives designated as hedging instruments: Cash flow hedges Fixed price - Natural gas ( Bcf ) Futures and swaps — (18.5 ) — (24.5 ) - Crude oil and NGLs ( MMBbl ) Futures, forwards and swaps 3.5 (10.7 ) 3.5 (11.1 ) Basis - Natural gas ( Bcf ) Futures and swaps — (18.5 ) — (24.5 ) Interest-rate contracts ( Millions of dollars ) Swaps $ 2,000.0 $ — $ 1,750.0 $ — Derivatives not designated as hedging instruments: Fixed price - NGLs ( MMBbl ) Futures, forwards and swaps 0.5 (0.5 ) 0.8 (0.8 ) These notional amounts are used to summarize the volume of financial instruments; however, they do not reflect the extent to which the positions offset one another and, consequently, do not reflect our actual exposure to market or credit risk. Cash Flow Hedges - At March 31, 2018 , our Consolidated Balance Sheet reflected a net loss of $174.7 million in accumulated other comprehensive loss. The portion of accumulated other comprehensive loss attributable to our commodity derivative financial instruments is an unrealized loss of $1.4 million , net of tax, which is expected to be realized within the next two years as the forecasted transactions affect earnings. If commodity prices remain at current levels, we will realize approximately $3.2 million in net losses , net of tax, over the next 12 months and approximately $1.8 million in net gains , net of tax, thereafter. The amount deferred in accumulated other comprehensive loss attributable to our settled interest-rate swaps is a loss of $104.0 million , net of tax, which will be recognized over the life of the long-term, fixed-rate debt, including losses of $17.5 million , net of tax, that will be reclassified into earnings during the next 12 months as the hedged items affect earnings. The remaining amounts in accumulated other comprehensive loss are attributable primarily to our pension and postretirement benefit plan obligations, which are expected to be amortized over the average remaining service period of employees participating in these plans. The following table sets forth the unrealized effect of cash flow hedges recognized in other comprehensive income (loss) for the periods indicated: Three Months Ended Derivatives in Cash Flow Hedging Relationships March 31, 2018 2017 ( Thousands of dollars ) Commodity contracts $ 20,925 $ 27,328 Interest-rate contracts 23,911 1,529 Total unrealized gain (loss) recognized in other comprehensive income (loss) on derivatives $ 44,836 $ 28,857 The following table sets forth the effect of cash flow hedges in our Consolidated Statements of Income for the periods indicated: Derivatives in Cash Flow Hedging Relationships Location of Gain (Loss) Reclassified from Accumulated Other Comprehensive Loss into Net Income Three Months Ended March 31, 2018 2017 ( Thousands of dollars ) Commodity contracts Commodity sales revenues $ (11,611 ) $ (15,319 ) Interest-rate contracts Interest expense (3,943 ) (5,329 ) Total gain (loss) reclassified from accumulated other comprehensive loss into net income on derivatives $ (15,554 ) $ (20,648 ) Credit Risk - We monitor the creditworthiness of our counterparties and compliance with policies and limits established by our Risk Oversight and Strategy Committee. We maintain credit policies with regard to our counterparties that we believe minimize overall credit risk. These policies include an evaluation of potential counterparties’ financial condition (including credit ratings, bond yields and credit default swap rates), collateral requirements under certain circumstances and the use of standardized master-netting agreements that allow us to net the positive and negative exposures associated with a single counterparty. We have counterparties whose credit is not rated, and for those customers, we use internally developed credit ratings. From time to time, we may enter into financial derivative instruments that contain provisions that require us to maintain an investment-grade credit rating from S&P and/or Moody’s. If our credit ratings on our senior unsecured long-term debt were to decline below investment grade, the counterparties to the derivative instruments could request collateralization on derivative instruments in net liability positions. There were no financial derivative instruments with contingent features related to credit risk at March 31, 2018 . The counterparties to our derivative contracts typically consist of major energy companies, financial institutions and commercial and industrial end users. This concentration of counterparties may affect our overall exposure to credit risk, either positively or negatively, in that the counterparties may be affected similarly by changes in economic, regulatory or other conditions. Based on our policies, exposures, credit and other reserves, we do not anticipate a material adverse effect on our financial position or results of operations as a result of counterparty nonperformance. At March 31, 2018 , the credit exposure from our derivative assets is with investment-grade companies in the financial services sector.

DEBT DEBT (Notes)

DEBT DEBT (Notes)	3 Months Ended
	Mar. 31, 2018
Debt Disclosure [Abstract]
Debt [Text Block]	DEBT The following table sets forth our consolidated debt for the periods indicated: March 31, December 31, ( Thousands of dollars ) ONEOK Commercial paper outstanding, bearing a weighted-average interest rate of 2.23% as of December 31, 2017 $ — $ 614,673 Senior unsecured obligations: $700,000 at 4.25% due February 2022 547,397 547,397 $500,000 at 7.5% due September 2023 500,000 500,000 $500,000 at 4.0% due July 2027 500,000 500,000 $100,000 at 6.875% due September 2028 100,000 100,000 $400,000 at 6.0% due June 2035 400,000 400,000 $700,000 at 4.95% due July 2047 700,000 700,000 ONEOK Partners Senior unsecured obligations: $425,000 at 3.2% due September 2018 425,000 425,000 $1,000,000 term loan, rate of 2.87% as of December 31, 2017, due January 2019 — 500,000 $500,000 at 8.625% due March 2019 500,000 500,000 $300,000 at 3.8% due March 2020 300,000 300,000 $900,000 at 3.375 % due October 2022 900,000 900,000 $425,000 at 5.0 % due September 2023 425,000 425,000 $500,000 at 4.9 % due March 2025 500,000 500,000 $600,000 at 6.65% due October 2036 600,000 600,000 $600,000 at 6.85% due October 2037 600,000 600,000 $650,000 at 6.125% due February 2041 650,000 650,000 $400,000 at 6.2% due September 2043 400,000 400,000 Guardian Pipeline Weighted average 7.85% due December 2022 34,695 36,607 Total debt 8,082,092 9,198,677 Unamortized portion of terminated swaps 18,038 18,468 Unamortized debt issuance costs and discounts (75,729 ) (78,193 ) Current maturities of long-term debt (932,650 ) (432,650 ) Short-term borrowings (a) — (614,673 ) Long-term debt $ 7,091,751 $ 8,091,629 (a) - Individual issuances of commercial paper under our commercial paper program generally mature in 90 days or less. These issuances are supported by and reduce the borrowing capacity under our $2.5 Billion Credit Agreement. $2.5 Billion Credit Agreement - Our $2.5 Billion Credit Agreement is a $2.5 billion revolving credit facility and contains certain financial, operational and legal covenants. Among other things, these covenants include maintaining a ratio of indebtedness to adjusted EBITDA (EBITDA, as defined in our $2.5 Billion Credit Agreement, adjusted for all noncash charges and increased for projected EBITDA from certain lender-approved capital expansion projects) of no more than 5.5 to 1 at March 31, 2018, and for the subsequent quarter and 5.0 to 1 thereafter. Once the covenant decreases to 5.0 to 1, if we consummate one or more acquisitions in which the aggregate purchase is $25 million or more, the allowable ratio of indebtedness to adjusted EBITDA will increase to 5.5 to 1 for the quarter in which the acquisition is completed and the two following quarters. Our $2.5 Billion Credit Agreement includes a $100 million sublimit for the issuance of standby letters of credit and a $200 million sublimit for swingline loans. Under the terms of our $2.5 Billion Credit Agreement, we may request an increase in the size of the facility to an aggregate of $3.5 billion by either commitments from new lenders or increased commitments from existing lenders. Our $2.5 Billion Credit Agreement contains provisions for an applicable margin rate and an annual facility fee, both of which adjust with changes in our credit ratings. Based on our current credit ratings, borrowings, if any, will accrue at LIBOR plus 110 basis points , and the annual facility fee is 15 basis points . We have the option to request two one-year extensions, subject to lender approval, which may be used for working capital, capital expenditures, acquisitions and mergers, the issuance of letters of credit and for other general corporate purposes. At March 31, 2018 , we had no borrowings outstanding, our ratio of indebtedness to adjusted EBITDA was 3.7 to 1, and we were in compliance with all covenants under our $2.5 Billion Credit Agreement. Repayments - In January 2018, we repaid the remaining $500 million balance outstanding on the Term Loan Agreement due 2019 with a combination of cash on hand and short-term borrowings. Debt Guarantees - Effective June 30, 2017, with the Merger Transaction, we, ONEOK Partners and the Intermediate Partnership issued, to the extent not already in place, guarantees of the indebtedness of ONEOK and ONEOK Partners.

EQUITY (Notes)

EQUITY (Notes)	3 Months Ended
	Mar. 31, 2018
Equity [Abstract]
EQUITY	EQUITY Ownership Interest in ONEOK Partners - As a result of the Merger Transaction in 2017, we and our subsidiaries owned 100 percent of ONEOK Partners at March 31, 2018 , and December 31, 2017 . At March 31, 2018 , the caption “Noncontrolling interests” on our Consolidated Balance Sheet reflects only the 20 percent of WTLPG that we do not own. Equity Issuances - In January 2018, we completed an underwritten public offering of 21.9 million shares of our common stock at a public offering price of $54.50 per share, generating net proceeds of $1.2 billion . We used the net proceeds from this offering to fund capital expenditures and for general corporate purposes, which included repaying a portion of our outstanding indebtedness. In July 2017, we established an “at-the-market” equity program for the offer and sale from time to time of our common stock up to an aggregate amount of $1 billion . The program allows us to offer and sell our common stock at prices we deem appropriate through a sales agent. Sales of our common stock may be made by means of ordinary brokers’ transactions on the NYSE, in block transactions or as otherwise agreed to between us and the sales agent. We are under no obligation to offer and sell common stock under the program. During the three months ended March 31, 2018 , no shares were sold through our “at-the-market” equity program. During the year ended December 31, 2017, we sold 8.4 million shares of common stock through our “at-the-market” equity program that resulted in net proceeds of $448.3 million . The net proceeds from these issuances were used for general corporate purposes, including repayment of outstanding indebtedness and to fund capital expenditures. Dividends - Holders of our common stock share equally in any dividend declared by our board of directors, subject to the rights of the holders of outstanding preferred stock. Dividends paid on our common stock in February 2018 were $0.77 per share. A dividend of $0.795 per share was declared for shareholders of record at the close of business on April 30, 2018 , payable May 15, 2018 . The Series E Preferred Stock pays quarterly dividends on each share of Series E Preferred Stock, when, as and if declared by our Board of Directors, at a rate of 5.5 percent per year. We paid dividends for the Series E Preferred Stock of $0.6 million in 2017 and $0.3 million in February 2018. Dividends totaling $0.3 million were declared for the Series E Preferred Stock and are payable May 15, 2018 . Cash Distributions - Prior to the consummation of the Merger Transaction, we received distributions from ONEOK Partners on our common and Class B units and our 2 percent general partner interest, which included our incentive distribution rights. As a result of the Merger Transaction in 2017, we are entitled to receive all available ONEOK Partners cash. Our incentive distribution rights effectively terminated at the close of the Merger Transaction. The following table sets forth ONEOK Partners’ distributions paid during the period prior to the closing of the Merger Transaction: Three Months Ended March 31, 2017 ( Thousands, except per unit amounts ) Distribution per unit $ 0.79 General partner distributions $ 6,660 Incentive distributions 100,538 Distributions to general partner 107,198 Limited partner distributions to ONEOK 90,323 Limited partner distributions to other unitholders 135,480 Total distributions paid $ 333,001

ACCUMULATED OTHER COMPREHENSIVE

ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) ACCUMULATED OTHER COMPREHENSIVE INCOME (Notes)	3 Months Ended
	Mar. 31, 2018
ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS)	ACCUMULATED OTHER COMPREHENSIVE LOSS The following table sets forth the balance in accumulated other comprehensive loss for the period indicated: Unrealized Gains (Losses) on Risk- Management Assets/Liabilities (a) Pension and Postretirement Benefit Plan Obligations (a) (b) Unrealized Gains (Losses) on Risk- Management Assets/Liabilities of Unconsolidated Affiliates (a) Accumulated Other Comprehensive Loss (a) ( Thousands of dollars ) January 1, 2018 $ (81,915 ) $ (105,411 ) $ (1,204 ) $ (188,530 ) Other comprehensive income (loss) before reclassifications 34,524 (601 ) 2,860 36,783 Amounts reclassified from accumulated other comprehensive loss 11,976 3,216 (36 ) 15,156 Net current-period other comprehensive income (loss) attributable to ONEOK 46,500 2,615 2,824 51,939 Impact of adoption of ASU 2018-02 (c) (17,935 ) (20,166 ) — (38,101 ) March 31, 2018 $ (53,350 ) $ (122,962 ) $ 1,620 $ (174,692 ) (a) - All amounts are presented net of tax. (b) - Includes amounts related to supplemental executive retirement plan. (c) - We elected to adopt this guidance in the first quarter 2018, which allows a reclassification from accumulated other comprehensive income/loss to retained earnings for the stranded tax effects resulting from the Tax Cuts and Jobs Act. After adopting and applying this guidance, our accumulated other comprehensive loss balance at March 31, 2018, does not include stranded taxes resulting from the Tax Cuts and Jobs Act. The following table sets forth the effect of reclassifications from accumulated other comprehensive loss in our Consolidated Statements of Income for the periods indicated: Details about Accumulated Other Components Three Months Ended Affected Line Item in the Statements of Income March 31, 2018 2017 ( Thousands of dollars ) Unrealized gains (losses) on risk-management assets/liabilities Commodity contracts $ (11,611 ) $ (15,319 ) Commodity sales revenues Interest-rate contracts (3,943 ) (5,329 ) Interest expense (15,554 ) (20,648 ) Income before income taxes 3,578 3,365 Income tax expense (11,976 ) (17,283 ) Net income Noncontrolling interests — (11,625 ) Less: Net income attributable to noncontrolling interests $ (11,976 ) $ (5,658 ) Net income attributable to ONEOK Pension and postretirement benefit plan obligations (a) Amortization of net loss $ (4,592 ) $ (3,812 ) Other income (expense) Amortization of unrecognized prior service credit 415 415 Other income (expense) (4,177 ) (3,397 ) Income before income taxes 961 1,359 Income tax expense $ (3,216 ) $ (2,038 ) Net income attributable to ONEOK Unrealized gains (losses) on risk-management assets/liabilities of unconsolidated affiliates $ 47 $ (96 ) Equity in net earnings from investments (11 ) 15 Income tax expense 36 (81 ) Net income Noncontrolling interests — (56 ) Less: Net income attributable to noncontrolling interests $ 36 $ (25 ) Net income attributable to ONEOK Total reclassifications for the period attributable to ONEOK $ (15,156 ) $ (7,721 ) Net income attributable to ONEOK (a) - These components of accumulated other comprehensive loss are included in the computation of net periodic benefit cost. See Note H for additional detail of our net periodic benefit cost.

EARNINGS PER SHARE EARNINGS PER

EARNINGS PER SHARE EARNINGS PER SHARE (Notes)	3 Months Ended
	Mar. 31, 2018
Earnings Per Share [Abstract]
Earnings Per Share [Text Block]	EARNINGS PER SHARE The following tables set forth the computation of basic and diluted EPS for the periods indicated: Three Months Ended March 31, 2018 Income Shares Per Share Amount ( Thousands, except per share amounts ) Basic EPS Net income attributable to ONEOK available for common stock $ 264,233 409,676 $ 0.65 Diluted EPS Effect of dilutive securities — 2,497 Net income attributable to ONEOK available for common stock and common stock equivalents $ 264,233 412,173 $ 0.64 Three Months Ended March 31, 2017 Income Shares Per Share Amount ( Thousands, except per share amounts ) Basic EPS Net income attributable to ONEOK available for common stock $ 87,361 211,619 $ 0.41 Diluted EPS Effect of dilutive securities — 1,983 Net income attributable to ONEOK available for common stock and common stock equivalents $ 87,361 213,602 $ 0.41

EMPLOYEE BENEFIT PLANS EMPLOYEE

EMPLOYEE BENEFIT PLANS EMPLOYEE BENEFIT PLANS (Notes)	3 Months Ended
	Mar. 31, 2018
Defined Benefit Plan [Abstract]
EMPLOYEE BENEFIT PLANS	EMPLOYEE BENEFIT PLANS The following tables set forth the components of net periodic benefit cost for our pension and postretirement benefit plans for the periods indicated: Pension Benefits Postretirement Benefits Three Months Ended Three Months Ended March 31, March 31, 2018 2017 2018 2017 ( Thousands of dollars ) Components of net periodic benefit cost Service cost $ 1,832 $ 1,722 $ 211 $ 165 Interest cost 4,408 4,655 527 565 Expected return on plan assets (5,969 ) (5,336 ) (672 ) (564 ) Amortization of prior service credit — — (415 ) (415 ) Amortization of net loss 4,258 3,392 334 420 Net periodic benefit cost (income) $ 4,529 $ 4,433 $ (15 ) $ 171

UNCONSOLIDATED AFFILIATES (Note

UNCONSOLIDATED AFFILIATES (Notes)	3 Months Ended
	Mar. 31, 2018
Equity Method Investments and Joint Ventures [Abstract]
UNCONSOLIDATED AFFILIATES	UNCONSOLIDATED AFFILIATES Equity in Net Earnings from Investments - The following table sets forth our equity in net earnings from investments for the periods indicated: Three Months Ended March 31, 2018 2017 ( Thousands of dollars ) Northern Border Pipeline $ 17,137 $ 18,817 Overland Pass Pipeline Company 16,387 13,566 Roadrunner Gas Transmission 4,958 4,405 Other 1,705 2,776 Equity in net earnings from investments $ 40,187 $ 39,564 Unconsolidated Affiliates Financial Information - The following table sets forth summarized combined financial information of our unconsolidated affiliates for the periods indicated: Three Months Ended March 31, 2018 2017 ( Thousands of dollars ) Income Statement Operating revenues $ 158,908 $ 154,280 Operating expenses $ 68,401 $ 66,936 Net income $ 84,480 $ 81,131 Distributions paid to us $ 49,816 $ 46,920 We incurred expenses in transactions with unconsolidated affiliates of $37.5 million and $36.7 million for the three months ended March 31, 2018 and 2017 , respectively, primarily related to Overland Pass Pipeline Company and Northern Border Pipeline. Accounts payable to our equity-method investees at March 31, 2018 , and December 31, 2017 , were $12.8 million and $13.6 million , respectively. Accounts receivable from our equity-method investees were $7.4 million at March 31, 2018 , and were not material at December 31, 2017 . Northern Border Pipeline - The Northern Border Pipeline partnership agreement provides that distributions to Northern Border Pipeline’s partners are to be made on a pro rata basis according to each partner’s percentage interest. The Northern Border Pipeline Management Committee determines the amount and timing of such distributions. Any changes to, or suspension of, the cash distribution policy of Northern Border Pipeline requires the unanimous approval of the Northern Border Pipeline Management Committee. Cash distributions are equal to 100 percent of distributable cash flow as determined from Northern Border Pipeline’s financial statements based upon EBITDA less interest expense and maintenance capital expenditures. Loans or other advances from Northern Border Pipeline to its partners or affiliates are prohibited under its credit agreement. Northern Border Pipeline entered into a settlement with shippers that was approved by the FERC in February 2018. The settlement provides for tiered rate reductions beginning January 1, 2018, that will reduce rates 12.5 percent by January 2020 compared with previous rates and requires new rates to be established by January 2024. We do not expect the resulting decrease in equity earnings and cash distributions from Northern Border Pipeline to be material to us. Overland Pass Pipeline Company - The Overland Pass Pipeline Company limited liability company agreement provides that distributions to Overland Pass Pipeline Company’s members are to be made on a pro rata basis according to each member’s percentage interest. The Overland Pass Pipeline Company Management Committee determines the amount and timing of such distributions. Any changes to, or suspension of, cash distributions from Overland Pass Pipeline Company requires the unanimous approval of the Overland Pass Pipeline Company Management Committee. Cash distributions are equal to 100 percent of available cash as defined in the limited liability company agreement. Roadrunner Gas Transmission - The Roadrunner limited liability company agreement provides that distributions to members are made on a pro rata basis according to each member’s ownership interest. As the operator, we have been delegated the authority to determine such distributions in accordance with, and on the frequency set forth in, the Roadrunner limited liability company agreement. Cash distributions are equal to 100 percent of available cash, as defined in the limited liability company agreement. During the three months ended March 31, 2017, we made contributions of $4 million to Roadrunner. We made no contributions to Roadrunner during the three months ended March 31, 2018. We have an operating agreement with Roadrunner that provides for reimbursement or payment to us for management services and certain operating costs. Reimbursements and payments from Roadrunner included in operating income in our Consolidated Statements of Income for the three months ended March 31, 2018 and 2017 , were not material.

