ONEOK (OKE) 10-K 27 Feb 18 2017 FY Annual report Financial data

Document And Entity Information

Document And Entity Information - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2017	Feb. 22, 2018	Jun. 30, 2017
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 Public Float			$ 19.5
Entity Common Stock, Shares Outstanding		410,634,227
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017

CONSOLIDATED STATEMENTS OF INCO

CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues
Commodity sales	$ 9,862,652	$ 6,858,456	$ 6,098,343
Services	2,311,255	2,062,478	1,664,863
Total revenues	12,173,907	8,920,934	7,763,206
Cost of sales and fuel (exclusive of items shown separately below)	9,538,045	6,496,124	5,641,052
Operations and maintenance	735,190	668,335	605,748
Depreciation and amortization	406,335	391,585	354,620
Impairment of long-lived assets (Note E)	15,970	0	83,673
General taxes	98,396	88,849	87,583
Gain on sale of assets	(924)	(9,635)	(5,629)
Operating income	1,380,895	1,285,676	996,159
Equity in net earnings from investments (Note N)	159,278	139,690	125,300
Impairment of equity investments (Note N)	(4,270)	0	(180,583)
Allowance for equity funds used during construction	107	209	2,179
Other income	15,385	6,091	368
Other expense	(24,936)	(4,059)	(4,760)
Interest expense (net of capitalized interest of $5,510, $10,591 and $36,572, respectively)	(485,658)	(469,651)	(416,787)
Income before income taxes	1,040,801	957,956	521,876
Income taxes (Note M)	(447,282)	(212,406)	(136,600)
Income from continuing operations	593,519	745,550	385,276
Income (loss) from discontinued operations, net of tax	0	(2,051)	(6,081)
Net income	593,519	743,499	379,195
Less: Net income attributable to noncontrolling interests	205,678	391,460	134,218
Net income attributable to ONEOK	387,841	352,039	244,977
Less: Preferred stock dividends	767	0	0
Net Income Available to Common Stockholders	387,074	352,039	244,977
Amounts available to common shareholders:
Income from continuing operations	387,074	354,090	251,058
Income (loss) from discontinued operations	0	(2,051)	(6,081)
Net Income Available to Common Stockholders	$ 387,074	$ 352,039	$ 244,977
Basic earnings per common share:
Income from continuing operations (Note J)	$ 1.30	$ 1.68	$ 1.19
Income (loss) from discontinued operations	0	(0.01)	(0.02)
Net income	1.30	1.67	1.17
Diluted earnings per common share:
Income from continuing operations (Note J)	1.29	1.67	1.19
Income (loss) from discontinued operations	0	(0.01)	(0.03)
Net income	$ 1.29	$ 1.66	$ 1.16
Average shares (thousands)
Basic	297,477	211,128	210,208
Diluted	299,780	212,383	210,541
Dividends declared per share of common stock	$ 2.72	$ 2.46	$ 2.43

CONSOLIDATED STATEMENTS OF INC3

CONSOLIDATED STATEMENTS OF INCOME CONSOLIDATED STATEMENT OF INCOME (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Interest Expense (net of capitalized interest)	$ 5,510	$ 10,591	$ 36,572

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net income	$ 64,812	$ 166,531	$ 175,991	$ 186,185	$ 194,465	$ 194,216	$ 179,859	$ 174,959	$ 593,519	$ 743,499	$ 379,195
Other comprehensive income (loss), net of tax
Unrealized gains (losses) on derivatives, net of tax of $19,006, $5,452 and $(6,138), respectively									(21,408)	(30,300)	41,362
Realized (gains) losses on derivatives recognized in net income, net of tax of $(26,899), $230 and $8,815, respectively									63,687	(6,977)	(54,709)
Unrealized holding gains (losses) on available-for-sale securities, net of tax of $0, $0 and $648, respectively									0	0	(955)
Change in pension and postretirement benefit plan liability, net of tax of $(878), $11,128 and $(10,278), respectively									(4,175)	(16,693)	15,416
Other comprehensive income (loss) on investments in unconsolidated affiliates, net of tax of $145, $270 and $293, respectively									(970)	(1,505)	(1,632)
Total other comprehensive income (loss), net of tax									37,134	(55,475)	(518)
Comprehensive income									630,653	688,024	378,677
Less: Comprehensive income attributable to noncontrolling interests									236,704	363,093	124,589
Comprehensive income attributable to ONEOK									$ 393,949	$ 324,931	$ 254,088

CONSOLIDATED STATEMENTS OF COM5

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Unrealized gains (losses) on derivatives, tax	$ 19,006	$ 5,542	$ (6,138)
Realized (gains) losses on derivatives in net income, tax	(26,899)	230	8,815
Unrealized holding gains (losses) on available-for-sale securities, tax	0	0	648
Change in pension and postretirement benefit plan liability, tax	(878)	11,128	(10,278)
Other comprehensive income (loss) on investments in unconsolidated affiliates, tax	$ 145	$ 270	$ 293

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets
Cash and cash equivalents	$ 37,193	$ 248,875
Accounts receivable, net	1,202,951	872,430
Materials and supplies	90,301	60,912
Natural gas and natural gas liquids in storage	342,293	140,034
Commodity imbalances	38,712	60,896
Other current assets	53,008	45,986
Assets of discontinued operations	0	551
Total current assets	1,764,458	1,429,684
Property, plant and equipment
Property, plant and equipment	15,559,667	15,078,497
Accumulated depreciation and amortization	2,861,541	2,507,094
Net property, plant and equipment (Note E)	12,698,126	12,571,403
Investments and other assets
Investments in unconsolidated affiliates (Note N)	1,003,156	958,807
Goodwill and intangible assets (Note F)	993,460	1,005,359
Deferred income taxes (Note M)	205,907	0
Other assets	180,830	162,998
Assets of discontinued operations	0	10,500
Total investments and other assets	2,383,353	2,137,664
Total assets	16,845,937	16,138,751
Current liabilities
Current maturities of long-term debt (Note G)	432,650	410,650
Short-term borrowings (Note G)	614,673	1,110,277
Accounts payable	1,140,571	874,731
Commodity imbalances	164,161	142,646
Accrued interest	135,309	112,514
Other current liabilities	179,971	166,042
Liabilities of discontinued operations	0	19,841
Total current liabilities	2,667,335	2,836,701
Long-term debt, excluding current maturities (Note G)	8,091,629	7,919,996
Deferred income taxes (Note M)	52,697	1,623,822
Other deferred credits	348,924	321,846
Liabilities of discontinued operations	0	7,471
Total deferred credits and other liabilities	401,621	1,953,139
Commitments and contingencies (Note O)
Equity
Preferred stock, $0.01 par value: issued 20,000 shares at December 31, 2017, and no shares at December 31, 2016	0	0
Common stock, $0.01 par value: authorized 1,200,000,000 shares; issued 423,166,234 shares and outstanding 388,703,543 shares at December 31, 2017; authorized 600,000,000 shares; issued 245,811,180 shares and outstanding 210,681,661 shares at December 31, 2016	4,232	2,458
Paid-in capital	6,588,878	1,234,314
Accumulated other comprehensive loss (Note I)	(188,530)	(154,350)
Retained earnings	0	0
Treasury stock, at cost: 34,462,691 shares at December 31, 2017, and 35,129,519 shares at December 31, 2016	(876,713)	(893,677)
Total ONEOK shareholders’ equity	5,527,867	188,745
Noncontrolling interests in consolidated subsidiaries	157,485	3,240,170
Total equity	5,685,352	3,428,915
Total liabilities and equity	$ 16,845,937	$ 16,138,751

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Equity (Note H)
Common stock, shares, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares, authorized (in shares)	1,200,000,000	600,000,000
Common stock, shares, issued (in shares)	423,166,234	245,811,180
Common stock, shares, outstanding (in shares)	388,703,543	210,681,661
Treasury stock, shares (in shares)	34,462,691	35,129,519
Preferred stock, shares, par value (in dollars per share)	$ 0.01	$ 0
Preferred stock, shares, issued (in shares)	20,000	0

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities
Net income	$ 593,519	$ 743,499	$ 379,195
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	406,335	391,585	354,620
Impairment charges	20,240	0	264,256
Noncash contribution of preferred stock, net of tax	12,600	0	0
Equity in net earnings from investments	(159,278)	(139,690)	(125,300)
Distributions received from unconsolidated affiliates	167,372	144,673	122,003
Deferred income taxes	437,917	211,638	137,737
Share-based compensation expense	26,262	40,563	16,435
Pension and postretirement benefit expense, net of contributions	4,079	11,643	14,814
Allowance for equity funds used during construction	(107)	(209)	(2,179)
Gain on sale of assets	(924)	(9,635)	(5,629)
Changes in assets and liabilities:
Accounts receivable	(330,521)	(285,806)	157,051
Natural gas and natural gas liquids in storage	(202,259)	(11,950)	6,050
Accounts payable	261,305	287,632	(205,143)
Commodity imbalances, net	43,699	45,971	(4,083)
Settlement of exit activities liabilities	(9,707)	(19,906)	(38,536)
Accrued interest	22,795	(16,529)	24,166
Risk-management assets and liabilities	37,617	(78,136)	(32,370)
Other assets and liabilities, net	(15,532)	37,998	(40,259)
Cash provided by operating activities	1,315,412	1,353,341	1,022,828
Investing activities
Capital expenditures (less allowance for equity funds used during construction)	(512,393)	(624,634)	(1,188,312)
Contributions to unconsolidated affiliates	(87,861)	(68,275)	(27,540)
Distributions received from unconsolidated affiliates in excess of cumulative earnings	28,742	52,044	33,915
Proceeds from sale of assets	3,879	25,420	3,825
Other	0	0	(12,607)
Cash used in investing activities	(567,633)	(615,445)	(1,190,719)
Financing activities
Dividends paid	(829,414)	(517,601)	(509,197)
Distributions to noncontrolling interests	(276,260)	(549,419)	(535,825)
Borrowing (repayment) of short-term borrowings, net	(495,604)	563,937	(508,956)
Issuance of long-term debt, net of discounts	1,190,496	1,000,000	1,291,506
Debt financing costs	(11,425)	(2,770)	(17,515)
Repayment of long-term debt	(994,776)	(1,108,040)	(7,753)
Issuance of common stock	471,358	21,971	20,669
Issuance of common units, net of issuance costs	0	0	375,660
Other	(13,836)	5,403	(15,848)
Cash provided (used in) by financing activities	(959,461)	(586,519)	92,741
Change in cash and cash equivalents	(211,682)	151,377	(75,150)
Change in cash and cash equivalents included in discontinued operations	0	(121)	(43)
Change in cash and cash equivalents from continuing operations	(211,682)	151,256	(75,193)
Cash and cash equivalents at beginning of period	248,875	97,619	172,812
Cash and cash equivalents at end of period	37,193	248,875	97,619
Supplemental cash flow information:
Cash paid for interest, net of amounts capitalized	432,210	461,208	367,835
Cash paid for income taxes	$ 6,633	$ 361	$ 3,324

CONSOLIDATED STATEMENT OF CHANG

CONSOLIDATED STATEMENT OF CHANGES IN EQUITY - USD ($) $ in Thousands	Total	Common Stock	Preferred Stock	Paid-in Capital	Accumulated Other Comprehensive Loss	Retained Earnings	Treasury Stock	Noncontrolling Interests in Consolidated Subsidiaries
Shares, issued, beginning balance at Dec. 31, 2014		245,811,180	0
Total equity, beginning balance at Dec. 31, 2014	$ 4,005,883	$ 2,458	$ 0	$ 1,541,583	$ (136,353)	$ 138,128	$ (953,701)	$ 3,413,768
Net income	379,195	0	0	0	0	244,977	0	134,218
Other comprehensive income (loss) (Note I)	(518)	0	0	0	9,111	0	0	(9,629)
Common stock issued	28,289	$ 0	0	(7,550)	0	0	35,839	0
Stock Issued During Period, Shares, Other		0
Common stock dividends	(509,197)	$ 0	0	(126,090)	0	(383,107)	0	0
Issuance of common units of ONEOK Partners	393,997	0	0	(34,446)	0	0	0	428,443
Distributions to noncontrolling interests	(535,825)	0	0	0	0	0	0	(535,825)
Other	4,512	$ 0	$ 0	4,947	0	2	0	(437)
Shares, issued, ending balance at Dec. 31, 2015		245,811,180	0
Total equity, ending balance at Dec. 31, 2015	3,766,336	$ 2,458	$ 0	1,378,444	(127,242)	0	(917,862)	3,430,538
Net income	743,499	0	0	0	0	352,039	0	391,460
Other comprehensive income (loss) (Note I)	(55,475)	0	0	0	(27,108)	0	0	(28,367)
Common stock issued	26,516	$ 0	0	2,331	0	0	24,185	0
Stock Issued During Period, Shares, Other		0
Common stock dividends	(517,601)	$ 0	0	(165,562)	0	(352,039)	0	0
Distributions to noncontrolling interests	(549,419)	0	0	0	0	0	0	(549,419)
Other	15,059	$ 0	$ 0	19,101	0	0	0	(4,042)
Shares, issued, ending balance at Dec. 31, 2016		245,811,180	0
Total equity, ending balance at Dec. 31, 2016	3,428,915	$ 2,458	$ 0	1,234,314	(154,350)	0	(893,677)	3,240,170
Cumulative effect adjustment for adoption of ASU 2016-09 at December 31, 2017	73,368	0	0	0	0	73,368	0	0
Net income	593,519	0	0	0	0	387,841	0	205,678
Other comprehensive income (loss) (Note I)	37,134	0	0	0	6,108	0	0	31,026
Common stock issued	473,586	$ 85	$ 0	456,537	0	0	16,964	0
Stock Issued During Period, Shares, Other		8,434,223	20,000
Preferred stock issued	20,000	$ 0	$ 0	20,000	0	0	0	0
Common stock dividends	(828,787)	0	0	(367,578)	0	(461,209)	0	0
Preferred stock dividends	(767)	0	0	(767)	0	0	0	0
Distributions to noncontrolling interests	(276,260)	$ 0	0	0	0	0	0	(276,260)
Stock Issued During Period, Shares, Acquisitions		168,920,831
Acquisition of ONEOK Partners' noncontrolling interests	2,146,462	$ 1,689	0	5,228,580	(40,288)	0	0	(3,043,519)
Other	18,182	$ 0	$ 0	17,792	0	0	0	390
Shares, issued, ending balance at Dec. 31, 2017		423,166,234	20,000
Total equity, ending balance at Dec. 31, 2017	$ 5,685,352	$ 4,232	$ 0	$ 6,588,878	$ (188,530)	$ 0	$ (876,713)	$ 157,485

CONSOLIDATED STATEMENT OF CHA10

CONSOLIDATED STATEMENT OF CHANGES IN EQUITY CONSOLIDATED STATEMENT OF CHANGES IN EQUITY (Parenthetical) - $ / shares	3 Months Ended												12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Stockholders' Equity [Abstract]
Dividends paid (in dollars per share)	$ 0.745	$ 0.745	$ 0.615	$ 0.615	$ 0.615	$ 0.615	$ 0.615	$ 0.615	$ 0.615	$ 0.605	$ 0.605	$ 0.605	$ 2.720	$ 2.460	$ 2.430

SUMMARY OF SIGNIFICANT ACCOUNTI

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Notes)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Organization and Nature of Operations - We are a corporation incorporated under the laws of the state of Oklahoma, and our common stock is listed on the NYSE under the trading symbol “OKE.” On June 30, 2017, we completed the Merger Transaction at a fixed exchange ratio of 0.985 of a share of our common stock for each ONEOK Partners common unit that we did not already own. 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. No fractional shares were issued in the Merger Transaction, and ONEOK Partners common unitholders instead received cash in lieu of fractional shares. As a result of the completion of the Merger Transaction, common units of ONEOK Partners are no longer publicly traded. For additional information on this transaction, see Note B. Our operations include gathering and processing of natural gas produced from crude oil and natural gas wells. We gather and process natural gas in the Mid-Continent region, which includes the NGL-rich STACK and SCOOP areas and the Cana-Woodford Shale, Woodford Shale, Springer Shale, Meramec, Granite Wash and Mississippian Lime formations of Oklahoma and Kansas, and the Hugoton and Central Kansas Uplift Basins in Kansas. We also gather and/or process natural gas in two producing basins in the Rocky Mountain region: the Williston Basin, which spans portions of North Dakota and Montana and includes the oil-producing, NGL-rich Bakken Shale and Three Forks formations; and the Powder River Basin located in Wyoming, which includes the NGL-rich Niobrara Shale and Frontier, Turner and Sussex formations in Wyoming. Our natural gas liquids assets consist of facilities that gather, fractionate and treat NGLs and store NGL products primarily in Oklahoma, Kansas, Texas, New Mexico and the Rocky Mountain region where we provide midstream services to producers of NGLs. We own or have an ownership interest in FERC-regulated natural gas liquids gathering and distribution pipelines in Oklahoma, Kansas, Texas, New Mexico, Montana, North Dakota, Wyoming and Colorado, and terminal and storage facilities in Missouri, Nebraska, Iowa and Illinois. We also own FERC-regulated natural gas liquids distribution and refined petroleum products pipelines in Kansas, Missouri, Nebraska, Iowa, Illinois and Indiana that connect our Mid-Continent assets with Midwest markets, including Chicago, Illinois. We own and operate truck- and rail-loading and -unloading facilities that interconnect with our NGL fractionation and pipeline assets. We operate interstate and intrastate natural gas transmission pipelines and natural gas storage facilities. Our FERC-regulated interstate natural gas pipeline assets transport natural gas through pipelines in North Dakota, Minnesota, Wisconsin, Illinois, Indiana, Kentucky, Tennessee, Oklahoma, Texas and New Mexico. Our intrastate natural gas pipeline assets in Oklahoma transport natural gas throughout the state and have access to the major natural gas producing areas in the Mid-Continent region, which include the STACK and SCOOP areas and the Cana-Woodford Shale, Woodford Shale, Springer Shale, Meramec, Granite Wash and Mississippian Lime formations. The Roadrunner pipeline transports natural gas from the Permian Basin in West Texas to the Mexican border near El Paso, Texas, and is fully subscribed with 25-year firm demand charge, fee-based agreements. We own underground natural gas storage facilities in Oklahoma and Texas that are connected to our intrastate natural gas pipeline assets. We also have underground natural gas storage facilities in Kansas. Consolidation - Our Consolidated Financial Statements include our accounts and the accounts of our subsidiaries over which we have control or are the primary beneficiary. All intercompany balances and transactions have been eliminated in consolidation. Investments in unconsolidated affiliates are accounted for using the equity method if we have the ability to exercise significant influence over operating and financial policies of our investee. Under this method, an investment is carried at its acquisition cost and adjusted each period for contributions made, distributions received and our share of the investee’s comprehensive income. For the investments we account for under the equity method, the premium or excess cost over underlying fair value of net assets is referred to as equity-method goodwill. Impairment of equity investments is recorded when the impairments are other than temporary. These amounts are recorded as investments in unconsolidated affiliates on our accompanying Consolidated Balance Sheets. See Note N for disclosures of our unconsolidated affiliates. Distributions paid to us from our unconsolidated affiliates are classified as operating activities on our Consolidated Statements of Cash Flows until the cumulative distributions exceed our proportionate share of income from the unconsolidated affiliate since the date of our initial investment. The amount of cumulative distributions paid to us that exceeds our cumulative proportionate share of income in each period represents a return of investment and is classified as an investing activity on our Consolidated Statements of Cash Flows. Use of Estimates - The preparation of our Consolidated Financial Statements and related disclosures in accordance with GAAP requires us to make estimates and assumptions with respect to values or conditions that cannot be known with certainty that affect the reported amounts on our Consolidated Financial Statements. Items that may be estimated include, but are not limited to, the economic useful life of assets, fair value of assets, liabilities and equity-method investments, obligations under employee benefit plans, provisions for uncollectible accounts receivable, expenses for services received but for which no invoice has been received, provision for income taxes, including any deferred tax valuation allowances, the results of litigation and various other recorded or disclosed amounts. In addition, a portion of our revenues and cost of sales and fuel are recorded based on current month estimated volumes and prices. The estimates are reversed in the following month and recorded with actual volumes and prices. We evaluate these estimates on an ongoing basis using historical experience, consultation with experts and other methods we consider reasonable based on the particular circumstances. Nevertheless, actual results may differ significantly from the estimates. Any effects on our financial position or results of operations from revisions to these estimates are recorded in the period when the facts that give rise to the revision become known. Fair Value Measurements - We define fair value as the price that would be received from the sale of an asset or the transfer of a liability in an orderly transaction between market participants at the measurement date. We use 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 primarily 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 comprised 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 for which ineffectiveness has not been material. Determining the appropriate classification of our fair value measurements within the fair value hierarchy requires management’s judgment regarding the degree to which market data is observable or corroborated by observable market data. We categorize derivatives for which fair value is determined using multiple inputs within a single level, based on the lowest level input that is significant to the fair value measurement in its entirety. See Note C for discussion of our fair value measurements. Cash and Cash Equivalents - Cash equivalents consist of highly liquid investments, which are readily convertible into cash and have original maturities of three months or less. Revenue Recognition - Our reportable segments recognize revenue when services are rendered or product is delivered. Our Natural Gas Gathering and Processing segment records revenues when natural gas is gathered or processed through our facilities. Our Natural Gas Liquids segment records revenues based upon contracted services and volumes exchanged or stored under service agreements in the period services are provided. A portion of our revenues for our Natural Gas Pipelines segment and our Natural Gas Liquids segment are recognized based upon contracted capacity and contracted volumes transported and stored under service agreements in the period services are provided. We disaggregate revenue on the Consolidated Statements of Income as follows: • Commodity sales - Commodity sales represent the sale of NGLs, condensate and residue natural gas. We generally purchase a supplier’s raw natural gas or unfractionated NGLs, which we process into marketable commodities and condensate, then we sell these commodities and condensate to downstream customers at a specified delivery point. Commodity sales are recognized upon delivery or title transfer to the customer, when revenue recognition criteria are met. • Service revenue - Service revenue represents the fees generated from the performance of our services. We enter into a variety of contract types that provide commodity sales and service revenue. We provide services primarily under the following types of contracts: • Fee-based - Under fee-based arrangements, we receive a fee or fees for one or more of the following services: gathering, compression, processing, transmission and storage of natural gas; and gathering, transportation, fractionation and storage of NGLs. The revenue we earn from these arrangements generally is directly related to the volume of natural gas and NGLs that flow through our systems and facilities, and is not normally directly dependent on commodity prices. However, to the extent a sustained decline in commodity prices results in a decline in volumes, our revenues from these arrangements would be reduced. In addition, many of our arrangements provide for fixed fee, minimum volume or firm demand charges. Fee-based arrangements are reported as service revenue on the Consolidated Statements of Income. • Percent-of-proceeds - Under POP arrangements in our Natural Gas Gathering and Processing segment, we generally purchase the producer’s raw natural gas which we process into natural gas and natural gas liquids, then we sell these commodities and condensate to downstream customers. We remit sales proceeds to the producer according to the contractual terms and retain our portion. Typically, our POP arrangements also include a fee-based component. In many cases, our Natural Gas Gathering and Processing segment provides services under contracts that contain a combination of the arrangements described above. When services are provided (in addition to raw natural gas purchased) under POP with fee contracts, we record such fees as service revenue on the Consolidated Statements of Income. The terms of our contracts vary based on natural gas quality conditions, the competitive environment when the contracts are signed and customer requirements. Update - Upon adoption of Topic 606 in January 2018, certain of our revenue recognition policies changed. Based on the new guidance, 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 considered commodity supply contracts, as we control the commodities prior to performing services. Therefore, contractual fees in these identified contracts will be recorded as a reduction of the commodity purchase price in cost of sales and fuel, rather than as services revenue. To the extent we hold inventory related to these purchases, typically only in our Natural Gas Liquids segment, 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 commodities purchased under our Natural Gas Gathering and Processing segment’s POP with fee contracts and our Natural Gas Liquids segment’s exchange services contracts that include the purchase of commodities, which is unchanged from our assessment under current guidance and will not result in any changes in the nature or timing of commodity sales revenue. The contractual fees on POP with fee contracts that include producer take-in-kind rights will continue to be recorded as services revenue, as we do not control the raw natural gas stream while we are providing midstream services. From time to time, differences in the timing of revenues earned and our right to invoice customers may create contract assets or liabilities. At adoption, the timing of revenue on transportation contracts with tiered rates will be presented as contract assets for our Natural Gas Pipelines segment. In addition, certain contributions in aid of construction from customers will be reflected as contract liabilities that will be recognized into revenue over the contract term. In 2017 and prior periods, we recorded these reimbursements as reductions to property, plant and equipment. Cost of Sales and Fuel - Cost of sales and fuel primarily includes (i) the cost of purchased commodities, including NGLs, natural gas and condensate, (ii) fees incurred for third-party transportation, fractionation and storage of commodities, and (iii) fuel and power costs incurred to operate our own facilities that gather, process, transport and store commodities. Update - As described above, upon adoption of Topic 606 in January 2018, cost of sales and fuel will be reduced by the fees we charge producers under our Natural Gas Gathering and Processing segment’s POP contracts and processors under our Natural Gas Liquids segment’s exchange services contracts that include the purchase of commodities. Operations and Maintenance - Operations and maintenance primarily includes (i) payroll and benefit costs, (ii) third-party costs for operations, maintenance and integrity management, regulatory compliance and environmental and safety, and (iii) other business related service costs. Accounts Receivable - Accounts receivable represent valid claims against nonaffiliated customers for products sold or services rendered, net of allowances for doubtful accounts. We assess the creditworthiness of our counterparties on an ongoing basis and require security, including prepayments and other forms of collateral, when appropriate. Outstanding customer receivables are reviewed regularly for possible nonpayment indicators, and allowances for doubtful accounts are recorded based upon management’s estimate of collectability at each balance sheet date. At December 31, 2017 and 2016 , our allowance for doubtful accounts was not material. Inventory - The values of current natural gas and NGLs in storage are determined using the lower of weighted-average cost or net realizable value. Noncurrent natural gas and NGLs are classified as property and valued at cost. Materials and supplies are valued at average cost. Commodity Imbalances - Commodity imbalances represent amounts payable or receivable for NGL exchange contracts and natural gas pipeline imbalances and are valued at market prices. Under the majority of our NGL exchange agreements, we physically receive volumes of unfractionated NGLs, including the risk of loss and legal title to such volumes, from the exchange counterparty. In turn, we deliver NGL products back to the customer and charge them gathering, fractionation and transportation fees. To the extent that the volumes we receive under such agreements differ from those we deliver, we record a net exchange receivable or payable position with the counterparties. These net exchange receivables and payables are settled with movements of NGL products rather than with cash. Natural gas pipeline imbalances are settled in cash or in-kind, subject to the terms of the pipelines’ tariffs or by agreement. Derivatives and Risk Management - We utilize derivatives to reduce our market-risk exposure to commodity price and interest-rate fluctuations and to achieve more predictable cash flows. We record all derivative instruments at fair value, with the exception of normal purchases and normal sales transactions that are expected to result in physical delivery. Commodity price and interest-rate volatility may have a significant impact on the fair value of derivative instruments as of a given date. The accounting for changes in the fair value of a derivative instrument depends on whether it has been designated and qualifies as part of a hedging relationship and, if so, the reason for holding it. The table below summarizes the various ways in which we account for our derivative instruments and the impact on our Consolidated Financial Statements: Recognition and Measurement Accounting Treatment Balance Sheet Income Statement Normal purchases and normal sales - Fair value not recorded - Change in fair value not recognized in earnings Mark-to-market - Recorded at fair value - Change in fair value recognized in earnings Cash flow hedge - Recorded at fair value - Ineffective portion of the gain or loss on the derivative instrument is recognized in earnings - Effective portion of the gain or loss on the derivative instrument is reported initially as a component of accumulated other comprehensive income (loss) - Effective portion of the gain or loss on the derivative instrument is reclassified out of accumulated other comprehensive income (loss) into earnings when the forecasted transaction affects earnings Fair value hedge - Recorded at fair value - The gain or loss on the derivative instrument is recognized in earnings - Change in fair value of the hedged item is recorded as an adjustment to book value - Change in fair value of the hedged item is recognized in earnings To reduce our exposure to fluctuations in natural gas, NGLs and condensate prices, we periodically enter into futures, forward purchases and sales, options or swap transactions in order to hedge anticipated purchases and sales of natural gas, NGLs and condensate. Interest-rate swaps are used from time to time to manage interest-rate risk. Under certain conditions, we designate our derivative instruments as a hedge of exposure to changes in fair values or cash flows. We formally document all relationships between hedging instruments and hedged items, as well as risk-management objectives and strategies for undertaking various hedge transactions, and methods for assessing and testing correlation and hedge ineffectiveness. We specifically identify the forecasted transaction that has been designated as the hedged item in a cash flow hedge relationship. We assess the effectiveness of hedging relationships quarterly by performing an effectiveness analysis on our fair value and cash flow hedging relationships to determine whether the hedge relationships are highly effective on a retrospective and prospective basis. We also document our normal purchases and normal sales transactions that we expect to result in physical delivery and that we elect to exempt from derivative accounting treatment. The realized revenues and purchase costs of our derivative instruments not considered held for trading purposes and derivatives that qualify as normal purchases or normal sales that are expected to result in physical delivery are reported on a gross basis. Cash flows from futures, forwards and swaps that are accounted for as hedges are included in the same category as the cash flows from the related hedged items in our Consolidated Statements of Cash Flows. See Notes C and D for more discussion of our fair value measurements and risk-management and hedging activities using derivatives. Property, Plant and Equipment - Our properties are stated at cost, including AFUDC and capitalized interest. In some cases, the cost of regulated property retired or sold, plus removal costs, less salvage, is charged to accumulated depreciation. Gains and losses from sales or transfers of nonregulated properties or an entire operating unit or system of our regulated properties are recognized in income. Maintenance and repairs are charged directly to expense. The interest portion of AFUDC and capitalized interest represent the cost of borrowed funds used to finance construction activities for regulated and nonregulated projects, respectively. We capitalize interest costs during the construction or upgrade of qualifying assets. These costs are recorded as a reduction to interest expense. The equity portion of AFUDC represents the capitalization of the estimated average cost of equity used during the construction of major projects and is recorded in the cost of our regulated properties and as a credit to the allowance for equity funds used during construction. Our properties are depreciated using the straight-line method over their estimated useful lives. Generally, we apply composite depreciation rates to functional groups of property having similar economic circumstances. We periodically conduct depreciation studies to assess the economic lives of our assets. For our regulated assets, these depreciation studies are completed as a part of our rate proceedings or tariff filings, and the changes in economic lives, if applicable, are implemented prospectively when the new rates are billed. For our nonregulated assets, if it is determined that the estimated economic life changes, the changes are made prospectively. Changes in the estimated economic lives of our property, plant and equipment could have a material effect on our financial position or results of operations. Property, plant and equipment on our Consolidated Balance Sheets includes construction work in process for capital projects that have not yet been placed in service and therefore are not being depreciated. Assets are transferred out of construction work in process when they are substantially complete and ready for their intended use. See Note E for disclosures of our property, plant and equipment. Impairment of Goodwill and Long-Lived Assets, Including Intangible Assets - We assess our goodwill for impairment at least annually on July 1, unless events or changes in circumstances indicate an impairment may have occurred before that time. Our qualitative goodwill impairment analysis performed as of July 1, 2017, did not result in an impairment charge nor did our analysis reflect any reporting units at risk, and subsequent to that date, no event has occurred indicating that the implied fair value of each of our reporting units is less than the carrying value of its net assets. As part of our goodwill impairment test, we may first assess qualitative factors (including macroeconomic conditions, industry and market considerations, cost factors and overall financial performance) to determine whether it is more likely than not that the fair value of each of our reporting units is less than its carrying amount. If further testing is necessary or a quantitative test is elected, we perform a two-step impairment test for goodwill. In the first step, an initial assessment is made by comparing the fair value of a reporting unit with its book value, including goodwill. If the fair value is less than the book value, an impairment is indicated, and we must perform a second test to measure the amount of the impairment. In the second test, we calculate the implied fair value of the goodwill by deducting the fair value of all tangible and intangible net assets of the reporting unit from the fair value determined in step one of the assessment. If the carrying value of the goodwill exceeds the implied fair value of the goodwill, we will record an impairment charge. To estimate the fair value of our reporting units, we use two generally accepted valuation approaches, an income approach and a market approach, using assumptions consistent with a market participant’s perspective. Under the income approach, we use anticipated cash flows over a period of years plus a terminal value and discount these amounts to their present value using appropriate discount rates. Under the market approach, we apply EBITDA multiples to forecasted EBITDA. The multiples used are consistent with historical asset transactions. The forecasted cash flows are based on average forecasted cash flows for a reporting unit over a period of years. We assess our long-lived assets for impairment whenever events or changes in circumstances indicate that an asset’s carrying amount may not be recoverable. An impairment is indicated if the carrying amount of a long-lived asset exceeds the sum of the undiscounted future cash flows expected to result from the use and eventual disposition of the asset. If an impairment is indicated, we record an impairment loss equal to the difference between the carrying value and the fair value of the long-lived asset. For the investments we account for under the equity method, the impairment test considers whether the fair value of the equity investment as a whole, not the underlying net assets, has declined and whether that decline is other than temporary. Therefore, we periodically evaluate the amount at which we carry our equity-method investments to determine whether current events or circumstances warrant adjustments to our carrying values. See Notes E , F and N for our long-lived assets, goodwill and intangible assets and investments in unconsolidated affiliates disclosures. Regulation - Our intrastate natural gas transmission and natural gas liquids pipelines are subject to the rate regulation and accounting requirements of the OCC, KCC and RRC, and our natural gas transmission pipelines are regulated by the FERC under the Natural Gas Policy Act for certain services where we deliver natural gas into FERC regulated natural gas pipelines. Our interstate natural gas and natural gas liquids pipelines are subject to regulation by the FERC. In Kansas and Texas, natural gas storage may be regulated by the state and the FERC for certain types of services. Accordingly, portions of our Natural Gas Liquids and Natural Gas Pipelines segments follow the accounting and reporting guidance for regulated operations. In our Consolidated Financial Statements and our Notes to Consolidated Financial Statements, regulated operations are defined pursuant to Financial Accounting Standards Board’s (FASB) ASC 980, Regulated Operations. During the rate-making process for certain of our assets, regulatory authorities set the framework for what we can charge customers for our services and establish the manner that our costs are accounted for, including allowing us to defer recognition of certain costs and permitting recovery of the amounts through rates over time as opposed to expensing such costs as incurred. Certain examples of types of regulatory guidance include costs for fuel and losses, acquisition costs, contributions in aid of construction, charges for depreciation, and gains or losses on disposition of assets. This allows us to stabilize rates over time rather than passing such costs on to the customer for immediate recovery. Actions by regulatory authorities could have an effect on the amount recovered from rate payers. Any difference in the amount recoverable and the amount deferred is recorded as income or expense at the time of the regulatory action. A write-off of regulatory assets and costs not recovered may be required if all or a portion of the regulated operations have rates that are no longer: • established by independent, third-party regulators; • designed to recover the specific entity’s costs of providing regulated services; and • set at levels that will recover our costs when considering the demand and competition for our services. At December 31, 2017 and 2016 , we recorded regulatory assets of $5.0 million and $5.5 million , respectively, which are currently being recovered and are expected to be recovered from our customers. Regulatory assets are being recovered as a result of approved rate proceedings over varying time periods up to 50 years. These assets are reflected in other assets on our Consolidated Balance Sheets. Retirement and Postretirement Employee Benefits - We have defined benefit retirement plans covering certain employees and former employees. We sponsor welfare plans that provide postretirement medical and life insurance benefits to certain employees hired prior to 2017 who retire with at least five years of service. The expense and liability related to these plans is calculated using statistical and other factors that attempt to anticipate future events. These factors include assumptions about the discount rate, expected return on plan assets, rate of future compen

ONEOK PARTNERS ACQUISITION ONEO

ONEOK PARTNERS ACQUISITION ONEOK PARTNERS ACQUISITION (Notes)	12 Months Ended
	Dec. 31, 2017
Business Acquisition [Line Items]
Business Acquisition, Description of Acquired Entity	ACQUISITION OF ONEOK PARTNERS 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. No fractional shares were issued in the Merger Transaction, and ONEOK Partners common unitholders instead received cash in lieu of fractional shares. As a result of the completion of the Merger Transaction, common units of ONEOK Partners are no longer publicly traded. As we controlled ONEOK Partners and continue to control ONEOK Partners after the Merger Transaction, the change in our ownership interest was accounted for as an equity transaction, and no gain or loss was recognized in our Consolidated Statements of Income resulting from the Merger Transaction. The Merger Transaction was a taxable exchange to the ONEOK Partners unitholders resulting in a book/tax difference in the basis of the underlying assets acquired. We recorded a deferred tax asset of $2.1 billion , computed as the net of the equity value exchanged of $8.8 billion and noncontrolling interests of $3.0 billion at a tax rate of 37 percent , based on a tax allocation of the transaction value. 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 equity interests in ONEOK Partners (which are consolidated in our financial statements) that were owned by the public until June 30, 2017, are reflected in “Noncontrolling interests” in our accompanying Consolidated Balance Sheet as of December 31, 2016. 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. Effective with the close of 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. Supplemental Cash Flow Information - Our noncash balance sheet activity related to the Merger Transaction is as follows (in millions): Common stock $ 1.7 Paid-in capital $ 5,228.6 Accumulated other comprehensive loss $ (40.3 ) Noncontrolling interests in consolidated subsidiaries $ (3,043.5 ) Deferred income taxes $ (2,146.5 )

FAIR VALUE MEASUREMENTS (Notes)

FAIR VALUE MEASUREMENTS (Notes)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	FAIR VALUE MEASUREMENTS Recurring Fair Value Measurements - The following tables set forth our recurring fair value measurements for the periods indicated: December 31, 2017 Level 1 Level 2 Level 3 Total - Gross Netting (a) Total - Net (b) ( 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. (b) - Included in other current assets, other assets or other current liabilities in our Consolidated Balance Sheets. December 31, 2016 Level 1 Level 2 Level 3 Total - Gross Netting (a) Total - Net (b) ( Thousands of dollars ) Derivative assets Commodity contracts Financial contracts $ 1,147 $ — $ 4,564 $ 5,711 $ (4,760 ) $ 951 Interest-rate contracts — 47,457 — 47,457 — 47,457 Total derivative assets $ 1,147 $ 47,457 $ 4,564 $ 53,168 $ (4,760 ) $ 48,408 Derivative liabilities Commodity contracts Financial contracts $ (31,458 ) $ — $ (24,861 ) $ (56,319 ) $ 56,319 $ — Physical contracts — — (3,022 ) (3,022 ) — (3,022 ) Interest-rate contracts — (12,795 ) — (12,795 ) — (12,795 ) Total derivative liabilities $ (31,458 ) $ (12,795 ) $ (27,883 ) $ (72,136 ) $ 56,319 $ (15,817 ) 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, 2016 , we held no cash and posted $67.7 million of cash with various counterparties, including $51.6 million of cash collateral that is offsetting derivative net liability positions under master-netting arrangements in the table above. The remaining $16.1 million of cash collateral in excess of derivative net liability positions is included in other current assets in our Consolidated Balance Sheets. (b) - Included in other current assets, other assets or other current liabilities in our Consolidated Balance Sheets. The following table sets forth a reconciliation of our Level 3 fair value measurements for the periods indicated: Years Ended December 31, Derivative Assets (Liabilities) 2017 2016 ( Thousands of dollars ) Net assets (liabilities) at beginning of period $ (23,319 ) $ 7,331 Total realized/unrealized gains (losses): Included in earnings (a) 212 (320 ) Included in other comprehensive income (loss) (9,731 ) (30,330 ) Net assets (liabilities) at end of period $ (32,838 ) $ (23,319 ) (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 years ended December 31, 2017 and 2016 , 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 years ended December 31, 2017 and 2016 , there were no transfers 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 comprised 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 $9.3 billion and $8.8 billion at December 31, 2017 and 2016 , respectively. The book value of our consolidated long-term debt, including current maturities, was $8.5 billion and $8.3 billion at December 31, 2017 and 2016 , 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)	12 Months Ended
	Dec. 31, 2017
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 exposed to location price differential risk, primarily as a result of the relative value of NGL purchases at one location and sales at another location. We are also exposed to commodity price risk resulting from the relative values of the various NGL products to each other, NGLs in storage and the relative value of NGLs to natural gas. 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 December 31, 2017 and 2016 , 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 July 2017, we settled $400 million of our forward-starting interest-rate swaps upon the completion of our underwritten public offering of $1.2 billion senior unsecured notes and $500 million of our interest-rate swaps used to hedge our LIBOR-based interest payments. In September 2017, we entered into forward-starting interest-rate swaps with notional amounts totaling $500 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 December 31, 2017 and 2016, we had forward-starting interest-rate swaps with notional amounts totaling $1.3 billion and $1.2 billion , respectively, to hedge the variability of interest payments on a portion of our forecasted debt issuances and interest-rate swaps with notional amounts totaling $500 million and $1.0 billion , respectively, to hedge the variability of our LIBOR-based interest payments. All of our interest-rate swaps are designated as cash flow hedges. In January 2018, we settled the remaining $500 million of our interest-rate swaps used to hedge our LIBOR-based interest payments. Fair Values of Derivative Instruments - The following table sets forth the fair values of our derivative instruments presented on a gross basis for the periods indicated: December 31, 2017 December 31, 2016 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 $ 16,978 $ (42,819 ) $ 1,155 $ (49,938 ) Other assets/other deferred credits — (3,838 ) 210 (2,142 ) Physical contracts Other current liabilities — (4,781 ) — (3,022 ) Interest-rate contracts Other current assets/other current liabilities 1,330 — — (12,795 ) Other assets 48,630 — 47,457 — Total derivatives designated as hedging instruments 66,938 (51,438 ) 48,822 (67,897 ) Derivatives not designated as hedging instruments Commodity contracts Financial contracts Other current assets/other current liabilities 7,477 (7,311 ) 4,346 (4,239 ) Total derivatives not designated as hedging instruments 7,477 (7,311 ) 4,346 (4,239 ) Total derivatives $ 74,415 $ (58,749 ) $ 53,168 $ (72,136 ) Notional Quantities for Derivative Instruments - The following table sets forth the notional quantities for derivative instruments held for the periods indicated: December 31, 2017 December 31, 2016 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 — (24.5 ) — (38.4 ) -Natural gas ( Bcf ) Put options — — 49.5 — -Crude oil and NGLs ( MMBbl ) Futures, forwards and swaps 3.5 (11.1 ) — (3.6 ) Basis -Natural gas ( Bcf ) Futures and swaps — (24.5 ) — (38.4 ) Interest-rate contracts ( Millions of dollars ) Swaps $ 1,750.0 $ — $ 2,150.0 $ — Derivatives not designated as hedging instruments: Fixed price -Natural gas ( Bcf ) Futures and swaps — — 0.4 — -NGLs ( MMBbl ) Futures, forwards and swaps 0.8 (0.8 ) 0.5 (0.7 ) Basis -Natural gas ( Bcf ) Futures and swaps — — 0.4 — 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 December 31, 2017 , our Consolidated Balance Sheet reflected a net loss of $ 188.5 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 $21.7 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 $19.3 million in net losses, net of tax, over the next 12 months and approximately $2.4 million in net losses, net of tax, thereafter. The amount deferred in accumulated other comprehensive loss attributable to our settled interest-rate swaps is a loss of $87.6 million net of tax, which will be recognized over the life of the long-term, fixed-rate debt, including losses of $14.0 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 forward-starting interest-rate swaps with future settlement dates, which are expected to be amortized to interest expense over the life of long-term, fixed-rate debt upon issuance of the debt. The following table sets forth the unrealized effect of cash flow hedges recognized in other comprehensive income (loss) for the periods indicated: Derivatives in Cash Flow Hedging Relationships Years Ended December 31, 2017 2016 2015 ( Thousands of dollars ) Commodity contracts $ (40,577 ) $ (78,513 ) $ 70,065 Interest-rate contracts 163 42,761 (22,565 ) Total unrealized gain (loss) recognized in other comprehensive income (loss) on derivatives (effective portion) $ (40,414 ) $ (35,752 ) $ 47,500 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 (Effective Portion) Years Ended December 31, 2017 2016 2015 ( Thousands of dollars ) Commodity contracts Commodity sales revenues $ (69,561 ) $ 26,422 $ 81,089 Interest-rate contracts Interest expense (21,025 ) (19,215 ) (17,565 ) Total gain (loss) reclassified from accumulated other comprehensive loss into net income on derivatives (effective portion) $ (90,586 ) $ 7,207 $ 63,524 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 December 31, 2017 . The counterparties to our derivative contracts consist primarily 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 December 31, 2017 , the net credit exposure from our derivative assets is with investment-grade companies in the financial services sector.

PROPERTY, PLANT AND EQUIPMENT (

PROPERTY, PLANT AND EQUIPMENT (Notes)	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
PROPERTY, PLANT AND EQUIPMENT	PROPERTY, PLANT AND EQUIPMENT The following table sets forth our property, plant and equipment by property type, for the periods indicated: Estimated Useful Lives (Years) December 31, December 31, ( Thousands of dollars ) Nonregulated Gathering pipelines and related equipment 5 to 40 $ 3,613,344 $ 3,352,963 Processing and fractionation and related equipment 3 to 40 3,873,709 3,831,966 Storage and related equipment 3 to 54 604,656 558,695 Transmission pipelines and related equipment 5 to 54 700,455 689,804 General plant and other 2 to 60 504,610 487,559 Construction work in process — 362,253 371,628 Regulated Storage and related equipment 5 to 25 12,486 13,524 Natural gas transmission pipelines and related equipment 5 to 77 1,406,780 1,345,740 Natural gas liquids transmission pipelines and related equipment 5 to 88 4,340,428 4,309,341 General plant and other 2 to 50 57,902 54,643 Construction work in process — 83,044 62,634 Property, plant and equipment 15,559,667 15,078,497 Accumulated depreciation and amortization - nonregulated (1,888,010 ) (1,641,490 ) Accumulated depreciation and amortization - regulated (973,531 ) (865,604 ) Net property, plant and equipment $ 12,698,126 $ 12,571,403 The average depreciation rates for our regulated property are set forth, by segment, in the following table for the periods indicated: Years Ended December 31, 2017 2016 2015 Natural Gas Liquids 1.9% 1.9% 1.9% Natural Gas Pipelines 2.1% 2.1% 2.1% We incurred costs for construction work in process that had not been paid at December 31, 2017, 2016 and 2015 , of $92.4 million , $83.0 million and $115.7 million , respectively. Such amounts are not included in capital expenditures (less AFUDC and capitalized interest) on the Consolidated Statements of Cash Flows. Impairment Charges - The following table sets forth impairment charges on our long-lived assets for the periods indicated: Years Ended December 31, 2017 2016 2015 Natural Gas Gathering and Processing $ 16.0 $ — $ 73.7 Natural Gas Liquids — — 10.0 Total Impairment of long-lived assets $ 16.0 $ — $ 83.7 In the third quarter 2017, following a review of nonstrategic assets for potential divestiture, we recorded $16.0 million of noncash impairment charges related to certain nonstrategic gathering and processing assets located in North Dakota. In 2015, we recorded a $63.5 million noncash impairment charge to long-lived assets in our Natural Gas Gathering and Processing segment related to our wholly owned coal-bed methane natural gas gathering system, which we shut down in 2016. We also recorded noncash impairment charges of $20.2 million for previously idled assets in our Natural Gas Gathering and Processing and Natural Gas Liquids segments, as our expectation for future use of these assets changed.

GOODWILL AND INTANGIBLE ASSETS

GOODWILL AND INTANGIBLE ASSETS (Notes)	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
GOODWILL AND INTANGIBLE ASSETS	GOODWILL AND INTANGIBLE ASSETS Goodwill - The following table sets forth our goodwill, by segment, for the periods indicated: December 31, 2017 December 31, 2016 ( Thousands of dollars ) Natural Gas Gathering and Processing $ 153,404 $ 122,291 Natural Gas Liquids 371,217 268,544 Natural Gas Pipelines 156,479 134,700 Total goodwill $ 681,100 $ 525,535 As a result of the Merger Transaction, we are entitled to receive all available ONEOK Partners cash. Our incentive distribution rights effectively terminated at the close of the Merger Transaction. As a result, the $155.6 million carrying value of the indefinite-lived intangible asset associated with our incentive distribution rights was reclassified to goodwill and allocated among our business segments. Intangible Assets - Our intangible assets relate primarily to contracts acquired through acquisitions in our Natural Gas Gathering and Processing and Natural Gas Liquids segments, which are being amortized over periods of 20 to 40 years. Amortization expense for intangible assets was $11.9 million in 2017, 2016 and 2015 , and the aggregate amortization expense for each of the next five years is estimated to be approximately $ 11.9 million . The following table reflects the gross carrying amount and accumulated amortization of intangible assets for the periods presented: December 31, December 31, ( Thousands of dollars ) Gross intangible assets $ 426,068 $ 581,633 Accumulated amortization (113,708 ) (101,809 ) Net intangible assets $ 312,360 $ 479,824

DEBT (Notes)

DEBT (Notes)	12 Months Ended
	Dec. 31, 2017
Long-term Debt, Unclassified [Abstract]
DEBT	DEBT The following table sets forth our consolidated debt for the periods indicated: December 31, December 31, ( Thousands of dollars ) ONEOK Commercial paper outstanding, bearing a weighted-average interest rate of 2.23% (a) $ 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 — $100,000 at 6.5% due September 2028 — 87,126 $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 — ONEOK Partners Commercial paper outstanding (a) — 1,110,277 Senior unsecured obligations: $400,000 at 2.0% due October 2017 — 400,000 $425,000 at 3.2% due September 2018 425,000 425,000 $1,000,000 term loan, at 2.87% and 2.04%, respectively, due January 2019 (b) 500,000 1,000,000 $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 36,607 44,257 Total debt 9,198,677 9,489,057 Unamortized portion of terminated swaps 18,468 20,186 Unamortized debt issuance costs and discounts (78,193 ) (68,320 ) Current maturities of long-term debt (432,650 ) (410,650 ) Short-term borrowings (c) (614,673 ) (1,110,277 ) Long-term debt $ 8,091,629 $ 7,919,996 (a) - In July 2017, the commercial paper outstanding under the ONEOK Partners commercial paper program was repaid as it matured with a combination of proceeds from new issuances from ONEOK’s recently established $2.5 billion commercial paper program, cash on hand and proceeds from our July 2017 $1.2 billion senior notes issuance. The $2.4 billion ONEOK Partners commercial paper program was terminated in July 2017. (b) - The remaining $ 500 million of the Term Loan Agreement was repaid in January 2018. (c) - 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 the $2.5 Billion Credit Agreement. 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. $2.5 Billion Credit Agreement - In April 2017, we entered into the $2.5 Billion Credit Agreement with a syndicate of banks, which became effective June 30, 2017, with the close of the Merger Transaction and the terminations of the ONEOK Credit Agreement and ONEOK Partners Credit Agreement. The $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 5.75 to 1 at December 31, 2017; 5.5 to 1 for the subsequent two quarters; 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. The $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 the $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. The $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 December 31, 2017, our ratio of indebtedness to adjusted EBITDA was 4.5 to 1, and we were in compliance with all covenants under the $2.5 Billion Credit Agreement. At December 31, 2017, we had $15.8 million of letters of credit issued and no borrowings outstanding under the $2.5 Billion Credit Agreement. At December 31, 2016, ONEOK had $1.1 million letters of credit issued and no borrowings outstanding under the ONEOK Credit Agreement, and ONEOK Partners had $14.0 million of letters of credit issued and no borrowings outstanding under the ONEOK Partners Credit Agreement. Senior Unsecured Obligations - All notes are senior unsecured obligations, ranking equally in right of payment with all of our existing and future unsecured senior indebtedness, and are structurally subordinate to any of the existing and future debt and other liabilities of any nonguarantor subsidiaries. Issuances - In July 2017, we completed an underwritten public offering of $1.2 billion senior unsecured notes consisting of $500 million , 4.0 percent senior notes due 2027, and $700 million , 4.95 percent senior notes due 2047. The net proceeds, after deducting underwriting discounts, commissions and offering expenses, were $1.2 billion . The proceeds were used for general corporate purposes, which included repayment of existing indebtedness and capital expenditures. In 2016, ONEOK Partners entered into the $1.0 billion senior unsecured Term Loan Agreement with a syndicate of banks maturing in 2019, bears interest at LIBOR plus 130 basis points based on our current credit ratings, allows prepayment without penalty or premium and contains substantially the same covenants as our $2.5 Billion Credit Agreement. As of January 2018, all amounts outstanding under the Term Loan Agreement have been repaid. See “repayments” section below. In August 2015, we completed an underwritten public offering of $500 million , 7.5 percent senior notes due 2023. The net proceeds, after deducting underwriting discounts, commissions and other expenses, were $487.1 million . We used the proceeds together with cash on hand to purchase $650 million of additional common units from ONEOK Partners. In March 2015, ONEOK Partners completed an underwritten public offering of $800 million of senior notes, consisting of $300 million , 3.8 percent senior notes due 2020, and $500 million , 4.9 percent senior notes due 2025. The net proceeds, after deducting underwriting discounts, commissions and offering expenses, were $792.3 million and were used to repay amounts outstanding under its commercial paper program and for general partnership purposes. Repayments - We repaid $500 million in both January 2018 and July 2017 on the Term Loan Agreement due 2019 with a combination of cash on hand and short-term borrowings. As of January 2018, all amounts outstanding under the Term Loan Agreement have been repaid. In September 2017, we repaid ONEOK Partners’ $400 million , 2.0 percent senior notes due in October 2017 with a combination of cash on hand and short-term borrowings. In July 2017, we redeemed our 6.5 percent senior notes due 2028 at a redemption price of $87.0 million , including the outstanding principal amount, plus accrued and unpaid interest, with cash on hand. In October 2016, ONEOK Partners repaid its $450 million , 6.15 percent senior notes at maturity with a combination of cash on hand and short-term borrowings. The aggregate maturities of long-term debt outstanding as of December 31, 2017, for the years 2018 through 2022 are shown below: Senior Notes Guardian Pipeline Total 2018 $ 425.0 $ 7.7 $ 432.7 2019 (a) $ 1,000.0 $ 7.7 $ 1,007.7 2020 $ 300.0 $ 7.7 $ 307.7 2021 $ — $ 7.7 $ 7.7 2022 $ 1,447.4 $ 5.8 $ 1,453.2 (a) $500 million of the $1.0 billion maturing in 2019 relates to the Term Loan Agreement, which was repaid in January 2018. ONEOK covenants - The indentures governing ONEOK’s 6.875 percent senior notes due 2028 include an event of default upon acceleration of other indebtedness of $15 million or more, and the indentures governing the senior notes due 2022, 2023, 2027, 2035 and 2047 include an event of default upon the acceleration of other indebtedness of $100 million or more. Such events of default would entitle the trustee or the holders of 25 percent in aggregate principal amount of the outstanding senior notes due 2022, 2023, 2027, 2028, 2035 and 2047 to declare those senior notes immediately due and payable in full. The indenture for the notes due 2023 also contains a provision that allows the holders of the notes to require ONEOK to offer to repurchase all or any part of their notes if a change of control and a credit rating downgrade occur at a purchase price of 101 percent of the principal amount, plus accrued and unpaid interest, if any. ONEOK may redeem its senior notes, in whole or in part, at any time prior to their maturity at a redemption price equal to the principal amount, plus accrued and unpaid interest and a make-whole premium. ONEOK may redeem the remaining balance of its senior notes due 2022, 2023, 2027 and 2047 at a redemption price equal to the principal amount, plus accrued and unpaid interest, starting three to six months before the maturity date as stipulated in the respective contract terms. ONEOK’s senior notes are senior unsecured obligations, ranking equally in right of payment with all of ONEOK’s existing and future unsecured senior indebtedness. ONEOK Partners covenants - ONEOK Partners’ senior notes are governed by an indenture containing covenants including, among other provisions, limitations on ONEOK Partners’ ability to place liens on its property or assets and to sell and lease back its property. The indenture includes an event of default upon acceleration of other indebtedness of $100 million or more. Such events of default would entitle the trustee or the holders of 25 percent in aggregate principal amount of any of ONEOK Partners’ outstanding senior notes to declare those notes immediately due and payable in full. The senior notes may be redeemed, in whole or in part, at any time prior to their maturity at a redemption price equal to the principal amount, plus accrued and unpaid interest and a make-whole premium. The senior notes due 2018, 2020, 2022, 2023, 2025, 2041 and 2043 may be redeemed at a redemption price equal to the principal amount, plus accrued and unpaid interest, starting one to six months before their maturity dates as stipulated in the respective contract terms. Guardian Pipeline Senior Notes - These senior notes were issued under a master shelf agreement dated November 8, 2001, with certain financial institutions. Principal payments are due quarterly through 2022. Guardian Pipeline’s senior notes contain financial covenants that require the maintenance of certain financial ratios as defined in the master shelf agreement based on Guardian Pipeline’s financial position and results of operations. Upon any breach of these covenants, all amounts outstanding under the master shelf agreement may become due and payable immediately . At December 31, 2017, Guardian Pipeline was in compliance with its financial covenants . Other - We amortize premiums, discounts and expenses incurred in connection with the issuance of long-term debt consistent with the terms of the respective debt instrument.

EQUITY EQUITY (Notes)

EQUITY EQUITY (Notes)	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
EQUITY	EQUITY Ownership Interest in ONEOK Partners - At December 31, 2016, 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 portion of ONEOK Partners that we did not own is reflected in our 2016 Consolidated Balance Sheet under the caption “Noncontrolling interests” along with the 20 percent of WTLPG that we do not own. At December 31, 2017, the caption “Noncontrolling interests” on our Consolidated Balance Sheet reflects only the 20 percent of WTLPG that we do not own. Series A and B Convertible Preferred Stock - There are no shares of Series A or Series B Preferred Stock currently issued or outstanding. Series E Preferred Stock - In April 2017, through a wholly owned subsidiary, we contributed 20,000 shares of newly issued Series E Preferred Stock, having an aggregate value of $20 million , to the Foundation for use in charitable and nonprofit causes. The contribution was recorded as a $20 million noncash expense in 2017 and is included in other expense in our Consolidated Statements of Income. 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 totaled $829.4 million , $517.6 million and $509.2 million for 2017, 2016 and 2015 , respectively. The following table sets forth the quarterly dividends per share paid on our common stock in the periods indicated: Years Ended December 31, 2017 2016 2015 First Quarter $ 0.615 $ 0.615 $ 0.605 Second Quarter 0.615 0.615 0.605 Third Quarter 0.745 0.615 0.605 Fourth Quarter 0.745 0.615 0.615 Total $ 2.72 $ 2.46 $ 2.43 Additionally, in February 2018, we paid a quarterly dividend of $0.77 per share ( $3.08 per share on an annualized basis), which was paid to shareholders of record as of January 29, 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. We paid dividends totaling $0.3 million for the Series E Preferred Stock in February 2018. The $20.0 million issuance of the shares of Series E Preferred Stock and the related accrued dividends of $0.1 million at December 31, 2017, represent noncash financing activities. 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. Under the Partnership Agreement, distributions were made to the partners with respect to each calendar quarter in an amount equal to 100 percent of available cash as defined in the Partnership Agreement. Available cash generally was distributed 98 percent to limited partners and 2 percent to the general partner. The general partner’s percentage interest in quarterly distributions were increased after certain specified target levels were met during the quarter. Under the incentive distribution provisions, as set forth in the Partnership Agreement, the general partner received: • 15 percent of amounts distributed in excess of $0.3025 per unit; • 25 percent of amounts distributed in excess of $0.3575 per unit; and • 50 percent of amounts distributed in excess of $0.4675 per unit. Distributions paid to ONEOK Partners unitholders of record at the close of business on January 30, 2017 , and May 1, 2017 , were $0.79 per unit. Our incentive distribution rights effectively terminated at the close of the Merger Transaction. The following table sets forth ONEOK Partners’ distributions paid during the periods prior to the closing of the Merger Transaction on June 30, 2017: Years Ended December 31, 2017 2016 2015 ( Thousands, except per unit amounts ) Distribution per unit $ 1.58 $ 3.16 $ 3.16 General partner distributions $ 13,320 $ 26,640 $ 24,610 Incentive distributions 201,076 402,152 371,500 Distributions to general partner 214,396 428,792 396,110 Limited partner distributions to ONEOK 180,646 361,292 310,230 Limited partner distributions to other unitholders 270,959 541,919 524,135 Total distributions paid $ 666,001 $ 1,332,003 $ 1,230,475 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 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. Prior to the close of the Merger Transaction, ONEOK Partners had an “at-the-market” equity program for the offer and sale from time to time of its common units, up to an aggregate amount of $650 million . During the six months ended June 30, 2017, and the year ended December 31, 2016, no common units were sold through ONEOK Partners’ “at-the-market” equity program. Upon the close of the Merger Transaction on June 30, 2017, the ONEOK Partners “at-the-market” equity program terminated. In August 2015, ONEOK Partners completed a private placement of 21.5 million common units at a price of $30.17 per unit. Additionally, ONEOK Partners completed a concurrent sale of 3.3 million common units at a price of $30.17 per unit to funds managed by Kayne Anderson Capital Advisors in a registered direct offering, which were issued through its existing “at-the-market” equity program. The combined offerings generated net cash proceeds of $749 million to ONEOK Partners. In conjunction with these issuances, ONEOK Partners GP contributed $15.3 million in order to maintain our 2 percent general partner interest in ONEOK Partners. ONEOK Partners used the proceeds for general partnership purposes, including capital expenditures and repayment of commercial paper borrowings. During the year ended December 31, 2015, ONEOK Partners sold 10.5 million common units through its “at-the-market” equity program, including the units sold to funds managed by Kayne Anderson Capital Advisors in the offering discussed above. The net proceeds, including ONEOK Partners GP’s contribution to maintain our 2 percent general partner interest in ONEOK Partners, were $381.6 million , which were used for general partnership purposes, including repayment of commercial paper borrowings.

ACCUMULATED OTHER COMPREHENSIVE

ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Notes)	12 Months Ended
	Dec. 31, 2017
ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS)	ACCUMULATED OTHER COMPREHENSIVE LOSS The following table sets forth the balance in accumulated other comprehensive loss for the periods 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, 2016 $ (42,199 ) $ (84,543 ) $ (500 ) $ (127,242 ) Other comprehensive income (loss) before reclassifications (9,280 ) (22,903 ) (475 ) (32,658 ) Amounts reclassified from accumulated other comprehensive loss (676 ) 6,210 16 5,550 Other comprehensive income (loss) attributable to ONEOK (9,956 ) (16,693 ) (459 ) (27,108 ) December 31, 2016 (52,155 ) (101,236 ) (959 ) (154,350 ) Other comprehensive income (loss) before reclassifications (35,013 ) (12,337 ) (409 ) (47,759 ) Amounts reclassified from accumulated other comprehensive loss 45,541 8,162 164 53,867 Impact of Merger Transaction (Note B) (c) (40,288 ) — — (40,288 ) Other comprehensive income (loss) attributable to ONEOK (29,760 ) (4,175 ) (245 ) (34,180 ) December 31, 2017 $ (81,915 ) $ (105,411 ) $ (1,204 ) $ (188,530 ) (a) All amounts are presented net of tax. (b) Includes amounts related to supplemental executive retirement plan. (c) Includes the remaining portion of ONEOK Partners’ accumulated other comprehensive loss at June 30, 2017, that we acquired in the Merger Transaction, related to commodity and interest-rate contracts. 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 Comprehensive Loss Components Years Ended December 31, Affected Line Item in the Consolidated Statements of Income 2017 2016 2015 ( Thousands of dollars ) Unrealized gains (losses) on risk-management assets/liabilities Commodity contracts $ (69,561 ) $ 26,422 $ 81,089 Commodity sales revenues Interest-rate contracts (21,025 ) (19,215 ) (17,565 ) Interest expense (90,586 ) 7,207 63,524 Income before income taxes 26,899 (230 ) (8,815 ) Income tax expense (63,687 ) 6,977 54,709 Net income Noncontrolling interests (18,146 ) 6,301 39,415 Less: Net income attributable noncontrolling interests $ (45,541 ) $ 676 $ 15,294 Net income attributable to ONEOK Pension and postretirement benefit plan obligations (a) Amortization of net loss $ (15,265 ) $ (12,012 ) $ (17,724 ) Amortization of unrecognized prior service cost 1,662 1,662 1,568 (13,603 ) (10,350 ) (16,156 ) Income before income taxes 5,441 4,140 6,462 Income tax expense $ (8,162 ) $ (6,210 ) $ (9,694 ) Net income attributable to ONEOK Unrealized gains (losses) on risk-management assets/liabilities of unconsolidated affiliates $ (367 ) $ (63 ) $ — Equity in net earnings from investments 97 10 — Income tax expense (270 ) (53 ) — Net income Noncontrolling interests (106 ) (37 ) — Less: Net income attributable to noncontrolling interests $ (164 ) $ (16 ) $ — Net income attributable to ONEOK Total reclassifications for the period attributable to ONEOK $ (53,867 ) $ (5,550 ) $ 5,600 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 L for additional detail of our net periodic benefit cost.