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Notes)	3 Months Ended
	Mar. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES Environmental Matters and Pipeline Safety - The operation of pipelines, plants and other facilities for the gathering, processing, transportation and storage of natural gas, NGLs, condensate and other products is subject to numerous and complex laws and regulations pertaining to health, safety and the environment. As an owner and/or operator of these facilities, we must comply with United States laws and regulations at the federal, state, local and tribal levels that relate to air and water quality, hazardous and solid waste management and disposal, cultural resource protection and other environmental matters. The cost of planning, designing, constructing and operating pipelines, plants and other facilities must incorporate compliance with these laws and regulations and safety standards. Failure to comply with these laws and regulations may trigger a variety of administrative, civil and potentially criminal enforcement measures, including citizen suits, which can include the assessment of monetary penalties, the imposition of remedial requirements and the issuance of injunctions or restrictions on operation or construction. Management believes that, based on currently known information, compliance with these laws and regulations will not have a material adverse effect on our results of operations, financial condition or cash flows. Regulatory - The Tax Cuts and Jobs Act makes extensive changes to the U.S. tax laws and includes provisions that reduce the U.S. corporate tax rate to 21 percent from 35 percent, increase expensing for capital investment, and limit the interest deduction and use of net operating losses to offset future taxable income. The Tax Cuts and Jobs Act may reduce future tariff rates charged on our regulated pipelines. The rates charged to our customers have generally been established through shipper specific negotiation, discounts and negotiated settlements, which do not ascribe any specific cost of service elements. We expect future tariff rate changes, if any, related to the change in the U.S. corporate tax rate to be established prospectively over time on a similar negotiated basis. We will continue to monitor applicable FERC rule-making, including the March 2018 notice of proposed rule-making on the impact of the Tax Cuts and Jobs Act on FERC-regulated rates for natural gas pipelines, which is subject to a public comment process prior to being finalized. If in the future the FERC or other regulatory bodies were to require us to establish a regulatory liability for amounts previously collected on our regulated pipelines, then we would expect to record a regulatory liability through a one-time charge to expense. We also continue to monitor the FERC’s March 2018 revised policy statement for master limited partnerships, which no longer allows interstate natural gas and oil pipelines owned by master limited partnerships to recover an income tax allowance in cost of service rates. This revised policy remains pending at the FERC based on various requests for reconsideration or rehearing. We do not expect this FERC action to be material to our results of operations, as we are organized as a C-corporation. Further, regardless of organizational structure, we do not expect this FERC action to materially affect us, as the rates charged to our customers have generally been established through shipper specific negotiation, discounts and negotiated settlements, which do not ascribe any specific cost of service elements. The FERC allows regulated NGL pipelines an annual index adjustment to transportation rates, which is intended to allow recovery of changes in costs without a complicated cost of service filing. The FERC is expected to evaluate how best to incorporate the effects of new tax policies in its next calculation of the rate index in 2020, for indexing effective July 2021. We do not expect to be materially impacted by any such change in the index calculation, as our regulated NGL pipeline revenues are primarily under negotiated agreements. Legal Proceedings - Gas Index Pricing Litigation - As previously reported, in March 2017, the United States District Court for the District of Nevada (the Court) granted summary judgment to OESC in Sinclair Oil Corporation v. ONEOK Energy Services Company, L.P. (filed in the United States District Court for the District of Wyoming in September 2005, transferred to MDL-1566 in the Court). In September 2017, the Court entered a final judgment in favor of OESC in Sinclair , which was appealed by Sinclair Oil Corporation to the Ninth Circuit Court of Appeals. We expect that future charges, if any, from the ultimate resolution of the Sinclair case will not be material to our results of operations, financial position or cash flows. Other Legal Proceedings - We are a party to various other litigation matters and claims that have arisen in the normal course of our operations. While the results of these litigation matters 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 consolidated results of operations, financial position or cash flows.

REVENUE REVENUE (Notes)

REVENUE REVENUE (Notes)	3 Months Ended
	Mar. 31, 2018
Revenue from Contract with Customer [Abstract]
Revenues [Text Block]	REVENUES Adoption of ASC Topic 606: Revenue from Contracts with Customers - We adopted Topic 606 on January 1, 2018, using the modified retrospective method applied to those contracts, which were active as of January 1, 2018. Results for reporting periods beginning after January 1, 2018, are presented under Topic 606, while prior periods are not adjusted and continue to be reported under the accounting standards in effect for those periods. We recorded a net increase to the beginning balance of retained earnings of approximately $1.7 million as of January 1, 2018, due to the cumulative impact of adopting the standard, primarily related to the timing of revenue on transportation contracts with tiered rates that resulted in contract assets in our Natural Gas Pipelines segment, contributions in aid of construction from customers that resulted in contract liabilities and an adjustment to NGL inventory related to contractual fees in our Natural Gas Liquids Segment, as described below. Based on the new guidance, we determined that certain Natural Gas Gathering and Processing segment POP with fee contracts and Natural Gas Liquids segment exchange services contracts that include the purchase of commodities are supplier contracts. Therefore, contractual fees in these identified contracts are now recorded as a reduction to cost of sales and fuel pursuant to ASC 705 rather than as services revenue. To the extent we hold inventory related to these purchases, the related fees previously recorded in services revenue will not be recognized until the inventory is sold. We continue to be principal on the downstream sales of those commodities, which is unchanged from our assessment under previous guidance. The impact on our Consolidated Income Statement and Balance Sheet is as follows (in thousands): Three Months Ended March 31, 2018 Income Statement As Reported Balance Without Adoption of Topic 606 Effect of Change Increase/(Decrease) Services revenue $ 282,073 $ 634,315 $ (352,242 ) Cost of sales and fuel (exclusive of depreciation and operating costs) $ 2,368,026 $ 2,725,774 $ (357,748 ) Depreciation and amortization $ 104,237 $ 104,092 $ 145 Income taxes $ 75,771 $ 74,539 $ 1,232 Net income $ 266,049 $ 261,920 $ 4,129 Net income attributable to noncontrolling interests $ 1,541 $ 1,539 $ 2 Net income attributable to ONEOK $ 264,508 $ 260,381 $ 4,127 March 31, 2018 Balance Sheet As Reported Balance Without Adoption of Topic 606 Effect of Change Increase/(Decrease) Natural gas and natural gas liquids in storage $ 185,298 $ 186,998 $ (1,700 ) Other current assets $ 106,067 $ 105,097 $ 970 Property, plant and equipment $ 15,838,443 $ 15,816,674 $ 21,769 Accumulated depreciation and amortization $ 2,960,254 $ 2,958,737 $ 1,517 Deferred income taxes $ 116,120 $ 117,854 $ (1,734 ) Other assets $ 159,428 $ 154,167 $ 5,261 Other current liabilities $ 122,922 $ 120,877 $ 2,045 Other deferred credits $ 366,701 $ 351,525 $ 15,176 Retained earnings/paid-in capital $ 7,735,173 $ 7,729,364 $ 5,809 Noncontrolling interests in consolidated subsidiaries $ 167,806 $ 167,787 $ 19 Revenue Recognition - Revenues are recognized when control of the promised goods or services is transferred to our customers in an amount that reflects the consideration we expect to be entitled to receive in exchange for those goods or services. Our payment terms vary by customer and contract type, including requiring payment before products or services are delivered to certain customers. However, the term between customer prepayments, completion of our performance obligations, invoicing and receipt of payment due is not significant. Practical Expedients - We do not disclose the value of unsatisfied performance obligations for (i) contracts with an original expected length of one year or less and (ii) variable consideration on contracts for which we recognize revenue at the amount to which we have the right to invoice for services performed. Receivables from Customers, Performance Obligations and Revenue Sources - The balances in accounts receivable on our Consolidated Balance Sheet at March 31, 2018, and December 31, 2017, include customer receivables of $832.1 million and $1.2 billion , respectively. Revenues sources are disaggregated in Note L and are derived from commodity sales and services revenues, as described below: Commodity Sales (all segments) - We contract to deliver residue natural gas, condensate, unfractionated NGLs and/or NGL products to customers at a specified delivery point. Our sales agreements may be daily or longer-term contracts for a specified volume. We consider the sale and delivery of each unit of a commodity an individual performance obligation as the customer is expected to control, accept and benefit from each unit individually. We record revenue when the commodity is delivered to the customer as this represents the point in time when control of the product is transferred to the customer. Revenue is recorded based on the contracted selling price, which is generally index-based and settled monthly. Services Gathering only contracts ( Natural Gas Gathering and Processing segment ) - Under this type of contract, we charge fees for providing midstream services, which include gathering our customer’s natural gas. Our performance obligation begins with delivery of raw natural gas to our system. This service is treated as one performance obligation that is satisfied over time. We use the output method based on delivery of product to our system as the measure of progress, as our services are performed simultaneously. POP contracts with producer take-in-kind rights ( Natural Gas Gathering and Processing segment ) - Under this type of contract, we do not control the stream of unprocessed gas that we receive at the wellhead due to the producer’s take-in-kind rights. We charge fees for providing midstream services, which include gathering and processing our customer’s natural gas. After performing these services, we return a portion of the natural gas to the producer and purchase the remaining commodities. Our performance obligation begins with delivery of raw natural gas to our system. This service is treated as one performance obligation that is satisfied over time. We use the output method based on delivery of product to our system as the measure of progress, as our services are performed simultaneously. Transportation and exchange contracts ( Natural Gas Liquids segment ) - Under this type of contract, we charge fees for providing midstream services, which may include a bundled combination of gathering, transporting and/or fractionation of our customer’s NGLs. Our performance obligation begins with delivery of unfractionated NGLs or NGL products to our system. These services represent a series of distinct services that are treated as one performance obligation that is satisfied over time. We use the output method based on delivery of product to our system as the measure of progress, as our services are performed simultaneously. For transportation services under a tariff on our NGL transportation pipelines, fees are recorded upon redelivery to our customer at the completion of the transportation services. Storage contracts ( Natural Gas Liquids and Natural Gas Pipelines segments ) - We reserve a stated storage capacity and inject/withdraw/store commodities for our customer. The capacity reservation and injection/withdrawal/storage services are considered a bundled service, as we integrate them into one stand-ready obligation provided on a daily basis over the life of the agreement and satisfied over time. Fixed capacity reservation fees are allocated and evenly recognized in revenue. Capacity reservation fees that vary based on a stated or implied economic index and correspond with the costs to provide our services are recognized in revenue based on daily effective fee rate. Transportation, injection and withdrawal fees are recognized in revenue as those services are provided and are dependent on the volume transported, injected or withdrawn by our customer, which is at our customer’s discretion. We use the output method based on the passage of time to measure satisfaction of the performance obligation associated with our daily stand-ready services. Firm service transportation contracts ( Natural Gas Pipelines segment ) - We reserve a stated transportation capacity and transport commodities for our customer. The capacity reservation and transportation services are considered a bundled service, as we integrate them into one stand-ready obligation provided on a daily basis over the life of the agreement and satisfied over time. Fixed capacity reservation fees are allocated and evenly recognized in revenue. Capacity reservation fees that vary based on a stated or implied economic index and correspond with the costs to provide our services are recognized in revenue based on a daily effective fee rate. If the capacity reservation fees vary solely as a contract feature, contract assets or liabilities are recorded for the difference between the amount recorded in revenue and the amount billed to the customer. Transportation fees are recognized in revenue as those services are provided and are dependent on the volume transported by our customer, which is at our customer’s discretion. We use the output method based on the passage of time to measure satisfaction of the performance obligation associated with our daily stand-ready services. Interruptible transportation contracts ( Natural Gas Pipelines segment ) - We agree to transport natural gas on our pipelines between the customer’s specified nomination and delivery points if capacity is available after satisfying firm transportation service obligations. Our performance obligations and those of our customer begin with delivery of natural gas onto our pipeline and is satisfied over time. The transaction price is based on the transportation fees times the volumes transported. These fees may change over time based on an index or other factors provided in the agreement. We use the output method based on delivery of product to the customer to measure satisfaction of the performance obligation. The total consideration for delivered volumes is recorded in revenue at the time of delivery, when the customer obtains control. Contract Assets and Contract Liabilities - Contract assets and contract liabilities are recorded when the amount of revenue recognized from a contract with a customer differs from the amount billed to the customer and recorded in accounts receivable. Our contract asset balances at the beginning and end of the period primarily relate to our firm service transportation contracts with tiered rates and were approximately $6.2 million and $6.4 million as of March 31, 2018, and January 1, 2018, respectively. At March 31, 2018, contract assets of $1.0 million and $5.2 million , are included in other current assets and other assets, respectively, in our Consolidated Balance Sheet. There have been no additions to our contract asset balance in 2018. Our contract liabilities primarily represent deferred revenue on NGL storage contracts for which revenue is recognized over a one-year term and deferred revenue on contributions in aid of construction received from customers for which revenue is recognized over the contract period, which averages approximately 10 years. Contract Liability ( Millions of dollars ) Balance at January 1, 2018 (a) $ 33.3 Revenue recognized included in beginning balance (17.3 ) Net additions 5.2 Balance at March 31, 2018 (b) $ 21.2 (a) - Balance includes $19.5 million of current liabilities. (b) - Contract liabilities of $6.0 million and $15.2 million are included in other current liabilities and other deferred credits, respectively, in our Consolidated Balance Sheet. Transaction Price Allocated to Unsatisfied Performance Obligations - The following table presents aggregate value allocated to unsatisfied performance obligations as of March 31, 2018, and the amounts we expect to recognize in revenue in future periods, related primarily to firm transportation and storage contracts with remaining contract terms ranging from one month to 26 years: Expected Period of Recognition in Revenue ( Millions of dollars ) Remainder of 2018 $ 242.9 2019 247.3 2020 215.4 2021 209.7 2022 and beyond 1,032.6 Total estimated transaction price allocated to unsatisfied performance obligations $ 1,947.9 The table above excludes variable consideration allocated entirely to wholly unsatisfied performance obligations, wholly unsatisfied promises to transfer distinct goods or services that are part of a single performance obligation and consideration we determine to be fully constrained. Information on the nature of the variable consideration excluded and the nature of the performance obligations to which the variable consideration relates can be found in the description of the major contract types discussed above. The amounts we determined to be fully constrained relate to future sales obligations under long-term sales contracts where the transaction price is not known and minimum volume agreements, which we consider to be fully constrained until invoiced.

SEGMENTS (Notes)

SEGMENTS (Notes)	3 Months Ended
	Mar. 31, 2018
Segment Reporting, Disclosure of Entity's Reportable Segments [Abstract]
SEGMENTS	SEGMENTS Segment Descriptions - Our operations are divided into three reportable business segments, as follows: • our Natural Gas Gathering and Processing segment gathers, treats and processes natural gas; • our Natural Gas Liquids segment gathers, treats, fractionates and transports NGLs and stores, markets and distributes NGL products; and • our Natural Gas Pipelines segment operates regulated interstate and intrastate natural gas transmission pipelines and natural gas storage facilities. Other and eliminations consist of corporate costs, the operating and leasing activities of our headquarters building and related parking facility and eliminations necessary to reconcile our reportable segments to our Consolidated Financial Statements. Accounting Policies - The accounting policies of the segments are described in Note A of the Notes to Consolidated Financial Statements in our Annual Report, updated as described in Note A of this Quarterly Report. Our chief operating decision-maker reviews the financial performance of each of our three segments, as well as our financial performance as a whole, on a regular basis. Adjusted EBITDA by segment is utilized in this evaluation. We believe this financial measure is useful to investors because it and similar measures are used by many companies in our industry as a measurement of financial performance and are commonly employed by financial analysts and others to evaluate our financial performance and to compare financial performance among companies in our industry. Adjusted EBITDA for each segment is defined as net income adjusted for interest expense, depreciation and amortization, noncash impairment charges, income taxes, allowance for equity funds used during construction, noncash compensation and other noncash items. This calculation may not be comparable with similarly titled measures of other companies. Customers - Our Natural Gas Gathering and Processing segment derives services revenue primarily from crude oil and natural gas producers, which include both large integrated and independent exploration and production companies. The downstream commodity sales customers of our Natural Gas Gathering and Processing segment are primarily utilities, large industrial companies, marketing companies and our NGL affiliate. Our Natural Gas Liquids segment’s customers are primarily NGL and natural gas gathering and processing companies; large integrated and independent crude oil and natural gas production companies; propane distributors; ethanol producers; and petrochemical, refining and NGL marketing companies. Our Natural Gas Pipelines segment’s customers are primarily local natural gas distribution companies, electric-generation companies, large industrial companies, municipalities, producers and marketing companies. For the three months ended March 31, 2018 and 2017 , we had no single customer from which we received 10 percent or more of our consolidated revenues. Operating Segment Information - The following tables set forth certain selected financial information for our operating segments for the periods indicated: Three Months Ended Natural Gas Gathering and Processing Natural Gas Liquids (a) Natural Gas Pipelines (b) Total ( Thousands of dollars ) NGL and condensate sales $ 413,157 $ 2,552,770 $ — $ 2,965,927 Residue natural gas sales 254,997 — 4,919 259,916 Gathering, processing and exchange services revenue 38,429 83,258 — 121,687 Transportation and storage revenue — 53,478 98,338 151,816 Other 1,408 2,963 6,654 11,025 Total revenues (c) 707,991 2,692,469 109,911 3,510,371 Cost of sales and fuel (exclusive of depreciation and operating costs) (492,622 ) (2,281,072 ) (5,454 ) (2,779,148 ) Operating costs (88,359 ) (88,592 ) (33,190 ) (210,141 ) Equity in net earnings from investments 1,668 16,424 22,095 40,187 Other 1,873 2,850 263 4,986 Segment adjusted EBITDA $ 130,551 $ 342,079 $ 93,625 $ 566,255 Depreciation and amortization $ (47,748 ) $ (42,427 ) $ (13,269 ) $ (103,444 ) Total assets $ 5,462,305 $ 8,370,364 $ 2,060,700 $ 15,893,369 Capital expenditures $ 111,729 $ 124,921 $ 19,898 $ 256,548 (a) - Our Natural Gas Liquids segment has regulated and nonregulated operations. Our Natural Gas Liquids segment’s regulated operations had revenues of $300.0 million , of which $253.4 million related to sales within the segment and cost of sales and fuel of $122.8 million . (b) - Our Natural Gas Pipelines segment has regulated and nonregulated operations. Our Natural Gas Pipelines segment’s regulated operations had revenues of $68.0 million and cost of sales and fuel of $9.1 million . (c) - Intersegment revenues for the Natural Gas Gathering and Processing, Natural Gas Liquids and Natural Gas Pipelines segments totaled $397.8 million , $9.0 million and $2.1 million respectively. Three Months Ended March 31, 2018 Total Segments Other and Eliminations Total ( Thousands of dollars ) Reconciliations of total segments to consolidated NGL and condensate sales $ 2,965,927 $ (408,910 ) $ 2,557,017 Residue natural gas sales 259,916 2,250 262,166 Gathering, processing and exchange services revenue 121,687 (21 ) 121,666 Transportation and storage revenue 151,816 (2,094 ) 149,722 Other 11,025 481 11,506 Total revenues (a) $ 3,510,371 $ (408,294 ) $ 3,102,077 Cost of sales and fuel (exclusive of depreciation and operating costs) $ (2,779,148 ) $ 411,122 $ (2,368,026 ) Operating costs $ (210,141 ) $ (63 ) $ (210,204 ) Depreciation and amortization $ (103,444 ) $ (793 ) $ (104,237 ) Equity in net earnings from investments $ 40,187 $ — $ 40,187 Total assets $ 15,893,369 $ 538,978 $ 16,432,347 Capital expenditures $ 256,548 $ 7,919 $ 264,467 (a) - Noncustomer revenue for the three months ended March 31, 2018, totaled $(9.0) million related primarily to losses reclassified from accumulated other comprehensive income from derivatives on commodity contracts. Three Months Ended Natural Gas Gathering and Processing Natural Gas Liquids (a) Natural Gas Pipelines (b) Total ( Thousands of dollars ) Sales to unaffiliated customers $ 400,149 $ 2,244,000 $ 104,924 $ 2,749,073 Intersegment revenues 261,127 147,984 1,894 411,005 Total revenues 661,276 2,391,984 106,818 3,160,078 Cost of sales and fuel (exclusive of depreciation and operating costs) (488,384 ) (2,048,693 ) (16,603 ) (2,553,680 ) Operating costs (71,328 ) (78,440 ) (31,563 ) (181,331 ) Equity in net earnings from investments 2,630 13,722 23,212 39,564 Other (227 ) (344 ) 1,094 523 Segment adjusted EBITDA $ 103,967 $ 278,229 $ 82,958 $ 465,154 Depreciation and amortization $ (44,968 ) $ (41,115 ) $ (12,543 ) $ (98,626 ) Total assets $ 5,296,359 $ 8,194,835 $ 1,945,407 $ 15,436,601 Capital expenditures $ 63,151 $ 20,453 $ 25,014 $ 108,618 (a) - Our Natural Gas Liquids segment has regulated and nonregulated operations. Our Natural Gas Liquids segment’s regulated operations had revenues of $296.3 million , of which $252.9 million related to sales within the segment and cost of sales and fuel of $116.5 million . (b) - Our Natural Gas Pipelines segment has regulated and nonregulated operations. Our Natural Gas Pipelines segment’s regulated operations had revenues of $68.9 million and cost of sales and fuel of $14.1 million . Three Months Ended March 31, 2017 Total Segments Other and Eliminations Total ( Thousands of dollars ) Reconciliations of total segments to consolidated Sales to unaffiliated customers $ 2,749,073 $ 538 $ 2,749,611 Intersegment revenues 411,005 (411,005 ) — Total revenues $ 3,160,078 $ (410,467 ) $ 2,749,611 Cost of sales and fuel (exclusive of depreciation and operating costs) $ (2,553,680 ) $ 409,837 $ (2,143,843 ) Operating costs $ (181,331 ) $ (7,874 ) $ (189,205 ) Depreciation and amortization $ (98,626 ) $ (793 ) $ (99,419 ) Equity in net earnings from investments $ 39,564 $ — $ 39,564 Total assets $ 15,436,601 $ 630,957 $ 16,067,558 Capital expenditures $ 108,618 $ 4,119 $ 112,737 Three Months Ended March 31, 2018 2017 Reconciliation of net income to total segment adjusted EBITDA ( Thousands of dollars ) Net income $ 266,049 $ 186,185 Add: Interest expense, net of capitalized interest 115,725 116,462 Depreciation and amortization 104,237 99,419 Income taxes 75,771 54,941 Noncash compensation expense 9,226 1,647 Other corporate costs and noncash items (4,753 ) 6,500 Total segment adjusted EBITDA $ 566,255 $ 465,154