EARNINGS PER SHARE EARNINGS PER

EARNINGS PER SHARE EARNINGS PER SHARE (Notes)	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Earnings Per Share [Text Block]	EARNINGS PER SHARE The following tables set forth the computation of basic and diluted EPS from continuing operations for the periods indicated: Year Ended December 31, 2017 Income Shares Per Share Amount ( Thousands, except per share amounts ) Basic EPS from continuing operations Income from continuing operations attributable to ONEOK available for common stock $ 387,074 297,477 $ 1.30 Diluted EPS from continuing operations Effect of dilutive securities — 2,303 Income from continuing operations attributable to ONEOK available for common stock and common stock equivalents $ 387,074 299,780 $ 1.29 Year Ended December 31, 2016 Income Shares Per Share Amount ( Thousands, except per share amounts ) Basic EPS from continuing operations Income from continuing operations attributable to ONEOK available for common stock $ 354,090 211,128 $ 1.68 Diluted EPS from continuing operations Effect of dilutive securities — 1,255 Income from continuing operations attributable to ONEOK available for common stock and common stock equivalents $ 354,090 212,383 $ 1.67 Year Ended December 31, 2015 Income Shares Per Share Amount ( Thousands, except per share amounts ) Basic EPS from continuing operations Income from continuing operations attributable to ONEOK available for common stock $ 251,058 210,208 $ 1.19 Diluted EPS from continuing operations Effect of dilutive securities — 333 Income from continuing operations attributable to ONEOK available for common stock and common stock equivalents $ 251,058 210,541 $ 1.19

SHARE-BASED PAYMENTS SHARE-BASE

SHARE-BASED PAYMENTS SHARE-BASED PAYMENTS (Notes)	12 Months Ended
	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
SHARE-BASED PAYMENTS	SHARE-BASED PAYMENTS The ONEOK, Inc. Equity Compensation Plan (ECP) and the ONEOK, Inc. Long-Term Incentive Plan (LTIP) provide for the granting of stock-based compensation, including incentive stock options, nonstatutory stock options, stock bonus awards, restricted stock awards, restricted stock unit awards, performance stock awards and performance unit awards to eligible employees and the granting of stock awards to nonemployee directors. We have reserved 10.0 million and 15.6 million shares of common stock for issuance under the ECP and LTIP, respectively. At December 31, 2017 , we had 1.9 million shares available for issuance under the ECP and no remaining shares available for issuance under the LTIP. This calculation of available shares reflects shares issued and estimated shares expected to be issued upon vesting of outstanding awards granted under these plans, excluding estimated forfeitures expected to be returned to the plans. These plans allow for the deferral of awards granted in stock or cash, in accordance with Internal Revenue Code section 409A requirements. Restricted Stock Units - We have granted restricted stock units to key employees that vest at the end of a three -year period and entitle the grantee to receive shares of our common stock. Restricted stock unit awards are measured at fair value as if they were vested and issued on the grant date and adjusted for estimated forfeitures. Restricted stock unit awards granted accrue dividend equivalents in the form of additional restricted stock units prior to vesting. Compensation expense is recognized on a straight-line basis over the vesting period of the award. Performance Unit Awards - We have granted performance unit awards to key employees. Outstanding performance units vest at the expiration of a three -year period. Upon vesting, a holder of outstanding performance units is entitled to receive a number of shares of our common stock equal to a percentage ( 0 percent to 200 percent ) of the performance units granted, based on our total shareholder return over the vesting period, compared with the total shareholder return of a peer group of other energy companies over the same period. Compensation expense is recognized on a straight-line basis over the period of the award. If paid, the outstanding performance unit awards entitle the grantee to receive the grant in shares of our common stock. Our outstanding performance unit awards are equity awards with a market-based condition, which results in the compensation cost for these awards being recognized over the requisite service period, provided that the requisite service period is fulfilled, regardless of when, if ever, the market condition is satisfied. The fair value of these performance units was estimated on the grant date based on a Monte Carlo model. Performance stock unit awards granted accrue dividend equivalents in the form of additional performance units prior to vesting. The compensation expense on these awards only will be adjusted for changes in forfeitures. Stock Compensation Plan for Non-Employee Directors The ONEOK, Inc. Stock Compensation Plan for Non-Employee Directors (the DSCP) provides for the granting of nonstatutory stock options, stock bonus awards, including performance unit awards and restricted stock awards. Under the DSCP, these awards may be granted by the Executive Compensation Committee at any time, until grants have been made for all shares authorized under the DSCP. We have reserved a total of 1.4 million shares of common stock for issuance under the DSCP, and at December 31, 2017 , we had 1.0 million shares available for issuance under the plan. The maximum number of shares of common stock that can be issued to a participant under the DSCP during any year is 40,000 . No performance unit awards or restricted stock awards have been made to nonemployee directors under the DSCP. There are no remaining options outstanding under the DSCP. General For all awards outstanding, we used a 3 percent forfeiture rate based on historical forfeitures under our share-based payment plans. We currently use treasury stock to satisfy our share-based payment obligations. Compensation expense for our share-based payment plans described above was $16.6 million , $30.7 million and $11.5 million during 2017, 2016 and 2015, respectively, which is net of tax benefits of $11.1 million , $9.8 million and $4.9 million , respectively. Restricted Stock Unit Activity As of December 31, 2017 , we had $12.5 million of total unrecognized compensation cost related to our nonvested restricted stock unit awards, which is expected to be recognized over a weighted-average period of 1.9 years . The following tables set forth activity and various statistics for our restricted stock unit awards: Number of Units Weighted Average Price Nonvested December 31, 2016 881,647 $ 31.25 Granted 281,167 $ 45.11 Released to participants (141,724 ) $ 51.21 Forfeited (19,285 ) $ 32.07 Nonvested December 31, 2017 1,001,805 $ 32.30 2017 2016 2015 Weighted-average grant date fair value (per share) $ 45.11 $ 20.04 $ 42.98 Fair value of units granted (thousands of dollars) $ 12,685 $ 11,081 $ 10,186 Fair value of units vested (thousands of dollars) $ 7,258 $ 4,429 $ 6,458 Performance Unit Activity As of December 31, 2017 , we had $17.4 million of total unrecognized compensation cost related to the nonvested performance unit awards, which is expected to be recognized over a weighted-average period of 1.9 years . The following tables set forth activity and various statistics related to the performance unit awards and the assumptions used in the valuations at the respective grant dates: Number of Units Weighted Average Price Nonvested December 31, 2016 1,005,751 $ 38.81 Granted 311,047 $ 56.65 Released to participants (123,459 ) $ 70.50 Forfeited (57,206 ) $ 42.29 Nonvested December 31, 2017 1,136,133 $ 40.08 2017 2016 2015 Volatility (a) 40.59% 39.94% 26.70% Dividend Yield 4.68% 11.32% 5.02% Risk-free Interest Rate 1.49% 0.93% 1.00% (a) - Volatility was based on historical volatility over three years using daily stock price observations. 2017 2016 2015 Weighted-average grant date fair value (per share) $ 56.65 $ 25.54 $ 50.30 Fair value of units granted (thousands of dollars) $ 17,621 $ 15,229 $ 13,370 Fair value of units vested (thousands of dollars) $ 8,704 $ — $ 13,736 Employee Stock Purchase Plan We have reserved a total of 11.6 million shares of common stock for issuance under our ONEOK, Inc. Employee Stock Purchase Plan (the ESPP). Subject to certain exclusions, all full-time employees are eligible to participate in the ESPP. Employees can choose to have up to 10 percent of their annual base pay withheld to purchase our common stock, subject to terms and limitations of the plan. The purchase price of the stock is 85 percent of the lower of its grant date or exercise date market price. Approximately 58 percent , 57 percent and 53 percent of employees participated in the plan in 2017, 2016 and 2015, respectively. Under the plan, we sold 151,803 shares at $44.20 per share in 2017, 232,553 shares at $27.21 per share in 2016 and 222,872 shares at $25.51 per share in 2015. Employee Stock Award Program Under our Employee Stock Award Program, we issued, for no monetary consideration, to all eligible employees one share of our common stock when the per-share closing price of our common stock on the NYSE was for the first time at or above $13 per share, and one additional share of common stock when the per-share closing price of our common stock on the NYSE was at or above each one dollar increment above $13. The total number of shares of our common stock available for issuance under this program is 900,000 . No shares were issued to employees under this program during 2017, 2016 or 2015. Deferred Compensation Plan for Non-Employee Directors The ONEOK, Inc. Nonqualified Deferred Compensation Plan for Non-Employee Directors provides our nonemployee directors the option to defer all or a portion of their compensation for their service on our Board of Directors. Under the plan, directors may elect either a cash deferral option or a phantom stock option. Under the cash deferral option, directors may elect to defer the receipt of all or a portion of their annual retainer fees, which will be credited with interest during the deferral period. Under the phantom stock option, directors may defer all or a portion of their annual retainer fees and receive such fees on a deferred basis in the form of shares of common stock under our Long-Term Incentive Plan or Equity Compensation Plan, which earn the equivalent of dividends declared on our common stock. Shares are distributed to nonemployee directors at the fair market value of our common stock at the date of distribution.

EMPLOYEE BENEFIT PLANS EMPLOYEE

EMPLOYEE BENEFIT PLANS EMPLOYEE BENEFIT PLANS (Notes)	12 Months Ended
	Dec. 31, 2017
Defined Benefit Plan [Abstract]
EMPLOYEE BENEFIT PLANS	EMPLOYEE BENEFIT PLANS Retirement and Postretirement Benefit Plans Retirement Plans - We have a defined benefit pension plan covering certain employees and former employees hired before January 1, 2005. Employees hired after December 31, 2004, and employees who accepted a one-time opportunity to opt out of our pension plan are covered by our Profit Sharing Plan. In addition, we have a supplemental executive retirement plan for the benefit of certain officers. No new participants in our supplemental executive retirement plan have been approved since 2005, and effective January 2014, the plan was formally closed to new participants. We fund our pension costs at a level needed to maintain or exceed the minimum funding levels required by the Employee Retirement Income Security Act of 1974, as amended, and the Pension Protection Act of 2006. Postretirement Benefit Plans - We sponsor health and welfare plans that provide postretirement medical and life insurance benefits to employees hired prior to 2017 who retire with at least five years of service. The postretirement medical plan is contributory with retiree contributions adjusted periodically and contains other cost-sharing features such as deductibles and coinsurance. Obligations and Funded Status - The following tables set forth our pension and postretirement benefit plans benefit obligations and fair value of plan assets for the periods indicated: Pension Benefits Postretirement Benefits December 31, December 31, 2017 2016 2017 2016 Change in benefit obligation ( Thousands of dollars ) Benefit obligation, beginning of period $ 428,386 $ 390,688 $ 54,823 $ 49,496 Service cost 6,896 6,501 662 596 Interest cost 18,645 19,820 2,261 2,404 Plan participants’ contributions — — 901 894 Actuarial loss 41,678 24,458 3,456 4,905 Benefits paid (13,990 ) (13,081 ) (4,165 ) (3,472 ) Benefit obligation, end of period 481,615 428,386 57,938 54,823 Change in plan assets Fair value of plan assets, beginning of period 261,671 258,635 29,550 28,641 Actual return on plan assets 50,827 16,117 5,385 1,902 Employer contributions 7,500 — 2,000 1,000 Plan participants’ contributions — — 901 894 Benefits paid (13,990 ) (13,081 ) (3,703 ) (2,887 ) Fair value of plan assets, end of period 306,008 261,671 34,133 29,550 Balance at December 31 $ (175,607 ) $ (166,715 ) $ (23,805 ) $ (25,273 ) Current liabilities $ (4,544 ) $ (4,363 ) $ — $ — Noncurrent liabilities (171,063 ) (162,352 ) (23,805 ) (25,273 ) Balance at December 31 $ (175,607 ) $ (166,715 ) $ (23,805 ) $ (25,273 ) The table above includes the supplemental executive retirement plan obligation. ONEOK has investments included in other assets on the Consolidated Balance Sheets, which totaled $93.2 million and $84.5 million at December 31, 2017 and 2016 , respectively, for the purpose of funding the obligation. These assets are excluded from the table above as those are not assets of the supplemental executive retirement plan. The accumulated benefit obligation for our pension plans was $456.6 million and $407.2 million at December 31, 2017 and 2016 , respectively. Components of Net Periodic Benefit Cost - The following table sets forth the components of net periodic benefit cost for our pension and postretirement benefit plans for the periods indicated: Pension Benefits Postretirement Benefits Years Ended December 31, Years Ended December 31, 2017 2016 2015 2017 2016 2015 ( Thousands of dollars ) Components of net periodic benefit cost Service cost $ 6,896 $ 6,501 $ 7,565 $ 662 $ 596 $ 743 Interest cost 18,645 19,820 18,218 2,261 2,404 2,347 Expected return on plan assets (21,376 ) (20,348 ) (20,900 ) (2,257 ) (2,124 ) (2,253 ) Amortization of prior service cost (credit) — — 94 (1,662 ) (1,662 ) (1,662 ) Amortization of net loss 13,586 10,966 15,981 1,679 1,046 1,743 Net periodic benefit cost $ 17,751 $ 16,939 $ 20,958 $ 683 $ 260 $ 918 Other Comprehensive Income (Loss) - The following table sets forth the amounts recognized in other comprehensive income (loss) related to our pension benefits and postretirement benefits for the periods indicated: Pension Benefits Postretirement Benefits Years Ended December 31, Years Ended December 31, 2017 2016 2015 2017 2016 2015 ( Thousands of dollars ) Net gain (loss) arising during the period $ (16,572 ) $ (33,043 ) $ 5,145 $ (328 ) $ (5,128 ) $ 4,393 Amortization of prior service cost (credit) — — 94 (1,662 ) (1,662 ) (1,662 ) Amortization of net loss 13,586 10,966 15,981 1,679 1,046 1,743 Deferred income taxes (960 ) 8,831 (8,488 ) 82 2,297 (1,790 ) Total recognized in other comprehensive income (loss) $ (3,946 ) $ (13,246 ) $ 12,732 $ (229 ) $ (3,447 ) $ 2,684 The table below sets forth the amounts in accumulated other comprehensive loss that had not yet been recognized as components of net periodic benefit expense for the periods indicated: Pension Benefits Postretirement Benefits December 31, December 31, 2017 2016 2017 2016 ( Thousands of dollars ) Prior service credit (cost) $ — $ — $ 1,889 $ 3,550 Accumulated loss (160,921 ) (157,935 ) (12,991 ) (14,341 ) Accumulated other comprehensive loss (160,921 ) (157,935 ) (11,102 ) (10,791 ) Deferred income taxes 62,214 63,174 4,398 4,316 Accumulated other comprehensive loss, net of tax $ (98,707 ) $ (94,761 ) $ (6,704 ) $ (6,475 ) The following table sets forth the amounts recognized in accumulated comprehensive loss expected to be recognized as components of net periodic benefit expense in the next fiscal year. Pension Benefits Postretirement Benefits Amounts to be recognized in 2018 ( Thousands of dollars ) Prior service (credit) cost $ — $ (1,662 ) Net loss $ 17,060 $ 1,338 Actuarial Assumptions - The following table sets forth the weighted-average assumptions used to determine benefit obligations for pension and postretirement benefits for the periods indicated: Pension Benefits Postretirement Benefits December 31, December 31, 2017 2016 2017 2016 Discount rate (a) 3.75% 4.50% 3.75% 4.25% Compensation increase rate 3.00% 3.10% N/A N/A (a) The decrease in the discount rate at December 31, 2017, compared with 2016, resulted primarily from narrower credit spreads associated with the bonds in the hypothetical portfolio discussed below. The following table sets forth the weighted-average assumptions used to determine net periodic benefit costs for the periods indicated: Years Ended December 31, 2017 2016 2015 Discount rate - pension plans 4.50% 5.25% 4.50% Discount rate - postretirement plans 4.25% 5.00% 4.25% Expected long-term return on plan assets 7.75% 7.75% 8.00% Compensation increase rate 3.10% 3.10% 3.15% We determine our overall expected long-term rate of return on plan assets based on our review of historical returns and economic growth models. We determine our discount rates annually. We estimate our discount rate based upon a comparison of the expected cash flows associated with our future payments under our pension and postretirement obligations to a hypothetical bond portfolio created using high-quality bonds that closely match expected cash flows. Bond portfolios are developed by selecting a bond for each of the next 60 years based on the maturity dates of the bonds. Bonds selected to be included in the portfolios are only those rated by Moody’s as AA- or better and exclude callable bonds, bonds with less than a minimum issue size, yield outliers and other filtering criteria to remove unsuitable bonds. Health Care Cost Trend Rates - The following table sets forth the assumed health care cost-trend rates for the periods indicated: 2017 2016 Health care cost-trend rate assumed for next year 7.00% 7.25% Rate to which the cost-trend rate is assumed to decline (the ultimate trend rate) 5.00% 5.00% Year that the rate reaches the ultimate trend rate 2022 2022 Assumed health care cost-trend rates have an impact on the amounts reported for our health care plans. As of December 31, 2017, a one percentage point change in assumed health care cost-trend rates would not be material to us. Plan Assets - Our investment strategy is to invest plan assets in accordance with sound investment practices that emphasize long-term fundamentals. The goal of this strategy is to maximize investment returns while managing risk in order to meet the plan’s current and projected financial obligations. The investment policy follows a glide path approach toward liability-driven investing that shifts a higher portfolio weighting to fixed income as the plan's funded status increases. The purpose of liability-driven investing is to structure the asset portfolio to more closely resemble the pension liability and thereby more effectively hedge against changes in the liability. The plan’s current investments include a diverse blend of various domestic and international equities, investments in various classes of debt securities, insurance contracts and venture capital. The target allocation for the assets of our pension plan as of December 31, 2017, is as follows: U.S. large-cap equities 37 % Long duration bonds 30 % Developed foreign large-cap equities 10 % Alternative investments 8 % Mid-cap equities 6 % Emerging markets equities 5 % Small-cap equities 4 % Total 100 % As part of our risk management for the plans, minimums and maximums have been set for each of the asset classes listed above. All investment managers for the plan are subject to certain restrictions on the securities they purchase and, with the exception of indexing purposes, are prohibited from owning our stock. The following tables set forth our pension benefits and postretirement benefits plan assets by fair value category as of the measurement date: Pension Benefits December 31, 2017 Asset Category Level 1 Level 2 Level 3 Subtotal Measured at NAV (d) Total ( Thousands of dollars ) Investments: Equity securities (a) $ 176,347 $ 19,199 $ — $ 195,546 $ — $ 195,546 Government obligations — 19,481 — 19,481 — 19,481 Corporate obligations (b) — 62,981 — 62,981 — 62,981 Common/collective trusts — 6,621 — 6,621 — 6,621 Cash 298 — — 298 — 298 Other investments (c) — — — — 21,081 21,081 Fair value of plan assets $ 176,645 $ 108,282 $ — $ 284,927 $ 21,081 $ 306,008 (a) - This category represents securities of the respective market sector from diverse industries. (b) - This category represents bonds from diverse industries. (c) - This category represents alternative investments in limited partnerships, which can be redeemed with a 30-day notice with no further restrictions. There are no unfunded capital commitments. (d) - Plan asset investments measured at fair value using the net asset value per share. Pension Benefits December 31, 2016 Asset Category Level 1 Level 2 Level 3 Subtotal Measured at NAV (d) Total ( Thousands of dollars ) Investments: Equity securities (a) $ 146,980 $ 13,606 $ — $ 160,586 $ — $ 160,586 Government obligations — 17,979 — 17,979 — 17,979 Corporate obligations (b) — 56,484 — 56,484 — 56,484 Common/collective trusts — 6,577 — 6,577 — 6,577 Cash 43 — — 43 — 43 Other investments (c) — — — — 20,002 20,002 Fair value of plan assets $ 147,023 $ 94,646 $ — $ 241,669 $ 20,002 $ 261,671 (a) - This category represents securities of the respective market sector from diverse industries. (b) - This category represents bonds from diverse industries. (c) - This category represents alternative investments in limited partnerships, which can be redeemed with a 30-day notice with no further restrictions. There are no unfunded capital commitments. (d) - Plan asset investments measured at fair value using the net asset value per share. Postretirement Benefits December 31, 2017 Asset Category Level 1 Level 2 Level 3 Total ( Thousands of dollars ) Investments: Equity securities (a) $ 1,951 $ — $ — $ 1,951 Money market funds — 1,515 — 1,515 Insurance and group annuity contracts — 30,667 — 30,667 Fair value of plan assets $ 1,951 $ 32,182 $ — $ 34,133 (a) - This category represents securities of the respective market sector from diverse industries. Postretirement Benefits December 31, 2016 Asset Category Level 1 Level 2 Level 3 Total ( Thousands of dollars ) Investments: Equity securities (a) $ 1,777 $ — $ — $ 1,777 Money market funds — 1,259 — 1,259 Insurance and group annuity contracts — 26,514 — 26,514 Fair value of plan assets $ 1,777 $ 27,773 $ — $ 29,550 (a) - This category represents securities of the respective market sector from diverse industries. Contributions - During 2017 , we made $7.5 million in contributions to our defined benefit pension plan and $2.0 million in contributions to our postretirement benefit plans. We contributed $12.3 million to our defined benefit pension plan in January 2018 and expect to make approximately $2.0 million in contributions to our postretirement plans in 2018. Pension and Postretirement Benefit Payments - Benefit payments for our pension and postretirement benefit plans for the period ending December 31, 2017 , were $ 14.0 million and $ 4.2 million , respectively. The following table sets forth the pension benefits and postretirement benefits payments expected to be paid in 2018 through 2027: Pension Benefits Postretirement Benefits Benefits to be paid in: ( Thousands of dollars ) 2018 $ 16,796 $ 3,452 2019 $ 18,011 $ 3,653 2020 $ 18,970 $ 3,859 2021 $ 20,206 $ 3,993 2022 $ 21,157 $ 4,023 2023 through 2027 $ 117,048 $ 19,302 The expected benefits to be paid are based on the same assumptions used to measure our benefit obligation at December 31, 2017 , and include estimated future employee service. Other Employee Benefit Plans 401(k) Plan - We have a 401(k) Plan covering all employees, and employee contributions are discretionary. We match 100 percent of employee contributions up to 6 percent of each participant’s eligible compensation, subject to certain limits. Our contributions made to the plan were $13.7 million , $11.9 million and $12.0 million in 2017, 2016 and 2015 , respectively. Profit Sharing Plan - We have a profit-sharing plan (Profit Sharing Plan) for all employees hired after December 31, 2004. Employees who were employed prior to January 1, 2005, were given a one-time opportunity to make an irrevocable election to participate in the Profit Sharing Plan and not accrue any additional benefits under our defined benefit pension plan after December 31, 2004. We plan to make a contribution to the Profit Sharing Plan each quarter equal to 1 percent of each participant’s eligible compensation during the quarter. Additional discretionary employer contributions may be made at the end of each year. Employee contributions are not allowed under the plan. Our contributions made to the plan were $7.4 million , $8.2 million and $4.9 million in 2017, 2016 and 2015 , respectively. Nonqualified Deferred Compensation Plan - The Nonqualified Deferred Compensation Plan provides select employees, as approved by our Chief Executive Officer, with the option to defer portions of their compensation and provides nonqualified deferred compensation benefits that are not available due to limitations on employer and employee contributions to qualified defined contribution plans under the federal tax laws. The plan also provides benefits in excess of applicable tax limits for certain participants in the defined benefit pension plan who are not participants in the supplemental executive retirement plan. Our contributions to the plan were not material in 2017, 2016 and 2015 .

INCOME TAXES (Notes)

INCOME TAXES (Notes)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES The following table sets forth our provision for income taxes for the periods indicated: Years Ended December 31, 2017 2016 2015 ( Thousands of dollars ) Current income tax provision Federal $ 295 $ 6,086 $ 13,191 State 1,670 2,449 2,967 Total current income taxes from continuing operations 1,965 8,535 16,158 Deferred income tax provision Federal 376,728 193,974 116,681 State 68,589 9,897 3,761 Total deferred income taxes from continuing operations 445,317 203,871 120,442 Total provision for income taxes from continuing operations 447,282 212,406 136,600 Discontinued operations — (1,250 ) 2,031 Total provision for income taxes $ 447,282 $ 211,156 $ 138,631 The following table is a reconciliation of our income tax provision from continuing operations and excludes discontinued operations for the periods indicated: Years Ended December 31, 2017 2016 2015 ( Thousands of dollars ) Income before income taxes $ 1,040,801 $ 957,956 $ 521,876 Less: Net income attributable to noncontrolling interests 205,678 391,460 134,218 Net income attributable to ONEOK before income taxes 835,123 566,496 387,658 Federal statutory income tax rate 35.0 % 35.0 % 35.0 % Provision for federal income taxes 292,293 198,274 135,680 State income taxes, net of federal benefit 16,197 12,303 5,800 Deferred tax rate change, inclusive of valuation allowance 141,283 43 928 Other, net (2,491 ) 1,786 (5,808 ) Income tax provision $ 447,282 $ 212,406 $ 136,600 The following table sets forth the tax effects of temporary differences that gave rise to significant portions of the deferred tax assets and liabilities for the periods indicated: December 31, December 31, Deferred tax assets ( Thousands of dollars ) Employee benefits and other accrued liabilities $ 85,355 $ 118,831 Federal net operating loss 159,162 26,334 State net operating loss and benefits 73,277 39,759 Derivative instruments 30,060 32,082 Other 13,546 2,425 Total deferred tax assets 361,400 219,431 Valuation allowance for state net operating loss and tax credits Carryforward expected to expire prior to utilization (66,632 ) (9,430 ) Net deferred tax assets 294,768 210,001 Deferred tax liabilities Excess of tax over book depreciation 64,508 107,249 Investment in partnerships 77,035 1,726,541 Regulatory assets 15 33 Total deferred tax liabilities 141,558 1,833,823 Net deferred tax assets (liabilities) before discontinued operations 153,210 (1,623,822 ) Discontinued operations — 10,500 Net deferred tax assets (liabilities) $ 153,210 $ (1,613,322 ) In December 2017, the Tax Cuts and Jobs Act was signed into law. The Tax Cuts and Jobs Act makes extensive changes to the U.S. tax laws and includes provisions that, beginning in 2018, reduce the U.S. corporate tax rate to 21 percent from 35 percent , increase expensing for capital-investment, limit the interest deduction, and limit the use of net operating losses to offset future taxable income. Due to the reduction in the corporate tax rate, we revalued our deferred tax assets and liabilities as required at enactment. Our net deferred tax assets represent expected corporate tax benefits in the future. The reduction in the federal corporate tax rate reduces these benefits, which resulted in a one-time noncash charge to net income through income tax expense of $141.3 million, inclusive of the valuation allowance described below, recorded in the fourth quarter 2017. We will continue to monitor U.S. Treasury Department and IRS implementation of the Tax Cuts and Jobs Act and will apply applicable guidance and rulemaking as it becomes available. Tax benefits related to certain state net operating loss and tax credit carryforwards will begin expiring in 2030 and 2020, respectively. Due to the new tax legislation and the impact of increased expensing for capital-investment, we believe that it is more likely than not that the tax benefits of certain state net operating loss and tax credit carryforwards will not be utilized prior to their expirations; therefore, we recorded a valuation allowance of $ 54.1 million related to these state tax benefits in the fourth quarter 2017. The Tax Cuts and Jobs Act may reduce future tariff rates charged on our regulated pipelines. For regulated companies, the effect on deferred tax assets and liabilities of a change in tax rates is recorded as regulatory assets and regulatory liabilities in the period that includes the enactment date, if, as a result of an action by a regulator, it is probable that the effect of the change in tax rates will be recovered from or returned to customers through future rates. The rates charged on substantially all of our regulated natural gas pipelines have been established through shipper specific negotiation, discounts and negotiated settlements, which do not ascribe any specific cost of service elements. The rates charged on substantially all of our regulated NGL pipelines are established through negotiated transportation service agreements that are not adjusted based on a traditional cost of service. We expect future tariff rate changes, if any, related to the change in U.S. corporate tax rate to be established prospectively over time on a similar negotiated basis. If in the future the FERC or other regulatory bodies were to require a refund of previously collected amounts on our regulated pipelines, then we may record a regulatory liability through a one-time charge to expense. On June 30, 2017, we completed the Merger Transaction in a taxable exchange to the ONEOK Partners unitholders resulting in a book/tax difference in the basis of the underlying assets acquired. We recorded a deferred tax asset of $2.1 billion , computed as the net of the equity value exchanged of $8.8 billion and noncontrolling interests of $3.0 billion at a tax rate of 37 percent . These deferred tax assets were revalued in December 2017, as described above. As a result of adopting ASU 2016-09 in first quarter 2017, we recorded an adjustment increasing beginning retained earnings and deferred tax assets of $73.4 million to recognize the cumulative tax benefits included in net operating loss carryforwards on the tax return but not reflected in deferred tax assets as of December 31, 2016 . Beginning in January 2017, all share-based payment tax effects have been recorded in earnings. In prior periods, tax benefits of employee share-based compensation were not recorded as a deferred tax asset as vesting occurred in periods we were in a net operation loss position, and a portion of the tax benefit did not reduce current taxes payable.

UNCONSOLIDATED AFFILIATES (Note

UNCONSOLIDATED AFFILIATES (Notes)	12 Months Ended
	Dec. 31, 2017
Equity Method Investments and Joint Ventures [Abstract]
UNCONSOLIDATED AFFILIATES	UNCONSOLIDATED AFFILIATES Investments in Unconsolidated Affiliates - The following table sets forth our investments in unconsolidated affiliates for the periods indicated: Net Ownership Interest December 31, December 31, ( Thousands of dollars ) Northern Border Pipeline 50% $ 396,800 $ 328,456 Overland Pass Pipeline Company 50% 436,111 444,138 Roadrunner Gas Transmission 50% 93,048 94,548 Other Various 77,197 91,665 Investments in unconsolidated affiliates (a) $ 1,003,156 $ 958,807 (a) - Equity-method goodwill (Note A ) was $38.8 million and $40.1 million at December 31, 2017 and 2016 , respectively. Equity in Net Earnings from Investments and Impairments - The following table sets forth our equity in net earnings from investments for the periods indicated: Years Ended December 31, 2017 2016 2015 ( Thousands of dollars ) Northern Border Pipeline $ 68,153 $ 69,990 $ 66,941 Overland Pass Pipeline Company 60,067 53,984 37,783 Roadrunner Gas Transmission 19,150 4,445 1,800 Other 11,908 11,271 18,776 Equity in net earnings from investments $ 159,278 $ 139,690 $ 125,300 Impairment of equity investments $ (4,270 ) $ — $ (180,583 ) Impairment Charges - In the third quarter 2017, following a review of nonstrategic assets for potential divestiture, we recorded $4.3 million of noncash impairment charges related to a nonstrategic equity investment located in Oklahoma, which was later sold. In 2015, due to the continued and greater than expected decline in volumes gathered in the dry natural gas area of the Powder River Basin and our decision to cease operations of our wholly owned coal-bed methane natural gas gathering system in 2016, we recorded noncash impairment charges of $180.6 million in 2015 related to our Bighorn Gas Gathering, Fort Union Gas Gathering and Lost Creek Gathering Company equity investments. Unconsolidated Affiliates Financial Information - The following tables set forth summarized combined financial information of our unconsolidated affiliates for the periods indicated: December 31, December 31, ( Thousands of dollars ) Balance Sheet Current assets $ 151,907 $ 143,317 Property, plant and equipment, net $ 2,490,692 $ 2,579,607 Other noncurrent assets $ 14,793 $ 20,784 Current liabilities $ 70,434 $ 77,388 Long-term debt $ 479,050 $ 649,539 Other noncurrent liabilities $ 53,830 $ 69,265 Accumulated other comprehensive loss $ (9,946 ) $ (7,450 ) Owners’ equity $ 2,064,024 $ 1,954,966 Years Ended December 31, 2017 2016 2015 ( Thousands of dollars ) Income Statement Operating revenues $ 639,102 $ 578,542 $ 524,496 Operating expenses (a) $ 277,121 $ 260,753 $ 304,930 Net income (a) $ 347,692 $ 293,921 $ 200,064 Distributions paid to us $ 196,114 $ 196,717 $ 155,918 (a) Includes long-lived asset impairment charges in 2015. We incurred expenses in transactions with unconsolidated affiliates of $156.1 million , $140.3 million and $104.7 million for 2017, 2016 and 2015 , respectively, primarily related to Overland Pass Pipeline Company and Northern Border Pipeline. Accounts payable to our equity-method investees at December 31, 2017 and 2016, was $13.6 million and $11.1 million , respectively. 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. In 2017, we made an equity contribution of $83 million to Northern Border Pipeline. Under the terms of settlement with shippers in 2012, Northern Border Pipeline was required to file a rate case by January 1, 2018. In December 2017, 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, the cash distributions from Overland Pass Pipeline Company requires the unanimous approval of the Overland Pass Pipeline Management Committee. Cash distributions are equal to 100 percent of available cash as defined in the limited liability company agreement. Roadrunner Gas Transmission - In March 2015, we entered into a 50-50 joint venture with a subsidiary of Fermaca, a Mexico City-based natural gas infrastructure company, to construct the Roadrunner pipeline to transport natural gas from the Permian Basin in West Texas to the Mexican border near El Paso, Texas. We contributed $4 million and $65 million to Roadrunner in 2017 and 2016, respectively. 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. 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 years ended December 31, 2017 , 2016 and 2015, were not material.

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Notes)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES Commitments - Operating leases represent future minimum lease payments under noncancelable leases covering office space and pipeline equipment. Rental expense in 2017, 2016 and 2015 was not material. We have no material operating leases. Firm transportation and storage contracts are fixed-price contracts that provide us with firm transportation and storage capacity. The following table sets forth our firm transportation and storage contract payments for the periods indicated: Firm Transportation and Storage Contracts ( Millions of dollars ) 2018 $ 46.1 2019 37.6 2020 37.3 2021 23.0 2022 14.2 Thereafter 20.8 Total $ 179.0 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. Legal Proceedings - Gas Index Pricing Litigation - As previously reported, we and our affiliate, ONEOK Energy Services Company, L.P. (OESC), along with several other energy companies, were named as defendants in multiple lawsuits arising from alleged market manipulation or false reporting of natural gas prices to natural gas-index publications alleged to have occurred prior to 2003. 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. In May 2017, the Court approved the following previously announced settlements: • Learjet, Inc., et al. v. ONEOK, Inc., et al. (filed in the District Court of Wyandotte, Kansas, in November 2005, transferred to MDL-1566 in the Court); • Arandell Corporation, et al. v. Xcel Energy, Inc., et al. (filed in the Circuit Court for Dane County, Wisconsin, in December 2006, transferred to MDL-1566 in the Court); • Heartland Regional Medical Center, et al. v. ONEOK, Inc., et al. (filed in the Circuit Court of Buchanan County, Missouri, in March 2007, transferred to MDL-1566 in the Court); and • NewPage Wisconsin System v. CMS Energy Resource Management Company, et al. (filed in the Circuit Court for Wood County, Wisconsin, in March 2009, transferred to MDL-1566 in the Court and consolidated with the Arandell case). The Court later entered a final judgment dismissing these actions with prejudice as to us and our affiliates, which became final and nonappealable in July 2017. The amount paid to settle these cases was not material to our results of operations, financial position or cash flows and was paid with cash on hand. 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.