SUPPLEMENTAL CONDENSED CONSOLID

SUPPLEMENTAL CONDENSED CONSOLIDATING FINANCIAL INFORMATION (Notes)	3 Months Ended
	Mar. 31, 2018
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Supplemental Condensed Consolidating Financial Information	SUPPLEMENTAL CONDENSED CONSOLIDATING FINANCIAL INFORMATION ONEOK and ONEOK Partners are issuers of certain public debt securities. Effective with the Merger Transaction in 2017, we, ONEOK Partners and the Intermediate Partnership issued, to the extent not already in place, guarantees of the indebtedness of ONEOK and ONEOK Partners. The Intermediate Partnership holds all of ONEOK Partners’ partnership interests and equity in its subsidiaries, as well as a 50 percent interest in Northern Border Pipeline. In lieu of providing separate financial statements for each subsidiary issuer and guarantor, we have included the accompanying condensed consolidating financial statements based on Rule 3-10 of the SEC’s Regulation S-X. We have presented each of the parent and subsidiary issuers in separate columns in this single set of condensed consolidating financial statements. For purposes of the following footnote: • we are referred to as “Parent Issuer and Guarantor”; • ONEOK Partners is referred to as “Subsidiary Issuer and Guarantor”; • the Intermediate Partnership is referred to as “Guarantor Subsidiary”; and • the “Non-Guarantor Subsidiaries” are all subsidiaries other than the Guarantor Subsidiary and Subsidiary Issuer and Guarantor. The following unaudited supplemental condensed consolidating financial information is presented on an equity-method basis reflecting the separate accounts of ONEOK, ONEOK Partners and the Intermediate Partnership, the combined accounts of the Non-Guarantor Subsidiaries, the combined consolidating adjustments and eliminations, and our consolidated amounts for the periods indicated. Condensed Consolidating Statements of Income Three Months Ended March 31, 2018 ( Unaudited ) Parent Issuer & Guarantor Subsidiary Issuer & Guarantor Guarantor Subsidiary Combined Non-Guarantor Subsidiaries Consolidating Entries Total ( Millions of dollars ) Revenues Commodity sales $ — $ — $ — $ 2,820.0 $ — $ 2,820.0 Services — — — 282.6 (0.5 ) 282.1 Total revenues — — — 3,102.6 (0.5 ) 3,102.1 Cost of sales and fuel (exclusive of items shown separately below) — — — 2,368.0 — 2,368.0 Operating expenses (0.7 ) — — 315.7 (0.5 ) 314.5 Gain on sale of assets — — — (0.1 ) — (0.1 ) Operating income 0.7 — — 419.0 — 419.7 Equity in net earnings from investments 368.5 370.9 370.9 28.6 (1,098.7 ) 40.2 Other income (expense), net 7.2 77.1 77.1 (9.6 ) (154.2 ) (2.4 ) Interest expense, net (39.8 ) (77.1 ) (77.1 ) (75.9 ) 154.2 (115.7 ) Income before income taxes 336.6 370.9 370.9 362.1 (1,098.7 ) 341.8 Income taxes (72.1 ) — — (3.7 ) — (75.8 ) Net income 264.5 370.9 370.9 358.4 (1,098.7 ) 266.0 Less: Net income attributable to noncontrolling interests — — — 1.5 — 1.5 Net income attributable to ONEOK 264.5 370.9 370.9 356.9 (1,098.7 ) 264.5 Less: Preferred stock dividends 0.3 — — — — 0.3 Net income available to common shareholders $ 264.2 $ 370.9 $ 370.9 $ 356.9 $ (1,098.7 ) $ 264.2 Three Months Ended March 31, 2017 ( Unaudited ) Parent Issuer & Guarantor Subsidiary Issuer & Guarantor Guarantor Subsidiary Combined Non-Guarantor Subsidiaries Consolidating Entries Total ( Millions of dollars ) Revenues Commodity sales $ — $ — $ — $ 2,216.7 $ — $ 2,216.7 Services — — — 532.9 — 532.9 Total revenues — — — 2,749.6 — 2,749.6 Cost of sales and fuel (exclusive of items shown separately below) — — — 2,143.8 — 2,143.8 Operating expenses 6.9 — — 281.8 — 288.7 Operating income (6.9 ) — — 324.0 — 317.1 Equity in net earnings from investments 268.7 269.1 269.1 20.7 (788.0 ) 39.6 Other income (expense), net 0.5 91.3 91.3 0.4 (182.6 ) 0.9 Interest expense, net (25.8 ) (91.3 ) (91.3 ) (90.7 ) 182.6 (116.5 ) Income before income taxes 236.5 269.1 269.1 254.4 (788.0 ) 241.1 Income taxes (51.2 ) — — (3.7 ) — (54.9 ) Net income 185.3 269.1 269.1 250.7 (788.0 ) 186.2 Less: Net income attributable to noncontrolling interests 97.9 — — 0.9 — 98.8 Net income attributable to ONEOK $ 87.4 $ 269.1 $ 269.1 $ 249.8 $ (788.0 ) $ 87.4 Condensed Consolidating Statements of Comprehensive Income Three Months Ended March 31, 2018 ( Unaudited ) Parent Issuer & Guarantor Subsidiary Issuer & Guarantor Guarantor Subsidiary Combined Non-Guarantor Subsidiaries Consolidating Entries Total ( Millions of dollars ) Net income $ 264.5 $ 370.9 $ 370.9 $ 358.4 $ (1,098.7 ) $ 266.0 Other comprehensive income (loss), net of tax Unrealized gains (losses) on derivatives, net of tax 18.4 20.9 20.9 16.1 (41.8 ) 34.5 Realized (gains) losses on derivatives in net income, net of tax 0.9 14.3 11.6 8.3 (23.1 ) 12.0 Change in pension and postretirement benefit plan liability, net of tax 3.2 (0.6 ) — — — 2.6 Other comprehensive income (loss) on investments in unconsolidated affiliates, net of tax — 3.7 3.7 2.8 (7.4 ) 2.8 Total other comprehensive income (loss), net of tax 22.5 38.3 36.2 27.2 (72.3 ) 51.9 Comprehensive income 287.0 409.2 407.1 385.6 (1,171.0 ) 317.9 Less: Comprehensive income attributable to noncontrolling interests — — — 1.5 — 1.5 Comprehensive income attributable to ONEOK $ 287.0 $ 409.2 $ 407.1 $ 384.1 $ (1,171.0 ) $ 316.4 Three Months Ended March 31, 2017 ( Unaudited ) Parent Issuer & Guarantor Subsidiary Issuer & Guarantor Guarantor Subsidiary Combined Non-Guarantor Subsidiaries Consolidating Entries Total ( Millions of dollars ) Net income $ 185.3 $ 269.1 $ 269.1 $ 250.7 $ (788.0 ) $ 186.2 Other comprehensive income (loss), net of tax Unrealized gains (losses) on derivatives, net of tax — 28.8 27.3 51.8 (83.4 ) 24.5 Realized (gains) losses on derivatives in net income, net of tax 0.5 19.8 15.3 32.1 (50.4 ) 17.3 Change in pension and postretirement benefit plan liability, net of tax 2.0 — — — — 2.0 Other comprehensive income (loss) on investments in unconsolidated affiliates, net of tax — 0.4 0.4 0.7 (1.2 ) 0.3 Total other comprehensive income (loss), net of tax 2.5 49.0 43.0 84.6 (135.0 ) 44.1 Comprehensive income 187.8 318.1 312.1 335.3 (923.0 ) 230.3 Less: Comprehensive income attributable to noncontrolling interests 126.8 — — 0.9 — 127.7 Comprehensive income attributable to ONEOK $ 61.0 $ 318.1 $ 312.1 $ 334.4 $ (923.0 ) $ 102.6 Condensed Consolidating Balance Sheets March 31, 2018 ( Unaudited ) Parent Issuer & Guarantor Subsidiary Issuer & Guarantor Guarantor Subsidiary Combined Non-Guarantor Subsidiaries Consolidating Entries Total Assets ( Millions of dollars ) Current assets Cash and cash equivalents $ 17.5 $ — $ — $ — $ — $ 17.5 Accounts receivable, net — — — 844.2 — 844.2 Natural gas and natural gas liquids in storage — — — 185.3 — 185.3 Other current assets 70.8 — — 172.9 — 243.7 Total current assets 88.3 — — 1,202.4 — 1,290.7 Property, plant and equipment Property, plant and equipment 134.1 — — 15,704.3 — 15,838.4 Accumulated depreciation and amortization 87.7 — — 2,872.5 — 2,960.2 Net property, plant and equipment 46.4 — — 12,831.8 — 12,878.2 Investments and other assets Investments 5,823.6 3,207.8 8,443.5 802.9 (17,280.4 ) 997.4 Intercompany notes receivable 3,450.2 8,118.3 2,882.6 — (14,451.1 ) — Other assets 305.4 — — 1,008.0 (47.4 ) 1,266.0 Total investments and other assets 9,579.2 11,326.1 11,326.1 1,810.9 (31,778.9 ) 2,263.4 Total assets $ 9,713.9 $ 11,326.1 $ 11,326.1 $ 15,845.1 $ (31,778.9 ) $ 16,432.3 Liabilities and equity Current liabilities Current maturities of long-term debt $ — $ 925.0 $ — $ 7.7 $ — $ 932.7 Accounts payable 6.3 — — 766.8 — 773.1 Other current liabilities 43.5 68.2 — 233.3 — 345.0 Total current liabilities 49.8 993.2 — 1,007.8 — 2,050.8 Intercompany debt — — 8,118.3 6,332.8 (14,451.1 ) — Long-term debt, excluding current maturities 2,726.8 4,338.1 — 26.9 — 7,091.8 Deferred credits and other liabilities 235.8 — — 232.0 (47.4 ) 420.4 Commitments and contingencies Equity Equity excluding noncontrolling interests in consolidated subsidiaries 6,701.5 5,994.8 3,207.8 8,077.8 (17,280.4 ) 6,701.5 Noncontrolling interests in consolidated subsidiaries — — — 167.8 — 167.8 Total equity 6,701.5 5,994.8 3,207.8 8,245.6 (17,280.4 ) 6,869.3 Total liabilities and equity $ 9,713.9 $ 11,326.1 $ 11,326.1 $ 15,845.1 $ (31,778.9 ) $ 16,432.3 December 31, 2017 ( Unaudited ) Parent Issuer & Guarantor Subsidiary Issuer & Guarantor Guarantor Subsidiary Combined Non-Guarantor Subsidiaries Consolidating Entries Total Assets ( Millions of dollars ) Current assets Cash and cash equivalents $ 37.2 $ — $ — $ — $ — $ 37.2 Accounts receivable, net — — — 1,203.0 — 1,203.0 Materials and supplies — — — 90.3 — 90.3 Natural gas and natural gas liquids in storage — — — 342.3 — 342.3 Other current assets 9.8 1.3 — 80.6 — 91.7 Total current assets 47.0 1.3 — 1,716.2 — — 1,764.5 Property, plant and equipment Property, plant and equipment 128.3 — — 15,431.3 — 15,559.6 Accumulated depreciation and amortization 86.4 — — 2,775.1 — 2,861.5 Net property, plant and equipment 41.9 — — 12,656.2 — 12,698.1 Investments and other assets Investments 5,752.1 3,133.7 8,058.4 803.0 (16,744.0 ) 1,003.2 Intercompany notes receivable 2,926.9 8,627.8 3,703.1 — (15,257.8 ) — Other assets 416.9 0.2 — 1,007.4 (44.4 ) 1,380.1 Total investments and other assets 9,095.9 11,761.7 11,761.5 1,810.4 (32,046.2 ) 2,383.3 Total assets $ 9,184.8 $ 11,763.0 $ 11,761.5 $ 16,182.8 $ (32,046.2 ) $ 16,845.9 Liabilities and equity Current liabilities Current maturities of long-term debt $ — $ 425.0 $ — $ 7.7 $ — $ 432.7 Short-term borrowings 614.7 — — — — 614.7 Accounts payable 12.0 — — 1,128.6 — 1,140.6 Other current liabilities 65.9 85.0 — 328.4 — 479.3 Total current liabilities 692.6 510.0 — 1,464.7 — 2,667.3 Intercompany debt — — 8,627.8 6,630.0 (15,257.8 ) — Long-term debt, excluding current maturities 2,726.4 5,336.4 — 28.8 — 8,091.6 Deferred credits and other liabilities 237.9 — — 208.1 (44.4 ) 401.6 Commitments and contingencies Equity Equity excluding noncontrolling interests in consolidated subsidiaries 5,527.9 5,916.6 3,133.7 7,693.7 (16,744.0 ) 5,527.9 Noncontrolling interests in consolidated subsidiaries — — — 157.5 — 157.5 Total equity 5,527.9 5,916.6 3,133.7 7,851.2 (16,744.0 ) 5,685.4 Total liabilities and equity $ 9,184.8 $ 11,763.0 $ 11,761.5 $ 16,182.8 $ (32,046.2 ) $ 16,845.9 Condensed Consolidating Statements of Cash Flows Three Months Ended March 31, 2018 ( Unaudited ) Parent Issuer & Guarantor Subsidiary Issuer & Guarantor Guarantor Subsidiary Combined Non-Guarantor Subsidiaries Consolidating Entries Total ( Millions of dollars ) Operating activities Cash provided by operating activities $ 266.8 $ 319.7 $ 17.1 $ 557.7 $ (666.0 ) $ 495.3 Investing activities Capital expenditures (5.7 ) — — (258.8 ) — (264.5 ) Contributions to unconsolidated affiliates — — — (0.1 ) — (0.1 ) Other investing activities — — 5.0 4.0 — 9.0 Cash provided by (used in) investing activities (5.7 ) — 5.0 (254.9 ) — (255.6 ) Financing activities Dividends paid (316.4 ) (333.0 ) (333.0 ) — 666.0 (316.4 ) Distributions to noncontrolling interests — — — (1.5 ) — (1.5 ) Intercompany borrowings (advances), net (514.5 ) 513.3 310.9 (309.7 ) — — Borrowing (repayment) of short-term borrowings, net (614.7 ) — — — — (614.7 ) Repayment of long-term debt — (500.0 ) — (1.9 ) — (501.9 ) Issuance of common stock 1,182.1 — — — — 1,182.1 Other, net (17.3 ) — — 10.3 — (7.0 ) Cash used in financing activities (280.8 ) (319.7 ) (22.1 ) — (302.8 ) 666.0 (259.4 ) Change in cash and cash equivalents (19.7 ) — — — — (19.7 ) Cash and cash equivalents at beginning of period 37.2 — — — — 37.2 Cash and cash equivalents at end of period $ 17.5 $ — $ — $ — $ — $ 17.5 Three Months Ended March 31, 2017 ( Unaudited ) Parent Issuer & Guarantor Subsidiary Issuer & Guarantor Guarantor Subsidiary Combined Non-Guarantor Subsidiaries Consolidating Entries Total ( Millions of dollars ) Operating activities Cash provided by operating activities $ 134.2 $ 322.1 $ 18.8 $ 324.5 $ (530.5 ) $ 269.1 Investing activities Capital expenditures (0.1 ) — — (112.6 ) — (112.7 ) Other investing activities — — 2.9 0.3 — 3.2 Cash provided by (used in) investing activities (0.1 ) — 2.9 (112.3 ) — (109.5 ) Financing activities Dividends paid (129.8 ) (333.0 ) (333.0 ) — 666.0 (129.8 ) Distributions to noncontrolling interests — — — (1.2 ) (135.5 ) (136.7 ) Intercompany borrowings (advances), net 52.1 (162.4 ) 319.4 (209.1 ) — — Borrowing (repayment) of short-term borrowings, net — 180.5 — — — 180.5 Repayment of long-term debt (0.1 ) — — (1.9 ) — (2.0 ) Issuance of common stock 3.7 — — — — 3.7 Other (6.2 ) (7.2 ) — — — (13.4 ) Cash used in financing activities (80.3 ) (322.1 ) (13.6 ) (212.2 ) 530.5 (97.7 ) Change in cash and cash equivalents 53.8 — 8.1 — — 61.9 Cash and cash equivalents at beginning of period 248.5 — 0.4 — — 248.9 Cash and cash equivalents at end of period $ 302.3 $ — $ 8.5 $ — $ — $ 310.8

SUMMARY OF SIGNIFICANT ACCOUN24

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	3 Months Ended
	Mar. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Basis of Accounting, Policy [Policy Text Block]	Our accompanying unaudited consolidated financial statements have been prepared pursuant to the rules and regulations of the SEC. These statements have been prepared in accordance with GAAP and reflect all adjustments that, in our opinion, are necessary for a fair statement of the results for the interim periods presented. All such adjustments are of a normal recurring nature. The 2017 year-end Consolidated Balance Sheet data was derived from our audited financial statements but does not include all disclosures required by GAAP. Certain reclassifications have been made in the prior-year financial statements to conform to the current year presentation. These unaudited consolidated financial statements should be read in conjunction with our audited consolidated financial statements in our Annual Report.
New Accounting Pronouncements, Policy [Policy Text Block]	Recently Issued Accounting Standards Update - Changes to GAAP are established by the Financial Accounting Standards Board (FASB) in the form of ASUs to the FASB Accounting Standards Codification. We consider the applicability and impact of all ASUs. ASUs not listed below were assessed and determined to be either not applicable or clarifications of ASUs listed below. We also exclude ASUs not yet adopted that were disclosed in our Annual Report to not materially impact us. The following tables provide a brief description of recent accounting pronouncements and our analysis of the effects on our financial statements: Standard Description Date of Adoption Effect on the Financial Statements or Other Significant Matters Standards that were adopted ASU 2014-09, “Revenue from Contracts with Customers (Topic 606)” The standard outlines the principles an entity must apply to measure and recognize revenue for entities that enter into contracts to provide goods or services to their customers. The core principle is that an entity should recognize revenue at an amount that reflects the consideration to which the entity expects to be entitled in exchange for transferring goods or services to a customer. The amendment also requires more extensive disaggregated revenue disclosures in interim and annual financial statements. First quarter 2018 We adopted this standard on January 1, 2018, using the modified retrospective method. We recognized the cumulative effect of adopting the new revenue standard as an increase to beginning retained earnings of $1.7 million. Results for reporting periods beginning after January 1, 2018, are presented under the new standard, while prior periods are not adjusted and continue to be reported under the accounting standards in effect for those periods. The adoption of Topic 606 was not material to our net income; however, a significant portion of amounts historically presented as services revenues are now presented as a reduction to cost of sales and fuel. See Note K for discussion of these changes and additional disclosures. Standard Description Date of Adoption Effect on the Financial Statements or Other Significant Matters Standards that were adopted ( continued ) ASU 2016-01, “Financial Instruments-Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities” The standard requires all equity investments, other than those accounted for using the equity method of accounting or those that result in consolidation of the investee, to be measured at fair value with changes in fair value recognized in net income, eliminates the available-for-sale classification for equity securities with readily determinable fair values and eliminates the cost method for equity investments without readily determinable fair values. First quarter 2018 We do not have any equity investments classified as available-for-sale or accounted for using the cost method, therefore, the impact of adopting of this standard was not material. ASU 2016-15, “Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments” The standard clarifies the classification of certain cash receipts and cash payments on the statement of cash flows where diversity in practice has been identified. First quarter 2018 The impact of adopting this standard was not material. ASU 2017-07, “Compensation - Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost” The standard requires the service cost component of net benefit cost to be reported in the same line item or items as other compensation costs from services rendered by the pertinent employees during the period. The other components of net benefit cost are required to be presented in the income statement separately from the service cost component and outside a subtotal of income from operations. First quarter 2018 We adopted this standard on January 1, 2018, and utilized the practical expedient to estimate the impact on the prior comparative period information presented. Immaterial reclassifications have been made to prior comparative period information to reflect the current period presentation. Prior to adoption, we expensed all components of the net periodic benefit costs for our pension and postretirement benefit plans in operations and maintenance expense. We now record only the service component of the net periodic benefit costs in operations and maintenance expense, with the remainder being recorded in other expense. There was no change to net income from the adoption of this standard. ASU 2017-12, “Derivatives and Hedging (Topic 815): Targeted Improvements to Accounting for Hedging Activities The standard more closely aligns hedge accounting with companies’ existing risk-management strategies by expanding the strategies eligible for hedge accounting, relaxing the timing requirements of hedge documentation and effectiveness assessments, permitting in certain cases, the use of qualitative assessments on an ongoing basis to assess hedge effectiveness, and requiring new disclosures and presentation. First quarter 2018 We adopted this standard in the first quarter 2018 and recorded an immaterial cumulative-effect adjustment to the opening balance of retained earnings and other comprehensive income to eliminate the separate measurement of hedge ineffectiveness. See Note C for changes to disclosures due to adopting this standard. ASU 2018-02, “Income Statement - Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income” This standard allows a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act. First quarter 2018 We adopted this standard in the first quarter 2018 and recorded a $38.1 million adjustment to retained earnings and accumulated other comprehensive income to eliminate the stranded tax effects resulting from the Tax Cuts and Jobs Act. Standard Description Date of Adoption Effect on the Financial Statements or Other Significant Matters Standards that are not yet adopted ASU 2016-02, “Leases (Topic 842)” The standard requires the recognition of lease assets and lease liabilities by lessees for those leases classified as operating leases under previous GAAP. It also requires qualitative disclosures along with specific quantitative disclosures by lessees and lessors to meet the objective of enabling users of financial statements to assess the amount, timing and uncertainty of cash flows arising from leases. First quarter 2019 We are evaluating our current leases and other contracts that may be considered leases under the new standard and the impact on our internal controls, accounting policies and financial statements and disclosures. Our evaluation process includes creating a database of our existing leases and identifying a central group to track and account for lease activity, which is ongoing. We are developing internal controls to ensure the completeness and accuracy of the data. Due to this ongoing work, we cannot yet determine the quantitative impact, but adoption of the standard will result in the recognition of right of use assets and lease liabilities not previously recorded that will be presented on our Consolidated Balance Sheet under Topic 842 and will require disclosure in our footnotes. We are also monitoring recent exposure drafts and clarifications issued by the FASB.

FAIR VALUE MEASUREMENTS FAIR VA

FAIR VALUE MEASUREMENTS FAIR VALUE MEASUREMENTS (Policies)	3 Months Ended
	Mar. 31, 2018
Fair Value Accounting Policy [Abstract]
Fair Value of Financial Instruments, Policy [Policy Text Block]	Determining Fair Value - 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 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. While many of the contracts in our derivative portfolio are executed in liquid markets where price transparency exists, some contracts are executed in markets for which market prices may exist, but the market may be relatively inactive. This results in limited price transparency that requires management’s judgment and assumptions to estimate fair values. For certain transactions, we utilize modeling techniques using NYMEX-settled pricing data and implied forward LIBOR curves. Inputs into our fair value estimates include commodity-exchange prices, over-the-counter quotes, historical correlations of pricing data, data obtained from third-party pricing services and LIBOR and other liquid money-market instrument rates. We validate our valuation inputs with third-party information and settlement prices from other sources, where available. In addition, as prescribed by the income approach, we compute the fair value of our derivative portfolio by discounting the projected future cash flows from our derivative assets and liabilities to present value using interest-rate yields to calculate present-value discount factors derived from LIBOR, Eurodollar futures and the LIBOR interest-rate swaps market. We also take into consideration the potential impact on market prices of liquidating positions in an orderly manner over a reasonable period of time under current market conditions. We consider current market data in evaluating counterparties’, as well as our own, nonperformance risk, net of collateral, by using specific and sector bond yields and monitoring the credit default swap markets. Although we use our best estimates to determine the fair value of the derivative contracts we have executed, the ultimate market prices realized could differ from our estimates, and the differences could be material. The fair value of our forward-starting interest-rate swaps are determined using financial models that incorporate the implied forward LIBOR yield curve for the same period as the future interest-rate swap settlements. 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 - fair value measurements are based on unadjusted quoted prices for identical securities in active markets, including NYMEX-settled prices. These balances are comprised predominantly of exchange-traded derivative contracts for natural gas and crude oil. • Level 2 - fair value measurements are based on significant observable pricing inputs, such as NYMEX-settled prices for natural gas and crude oil, and financial models that utilize implied forward LIBOR yield curves for interest-rate swaps. • Level 3 - fair value measurements are based on inputs that may include one or more unobservable inputs, including internally developed natural gas basis and NGL price curves that incorporate observable and unobservable market data from broker quotes, third-party pricing services, market volatilities derived from the most recent NYMEX close spot prices and forward LIBOR curves, and adjustments for the credit risk of our counterparties. We corroborate the data on which our fair value estimates are based using our market knowledge of recent transactions, analysis of historical correlations and validation with independent broker quotes. These balances categorized as Level 3 are composed of derivatives for natural gas and NGLs. We do not believe that our Level 3 fair value estimates have a material impact on our results of operations, as the majority of our derivatives are accounted for as hedges. 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.

EQUITY (Policies)

EQUITY (Policies)	6 Months Ended
	Jun. 30, 2017
Equity [Abstract]
Partnership agreement	Cash Distributions - Prior to the consummation of the Merger Transaction, we received distributions from ONEOK Partners on our common and Class B units and our 2 percent general partner interest, which included our incentive distribution rights.

SEGMENTS SEGMENTS (Policies)

SEGMENTS SEGMENTS (Policies)	3 Months Ended
	Mar. 31, 2018
Segment Reporting [Abstract]
Segment Accounting Policy [Policy Text Block]	Accounting Policies - The accounting policies of the segments are described in Note A of the Notes to Consolidated Financial Statements in our Annual Report, updated as described in Note A of this Quarterly Report. Our chief operating decision-maker reviews the financial performance of each of our three segments, as well as our financial performance as a whole, on a regular basis. Adjusted EBITDA by segment is utilized in this evaluation. We believe this financial measure is useful to investors because it and similar measures are used by many companies in our industry as a measurement of financial performance and are commonly employed by financial analysts and others to evaluate our financial performance and to compare financial performance among companies in our industry. Adjusted EBITDA for each segment is defined as net income adjusted for interest expense, depreciation and amortization, noncash impairment charges, income taxes, allowance for equity funds used during construction, noncash compensation and other noncash items. This calculation may not be comparable with similarly titled measures of other companies.

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	3 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Recurring Fair Value Measurements	The following tables set forth our recurring fair value measurements for the periods indicated: March 31, 2018 Level 1 Level 2 Level 3 Total - Gross Netting (a) Total - Net ( Thousands of dollars ) Derivative assets Commodity contracts Financial contracts $ 3,180 $ — $ 20,065 $ 23,245 $ (23,245 ) $ — Physical contracts — — 40 40 — 40 Interest-rate contracts — 83,513 — 83,513 — 83,513 Total derivative assets $ 3,180 $ 83,513 $ 20,105 $ 106,798 $ (23,245 ) $ 83,553 Derivative liabilities Commodity contracts Financial contracts $ (8,121 ) $ — $ (15,799 ) $ (23,920 ) $ 23,920 $ — Physical contracts — — (1,208 ) (1,208 ) — (1,208 ) Interest-rate contracts — (11,169 ) — (11,169 ) — (11,169 ) Total derivative liabilities $ (8,121 ) $ (11,169 ) $ (17,007 ) $ (36,297 ) $ 23,920 $ (12,377 ) (a) - Derivative assets and liabilities are presented in our Consolidated Balance Sheets on a net basis. We net derivative assets and liabilities when a legally enforceable master-netting arrangement exists between the counterparty to a derivative contract and us. At March 31, 2018 , we held no cash and posted $18.5 million of cash with various counterparties, including $0.7 million of cash collateral that is offsetting derivative net liability positions under master-netting arrangements in the table above. The remaining $17.8 million of cash collateral in excess of derivative net liability positions is included in other current assets in our Consolidated Balance Sheets. December 31, 2017 Level 1 Level 2 Level 3 Total - Gross Netting (a) Total - Net ( Thousands of dollars ) Derivative assets Commodity contracts Financial contracts $ 4,252 $ — $ 20,203 $ 24,455 $ (24,455 ) $ — Interest rate contracts — 49,960 — 49,960 — 49,960 Total derivative assets $ 4,252 $ 49,960 $ 20,203 $ 74,415 $ (24,455 ) $ 49,960 Derivative liabilities Commodity contracts Financial contracts $ (5,708 ) $ — $ (48,260 ) $ (53,968 ) $ 53,936 $ (32 ) Physical contracts — — (4,781 ) (4,781 ) — (4,781 ) Total derivative liabilities $ (5,708 ) $ — $ (53,041 ) $ (58,749 ) $ 53,936 $ (4,813 ) (a) - Derivative assets and liabilities are presented in our Consolidated Balance Sheets on a net basis. We net derivative assets and liabilities when a legally enforceable master-netting arrangement exists between the counterparty to a derivative contract and us. At December 31, 2017 , we held no cash and posted $49.7 million of cash with various counterparties, including $29.5 million of cash collateral that is offsetting derivative net liability positions under master-netting arrangements in the table above. The remaining $20.2 million of cash collateral in excess of derivative net liability positions is included in other current assets in our Consolidated Balance Sheets.
Reconciliation of Level 3 Fair Value Measurements	The following table sets forth a reconciliation of our Level 3 fair value measurements for the periods indicated: Three Months Ended March 31, Derivative Assets (Liabilities) 2018 2017 ( Thousands of dollars ) Net assets (liabilities) at beginning of period $ (32,838 ) $ (23,319 ) Total realized/unrealized gains (losses): Included in earnings (a) (85 ) 913 Included in other comprehensive income (loss) 36,021 21,634 Net assets (liabilities) at end of period $ 3,098 $ (772 ) (a) - Included in commodity sales revenues in our Consolidated Statements of Income.

RISK MANAGEMENT AND HEDGING A29

RISK MANAGEMENT AND HEDGING ACTIVITIES USING DERIVATIVES (Tables)	3 Months Ended
	Mar. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Fair Value of Derivatives	The following table sets forth the fair values of our derivative instruments presented on a gross basis for the periods indicated: March 31, 2018 December 31, 2017 Location in our Consolidated Balance Sheets Assets (Liabilities) Assets (Liabilities) ( Thousands of dollars ) Derivatives designated as hedging instruments Commodity contracts Financial contracts Other current assets/other current liabilities $ 16,719 $ (19,764 ) $ 16,978 $ (42,819 ) Other assets/other deferred credits 3,061 (747 ) — (3,838 ) Physical contracts Other current assets/other current liabilities 40 (1,208 ) — (4,781 ) Interest-rate contracts Other current assets 59,502 — 1,330 — Other assets/other deferred credits 24,011 (11,169 ) 48,630 — Total derivatives designated as hedging instruments 103,333 (32,888 ) 66,938 (51,438 ) Derivatives not designated as hedging instruments Commodity contracts Financial contracts Other current assets/other current liabilities 3,465 (3,409 ) 7,477 (7,311 ) Total derivatives not designated as hedging instruments 3,465 (3,409 ) 7,477 (7,311 ) Total derivatives $ 106,798 $ (36,297 ) $ 74,415 $ (58,749 )
Notional Amounts of Derivative Instruments	The following table sets forth the notional quantities for derivative instruments held for the periods indicated: March 31, 2018 December 31, 2017 Contract Type Purchased/ Payor Sold/ Receiver Purchased/ Payor Sold/ Receiver Derivatives designated as hedging instruments: Cash flow hedges Fixed price - Natural gas ( Bcf ) Futures and swaps — (18.5 ) — (24.5 ) - Crude oil and NGLs ( MMBbl ) Futures, forwards and swaps 3.5 (10.7 ) 3.5 (11.1 ) Basis - Natural gas ( Bcf ) Futures and swaps — (18.5 ) — (24.5 ) Interest-rate contracts ( Millions of dollars ) Swaps $ 2,000.0 $ — $ 1,750.0 $ — Derivatives not designated as hedging instruments: Fixed price - NGLs ( MMBbl ) Futures, forwards and swaps 0.5 (0.5 ) 0.8 (0.8 )
Schedule of Cash Flow Hedging Instruments Effect on Comprehensive Income (Loss)	The following table sets forth the unrealized effect of cash flow hedges recognized in other comprehensive income (loss) for the periods indicated: Three Months Ended Derivatives in Cash Flow Hedging Relationships March 31, 2018 2017 ( Thousands of dollars ) Commodity contracts $ 20,925 $ 27,328 Interest-rate contracts 23,911 1,529 Total unrealized gain (loss) recognized in other comprehensive income (loss) on derivatives $ 44,836 $ 28,857
Schedule of Cash Flow Hedging Instruments Effect on Income	The following table sets forth the effect of cash flow hedges in our Consolidated Statements of Income for the periods indicated: Derivatives in Cash Flow Hedging Relationships Location of Gain (Loss) Reclassified from Accumulated Other Comprehensive Loss into Net Income Three Months Ended March 31, 2018 2017 ( Thousands of dollars ) Commodity contracts Commodity sales revenues $ (11,611 ) $ (15,319 ) Interest-rate contracts Interest expense (3,943 ) (5,329 ) Total gain (loss) reclassified from accumulated other comprehensive loss into net income on derivatives $ (15,554 ) $ (20,648 )

DEBT DEBT (Tables)

DEBT DEBT (Tables)	3 Months Ended
	Mar. 31, 2018
Debt Instrument [Line Items]
Debt [Table Text Block]	The following table sets forth our consolidated debt for the periods indicated: March 31, December 31, ( Thousands of dollars ) ONEOK Commercial paper outstanding, bearing a weighted-average interest rate of 2.23% as of December 31, 2017 $ — $ 614,673 Senior unsecured obligations: $700,000 at 4.25% due February 2022 547,397 547,397 $500,000 at 7.5% due September 2023 500,000 500,000 $500,000 at 4.0% due July 2027 500,000 500,000 $100,000 at 6.875% due September 2028 100,000 100,000 $400,000 at 6.0% due June 2035 400,000 400,000 $700,000 at 4.95% due July 2047 700,000 700,000 ONEOK Partners Senior unsecured obligations: $425,000 at 3.2% due September 2018 425,000 425,000 $1,000,000 term loan, rate of 2.87% as of December 31, 2017, due January 2019 — 500,000 $500,000 at 8.625% due March 2019 500,000 500,000 $300,000 at 3.8% due March 2020 300,000 300,000 $900,000 at 3.375 % due October 2022 900,000 900,000 $425,000 at 5.0 % due September 2023 425,000 425,000 $500,000 at 4.9 % due March 2025 500,000 500,000 $600,000 at 6.65% due October 2036 600,000 600,000 $600,000 at 6.85% due October 2037 600,000 600,000 $650,000 at 6.125% due February 2041 650,000 650,000 $400,000 at 6.2% due September 2043 400,000 400,000 Guardian Pipeline Weighted average 7.85% due December 2022 34,695 36,607 Total debt 8,082,092 9,198,677 Unamortized portion of terminated swaps 18,038 18,468 Unamortized debt issuance costs and discounts (75,729 ) (78,193 ) Current maturities of long-term debt (932,650 ) (432,650 ) Short-term borrowings (a) — (614,673 ) Long-term debt $ 7,091,751 $ 8,091,629 (a) - Individual issuances of commercial paper under our commercial paper program generally mature in 90 days or less. These issuances are supported by and reduce the borrowing capacity under our $2.5 Billion Credit Agreement.

EQUITY (Tables)

EQUITY (Tables)	3 Months Ended
	Mar. 31, 2017
Equity [Abstract]
Schedule of distributions made to general or limited partner	The following table sets forth ONEOK Partners’ distributions paid during the period prior to the closing of the Merger Transaction: Three Months Ended March 31, 2017 ( Thousands, except per unit amounts ) Distribution per unit $ 0.79 General partner distributions $ 6,660 Incentive distributions 100,538 Distributions to general partner 107,198 Limited partner distributions to ONEOK 90,323 Limited partner distributions to other unitholders 135,480 Total distributions paid $ 333,001

ACCUMULATED OTHER COMPREHENSI32

ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) ACCUMULATED OTHER COMPREHENSIVE INCOME (Tables)	3 Months Ended
	Mar. 31, 2018
Accumulated Other Comprehensive Income (Loss)	The following table sets forth the balance in accumulated other comprehensive loss for the period indicated: Unrealized Gains (Losses) on Risk- Management Assets/Liabilities (a) Pension and Postretirement Benefit Plan Obligations (a) (b) Unrealized Gains (Losses) on Risk- Management Assets/Liabilities of Unconsolidated Affiliates (a) Accumulated Other Comprehensive Loss (a) ( Thousands of dollars ) January 1, 2018 $ (81,915 ) $ (105,411 ) $ (1,204 ) $ (188,530 ) Other comprehensive income (loss) before reclassifications 34,524 (601 ) 2,860 36,783 Amounts reclassified from accumulated other comprehensive loss 11,976 3,216 (36 ) 15,156 Net current-period other comprehensive income (loss) attributable to ONEOK 46,500 2,615 2,824 51,939 Impact of adoption of ASU 2018-02 (c) (17,935 ) (20,166 ) — (38,101 ) March 31, 2018 $ (53,350 ) $ (122,962 ) $ 1,620 $ (174,692 ) (a) - All amounts are presented net of tax. (b) - Includes amounts related to supplemental executive retirement plan. (c) - We elected to adopt this guidance in the first quarter 2018, which allows a reclassification from accumulated other comprehensive income/loss to retained earnings for the stranded tax effects resulting from the Tax Cuts and Jobs Act. After adopting and applying this guidance, our accumulated other comprehensive loss balance at March 31, 2018, does not include stranded taxes resulting from the Tax Cuts and Jobs Act.
Reclassification out of Accumulated Other Comprehensive Income (Loss)	The following table sets forth the effect of reclassifications from accumulated other comprehensive loss in our Consolidated Statements of Income for the periods indicated: Details about Accumulated Other Components Three Months Ended Affected Line Item in the Statements of Income March 31, 2018 2017 ( Thousands of dollars ) Unrealized gains (losses) on risk-management assets/liabilities Commodity contracts $ (11,611 ) $ (15,319 ) Commodity sales revenues Interest-rate contracts (3,943 ) (5,329 ) Interest expense (15,554 ) (20,648 ) Income before income taxes 3,578 3,365 Income tax expense (11,976 ) (17,283 ) Net income Noncontrolling interests — (11,625 ) Less: Net income attributable to noncontrolling interests $ (11,976 ) $ (5,658 ) Net income attributable to ONEOK Pension and postretirement benefit plan obligations (a) Amortization of net loss $ (4,592 ) $ (3,812 ) Other income (expense) Amortization of unrecognized prior service credit 415 415 Other income (expense) (4,177 ) (3,397 ) Income before income taxes 961 1,359 Income tax expense $ (3,216 ) $ (2,038 ) Net income attributable to ONEOK Unrealized gains (losses) on risk-management assets/liabilities of unconsolidated affiliates $ 47 $ (96 ) Equity in net earnings from investments (11 ) 15 Income tax expense 36 (81 ) Net income Noncontrolling interests — (56 ) Less: Net income attributable to noncontrolling interests $ 36 $ (25 ) Net income attributable to ONEOK Total reclassifications for the period attributable to ONEOK $ (15,156 ) $ (7,721 ) Net income attributable to ONEOK (a) - These components of accumulated other comprehensive loss are included in the computation of net periodic benefit cost. See Note H for additional detail of our net periodic benefit cost.

EARNINGS PER SHARE EARNINGS P33

EARNINGS PER SHARE EARNINGS PER SHARE (Tables)	3 Months Ended
	Mar. 31, 2018
Earnings Per Share [Abstract]
Earnings Per Share	The following tables set forth the computation of basic and diluted EPS for the periods indicated: Three Months Ended March 31, 2018 Income Shares Per Share Amount ( Thousands, except per share amounts ) Basic EPS Net income attributable to ONEOK available for common stock $ 264,233 409,676 $ 0.65 Diluted EPS Effect of dilutive securities — 2,497 Net income attributable to ONEOK available for common stock and common stock equivalents $ 264,233 412,173 $ 0.64 Three Months Ended March 31, 2017 Income Shares Per Share Amount ( Thousands, except per share amounts ) Basic EPS Net income attributable to ONEOK available for common stock $ 87,361 211,619 $ 0.41 Diluted EPS Effect of dilutive securities — 1,983 Net income attributable to ONEOK available for common stock and common stock equivalents $ 87,361 213,602 $ 0.41

EMPLOYEE BENEFIT PLANS EMPLOY34

EMPLOYEE BENEFIT PLANS EMPLOYEE BENEFIT PLANS (Tables)	3 Months Ended
	Mar. 31, 2018
Defined Benefit Plan [Abstract]
Components of net periodic benefit cost for pension and postretirement benefit plans	The following tables set forth the components of net periodic benefit cost for our pension and postretirement benefit plans for the periods indicated: Pension Benefits Postretirement Benefits Three Months Ended Three Months Ended March 31, March 31, 2018 2017 2018 2017 ( Thousands of dollars ) Components of net periodic benefit cost Service cost $ 1,832 $ 1,722 $ 211 $ 165 Interest cost 4,408 4,655 527 565 Expected return on plan assets (5,969 ) (5,336 ) (672 ) (564 ) Amortization of prior service credit — — (415 ) (415 ) Amortization of net loss 4,258 3,392 334 420 Net periodic benefit cost (income) $ 4,529 $ 4,433 $ (15 ) $ 171

UNCONSOLIDATED AFFILIATES (Tabl

UNCONSOLIDATED AFFILIATES (Tables)	3 Months Ended
	Mar. 31, 2018
Equity In Net Earnings From Investments
Schedule of Equity Method Investments [Line Items]
Schedule of Equity Method Investments [Table Text Block]	The following table sets forth our equity in net earnings from investments for the periods indicated: Three Months Ended March 31, 2018 2017 ( Thousands of dollars ) Northern Border Pipeline $ 17,137 $ 18,817 Overland Pass Pipeline Company 16,387 13,566 Roadrunner Gas Transmission 4,958 4,405 Other 1,705 2,776 Equity in net earnings from investments $ 40,187 $ 39,564
Unconsolidated Affiliates Financial Information
Schedule of Equity Method Investments [Line Items]
Schedule of Equity Method Investments [Table Text Block]	The following table sets forth summarized combined financial information of our unconsolidated affiliates for the periods indicated: Three Months Ended March 31, 2018 2017 ( Thousands of dollars ) Income Statement Operating revenues $ 158,908 $ 154,280 Operating expenses $ 68,401 $ 66,936 Net income $ 84,480 $ 81,131 Distributions paid to us $ 49,816 $ 46,920

REVENUE REVENUE (Tables)

REVENUE REVENUE (Tables)	3 Months Ended
	Mar. 31, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Disaggregation of Revenue [Table Text Block]	The impact on our Consolidated Income Statement and Balance Sheet is as follows (in thousands): Three Months Ended March 31, 2018 Income Statement As Reported Balance Without Adoption of Topic 606 Effect of Change Increase/(Decrease) Services revenue $ 282,073 $ 634,315 $ (352,242 ) Cost of sales and fuel (exclusive of depreciation and operating costs) $ 2,368,026 $ 2,725,774 $ (357,748 ) Depreciation and amortization $ 104,237 $ 104,092 $ 145 Income taxes $ 75,771 $ 74,539 $ 1,232 Net income $ 266,049 $ 261,920 $ 4,129 Net income attributable to noncontrolling interests $ 1,541 $ 1,539 $ 2 Net income attributable to ONEOK $ 264,508 $ 260,381 $ 4,127 March 31, 2018 Balance Sheet As Reported Balance Without Adoption of Topic 606 Effect of Change Increase/(Decrease) Natural gas and natural gas liquids in storage $ 185,298 $ 186,998 $ (1,700 ) Other current assets $ 106,067 $ 105,097 $ 970 Property, plant and equipment $ 15,838,443 $ 15,816,674 $ 21,769 Accumulated depreciation and amortization $ 2,960,254 $ 2,958,737 $ 1,517 Deferred income taxes $ 116,120 $ 117,854 $ (1,734 ) Other assets $ 159,428 $ 154,167 $ 5,261 Other current liabilities $ 122,922 $ 120,877 $ 2,045 Other deferred credits $ 366,701 $ 351,525 $ 15,176 Retained earnings/paid-in capital $ 7,735,173 $ 7,729,364 $ 5,809 Noncontrolling interests in consolidated subsidiaries $ 167,806 $ 167,787 $ 19
Revenue, Initial Application Period Cumulative Effect Transition [Table Text Block]	Contract Liability ( Millions of dollars ) Balance at January 1, 2018 (a) $ 33.3 Revenue recognized included in beginning balance (17.3 ) Net additions 5.2 Balance at March 31, 2018 (b) $ 21.2 (a) - Balance includes $19.5 million of current liabilities. (b) - Contract liabilities of $6.0 million and $15.2 million are included in other current liabilities and other deferred credits, respectively, in our Consolidated Balance Sheet.
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Table Text Block]	The following table presents aggregate value allocated to unsatisfied performance obligations as of March 31, 2018, and the amounts we expect to recognize in revenue in future periods, related primarily to firm transportation and storage contracts with remaining contract terms ranging from one month to 26 years: Expected Period of Recognition in Revenue ( Millions of dollars ) Remainder of 2018 $ 242.9 2019 247.3 2020 215.4 2021 209.7 2022 and beyond 1,032.6 Total estimated transaction price allocated to unsatisfied performance obligations $ 1,947.9