SEGMENTS (Notes)

SEGMENTS (Notes)	12 Months Ended
	Dec. 31, 2017
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 the corporate and Merger Transaction-related 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 . 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. Beginning in 2016, 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. Prior periods have been adjusted to conform to current presentation. 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 each of the years ended December 31, 2017, 2016 and 2015 , 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: Year Ended December 31, 2017 Natural Gas Gathering and Processing Natural Gas Liquids (a) Natural Gas Pipelines (b) Total Segments ( Thousands of dollars ) Sales to unaffiliated customers $ 1,750,655 $ 10,009,576 $ 411,490 $ 12,171,721 Intersegment revenues 1,275,919 616,628 8,442 1,900,989 Total revenues 3,026,574 10,626,204 419,932 14,072,710 Cost of sales and fuel (exclusive of depreciation and items shown separately below) (2,216,355 ) (9,176,494 ) (43,424 ) (11,436,273 ) Operating costs (309,536 ) (359,753 ) (126,241 ) (795,530 ) Equity in net earnings from investments 12,098 59,876 87,304 159,278 Other 5,691 5,106 2,247 13,044 Segment adjusted EBITDA $ 518,472 $ 1,154,939 $ 339,818 $ 2,013,229 Depreciation and amortization $ (184,923 ) $ (167,277 ) $ (51,025 ) $ (403,225 ) Impairment of long-lived assets and equity investments $ (20,240 ) $ — $ — $ (20,240 ) Total assets $ 5,495,163 $ 8,782,700 $ 2,055,020 $ 16,332,883 Capital expenditures $ 284,205 $ 114,267 $ 95,564 $ 494,036 (a) - Our Natural Gas Liquids segment has regulated and nonregulated operations. Our Natural Gas Liquids segment’s regulated operations had revenues of $1.2 billion , of which $1.0 billion related to sales within the segment and cost of sales and fuel of $497.4 million . (b) - Our Natural Gas Pipelines segment has regulated and nonregulated operations. Our Natural Gas Pipelines segment’s regulated operations had revenues of $264.9 million and cost of sales and fuel of $44.0 million . Year Ended December 31, 2017 Total Segments Other and Eliminations Total ( Thousands of dollars ) Reconciliations of total segments to consolidated Sales to unaffiliated customers $ 12,171,721 $ 2,186 $ 12,173,907 Intersegment revenues 1,900,989 (1,900,989 ) — Total revenues $ 14,072,710 $ (1,898,803 ) $ 12,173,907 Cost of sales and fuel (exclusive of depreciation and operating costs) $ (11,436,273 ) $ 1,898,228 $ (9,538,045 ) Operating costs $ (795,530 ) $ (38,056 ) $ (833,586 ) Depreciation and amortization $ (403,225 ) $ (3,110 ) $ (406,335 ) Impairment of long-lived assets and equity investments $ (20,240 ) $ — $ (20,240 ) Equity in net earnings from investments $ 159,278 $ — $ 159,278 Total assets $ 16,332,883 $ 513,054 $ 16,845,937 Capital expenditures $ 494,036 $ 18,357 $ 512,393 Year Ended December 31, 2016 Natural Gas Gathering and Processing Natural Gas Liquids (a) Natural Gas Pipelines (b) Total Segments ( Thousands of dollars ) Sales to unaffiliated customers $ 1,375,738 $ 7,168,983 $ 373,738 $ 8,918,459 Intersegment revenues 675,839 506,671 5,623 1,188,133 Total revenues 2,051,577 7,675,654 379,361 10,106,592 Cost of sales and fuel (exclusive of depreciation and items shown separately below) (1,331,542 ) (6,321,377 ) (30,561 ) (7,683,480 ) Operating costs (285,599 ) (327,597 ) (115,628 ) (728,824 ) Equity in net earnings from investments 10,742 54,513 74,435 139,690 Other 1,600 (1,574 ) 5,530 5,556 Segment adjusted EBITDA $ 446,778 $ 1,079,619 $ 313,137 $ 1,839,534 Depreciation and amortization $ (178,548 ) $ (163,303 ) $ (46,718 ) $ (388,569 ) Total assets $ 5,320,666 $ 8,347,961 $ 1,946,318 $ 15,614,945 Capital expenditures $ 410,485 $ 105,861 $ 96,274 $ 612,620 (a) - Our Natural Gas Liquids segment has regulated and nonregulated operations. Our Natural Gas Liquids segment’s regulated operations had revenues of $1.2 billion , of which $992.8 million related to sales within the segment and cost of sales and fuel of $458.7 million . (b) - Our Natural Gas Pipelines segment has regulated and nonregulated operations. Our Natural Gas Pipelines segment’s regulated operations had revenues of $238.7 million and cost of sales and fuel of $30.0 million . Year Ended December 31, 2016 Total Segments Other and Eliminations Total ( Thousands of dollars ) Reconciliations of total segments to consolidated Sales to unaffiliated customers $ 8,918,459 $ 2,475 $ 8,920,934 Intersegment revenues 1,188,133 (1,188,133 ) — Total revenues $ 10,106,592 $ (1,185,658 ) $ 8,920,934 Cost of sales and fuel (exclusive of depreciation and operating costs) $ (7,683,480 ) $ 1,187,356 $ (6,496,124 ) Operating costs $ (728,824 ) $ (28,360 ) $ (757,184 ) Depreciation and amortization $ (388,569 ) $ (3,016 ) $ (391,585 ) Equity in net earnings from investments $ 139,690 $ — $ 139,690 Total assets $ 15,614,945 $ 523,806 $ 16,138,751 Capital expenditures $ 612,620 $ 12,014 $ 624,634 Year Ended December 31, 2015 Natural Gas Gathering and Processing Natural Gas Liquids (a) Natural Gas Pipelines (b) Total Segments ( Thousands of dollars ) Sales to unaffiliated customers $ 1,187,390 $ 6,248,002 $ 325,676 $ 7,761,068 Intersegment revenues 649,726 331,697 6,771 988,194 Total revenues 1,837,116 6,579,699 332,447 8,749,262 Cost of sales and fuel (exclusive of depreciation and items shown separately below) (1,265,617 ) (5,328,256 ) (34,481 ) (6,628,354 ) Operating costs (272,418 ) (314,505 ) (105,720 ) (692,643 ) Equity in net earnings from investments 17,863 38,696 68,741 125,300 Other 1,610 (3,342 ) 13,993 12,261 Segment adjusted EBITDA $ 318,554 $ 972,292 $ 274,980 $ 1,565,826 Depreciation and amortization $ (150,008 ) $ (158,709 ) $ (43,479 ) $ (352,196 ) Impairment of long-lived assets $ (73,681 ) $ (9,992 ) $ — $ (83,673 ) Impairment of equity investments $ (180,583 ) $ — $ — $ (180,583 ) Total assets $ 5,123,450 $ 8,017,799 $ 1,851,857 $ 14,993,106 Capital expenditures $ 887,938 $ 226,135 $ 58,215 $ 1,172,288 (a) - Our Natural Gas Liquids segment has regulated and nonregulated operations. Our Natural Gas Liquids segment’s regulated operations had revenues of $954.8 million , of which $770.1 million related to sales within the segment and cost of sales and fuel of $412.6 million . (b) - Our Natural Gas Pipelines segment has regulated and nonregulated operations. Our Natural Gas Pipelines segment’s regulated operations had revenues of $266.9 million and cost of sales and fuel of $31.1 million . Year Ended December 31, 2015 Total Segments Other and Eliminations Total ( Thousands of dollars ) Reconciliations of total segments to consolidated Sales to unaffiliated customers $ 7,761,068 $ 2,138 $ 7,763,206 Intersegment revenues 988,194 (988,194 ) — Total revenues $ 8,749,262 $ (986,056 ) $ 7,763,206 Cost of sales and fuel (exclusive of depreciation and operating costs) $ (6,628,354 ) $ 987,302 $ (5,641,052 ) Operating costs $ (692,643 ) $ (688 ) $ (693,331 ) Depreciation and amortization $ (352,196 ) $ (2,424 ) $ (354,620 ) Impairment of long-lived assets $ (83,673 ) $ — $ (83,673 ) Impairment of equity investments $ (180,583 ) $ — $ (180,583 ) Equity in net earnings from investments $ 125,300 $ — $ 125,300 Total assets $ 14,993,106 $ 453,005 $ 15,446,111 Capital expenditures $ 1,172,288 $ 16,024 $ 1,188,312 Years Ended December 31, ( Unaudited ) 2017 2016 2015 Reconciliation of income from continuing operations to total segment adjusted EBITDA ( Thousands of dollars ) Income from continuing operations $ 593,519 $ 745,550 $ 385,276 Add: Interest expense, net of capitalized interest 485,658 469,651 416,787 Depreciation and amortization 406,335 391,585 354,620 Income taxes 447,282 212,406 136,600 Impairment charges 20,240 — 264,256 Noncash compensation expense 13,421 31,981 13,799 Other corporate costs and noncash items (a) 46,774 (11,639 ) (5,512 ) Total segment adjusted EBITDA $ 2,013,229 $ 1,839,534 $ 1,565,826 (a) - The year ended December 31, 2017, includes our April 2017 $20.0 million contribution of Series E Preferred Stock to the Foundation and costs related to the Merger Transaction of $30.0 million .

QUARTERLY FINANCIAL DATA (UNAUD

QUARTERLY FINANCIAL DATA (UNAUDITED) (Notes)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Data [Abstract]
QUARTERLY FINANCIAL DATA (UNAUDITED)	QUARTERLY FINANCIAL DATA (UNAUDITED) Year Ended December 31, 2017 First Quarter Second Quarter Third Quarter Fourth Quarter ( Thousands of dollars, except per share amounts ) Total revenues $ 2,749,611 $ 2,725,772 $ 2,906,366 $ 3,792,158 Net income $ 186,185 $ 175,991 $ 166,531 $ 64,812 Net income attributable to ONEOK $ 87,361 $ 71,693 $ 165,742 $ 63,045 Net income attributable to common shareholders $ 87,361 $ 71,476 $ 165,466 $ 62,771 Earnings per share total Basic $ 0.41 $ 0.34 $ 0.43 $ 0.16 Diluted $ 0.41 $ 0.33 $ 0.43 $ 0.16 The fourth quarter 2017 includes a one-time noncash charge of $ 141.3 million related to revaluation of our deferred tax balances and a valuation allowance on certain state net operating loss and tax credit carryforwards resulting from the enactment of the Tax Cuts and Jobs Act, as described in Note M. The third quarter 2017 includes noncash impairment charges of $20.2 million related to Natural Gas Gathering and Processing assets and equity investments. The second quarter 2017 includes a $20.0 million noncash expense related to our Series E Preferred Stock contribution to the Foundation and operating costs related to the Merger Transaction of $30.0 million . First Quarter Second Quarter Third Quarter Fourth Quarter Year Ended December 31, 2016 ( Thousands of dollars except per share amounts ) Total revenues $ 1,774,459 $ 2,134,107 $ 2,357,907 $ 2,654,461 Income from continuing operations $ 175,911 $ 180,086 $ 194,792 $ 194,761 Income (loss) from discontinued operations, net of tax $ (952 ) $ (227 ) $ (576 ) $ (296 ) Net income $ 174,959 $ 179,859 $ 194,216 $ 194,465 Net income attributable to ONEOK $ 83,446 $ 85,944 $ 92,144 $ 90,505 Earnings per share total Basic $ 0.40 $ 0.41 $ 0.44 $ 0.43 Diluted $ 0.40 $ 0.40 $ 0.43 $ 0.43

SUPPLEMENTAL CONDENSED CONSOLID

SUPPLEMENTAL CONDENSED CONSOLIDATING FINANCIAL INFORMATION (Notes)	12 Months Ended
	Dec. 31, 2017
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, 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 the equity in ONEOK Partners’ 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 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 Year Ended December 31, 2017 Parent Issuer & Guarantor Subsidiary Issuer & Guarantor Guarantor Subsidiary Combined Non-Guarantor Subsidiaries Consolidating Entries Total ( Millions of dollars ) Revenues Commodity sales $ — $ — $ — $ 9,862.7 $ — $ 9,862.7 Services — — — 2,313.2 (2.0 ) 2,311.2 Total revenues — — — 12,175.9 (2.0 ) 12,173.9 Cost of sales and fuel (exclusive of items shown separately below) — — — 9,538.0 — 9,538.0 Operating expenses 28.7 — 9.2 1,204.0 (2.0 ) 1,239.9 Impairment of long-lived assets — — — 16.0 — 16.0 Gain on sale of assets — — — (0.9 ) — (0.9 ) Operating income (28.7 ) — (9.2 ) 1,418.8 — 1,380.9 Equity in net earnings from investments 1,236.6 1,215.7 1,224.9 100.7 (3,618.6 ) 159.3 Impairment of equity investments — — — (4.3 ) — (4.3 ) Other income (expense), net (1.4 ) 353.1 353.1 (8.0 ) (706.2 ) (9.4 ) Interest expense, net (137.1 ) (353.1 ) (353.1 ) (348.6 ) 706.2 (485.7 ) Income before income taxes 1,069.4 1,215.7 1,215.7 1,158.6 (3,618.6 ) 1,040.8 Income taxes (480.2 ) — — 32.9 — (447.3 ) Net income 589.2 1,215.7 1,215.7 1,191.5 (3,618.6 ) 593.5 Less: Net income attributable to noncontrolling interests 201.4 — — 4.3 — 205.7 Net income attributable to ONEOK 387.8 1,215.7 1,215.7 1,187.2 (3,618.6 ) 387.8 Less: Preferred stock dividends 0.8 — — — — 0.8 Net income available to common shareholders $ 387.0 $ 1,215.7 $ 1,215.7 $ 1,187.2 $ (3,618.6 ) $ 387.0 Year Ending December 31, 2016 Parent Issuer & Guarantor Subsidiary Issuer & Guarantor Guarantor Subsidiary Combined Non-Guarantor Subsidiaries Consolidating Entries Total ( Millions of dollars ) Revenues Commodity sales $ — $ — $ — $ 6,858.5 $ — $ 6,858.5 Services — — — 2,064.3 (1.8 ) 2,062.5 Total revenues — — — 8,922.8 (1.8 ) 8,921.0 Cost of sales and fuel (exclusive of items shown separately below) — — — 6,496.1 — 6,496.1 Operating expenses 28.8 — — 1,121.8 (1.8 ) 1,148.8 (Gain) loss on sale of assets 0.3 — — (9.9 ) — (9.6 ) Operating income (29.1 ) — — 1,314.8 — 1,285.7 Equity in net earnings from investments 1,063.9 1,066.8 1,066.8 69.7 (3,127.5 ) 139.7 Other income (expense), net 5.1 373.5 373.5 (2.8 ) (747.0 ) 2.3 Interest expense, net (102.9 ) (373.5 ) (373.5 ) (366.8 ) 747.0 (469.7 ) Income before income taxes 937.0 1,066.8 1,066.8 1,014.9 (3,127.5 ) 958.0 Income taxes (199.0 ) — — (13.4 ) — (212.4 ) Income from continuing operations 738.0 1,066.8 1,066.8 1,001.5 (3,127.5 ) 745.6 Income (loss) from discontinued operations, net of tax — — — (2.1 ) — (2.1 ) Net income 738.0 1,066.8 1,066.8 999.4 (3,127.5 ) 743.5 Less: Net income attributable to noncontrolling interests 386.0 — — 5.5 — 391.5 Net income attributable to ONEOK $ 352.0 $ 1,066.8 $ 1,066.8 $ 993.9 $ (3,127.5 ) $ 352.0 Year Ending December 31, 2015 Parent Issuer & Guarantor Subsidiary Issuer & Guarantor Guarantor Subsidiary Combined Non-Guarantor Subsidiaries Consolidating Entries Total ( Millions of dollars ) Revenues Commodity sales $ — $ — $ — $ 6,098.3 $ — $ 6,098.3 Services — — — 1,669.8 (4.9 ) 1,664.9 Total revenues — — — 7,768.1 (4.9 ) 7,763.2 Cost of sales and fuel (exclusive of items shown separately below) — — — 5,641.1 — 5,641.1 Operating expenses 1.2 — — 1,051.5 (4.9 ) 1,047.8 Impairment of long-lived assets — — — 83.7 — 83.7 Gain on sale of assets — — — (5.6 ) — (5.6 ) Operating income (1.2 ) — — 997.4 — 996.2 Equity in net earnings from investments 583.8 589.5 589.5 58.4 (1,695.9 ) 125.3 Impairment of equity investments — — — (180.6 ) — (180.6 ) Other income (expense), net 4.0 371.0 371.0 (6.2 ) (742.0 ) (2.2 ) Interest expense, net (85.1 ) (371.0 ) (371.0 ) (331.7 ) 742.0 (416.8 ) Income before income taxes 501.5 589.5 589.5 537.3 (1,695.9 ) 521.9 Income taxes (130.7 ) — — (5.9 ) — (136.6 ) Income from continuing operations 370.8 589.5 589.5 531.4 (1,695.9 ) 385.3 Income (loss) from discontinued operations, net of tax — — — (6.1 ) — (6.1 ) Net income 370.8 589.5 589.5 525.3 (1,695.9 ) 379.2 Less: Net income attributable to noncontrolling interests 125.8 — — 8.4 — 134.2 Net income attributable to ONEOK $ 245.0 $ 589.5 $ 589.5 $ 516.9 $ (1,695.9 ) $ 245.0 Condensed Consolidating Statements of Comprehensive Income Year Ended December 31, 2017 Parent Issuer & Guarantor Subsidiary Issuer & Guarantor Guarantor Subsidiary Combined Non-Guarantor Subsidiaries Consolidating Entries Total ( Millions of dollars ) Net income $ 589.2 $ 1,215.7 $ 1,215.7 $ 1,191.5 $ (3,618.6 ) $ 593.5 Other comprehensive income (loss), net of tax Unrealized gains (losses) on derivatives, net of tax 19.1 (72.2 ) (40.6 ) (8.8 ) 81.1 (21.4 ) Realized (gains) losses on derivatives in net income, net of tax 2.5 86.5 69.6 44.3 (139.2 ) 63.7 Change in pension and postretirement benefit plan liability, net of tax (4.2 ) — — — — (4.2 ) Other comprehensive income (loss) on investments in unconsolidated affiliates, net of tax — (1.1 ) (1.1 ) (1.0 ) 2.2 (1.0 ) Total other comprehensive income (loss), net of tax 17.4 13.2 27.9 34.5 (55.9 ) 37.1 Comprehensive income 606.6 1,228.9 1,243.6 1,226.0 (3,674.5 ) 630.6 Less: Comprehensive income attributable to noncontrolling interests 232.4 — — 4.3 — 236.7 Comprehensive income attributable to ONEOK $ 374.2 $ 1,228.9 $ 1,243.6 $ 1,221.7 $ (3,674.5 ) $ 393.9 Year Ending December 31, 2016 Parent Issuer & Guarantor Subsidiary Issuer & Guarantor Guarantor Subsidiary Combined Non-Guarantor Subsidiaries Consolidating Entries Total ( Millions of dollars ) Net income $ 738.0 $ 1,066.8 $ 1,066.8 $ 999.4 $ (3,127.5 ) $ 743.5 Other comprehensive income (loss), net of tax Unrealized gains (losses) on derivatives, net of tax — (35.8 ) (78.5 ) (108.8 ) 192.8 (30.3 ) Realized (gains) losses on derivatives in net income, net of tax 2.1 (10.7 ) (26.4 ) (33.4 ) 61.4 (7.0 ) Change in pension and postretirement benefit plan liability, net of tax (16.7 ) — — — — (16.7 ) Other comprehensive income (loss) on investments in unconsolidated affiliates, net of tax — (1.8 ) (1.8 ) (3.3 ) 5.4 (1.5 ) Total other comprehensive income (loss), net of tax (14.6 ) (48.3 ) (106.7 ) (145.5 ) 259.6 (55.5 ) Comprehensive income 723.4 1,018.5 960.1 853.9 (2,867.9 ) 688.0 Less: Comprehensive income attributable to noncontrolling interests 357.6 — — 5.5 — 363.1 Comprehensive income attributable to ONEOK $ 365.8 $ 1,018.5 $ 960.1 $ 848.4 $ (2,867.9 ) $ 324.9 Year Ending December 31, 2015 Parent Issuer & Guarantor Subsidiary Issuer & Guarantor Guarantor Subsidiary Combined Non-Guarantor Subsidiaries Consolidating Entries Total ( Millions of dollars ) Net income $ 370.8 $ 589.5 $ 589.5 $ 525.3 $ (1,695.9 ) $ 379.2 Other comprehensive income (loss), net of tax Unrealized gains (losses) on derivatives, net of tax — 47.5 70.1 111.5 (187.7 ) 41.4 Realized (gains) losses on derivatives in net income, net of tax 2.1 (67.0 ) (81.1 ) (137.9 ) 229.2 (54.7 ) Unrealized holding gains (losses) on available-for-sale securities, net of tax — — — (1.0 ) — (1.0 ) Change in pension and postretirement benefit plan liability, net of tax 15.4 — — — — 15.4 Other comprehensive income (loss) on investments in unconsolidated affiliates, net of tax — (1.9 ) (1.9 ) (3.5 ) 5.7 (1.6 ) Total other comprehensive income (loss), net of tax 17.5 (21.4 ) (12.9 ) (30.9 ) 47.2 (0.5 ) Comprehensive income 388.3 568.1 576.6 494.4 (1,648.7 ) 378.7 Less: Comprehensive income attributable to noncontrolling interests 116.2 — — 8.4 — 124.6 Comprehensive income attributable to ONEOK $ 272.1 $ 568.1 $ 576.6 $ 486.0 $ (1,648.7 ) $ 254.1 Condensed Consolidating Balance Sheets December 31, 2017 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 December 31, 2016 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 $ 248.5 $ — $ 0.4 $ — $ — $ 248.9 Accounts receivable, net — — — 872.4 — 872.4 Materials and supplies — — — 60.9 — 60.9 Natural gas and natural gas liquids in storage — — — 140.0 — 140.0 Other current assets 7.2 — — 99.7 — 106.9 Assets of discontinued operations — — — 0.6 — 0.6 Total current assets 255.7 — 0.4 1,173.6 — 1,429.7 Property, plant and equipment Property, plant and equipment 139.8 — — 14,938.7 — 15,078.5 Accumulated depreciation and amortization 90.4 — — 2,416.7 — 2,507.1 Net property, plant and equipment 49.4 — — 12,522.0 — 12,571.4 Investments and other assets Investments 2,931.9 3,222.1 6,805.4 631.1 (12,631.7 ) 958.8 Intercompany notes receivable 205.2 10,615.0 7,031.3 — (17,851.5 ) — Goodwill and intangible assets — — — 1,005.4 — 1,005.4 Other assets 103.4 47.5 — 12.1 — 163.0 Assets of discontinued operations — — — 10.5 — 10.5 Total investments and other assets 3,240.5 13,884.6 13,836.7 1,659.1 (30,483.2 ) 2,137.7 Total assets $ 3,545.6 $ 13,884.6 $ 13,837.1 $ 15,354.7 $ (30,483.2 ) $ 16,138.8 Liabilities and equity Current liabilities Current maturities of long-term debt $ 3.0 $ 400.0 $ — $ 7.7 $ — $ 410.7 Short-term borrowings — 1,110.3 — — — 1,110.3 Accounts payable 13.0 — — 861.7 — 874.7 Commodity imbalances — — — 142.6 — 142.6 Accrued interest 25.4 87.1 — — — 112.5 Other current liabilities 19.3 12.8 — 134.1 — 166.2 Liabilities of discontinued operations — — — 19.8 — 19.8 Total current liabilities 60.7 1,610.2 — 1,165.9 — 2,836.8 Intercompany debt — — 10,615.0 7,236.5 (17,851.5 ) — Long-term debt, excluding current maturities 1,628.7 6,254.7 — 36.6 — 7,920.0 Deferred credits and other liabilities 1,667.5 — — 285.6 — 1,953.1 Commitments and contingencies Equity Equity excluding noncontrolling interests in consolidated subsidiaries 188.7 6,019.7 3,222.1 6,472.0 (15,713.8 ) 188.7 Noncontrolling interests in consolidated subsidiaries — — — 158.1 3,082.1 3,240.2 Total equity 188.7 6,019.7 3,222.1 6,630.1 (12,631.7 ) 3,428.9 Total liabilities and equity $ 3,545.6 $ 13,884.6 $ 13,837.1 $ 15,354.7 $ (30,483.2 ) $ 16,138.8 Condensed Consolidating Statements of Cash Flows Year Ended December 31, 2017 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 $ 947.4 $ 1,348.3 $ 59.0 $ 1,353.7 $ (2,393.0 ) $ 1,315.4 Investing activities Capital expenditures — — — (512.4 ) — (512.4 ) Contributions to unconsolidated affiliates — — (83.0 ) (4.9 ) — (87.9 ) Other investing activities — — 14.8 17.9 — 32.7 Cash used in investing activities — — (68.2 ) (499.4 ) — (567.6 ) Financing activities Dividends paid (829.4 ) (1,332.0 ) (1,332.0 ) — 2,664.0 (829.4 ) Distributions to noncontrolling interests — — — (5.3 ) (271.0 ) (276.3 ) Intercompany borrowings (advances), net (2,500.7 ) 2,001.2 1,340.8 (841.3 ) — — Borrowing (repayment) of short-term borrowings, net 614.7 (1,110.3 ) — — — (495.6 ) Issuance of long-term debt, net of discounts 1,190.5 — — — — 1,190.5 Repayment of long-term debt (87.1 ) (900.0 ) — (7.7 ) — (994.8 ) Issuance of common stock 471.4 — — — — 471.4 Other (18.1 ) (7.2 ) — — — (25.3 ) Cash provided by (used in) financing activities (1,158.7 ) (1,348.3 ) 8.8 (854.3 ) 2,393.0 (959.5 ) Change in cash and cash equivalents (211.3 ) — (0.4 ) — — (211.7 ) Cash and cash equivalents at beginning of period 248.5 — 0.4 — — 248.9 Cash and cash equivalents at end of period $ 37.2 $ — $ — $ — $ — $ 37.2 Year Ending December 31, 2016 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 $ 717.0 $ 1,334.5 $ 70.0 $ 1,353.9 $ (2,122.1 ) $ 1,353.3 Investing activities Capital expenditures (0.2 ) — — (624.4 ) — (624.6 ) Other investing activities — — 34.9 (25.7 ) — 9.2 Cash provided by (used in) investing activities (0.2 ) — 34.9 (650.1 ) — (615.4 ) Financing activities Dividends paid (517.6 ) (1,332.0 ) (1,332.0 ) — 2,664.0 (517.6 ) Distributions to noncontrolling interests — — — (7.5 ) (541.9 ) (549.4 ) Intercompany borrowings (advances), net (63.1 ) (470.8 ) 1,222.4 (688.5 ) — — Borrowing (repayment) of short-term borrowings, net — 563.9 — — — 563.9 Issuance of long-term debt, net of discounts — 1,000.0 — — — 1,000.0 Debt financing costs — (2.8 ) — — — (2.8 ) Repayment of long-term debt (0.3 ) (1,100.0 ) — (7.7 ) — (1,108.0 ) Issuance of common stock 22.0 — — — — 22.0 Other (1.7 ) 7.2 — (0.1 ) — 5.4 Cash used in financing activities (560.7 ) (1,334.5 ) (109.6 ) (703.8 ) 2,122.1 (586.5 ) Change in cash and cash equivalents 156.1 — (4.7 ) — — 151.4 Change in cash and cash equivalents included in discontinued operations (0.1 ) — — — — (0.1 ) Change in cash and cash equivalents included in continuing operations 156.0 — (4.7 ) — — 151.3 Cash and cash equivalents at beginning of period 92.5 — 5.1 — — 97.6 Cash and cash equivalents at end of period $ 248.5 $ — $ 0.4 $ — $ — $ 248.9 Year Ending December 31, 2015 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 $ 650.3 $ 1,196.7 $ 66.9 $ 1,045.7 $ (1,936.8 ) $ 1,022.8 Investing activities Capital expenditures (0.1 ) — — (1,188.2 ) — (1,188.3 ) Contributions to investments (671.0 ) — — (27.5 ) 671.0 (27.5 ) Other investing activities — — 24.1 1.0 — 25.1 Cash provided by (used in) investing activities (671.1 ) — 24.1 (1,214.7 ) 671.0 (1,190.7 ) Financing activities Dividends paid (509.2 ) (1,230.5 ) (1,230.5 ) — 2,461.0 (509.2 ) Distributions to noncontrolling interests — — — (11.7 ) (524.2 ) (535.9 ) Intercompany borrowings (advances), net 4.6 (1,295.1 ) 1,102.1 188.4 — — Borrowing (repayment) of short-term borrowings, net — (509.0 ) — — — (509.0 ) Issuance of long-term debt, net of discounts 492.6 798.9 — — — 1,291.5 Debt financing costs (9.8 ) (7.7 ) — — — (17.5 ) Repayment of long-term debt (0.1 ) — — (7.7 ) — (7.8 ) Issuance of common stock 20.7 — — — — 20.7 Issuance of common units, net of issuance costs — 1,025.7 — — (650.0 ) 375.7 Contribution from general partner — 21.0 — — (21.0 ) — Other (15.8 ) — — — — (15.8 ) Cash provided by (used) in financing activities (17.0 ) (1,196.7 ) (128.4 ) 169.0 1,265.8 92.7 Change in cash and cash equivalents (37.8 ) — (37.4 ) — — (75.2 ) Cash and cash equivalents at beginning of period 130.3 — 42.5 — — 172.8 Cash and cash equivalents at end of period $ 92.5 $ — $ 5.1 $ — $ — $ 97.6

SUMMARY OF SIGNIFICANT ACCOUN29

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Consolidation	Consolidation - Our Consolidated Financial Statements include our accounts and the accounts of our subsidiaries over which we have control or are the primary beneficiary. All intercompany balances and transactions have been eliminated in consolidation. Investments in unconsolidated affiliates are accounted for using the equity method if we have the ability to exercise significant influence over operating and financial policies of our investee. Under this method, an investment is carried at its acquisition cost and adjusted each period for contributions made, distributions received and our share of the investee’s comprehensive income. For the investments we account for under the equity method, the premium or excess cost over underlying fair value of net assets is referred to as equity-method goodwill. Impairment of equity investments is recorded when the impairments are other than temporary. These amounts are recorded as investments in unconsolidated affiliates on our accompanying Consolidated Balance Sheets. See Note N for disclosures of our unconsolidated affiliates. Distributions paid to us from our unconsolidated affiliates are classified as operating activities on our Consolidated Statements of Cash Flows until the cumulative distributions exceed our proportionate share of income from the unconsolidated affiliate since the date of our initial investment. The amount of cumulative distributions paid to us that exceeds our cumulative proportionate share of income in each period represents a return of investment and is classified as an investing activity on our Consolidated Statements of Cash Flows.
Use of Estimates	Use of Estimates - The preparation of our Consolidated Financial Statements and related disclosures in accordance with GAAP requires us to make estimates and assumptions with respect to values or conditions that cannot be known with certainty that affect the reported amounts on our Consolidated Financial Statements. Items that may be estimated include, but are not limited to, the economic useful life of assets, fair value of assets, liabilities and equity-method investments, obligations under employee benefit plans, provisions for uncollectible accounts receivable, expenses for services received but for which no invoice has been received, provision for income taxes, including any deferred tax valuation allowances, the results of litigation and various other recorded or disclosed amounts. In addition, a portion of our revenues and cost of sales and fuel are recorded based on current month estimated volumes and prices. The estimates are reversed in the following month and recorded with actual volumes and prices. We evaluate these estimates on an ongoing basis using historical experience, consultation with experts and other methods we consider reasonable based on the particular circumstances. Nevertheless, actual results may differ significantly from the estimates. Any effects on our financial position or results of operations from revisions to these estimates are recorded in the period when the facts that give rise to the revision become known.
Fair Value Measurements	Fair Value Measurements - We define fair value as the price that would be received from the sale of an asset or the transfer of a liability in an orderly transaction between market participants at the measurement date. We use 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 primarily 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 comprised 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 for which ineffectiveness has not been material. Determining the appropriate classification of our fair value measurements within the fair value hierarchy requires management’s judgment regarding the degree to which market data is observable or corroborated by observable market data. We categorize derivatives for which fair value is determined using multiple inputs within a single level, based on the lowest level input that is significant to the fair value measurement in its entirety. See Note C for discussion of our fair value measurements.
Cash and Cash Equivalents	Cash and Cash Equivalents - Cash equivalents consist of highly liquid investments, which are readily convertible into cash and have original maturities of three months or less.
Revenue Recognition	Revenue Recognition - Our reportable segments recognize revenue when services are rendered or product is delivered. Our Natural Gas Gathering and Processing segment records revenues when natural gas is gathered or processed through our facilities. Our Natural Gas Liquids segment records revenues based upon contracted services and volumes exchanged or stored under service agreements in the period services are provided. A portion of our revenues for our Natural Gas Pipelines segment and our Natural Gas Liquids segment are recognized based upon contracted capacity and contracted volumes transported and stored under service agreements in the period services are provided. We disaggregate revenue on the Consolidated Statements of Income as follows: • Commodity sales - Commodity sales represent the sale of NGLs, condensate and residue natural gas. We generally purchase a supplier’s raw natural gas or unfractionated NGLs, which we process into marketable commodities and condensate, then we sell these commodities and condensate to downstream customers at a specified delivery point. Commodity sales are recognized upon delivery or title transfer to the customer, when revenue recognition criteria are met. • Service revenue - Service revenue represents the fees generated from the performance of our services. We enter into a variety of contract types that provide commodity sales and service revenue. We provide services primarily under the following types of contracts: • Fee-based - Under fee-based arrangements, we receive a fee or fees for one or more of the following services: gathering, compression, processing, transmission and storage of natural gas; and gathering, transportation, fractionation and storage of NGLs. The revenue we earn from these arrangements generally is directly related to the volume of natural gas and NGLs that flow through our systems and facilities, and is not normally directly dependent on commodity prices. However, to the extent a sustained decline in commodity prices results in a decline in volumes, our revenues from these arrangements would be reduced. In addition, many of our arrangements provide for fixed fee, minimum volume or firm demand charges. Fee-based arrangements are reported as service revenue on the Consolidated Statements of Income. • Percent-of-proceeds - Under POP arrangements in our Natural Gas Gathering and Processing segment, we generally purchase the producer’s raw natural gas which we process into natural gas and natural gas liquids, then we sell these commodities and condensate to downstream customers. We remit sales proceeds to the producer according to the contractual terms and retain our portion. Typically, our POP arrangements also include a fee-based component. In many cases, our Natural Gas Gathering and Processing segment provides services under contracts that contain a combination of the arrangements described above. When services are provided (in addition to raw natural gas purchased) under POP with fee contracts, we record such fees as service revenue on the Consolidated Statements of Income. The terms of our contracts vary based on natural gas quality conditions, the competitive environment when the contracts are signed and customer requirements. Update - Upon adoption of Topic 606 in January 2018, certain of our revenue recognition policies changed. Based on the new guidance, 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 considered commodity supply contracts, as we control the commodities prior to performing services. Therefore, contractual fees in these identified contracts will be recorded as a reduction of the commodity purchase price in cost of sales and fuel, rather than as services revenue. To the extent we hold inventory related to these purchases, typically only in our Natural Gas Liquids segment, 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 commodities purchased under our Natural Gas Gathering and Processing segment’s POP with fee contracts and our Natural Gas Liquids segment’s exchange services contracts that include the purchase of commodities, which is unchanged from our assessment under current guidance and will not result in any changes in the nature or timing of commodity sales revenue. The contractual fees on POP with fee contracts that include producer take-in-kind rights will continue to be recorded as services revenue, as we do not control the raw natural gas stream while we are providing midstream services. From time to time, differences in the timing of revenues earned and our right to invoice customers may create contract assets or liabilities. At adoption, the timing of revenue on transportation contracts with tiered rates will be presented as contract assets for our Natural Gas Pipelines segment. In addition, certain contributions in aid of construction from customers will be reflected as contract liabilities that will be recognized into revenue over the contract term. In 2017 and prior periods, we recorded these reimbursements as reductions to property, plant and equipment.
Cost of Sales and Fuel	Cost of Sales and Fuel - Cost of sales and fuel primarily includes (i) the cost of purchased commodities, including NGLs, natural gas and condensate, (ii) fees incurred for third-party transportation, fractionation and storage of commodities, and (iii) fuel and power costs incurred to operate our own facilities that gather, process, transport and store commodities. Update - As described above, upon adoption of Topic 606 in January 2018, cost of sales and fuel will be reduced by the fees we charge producers under our Natural Gas Gathering and Processing segment’s POP contracts and processors under our Natural Gas Liquids segment’s exchange services contracts that include the purchase of commodities.
Operations and Maintenance	Operations and Maintenance - Operations and maintenance primarily includes (i) payroll and benefit costs, (ii) third-party costs for operations, maintenance and integrity management, regulatory compliance and environmental and safety, and (iii) other business related service costs.
Accounts Receivable	Accounts Receivable - Accounts receivable represent valid claims against nonaffiliated customers for products sold or services rendered, net of allowances for doubtful accounts. We assess the creditworthiness of our counterparties on an ongoing basis and require security, including prepayments and other forms of collateral, when appropriate. Outstanding customer receivables are reviewed regularly for possible nonpayment indicators, and allowances for doubtful accounts are recorded based upon management’s estimate of collectability at each balance sheet date. At December 31, 2017 and 2016 , our allowance for doubtful accounts was not material.
Inventory	Inventory - The values of current natural gas and NGLs in storage are determined using the lower of weighted-average cost or net realizable value. Noncurrent natural gas and NGLs are classified as property and valued at cost. Materials and supplies are valued at average cost.
Commodity Imbalances	Commodity Imbalances - Commodity imbalances represent amounts payable or receivable for NGL exchange contracts and natural gas pipeline imbalances and are valued at market prices. Under the majority of our NGL exchange agreements, we physically receive volumes of unfractionated NGLs, including the risk of loss and legal title to such volumes, from the exchange counterparty. In turn, we deliver NGL products back to the customer and charge them gathering, fractionation and transportation fees. To the extent that the volumes we receive under such agreements differ from those we deliver, we record a net exchange receivable or payable position with the counterparties. These net exchange receivables and payables are settled with movements of NGL products rather than with cash. Natural gas pipeline imbalances are settled in cash or in-kind, subject to the terms of the pipelines’ tariffs or by agreement.
Derivatives and Risk Management	Derivatives and Risk Management - We utilize derivatives to reduce our market-risk exposure to commodity price and interest-rate fluctuations and to achieve more predictable cash flows. We record all derivative instruments at fair value, with the exception of normal purchases and normal sales transactions that are expected to result in physical delivery. Commodity price and interest-rate volatility may have a significant impact on the fair value of derivative instruments as of a given date. The accounting for changes in the fair value of a derivative instrument depends on whether it has been designated and qualifies as part of a hedging relationship and, if so, the reason for holding it. The table below summarizes the various ways in which we account for our derivative instruments and the impact on our Consolidated Financial Statements: Recognition and Measurement Accounting Treatment Balance Sheet Income Statement Normal purchases and normal sales - Fair value not recorded - Change in fair value not recognized in earnings Mark-to-market - Recorded at fair value - Change in fair value recognized in earnings Cash flow hedge - Recorded at fair value - Ineffective portion of the gain or loss on the derivative instrument is recognized in earnings - Effective portion of the gain or loss on the derivative instrument is reported initially as a component of accumulated other comprehensive income (loss) - Effective portion of the gain or loss on the derivative instrument is reclassified out of accumulated other comprehensive income (loss) into earnings when the forecasted transaction affects earnings Fair value hedge - Recorded at fair value - The gain or loss on the derivative instrument is recognized in earnings - Change in fair value of the hedged item is recorded as an adjustment to book value - Change in fair value of the hedged item is recognized in earnings To reduce our exposure to fluctuations in natural gas, NGLs and condensate prices, we periodically enter into futures, forward purchases and sales, options or swap transactions in order to hedge anticipated purchases and sales of natural gas, NGLs and condensate. Interest-rate swaps are used from time to time to manage interest-rate risk. Under certain conditions, we designate our derivative instruments as a hedge of exposure to changes in fair values or cash flows. We formally document all relationships between hedging instruments and hedged items, as well as risk-management objectives and strategies for undertaking various hedge transactions, and methods for assessing and testing correlation and hedge ineffectiveness. We specifically identify the forecasted transaction that has been designated as the hedged item in a cash flow hedge relationship. We assess the effectiveness of hedging relationships quarterly by performing an effectiveness analysis on our fair value and cash flow hedging relationships to determine whether the hedge relationships are highly effective on a retrospective and prospective basis. We also document our normal purchases and normal sales transactions that we expect to result in physical delivery and that we elect to exempt from derivative accounting treatment. The realized revenues and purchase costs of our derivative instruments not considered held for trading purposes and derivatives that qualify as normal purchases or normal sales that are expected to result in physical delivery are reported on a gross basis. Cash flows from futures, forwards and swaps that are accounted for as hedges are included in the same category as the cash flows from the related hedged items in our Consolidated Statements of Cash Flows. See Notes C and D for more discussion of our fair value measurements and risk-management and hedging activities using derivatives.
Property, Plant and Equipment	Property, Plant and Equipment - Our properties are stated at cost, including AFUDC and capitalized interest. In some cases, the cost of regulated property retired or sold, plus removal costs, less salvage, is charged to accumulated depreciation. Gains and losses from sales or transfers of nonregulated properties or an entire operating unit or system of our regulated properties are recognized in income. Maintenance and repairs are charged directly to expense. The interest portion of AFUDC and capitalized interest represent the cost of borrowed funds used to finance construction activities for regulated and nonregulated projects, respectively. We capitalize interest costs during the construction or upgrade of qualifying assets. These costs are recorded as a reduction to interest expense. The equity portion of AFUDC represents the capitalization of the estimated average cost of equity used during the construction of major projects and is recorded in the cost of our regulated properties and as a credit to the allowance for equity funds used during construction. Our properties are depreciated using the straight-line method over their estimated useful lives. Generally, we apply composite depreciation rates to functional groups of property having similar economic circumstances. We periodically conduct depreciation studies to assess the economic lives of our assets. For our regulated assets, these depreciation studies are completed as a part of our rate proceedings or tariff filings, and the changes in economic lives, if applicable, are implemented prospectively when the new rates are billed. For our nonregulated assets, if it is determined that the estimated economic life changes, the changes are made prospectively. Changes in the estimated economic lives of our property, plant and equipment could have a material effect on our financial position or results of operations. Property, plant and equipment on our Consolidated Balance Sheets includes construction work in process for capital projects that have not yet been placed in service and therefore are not being depreciated. Assets are transferred out of construction work in process when they are substantially complete and ready for their intended use. See Note E for disclosures of our property, plant and equipment.
Impairment of Goodwill and Long-Lived Assets, including Intangible Assets	Impairment of Goodwill and Long-Lived Assets, Including Intangible Assets - We assess our goodwill for impairment at least annually on July 1, unless events or changes in circumstances indicate an impairment may have occurred before that time. Our qualitative goodwill impairment analysis performed as of July 1, 2017, did not result in an impairment charge nor did our analysis reflect any reporting units at risk, and subsequent to that date, no event has occurred indicating that the implied fair value of each of our reporting units is less than the carrying value of its net assets. As part of our goodwill impairment test, we may first assess qualitative factors (including macroeconomic conditions, industry and market considerations, cost factors and overall financial performance) to determine whether it is more likely than not that the fair value of each of our reporting units is less than its carrying amount. If further testing is necessary or a quantitative test is elected, we perform a two-step impairment test for goodwill. In the first step, an initial assessment is made by comparing the fair value of a reporting unit with its book value, including goodwill. If the fair value is less than the book value, an impairment is indicated, and we must perform a second test to measure the amount of the impairment. In the second test, we calculate the implied fair value of the goodwill by deducting the fair value of all tangible and intangible net assets of the reporting unit from the fair value determined in step one of the assessment. If the carrying value of the goodwill exceeds the implied fair value of the goodwill, we will record an impairment charge. To estimate the fair value of our reporting units, we use two generally accepted valuation approaches, an income approach and a market approach, using assumptions consistent with a market participant’s perspective. Under the income approach, we use anticipated cash flows over a period of years plus a terminal value and discount these amounts to their present value using appropriate discount rates. Under the market approach, we apply EBITDA multiples to forecasted EBITDA. The multiples used are consistent with historical asset transactions. The forecasted cash flows are based on average forecasted cash flows for a reporting unit over a period of years. We assess our long-lived assets for impairment whenever events or changes in circumstances indicate that an asset’s carrying amount may not be recoverable. An impairment is indicated if the carrying amount of a long-lived asset exceeds the sum of the undiscounted future cash flows expected to result from the use and eventual disposition of the asset. If an impairment is indicated, we record an impairment loss equal to the difference between the carrying value and the fair value of the long-lived asset. For the investments we account for under the equity method, the impairment test considers whether the fair value of the equity investment as a whole, not the underlying net assets, has declined and whether that decline is other than temporary. Therefore, we periodically evaluate the amount at which we carry our equity-method investments to determine whether current events or circumstances warrant adjustments to our carrying values. See Notes E , F and N for our long-lived assets, goodwill and intangible assets and investments in unconsolidated affiliates disclosures.
Regulation	Regulation - Our intrastate natural gas transmission and natural gas liquids pipelines are subject to the rate regulation and accounting requirements of the OCC, KCC and RRC, and our natural gas transmission pipelines are regulated by the FERC under the Natural Gas Policy Act for certain services where we deliver natural gas into FERC regulated natural gas pipelines. Our interstate natural gas and natural gas liquids pipelines are subject to regulation by the FERC. In Kansas and Texas, natural gas storage may be regulated by the state and the FERC for certain types of services. Accordingly, portions of our Natural Gas Liquids and Natural Gas Pipelines segments follow the accounting and reporting guidance for regulated operations. In our Consolidated Financial Statements and our Notes to Consolidated Financial Statements, regulated operations are defined pursuant to Financial Accounting Standards Board’s (FASB) ASC 980, Regulated Operations. During the rate-making process for certain of our assets, regulatory authorities set the framework for what we can charge customers for our services and establish the manner that our costs are accounted for, including allowing us to defer recognition of certain costs and permitting recovery of the amounts through rates over time as opposed to expensing such costs as incurred. Certain examples of types of regulatory guidance include costs for fuel and losses, acquisition costs, contributions in aid of construction, charges for depreciation, and gains or losses on disposition of assets. This allows us to stabilize rates over time rather than passing such costs on to the customer for immediate recovery. Actions by regulatory authorities could have an effect on the amount recovered from rate payers. Any difference in the amount recoverable and the amount deferred is recorded as income or expense at the time of the regulatory action. A write-off of regulatory assets and costs not recovered may be required if all or a portion of the regulated operations have rates that are no longer: • established by independent, third-party regulators; • designed to recover the specific entity’s costs of providing regulated services; and • set at levels that will recover our costs when considering the demand and competition for our services. At December 31, 2017 and 2016 , we recorded regulatory assets of $5.0 million and $5.5 million , respectively, which are currently being recovered and are expected to be recovered from our customers. Regulatory assets are being recovered as a result of approved rate proceedings over varying time periods up to 50 years. These assets are reflected in other assets on our Consolidated Balance Sheets.
Pension and Other Postretirement Employee Benefits	Retirement and Postretirement Employee Benefits - We have defined benefit retirement plans covering certain employees and former employees. We sponsor welfare plans that provide postretirement medical and life insurance benefits to certain employees hired prior to 2017 who retire with at least five years of service. The expense and liability related to these plans is calculated using statistical and other factors that attempt to anticipate future events. These factors include assumptions about the discount rate, expected return on plan assets, rate of future compensation increases, mortality and employment length. In determining the projected benefit obligations and costs, assumptions can change from period to period and may result in material changes in the costs and liabilities we recognize. See Note L for more discussion of pension and postretirement employee benefits. We determine our overall expected long-term rate of return on plan assets based on our review of historical returns and economic growth models. We determine our discount rates annually. We estimate our discount rate based upon a comparison of the expected cash flows associated with our future payments under our pension and postretirement obligations to a hypothetical bond portfolio created using high-quality bonds that closely match expected cash flows. Bond portfolios are developed by selecting a bond for each of the next 60 years based on the maturity dates of the bonds. Bonds selected to be included in the portfolios are only those rated by Moody’s as AA- or better and exclude callable bonds, bonds with less than a minimum issue size, yield outliers and other filtering criteria to remove unsuitable bonds.
Income Taxes	Income Taxes - Deferred income taxes are provided for the difference between the financial statement and income tax basis of assets and liabilities and carryforward items based on income tax laws and rates existing at the time the temporary differences are expected to reverse. Generally, the effect of a change in tax rates on deferred tax assets and liabilities is recognized in income in the period that includes the enactment date of the rate change. For regulated companies, the effect on deferred tax assets and liabilities of a change in tax rates is recorded as regulatory assets and regulatory liabilities in the period that includes the enactment date, if, as a result of an action by a regulator, it is probable that the effect of the change in tax rates will be recovered from or returned to customers through future rates. We utilize a more-likely-than-not recognition threshold and measurement attribute for the financial statement recognition and measurement of a tax position that is taken or expected to be taken in a tax return. We reflect penalties and interest as part of income tax expense as they become applicable for tax provisions that do not meet the more-likely-than-not recognition threshold and measurement attribute. During 2017, 2016 and 2015 , our tax positions did not require an establishment of a material reserve. We utilize the “with-and-without” approach for intra-period tax allocation for purposes of allocating total tax expense (or benefit) for the year among the various financial statement components. We file numerous consolidated and separate income tax returns with federal tax authorities of the United States along with the tax authorities of several states. We are not under any United States federal audits or statute waivers at this time. See Note M for additional discussion of income taxes.
Asset Retirement Obligations	Asset Retirement Obligations - Asset retirement obligations represent legal obligations associated with the retirement of long-lived assets that result from the acquisition, construction, development and/or normal use of the asset. Certain of our natural gas gathering and processing, natural gas liquids and natural gas pipeline facilities are subject to agreements or regulations that give rise to our asset retirement obligations for removal or other disposition costs associated with retiring the assets in place upon the discontinued use of the assets. We recognize the fair value of a liability for an asset retirement obligation in the period when it is incurred if a reasonable estimate of the fair value can be made. We are not able to estimate reasonably the fair value of the asset retirement obligations for portions of our assets, primarily certain pipeline assets, because the settlement dates are indeterminable given our expected continued use of the assets with proper maintenance. We expect our pipeline assets, for which we are unable to estimate reasonably the fair value of the asset retirement obligation, will continue in operation as long as supply and demand for natural gas and natural gas liquids exists. Based on the widespread use of natural gas for heating and cooking activities for residential users and electric-power generation for commercial users, as well as use of natural gas liquids by the petrochemical industry, we expect supply and demand to exist for the foreseeable future. For our assets that we are able to make an estimate, the fair value of the liability is added to the carrying amount of the associated asset, and this additional carrying amount is depreciated over the life of the asset. The liability is accreted at the end of each period through charges to operating expense. If the obligation is settled for an amount other than the carrying amount of the liability, we will recognize a gain or loss on settlement. The depreciation and accretion expense are immaterial to our Consolidated Financial Statements. In accordance with long-standing regulatory treatment, we collect, through rates, the estimated costs of removal on certain regulated properties through depreciation expense, with a corresponding credit to accumulated depreciation and amortization. These removal costs collected through rates include legal and nonlegal removal obligations; however, the amounts collected in excess of the asset removal costs incurred are accounted for as a regulatory liability for financial reporting purposes. Historically, the regulatory authorities that have jurisdiction over our regulated operations have not required us to quantify this amount; rather, these costs are addressed prospectively in depreciation rates and are set in each general rate order. We have made an estimate of our regulatory liability using current rates since the last general rate order in each of our jurisdictions; however, for financial reporting purposes, significant uncertainty exists regarding the ultimate disposition of this regulatory liability pending, among other issues, clarification of regulatory intent. We continue to monitor regulatory requirements, and the liability may be adjusted as more information is obtained.
Contingencies	Contingencies - Our accounting for contingencies covers a variety of business activities, including contingencies for legal and environmental exposures. We accrue these contingencies when our assessments indicate that it is probable that a liability has been incurred or an asset will not be recovered and an amount can be estimated reasonably. We expense legal fees as incurred and base our legal liability estimates on currently available facts and our estimates of the ultimate outcome or resolution. Accruals for estimated losses from environmental remediation obligations generally are recognized no later than completion of a remediation feasibility study. Recoveries of environmental remediation costs from other parties are recorded as assets when their receipt is deemed probable. Our expenditures for environmental evaluation, mitigation, remediation and compliance to date have not been significant in relation to our financial position or results of operations, and our expenditures related to environmental matters had no material effect on earnings or cash flows during 2017, 2016 and 2015 . Actual results may differ from our estimates resulting in an impact, positive or negative, on earnings. See Note O for additional discussion of contingencies.
Share-Based Payments	Share-Based Payments - We expense the fair value of share-based payments net of estimated forfeitures. We estimate forfeiture rates based on historical forfeitures under our share-based payment plans.
Earnings per Common Share	Earnings per Common Share - Basic EPS is calculated based on the daily weighted-average number of shares of common stock outstanding during the period, vested restricted and performance units that have been deferred and share awards deferred under the compensation plan for nonemployee directors. Diluted EPS is calculated based on the daily weighted-average number of shares of common stock outstanding during the period plus potentially dilutive components. The dilutive components are calculated based on the dilutive effect for each quarter. For fiscal-year periods, the dilutive components for each quarter are averaged to arrive at the fiscal year-to-date dilutive component.
Discontinued Operations, Policy [Policy Text Block]	Discontinued Operations - Beginning in 2017, the results of operations and financial position of our former energy services business are no longer reflected as discontinued operations in our Consolidated Financial Statements and Notes to the Consolidated Financial Statements, as they are not material.
New Accounting Pronouncements	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 2015-11, “Inventory (Topic 330): Simplifying the Measurement of Inventory” The standard requires that inventory, excluding inventory measured using last-in, first-out (LIFO) or the retail inventory method, be measured at the lower of cost or net realizable value. First quarter 2017 As a result of adopting this guidance, we updated our accounting policy for inventory valuation accordingly. The financial impact of adopting this guidance was not material. ASU 2016-05, “Derivatives and Hedging (Topic 815): Effect of Derivative Contract Novations on Existing Hedge Accounting Relationships” The standard clarifies that a change in the counterparty to a derivative instrument that has been designated as the hedging instrument under Topic 815 does not, in and of itself, require dedesignation of that hedging relationship provided that all other hedge accounting criteria continue to be met. First quarter 2017 The impact of adopting this standard was not material. ASU 2016-06, “Derivatives and Hedging (Topic 815): Contingent Put and Call Options in Debt Instruments” The standard clarifies the requirements for assessing whether a contingent call (put) option that can accelerate the payment of principal on a debt instrument is clearly and closely related to its debt host. First quarter 2017 The impact of adopting this standard was not material. ASU 2016-09, “Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting” The standard provides simplified accounting for share-based payment transactions in relation to income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows. First quarter 2017 As a result of adopting this guidance, we recorded an adjustment increasing beginning retained earnings and deferred tax assets in the first quarter 2017 of $73.4 million to recognize previously unrecognized cumulative excess tax benefits related to share-based payments on a modified retrospective basis. Beginning in January 2017, all share-based payment tax effects are recorded in earnings. The other effects of adopting this standard were not material. Standard Description Date of Adoption Effect on the Financial Statements or Other Significant Matters Standards that are not yet adopted as of December 31, 2017 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. The cumulative effect of adopting the new standard was immaterial and related primarily to contract asset and liabilities described in our revenue recognition policies update. We do not expect adoption of the standard to be material to our operating income or net income; however, we expect a significant reduction to cost of sales and fuel in 2018 for amounts previously reported as services revenue in 2017 and prior periods, as described in our revenue recognition policies update. We have drafted required disclosures and expect to disaggregate revenues on a segment basis similar to our current presentation in Management’s Discussion and Analysis. We expect our disclosure of unsatisfied performance obligations to relate primarily to firm transportation contracts. We do not expect a material contract asset balance and expect our contract liability balance to include storage contracts that have been prepaid by customers and contributions in aid of construction received from customers. 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, we do not expect adoption of this standard to materially impact us. 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 We do not expect the adoption of this standard to materially impact us. 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 do not expect the adoption of this standard to materially impact us. 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. At adoption, we 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. We expect immaterial changes to disclosures as a result of adopting this standard. Standard Description Date of Adoption Effect on the Financial Statements or Other Significant Matters Standards that are not yet adopted as of December 31, 2017 ( continued ) 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. 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 2019 We are evaluating the impact of this standard on us. ASU 2016-13, “Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments” The standard requires a financial asset (or a group of financial assets) measured at amortized cost basis to be presented net of the allowance for credit losses to reflect the net carrying value at the amount expected to be collected on the financial asset; and the initial allowance for credit losses for purchased financial assets, including available-for-sale debt securities, to be added to the purchase price rather than being reported as a credit loss expense. First quarter 2020 We do not expect the adoption of this standard to materially impact us. ASU 2017-04, “Intangibles- Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment” The standard simplifies the subsequent measurement of goodwill by eliminating the requirement to calculate the implied fair value of goodwill under step 2. Instead, an entity will recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value. The standard does not change step zero or step 1 assessments. First quarter 2020 We do not expect the adoption of this standard to materially impact us.

DEBT DEBT (Policies)

DEBT DEBT (Policies)	12 Months Ended
	Dec. 31, 2017
Debt Instrument [Line Items]
Debt Policy	We amortize premiums, discounts and expenses incurred in connection with the issuance of long-term debt consistent with the terms of the respective debt instrument.

EQUITY Equity (Policies)

EQUITY Equity (Policies)	6 Months Ended
	Jun. 30, 2017
Equity [Abstract]
Incentive Distribution Policy, Managing Member or General Partner, Description [Policy Text Block]	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. Under the Partnership Agreement, distributions were made to the partners with respect to each calendar quarter in an amount equal to 100 percent of available cash as defined in the Partnership Agreement. Available cash generally was distributed 98 percent to limited partners and 2 percent to the general partner. The general partner’s percentage interest in quarterly distributions were increased after certain specified target levels were met during the quarter. Under the incentive distribution provisions, as set forth in the Partnership Agreement, the general partner received: • 15 percent of amounts distributed in excess of $0.3025 per unit; • 25 percent of amounts distributed in excess of $0.3575 per unit; and • 50 percent of amounts distributed in excess of $0.4675 per unit.

EMPLOYEE BENEFIT PLANS EMPLOY32

EMPLOYEE BENEFIT PLANS EMPLOYEE BENEFIT PLANS (Policies)	12 Months Ended
	Dec. 31, 2017
Defined Benefit Plan [Abstract]
Pension and Other Postretirement Plans, Policy [Policy Text Block]	Retirement and Postretirement Employee Benefits - We have defined benefit retirement plans covering certain employees and former employees. We sponsor welfare plans that provide postretirement medical and life insurance benefits to certain employees hired prior to 2017 who retire with at least five years of service. The expense and liability related to these plans is calculated using statistical and other factors that attempt to anticipate future events. These factors include assumptions about the discount rate, expected return on plan assets, rate of future compensation increases, mortality and employment length. In determining the projected benefit obligations and costs, assumptions can change from period to period and may result in material changes in the costs and liabilities we recognize. See Note L for more discussion of pension and postretirement employee benefits. We determine our overall expected long-term rate of return on plan assets based on our review of historical returns and economic growth models. We determine our discount rates annually. We estimate our discount rate based upon a comparison of the expected cash flows associated with our future payments under our pension and postretirement obligations to a hypothetical bond portfolio created using high-quality bonds that closely match expected cash flows. Bond portfolios are developed by selecting a bond for each of the next 60 years based on the maturity dates of the bonds. Bonds selected to be included in the portfolios are only those rated by Moody’s as AA- or better and exclude callable bonds, bonds with less than a minimum issue size, yield outliers and other filtering criteria to remove unsuitable bonds.

SEGMENTS SEGMENTS (Policies)

SEGMENTS SEGMENTS (Policies)	12 Months Ended
	Dec. 31, 2017
Segment Reporting [Abstract]
Segment Accounting Policy [Text Block]	The accounting policies of the segments are described in Note A . 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. Beginning in 2016, 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. Prior periods have been adjusted to conform to current presentation. This calculation may not be comparable with similarly titled measures of other companies.

ONEOK PARTNERS ACQUISITION ON34

ONEOK PARTNERS ACQUISITION ONEOK PARTNERS ACQUISITION (Tables)	6 Months Ended
	Jun. 30, 2017
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Cash Flow, Supplemental Disclosures [Text Block]	Our noncash balance sheet activity related to the Merger Transaction is as follows (in millions): Common stock $ 1.7 Paid-in capital $ 5,228.6 Accumulated other comprehensive loss $ (40.3 ) Noncontrolling interests in consolidated subsidiaries $ (3,043.5 ) Deferred income taxes $ (2,146.5 )

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	12 Months Ended
	Dec. 31, 2017
Fair Value Disclosures [Abstract]
Recurring Fair Value Measurements	Recurring Fair Value Measurements - The following tables set forth our recurring fair value measurements for the periods indicated: December 31, 2017 Level 1 Level 2 Level 3 Total - Gross Netting (a) Total - Net (b) ( 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. (b) - Included in other current assets, other assets or other current liabilities in our Consolidated Balance Sheets. December 31, 2016 Level 1 Level 2 Level 3 Total - Gross Netting (a) Total - Net (b) ( Thousands of dollars ) Derivative assets Commodity contracts Financial contracts $ 1,147 $ — $ 4,564 $ 5,711 $ (4,760 ) $ 951 Interest-rate contracts — 47,457 — 47,457 — 47,457 Total derivative assets $ 1,147 $ 47,457 $ 4,564 $ 53,168 $ (4,760 ) $ 48,408 Derivative liabilities Commodity contracts Financial contracts $ (31,458 ) $ — $ (24,861 ) $ (56,319 ) $ 56,319 $ — Physical contracts — — (3,022 ) (3,022 ) — (3,022 ) Interest-rate contracts — (12,795 ) — (12,795 ) — (12,795 ) Total derivative liabilities $ (31,458 ) $ (12,795 ) $ (27,883 ) $ (72,136 ) $ 56,319 $ (15,817 ) 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, 2016 , we held no cash and posted $67.7 million of cash with various counterparties, including $51.6 million of cash collateral that is offsetting derivative net liability positions under master-netting arrangements in the table above. The remaining $16.1 million of cash collateral in excess of derivative net liability positions is included in other current assets in our Consolidated Balance Sheets. (b) - Included in other current assets, other assets or other current liabilities 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: Years Ended December 31, Derivative Assets (Liabilities) 2017 2016 ( Thousands of dollars ) Net assets (liabilities) at beginning of period $ (23,319 ) $ 7,331 Total realized/unrealized gains (losses): Included in earnings (a) 212 (320 ) Included in other comprehensive income (loss) (9,731 ) (30,330 ) Net assets (liabilities) at end of period $ (32,838 ) $ (23,319 ) (a) - Included in commodity sales revenues in our Consolidated Statements of Income.