SEGMENTS (Tables)

SEGMENTS (Tables)	3 Months Ended
	Mar. 31, 2018
Segment Reporting, Disclosure of Entity's Reportable Segments [Abstract]
Segments	The following tables set forth certain selected financial information for our operating segments for the periods indicated: Three Months Ended Natural Gas Gathering and Processing Natural Gas Liquids (a) Natural Gas Pipelines (b) Total ( Thousands of dollars ) NGL and condensate sales $ 413,157 $ 2,552,770 $ — $ 2,965,927 Residue natural gas sales 254,997 — 4,919 259,916 Gathering, processing and exchange services revenue 38,429 83,258 — 121,687 Transportation and storage revenue — 53,478 98,338 151,816 Other 1,408 2,963 6,654 11,025 Total revenues (c) 707,991 2,692,469 109,911 3,510,371 Cost of sales and fuel (exclusive of depreciation and operating costs) (492,622 ) (2,281,072 ) (5,454 ) (2,779,148 ) Operating costs (88,359 ) (88,592 ) (33,190 ) (210,141 ) Equity in net earnings from investments 1,668 16,424 22,095 40,187 Other 1,873 2,850 263 4,986 Segment adjusted EBITDA $ 130,551 $ 342,079 $ 93,625 $ 566,255 Depreciation and amortization $ (47,748 ) $ (42,427 ) $ (13,269 ) $ (103,444 ) Total assets $ 5,462,305 $ 8,370,364 $ 2,060,700 $ 15,893,369 Capital expenditures $ 111,729 $ 124,921 $ 19,898 $ 256,548 (a) - Our Natural Gas Liquids segment has regulated and nonregulated operations. Our Natural Gas Liquids segment’s regulated operations had revenues of $300.0 million , of which $253.4 million related to sales within the segment and cost of sales and fuel of $122.8 million . (b) - Our Natural Gas Pipelines segment has regulated and nonregulated operations. Our Natural Gas Pipelines segment’s regulated operations had revenues of $68.0 million and cost of sales and fuel of $9.1 million . (c) - Intersegment revenues for the Natural Gas Gathering and Processing, Natural Gas Liquids and Natural Gas Pipelines segments totaled $397.8 million , $9.0 million and $2.1 million respectively. Three Months Ended March 31, 2018 Total Segments Other and Eliminations Total ( Thousands of dollars ) Reconciliations of total segments to consolidated NGL and condensate sales $ 2,965,927 $ (408,910 ) $ 2,557,017 Residue natural gas sales 259,916 2,250 262,166 Gathering, processing and exchange services revenue 121,687 (21 ) 121,666 Transportation and storage revenue 151,816 (2,094 ) 149,722 Other 11,025 481 11,506 Total revenues (a) $ 3,510,371 $ (408,294 ) $ 3,102,077 Cost of sales and fuel (exclusive of depreciation and operating costs) $ (2,779,148 ) $ 411,122 $ (2,368,026 ) Operating costs $ (210,141 ) $ (63 ) $ (210,204 ) Depreciation and amortization $ (103,444 ) $ (793 ) $ (104,237 ) Equity in net earnings from investments $ 40,187 $ — $ 40,187 Total assets $ 15,893,369 $ 538,978 $ 16,432,347 Capital expenditures $ 256,548 $ 7,919 $ 264,467 (a) - Noncustomer revenue for the three months ended March 31, 2018, totaled $(9.0) million related primarily to losses reclassified from accumulated other comprehensive income from derivatives on commodity contracts. Three Months Ended Natural Gas Gathering and Processing Natural Gas Liquids (a) Natural Gas Pipelines (b) Total ( Thousands of dollars ) Sales to unaffiliated customers $ 400,149 $ 2,244,000 $ 104,924 $ 2,749,073 Intersegment revenues 261,127 147,984 1,894 411,005 Total revenues 661,276 2,391,984 106,818 3,160,078 Cost of sales and fuel (exclusive of depreciation and operating costs) (488,384 ) (2,048,693 ) (16,603 ) (2,553,680 ) Operating costs (71,328 ) (78,440 ) (31,563 ) (181,331 ) Equity in net earnings from investments 2,630 13,722 23,212 39,564 Other (227 ) (344 ) 1,094 523 Segment adjusted EBITDA $ 103,967 $ 278,229 $ 82,958 $ 465,154 Depreciation and amortization $ (44,968 ) $ (41,115 ) $ (12,543 ) $ (98,626 ) Total assets $ 5,296,359 $ 8,194,835 $ 1,945,407 $ 15,436,601 Capital expenditures $ 63,151 $ 20,453 $ 25,014 $ 108,618 (a) - Our Natural Gas Liquids segment has regulated and nonregulated operations. Our Natural Gas Liquids segment’s regulated operations had revenues of $296.3 million , of which $252.9 million related to sales within the segment and cost of sales and fuel of $116.5 million . (b) - Our Natural Gas Pipelines segment has regulated and nonregulated operations. Our Natural Gas Pipelines segment’s regulated operations had revenues of $68.9 million and cost of sales and fuel of $14.1 million . Three Months Ended March 31, 2017 Total Segments Other and Eliminations Total ( Thousands of dollars ) Reconciliations of total segments to consolidated Sales to unaffiliated customers $ 2,749,073 $ 538 $ 2,749,611 Intersegment revenues 411,005 (411,005 ) — Total revenues $ 3,160,078 $ (410,467 ) $ 2,749,611 Cost of sales and fuel (exclusive of depreciation and operating costs) $ (2,553,680 ) $ 409,837 $ (2,143,843 ) Operating costs $ (181,331 ) $ (7,874 ) $ (189,205 ) Depreciation and amortization $ (98,626 ) $ (793 ) $ (99,419 ) Equity in net earnings from investments $ 39,564 $ — $ 39,564 Total assets $ 15,436,601 $ 630,957 $ 16,067,558 Capital expenditures $ 108,618 $ 4,119 $ 112,737 Three Months Ended March 31, 2018 2017 Reconciliation of net income to total segment adjusted EBITDA ( Thousands of dollars ) Net income $ 266,049 $ 186,185 Add: Interest expense, net of capitalized interest 115,725 116,462 Depreciation and amortization 104,237 99,419 Income taxes 75,771 54,941 Noncash compensation expense 9,226 1,647 Other corporate costs and noncash items (4,753 ) 6,500 Total segment adjusted EBITDA $ 566,255 $ 465,154

SUPPLEMENTAL CONDENSED CONSOL38

SUPPLEMENTAL CONDENSED CONSOLIDATING FINANCIAL INFORMATION (Tables)	3 Months Ended
	Mar. 31, 2018
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Condensed Consolidating Statements of Income	Condensed Consolidating Statements of Income Three Months Ended March 31, 2018 ( Unaudited ) Parent Issuer & Guarantor Subsidiary Issuer & Guarantor Guarantor Subsidiary Combined Non-Guarantor Subsidiaries Consolidating Entries Total ( Millions of dollars ) Revenues Commodity sales $ — $ — $ — $ 2,820.0 $ — $ 2,820.0 Services — — — 282.6 (0.5 ) 282.1 Total revenues — — — 3,102.6 (0.5 ) 3,102.1 Cost of sales and fuel (exclusive of items shown separately below) — — — 2,368.0 — 2,368.0 Operating expenses (0.7 ) — — 315.7 (0.5 ) 314.5 Gain on sale of assets — — — (0.1 ) — (0.1 ) Operating income 0.7 — — 419.0 — 419.7 Equity in net earnings from investments 368.5 370.9 370.9 28.6 (1,098.7 ) 40.2 Other income (expense), net 7.2 77.1 77.1 (9.6 ) (154.2 ) (2.4 ) Interest expense, net (39.8 ) (77.1 ) (77.1 ) (75.9 ) 154.2 (115.7 ) Income before income taxes 336.6 370.9 370.9 362.1 (1,098.7 ) 341.8 Income taxes (72.1 ) — — (3.7 ) — (75.8 ) Net income 264.5 370.9 370.9 358.4 (1,098.7 ) 266.0 Less: Net income attributable to noncontrolling interests — — — 1.5 — 1.5 Net income attributable to ONEOK 264.5 370.9 370.9 356.9 (1,098.7 ) 264.5 Less: Preferred stock dividends 0.3 — — — — 0.3 Net income available to common shareholders $ 264.2 $ 370.9 $ 370.9 $ 356.9 $ (1,098.7 ) $ 264.2 Three Months Ended March 31, 2017 ( Unaudited ) Parent Issuer & Guarantor Subsidiary Issuer & Guarantor Guarantor Subsidiary Combined Non-Guarantor Subsidiaries Consolidating Entries Total ( Millions of dollars ) Revenues Commodity sales $ — $ — $ — $ 2,216.7 $ — $ 2,216.7 Services — — — 532.9 — 532.9 Total revenues — — — 2,749.6 — 2,749.6 Cost of sales and fuel (exclusive of items shown separately below) — — — 2,143.8 — 2,143.8 Operating expenses 6.9 — — 281.8 — 288.7 Operating income (6.9 ) — — 324.0 — 317.1 Equity in net earnings from investments 268.7 269.1 269.1 20.7 (788.0 ) 39.6 Other income (expense), net 0.5 91.3 91.3 0.4 (182.6 ) 0.9 Interest expense, net (25.8 ) (91.3 ) (91.3 ) (90.7 ) 182.6 (116.5 ) Income before income taxes 236.5 269.1 269.1 254.4 (788.0 ) 241.1 Income taxes (51.2 ) — — (3.7 ) — (54.9 ) Net income 185.3 269.1 269.1 250.7 (788.0 ) 186.2 Less: Net income attributable to noncontrolling interests 97.9 — — 0.9 — 98.8 Net income attributable to ONEOK $ 87.4 $ 269.1 $ 269.1 $ 249.8 $ (788.0 ) $ 87.4
Condensed Consolidating Statements of Comprehensive Income	Condensed Consolidating Statements of Comprehensive Income Three Months Ended March 31, 2018 ( Unaudited ) Parent Issuer & Guarantor Subsidiary Issuer & Guarantor Guarantor Subsidiary Combined Non-Guarantor Subsidiaries Consolidating Entries Total ( Millions of dollars ) Net income $ 264.5 $ 370.9 $ 370.9 $ 358.4 $ (1,098.7 ) $ 266.0 Other comprehensive income (loss), net of tax Unrealized gains (losses) on derivatives, net of tax 18.4 20.9 20.9 16.1 (41.8 ) 34.5 Realized (gains) losses on derivatives in net income, net of tax 0.9 14.3 11.6 8.3 (23.1 ) 12.0 Change in pension and postretirement benefit plan liability, net of tax 3.2 (0.6 ) — — — 2.6 Other comprehensive income (loss) on investments in unconsolidated affiliates, net of tax — 3.7 3.7 2.8 (7.4 ) 2.8 Total other comprehensive income (loss), net of tax 22.5 38.3 36.2 27.2 (72.3 ) 51.9 Comprehensive income 287.0 409.2 407.1 385.6 (1,171.0 ) 317.9 Less: Comprehensive income attributable to noncontrolling interests — — — 1.5 — 1.5 Comprehensive income attributable to ONEOK $ 287.0 $ 409.2 $ 407.1 $ 384.1 $ (1,171.0 ) $ 316.4 Three Months Ended March 31, 2017 ( Unaudited ) Parent Issuer & Guarantor Subsidiary Issuer & Guarantor Guarantor Subsidiary Combined Non-Guarantor Subsidiaries Consolidating Entries Total ( Millions of dollars ) Net income $ 185.3 $ 269.1 $ 269.1 $ 250.7 $ (788.0 ) $ 186.2 Other comprehensive income (loss), net of tax Unrealized gains (losses) on derivatives, net of tax — 28.8 27.3 51.8 (83.4 ) 24.5 Realized (gains) losses on derivatives in net income, net of tax 0.5 19.8 15.3 32.1 (50.4 ) 17.3 Change in pension and postretirement benefit plan liability, net of tax 2.0 — — — — 2.0 Other comprehensive income (loss) on investments in unconsolidated affiliates, net of tax — 0.4 0.4 0.7 (1.2 ) 0.3 Total other comprehensive income (loss), net of tax 2.5 49.0 43.0 84.6 (135.0 ) 44.1 Comprehensive income 187.8 318.1 312.1 335.3 (923.0 ) 230.3 Less: Comprehensive income attributable to noncontrolling interests 126.8 — — 0.9 — 127.7 Comprehensive income attributable to ONEOK $ 61.0 $ 318.1 $ 312.1 $ 334.4 $ (923.0 ) $ 102.6
Condensed Consolidating Balance Sheets	Condensed Consolidating Balance Sheets March 31, 2018 ( Unaudited ) Parent Issuer & Guarantor Subsidiary Issuer & Guarantor Guarantor Subsidiary Combined Non-Guarantor Subsidiaries Consolidating Entries Total Assets ( Millions of dollars ) Current assets Cash and cash equivalents $ 17.5 $ — $ — $ — $ — $ 17.5 Accounts receivable, net — — — 844.2 — 844.2 Natural gas and natural gas liquids in storage — — — 185.3 — 185.3 Other current assets 70.8 — — 172.9 — 243.7 Total current assets 88.3 — — 1,202.4 — 1,290.7 Property, plant and equipment Property, plant and equipment 134.1 — — 15,704.3 — 15,838.4 Accumulated depreciation and amortization 87.7 — — 2,872.5 — 2,960.2 Net property, plant and equipment 46.4 — — 12,831.8 — 12,878.2 Investments and other assets Investments 5,823.6 3,207.8 8,443.5 802.9 (17,280.4 ) 997.4 Intercompany notes receivable 3,450.2 8,118.3 2,882.6 — (14,451.1 ) — Other assets 305.4 — — 1,008.0 (47.4 ) 1,266.0 Total investments and other assets 9,579.2 11,326.1 11,326.1 1,810.9 (31,778.9 ) 2,263.4 Total assets $ 9,713.9 $ 11,326.1 $ 11,326.1 $ 15,845.1 $ (31,778.9 ) $ 16,432.3 Liabilities and equity Current liabilities Current maturities of long-term debt $ — $ 925.0 $ — $ 7.7 $ — $ 932.7 Accounts payable 6.3 — — 766.8 — 773.1 Other current liabilities 43.5 68.2 — 233.3 — 345.0 Total current liabilities 49.8 993.2 — 1,007.8 — 2,050.8 Intercompany debt — — 8,118.3 6,332.8 (14,451.1 ) — Long-term debt, excluding current maturities 2,726.8 4,338.1 — 26.9 — 7,091.8 Deferred credits and other liabilities 235.8 — — 232.0 (47.4 ) 420.4 Commitments and contingencies Equity Equity excluding noncontrolling interests in consolidated subsidiaries 6,701.5 5,994.8 3,207.8 8,077.8 (17,280.4 ) 6,701.5 Noncontrolling interests in consolidated subsidiaries — — — 167.8 — 167.8 Total equity 6,701.5 5,994.8 3,207.8 8,245.6 (17,280.4 ) 6,869.3 Total liabilities and equity $ 9,713.9 $ 11,326.1 $ 11,326.1 $ 15,845.1 $ (31,778.9 ) $ 16,432.3 December 31, 2017 ( Unaudited ) Parent Issuer & Guarantor Subsidiary Issuer & Guarantor Guarantor Subsidiary Combined Non-Guarantor Subsidiaries Consolidating Entries Total Assets ( Millions of dollars ) Current assets Cash and cash equivalents $ 37.2 $ — $ — $ — $ — $ 37.2 Accounts receivable, net — — — 1,203.0 — 1,203.0 Materials and supplies — — — 90.3 — 90.3 Natural gas and natural gas liquids in storage — — — 342.3 — 342.3 Other current assets 9.8 1.3 — 80.6 — 91.7 Total current assets 47.0 1.3 — 1,716.2 — — 1,764.5 Property, plant and equipment Property, plant and equipment 128.3 — — 15,431.3 — 15,559.6 Accumulated depreciation and amortization 86.4 — — 2,775.1 — 2,861.5 Net property, plant and equipment 41.9 — — 12,656.2 — 12,698.1 Investments and other assets Investments 5,752.1 3,133.7 8,058.4 803.0 (16,744.0 ) 1,003.2 Intercompany notes receivable 2,926.9 8,627.8 3,703.1 — (15,257.8 ) — Other assets 416.9 0.2 — 1,007.4 (44.4 ) 1,380.1 Total investments and other assets 9,095.9 11,761.7 11,761.5 1,810.4 (32,046.2 ) 2,383.3 Total assets $ 9,184.8 $ 11,763.0 $ 11,761.5 $ 16,182.8 $ (32,046.2 ) $ 16,845.9 Liabilities and equity Current liabilities Current maturities of long-term debt $ — $ 425.0 $ — $ 7.7 $ — $ 432.7 Short-term borrowings 614.7 — — — — 614.7 Accounts payable 12.0 — — 1,128.6 — 1,140.6 Other current liabilities 65.9 85.0 — 328.4 — 479.3 Total current liabilities 692.6 510.0 — 1,464.7 — 2,667.3 Intercompany debt — — 8,627.8 6,630.0 (15,257.8 ) — Long-term debt, excluding current maturities 2,726.4 5,336.4 — 28.8 — 8,091.6 Deferred credits and other liabilities 237.9 — — 208.1 (44.4 ) 401.6 Commitments and contingencies Equity Equity excluding noncontrolling interests in consolidated subsidiaries 5,527.9 5,916.6 3,133.7 7,693.7 (16,744.0 ) 5,527.9 Noncontrolling interests in consolidated subsidiaries — — — 157.5 — 157.5 Total equity 5,527.9 5,916.6 3,133.7 7,851.2 (16,744.0 ) 5,685.4 Total liabilities and equity $ 9,184.8 $ 11,763.0 $ 11,761.5 $ 16,182.8 $ (32,046.2 ) $ 16,845.9
Condensed Consolidating Statements of Cash Flows	Condensed Consolidating Statements of Cash Flows Three Months Ended March 31, 2018 ( Unaudited ) Parent Issuer & Guarantor Subsidiary Issuer & Guarantor Guarantor Subsidiary Combined Non-Guarantor Subsidiaries Consolidating Entries Total ( Millions of dollars ) Operating activities Cash provided by operating activities $ 266.8 $ 319.7 $ 17.1 $ 557.7 $ (666.0 ) $ 495.3 Investing activities Capital expenditures (5.7 ) — — (258.8 ) — (264.5 ) Contributions to unconsolidated affiliates — — — (0.1 ) — (0.1 ) Other investing activities — — 5.0 4.0 — 9.0 Cash provided by (used in) investing activities (5.7 ) — 5.0 (254.9 ) — (255.6 ) Financing activities Dividends paid (316.4 ) (333.0 ) (333.0 ) — 666.0 (316.4 ) Distributions to noncontrolling interests — — — (1.5 ) — (1.5 ) Intercompany borrowings (advances), net (514.5 ) 513.3 310.9 (309.7 ) — — Borrowing (repayment) of short-term borrowings, net (614.7 ) — — — — (614.7 ) Repayment of long-term debt — (500.0 ) — (1.9 ) — (501.9 ) Issuance of common stock 1,182.1 — — — — 1,182.1 Other, net (17.3 ) — — 10.3 — (7.0 ) Cash used in financing activities (280.8 ) (319.7 ) (22.1 ) — (302.8 ) 666.0 (259.4 ) Change in cash and cash equivalents (19.7 ) — — — — (19.7 ) Cash and cash equivalents at beginning of period 37.2 — — — — 37.2 Cash and cash equivalents at end of period $ 17.5 $ — $ — $ — $ — $ 17.5 Three Months Ended March 31, 2017 ( Unaudited ) Parent Issuer & Guarantor Subsidiary Issuer & Guarantor Guarantor Subsidiary Combined Non-Guarantor Subsidiaries Consolidating Entries Total ( Millions of dollars ) Operating activities Cash provided by operating activities $ 134.2 $ 322.1 $ 18.8 $ 324.5 $ (530.5 ) $ 269.1 Investing activities Capital expenditures (0.1 ) — — (112.6 ) — (112.7 ) Other investing activities — — 2.9 0.3 — 3.2 Cash provided by (used in) investing activities (0.1 ) — 2.9 (112.3 ) — (109.5 ) Financing activities Dividends paid (129.8 ) (333.0 ) (333.0 ) — 666.0 (129.8 ) Distributions to noncontrolling interests — — — (1.2 ) (135.5 ) (136.7 ) Intercompany borrowings (advances), net 52.1 (162.4 ) 319.4 (209.1 ) — — Borrowing (repayment) of short-term borrowings, net — 180.5 — — — 180.5 Repayment of long-term debt (0.1 ) — — (1.9 ) — (2.0 ) Issuance of common stock 3.7 — — — — 3.7 Other (6.2 ) (7.2 ) — — — (13.4 ) Cash used in financing activities (80.3 ) (322.1 ) (13.6 ) (212.2 ) 530.5 (97.7 ) Change in cash and cash equivalents 53.8 — 8.1 — — 61.9 Cash and cash equivalents at beginning of period 248.5 — 0.4 — — 248.9 Cash and cash equivalents at end of period $ 302.3 $ — $ 8.5 $ — $ — $ 310.8