RISK MANAGEMENT AND HEDGING A36

RISK MANAGEMENT AND HEDGING ACTIVITIES USING DERIVATIVES (Tables)	12 Months Ended
	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Fair Value of Derivatives	Fair Values of Derivative Instruments - The following table sets forth the fair values of our derivative instruments presented on a gross basis for the periods indicated: December 31, 2017 December 31, 2016 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 $ 16,978 $ (42,819 ) $ 1,155 $ (49,938 ) Other assets/other deferred credits — (3,838 ) 210 (2,142 ) Physical contracts Other current liabilities — (4,781 ) — (3,022 ) Interest-rate contracts Other current assets/other current liabilities 1,330 — — (12,795 ) Other assets 48,630 — 47,457 — Total derivatives designated as hedging instruments 66,938 (51,438 ) 48,822 (67,897 ) Derivatives not designated as hedging instruments Commodity contracts Financial contracts Other current assets/other current liabilities 7,477 (7,311 ) 4,346 (4,239 ) Total derivatives not designated as hedging instruments 7,477 (7,311 ) 4,346 (4,239 ) Total derivatives $ 74,415 $ (58,749 ) $ 53,168 $ (72,136 )
Notional Amounts of Derivative Instruments	Notional Quantities for Derivative Instruments - The following table sets forth the notional quantities for derivative instruments held for the periods indicated: December 31, 2017 December 31, 2016 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 — (24.5 ) — (38.4 ) -Natural gas ( Bcf ) Put options — — 49.5 — -Crude oil and NGLs ( MMBbl ) Futures, forwards and swaps 3.5 (11.1 ) — (3.6 ) Basis -Natural gas ( Bcf ) Futures and swaps — (24.5 ) — (38.4 ) Interest-rate contracts ( Millions of dollars ) Swaps $ 1,750.0 $ — $ 2,150.0 $ — Derivatives not designated as hedging instruments: Fixed price -Natural gas ( Bcf ) Futures and swaps — — 0.4 — -NGLs ( MMBbl ) Futures, forwards and swaps 0.8 (0.8 ) 0.5 (0.7 ) Basis -Natural gas ( Bcf ) Futures and swaps — — 0.4 —
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: Derivatives in Cash Flow Hedging Relationships Years Ended December 31, 2017 2016 2015 ( Thousands of dollars ) Commodity contracts $ (40,577 ) $ (78,513 ) $ 70,065 Interest-rate contracts 163 42,761 (22,565 ) Total unrealized gain (loss) recognized in other comprehensive income (loss) on derivatives (effective portion) $ (40,414 ) $ (35,752 ) $ 47,500
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 (Effective Portion) Years Ended December 31, 2017 2016 2015 ( Thousands of dollars ) Commodity contracts Commodity sales revenues $ (69,561 ) $ 26,422 $ 81,089 Interest-rate contracts Interest expense (21,025 ) (19,215 ) (17,565 ) Total gain (loss) reclassified from accumulated other comprehensive loss into net income on derivatives (effective portion) $ (90,586 ) $ 7,207 $ 63,524

PROPERTY, PLANT AND EQUIPMENT37

PROPERTY, PLANT AND EQUIPMENT (Tables)	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment by Property Type	The following table sets forth our property, plant and equipment by property type, for the periods indicated: Estimated Useful Lives (Years) December 31, December 31, ( Thousands of dollars ) Nonregulated Gathering pipelines and related equipment 5 to 40 $ 3,613,344 $ 3,352,963 Processing and fractionation and related equipment 3 to 40 3,873,709 3,831,966 Storage and related equipment 3 to 54 604,656 558,695 Transmission pipelines and related equipment 5 to 54 700,455 689,804 General plant and other 2 to 60 504,610 487,559 Construction work in process — 362,253 371,628 Regulated Storage and related equipment 5 to 25 12,486 13,524 Natural gas transmission pipelines and related equipment 5 to 77 1,406,780 1,345,740 Natural gas liquids transmission pipelines and related equipment 5 to 88 4,340,428 4,309,341 General plant and other 2 to 50 57,902 54,643 Construction work in process — 83,044 62,634 Property, plant and equipment 15,559,667 15,078,497 Accumulated depreciation and amortization - nonregulated (1,888,010 ) (1,641,490 ) Accumulated depreciation and amortization - regulated (973,531 ) (865,604 ) Net property, plant and equipment $ 12,698,126 $ 12,571,403
Average Depreciation Rates for Regulated Property	The average depreciation rates for our regulated property are set forth, by segment, in the following table for the periods indicated: Years Ended December 31, 2017 2016 2015 Natural Gas Liquids 1.9% 1.9% 1.9% Natural Gas Pipelines 2.1% 2.1% 2.1%
Impairment of long lived assets [Table Text Block]	The following table sets forth impairment charges on our long-lived assets for the periods indicated: Years Ended December 31, 2017 2016 2015 Natural Gas Gathering and Processing $ 16.0 $ — $ 73.7 Natural Gas Liquids — — 10.0 Total Impairment of long-lived assets $ 16.0 $ — $ 83.7

GOODWILL AND INTANGIBLE ASSET38

GOODWILL AND INTANGIBLE ASSETS (Tables)	12 Months Ended
	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill by Segment	The following table sets forth our goodwill, by segment, for the periods indicated: December 31, 2017 December 31, 2016 ( Thousands of dollars ) Natural Gas Gathering and Processing $ 153,404 $ 122,291 Natural Gas Liquids 371,217 268,544 Natural Gas Pipelines 156,479 134,700 Total goodwill $ 681,100 $ 525,535
Gross Carrying Amount and Accumulated Amortization of Intangible Assets	The following table reflects the gross carrying amount and accumulated amortization of intangible assets for the periods presented: December 31, December 31, ( Thousands of dollars ) Gross intangible assets $ 426,068 $ 581,633 Accumulated amortization (113,708 ) (101,809 ) Net intangible assets $ 312,360 $ 479,824

DEBT (Tables)

DEBT (Tables)	12 Months Ended
	Dec. 31, 2017
Long-term Debt, Unclassified [Abstract]
Debt	The following table sets forth our consolidated debt for the periods indicated: December 31, December 31, ( Thousands of dollars ) ONEOK Commercial paper outstanding, bearing a weighted-average interest rate of 2.23% (a) $ 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 — $100,000 at 6.5% due September 2028 — 87,126 $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 — ONEOK Partners Commercial paper outstanding (a) — 1,110,277 Senior unsecured obligations: $400,000 at 2.0% due October 2017 — 400,000 $425,000 at 3.2% due September 2018 425,000 425,000 $1,000,000 term loan, at 2.87% and 2.04%, respectively, due January 2019 (b) 500,000 1,000,000 $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 36,607 44,257 Total debt 9,198,677 9,489,057 Unamortized portion of terminated swaps 18,468 20,186 Unamortized debt issuance costs and discounts (78,193 ) (68,320 ) Current maturities of long-term debt (432,650 ) (410,650 ) Short-term borrowings (c) (614,673 ) (1,110,277 ) Long-term debt $ 8,091,629 $ 7,919,996 (a) - In July 2017, the commercial paper outstanding under the ONEOK Partners commercial paper program was repaid as it matured with a combination of proceeds from new issuances from ONEOK’s recently established $2.5 billion commercial paper program, cash on hand and proceeds from our July 2017 $1.2 billion senior notes issuance. The $2.4 billion ONEOK Partners commercial paper program was terminated in July 2017. (b) - The remaining $ 500 million of the Term Loan Agreement was repaid in January 2018. (c) - 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 the $2.5 Billion Credit Agreement.
Aggregate maturities of long-term debt outstanding	The aggregate maturities of long-term debt outstanding as of December 31, 2017, for the years 2018 through 2022 are shown below: Senior Notes Guardian Pipeline Total 2018 $ 425.0 $ 7.7 $ 432.7 2019 (a) $ 1,000.0 $ 7.7 $ 1,007.7 2020 $ 300.0 $ 7.7 $ 307.7 2021 $ — $ 7.7 $ 7.7 2022 $ 1,447.4 $ 5.8 $ 1,453.2 (a) $500 million of the $1.0 billion maturing in 2019 relates to the Term Loan Agreement, which was repaid in January 2018.

EQUITY EQUITY (Tables)

EQUITY EQUITY (Tables)	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Quarterly dividends per share paid on common stock	The following table sets forth the quarterly dividends per share paid on our common stock in the periods indicated: Years Ended December 31, 2017 2016 2015 First Quarter $ 0.615 $ 0.615 $ 0.605 Second Quarter 0.615 0.615 0.605 Third Quarter 0.745 0.615 0.605 Fourth Quarter 0.745 0.615 0.615 Total $ 2.72 $ 2.46 $ 2.43
Schedule of distributions made to general partner or limited partner	The following table sets forth ONEOK Partners’ distributions paid during the periods prior to the closing of the Merger Transaction on June 30, 2017: Years Ended December 31, 2017 2016 2015 ( Thousands, except per unit amounts ) Distribution per unit $ 1.58 $ 3.16 $ 3.16 General partner distributions $ 13,320 $ 26,640 $ 24,610 Incentive distributions 201,076 402,152 371,500 Distributions to general partner 214,396 428,792 396,110 Limited partner distributions to ONEOK 180,646 361,292 310,230 Limited partner distributions to other unitholders 270,959 541,919 524,135 Total distributions paid $ 666,001 $ 1,332,003 $ 1,230,475

ACCUMULATED OTHER COMPREHENSI41

ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Tables)	12 Months Ended
	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss)	The following table sets forth the balance in accumulated other comprehensive loss for the periods 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, 2016 $ (42,199 ) $ (84,543 ) $ (500 ) $ (127,242 ) Other comprehensive income (loss) before reclassifications (9,280 ) (22,903 ) (475 ) (32,658 ) Amounts reclassified from accumulated other comprehensive loss (676 ) 6,210 16 5,550 Other comprehensive income (loss) attributable to ONEOK (9,956 ) (16,693 ) (459 ) (27,108 ) December 31, 2016 (52,155 ) (101,236 ) (959 ) (154,350 ) Other comprehensive income (loss) before reclassifications (35,013 ) (12,337 ) (409 ) (47,759 ) Amounts reclassified from accumulated other comprehensive loss 45,541 8,162 164 53,867 Impact of Merger Transaction (Note B) (c) (40,288 ) — — (40,288 ) Other comprehensive income (loss) attributable to ONEOK (29,760 ) (4,175 ) (245 ) (34,180 ) December 31, 2017 $ (81,915 ) $ (105,411 ) $ (1,204 ) $ (188,530 ) (a) All amounts are presented net of tax. (b) Includes amounts related to supplemental executive retirement plan. (c) Includes the remaining portion of ONEOK Partners’ accumulated other comprehensive loss at June 30, 2017, that we acquired in the Merger Transaction, related to commodity and interest-rate contracts.
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 Comprehensive Loss Components Years Ended December 31, Affected Line Item in the Consolidated Statements of Income 2017 2016 2015 ( Thousands of dollars ) Unrealized gains (losses) on risk-management assets/liabilities Commodity contracts $ (69,561 ) $ 26,422 $ 81,089 Commodity sales revenues Interest-rate contracts (21,025 ) (19,215 ) (17,565 ) Interest expense (90,586 ) 7,207 63,524 Income before income taxes 26,899 (230 ) (8,815 ) Income tax expense (63,687 ) 6,977 54,709 Net income Noncontrolling interests (18,146 ) 6,301 39,415 Less: Net income attributable noncontrolling interests $ (45,541 ) $ 676 $ 15,294 Net income attributable to ONEOK Pension and postretirement benefit plan obligations (a) Amortization of net loss $ (15,265 ) $ (12,012 ) $ (17,724 ) Amortization of unrecognized prior service cost 1,662 1,662 1,568 (13,603 ) (10,350 ) (16,156 ) Income before income taxes 5,441 4,140 6,462 Income tax expense $ (8,162 ) $ (6,210 ) $ (9,694 ) Net income attributable to ONEOK Unrealized gains (losses) on risk-management assets/liabilities of unconsolidated affiliates $ (367 ) $ (63 ) $ — Equity in net earnings from investments 97 10 — Income tax expense (270 ) (53 ) — Net income Noncontrolling interests (106 ) (37 ) — Less: Net income attributable to noncontrolling interests $ (164 ) $ (16 ) $ — Net income attributable to ONEOK Total reclassifications for the period attributable to ONEOK $ (53,867 ) $ (5,550 ) $ 5,600 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 L for additional detail of our net periodic benefit cost.

EARNINGS PER SHARE EARNINGS P42

EARNINGS PER SHARE EARNINGS PER SHARE (Tables)	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Earnings Per Share	The following tables set forth the computation of basic and diluted EPS from continuing operations for the periods indicated: Year Ended December 31, 2017 Income Shares Per Share Amount ( Thousands, except per share amounts ) Basic EPS from continuing operations Income from continuing operations attributable to ONEOK available for common stock $ 387,074 297,477 $ 1.30 Diluted EPS from continuing operations Effect of dilutive securities — 2,303 Income from continuing operations attributable to ONEOK available for common stock and common stock equivalents $ 387,074 299,780 $ 1.29 Year Ended December 31, 2016 Income Shares Per Share Amount ( Thousands, except per share amounts ) Basic EPS from continuing operations Income from continuing operations attributable to ONEOK available for common stock $ 354,090 211,128 $ 1.68 Diluted EPS from continuing operations Effect of dilutive securities — 1,255 Income from continuing operations attributable to ONEOK available for common stock and common stock equivalents $ 354,090 212,383 $ 1.67 Year Ended December 31, 2015 Income Shares Per Share Amount ( Thousands, except per share amounts ) Basic EPS from continuing operations Income from continuing operations attributable to ONEOK available for common stock $ 251,058 210,208 $ 1.19 Diluted EPS from continuing operations Effect of dilutive securities — 333 Income from continuing operations attributable to ONEOK available for common stock and common stock equivalents $ 251,058 210,541 $ 1.19

SHARE-BASED PAYMENTS SHARE-BA43

SHARE-BASED PAYMENTS SHARE-BASED PAYMENTS (Tables)	12 Months Ended
	Dec. 31, 2017
Restricted Stock Units Activity
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of Share-based Compensation, Activity	The following tables set forth activity and various statistics for our restricted stock unit awards: Number of Units Weighted Average Price Nonvested December 31, 2016 881,647 $ 31.25 Granted 281,167 $ 45.11 Released to participants (141,724 ) $ 51.21 Forfeited (19,285 ) $ 32.07 Nonvested December 31, 2017 1,001,805 $ 32.30 2017 2016 2015 Weighted-average grant date fair value (per share) $ 45.11 $ 20.04 $ 42.98 Fair value of units granted (thousands of dollars) $ 12,685 $ 11,081 $ 10,186 Fair value of units vested (thousands of dollars) $ 7,258 $ 4,429 $ 6,458
Performance-Unit Activity
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of Share-based Compensation, Activity	The following tables set forth activity and various statistics related to the performance unit awards and the assumptions used in the valuations at the respective grant dates: Number of Units Weighted Average Price Nonvested December 31, 2016 1,005,751 $ 38.81 Granted 311,047 $ 56.65 Released to participants (123,459 ) $ 70.50 Forfeited (57,206 ) $ 42.29 Nonvested December 31, 2017 1,136,133 $ 40.08 2017 2016 2015 Volatility (a) 40.59% 39.94% 26.70% Dividend Yield 4.68% 11.32% 5.02% Risk-free Interest Rate 1.49% 0.93% 1.00% (a) - Volatility was based on historical volatility over three years using daily stock price observations. 2017 2016 2015 Weighted-average grant date fair value (per share) $ 56.65 $ 25.54 $ 50.30 Fair value of units granted (thousands of dollars) $ 17,621 $ 15,229 $ 13,370 Fair value of units vested (thousands of dollars) $ 8,704 $ — $ 13,736

EMPLOYEE BENEFIT PLANS EMPLOY44

EMPLOYEE BENEFIT PLANS EMPLOYEE BENEFIT PLANS (Tables)	12 Months Ended
	Dec. 31, 2017
Defined Benefit Plan [Abstract]
Pension and postretirement benefit plans obligations and fair value of plan assets	Obligations and Funded Status - The following tables set forth our pension and postretirement benefit plans benefit obligations and fair value of plan assets for the periods indicated: Pension Benefits Postretirement Benefits December 31, December 31, 2017 2016 2017 2016 Change in benefit obligation ( Thousands of dollars ) Benefit obligation, beginning of period $ 428,386 $ 390,688 $ 54,823 $ 49,496 Service cost 6,896 6,501 662 596 Interest cost 18,645 19,820 2,261 2,404 Plan participants’ contributions — — 901 894 Actuarial loss 41,678 24,458 3,456 4,905 Benefits paid (13,990 ) (13,081 ) (4,165 ) (3,472 ) Benefit obligation, end of period 481,615 428,386 57,938 54,823 Change in plan assets Fair value of plan assets, beginning of period 261,671 258,635 29,550 28,641 Actual return on plan assets 50,827 16,117 5,385 1,902 Employer contributions 7,500 — 2,000 1,000 Plan participants’ contributions — — 901 894 Benefits paid (13,990 ) (13,081 ) (3,703 ) (2,887 ) Fair value of plan assets, end of period 306,008 261,671 34,133 29,550 Balance at December 31 $ (175,607 ) $ (166,715 ) $ (23,805 ) $ (25,273 ) Current liabilities $ (4,544 ) $ (4,363 ) $ — $ — Noncurrent liabilities (171,063 ) (162,352 ) (23,805 ) (25,273 ) Balance at December 31 $ (175,607 ) $ (166,715 ) $ (23,805 ) $ (25,273 )
Components of net periodic benefit cost for pension and postretirement benefit plans	Components of Net Periodic Benefit Cost - The following table sets forth the components of net periodic benefit cost for our pension and postretirement benefit plans for the periods indicated: Pension Benefits Postretirement Benefits Years Ended December 31, Years Ended December 31, 2017 2016 2015 2017 2016 2015 ( Thousands of dollars ) Components of net periodic benefit cost Service cost $ 6,896 $ 6,501 $ 7,565 $ 662 $ 596 $ 743 Interest cost 18,645 19,820 18,218 2,261 2,404 2,347 Expected return on plan assets (21,376 ) (20,348 ) (20,900 ) (2,257 ) (2,124 ) (2,253 ) Amortization of prior service cost (credit) — — 94 (1,662 ) (1,662 ) (1,662 ) Amortization of net loss 13,586 10,966 15,981 1,679 1,046 1,743 Net periodic benefit cost $ 17,751 $ 16,939 $ 20,958 $ 683 $ 260 $ 918
Amounts recognized in other comprehensive income (loss)	Other Comprehensive Income (Loss) - The following table sets forth the amounts recognized in other comprehensive income (loss) related to our pension benefits and postretirement benefits for the periods indicated: Pension Benefits Postretirement Benefits Years Ended December 31, Years Ended December 31, 2017 2016 2015 2017 2016 2015 ( Thousands of dollars ) Net gain (loss) arising during the period $ (16,572 ) $ (33,043 ) $ 5,145 $ (328 ) $ (5,128 ) $ 4,393 Amortization of prior service cost (credit) — — 94 (1,662 ) (1,662 ) (1,662 ) Amortization of net loss 13,586 10,966 15,981 1,679 1,046 1,743 Deferred income taxes (960 ) 8,831 (8,488 ) 82 2,297 (1,790 ) Total recognized in other comprehensive income (loss) $ (3,946 ) $ (13,246 ) $ 12,732 $ (229 ) $ (3,447 ) $ 2,684
Amounts in accumulated other comprehensive income (loss)	The table below sets forth the amounts in accumulated other comprehensive loss that had not yet been recognized as components of net periodic benefit expense for the periods indicated: Pension Benefits Postretirement Benefits December 31, December 31, 2017 2016 2017 2016 ( Thousands of dollars ) Prior service credit (cost) $ — $ — $ 1,889 $ 3,550 Accumulated loss (160,921 ) (157,935 ) (12,991 ) (14,341 ) Accumulated other comprehensive loss (160,921 ) (157,935 ) (11,102 ) (10,791 ) Deferred income taxes 62,214 63,174 4,398 4,316 Accumulated other comprehensive loss, net of tax $ (98,707 ) $ (94,761 ) $ (6,704 ) $ (6,475 )
Amounts in accumulated comprehensive income (loss) expected to be recognized as components of net periodic benefit expense	The following table sets forth the amounts recognized in accumulated comprehensive loss expected to be recognized as components of net periodic benefit expense in the next fiscal year. Pension Benefits Postretirement Benefits Amounts to be recognized in 2018 ( Thousands of dollars ) Prior service (credit) cost $ — $ (1,662 ) Net loss $ 17,060 $ 1,338
Weighted-average assumptions used to determine benefit obligations and net periodic benefit costs	Actuarial Assumptions - The following table sets forth the weighted-average assumptions used to determine benefit obligations for pension and postretirement benefits for the periods indicated: Pension Benefits Postretirement Benefits December 31, December 31, 2017 2016 2017 2016 Discount rate (a) 3.75% 4.50% 3.75% 4.25% Compensation increase rate 3.00% 3.10% N/A N/A (a) The decrease in the discount rate at December 31, 2017, compared with 2016, resulted primarily from narrower credit spreads associated with the bonds in the hypothetical portfolio discussed below. The following table sets forth the weighted-average assumptions used to determine net periodic benefit costs for the periods indicated: Years Ended December 31, 2017 2016 2015 Discount rate - pension plans 4.50% 5.25% 4.50% Discount rate - postretirement plans 4.25% 5.00% 4.25% Expected long-term return on plan assets 7.75% 7.75% 8.00% Compensation increase rate 3.10% 3.10% 3.15%
Assumed health care cost trend rates	Health Care Cost Trend Rates - The following table sets forth the assumed health care cost-trend rates for the periods indicated: 2017 2016 Health care cost-trend rate assumed for next year 7.00% 7.25% Rate to which the cost-trend rate is assumed to decline (the ultimate trend rate) 5.00% 5.00% Year that the rate reaches the ultimate trend rate 2022 2022
Schedule of allocation of plan assets	Plan Assets - Our investment strategy is to invest plan assets in accordance with sound investment practices that emphasize long-term fundamentals. The goal of this strategy is to maximize investment returns while managing risk in order to meet the plan’s current and projected financial obligations. The investment policy follows a glide path approach toward liability-driven investing that shifts a higher portfolio weighting to fixed income as the plan's funded status increases. The purpose of liability-driven investing is to structure the asset portfolio to more closely resemble the pension liability and thereby more effectively hedge against changes in the liability. The plan’s current investments include a diverse blend of various domestic and international equities, investments in various classes of debt securities, insurance contracts and venture capital. The target allocation for the assets of our pension plan as of December 31, 2017, is as follows: U.S. large-cap equities 37 % Long duration bonds 30 % Developed foreign large-cap equities 10 % Alternative investments 8 % Mid-cap equities 6 % Emerging markets equities 5 % Small-cap equities 4 % Total 100 % As part of our risk management for the plans, minimums and maximums have been set for each of the asset classes listed above. All investment managers for the plan are subject to certain restrictions on the securities they purchase and, with the exception of indexing purposes, are prohibited from owning our stock. The following tables set forth our pension benefits and postretirement benefits plan assets by fair value category as of the measurement date: Pension Benefits December 31, 2017 Asset Category Level 1 Level 2 Level 3 Subtotal Measured at NAV (d) Total ( Thousands of dollars ) Investments: Equity securities (a) $ 176,347 $ 19,199 $ — $ 195,546 $ — $ 195,546 Government obligations — 19,481 — 19,481 — 19,481 Corporate obligations (b) — 62,981 — 62,981 — 62,981 Common/collective trusts — 6,621 — 6,621 — 6,621 Cash 298 — — 298 — 298 Other investments (c) — — — — 21,081 21,081 Fair value of plan assets $ 176,645 $ 108,282 $ — $ 284,927 $ 21,081 $ 306,008 (a) - This category represents securities of the respective market sector from diverse industries. (b) - This category represents bonds from diverse industries. (c) - This category represents alternative investments in limited partnerships, which can be redeemed with a 30-day notice with no further restrictions. There are no unfunded capital commitments. (d) - Plan asset investments measured at fair value using the net asset value per share. Pension Benefits December 31, 2016 Asset Category Level 1 Level 2 Level 3 Subtotal Measured at NAV (d) Total ( Thousands of dollars ) Investments: Equity securities (a) $ 146,980 $ 13,606 $ — $ 160,586 $ — $ 160,586 Government obligations — 17,979 — 17,979 — 17,979 Corporate obligations (b) — 56,484 — 56,484 — 56,484 Common/collective trusts — 6,577 — 6,577 — 6,577 Cash 43 — — 43 — 43 Other investments (c) — — — — 20,002 20,002 Fair value of plan assets $ 147,023 $ 94,646 $ — $ 241,669 $ 20,002 $ 261,671 (a) - This category represents securities of the respective market sector from diverse industries. (b) - This category represents bonds from diverse industries. (c) - This category represents alternative investments in limited partnerships, which can be redeemed with a 30-day notice with no further restrictions. There are no unfunded capital commitments. (d) - Plan asset investments measured at fair value using the net asset value per share. Postretirement Benefits December 31, 2017 Asset Category Level 1 Level 2 Level 3 Total ( Thousands of dollars ) Investments: Equity securities (a) $ 1,951 $ — $ — $ 1,951 Money market funds — 1,515 — 1,515 Insurance and group annuity contracts — 30,667 — 30,667 Fair value of plan assets $ 1,951 $ 32,182 $ — $ 34,133 (a) - This category represents securities of the respective market sector from diverse industries. Postretirement Benefits December 31, 2016 Asset Category Level 1 Level 2 Level 3 Total ( Thousands of dollars ) Investments: Equity securities (a) $ 1,777 $ — $ — $ 1,777 Money market funds — 1,259 — 1,259 Insurance and group annuity contracts — 26,514 — 26,514 Fair value of plan assets $ 1,777 $ 27,773 $ — $ 29,550 (a) - This category represents securities of the respective market sector from diverse industries.
Pension benefits and postretirement benefit payments expected to be paid	The following table sets forth the pension benefits and postretirement benefits payments expected to be paid in 2018 through 2027: Pension Benefits Postretirement Benefits Benefits to be paid in: ( Thousands of dollars ) 2018 $ 16,796 $ 3,452 2019 $ 18,011 $ 3,653 2020 $ 18,970 $ 3,859 2021 $ 20,206 $ 3,993 2022 $ 21,157 $ 4,023 2023 through 2027 $ 117,048 $ 19,302

INCOME TAXES (Tables)

INCOME TAXES (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Provision for Income Taxes	The following table sets forth our provision for income taxes for the periods indicated: Years Ended December 31, 2017 2016 2015 ( Thousands of dollars ) Current income tax provision Federal $ 295 $ 6,086 $ 13,191 State 1,670 2,449 2,967 Total current income taxes from continuing operations 1,965 8,535 16,158 Deferred income tax provision Federal 376,728 193,974 116,681 State 68,589 9,897 3,761 Total deferred income taxes from continuing operations 445,317 203,871 120,442 Total provision for income taxes from continuing operations 447,282 212,406 136,600 Discontinued operations — (1,250 ) 2,031 Total provision for income taxes $ 447,282 $ 211,156 $ 138,631
Reconciliation of Income Tax Provision	The following table is a reconciliation of our income tax provision from continuing operations and excludes discontinued operations for the periods indicated: Years Ended December 31, 2017 2016 2015 ( Thousands of dollars ) Income before income taxes $ 1,040,801 $ 957,956 $ 521,876 Less: Net income attributable to noncontrolling interests 205,678 391,460 134,218 Net income attributable to ONEOK before income taxes 835,123 566,496 387,658 Federal statutory income tax rate 35.0 % 35.0 % 35.0 % Provision for federal income taxes 292,293 198,274 135,680 State income taxes, net of federal benefit 16,197 12,303 5,800 Deferred tax rate change, inclusive of valuation allowance 141,283 43 928 Other, net (2,491 ) 1,786 (5,808 ) Income tax provision $ 447,282 $ 212,406 $ 136,600
Schedule of Deferred Tax Assets and Liabilities	The following table sets forth the tax effects of temporary differences that gave rise to significant portions of the deferred tax assets and liabilities for the periods indicated: December 31, December 31, Deferred tax assets ( Thousands of dollars ) Employee benefits and other accrued liabilities $ 85,355 $ 118,831 Federal net operating loss 159,162 26,334 State net operating loss and benefits 73,277 39,759 Derivative instruments 30,060 32,082 Other 13,546 2,425 Total deferred tax assets 361,400 219,431 Valuation allowance for state net operating loss and tax credits Carryforward expected to expire prior to utilization (66,632 ) (9,430 ) Net deferred tax assets 294,768 210,001 Deferred tax liabilities Excess of tax over book depreciation 64,508 107,249 Investment in partnerships 77,035 1,726,541 Regulatory assets 15 33 Total deferred tax liabilities 141,558 1,833,823 Net deferred tax assets (liabilities) before discontinued operations 153,210 (1,623,822 ) Discontinued operations — 10,500 Net deferred tax assets (liabilities) $ 153,210 $ (1,613,322 )

UNCONSOLIDATED AFFILIATES (Tabl

UNCONSOLIDATED AFFILIATES (Tables)	12 Months Ended
	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Schedule of Equity Method Investments	Investments in Unconsolidated Affiliates - The following table sets forth our investments in unconsolidated affiliates for the periods indicated: Net Ownership Interest December 31, December 31, ( Thousands of dollars ) Northern Border Pipeline 50% $ 396,800 $ 328,456 Overland Pass Pipeline Company 50% 436,111 444,138 Roadrunner Gas Transmission 50% 93,048 94,548 Other Various 77,197 91,665 Investments in unconsolidated affiliates (a) $ 1,003,156 $ 958,807 (a) - Equity-method goodwill (Note A ) was $38.8 million and $40.1 million at December 31, 2017 and 2016 , respectively.
Equity In Net Earnings From Investments
Schedule of Equity Method Investments [Line Items]
Schedule of Equity Method Investments	Equity in Net Earnings from Investments and Impairments - The following table sets forth our equity in net earnings from investments for the periods indicated: Years Ended December 31, 2017 2016 2015 ( Thousands of dollars ) Northern Border Pipeline $ 68,153 $ 69,990 $ 66,941 Overland Pass Pipeline Company 60,067 53,984 37,783 Roadrunner Gas Transmission 19,150 4,445 1,800 Other 11,908 11,271 18,776 Equity in net earnings from investments $ 159,278 $ 139,690 $ 125,300 Impairment of equity investments $ (4,270 ) $ — $ (180,583 )
Unconsolidated Affiliates Financial Information
Schedule of Equity Method Investments [Line Items]
Schedule of Equity Method Investments	Unconsolidated Affiliates Financial Information - The following tables set forth summarized combined financial information of our unconsolidated affiliates for the periods indicated: December 31, December 31, ( Thousands of dollars ) Balance Sheet Current assets $ 151,907 $ 143,317 Property, plant and equipment, net $ 2,490,692 $ 2,579,607 Other noncurrent assets $ 14,793 $ 20,784 Current liabilities $ 70,434 $ 77,388 Long-term debt $ 479,050 $ 649,539 Other noncurrent liabilities $ 53,830 $ 69,265 Accumulated other comprehensive loss $ (9,946 ) $ (7,450 ) Owners’ equity $ 2,064,024 $ 1,954,966 Years Ended December 31, 2017 2016 2015 ( Thousands of dollars ) Income Statement Operating revenues $ 639,102 $ 578,542 $ 524,496 Operating expenses (a) $ 277,121 $ 260,753 $ 304,930 Net income (a) $ 347,692 $ 293,921 $ 200,064 Distributions paid to us $ 196,114 $ 196,717 $ 155,918 (a) Includes long-lived asset impairment charges in 2015.

COMMITMENTS AND CONTINGENCIES47

COMMITMENTS AND CONTINGENCIES (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Future Minimum Rental Payments for Firm Transportation and Storage Contracts	The following table sets forth our firm transportation and storage contract payments for the periods indicated: Firm Transportation and Storage Contracts ( Millions of dollars ) 2018 $ 46.1 2019 37.6 2020 37.3 2021 23.0 2022 14.2 Thereafter 20.8 Total $ 179.0

SEGMENTS (Tables)

SEGMENTS (Tables)	12 Months Ended
	Dec. 31, 2017
Segment Reporting, Disclosure of Entity's Reportable Segments [Abstract]
Segments	Operating Segment Information - The following tables set forth certain selected financial information for our operating segments for the periods indicated: Year Ended December 31, 2017 Natural Gas Gathering and Processing Natural Gas Liquids (a) Natural Gas Pipelines (b) Total Segments ( Thousands of dollars ) Sales to unaffiliated customers $ 1,750,655 $ 10,009,576 $ 411,490 $ 12,171,721 Intersegment revenues 1,275,919 616,628 8,442 1,900,989 Total revenues 3,026,574 10,626,204 419,932 14,072,710 Cost of sales and fuel (exclusive of depreciation and items shown separately below) (2,216,355 ) (9,176,494 ) (43,424 ) (11,436,273 ) Operating costs (309,536 ) (359,753 ) (126,241 ) (795,530 ) Equity in net earnings from investments 12,098 59,876 87,304 159,278 Other 5,691 5,106 2,247 13,044 Segment adjusted EBITDA $ 518,472 $ 1,154,939 $ 339,818 $ 2,013,229 Depreciation and amortization $ (184,923 ) $ (167,277 ) $ (51,025 ) $ (403,225 ) Impairment of long-lived assets and equity investments $ (20,240 ) $ — $ — $ (20,240 ) Total assets $ 5,495,163 $ 8,782,700 $ 2,055,020 $ 16,332,883 Capital expenditures $ 284,205 $ 114,267 $ 95,564 $ 494,036 (a) - Our Natural Gas Liquids segment has regulated and nonregulated operations. Our Natural Gas Liquids segment’s regulated operations had revenues of $1.2 billion , of which $1.0 billion related to sales within the segment and cost of sales and fuel of $497.4 million . (b) - Our Natural Gas Pipelines segment has regulated and nonregulated operations. Our Natural Gas Pipelines segment’s regulated operations had revenues of $264.9 million and cost of sales and fuel of $44.0 million . Year Ended December 31, 2017 Total Segments Other and Eliminations Total ( Thousands of dollars ) Reconciliations of total segments to consolidated Sales to unaffiliated customers $ 12,171,721 $ 2,186 $ 12,173,907 Intersegment revenues 1,900,989 (1,900,989 ) — Total revenues $ 14,072,710 $ (1,898,803 ) $ 12,173,907 Cost of sales and fuel (exclusive of depreciation and operating costs) $ (11,436,273 ) $ 1,898,228 $ (9,538,045 ) Operating costs $ (795,530 ) $ (38,056 ) $ (833,586 ) Depreciation and amortization $ (403,225 ) $ (3,110 ) $ (406,335 ) Impairment of long-lived assets and equity investments $ (20,240 ) $ — $ (20,240 ) Equity in net earnings from investments $ 159,278 $ — $ 159,278 Total assets $ 16,332,883 $ 513,054 $ 16,845,937 Capital expenditures $ 494,036 $ 18,357 $ 512,393 Year Ended December 31, 2016 Natural Gas Gathering and Processing Natural Gas Liquids (a) Natural Gas Pipelines (b) Total Segments ( Thousands of dollars ) Sales to unaffiliated customers $ 1,375,738 $ 7,168,983 $ 373,738 $ 8,918,459 Intersegment revenues 675,839 506,671 5,623 1,188,133 Total revenues 2,051,577 7,675,654 379,361 10,106,592 Cost of sales and fuel (exclusive of depreciation and items shown separately below) (1,331,542 ) (6,321,377 ) (30,561 ) (7,683,480 ) Operating costs (285,599 ) (327,597 ) (115,628 ) (728,824 ) Equity in net earnings from investments 10,742 54,513 74,435 139,690 Other 1,600 (1,574 ) 5,530 5,556 Segment adjusted EBITDA $ 446,778 $ 1,079,619 $ 313,137 $ 1,839,534 Depreciation and amortization $ (178,548 ) $ (163,303 ) $ (46,718 ) $ (388,569 ) Total assets $ 5,320,666 $ 8,347,961 $ 1,946,318 $ 15,614,945 Capital expenditures $ 410,485 $ 105,861 $ 96,274 $ 612,620 (a) - Our Natural Gas Liquids segment has regulated and nonregulated operations. Our Natural Gas Liquids segment’s regulated operations had revenues of $1.2 billion , of which $992.8 million related to sales within the segment and cost of sales and fuel of $458.7 million . (b) - Our Natural Gas Pipelines segment has regulated and nonregulated operations. Our Natural Gas Pipelines segment’s regulated operations had revenues of $238.7 million and cost of sales and fuel of $30.0 million . Year Ended December 31, 2016 Total Segments Other and Eliminations Total ( Thousands of dollars ) Reconciliations of total segments to consolidated Sales to unaffiliated customers $ 8,918,459 $ 2,475 $ 8,920,934 Intersegment revenues 1,188,133 (1,188,133 ) — Total revenues $ 10,106,592 $ (1,185,658 ) $ 8,920,934 Cost of sales and fuel (exclusive of depreciation and operating costs) $ (7,683,480 ) $ 1,187,356 $ (6,496,124 ) Operating costs $ (728,824 ) $ (28,360 ) $ (757,184 ) Depreciation and amortization $ (388,569 ) $ (3,016 ) $ (391,585 ) Equity in net earnings from investments $ 139,690 $ — $ 139,690 Total assets $ 15,614,945 $ 523,806 $ 16,138,751 Capital expenditures $ 612,620 $ 12,014 $ 624,634 Year Ended December 31, 2015 Natural Gas Gathering and Processing Natural Gas Liquids (a) Natural Gas Pipelines (b) Total Segments ( Thousands of dollars ) Sales to unaffiliated customers $ 1,187,390 $ 6,248,002 $ 325,676 $ 7,761,068 Intersegment revenues 649,726 331,697 6,771 988,194 Total revenues 1,837,116 6,579,699 332,447 8,749,262 Cost of sales and fuel (exclusive of depreciation and items shown separately below) (1,265,617 ) (5,328,256 ) (34,481 ) (6,628,354 ) Operating costs (272,418 ) (314,505 ) (105,720 ) (692,643 ) Equity in net earnings from investments 17,863 38,696 68,741 125,300 Other 1,610 (3,342 ) 13,993 12,261 Segment adjusted EBITDA $ 318,554 $ 972,292 $ 274,980 $ 1,565,826 Depreciation and amortization $ (150,008 ) $ (158,709 ) $ (43,479 ) $ (352,196 ) Impairment of long-lived assets $ (73,681 ) $ (9,992 ) $ — $ (83,673 ) Impairment of equity investments $ (180,583 ) $ — $ — $ (180,583 ) Total assets $ 5,123,450 $ 8,017,799 $ 1,851,857 $ 14,993,106 Capital expenditures $ 887,938 $ 226,135 $ 58,215 $ 1,172,288 (a) - Our Natural Gas Liquids segment has regulated and nonregulated operations. Our Natural Gas Liquids segment’s regulated operations had revenues of $954.8 million , of which $770.1 million related to sales within the segment and cost of sales and fuel of $412.6 million . (b) - Our Natural Gas Pipelines segment has regulated and nonregulated operations. Our Natural Gas Pipelines segment’s regulated operations had revenues of $266.9 million and cost of sales and fuel of $31.1 million . Year Ended December 31, 2015 Total Segments Other and Eliminations Total ( Thousands of dollars ) Reconciliations of total segments to consolidated Sales to unaffiliated customers $ 7,761,068 $ 2,138 $ 7,763,206 Intersegment revenues 988,194 (988,194 ) — Total revenues $ 8,749,262 $ (986,056 ) $ 7,763,206 Cost of sales and fuel (exclusive of depreciation and operating costs) $ (6,628,354 ) $ 987,302 $ (5,641,052 ) Operating costs $ (692,643 ) $ (688 ) $ (693,331 ) Depreciation and amortization $ (352,196 ) $ (2,424 ) $ (354,620 ) Impairment of long-lived assets $ (83,673 ) $ — $ (83,673 ) Impairment of equity investments $ (180,583 ) $ — $ (180,583 ) Equity in net earnings from investments $ 125,300 $ — $ 125,300 Total assets $ 14,993,106 $ 453,005 $ 15,446,111 Capital expenditures $ 1,172,288 $ 16,024 $ 1,188,312 Years Ended December 31, ( Unaudited ) 2017 2016 2015 Reconciliation of income from continuing operations to total segment adjusted EBITDA ( Thousands of dollars ) Income from continuing operations $ 593,519 $ 745,550 $ 385,276 Add: Interest expense, net of capitalized interest 485,658 469,651 416,787 Depreciation and amortization 406,335 391,585 354,620 Income taxes 447,282 212,406 136,600 Impairment charges 20,240 — 264,256 Noncash compensation expense 13,421 31,981 13,799 Other corporate costs and noncash items (a) 46,774 (11,639 ) (5,512 ) Total segment adjusted EBITDA $ 2,013,229 $ 1,839,534 $ 1,565,826 (a) - The year ended December 31, 2017, includes our April 2017 $20.0 million contribution of Series E Preferred Stock to the Foundation and costs related to the Merger Transaction of $30.0 million .