SUMMARY OF SIGNIFICANT ACCOUN39

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) - shares	3 Months Ended	6 Months Ended	12 Months Ended
	Mar. 31, 2018	Jun. 30, 2017	Dec. 31, 2017
Entity Information [Line Items]
Common Stock, Shares, Issued	445,016,234		423,166,234
Business Acquisition, Description of Acquired Entity		On June 30, 2017, we completed the acquisition of all of the outstanding common units of ONEOK Partners that we did not already own at a fixed exchange ratio of 0.985 of a share of our common stock for each ONEOK Partners common unit. We issued 168.9 million shares of our common stock to third-party common unitholders of ONEOK Partners in exchange for all of the 171.5 million outstanding common units of ONEOK Partners that we previously did not own. As a result of the completion of the Merger Transaction, common units of ONEOK Partners are no longer publicly traded.
General partnership ownership interest	100.00%	41.20%	100.00%

FAIR VALUE MEASUREMENTS - Part

FAIR VALUE MEASUREMENTS - Part 1 (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash held - offsetting derivative net asset positions under master-netting arrangements	$ 0	$ 0
Cash posted - total	18,500	49,700
Cash posted - offsetting derivative net liability positions under master-netting arrangements	700	29,500
Cash posted - remaining in excess of derivative net liability positions included in consolidated Balance Sheets	17,800	20,200
Long-term debt, Fair Value	8,700,000	9,300,000
Long-term debt	8,000,000	8,500,000
Fair Value, Measurements, Recurring [Member]
Derivative assets
Financial contracts	0	0
Physical contracts	40
Interest-rate contracts	83,513	49,960
Total derivative assets	83,553	49,960
Derivative assets netting	(23,245)	(24,455)
Derivative liabilities
Financial contracts	0	(32)
Physical contracts	(1,208)	(4,781)
Interest-rate contracts	(11,169)
Total derivative liabilities	(12,377)	(4,813)
Derivative liabilities netting	23,920	53,936
Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member]
Derivative assets
Financial contracts	23,245	24,455
Physical contracts	40
Interest-rate contracts	83,513	49,960
Total derivative assets	106,798	74,415
Derivative liabilities
Financial contracts	(23,920)	(53,968)
Physical contracts	(1,208)	(4,781)
Interest-rate contracts	(11,169)
Total derivative liabilities	(36,297)	(58,749)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Derivative assets
Financial contracts	3,180	4,252
Physical contracts	0
Interest-rate contracts	0	0
Total derivative assets	3,180	4,252
Derivative liabilities
Financial contracts	(8,121)	(5,708)
Physical contracts	0	0
Interest-rate contracts	0
Total derivative liabilities	(8,121)	(5,708)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Derivative assets
Financial contracts	0	0
Physical contracts	0
Interest-rate contracts	83,513	49,960
Total derivative assets	83,513	49,960
Derivative liabilities
Financial contracts	0	0
Physical contracts	0	0
Interest-rate contracts	(11,169)
Total derivative liabilities	(11,169)	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Derivative assets
Financial contracts	20,065	20,203
Physical contracts	40
Interest-rate contracts	0	0
Total derivative assets	20,105	20,203
Derivative liabilities
Financial contracts	(15,799)	(48,260)
Physical contracts	(1,208)	(4,781)
Interest-rate contracts	0
Total derivative liabilities	$ (17,007)	$ (53,041)

FAIR VALUE MEASUREMENTS - Par41

FAIR VALUE MEASUREMENTS - Part 2 (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Fair Value, Assets And Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Net assets (liabilities) at beginning of period	$ (32,838)	$ (23,319)
Total realized/unrealized gains (losses):
Included in earnings	(85)	913
Included in other comprehensive income (loss)	36,021	21,634
Net assets (liabilities) at end of period	3,098	(772)
Transfers between levels	$ 0	$ 0

RISK MANAGEMENT AND HEDGING A42

RISK MANAGEMENT AND HEDGING ACTIVITIES USING DERIVATIVES Part 1 (Details) - USD ($)	Mar. 31, 2018	Dec. 31, 2017
Derivative, Fair Value [Line Items]
Assets	$ 106,798,000	$ 74,415,000
(Liabilities)	(36,297,000)	(58,749,000)
Derivative, Net Liability Position, Aggregate Fair Value	0
Derivatives designated as hedging instruments
Derivative, Fair Value [Line Items]
Assets	103,333,000	66,938,000
(Liabilities)	(32,888,000)	(51,438,000)
Derivatives not designated as hedging instruments
Derivative, Fair Value [Line Items]
Assets	3,465,000	7,477,000
(Liabilities)	(3,409,000)	(7,311,000)
Natural Gas Pipelines [Member]
Derivative, Fair Value [Line Items]
Derivative, Fair Value, Net	0	0
Other Current Assets [Member] | Commodity contracts | Financial contracts | Derivatives designated as hedging instruments
Derivative, Fair Value [Line Items]
Assets	16,719,000	16,978,000
Other Current Assets [Member] | Commodity contracts | Financial contracts | Derivatives not designated as hedging instruments
Derivative, Fair Value [Line Items]
Assets	3,465,000	7,477,000
Other Current Assets [Member] | Commodity contracts | Physical contracts | Derivatives designated as hedging instruments
Derivative, Fair Value [Line Items]
Assets	40,000	0
Other Current Assets [Member] | Interest-rate contracts | Derivatives designated as hedging instruments
Derivative, Fair Value [Line Items]
Assets	59,502,000	1,330,000
Other Current Liabilities [Member] | Commodity contracts | Financial contracts | Derivatives designated as hedging instruments
Derivative, Fair Value [Line Items]
(Liabilities)	(19,764,000)	(42,819,000)
Other Current Liabilities [Member] | Commodity contracts | Financial contracts | Derivatives not designated as hedging instruments
Derivative, Fair Value [Line Items]
(Liabilities)	(3,409,000)	(7,311,000)
Other Current Liabilities [Member] | Commodity contracts | Physical contracts | Derivatives designated as hedging instruments
Derivative, Fair Value [Line Items]
(Liabilities)	(1,208,000)	(4,781,000)
Other Current Liabilities [Member] | Interest-rate contracts | Derivatives designated as hedging instruments
Derivative, Fair Value [Line Items]
(Liabilities)	0	0
Other Assets [Member] | Commodity contracts | Financial contracts | Derivatives designated as hedging instruments
Derivative, Fair Value [Line Items]
Assets	3,061,000	0
Other Assets [Member] | Interest-rate contracts | Derivatives designated as hedging instruments
Derivative, Fair Value [Line Items]
Assets	24,011,000	48,630,000
Other Liabilities [Member] | Commodity contracts | Financial contracts | Derivatives designated as hedging instruments
Derivative, Fair Value [Line Items]
(Liabilities)	(747,000)	(3,838,000)
Other Liabilities [Member] | Interest-rate contracts | Derivatives designated as hedging instruments
Derivative, Fair Value [Line Items]
(Liabilities)	$ (11,169,000)	$ 0

RISK MANAGEMENT AND HEDGING A43

RISK MANAGEMENT AND HEDGING ACTIVITIES USING DERIVATIVES, Part 2 (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018USD ($)MMcfMMBbls	Dec. 31, 2017USD ($)MMcfMMBbls
Designated as Hedging Instrument [Member] | Futures and swaps | - Natural gas (Bcf) | Fixed price | Purchased/ Payor
Derivative [Line Items]
Notional Amount | MMcf	0	0
Designated as Hedging Instrument [Member] | Futures and swaps | - Natural gas (Bcf) | Fixed price | Sold/ Receiver
Derivative [Line Items]
Notional Amount | MMcf	(18,500)	(24,500)
Designated as Hedging Instrument [Member] | Futures and swaps | - Natural gas (Bcf) | Basis | Purchased/ Payor
Derivative [Line Items]
Notional Amount | MMcf	0	0
Designated as Hedging Instrument [Member] | Futures and swaps | - Natural gas (Bcf) | Basis | Sold/ Receiver
Derivative [Line Items]
Notional Amount | MMcf	(18,500)	(24,500)
Designated as Hedging Instrument [Member] | Futures, forwards and swaps | - Crude oil and NGLs (MMBbl) | Fixed price | Purchased/ Payor
Derivative [Line Items]
Notional Amount | MMBbls	3.5	3.5
Designated as Hedging Instrument [Member] | Futures, forwards and swaps | - Crude oil and NGLs (MMBbl) | Fixed price | Sold/ Receiver
Derivative [Line Items]
Notional Amount | MMBbls	(10.7)	(11.1)
Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Purchased/ Payor
Derivative [Line Items]
Derivative, Notional Amount	$ 2,000,000	$ 1,750,000
Designated as Hedging Instrument [Member] | Interest Rate Contract [Member] | Sold/ Receiver
Derivative [Line Items]
Derivative, Notional Amount	$ 0	$ 0
Not Designated as Hedging Instrument [Member] | Futures, forwards and swaps | - Crude oil and NGLs (MMBbl) | Fixed price | Purchased/ Payor
Derivative [Line Items]
Notional Amount | MMBbls	0.5	0.8
Not Designated as Hedging Instrument [Member] | Futures, forwards and swaps | - Crude oil and NGLs (MMBbl) | Fixed price | Sold/ Receiver
Derivative [Line Items]
Notional Amount | MMBbls	(0.5)	(0.8)
LIBOR Based Interest Payments [Member] | Cash Flow Hedging [Member] | Forward Contracts [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Notional Amount Of Cash Flow Hedge Instruments Settled	$ 500,000
Derivative, Notional Amount		$ 500,000
Forecasted Debt Issuances [Member] | Cash Flow Hedging [Member] | Forward Contracts [Member] | Interest Rate Contract [Member]
Derivative [Line Items]
Derivative, Notional Amount	2,000,000	$ 1,300,000
Derivative, Notional Amount, New Contracts	$ 750,000

RISK MANAGEMENT AND HEDGING A44

RISK MANAGEMENT AND HEDGING ACTIVITIES USING DERIVATIVES Part 3 (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Derivative Instruments, Gain (Loss) [Line Items]
Accumulated Other Comprehensive Income (Loss), Net of Tax	$ (174,692)		$ (188,530)
Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive (Loss), Net	44,836	$ 28,857
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Net	(15,554)	(20,648)
Commodity Contract [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Unrealized Gain (Loss) On Cash Flow Hedges Net Of Tax Accumulated Other Comprehensive Income Loss	(1,400)
Price Risk Cash Flow Hedge Unrealized Gain (Loss) to be Reclassified During Next 12 Months	(3,200)
Commodity Cash Flow Hedge Gain (Loss) To Be Reclassified After Next 12 Months Net	1,800
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive (Loss), Net	20,925	27,328
Commodity Contract [Member] | Commodity sales revenues | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Net	(11,611)	(15,319)
Interest Rate Contract [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of accumulated other comprehensive income (loss) attributable primarily to settled interest-rate swaps.	(104,000)
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net	(17,500)
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive (Loss), Net	23,911	1,529
Interest Rate Contract [Member] | Interest expense | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Net	$ (3,943)	$ (5,329)

DEBT DEBT (Details)

DEBT DEBT (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018USD ($)Rate	Dec. 31, 2017USD ($)Rate
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 8,082,092	$ 9,198,677
Unamortized Portion of Terminated Swaps	18,038	18,468
Unamortized debt issuance costs and discounts	(75,729)	(78,193)
Current maturities of long-term debt	(932,650)	(432,650)
Short-term borrowings	0	(614,673)
Long-term debt	$ 7,091,751	8,091,629
ONEOK Credit Agreement 2017 [Member]
Debt Instrument [Line Items]
Debt Instrument, Covenant Description	Among other things, these covenants include maintaining a ratio of indebtedness to adjusted EBITDA (EBITDA, as defined in our $2.5 Billion Credit Agreement, adjusted for all noncash charges and increased for projected EBITDA from certain lender-approved capital expansion projects) of no more than 5.5 to 1 at March 31, 2018, for the subsequent quarter and 5.0 to 1 thereafter. Once the covenant decreases to 5.0 to 1, if we consummate one or more acquisitions in which the aggregate purchase is $25 million or more, the allowable ratio of indebtedness to adjusted EBITDA will increase to 5.5 to 1 for the quarter in which the acquisition is completed and the two following quarters. Our $2.5 Billion Credit Agreement includes a $100 million sublimit for the issuance of standby letters of credit and a $200 million sublimit for swingline loans. Under the terms of our $2.5 Billion Credit Agreement, we may request an increase in the size of the facility to an aggregate of $3.5 billion by either commitments from new lenders or increased commitments from existing lenders. Our $2.5 Billion Credit Agreement contains provisions for an applicable margin rate and an annual facility fee, both of which adjust with changes in our credit ratings. Based on our current credit ratings, borrowings, if any, will accrue at LIBOR plus 110 basis points, and the annual facility fee is 15 basis points. We have the option to request two one-year extensions, subject to lender approval, which may be used for working capital, capital expenditures, acquisitions and mergers, the issuance of letters of credit and for other general corporate purposes. At March 31, 2018, our ratio of indebtedness to adjusted EBITDA was 3.7 to 1, and we were in compliance with all covenants under our $2.5 Billion Credit Agreement.
$2.5 Billion Credit Agreement [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 2,500,000
Line of credit facility sublimit	100,000
Line of Credit Facility Swingline Subfacility	200,000
Line Of Credit Facility Option To Increase Borrowing Capacity	$ 3,500,000
Line of Credit Facility, Interest Rate Description	borrowings, if any, will accrue at LIBOR plus 110 basis points
Line Of Credit Facility, Annual Facility Fee Description	the annual facility fee is 15 basis points
Indebtedness To Adjusted Ebitda Current	3.7
Guardian Pipeline [Member] | Notes Payables 1 due 2022 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 34,695	36,607
Weighed Average Interest Rate (in hundredths) | Rate	7.85%
Parent Company
Debt Instrument [Line Items]
Commercial Paper	$ 0	$ 614,673
Short-term Debt, Weighted Average Interest Rate, at Point in Time | Rate		2.23%
Parent Company | Note Payable from Public Offering Due 2022 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 547,397	$ 547,397
Interest Rate (in hundredths) | Rate	4.25%
Parent Company | Note Payable Due 2023 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 500,000	500,000
Interest Rate (in hundredths) | Rate	7.50%
Parent Company | Note Payable Due 2027 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 500,000	500,000
Interest Rate (in hundredths) | Rate	4.00%
Parent Company | Note Payables 2 due 2028 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 100,000	100,000
Interest Rate (in hundredths) | Rate	6.875%
Parent Company | Notes Payables due 2035 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 400,000	400,000
Interest Rate (in hundredths) | Rate	6.00%
Parent Company | Notes Payables due 2047 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 700,000	700,000
Interest Rate (in hundredths) | Rate	4.95%
Partnership Interest [Member] | Note Payable from Public Offering Due 2018 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 425,000	425,000
Interest Rate (in hundredths) | Rate	3.20%
Partnership Interest [Member] | Term Loan Agreement [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 0	$ 500,000
Repayment of Senior Notes	500,000
Long-term Debt, Percentage Bearing Variable Interest, Percentage Rate | Rate		2.87%
Partnership Interest [Member] | Notes Payables due 2019 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 500,000	$ 500,000
Interest Rate (in hundredths) | Rate	8.625%
Partnership Interest [Member] | Note Payable from Public Offering Due 2020 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 300,000	300,000
Interest Rate (in hundredths) | Rate	3.80%
Partnership Interest [Member] | Note Payable 2 from Public Offering Due 2022 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 900,000	900,000
Interest Rate (in hundredths) | Rate	3.375%
Partnership Interest [Member] | Note Payable from Public Offering Due 2023 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 425,000	425,000
Interest Rate (in hundredths) | Rate	5.00%
Partnership Interest [Member] | Note Payable from Public Offering Due 2025 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 500,000	500,000
Interest Rate (in hundredths) | Rate	4.90%
Partnership Interest [Member] | Notes Payables due 2036 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 600,000	600,000
Interest Rate (in hundredths) | Rate	6.65%
Partnership Interest [Member] | Notes Payables due 2037 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 600,000	600,000
Interest Rate (in hundredths) | Rate	6.85%
Partnership Interest [Member] | Note Payable from Public Offering Due 2041 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 650,000	650,000
Interest Rate (in hundredths) | Rate	6.125%
Partnership Interest [Member] | Note Payable from Public Offering Due 2043 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 400,000	$ 400,000
Interest Rate (in hundredths) | Rate	6.20%

EQUITY (Details)

EQUITY (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended			6 Months Ended	12 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Mar. 31, 2017	Jun. 30, 2017	Dec. 31, 2017
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners		20.00%
Stock Issued During Period, Shares, New Issues		21,900,000
Share Price		$ 54.50
Proceeds from Sale of Common Stock		$ 1,200,000
Common Stock, Dividends, Per Share, Cash Paid		$ 0.770	$ 0.615
Common Stock, Dividends, Per Share, Declared		$ 0.770	0.615
Dividends, Preferred Stock, Cash		$ 300			$ 600
Preferred Stock, Dividends, Declared		$ 275
Partnership Capital Distributions [Line Items]
General partnership ownership interest		100.00%		41.20%	100.00%
Issued Under Equity Agreement [Member]
Proceeds from Sale of Common Stock					$ 448,300
Common Stock Sold Under Equity Distribution Agreement		0			8,400,000
Series E Preferred Stock [Member]
Preferred Stock, Dividend Rate, Percentage		5.50%
Subsequent Event [Member]
Common Stock, Dividends, Per Share, Declared	$ 0.795
Dividends Payable, Date of Record	Apr. 30, 2018
Dividends Payable, Date to be Paid	May 15, 2018
Preferred Stock, Dividends, Declared	$ 300
Distribution Paid [Member]
Partnership Capital Distributions [Line Items]
Distribution per unit			$ 0.79
Total distributions paid			$ 333,001
ONEOK [Member] | Distribution Paid [Member]
Partnership Capital Distributions [Line Items]
Limited partner distributions to ONEOK			90,323
General Partner [Member]
Partnership Capital Distributions [Line Items]
General partnership ownership interest				2.00%
General Partner [Member] | Distribution Paid [Member]
Partnership Capital Distributions [Line Items]
General partner distributions			6,660
Incentive distributions			100,538
Distributions to general partner			107,198
Limited Partner [Member] | Distribution Paid [Member]
Partnership Capital Distributions [Line Items]
Limited partner distributions to other unitholders			$ 135,480
ONEOK [Member]
Aggregate Amount Of Common Shares Available For Issuance And Sale Under Equity Distribution Agreement		$ 1,000,000

ACCUMULATED OTHER COMPREHENSI47

ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) ACCUMULATED OTHER COMPREHENSIVE INCOME (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Unrealized gains (losses) on risk management assets/liabilities - January 1	$ (81,915)
Pension and Postretirement Benefit Plan Obligations - January 1	(105,411)
Unrealized gains (losses) on risk-management assets/liabilities of unconsolidated affiliates - January 1	(1,204)
Accumulated other comprehensive loss - January 1	(188,530)
Other Comprehensive Income (Loss) Before Reclassifications, Unrealized Gains (Losses) on Risk-Management Assets/Liabilities	34,524
Other Comprehensive (Income) Loss Before Reclassification, Pension and Postretirement Benefit Plan Obligations	(601)
Other Comprehensive Income (Loss) Before Reclassification, Unrealized Gains (Losses) on Risk-Management Assets/Liabilities of Unconsolidated Affiliates	2,860
Other comprehensive income (loss) before reclassifications	36,783
Other Comprehensive Income (Loss) Reclassification Adjustment from AOCI for Unrealized Gains (Losses) on Risk-Management Assets/Liabilities	11,976	$ 17,283
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Other Comprehensive Income Attributable to Unconsolidated Affiliates, Net of Tax	(36)
Other Comprehensive Income (Loss), Reclassification Adjustment included in Net Income, Net of Tax	15,156	7,721
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax, Portion Attributable to Parent	46,500
Other Comprehensive (Income) Loss, Pension and Postretirement Benefit Plans, after Reclassification Adjustment, after Tax	2,615	2,041
Other comprehensive income (loss) on investment in unconsolidated affiliates	2,824
Net current-period other comprehensive income (loss) attributable to ONEOK	51,939
Impact of Adoption of ASU 2018-02 On Unrealized Gains (Losses) on Risk Management Assets/Liabilities	(17,935)
Impact of Adoption of ASU 2018-02 ON Pension and Postretirement Benefit Plan Obligations	(20,166)
Impact of Adoption of ASU 2018-02 ON Unrealized Gains (Losses) on Risk Management Assets/Liabilities of Unconsolidated Affiliates	0
Impact of Adoption of ASU 2018-02 on AOCI, Total	(38,101)
Unrealized gains (losses) on risk management assets/liabilities - March 31	(53,350)
Pension and Postretirement Benefit Plan Obligations - March 31	(122,962)
Unrealized gains (losses) on risk-management assets/liabilities of unconsolidated affiliates - March 31	1,620
Accumulated other comprehensive loss - March 31	(174,692)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Risk Management Assets/Liabilities	3,578	3,365
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Other Comprehensive Income (Loss) Reclassification Adjustment from AOCI for Unrealized Gains (Losses) on Risk-Management Assets/Liabilities	11,976	5,658
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] | Sales [Member] | Commodity Contract [Member]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income	(11,611)	(15,319)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] | Interest Expense [Member] | Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income	(3,943)	(5,329)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] | Total before tax [Member]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income	(15,554)	(20,648)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] | Tax Expense [Member]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Risk Management Assets/Liabilities	3,578	3,365
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] | Net of tax [Member]
Other Comprehensive Income (Loss) Reclassification Adjustment from AOCI for Unrealized Gains (Losses) on Risk-Management Assets/Liabilities	11,976	17,283
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] | Net income attributable to noncontrolling interest [Member]
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax, Portion Attributable to Noncontrolling Interest	0	(11,625)
Accumulated Pension and Postretirement Benefit Plans Adjustment Attributable to Parent [Member]
Other Comprehensive (Income) Loss, Pension and Postretirement Benefit Plans, Reclassification Adjustment from AOCI, after Tax	(3,216)	(2,038)
Pension and Postretirement Benefit Plans, Amortization of Gain (Loss)	(4,592)	(3,812)
Pension and Postretirement Benefit Plans, Amortization of Prior Service Cost (Credit)	415	415
Other Comprehensive Income (Loss), Pension and Postretirement Benefit Plans, Gain (Loss), Reclassification Adjustment from AOCI, before Tax	(4,177)	(3,397)
Other Comprehensive Income (Loss), Pensions and Postretirement Benefit Plans, Gain (Loss), Reclassification Adjustment from AOCI, Tax	961	1,359
Accumulated Other Comprehensive Income from Investments in Unconsolidated Affiliates Attributable to Parent [Member]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Other Comprehensive Income Attributable to Unconsolidated Affiliates, Net of Tax	36	(25)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Other Comprehensive Income Attributable to Unconsolidated Affiliates, Before Tax	47	(96)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Other Comprehensive Income Attributable to Unconsolidated Affiliates, Net of Tax	(11)	15
Accumulated Other Comprehensive Income from Investments in Unconsolidated Affiliates Attributable to Parent [Member] | Net of tax [Member]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Other Comprehensive Income Attributable to Unconsolidated Affiliates, Net of Tax	36	(81)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Other Comprehensive Income Attributable to Unconsolidated Affiliates, Net of Tax, Portion Attributable to Noncontrolling Interests	$ 0	$ (56)

EARNINGS PER SHARE EARNINGS P48

EARNINGS PER SHARE EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Basic EPS
Net income attributable to ONEOK available for common stock	$ 264,233	$ 87,361
Shares	409,676	211,619
Basic (in dollars per share)	$ 0.65	$ 0.41
Diluted EPS
Effect of dilutive securities	$ 0	$ 0
Effect of dilutive securities, number of shares, shares	2,497	1,983
Net income attributable to ONEOK available for common stock and common stock equivalents	$ 264,233	$ 87,361
Shares	412,173	213,602
Earnings Per Share, Diluted	$ 0.64	$ 0.41

EMPLOYEE BENEFIT PLANS EMPLOY49

EMPLOYEE BENEFIT PLANS EMPLOYEE BENEFIT PLANS (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Pension Benefits
Components of net periodic benefit cost
Service cost	$ 1,832	$ 1,722
Interest cost	4,408	4,655
Expected return on plan assets	(5,969)	(5,336)
Amortization of prior service credit	0	0
Amortization of net loss	4,258	3,392
Net periodic benefit cost (income)	4,529	4,433
Postretirement Benefits
Components of net periodic benefit cost
Service cost	211	165
Interest cost	527	565
Expected return on plan assets	(672)	(564)
Amortization of prior service credit	(415)	(415)
Amortization of net loss	334	420
Net periodic benefit cost (income)	$ (15)	$ 171

UNCONSOLIDATED AFFILIATES (Deta

UNCONSOLIDATED AFFILIATES (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Equity in net earnings from investments	$ 40,187	$ 39,564
Accounts Payable, Related Parties, Current	12,800		$ 13,600
Income Statement [Abstract]
Operating revenues	158,908	154,280
Operating expenses	68,401	66,936
Net income	84,480	81,131
Distributions paid to us	49,816	46,920
Accounts Receivable, Related Parties, Current	7,400
Unconsolidated Affiliates [Member]
Schedule of Equity Method Investments [Line Items]
Related Party Transaction, Expenses from Transactions with Related Parties	37,500	36,700
Northern Border Pipeline
Schedule of Equity Method Investments [Line Items]
Equity in net earnings from investments	17,137	18,817
Overland Pass Pipeline Company
Schedule of Equity Method Investments [Line Items]
Equity in net earnings from investments	16,387	13,566
Roadrunner Gas Transmission
Schedule of Equity Method Investments [Line Items]
Equity in net earnings from investments	4,958	4,405
Income Statement [Abstract]
Payments to Acquire Equity Method Investments	0	4,000
Other Unconsolidated Affiliates
Schedule of Equity Method Investments [Line Items]
Equity in net earnings from investments	$ 1,705	$ 2,776

REVENUE REVENUE (Details)

REVENUE REVENUE (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Retained earnings increase	$ 0			$ 0
Services revenue	282,073,000	$ 532,894,000
Cost of sales and fuel (exclusive of depreciation and operating costs)	2,368,026,000	2,143,843,000
Depreciation and amortization	104,237,000	99,419,000
Income taxes	75,771,000	54,941,000
Net income	266,049,000	186,185,000
Net Income Attributable to Noncontrolling Interests	1,541,000	98,824,000
Net Income Attributable to ONEOK	264,508,000	$ 87,361,000
Natural gas and natural gas liquids in storage	185,298,000			342,293,000
Other current assets	106,067,000			53,008,000
Property, plant and equipment	15,838,443,000			15,559,667,000
Accumulated depreciation and amortization	2,960,254,000			2,861,541,000
Deferred income taxes	116,120,000			205,907,000
Other assets	159,428,000			180,830,000
Other current liabilities	122,922,000			179,971,000
Other deferred credits	366,701,000			348,924,000
Retained earnings/paid-in capital	7,735,173,000			6,588,878,000
Noncontrolling interests in consolidated subsidiaries	167,806,000			157,485,000
Customer receivables	832,000,000			$ 1,200,000,000
Contract asset balance	6,200,000		$ 6,400,000
Contract with Customer, Asset, Net, Current	1,000,000
Contract with Customer, Asset, Net, Noncurrent	5,200,000
Contract with Customer, Liability	21.2		33.3
Revenue recognized included in beginning balance	(17.3)
Contract with Customer, Liability, Current	5.2
Contract with Customer, Liability, Current	6,000,000		$ 19,500,000
Contract with Customer, Liability, Noncurrent	15,200,000
Performance obligations expected to be recognized in revenue	1,947,900,000
2018 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Performance obligations expected to be recognized in revenue	242,916,000
2019 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Performance obligations expected to be recognized in revenue	247,250,000
2020 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Performance obligations expected to be recognized in revenue	215,387,000
2021 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Performance obligations expected to be recognized in revenue	209,654,000
Thereafter [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Performance obligations expected to be recognized in revenue	1,032,583,000
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Services revenue	634,315,000
Cost of sales and fuel (exclusive of depreciation and operating costs)	2,725,774,000
Depreciation and amortization	104,092,000
Income taxes	74,539,000
Net income	261,920,000
Net Income Attributable to Noncontrolling Interests	1,539,000
Net Income Attributable to ONEOK	260,381,000
Natural gas and natural gas liquids in storage	186,998,000
Other current assets	105,097,000
Property, plant and equipment	15,816,674,000
Accumulated depreciation and amortization	2,958,737,000
Deferred income taxes	117,854,000
Other assets	154,167,000
Other current liabilities	120,877,000
Other deferred credits	351,525,000
Retained earnings/paid-in capital	7,729,364,000
Noncontrolling interests in consolidated subsidiaries	167,787,000
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Services revenue	(352,242,000)
Cost of sales and fuel (exclusive of depreciation and operating costs)	(357,748,000)
Depreciation and amortization	145,000
Income taxes	1,232,000
Net income	4,129,000
Net Income Attributable to Noncontrolling Interests	2,000
Net Income Attributable to ONEOK	4,127,000
Natural gas and natural gas liquids in storage	(1,700,000)
Other current assets	970,000
Property, plant and equipment	21,769,000
Accumulated depreciation and amortization	1,517,000
Deferred income taxes	(1,734,000)
Other assets	5,261,000
Other current liabilities	2,045,000
Other deferred credits	15,176,000
Retained earnings/paid-in capital	5,809,000
Noncontrolling interests in consolidated subsidiaries	19,000
Retained Earnings
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Retained earnings increase	$ 1,700,000

SEGMENTS (Details)

SEGMENTS (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Segment disclosure [Abstract]
Segment Reporting, Disclosure of Major Customers	For the three months ended March 31, 2018, we had no single customer from which we received 10 percent or more of our consolidated revenues.	For the three months ended March 31, 2017, we had no single customer from which we received 10 percent or more of our consolidated revenues.
Revenues	$ 3,102,077	$ 2,749,611
Cost of sales and fuel (exclusive of depreciation and operating costs)	(2,368,026)	(2,143,843)
Operating costs	(210,204)	(189,205)
Equity in net earnings from investments	40,187	39,564
Depreciation and amortization	(104,237)	(99,419)
Total assets	16,432,347	16,067,558	$ 16,845,937
Capital expenditures	264,467	112,737
Net income	266,049	186,185
Interest expense, net of capitalized interest	115,725	116,462
Income taxes	75,771	54,941
Noncash compensation expense	9,226	1,647
Other corporate costs and noncash items	(4,753)	6,500
Natural Gas Gathering And Processing [Member]
Segment disclosure [Abstract]
Revenues	707,991	661,276
Cost of sales and fuel (exclusive of depreciation and operating costs)	(492,622)	(488,384)
Operating costs	(88,359)	(71,328)
Equity in net earnings from investments	1,668	2,630
Other	1,873	(227)
Segment adjusted EBITDA	130,551	103,967
Depreciation and amortization	(47,748)	(44,968)
Total assets	5,462,305	5,296,359
Capital expenditures	111,729	63,151
Natural Gas Gathering And Processing [Member] | Natural Gas Gathering and Processing Intersegment [Member]
Segment disclosure [Abstract]
Revenues	397,800
Natural Gas Liquids [Member]
Segment disclosure [Abstract]
Revenues	2,692,469	2,391,984
Cost of sales and fuel (exclusive of depreciation and operating costs)	(2,281,072)	(2,048,693)
Operating costs	(88,592)	(78,440)
Equity in net earnings from investments	16,424	13,722
Other	2,850	(344)
Segment adjusted EBITDA	342,079	278,229
Depreciation and amortization	(42,427)	(41,115)
Total assets	8,370,364	8,194,835
Capital expenditures	124,921	20,453
Natural Gas Liquids [Member] | Natural Gas Liquids Intersegment [Member]
Segment disclosure [Abstract]
Revenues	9,000
Natural Gas Liquids [Member] | Natural Gas Liquids Regulated [Member]
Segment disclosure [Abstract]
Revenues	300,000	296,300
Cost of sales and fuel (exclusive of depreciation and operating costs)	(122,800)	(116,500)
Natural Gas Pipelines [Member]
Segment disclosure [Abstract]
Revenues	109,911	106,818
Cost of sales and fuel (exclusive of depreciation and operating costs)	(5,454)	(16,603)
Operating costs	(33,190)	(31,563)
Equity in net earnings from investments	22,095	23,212
Other	263	1,094
Segment adjusted EBITDA	93,625	82,958
Depreciation and amortization	(13,269)	(12,543)
Total assets	2,060,700	1,945,407
Capital expenditures	19,898	25,014
Natural Gas Pipelines [Member] | Natural Gas Pipelines Intersegment [Member]
Segment disclosure [Abstract]
Revenues	2,100
Natural Gas Pipelines [Member] | Natural Gas Pipelines Regulated [Member]
Segment disclosure [Abstract]
Revenues	68,000	68,900
Cost of sales and fuel (exclusive of depreciation and operating costs)	(9,100)	(14,100)
Total Segments [Member]
Segment disclosure [Abstract]
Revenues	3,510,371	3,160,078
Cost of sales and fuel (exclusive of depreciation and operating costs)	(2,779,148)	(2,553,680)
Operating costs	(210,141)	(181,331)
Equity in net earnings from investments	40,187	39,564
Other	4,986	523
Segment adjusted EBITDA	566,255	465,154
Depreciation and amortization	(103,444)	(98,626)
Total assets	15,893,369	15,436,601
Capital expenditures	256,548	108,618
Other and Eliminations
Segment disclosure [Abstract]
Revenues	(408,294)	(410,467)
Cost of sales and fuel (exclusive of depreciation and operating costs)	411,122	409,837
Operating costs	(63)	(7,874)
Equity in net earnings from investments	0	0
Depreciation and amortization	(793)	(793)
Total assets	538,978	630,957
Capital expenditures	7,919	4,119
Unaffiliated entity [Member]
Segment disclosure [Abstract]
Revenues		2,749,611
Unaffiliated entity [Member] | Natural Gas Gathering And Processing [Member]
Segment disclosure [Abstract]
Revenues		400,149
Unaffiliated entity [Member] | Natural Gas Liquids [Member]
Segment disclosure [Abstract]
Revenues		2,244,000
Unaffiliated entity [Member] | Natural Gas Pipelines [Member]
Segment disclosure [Abstract]
Revenues		104,924
Unaffiliated entity [Member] | Total Segments [Member]
Segment disclosure [Abstract]
Revenues		2,749,073
Unaffiliated entity [Member] | Other and Eliminations
Segment disclosure [Abstract]
Revenues		538
Operating Segments [Member]
Segment disclosure [Abstract]
Revenues		0
Operating Segments [Member] | Natural Gas Gathering And Processing [Member]
Segment disclosure [Abstract]
Revenues		261,127
Operating Segments [Member] | Natural Gas Liquids [Member]
Segment disclosure [Abstract]
Revenues		147,984
Operating Segments [Member] | Natural Gas Liquids [Member] | Natural Gas Liquids Regulated [Member]
Segment disclosure [Abstract]
Revenues	253,400	252,900
Operating Segments [Member] | Natural Gas Pipelines [Member]
Segment disclosure [Abstract]
Revenues		1,894
Operating Segments [Member] | Total Segments [Member]
Segment disclosure [Abstract]
Revenues		411,005
Operating Segments [Member] | Other and Eliminations
Segment disclosure [Abstract]
Revenues		$ (411,005)
Noncustomer [Domain]
Segment disclosure [Abstract]
Revenues	(9,000)
NGL and Condensate Sales [Member]
Segment disclosure [Abstract]
Revenues	2,557,017
NGL and Condensate Sales [Member] | Natural Gas Gathering And Processing [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	413,157
NGL and Condensate Sales [Member] | Natural Gas Liquids [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	2,552,770
NGL and Condensate Sales [Member] | Natural Gas Pipelines [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	0
NGL and Condensate Sales [Member] | Total Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	2,965,927
NGL and Condensate Sales [Member] | Other and Eliminations
Segment disclosure [Abstract]
Revenues	(408,910)
Residue Natural Gas Sales [Member]
Segment disclosure [Abstract]
Revenues	262,166
Residue Natural Gas Sales [Member] | Natural Gas Gathering And Processing [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	254,997
Residue Natural Gas Sales [Member] | Natural Gas Liquids [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	0
Residue Natural Gas Sales [Member] | Natural Gas Pipelines [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	4,919
Residue Natural Gas Sales [Member] | Total Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	259,916
Residue Natural Gas Sales [Member] | Other and Eliminations
Segment disclosure [Abstract]
Revenues	2,250
Gathering and Exchange Services Revenue [Member]
Segment disclosure [Abstract]
Revenues	121,666
Gathering and Exchange Services Revenue [Member] | Natural Gas Gathering And Processing [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	38,429
Gathering and Exchange Services Revenue [Member] | Natural Gas Liquids [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	83,258
Gathering and Exchange Services Revenue [Member] | Natural Gas Pipelines [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	0
Gathering and Exchange Services Revenue [Member] | Total Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	121,687
Gathering and Exchange Services Revenue [Member] | Other and Eliminations
Segment disclosure [Abstract]
Revenues	(21)
Transportation and Storage Revenue [Member]
Segment disclosure [Abstract]
Revenues	149,722
Transportation and Storage Revenue [Member] | Natural Gas Gathering And Processing [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	0
Transportation and Storage Revenue [Member] | Natural Gas Liquids [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	53,478
Transportation and Storage Revenue [Member] | Natural Gas Pipelines [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	98,338
Transportation and Storage Revenue [Member] | Total Segments [Member]
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	151,816
Transportation and Storage Revenue [Member] | Other and Eliminations
Segment disclosure [Abstract]
Revenues	(2,094)
Other [Member]
Segment disclosure [Abstract]
Revenues	11,506
Other [Member] | Natural Gas Gathering And Processing [Member]
Segment disclosure [Abstract]
Revenues	1,408
Other [Member] | Natural Gas Liquids [Member]
Segment disclosure [Abstract]
Revenues	2,963
Other [Member] | Natural Gas Pipelines [Member]
Segment disclosure [Abstract]
Revenues	6,654
Other [Member] | Total Segments [Member]
Segment disclosure [Abstract]
Revenues	11,025
Other [Member] | Other and Eliminations
Segment disclosure [Abstract]
Revenues	$ 481

SUPPLEMENTAL CONDENSED CONSOL53

SUPPLEMENTAL CONDENSED CONSOLIDATING FINANCIAL INFORMATION, Income Statement (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Condensed Financial Statements, Captions [Line Items]
Commodity sales	$ 2,820,004	$ 2,216,717
Services	282,073	532,894
Total revenues	3,102,077	2,749,611
Cost of sales and fuel (exclusive of items shown separately below)	2,368,026	2,143,843
Gain on sale of assets	(89)	7
Operating income	419,699	317,137
Equity in net earnings from investments	40,187	39,564
Interest expense, net	(115,725)	(116,462)
Income before income taxes	341,820	241,126
Income taxes	(75,771)	(54,941)
Net income	266,049	186,185
Less: Net income attributable to noncontrolling interests	1,541	98,824
Net income attributable to ONEOK	264,508	87,361
Less: Preferred stock dividends	275	0
Net income available to common shareholders	$ 264,233	87,361
Northern Border Pipeline
Condensed Financial Statements, Captions [Line Items]
Equity Method Investment, Ownership Percentage	50.00%
Equity in net earnings from investments	$ 17,137	18,817
Reportable Legal Entities | Parent Issuer & Guarantor
Condensed Financial Statements, Captions [Line Items]
Commodity sales	0	0
Services	0	0
Total revenues	0	0
Cost of sales and fuel (exclusive of items shown separately below)	0	0
Operating expenses	(700)	6,900
Gain on sale of assets	0
Operating income	700	(6,900)
Equity in net earnings from investments	368,500	268,700
Other income (expense), net	7,200	500
Interest expense, net	(39,800)	(25,800)
Income before income taxes	336,600	236,500
Income taxes	(72,100)	(51,200)
Net income	264,500	185,300
Less: Net income attributable to noncontrolling interests	0	97,900
Net income attributable to ONEOK	264,500	87,400
Less: Preferred stock dividends	300
Net income available to common shareholders	264,200
Reportable Legal Entities | Subsidiary Issuer & Guarantor
Condensed Financial Statements, Captions [Line Items]
Commodity sales	0	0
Services	0	0
Total revenues	0	0
Cost of sales and fuel (exclusive of items shown separately below)	0	0
Operating expenses	0	0
Gain on sale of assets	0
Operating income	0	0
Equity in net earnings from investments	370,900	269,100
Other income (expense), net	77,100	91,300
Interest expense, net	(77,100)	(91,300)
Income before income taxes	370,900	269,100
Income taxes	0	0
Net income	370,900	269,100
Less: Net income attributable to noncontrolling interests	0	0
Net income attributable to ONEOK	370,900	269,100
Less: Preferred stock dividends	0
Net income available to common shareholders	370,900
Reportable Legal Entities | Guarantor Subsidiary
Condensed Financial Statements, Captions [Line Items]
Commodity sales	0	0
Services	0	0
Total revenues	0	0
Cost of sales and fuel (exclusive of items shown separately below)	0	0
Operating expenses	0	0
Gain on sale of assets	0
Operating income	0	0
Equity in net earnings from investments	370,900	269,100
Other income (expense), net	77,100	91,300
Interest expense, net	(77,100)	(91,300)
Income before income taxes	370,900	269,100
Income taxes	0	0
Net income	370,900	269,100
Less: Net income attributable to noncontrolling interests	0	0
Net income attributable to ONEOK	370,900	269,100
Less: Preferred stock dividends	0
Net income available to common shareholders	370,900
Reportable Legal Entities | Combined Non-Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Commodity sales	2,820,000	2,216,700
Services	282,600	532,900
Total revenues	3,102,600	2,749,600
Cost of sales and fuel (exclusive of items shown separately below)	2,368,000	2,143,800
Operating expenses	315,700	281,800
Gain on sale of assets	(100)
Operating income	419,000	324,000
Equity in net earnings from investments	28,600	20,700
Other income (expense), net	(9,600)	400
Interest expense, net	(75,900)	(90,700)
Income before income taxes	362,100	254,400
Income taxes	(3,700)	(3,700)
Net income	358,400	250,700
Less: Net income attributable to noncontrolling interests	1,500	900
Net income attributable to ONEOK	356,900	249,800
Less: Preferred stock dividends	0
Net income available to common shareholders	356,900
Reportable Legal Entities | Total
Condensed Financial Statements, Captions [Line Items]
Commodity sales	2,820,000	2,216,700
Services	282,100	532,900
Total revenues	3,102,100	2,749,600
Cost of sales and fuel (exclusive of items shown separately below)	2,368,000	2,143,800
Operating expenses	314,500	288,700
Gain on sale of assets	(100)
Operating income	419,700	317,100
Equity in net earnings from investments	40,200	39,600
Other income (expense), net	(2,400)	900
Interest expense, net	(115,700)	(116,500)
Income before income taxes	341,800	241,100
Income taxes	(75,800)	(54,900)
Net income	266,000	186,200
Less: Net income attributable to noncontrolling interests	1,500	98,800
Net income attributable to ONEOK	264,500	87,400
Less: Preferred stock dividends	300
Net income available to common shareholders	264,200
Consolidating Entries
Condensed Financial Statements, Captions [Line Items]
Commodity sales	0	0
Services	(500)	0
Total revenues	(500)	0
Cost of sales and fuel (exclusive of items shown separately below)	0	0
Operating expenses	(500)	0
Gain on sale of assets	0
Operating income	0	0
Equity in net earnings from investments	(1,098,700)	(788,000)
Other income (expense), net	(154,200)	(182,600)
Interest expense, net	154,200	182,600
Income before income taxes	(1,098,700)	(788,000)
Income taxes	0	0
Net income	(1,098,700)	(788,000)
Less: Net income attributable to noncontrolling interests	0	0
Net income attributable to ONEOK	(1,098,700)	$ (788,000)
Less: Preferred stock dividends	0
Net income available to common shareholders	$ (1,098,700)