QUARTERLY FINANCIAL DATA (UNA49

QUARTERLY FINANCIAL DATA (UNAUDITED) (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Data [Abstract]
Quarterly Financial Data	Year Ended December 31, 2017 First Quarter Second Quarter Third Quarter Fourth Quarter ( Thousands of dollars, except per share amounts ) Total revenues $ 2,749,611 $ 2,725,772 $ 2,906,366 $ 3,792,158 Net income $ 186,185 $ 175,991 $ 166,531 $ 64,812 Net income attributable to ONEOK $ 87,361 $ 71,693 $ 165,742 $ 63,045 Net income attributable to common shareholders $ 87,361 $ 71,476 $ 165,466 $ 62,771 Earnings per share total Basic $ 0.41 $ 0.34 $ 0.43 $ 0.16 Diluted $ 0.41 $ 0.33 $ 0.43 $ 0.16 The fourth quarter 2017 includes a one-time noncash charge of $ 141.3 million related to revaluation of our deferred tax balances and a valuation allowance on certain state net operating loss and tax credit carryforwards resulting from the enactment of the Tax Cuts and Jobs Act, as described in Note M. The third quarter 2017 includes noncash impairment charges of $20.2 million related to Natural Gas Gathering and Processing assets and equity investments. The second quarter 2017 includes a $20.0 million noncash expense related to our Series E Preferred Stock contribution to the Foundation and operating costs related to the Merger Transaction of $30.0 million . First Quarter Second Quarter Third Quarter Fourth Quarter Year Ended December 31, 2016 ( Thousands of dollars except per share amounts ) Total revenues $ 1,774,459 $ 2,134,107 $ 2,357,907 $ 2,654,461 Income from continuing operations $ 175,911 $ 180,086 $ 194,792 $ 194,761 Income (loss) from discontinued operations, net of tax $ (952 ) $ (227 ) $ (576 ) $ (296 ) Net income $ 174,959 $ 179,859 $ 194,216 $ 194,465 Net income attributable to ONEOK $ 83,446 $ 85,944 $ 92,144 $ 90,505 Earnings per share total Basic $ 0.40 $ 0.41 $ 0.44 $ 0.43 Diluted $ 0.40 $ 0.40 $ 0.43 $ 0.43

SUPPLEMENTAL CONDENSED CONSOL50

SUPPLEMENTAL CONDENSED CONSOLIDATING FINANCIAL INFORMATION (Tables)	12 Months Ended
	Dec. 31, 2017
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Condensed Consolidating Statements of Income	Year Ended December 31, 2017 Parent Issuer & Guarantor Subsidiary Issuer & Guarantor Guarantor Subsidiary Combined Non-Guarantor Subsidiaries Consolidating Entries Total ( Millions of dollars ) Revenues Commodity sales $ — $ — $ — $ 9,862.7 $ — $ 9,862.7 Services — — — 2,313.2 (2.0 ) 2,311.2 Total revenues — — — 12,175.9 (2.0 ) 12,173.9 Cost of sales and fuel (exclusive of items shown separately below) — — — 9,538.0 — 9,538.0 Operating expenses 28.7 — 9.2 1,204.0 (2.0 ) 1,239.9 Impairment of long-lived assets — — — 16.0 — 16.0 Gain on sale of assets — — — (0.9 ) — (0.9 ) Operating income (28.7 ) — (9.2 ) 1,418.8 — 1,380.9 Equity in net earnings from investments 1,236.6 1,215.7 1,224.9 100.7 (3,618.6 ) 159.3 Impairment of equity investments — — — (4.3 ) — (4.3 ) Other income (expense), net (1.4 ) 353.1 353.1 (8.0 ) (706.2 ) (9.4 ) Interest expense, net (137.1 ) (353.1 ) (353.1 ) (348.6 ) 706.2 (485.7 ) Income before income taxes 1,069.4 1,215.7 1,215.7 1,158.6 (3,618.6 ) 1,040.8 Income taxes (480.2 ) — — 32.9 — (447.3 ) Net income 589.2 1,215.7 1,215.7 1,191.5 (3,618.6 ) 593.5 Less: Net income attributable to noncontrolling interests 201.4 — — 4.3 — 205.7 Net income attributable to ONEOK 387.8 1,215.7 1,215.7 1,187.2 (3,618.6 ) 387.8 Less: Preferred stock dividends 0.8 — — — — 0.8 Net income available to common shareholders $ 387.0 $ 1,215.7 $ 1,215.7 $ 1,187.2 $ (3,618.6 ) $ 387.0 Year Ending December 31, 2016 Parent Issuer & Guarantor Subsidiary Issuer & Guarantor Guarantor Subsidiary Combined Non-Guarantor Subsidiaries Consolidating Entries Total ( Millions of dollars ) Revenues Commodity sales $ — $ — $ — $ 6,858.5 $ — $ 6,858.5 Services — — — 2,064.3 (1.8 ) 2,062.5 Total revenues — — — 8,922.8 (1.8 ) 8,921.0 Cost of sales and fuel (exclusive of items shown separately below) — — — 6,496.1 — 6,496.1 Operating expenses 28.8 — — 1,121.8 (1.8 ) 1,148.8 (Gain) loss on sale of assets 0.3 — — (9.9 ) — (9.6 ) Operating income (29.1 ) — — 1,314.8 — 1,285.7 Equity in net earnings from investments 1,063.9 1,066.8 1,066.8 69.7 (3,127.5 ) 139.7 Other income (expense), net 5.1 373.5 373.5 (2.8 ) (747.0 ) 2.3 Interest expense, net (102.9 ) (373.5 ) (373.5 ) (366.8 ) 747.0 (469.7 ) Income before income taxes 937.0 1,066.8 1,066.8 1,014.9 (3,127.5 ) 958.0 Income taxes (199.0 ) — — (13.4 ) — (212.4 ) Income from continuing operations 738.0 1,066.8 1,066.8 1,001.5 (3,127.5 ) 745.6 Income (loss) from discontinued operations, net of tax — — — (2.1 ) — (2.1 ) Net income 738.0 1,066.8 1,066.8 999.4 (3,127.5 ) 743.5 Less: Net income attributable to noncontrolling interests 386.0 — — 5.5 — 391.5 Net income attributable to ONEOK $ 352.0 $ 1,066.8 $ 1,066.8 $ 993.9 $ (3,127.5 ) $ 352.0 Year Ending December 31, 2015 Parent Issuer & Guarantor Subsidiary Issuer & Guarantor Guarantor Subsidiary Combined Non-Guarantor Subsidiaries Consolidating Entries Total ( Millions of dollars ) Revenues Commodity sales $ — $ — $ — $ 6,098.3 $ — $ 6,098.3 Services — — — 1,669.8 (4.9 ) 1,664.9 Total revenues — — — 7,768.1 (4.9 ) 7,763.2 Cost of sales and fuel (exclusive of items shown separately below) — — — 5,641.1 — 5,641.1 Operating expenses 1.2 — — 1,051.5 (4.9 ) 1,047.8 Impairment of long-lived assets — — — 83.7 — 83.7 Gain on sale of assets — — — (5.6 ) — (5.6 ) Operating income (1.2 ) — — 997.4 — 996.2 Equity in net earnings from investments 583.8 589.5 589.5 58.4 (1,695.9 ) 125.3 Impairment of equity investments — — — (180.6 ) — (180.6 ) Other income (expense), net 4.0 371.0 371.0 (6.2 ) (742.0 ) (2.2 ) Interest expense, net (85.1 ) (371.0 ) (371.0 ) (331.7 ) 742.0 (416.8 ) Income before income taxes 501.5 589.5 589.5 537.3 (1,695.9 ) 521.9 Income taxes (130.7 ) — — (5.9 ) — (136.6 ) Income from continuing operations 370.8 589.5 589.5 531.4 (1,695.9 ) 385.3 Income (loss) from discontinued operations, net of tax — — — (6.1 ) — (6.1 ) Net income 370.8 589.5 589.5 525.3 (1,695.9 ) 379.2 Less: Net income attributable to noncontrolling interests 125.8 — — 8.4 — 134.2 Net income attributable to ONEOK $ 245.0 $ 589.5 $ 589.5 $ 516.9 $ (1,695.9 ) $ 245.0
Condensed Consolidating Statements of Comprehensive Income	Year Ended December 31, 2017 Parent Issuer & Guarantor Subsidiary Issuer & Guarantor Guarantor Subsidiary Combined Non-Guarantor Subsidiaries Consolidating Entries Total ( Millions of dollars ) Net income $ 589.2 $ 1,215.7 $ 1,215.7 $ 1,191.5 $ (3,618.6 ) $ 593.5 Other comprehensive income (loss), net of tax Unrealized gains (losses) on derivatives, net of tax 19.1 (72.2 ) (40.6 ) (8.8 ) 81.1 (21.4 ) Realized (gains) losses on derivatives in net income, net of tax 2.5 86.5 69.6 44.3 (139.2 ) 63.7 Change in pension and postretirement benefit plan liability, net of tax (4.2 ) — — — — (4.2 ) Other comprehensive income (loss) on investments in unconsolidated affiliates, net of tax — (1.1 ) (1.1 ) (1.0 ) 2.2 (1.0 ) Total other comprehensive income (loss), net of tax 17.4 13.2 27.9 34.5 (55.9 ) 37.1 Comprehensive income 606.6 1,228.9 1,243.6 1,226.0 (3,674.5 ) 630.6 Less: Comprehensive income attributable to noncontrolling interests 232.4 — — 4.3 — 236.7 Comprehensive income attributable to ONEOK $ 374.2 $ 1,228.9 $ 1,243.6 $ 1,221.7 $ (3,674.5 ) $ 393.9 Year Ending December 31, 2016 Parent Issuer & Guarantor Subsidiary Issuer & Guarantor Guarantor Subsidiary Combined Non-Guarantor Subsidiaries Consolidating Entries Total ( Millions of dollars ) Net income $ 738.0 $ 1,066.8 $ 1,066.8 $ 999.4 $ (3,127.5 ) $ 743.5 Other comprehensive income (loss), net of tax Unrealized gains (losses) on derivatives, net of tax — (35.8 ) (78.5 ) (108.8 ) 192.8 (30.3 ) Realized (gains) losses on derivatives in net income, net of tax 2.1 (10.7 ) (26.4 ) (33.4 ) 61.4 (7.0 ) Change in pension and postretirement benefit plan liability, net of tax (16.7 ) — — — — (16.7 ) Other comprehensive income (loss) on investments in unconsolidated affiliates, net of tax — (1.8 ) (1.8 ) (3.3 ) 5.4 (1.5 ) Total other comprehensive income (loss), net of tax (14.6 ) (48.3 ) (106.7 ) (145.5 ) 259.6 (55.5 ) Comprehensive income 723.4 1,018.5 960.1 853.9 (2,867.9 ) 688.0 Less: Comprehensive income attributable to noncontrolling interests 357.6 — — 5.5 — 363.1 Comprehensive income attributable to ONEOK $ 365.8 $ 1,018.5 $ 960.1 $ 848.4 $ (2,867.9 ) $ 324.9 Year Ending December 31, 2015 Parent Issuer & Guarantor Subsidiary Issuer & Guarantor Guarantor Subsidiary Combined Non-Guarantor Subsidiaries Consolidating Entries Total ( Millions of dollars ) Net income $ 370.8 $ 589.5 $ 589.5 $ 525.3 $ (1,695.9 ) $ 379.2 Other comprehensive income (loss), net of tax Unrealized gains (losses) on derivatives, net of tax — 47.5 70.1 111.5 (187.7 ) 41.4 Realized (gains) losses on derivatives in net income, net of tax 2.1 (67.0 ) (81.1 ) (137.9 ) 229.2 (54.7 ) Unrealized holding gains (losses) on available-for-sale securities, net of tax — — — (1.0 ) — (1.0 ) Change in pension and postretirement benefit plan liability, net of tax 15.4 — — — — 15.4 Other comprehensive income (loss) on investments in unconsolidated affiliates, net of tax — (1.9 ) (1.9 ) (3.5 ) 5.7 (1.6 ) Total other comprehensive income (loss), net of tax 17.5 (21.4 ) (12.9 ) (30.9 ) 47.2 (0.5 ) Comprehensive income 388.3 568.1 576.6 494.4 (1,648.7 ) 378.7 Less: Comprehensive income attributable to noncontrolling interests 116.2 — — 8.4 — 124.6 Comprehensive income attributable to ONEOK $ 272.1 $ 568.1 $ 576.6 $ 486.0 $ (1,648.7 ) $ 254.1
Condensed Consolidating Balance Sheets	December 31, 2017 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 December 31, 2016 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 $ 248.5 $ — $ 0.4 $ — $ — $ 248.9 Accounts receivable, net — — — 872.4 — 872.4 Materials and supplies — — — 60.9 — 60.9 Natural gas and natural gas liquids in storage — — — 140.0 — 140.0 Other current assets 7.2 — — 99.7 — 106.9 Assets of discontinued operations — — — 0.6 — 0.6 Total current assets 255.7 — 0.4 1,173.6 — 1,429.7 Property, plant and equipment Property, plant and equipment 139.8 — — 14,938.7 — 15,078.5 Accumulated depreciation and amortization 90.4 — — 2,416.7 — 2,507.1 Net property, plant and equipment 49.4 — — 12,522.0 — 12,571.4 Investments and other assets Investments 2,931.9 3,222.1 6,805.4 631.1 (12,631.7 ) 958.8 Intercompany notes receivable 205.2 10,615.0 7,031.3 — (17,851.5 ) — Goodwill and intangible assets — — — 1,005.4 — 1,005.4 Other assets 103.4 47.5 — 12.1 — 163.0 Assets of discontinued operations — — — 10.5 — 10.5 Total investments and other assets 3,240.5 13,884.6 13,836.7 1,659.1 (30,483.2 ) 2,137.7 Total assets $ 3,545.6 $ 13,884.6 $ 13,837.1 $ 15,354.7 $ (30,483.2 ) $ 16,138.8 Liabilities and equity Current liabilities Current maturities of long-term debt $ 3.0 $ 400.0 $ — $ 7.7 $ — $ 410.7 Short-term borrowings — 1,110.3 — — — 1,110.3 Accounts payable 13.0 — — 861.7 — 874.7 Commodity imbalances — — — 142.6 — 142.6 Accrued interest 25.4 87.1 — — — 112.5 Other current liabilities 19.3 12.8 — 134.1 — 166.2 Liabilities of discontinued operations — — — 19.8 — 19.8 Total current liabilities 60.7 1,610.2 — 1,165.9 — 2,836.8 Intercompany debt — — 10,615.0 7,236.5 (17,851.5 ) — Long-term debt, excluding current maturities 1,628.7 6,254.7 — 36.6 — 7,920.0 Deferred credits and other liabilities 1,667.5 — — 285.6 — 1,953.1 Commitments and contingencies Equity Equity excluding noncontrolling interests in consolidated subsidiaries 188.7 6,019.7 3,222.1 6,472.0 (15,713.8 ) 188.7 Noncontrolling interests in consolidated subsidiaries — — — 158.1 3,082.1 3,240.2 Total equity 188.7 6,019.7 3,222.1 6,630.1 (12,631.7 ) 3,428.9 Total liabilities and equity $ 3,545.6 $ 13,884.6 $ 13,837.1 $ 15,354.7 $ (30,483.2 ) $ 16,138.8
Condensed Consolidating Statements of Cash Flows	Year Ended December 31, 2017 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 $ 947.4 $ 1,348.3 $ 59.0 $ 1,353.7 $ (2,393.0 ) $ 1,315.4 Investing activities Capital expenditures — — — (512.4 ) — (512.4 ) Contributions to unconsolidated affiliates — — (83.0 ) (4.9 ) — (87.9 ) Other investing activities — — 14.8 17.9 — 32.7 Cash used in investing activities — — (68.2 ) (499.4 ) — (567.6 ) Financing activities Dividends paid (829.4 ) (1,332.0 ) (1,332.0 ) — 2,664.0 (829.4 ) Distributions to noncontrolling interests — — — (5.3 ) (271.0 ) (276.3 ) Intercompany borrowings (advances), net (2,500.7 ) 2,001.2 1,340.8 (841.3 ) — — Borrowing (repayment) of short-term borrowings, net 614.7 (1,110.3 ) — — — (495.6 ) Issuance of long-term debt, net of discounts 1,190.5 — — — — 1,190.5 Repayment of long-term debt (87.1 ) (900.0 ) — (7.7 ) — (994.8 ) Issuance of common stock 471.4 — — — — 471.4 Other (18.1 ) (7.2 ) — — — (25.3 ) Cash provided by (used in) financing activities (1,158.7 ) (1,348.3 ) 8.8 (854.3 ) 2,393.0 (959.5 ) Change in cash and cash equivalents (211.3 ) — (0.4 ) — — (211.7 ) Cash and cash equivalents at beginning of period 248.5 — 0.4 — — 248.9 Cash and cash equivalents at end of period $ 37.2 $ — $ — $ — $ — $ 37.2 Year Ending December 31, 2016 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 $ 717.0 $ 1,334.5 $ 70.0 $ 1,353.9 $ (2,122.1 ) $ 1,353.3 Investing activities Capital expenditures (0.2 ) — — (624.4 ) — (624.6 ) Other investing activities — — 34.9 (25.7 ) — 9.2 Cash provided by (used in) investing activities (0.2 ) — 34.9 (650.1 ) — (615.4 ) Financing activities Dividends paid (517.6 ) (1,332.0 ) (1,332.0 ) — 2,664.0 (517.6 ) Distributions to noncontrolling interests — — — (7.5 ) (541.9 ) (549.4 ) Intercompany borrowings (advances), net (63.1 ) (470.8 ) 1,222.4 (688.5 ) — — Borrowing (repayment) of short-term borrowings, net — 563.9 — — — 563.9 Issuance of long-term debt, net of discounts — 1,000.0 — — — 1,000.0 Debt financing costs — (2.8 ) — — — (2.8 ) Repayment of long-term debt (0.3 ) (1,100.0 ) — (7.7 ) — (1,108.0 ) Issuance of common stock 22.0 — — — — 22.0 Other (1.7 ) 7.2 — (0.1 ) — 5.4 Cash used in financing activities (560.7 ) (1,334.5 ) (109.6 ) (703.8 ) 2,122.1 (586.5 ) Change in cash and cash equivalents 156.1 — (4.7 ) — — 151.4 Change in cash and cash equivalents included in discontinued operations (0.1 ) — — — — (0.1 ) Change in cash and cash equivalents included in continuing operations 156.0 — (4.7 ) — — 151.3 Cash and cash equivalents at beginning of period 92.5 — 5.1 — — 97.6 Cash and cash equivalents at end of period $ 248.5 $ — $ 0.4 $ — $ — $ 248.9 Year Ending December 31, 2015 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 $ 650.3 $ 1,196.7 $ 66.9 $ 1,045.7 $ (1,936.8 ) $ 1,022.8 Investing activities Capital expenditures (0.1 ) — — (1,188.2 ) — (1,188.3 ) Contributions to investments (671.0 ) — — (27.5 ) 671.0 (27.5 ) Other investing activities — — 24.1 1.0 — 25.1 Cash provided by (used in) investing activities (671.1 ) — 24.1 (1,214.7 ) 671.0 (1,190.7 ) Financing activities Dividends paid (509.2 ) (1,230.5 ) (1,230.5 ) — 2,461.0 (509.2 ) Distributions to noncontrolling interests — — — (11.7 ) (524.2 ) (535.9 ) Intercompany borrowings (advances), net 4.6 (1,295.1 ) 1,102.1 188.4 — — Borrowing (repayment) of short-term borrowings, net — (509.0 ) — — — (509.0 ) Issuance of long-term debt, net of discounts 492.6 798.9 — — — 1,291.5 Debt financing costs (9.8 ) (7.7 ) — — — (17.5 ) Repayment of long-term debt (0.1 ) — — (7.7 ) — (7.8 ) Issuance of common stock 20.7 — — — — 20.7 Issuance of common units, net of issuance costs — 1,025.7 — — (650.0 ) 375.7 Contribution from general partner — 21.0 — — (21.0 ) — Other (15.8 ) — — — — (15.8 ) Cash provided by (used) in financing activities (17.0 ) (1,196.7 ) (128.4 ) 169.0 1,265.8 92.7 Change in cash and cash equivalents (37.8 ) — (37.4 ) — — (75.2 ) Cash and cash equivalents at beginning of period 130.3 — 42.5 — — 172.8 Cash and cash equivalents at end of period $ 92.5 $ — $ 5.1 $ — $ — $ 97.6

SUMMARY OF SIGNIFICANT ACCOUN51

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Entity [Line Items]
Common Stock, Shares, Issued	423,166,234		245,811,180
Regulatory Assets	$ 5		$ 5.5
Maximum Time Period Regulatory Assets Are Being Recovered (In Years)	50 years
Number Of Years Of Service Employees Must Work To Be Entitled To Postretirement Medical And Life Insurance Benefits	5 years
ONEOK
Entity [Line Items]
Common Stock, Shares, Issued		168,900,000
Oneok Partners [Member]
Entity [Line Items]
Common Units, Outstanding		171,500,000

ONEOK PARTNERS ACQUISITION ON52

ONEOK PARTNERS ACQUISITION ONEOK PARTNERS ACQUISITION (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Business Acquisition, Date of Acquisition Agreement	Jun. 30, 2017
Business Acquisition, Description of Acquired Entity	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. No fractional shares were issued in the Merger Transaction, and ONEOK Partners common unitholders instead received cash in lieu of fractional shares. As a result of the completion of the Merger Transaction, common units of ONEOK Partners are no longer publicly traded.
Deferred Tax Assets, Gross, Noncurrent	$ 2,100,000
Deferred Tax Asset, Tax Basis	8,800,000
Deferred Tax Asset, Book Basis	$ 3,000,000
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		21.00%	35.00%	35.00%	35.00%
General partner ownership interest	41.20%
Common stock			$ 471,358	$ 21,971	$ 20,669
Accumulated other comprehensive loss			(40,288)
Noncontrolling interests in consolidated subsidiaries			$ 2,146,462
ONEOK
Business Acquisition [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	37.00%
Common stock	$ 1,700
Paid-in capital	5,228,600
Accumulated other comprehensive loss	(40,300)
Noncontrolling interests in consolidated subsidiaries	(3,043,500)
Deferred income taxes	$ (2,146,500)

FAIR VALUE MEASUREMENTS - Part

FAIR VALUE MEASUREMENTS - Part 1 (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
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	49,700	67,700
Cash posted - offsetting derivative net liability positions under master-netting arrangements	29,500	51,600
Cash posted - remaining in excess of derivative net liability positions included in consolidated Balance Sheets	20,200	16,100
Long-term Debt, Fair Value	9,300,000	8,800,000
Long-term Debt	8,500,000	8,300,000
Fair Value, Measurements, Recurring [Member]
Derivative assets
Financial contracts	0	951
Interest-rate contracts	49,960	47,457
Total derivative assets	49,960	48,408
Derivative assets netting	(24,455)	(4,760)
Derivative Liabilities
Financial contracts	(32)	0
Physical contracts	(4,781)	(3,022)
Interest-rate contracts		(12,795)
Total derivative liabilities	(4,813)	(15,817)
Derivative liabilities netting	53,936	56,319
Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member]
Derivative assets
Financial contracts	24,455	5,711
Interest-rate contracts	49,960	47,457
Total derivative assets	74,415	53,168
Derivative Liabilities
Financial contracts	(53,968)	(56,319)
Physical contracts	(4,781)	(3,022)
Interest-rate contracts		(12,795)
Total derivative liabilities	(58,749)	(72,136)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Derivative assets
Financial contracts	4,252	1,147
Interest-rate contracts	0	0
Total derivative assets	4,252	1,147
Derivative Liabilities
Financial contracts	(5,708)	(31,458)
Physical contracts	0	0
Interest-rate contracts		0
Total derivative liabilities	(5,708)	(31,458)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Derivative assets
Financial contracts	0	0
Interest-rate contracts	49,960	47,457
Total derivative assets	49,960	47,457
Derivative Liabilities
Financial contracts	0	0
Physical contracts	0	0
Interest-rate contracts		(12,795)
Total derivative liabilities	0	(12,795)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Derivative assets
Financial contracts	20,203	4,564
Interest-rate contracts	0	0
Total derivative assets	20,203	4,564
Derivative Liabilities
Financial contracts	(48,260)	(24,861)
Physical contracts	(4,781)	(3,022)
Interest-rate contracts		0
Total derivative liabilities	$ (53,041)	$ (27,883)

FAIR VALUE MEASUREMENTS - Par54

FAIR VALUE MEASUREMENTS - Part 2 (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets And Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Net assets (liabilities) at beginning of period	$ (23,319)	$ 7,331
Total realized/unrealized gains (losses):
Included in earnings	212	(320)
Included in other comprehensive income (loss)	(9,731)	(30,330)
Net assets (liabilities) at end of period	(32,838)	(23,319)
Transfers between levels	$ 0	$ 0

RISK MANAGEMENT AND HEDGING A55

RISK MANAGEMENT AND HEDGING ACTIVITIES USING DERIVATIVES - Part 1 (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Assets	$ 74,415,000	$ 53,168,000
(Liabilities)	(58,749,000)	(72,136,000)
Derivative, Net Liability Position, Aggregate Fair Value	0
Derivatives designated as hedging instruments
Derivatives, Fair Value [Line Items]
Assets	66,938,000	48,822,000
(Liabilities)	(51,438,000)	(67,897,000)
Derivatives not designated as hedging instruments
Derivatives, Fair Value [Line Items]
Assets	7,477,000	4,346,000
(Liabilities)	(7,311,000)	(4,239,000)
Natural Gas Pipelines
Derivatives, Fair Value [Line Items]
Derivative, Fair Value, Net	0	0
Other Current Assets [Member] | Commodity contracts | Financial contracts | Derivatives designated as hedging instruments
Derivatives, Fair Value [Line Items]
Assets	16,978,000	1,155,000
Other Current Assets [Member] | Commodity contracts | Financial contracts | Derivatives not designated as hedging instruments
Derivatives, Fair Value [Line Items]
Assets	7,477,000	4,346,000
Other Current Assets [Member] | Commodity contracts | Physical contracts | Derivatives designated as hedging instruments
Derivatives, Fair Value [Line Items]
Assets	0	0
Other Current Assets [Member] | Interest Rate Contracts | Derivatives designated as hedging instruments
Derivatives, Fair Value [Line Items]
Assets	1,330,000	0
Other Current Liabilities [Member] | Commodity contracts | Financial contracts | Derivatives designated as hedging instruments
Derivatives, Fair Value [Line Items]
(Liabilities)	(42,819,000)	(49,938,000)
Other Current Liabilities [Member] | Commodity contracts | Financial contracts | Derivatives not designated as hedging instruments
Derivatives, Fair Value [Line Items]
(Liabilities)	(7,311,000)	(4,239,000)
Other Current Liabilities [Member] | Commodity contracts | Physical contracts | Derivatives designated as hedging instruments
Derivatives, Fair Value [Line Items]
(Liabilities)	(4,781,000)	(3,022,000)
Other Current Liabilities [Member] | Interest Rate Contracts | Derivatives designated as hedging instruments
Derivatives, Fair Value [Line Items]
(Liabilities)	0	(12,795,000)
Other Assets [Member] | Commodity contracts | Financial contracts | Derivatives designated as hedging instruments
Derivatives, Fair Value [Line Items]
Assets	0	210,000
Other Assets [Member] | Interest Rate Contracts | Derivatives designated as hedging instruments
Derivatives, Fair Value [Line Items]
Assets	48,630,000	47,457,000
Other Deferred Credits | Commodity contracts | Financial contracts | Derivatives designated as hedging instruments
Derivatives, Fair Value [Line Items]
(Liabilities)	(3,838,000)	(2,142,000)
Other Deferred Credits | Interest Rate Contracts | Derivatives designated as hedging instruments
Derivatives, Fair Value [Line Items]
(Liabilities)	$ 0	$ 0