SUPPLEMENTAL CONDENSED CONSOL54

SUPPLEMENTAL CONDENSED CONSOLIDATING FINANCIAL INFORMATION, Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Condensed Financial Statements, Captions [Line Items]
Net income	$ 266,049	$ 186,185
Other comprehensive income (loss), net of tax
Unrealized gains (losses) on derivatives, net of tax	34,524	24,456
Realized (gains) losses on derivatives in net income, net of tax	(11,976)	(17,283)
Change in pension and postretirement benefit plan liability, net of tax	(2,615)	(2,041)
Other comprehensive income (loss) on investments in unconsolidated affiliates, net of tax	2,824	325
Total other comprehensive income (loss), net of tax	51,939	44,105
Comprehensive income	317,988	230,290
Less: Comprehensive income attributable to noncontrolling interests	1,541	127,641
Comprehensive income attributable to ONEOK	316,447	102,649
Reportable Legal Entities | Parent Issuer & Guarantor
Condensed Financial Statements, Captions [Line Items]
Net income	264,500	185,300
Other comprehensive income (loss), net of tax
Unrealized gains (losses) on derivatives, net of tax	18,400	0
Realized (gains) losses on derivatives in net income, net of tax	900	500
Change in pension and postretirement benefit plan liability, net of tax	3,200	2,000
Other comprehensive income (loss) on investments in unconsolidated affiliates, net of tax	0	0
Total other comprehensive income (loss), net of tax	22,500	2,500
Comprehensive income	287,000	187,800
Less: Comprehensive income attributable to noncontrolling interests	0	126,800
Comprehensive income attributable to ONEOK	287,000	61,000
Reportable Legal Entities | Subsidiary Issuer & Guarantor
Condensed Financial Statements, Captions [Line Items]
Net income	370,900	269,100
Other comprehensive income (loss), net of tax
Unrealized gains (losses) on derivatives, net of tax	20,900	28,800
Realized (gains) losses on derivatives in net income, net of tax	14,300	19,800
Change in pension and postretirement benefit plan liability, net of tax	(600)	0
Other comprehensive income (loss) on investments in unconsolidated affiliates, net of tax	3,700	400
Total other comprehensive income (loss), net of tax	38,300	49,000
Comprehensive income	409,200	318,100
Less: Comprehensive income attributable to noncontrolling interests	0	0
Comprehensive income attributable to ONEOK	409,200	318,100
Reportable Legal Entities | Guarantor Subsidiary
Condensed Financial Statements, Captions [Line Items]
Net income	370,900	269,100
Other comprehensive income (loss), net of tax
Unrealized gains (losses) on derivatives, net of tax	20,900	27,300
Realized (gains) losses on derivatives in net income, net of tax	11,600	15,300
Change in pension and postretirement benefit plan liability, net of tax	0	0
Other comprehensive income (loss) on investments in unconsolidated affiliates, net of tax	3,700	400
Total other comprehensive income (loss), net of tax	36,200	43,000
Comprehensive income	407,100	312,100
Less: Comprehensive income attributable to noncontrolling interests	0	0
Comprehensive income attributable to ONEOK	407,100	312,100
Reportable Legal Entities | Combined Non-Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Net income	358,400	250,700
Other comprehensive income (loss), net of tax
Unrealized gains (losses) on derivatives, net of tax	16,100	51,800
Realized (gains) losses on derivatives in net income, net of tax	8,300	32,100
Change in pension and postretirement benefit plan liability, net of tax	0	0
Other comprehensive income (loss) on investments in unconsolidated affiliates, net of tax	2,800	700
Total other comprehensive income (loss), net of tax	27,200	84,600
Comprehensive income	385,600	335,300
Less: Comprehensive income attributable to noncontrolling interests	1,500	900
Comprehensive income attributable to ONEOK	384,100	334,400
Reportable Legal Entities | Total
Condensed Financial Statements, Captions [Line Items]
Net income	266,000	186,200
Other comprehensive income (loss), net of tax
Unrealized gains (losses) on derivatives, net of tax	34,500	24,500
Realized (gains) losses on derivatives in net income, net of tax	12,000	17,300
Change in pension and postretirement benefit plan liability, net of tax	2,600	2,000
Other comprehensive income (loss) on investments in unconsolidated affiliates, net of tax	2,800	300
Total other comprehensive income (loss), net of tax	51,900	44,100
Comprehensive income	317,900	230,300
Less: Comprehensive income attributable to noncontrolling interests	1,500	127,700
Comprehensive income attributable to ONEOK	316,400	102,600
Consolidating Entries
Condensed Financial Statements, Captions [Line Items]
Net income	(1,098,700)	(788,000)
Other comprehensive income (loss), net of tax
Unrealized gains (losses) on derivatives, net of tax	(41,800)	(83,400)
Realized (gains) losses on derivatives in net income, net of tax	(23,100)	(50,400)
Change in pension and postretirement benefit plan liability, net of tax	0	0
Other comprehensive income (loss) on investments in unconsolidated affiliates, net of tax	(7,400)	(1,200)
Total other comprehensive income (loss), net of tax	(72,300)	(135,000)
Comprehensive income	(1,171,000)	(923,000)
Less: Comprehensive income attributable to noncontrolling interests	0	0
Comprehensive income attributable to ONEOK	$ (1,171,000)	$ (923,000)

SUPPLEMENTAL CONDENSED CONSOL55

SUPPLEMENTAL CONDENSED CONSOLIDATING FINANCIAL INFORMATION, Balance Sheet (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Current assets
Cash and cash equivalents	$ 17,474	$ 37,193	$ 310,808	$ 248,875
Accounts receivable, net	844,218	1,202,951
Materials and supplies	98,695	90,301
Natural gas and natural gas liquids in storage	185,298	342,293
Other current assets	106,067	53,008
Total current assets	1,290,745	1,764,458
Property, plant and equipment
Property, plant and equipment	15,838,443	15,559,667
Accumulated depreciation and amortization	2,960,254	2,861,541
Net property, plant and equipment	12,878,189	12,698,126
Investments and other assets
Investments	997,380	1,003,156
Other assets	159,428	180,830
Total investments and other assets	2,263,413	2,383,353
Total assets	16,432,347	16,845,937	16,067,558
Current liabilities
Current maturities of long-term debt	932,650	432,650
Short-term borrowings	0	614,673
Accounts payable	773,054	1,140,571
Other current liabilities	122,922	179,971
Total current liabilities	2,050,838	2,667,335
Long-term debt, excluding current maturities	7,091,751	8,091,629
Deferred credits and other liabilities	420,506	401,621
Commitments and contingencies
Equity
Equity excluding noncontrolling interests in consolidated subsidiaries	6,701,446	5,527,867
Noncontrolling interests in consolidated subsidiaries	167,806	157,485
Total equity	6,869,252	5,685,352	3,469,513	3,428,915
Total liabilities and equity	16,432,347	16,845,937
Reportable Legal Entities | Parent Issuer & Guarantor
Current assets
Cash and cash equivalents	17,500	37,200	302,300	248,500
Accounts receivable, net	0	0
Materials and supplies		0
Natural gas and natural gas liquids in storage	0	0
Other current assets	70,800	9,800
Total current assets	88,300	47,000
Property, plant and equipment
Property, plant and equipment	134,100	128,300
Accumulated depreciation and amortization	87,700	86,400
Net property, plant and equipment	46,400	41,900
Investments and other assets
Investments	5,823,600	5,752,100
Intercompany notes receivable	3,450,200	2,926,900
Other assets	305,400	416,900
Total investments and other assets	9,579,200	9,095,900
Total assets	9,713,900	9,184,800
Current liabilities
Current maturities of long-term debt	0	0
Short-term borrowings		614,700
Accounts payable	6,300	12,000
Other current liabilities	43,500	65,900
Total current liabilities	49,800	692,600
Intercompany debt	0	0
Long-term debt, excluding current maturities	2,726,800	2,726,400
Deferred credits and other liabilities	235,800	237,900
Commitments and contingencies
Equity
Equity excluding noncontrolling interests in consolidated subsidiaries	6,701,500	5,527,900
Noncontrolling interests in consolidated subsidiaries	0	0
Total equity	6,701,500	5,527,900
Total liabilities and equity	9,713,900	9,184,800
Reportable Legal Entities | Subsidiary Issuer & Guarantor
Current assets
Cash and cash equivalents	0	0	0	0
Accounts receivable, net	0	0
Materials and supplies		0
Natural gas and natural gas liquids in storage	0	0
Other current assets	0	1,300
Total current assets	0	1,300
Property, plant and equipment
Property, plant and equipment	0	0
Accumulated depreciation and amortization	0	0
Net property, plant and equipment	0	0
Investments and other assets
Investments	3,207,800	3,133,700
Intercompany notes receivable	8,118,300	8,627,800
Other assets	0	200
Total investments and other assets	11,326,100	11,761,700
Total assets	11,326,100	11,763,000
Current liabilities
Current maturities of long-term debt	925,000	425,000
Short-term borrowings		0
Accounts payable	0	0
Other current liabilities	68,200	85,000
Total current liabilities	993,200	510,000
Intercompany debt	0	0
Long-term debt, excluding current maturities	4,338,100	5,336,400
Deferred credits and other liabilities	0	0
Commitments and contingencies
Equity
Equity excluding noncontrolling interests in consolidated subsidiaries	5,994,800	5,916,600
Noncontrolling interests in consolidated subsidiaries	0	0
Total equity	5,994,800	5,916,600
Total liabilities and equity	11,326,100	11,763,000
Reportable Legal Entities | Guarantor Subsidiary
Current assets
Cash and cash equivalents	0	0	8,500	400
Accounts receivable, net	0	0
Materials and supplies		0
Natural gas and natural gas liquids in storage	0	0
Other current assets	0	0
Total current assets	0	0
Property, plant and equipment
Property, plant and equipment	0	0
Accumulated depreciation and amortization	0	0
Net property, plant and equipment	0	0
Investments and other assets
Investments	8,443,500	8,058,400
Intercompany notes receivable	2,882,600	3,703,100
Other assets	0	0
Total investments and other assets	11,326,100	11,761,500
Total assets	11,326,100	11,761,500
Current liabilities
Current maturities of long-term debt	0	0
Short-term borrowings		0
Accounts payable	0	0
Other current liabilities	0	0
Total current liabilities	0	0
Intercompany debt	8,118,300	8,627,800
Long-term debt, excluding current maturities	0	0
Deferred credits and other liabilities	0	0
Commitments and contingencies
Equity
Equity excluding noncontrolling interests in consolidated subsidiaries	3,207,800	3,133,700
Noncontrolling interests in consolidated subsidiaries	0	0
Total equity	3,207,800	3,133,700
Total liabilities and equity	11,326,100	11,761,500
Reportable Legal Entities | Combined Non-Guarantor Subsidiaries
Current assets
Cash and cash equivalents	0	0	0	0
Accounts receivable, net	844,200	1,203,000
Materials and supplies		90,300
Natural gas and natural gas liquids in storage	185,300	342,300
Other current assets	172,900	80,600
Total current assets	1,202,400	1,716,200
Property, plant and equipment
Property, plant and equipment	15,704,300	15,431,300
Accumulated depreciation and amortization	2,872,500	2,775,100
Net property, plant and equipment	12,831,800	12,656,200
Investments and other assets
Investments	802,900	803,000
Intercompany notes receivable	0	0
Other assets	1,008,000	1,007,400
Total investments and other assets	1,810,900	1,810,400
Total assets	15,845,100	16,182,800
Current liabilities
Current maturities of long-term debt	7,700	7,700
Short-term borrowings		0
Accounts payable	766,800	1,128,600
Other current liabilities	233,300	328,400
Total current liabilities	1,007,800	1,464,700
Intercompany debt	6,332,800	6,630,000
Long-term debt, excluding current maturities	26,900	28,800
Deferred credits and other liabilities	232,000	208,100
Commitments and contingencies
Equity
Equity excluding noncontrolling interests in consolidated subsidiaries	8,077,800	7,693,700
Noncontrolling interests in consolidated subsidiaries	167,800	157,500
Total equity	8,245,600	7,851,200
Total liabilities and equity	15,845,100	16,182,800
Reportable Legal Entities | Total
Current assets
Cash and cash equivalents	17,500	37,200	310,800	248,900
Accounts receivable, net	844,200	1,203,000
Materials and supplies		90,300
Natural gas and natural gas liquids in storage	185,300	342,300
Other current assets	243,700	91,700
Total current assets	1,290,700	1,764,500
Property, plant and equipment
Property, plant and equipment	15,838,400	15,559,600
Accumulated depreciation and amortization	2,960,200	2,861,500
Net property, plant and equipment	12,878,200	12,698,100
Investments and other assets
Investments	997,400	1,003,200
Intercompany notes receivable	0	0
Other assets	1,266,000	1,380,100
Total investments and other assets	2,263,400	2,383,300
Total assets	16,432,300	16,845,900
Current liabilities
Current maturities of long-term debt	932,700	432,700
Short-term borrowings		614,700
Accounts payable	773,100	1,140,600
Other current liabilities	345,000	479,300
Total current liabilities	2,050,800	2,667,300
Intercompany debt	0	0
Long-term debt, excluding current maturities	7,091,800	8,091,600
Deferred credits and other liabilities	420,400	401,600
Commitments and contingencies
Equity
Equity excluding noncontrolling interests in consolidated subsidiaries	6,701,500	5,527,900
Noncontrolling interests in consolidated subsidiaries	167,800	157,500
Total equity	6,869,300	5,685,400
Total liabilities and equity	16,432,300	16,845,900
Consolidating Entries
Current assets
Cash and cash equivalents	0	0	$ 0	$ 0
Accounts receivable, net	0	0
Materials and supplies		0
Natural gas and natural gas liquids in storage	0	0
Other current assets	0	0
Total current assets	0	0
Property, plant and equipment
Property, plant and equipment	0	0
Accumulated depreciation and amortization	0	0
Net property, plant and equipment	0	0
Investments and other assets
Investments	(17,280,400)	(16,744,000)
Intercompany notes receivable	(14,451,100)	(15,257,800)
Other assets	(47,400)	(44,400)
Total investments and other assets	(31,778,900)	(32,046,200)
Total assets	(31,778,900)	(32,046,200)
Current liabilities
Current maturities of long-term debt	0	0
Short-term borrowings		0
Accounts payable	0	0
Other current liabilities	0	0
Total current liabilities	0	0
Intercompany debt	(14,451,100)	(15,257,800)
Long-term debt, excluding current maturities	0	0
Deferred credits and other liabilities	(47,400)	(44,400)
Commitments and contingencies
Equity
Equity excluding noncontrolling interests in consolidated subsidiaries	(17,280,400)	(16,744,000)
Noncontrolling interests in consolidated subsidiaries	0	0
Total equity	(17,280,400)	(16,744,000)
Total liabilities and equity	$ (31,778,900)	$ (32,046,200)

SUPPLEMENTAL CONDENSED CONSOL56

SUPPLEMENTAL CONDENSED CONSOLIDATING FINANCIAL INFORMATION, Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Operating activities
Cash provided by operating activities	$ 495,321	$ 269,090
Investing activities
Capital expenditures	(264,467)	(112,737)
Contributions to unconsolidated affiliates	(147)	(4,422)
Cash provided by (used in) investing activities	(255,652)	(109,463)
Financing activities
Dividends paid	(316,408)	(129,842)
Distributions to noncontrolling interests	(1,500)	(136,680)
Borrowing (repayment) of short-term borrowings, net	(614,673)	180,452
Repayment of long-term debt	(501,913)	(1,951)
Issuance of common stock	1,182,117	3,722
Other, net	(7,011)	(13,395)
Cash used in financing activities	(259,388)	(97,694)
Change in cash and cash equivalents	(19,719)	61,933
Cash and cash equivalents at beginning of period	37,193	248,875
Cash and cash equivalents at end of period	17,474	310,808
Reportable Legal Entities | Parent Issuer & Guarantor
Operating activities
Cash provided by operating activities	266,800	134,200
Investing activities
Capital expenditures	(5,700)	(100)
Contributions to unconsolidated affiliates	0
Other investing activities	0	0
Cash provided by (used in) investing activities	(5,700)	(100)
Financing activities
Dividends paid	(316,400)	(129,800)
Distributions to noncontrolling interests	0	0
Intercompany borrowings (advances), net	(514,500)	52,100
Borrowing (repayment) of short-term borrowings, net	(614,700)	0
Repayment of long-term debt	0	(100)
Issuance of common stock	1,182,100	3,700
Other, net	(17,300)	(6,200)
Cash used in financing activities	(280,800)	(80,300)
Change in cash and cash equivalents	(19,700)	53,800
Cash and cash equivalents at beginning of period	37,200	248,500
Cash and cash equivalents at end of period	17,500	302,300
Reportable Legal Entities | Subsidiary Issuer & Guarantor
Operating activities
Cash provided by operating activities	319,700	322,100
Investing activities
Capital expenditures	0	0
Contributions to unconsolidated affiliates	0
Other investing activities	0	0
Cash provided by (used in) investing activities	0	0
Financing activities
Dividends paid	(333,000)	(333,000)
Distributions to noncontrolling interests	0	0
Intercompany borrowings (advances), net	513,300	(162,400)
Borrowing (repayment) of short-term borrowings, net	0	180,500
Repayment of long-term debt	(500,000)	0
Issuance of common stock	0	0
Other, net	0	(7,200)
Cash used in financing activities	(319,700)	(322,100)
Change in cash and cash equivalents	0	0
Cash and cash equivalents at beginning of period	0	0
Cash and cash equivalents at end of period	0	0
Reportable Legal Entities | Guarantor Subsidiary
Operating activities
Cash provided by operating activities	17,100	18,800
Investing activities
Capital expenditures	0	0
Contributions to unconsolidated affiliates	0
Other investing activities	5,000	2,900
Cash provided by (used in) investing activities	5,000	2,900
Financing activities
Dividends paid	(333,000)	(333,000)
Distributions to noncontrolling interests	0	0
Intercompany borrowings (advances), net	310,900	319,400
Borrowing (repayment) of short-term borrowings, net	0	0
Repayment of long-term debt	0	0
Issuance of common stock	0	0
Other, net	0	0
Cash used in financing activities	(22,100)	(13,600)
Change in cash and cash equivalents	0	8,100
Cash and cash equivalents at beginning of period	0	400
Cash and cash equivalents at end of period	0	8,500
Reportable Legal Entities | Combined Non-Guarantor Subsidiaries
Operating activities
Cash provided by operating activities	557,700	324,500
Investing activities
Capital expenditures	(258,800)	(112,600)
Contributions to unconsolidated affiliates	(100)
Other investing activities	4,000	300
Cash provided by (used in) investing activities	(254,900)	(112,300)
Financing activities
Dividends paid	0	0
Distributions to noncontrolling interests	(1,500)	(1,200)
Intercompany borrowings (advances), net	(309,700)	(209,100)
Borrowing (repayment) of short-term borrowings, net	0	0
Repayment of long-term debt	(1,900)	(1,900)
Issuance of common stock	0	0
Other, net	10,300	0
Cash used in financing activities	(302,800)	(212,200)
Change in cash and cash equivalents	0	0
Cash and cash equivalents at beginning of period	0	0
Cash and cash equivalents at end of period	0	0
Reportable Legal Entities | Total
Operating activities
Cash provided by operating activities	495,300	269,100
Investing activities
Capital expenditures	(264,500)	(112,700)
Contributions to unconsolidated affiliates	(100)
Other investing activities	9,000	3,200
Cash provided by (used in) investing activities	(255,600)	(109,500)
Financing activities
Dividends paid	(316,400)	(129,800)
Distributions to noncontrolling interests	(1,500)	(136,700)
Intercompany borrowings (advances), net	0	0
Borrowing (repayment) of short-term borrowings, net	(614,700)	180,500
Repayment of long-term debt	(501,900)	(2,000)
Issuance of common stock	1,182,100	3,700
Other, net	(7,000)	(13,400)
Cash used in financing activities	(259,400)	(97,700)
Change in cash and cash equivalents	(19,700)	61,900
Cash and cash equivalents at beginning of period	37,200	248,900
Cash and cash equivalents at end of period	17,500	310,800
Consolidating Entries
Operating activities
Cash provided by operating activities	(666,000)	(530,500)
Investing activities
Capital expenditures	0	0
Contributions to unconsolidated affiliates	0
Other investing activities	0	0
Cash provided by (used in) investing activities	0	0
Financing activities
Dividends paid	666,000	666,000
Distributions to noncontrolling interests	0	(135,500)
Intercompany borrowings (advances), net	0	0
Borrowing (repayment) of short-term borrowings, net	0	0
Repayment of long-term debt	0	0
Issuance of common stock	0	0
Other, net	0	0
Cash used in financing activities	666,000	530,500
Change in cash and cash equivalents	0	0
Cash and cash equivalents at beginning of period	0	0
Cash and cash equivalents at end of period	$ 0	$ 0