RISK MANAGEMENT AND HEDGING A56

RISK MANAGEMENT AND HEDGING ACTIVITIES USING DERIVATIVES - Part 2 (Details) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)MMcfMMBbls	Sep. 30, 2017USD ($)	Dec. 31, 2016USD ($)MMcfMMBbls
Derivative [Line Items]
Notional Amount Of Cash Flow Hedge Instruments Settled | $		$ 400
Senior Notes, Noncurrent | $		$ 1,200	$ 1,200
Derivatives designated as hedging instruments | Futures and swaps | Natural gas (Bcf) | Fixed price | Purchased/Payor
Derivative [Line Items]
Notional amount		0		0
Derivatives designated as hedging instruments | Futures and swaps | Natural gas (Bcf) | Fixed price | Sold/Receiver
Derivative [Line Items]
Notional amount		(24,500)		(38,400)
Derivatives designated as hedging instruments | Futures and swaps | Natural gas (Bcf) | Basis | Purchased/Payor
Derivative [Line Items]
Notional amount		0		0
Derivatives designated as hedging instruments | Futures and swaps | Natural gas (Bcf) | Basis | Sold/Receiver
Derivative [Line Items]
Notional amount		(24,500)		(38,400)
Derivatives designated as hedging instruments | Put options | Natural gas (Bcf) | Fixed price | Purchased/Payor
Derivative [Line Items]
Notional amount		0		49,500
Derivatives designated as hedging instruments | Put options | Natural gas (Bcf) | Fixed price | Sold/Receiver
Derivative [Line Items]
Notional amount		0		0
Derivatives designated as hedging instruments | Futures, forwards and swaps | Crude oils and NGLs (MMBbl) | Fixed price | Purchased/Payor
Derivative [Line Items]
Notional amount | MMBbls		3.5		0
Derivatives designated as hedging instruments | Futures, forwards and swaps | Crude oils and NGLs (MMBbl) | Fixed price | Sold/Receiver
Derivative [Line Items]
Notional amount | MMBbls		(11.1)		(3.6)
Derivatives designated as hedging instruments | Interest Rate Contracts | Purchased/Payor
Derivative [Line Items]
Derivative, Notional Amount | $		$ 1,750		$ 2,150
Derivatives designated as hedging instruments | Interest Rate Contracts | Sold/Receiver
Derivative [Line Items]
Derivative, Notional Amount | $		$ 0		$ 0
Derivatives not designated as hedging instruments | Futures and swaps | Natural gas (Bcf) | Fixed price | Purchased/Payor
Derivative [Line Items]
Notional amount		0		400
Derivatives not designated as hedging instruments | Futures and swaps | Natural gas (Bcf) | Fixed price | Sold/Receiver
Derivative [Line Items]
Notional amount		0		0
Derivatives not designated as hedging instruments | Futures and swaps | Natural gas (Bcf) | Basis | Purchased/Payor
Derivative [Line Items]
Notional amount		0		400
Derivatives not designated as hedging instruments | Futures and swaps | Natural gas (Bcf) | Basis | Sold/Receiver
Derivative [Line Items]
Notional amount		0		0
Derivatives not designated as hedging instruments | Futures, forwards and swaps | Crude oils and NGLs (MMBbl) | Fixed price | Purchased/Payor
Derivative [Line Items]
Notional amount | MMBbls		0.8		0.5
Derivatives not designated as hedging instruments | Futures, forwards and swaps | Crude oils and NGLs (MMBbl) | Fixed price | Sold/Receiver
Derivative [Line Items]
Notional amount | MMBbls		(0.8)		(0.7)
LIBOR Based Interest Payments [Member] | Cash Flow Hedging [Member] | Forward contracts | Interest Rate Contracts
Derivative [Line Items]
Derivative, Notional Amount | $		$ 500		$ 1,000
LIBOR Based Interest Payments [Member] | Cash Flow Hedging [Member] | Forward contracts | Interest Rate Contracts | Subsequent Event [Member]
Derivative [Line Items]
Notional Amount Of Cash Flow Hedge Instruments Settled | $	$ 500
Forecasted Debt Issuances [Member] | Cash Flow Hedging [Member] | Forward contracts | Interest Rate Contracts
Derivative [Line Items]
Derivative, Notional Amount | $		1,300		$ 1,200
Derivative, Notional Amount, New Contracts | $		$ 500

RISK MANAGEMENT AND HEDGING A57

RISK MANAGEMENT AND HEDGING ACTIVITIES USING DERIVATIVES - Part 3 (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Accumulated other comprehensive loss	$ (188,530)	$ (154,350)	$ (127,242)
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	(35,013)	(9,280)
Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	(40,414)	(35,752)	47,500
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(90,586)	7,207	63,524
Commodity contracts | 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	(21,700)
Price Risk Cash Flow Hedge Unrealized Gain (Loss) to be Reclassified During Next 12 Months	(19,300)
Commodity Cash Flow Hedge Gain (Loss) To Be Reclassified After Next 12 Months Net	(2,400)
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	(40,577)	(78,513)	70,065
Commodity contracts | Commodity sales revenues | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	(69,561)	26,422	81,089
Interest Rate Contracts | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of accumulated other comprehensive income (loss) attributable primarily to settled interest-rate swaps.	(87,600)
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net	(14,000)
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	163	42,761	(22,565)
Interest Rate Contracts | Interest expense | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	$ (21,025)	$ (19,215)	$ (17,565)

PROPERTY, PLANT AND EQUIPMENT -

PROPERTY, PLANT AND EQUIPMENT - (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 15,559,667,000	$ 15,078,497,000
Accumulated depreciation and amortization	(2,861,541,000)	(2,507,094,000)
Property, Plant and Equipment, Net	12,698,126,000	12,571,403,000
Construction in Progress Expenditures Incurred but Not yet Paid	92,400,000	83,000,000	$ 115,700,000
Impairment of long-lived assets	15,970,000	0	83,673,000
Equity Method Investment, Other than Temporary Impairment	4,270,000	0	180,583,000
Natural Gas Gathering And Processing
Property, Plant and Equipment [Line Items]
Impairment of long-lived assets			63,500,000
Natural Gas Gathering And Processing and Natural Gas Liquids [Member]
Property, Plant and Equipment [Line Items]
Impairment of long-lived assets			20,200,000
Natural Gas Gathering And Processing
Property, Plant and Equipment [Line Items]
Impairment of long-lived assets	15,970,000	0	73,681,000
Equity Method Investment, Other than Temporary Impairment			180,583,000
Natural Gas Liquids
Property, Plant and Equipment [Line Items]
Impairment of long-lived assets	0	0	9,992,000
Equity Method Investment, Other than Temporary Impairment			$ 0
Non-Regulated Property, Plant and Equipment [Member]
Property, Plant and Equipment [Line Items]
Accumulated depreciation and amortization	(1,888,010,000)	(1,641,490,000)
Non-Regulated Property, Plant and Equipment [Member] | Gathering pipelines and related equipment
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 3,613,344,000	3,352,963,000
Non-Regulated Property, Plant and Equipment [Member] | Gathering pipelines and related equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	5 years
Non-Regulated Property, Plant and Equipment [Member] | Gathering pipelines and related equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	40 years
Non-Regulated Property, Plant and Equipment [Member] | Processing and fractionation and related equipment
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 3,873,709,000	3,831,966,000
Non-Regulated Property, Plant and Equipment [Member] | Processing and fractionation and related equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Non-Regulated Property, Plant and Equipment [Member] | Processing and fractionation and related equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	40 years
Non-Regulated Property, Plant and Equipment [Member] | Storage and related equipment
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 604,656,000	558,695,000
Non-Regulated Property, Plant and Equipment [Member] | Storage and related equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Non-Regulated Property, Plant and Equipment [Member] | Storage and related equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	54 years
Non-Regulated Property, Plant and Equipment [Member] | Transmission pipelines and related equipment
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 700,455,000	689,804,000
Non-Regulated Property, Plant and Equipment [Member] | Transmission pipelines and related equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	5 years
Non-Regulated Property, Plant and Equipment [Member] | Transmission pipelines and related equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	54 years
Non-Regulated Property, Plant and Equipment [Member] | General plant and other
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 504,610,000	487,559,000
Non-Regulated Property, Plant and Equipment [Member] | General plant and other | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	2 years
Non-Regulated Property, Plant and Equipment [Member] | General plant and other | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	60 years
Non-Regulated Property, Plant and Equipment [Member] | Construction work in process
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 362,253,000	371,628,000
Regulated Property Plant and Equipment [Member]
Property, Plant and Equipment [Line Items]
Accumulated depreciation and amortization	$ (973,531,000)	$ (865,604,000)
Regulated Property Plant and Equipment [Member] | Natural Gas Liquids
Property, Plant and Equipment [Line Items]
Average Depreciation Rate	1.90%	1.90%	1.90%
Regulated Property Plant and Equipment [Member] | Natural Gas Pipelines
Property, Plant and Equipment [Line Items]
Average Depreciation Rate	2.10%	2.10%	2.10%
Regulated Property Plant and Equipment [Member] | Storage and related equipment
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 12,486,000	$ 13,524,000
Regulated Property Plant and Equipment [Member] | Storage and related equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	5 years
Regulated Property Plant and Equipment [Member] | Storage and related equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	25 years
Regulated Property Plant and Equipment [Member] | General plant and other
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 57,902,000	54,643,000
Regulated Property Plant and Equipment [Member] | General plant and other | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	2 years
Regulated Property Plant and Equipment [Member] | General plant and other | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	50 years
Regulated Property Plant and Equipment [Member] | Construction work in process
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 83,044,000	62,634,000
Regulated Property Plant and Equipment [Member] | Natural gas transmission pipelines and related equipment
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 1,406,780,000	1,345,740,000
Regulated Property Plant and Equipment [Member] | Natural gas transmission pipelines and related equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	5 years
Regulated Property Plant and Equipment [Member] | Natural gas transmission pipelines and related equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	77 years
Regulated Property Plant and Equipment [Member] | Natural gas liquids transmission pipelines and related equipment
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 4,340,428,000	$ 4,309,341,000
Regulated Property Plant and Equipment [Member] | Natural gas liquids transmission pipelines and related equipment | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	5 years
Regulated Property Plant and Equipment [Member] | Natural gas liquids transmission pipelines and related equipment | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Useful Life	88 years

GOODWILL AND INTANGIBLE ASSET59

GOODWILL AND INTANGIBLE ASSETS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Goodwill	$ 681,100	$ 525,535
Amortization expense for intangible assets	11,900	11,900	$ 11,900
Gross intangible assets and accumulated amortization [Abstract]
Gross intangible assets	426,068	581,633
Accumulated amortization	(113,708)	(101,809)
Net intangible assets	312,360	479,824
Future amortization expense for next five years [Abstract]
Future amortization expense, year one	11,900
Future amortization expense, year two	11,900
Future amortization expense, year three	11,900
Future amortization expense, year four	11,900
Future amortization expense, year five	$ 11,900
Natural Gas Gathering And Processing and Natural Gas Liquids [Member] | Minimum [Member]
Segment Reporting Information [Line Items]
Finite-Lived Intangible Asset, Useful Life	20 years
Natural Gas Gathering And Processing and Natural Gas Liquids [Member] | Maximum [Member]
Segment Reporting Information [Line Items]
Finite-Lived Intangible Asset, Useful Life	40 years
Natural Gas Gathering and Processing
Segment Reporting Information [Line Items]
Goodwill	$ 153,404	122,291
Natural Gas Liquids
Segment Reporting Information [Line Items]
Goodwill	371,217	268,544
Natural Gas Pipelines
Segment Reporting Information [Line Items]
Goodwill	156,479	$ 134,700
ONEOK
Segment Reporting Information [Line Items]
Goodwill	$ 155,600

DEBT (Details)

DEBT (Details) $ in Thousands	3 Months Ended	9 Months Ended		12 Months Ended
	Mar. 31, 2015USD ($)Rate	Sep. 30, 2017USD ($)Rate	Sep. 30, 2015USD ($)Rate	Dec. 31, 2017USD ($)Rate	Dec. 31, 2016USD ($)Rate	Dec. 31, 2015USD ($)	Mar. 31, 2018USD ($)
Debt Instrument [Line Items]
Impairment of long-lived assets				$ 15,970	$ 0	$ 83,673
Long-term Debt, Gross				9,198,677	9,489,057
Unamortized Portion of Terminated Swaps				18,468	20,186
Unamortized debt issuance costs and discounts				(78,193)	(68,320)
Current maturities of long-term debt				(432,650)	(410,650)
Short-term borrowings				(614,673)	(1,110,277)
Long-term debt				8,091,629	7,919,996
Senior Notes, Noncurrent		$ 1,200,000		1,200,000
Payments to Acquire Interest in Subsidiaries and Affiliates			$ 650,000
Long-term Debt, by Maturity [Abstract]
2,018				432,700
2,019				1,007,700
2,020				307,700
2,021				7,700
2,022				1,453,200
ONEOK, Inc. Commercial Paper Program [Domain]
Debt Instrument [Line Items]
Commercial Paper				614,673	0
Maximum Amount Of Commercial Paper				2,500,000
ONEOK Partners Commercial Paper Program [Domain]
Debt Instrument [Line Items]
Maximum Amount Of Commercial Paper		2,400,000
$2.5 Billion Credit Agreement [Member]
Debt Instrument [Line Items]
Letters of Credit Outstanding, Amount				15,800
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				4.5
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 5.75 to 1 at December 31, 2017, and for the following quarter; 5.5 to 1 for the subsequent two quarters; 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. The $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 the $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. The $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 December 31, 2017, our ratio of indebtedness to adjusted EBITDA was 4.5 to 1, and we were in compliance with all covenants under the $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
ONEOK Credit Agreement [Domain]
Debt Instrument [Line Items]
Letters of Credit Outstanding, Amount					1,100
Partnership Credit Agreement [Member]
Debt Instrument [Line Items]
Letters of Credit Outstanding, Amount					14,000
Senior Notes [Member]
Debt Instrument [Line Items]
Proceeds from Debt, Net of Issuance Costs		1,180,000
Note Payable from Public Offering Due 2018 [Member]
Long-term Debt, by Maturity [Abstract]
2,018				425,000
Notes Payables due 2019 [Member]
Long-term Debt, by Maturity [Abstract]
2,019				1,000,000
Note Payable from Public Offering Due 2020 [Member]
Long-term Debt, by Maturity [Abstract]
2,020				300,000
Note Payable 2 from Public Offering Due 2022 [Member]
Long-term Debt, by Maturity [Abstract]
2,022				1,447,400
Note Payable Due 2021 [Domain]
Long-term Debt, by Maturity [Abstract]
2,021				$ 0
Partnership Interest [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Senior Notes, Noncurrent	$ 800,000
Proceeds from Debt, Net of Issuance Costs	792,300
Partnership Interest [Member] | Note Payable from Public Offering Due 2020 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 300,000
Interest rates (in hundredths) | Rate	3.80%
Partnership Interest [Member] | Note Payable from Public Offering Due 2025 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 500,000
Interest rates (in hundredths) | Rate	4.90%
Parent Company | Note Payable Due 2023 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross			500,000
Proceeds from Debt, Net of Issuance Costs			$ 487,100
Interest rates (in hundredths) | Rate			7.50%
Guardian Pipeline [Member]
Debt Instrument [Line Items]
Debt instrument covenant description				Guardian Pipeline’s senior notes contain financial covenants that require the maintenance of certain financial ratios as defined in the master shelf agreement based on Guardian Pipeline’s financial position and results of operations. Upon any breach of these covenants, all amounts outstanding under the master shelf agreement may become due and payable immediately
Debt Instrument, Covenant Compliance				At December 31, 2017, Guardian Pipeline was in compliance with its financial covenants
Guardian Pipeline [Member] | Notes Payables due 2022 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 36,607	44,257
Average interest rate (in hundredths) | Rate				7.85%
Long-term Debt, by Maturity [Abstract]
2,018				$ 7,700
2,019				7,700
2,020				7,700
2,021				7,700
2,022				$ 5,800
Parent Company
Debt Instrument [Line Items]
Short-term Debt, Weighted Average Interest Rate, at Point in Time | Rate				2.23%
Parent Company | Senior Notes [Member]
Debt Instrument [Line Items]
Debt instrument covenant description				The indentures governing ONEOK’s 6.875 percent senior notes due 2028 include an event of default upon acceleration of other indebtedness of $15 million or more, and the indentures governing the senior notes due 2022, 2023, 2027, 2035 and 2047 include an event of default upon the acceleration of other indebtedness of $100 million or more. Such events of default would entitle the trustee or the holders of 25 percent in aggregate principal amount of the outstanding senior notes due 2022, 2023, 2027, 2028, 2035 and 2047 to declare those senior notes immediately due and payable in full. The indenture for the notes due 2023 also contains a provision that allows the holders of the notes to require ONEOK to offer to repurchase all or any part of their notes if a change of control and a credit rating downgrade occur at a purchase price of 101 percent of the principal amount, plus accrued and unpaid interest, if any.
Debt instrument call feature				ONEOK may redeem its senior notes, in whole or in part, at any time prior to their maturity at a redemption price equal to the principal amount, plus accrued and unpaid interest and a make-whole premium. ONEOK may redeem the remaining balance of its senior notes due 2022, 2023, 2027 and 2047 at a redemption price equal to the principal amount, plus accrued and unpaid interest, starting three to six months before the maturity date as stipulated in the respective contract terms. ONEOK’s senior notes are senior unsecured obligations, ranking equally in right of payment with all of ONEOK’s existing and future unsecured senior indebtedness.
Parent Company | Note Payable Due 2027 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 500,000
Interest rates (in hundredths) | Rate		4.00%
Parent Company | Notes Payables due 2047 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 700,000
Interest rates (in hundredths) | Rate		4.95%
Parent Company | Note Payable from Public Offering Due 2022 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 547,397	547,397
Interest rates (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 rates (in hundredths) | Rate				7.50%
Parent Company | Note Payable from Public Offering Due 2027 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 500,000	0
Interest rates (in hundredths) | Rate				4.00%
Parent Company | Note Payables 1 due 2028 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 0	87,126
Repayment of Senior Notes		$ 87,000
Interest rates (in hundredths) | Rate		6.50%		6.50%
Parent Company | Note Payables 2 due 2028 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 100,000	100,000
Interest rates (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 rates (in hundredths) | Rate				6.00%
Parent Company | Note Payable from Public Offering Due 2047 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 700,000	0
Interest rates (in hundredths) | Rate				4.95%
Partnership Interest [Member]
Debt Instrument [Line Items]
Commercial Paper				$ 0	1,110,277
Partnership Interest [Member] | Senior Notes [Member]
Debt Instrument [Line Items]
Debt instrument covenant description				ONEOK Partners’ senior notes are governed by an indenture containing covenants including, among other provisions, limitations on ONEOK Partners’ ability to place liens on its property or assets and to sell and lease back its property. The indenture includes an event of default upon acceleration of other indebtedness of $100 million or more. Such events of default would entitle the trustee or the holders of 25 percent in aggregate principal amount of any of ONEOK Partners’ outstanding senior notes to declare those notes immediately due and payable in full.
Debt instrument call feature				The senior notes may be redeemed, in whole or in part, at any time prior to their maturity at a redemption price equal to the principal amount, plus accrued and unpaid interest and a make-whole premium. The senior notes due 2018, 2020, 2022, 2023, 2025, 2041 and 2043 may be redeemed at a redemption price equal to the principal amount, plus accrued and unpaid interest, starting one to six months before their maturity dates as stipulated in the respective contract terms.
Partnership Interest [Member] | Note Payable from Public Offering Due 2017 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 0	400,000
Repayment of Senior Notes		$ 400,000
Interest rates (in hundredths) | Rate		2.00%		2.00%
Partnership Interest [Member] | Note Payable from Public Offering Due 2018 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 425,000	425,000
Interest rates (in hundredths) | Rate				3.20%
Partnership Interest [Member] | Term Loan Agreement [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 500,000	1,000,000
Repayment of Senior Notes		$ 500,000					$ 500,000
Delayed-Draw Unsecured Senior Term Loan					$ 1,000,000
Long-term Debt, Percentage Bearing Variable Interest, Percentage Rate | Rate				2.87%	2.04%
Partnership Interest [Member] | Notes Payables due 2019 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross				$ 500,000	$ 500,000
Interest rates (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 rates (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 rates (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 rates (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 rates (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 rates (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 rates (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 rates (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 rates (in hundredths) | Rate				6.20%
Partnership Interest [Member] | Notes Payable due 2016 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross					$ 450,000
Interest rates (in hundredths) | Rate					6.15%
Natural Gas Gathering And Processing and Natural Gas Liquids [Member]
Debt Instrument [Line Items]
Impairment of long-lived assets						$ 20,200

EQUITY EQUITY (Details)

EQUITY EQUITY (Details) - USD ($)	3 Months Ended													6 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Public Offering Price of Common Stock	$ 54.50
General partner ownership interest														41.20%
Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners		20.00%													20.00%
Common Stock, Shares, Issued		423,166,234				245,811,180									423,166,234	245,811,180
Dividends, Common Stock															$ 829,400,000	$ 517,600,000	$ 509,200,000
Common Stock, Dividends, Per Share, Declared															$ 2.72	$ 2.46	$ 2.43
Common Stock, Dividends, Per Share, Cash Paid		$ 0.745	$ 0.745	$ 0.615	$ 0.615	$ 0.615	$ 0.615	$ 0.615	$ 0.615	$ 0.615	$ 0.605	$ 0.605	$ 0.605		$ 2.720	$ 2.460	$ 2.430
Stock Issued During Period, Shares, New Issues	21,900,000
Noncash Contribution Expense															$ 12,600,000	$ 0	$ 0
Dividends, Preferred Stock, Cash		$ 100,000													600,000
Preferred stock dividends paid															$ 767,000
Proceeds from Issuance or Sale of Equity	$ 1,200,000,000
Aggregate Amount Of Common Units Available For Issuance And Sale Under Equity Distribution Agreement														$ 650,000,000		$ 650,000,000
Noncontrolling Interest, Increase from Subsidiary Equity Issuance																	$ 393,997,000
Key Provisions of Operating or Partnership Agreement, Description														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. Under the Partnership Agreement, distributions were made to the partners with respect to each calendar quarter in an amount equal to 100 percent of available cash as defined in the Partnership Agreement. Available cash generally was distributed 98 percent to limited partners and 2 percent to the general partner. The general partner’s percentage interest in quarterly distributions were increased after certain specified target levels were met during the quarter. Under the incentive distribution provisions, as set forth in the Partnership Agreement, the general partner received:15 percent of amounts distributed in excess of $0.3025 per unit; 25 percent of amounts distributed in excess of $0.3575 per unit; and 50 percent of amounts distributed in excess of $0.4675 per unit.
Issued Under Equity Distribution Agreement
Partners Capital Account Units Sold Under Equity Distribution Agreement														0		0
Subsequent Event [Member]
Common Stock, Dividends, Per Share, Declared, Annualized	$ 3.080
Common Stock, Dividends, Per Share, Declared	$ 0.770
Preferred stock dividends paid	$ 300,000
Dividends Payable, Date to be Paid	Jan. 29, 2018
Issued Under Equity Agreement
Common Stock Sold Under Equity Distribution Agreement															8,400,000
Issued Under Equity Agreement | Subsequent Event [Member]
Proceeds from Issuance or Sale of Equity															$ 448,300,000
Private Placement
Partners' Capital Account, Units, Sold in Private Placement											21,500,000
Per Unit Offering Price Under Private Placement											$ 30.17
Partners Capital Account Units Sold Under Equity Distribution Agreement											3,300,000
Proceeds from Sale of Interest in Partnership Unit											$ 749,000,000
Partners' Capital Account, Contributions											$ 15,300,000
Issued Under Equity Distribution Agreement
Partners Capital Account Units Sold Under Equity Distribution Agreement																	10,500,000
Proceeds from Sale of Interest in Partnership Unit																	$ 381,600,000
Series E Preferred Stock [Member]
Stock Issued During Period, Shares, New Issues															20,000
Stock Issued During Period, Value, New Issues															$ 20,000,000
Noncash Contribution Expense															$ 20,000,000
Preferred Stock, Dividend Rate, Percentage															5.50%
Distribution Declared
Distribution Made to Limited Partner, Distribution Date				May 1, 2017	Jan. 30, 2017
Distributions Per Unit				$ 0.79	$ 0.79
Distribution Paid
Distributions Per Unit															$ 1.58	$ 3.16	$ 3.16
Total distributions paid															$ 666,001,000	$ 1,332,003,000	$ 1,230,475,000
General Partner
General partner ownership interest														2.00%
ONEOK
Common Stock, Shares, Issued				168,900,000										168,900,000
Aggregate Amount Of Common Shares Available For Issuance And Sale Under Equity Distribution Agreement															1,000,000,000
General Partner | Distribution Paid
General partner distributions															13,320,000	26,640,000	24,610,000
Incentive distributions															201,076,000	402,152,000	371,500,000
Distributions to general partner															214,396,000	428,792,000	396,110,000
ONEOK | Distribution Paid
Limited partner distributions to ONEOK															180,646,000	361,292,000	310,230,000
Limited Partner | Distribution Paid
Limited partner distributions to other unitholders															$ 270,959,000	$ 541,919,000	$ 524,135,000

ACCUMULATED OTHER COMPREHENSI62

ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Unrealized gains (losses) on risk management assets/liabilities - January 1	$ (52,155)	$ (42,199)
Pension and Postretirement Benefit Plan Obligations - January 1	(101,236)	(84,543)
Unrealized gains (losses) on risk-management assets/liabilities of unconsolidated affiliates - January 1	(959)	(500)
Accumulated other comprehensive loss - January 1	(154,350)	(127,242)
Other comprehensive income (loss), unrealized gain (loss) on derivatives arising during period, net of tax	(35,013)	(9,280)
Other comprehensive (income) loss, defined benefit plan, before reclassification adjustment, after tax	(12,337)	(22,903)
Other comprehensive income (loss), amount attributable to equity method investments, before reclassification adjustments, net of tax	(409)	(475)
Other comprehensive income (loss) before reclassifications	(47,759)	(32,658)
Realized (gains) losses on derivatives in net income, net of tax	63,687	(6,977)	$ (54,709)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Other Comprehensive Income Attributable to Equity Method Investments, Net of Tax	164	16
Other Comprehensive Income (Loss), Reclassification Adjustment included in Net Income, Net of Tax	53,867	5,550	(5,600)
Impact of Merger Transaction On Unrealized Gains (Losses) on Risk Management Assets/Liabilities	(40,288)
Impact of Merger Transaction on Pension and Postretirement Benefit Plan Obligations	0
Impact of Merger Transaction on Unrealized Gains (Losses) on Risk Management Assets/Liabilities of Unconsolidated Affiliates	0
Impact of Merger Transaction on AOCI, Total	(40,288)
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax, Portion Attributable to Parent	(29,760)	(9,956)
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax	(4,175)	(16,693)	15,416
Other Comprehensive Income (Loss) on Investment in Unconsolidated Affiliates	(245)	(459)
Net Current-Period Other Comprehensive Income (Loss) Attributable to ONEOK	(34,180)	(27,108)
Unrealized gains (losses) on risk management assets/liabilities - December 31	(81,915)	(52,155)	(42,199)
Pension and Postretirement Benefit Plan Obligations - December 31	(105,411)	(101,236)	(84,543)
Unrealized gains (losses) on risk-management assets/liabilities of unconsolidated affiliates - December 31	(1,204)	(959)	(500)
Accumulated other comprehensive loss - December 31	(188,530)	(154,350)	(127,242)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Tax	26,899	(230)	(8,815)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Realized (gains) losses on derivatives in net income, net of tax	45,541	(676)	(15,294)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, after Tax	(8,162)	(6,210)	(9,694)
Defined Benefit Plan, Amortization of Gain (Loss)	(15,265)	(12,012)	(17,724)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	1,662	1,662	1,568
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax	(13,603)	(10,350)	(16,156)
Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, Tax	5,441	4,140	6,462
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 Equity Method Investments, Net of Tax	164	16	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Other Comprehensive Income Attributable to Equity Method Investments, Before Tax	(367)	(63)	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Other Comprehensive Income Attributable to Equity Method Investments, Tax	97	10	0
Sales [Member] | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] | Commodity Contract [Member]
Amounts reclassified from accumulated other comprehensive income (loss)	(69,561)	26,422	81,089
Interest Expense [Member] | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] | Interest Rate Contracts
Amounts reclassified from accumulated other comprehensive income (loss)	(21,025)	(19,215)	(17,565)
Total before tax [Member] | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Amounts reclassified from accumulated other comprehensive income (loss)	(90,586)	7,207	63,524
Tax Expense [Member] | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Tax	26,899	(230)	(8,815)
Net of tax [Member] | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Realized (gains) losses on derivatives in net income, net of tax	63,687	(6,977)	(54,709)
Net of tax [Member] | 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 Equity Method Investments, Net of Tax	270	53	0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Other Comprehensive Income Attributable to Equity Method Investments, Net of Tax, Portion Attributable to Noncont Interests	(106)	(37)	0
Net income attributable to noncontrolling interest [Member] | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax, Portion Attributable to Noncontrolling Interest	$ (18,146)	$ 6,301	$ 39,415

EARNINGS PER SHARE EARNINGS P63

EARNINGS PER SHARE EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Basic EPS from Continuing Operations [Abstract]
Income from continuing operations attributable to ONEOK available for common stock									$ 387,074	$ 354,090	$ 251,058
Shares									297,477	211,128	210,208
Basic	$ 0.16	$ 0.43	$ 0.34	$ 0.41	$ 0.43	$ 0.44	$ 0.41	$ 0.40	$ 1.30	$ 1.68	$ 1.19
Diluted EPS from Continuing Operations [Abstract]
Effect of options and other dilutive securities									$ 0	$ 0	$ 0
Effect of options and other dilutive securities, number of shares, shares									2,303	1,255	333
Income from continuing operations attributable to ONEOK available for common stock and common stock equivalents									$ 387,074	$ 354,090	$ 251,058
Shares									299,780	212,383	210,541
Diluted	$ 0.16	$ 0.43	$ 0.33	$ 0.41	$ 0.43	$ 0.43	$ 0.40	$ 0.40	$ 1.29	$ 1.67	$ 1.19

SHARE-BASED PAYMENTS SHARE-BA64

SHARE-BASED PAYMENTS SHARE-BASED PAYMENTS (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Forfeiture rate maximum (in hundredths)	3.00%
Allocated Share-based Compensation Expense	$ 16,600	$ 30,700	$ 11,500
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense	$ 11,100	$ 9,800	$ 4,900
Equity Compensation Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common Stock, Capital Shares Reserved for Future Issuance	10,000,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	1,900,000
Long Term Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common Stock, Capital Shares Reserved for Future Issuance	15,600,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	0
Performance Unit Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	3 years
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized	$ 17,400
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	1 year 11 months 2 days
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	1,136,133	1,005,751
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	311,047
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period	(123,459)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period	(57,206)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value	$ 40.08	$ 38.81
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	56.65	$ 25.54	$ 50.30
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value	70.50
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value	$ 42.29
Share Based Compensation Arrangement By Share Based Payment Award, Equity Instruments Other Than Options, Granted in Period, Fair Value	$ 17,621	$ 15,229	$ 13,370
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value	$ 8,704	$ 0	$ 13,736
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate	40.59%	39.94%	26.70%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate	4.68%	11.32%	5.02%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate	1.49%	0.93%	1.00%
Non-employees and Directors [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common Stock, Capital Shares Reserved for Future Issuance	1,400,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	1,000,000
Maximum Number Of Shares For Which Options Or Other Awards May Be Granted To Any Employee During Any Year	40,000
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	3 years
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized	$ 12,500
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	1 year 11 months 3 days
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	1,001,805	881,647
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	281,167
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period	(141,724)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period	(19,285)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value	$ 32.30	$ 31.25
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	45.11	$ 20.04	$ 42.98
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value	51.21
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value	$ 32.07
Share Based Compensation Arrangement By Share Based Payment Award, Equity Instruments Other Than Options, Granted in Period, Fair Value	$ 12,685	$ 11,081	$ 10,186
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value	$ 7,258	$ 4,429	$ 6,458
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common Stock, Capital Shares Reserved for Future Issuance	11,600,000
Maximum allowable percentage of annual base pay withheld to purchase our common stock	10.00%
Purchase price percentage of the lower of its grant date or exercise date market price	85.00%
Employee participation in the plan (in hundredths)	58.00%	57.00%	53.00%
Shares sold under the Employee Stock Purchase Plan	151,803	232,553	222,872
Share Price of Shares Sold Under the Employee Stock Purchase Plan (In Dollars per Share)	$ 44.20	$ 27.21	$ 25.51
Employee Stock Award Program [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Description	Under our Employee Stock Award Program, we issued, for no monetary consideration, to all eligible employees one share of our common stock when the per-share closing price of our common stock on the NYSE was for the first time at or above $13 per share, and one additional share of common stock when the per-share closing price of our common stock on the NYSE was at or above each one dollar increment above $13.
Common Stock, Capital Shares Reserved for Future Issuance	900,000
Shares Awarded Under Employee Stock Award Program	0	0	0

EMPLOYEE BENEFIT PLANS EMPLOY65

EMPLOYEE BENEFIT PLANS EMPLOYEE BENEFIT PLANS (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Investments Included in Other Assets, Supplemental Executive Retirement Plan		$ 93,200	$ 84,500
Deferred income taxes		(878)	11,128	$ (10,278)
Total recognized in other comprehensive income (loss)		(4,175)	(16,693)	15,416
Accumulated other comprehensive loss, net of tax		$ (105,411)	$ (101,236)	$ (84,543)
Expected long-term return on plan assets		7.75%	7.75%	8.00%
Compensation increase rate		3.10%	3.10%	3.15%
Defined Benefit Plan, Narrative Description of Basis Used to Determine Overall Expected Long-term Rate-of-Return on Assets Assumption		We determine our overall expected long-term rate of return on plan assets based on our review of historical returns and economic growth models. We determine our discount rates annually. We estimate our discount rate based upon a comparison of the expected cash flows associated with our future payments under our pension and postretirement obligations to a hypothetical bond portfolio created using high-quality bonds that closely match expected cash flows. Bond portfolios are developed by selecting a bond for each of the next 60 years based on the maturity dates of the bonds. Bonds selected to be included in the portfolios are only those rated by Moody’s as AA- or better and exclude callable bonds, bonds with less than a minimum issue size, yield outliers and other filtering criteria to remove unsuitable bonds.
Percent of employee contributions matched of eligible compensation (in hundredths)		100.00%
Maximum Percentage Of Each Participants Eligible Compensation Subject To Certain Limits Matching In Hundredths		6.00%
Contributions made to the Thrift Plan		$ 13,700	$ 11,900	$ 12,000
Profit sharing contribution percentage		1.00%
Contributions made to the Profit-Sharing Plan		$ 7,400	8,200	4,900
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation		481,615	428,386	390,688
Service cost		6,896	6,501	7,565
Interest cost		18,645	19,820	18,218
Plan participants’ contributions		0	0
Actuarial loss		41,678	24,458
Benefits paid		(13,990)	(13,081)
Fair value of plan assets		306,008	261,671	258,635
Actual return on plan assets		50,827	16,117
Employer contributions		7,500	0
Plan participants’ contributions		0	0
Benefits paid		(13,990)	(13,081)
Balance at December 31		(175,607)	(166,715)
Current liabilities		(4,544)	(4,363)
Noncurrent liabilities		(171,063)	(162,352)
Balance at December 31		(175,607)	(166,715)
Defined Benefit Plan, Accumulated Benefit Obligation		456,600	407,200
Expected return on plan assets		(21,376)	(20,348)	(20,900)
Amortization of prior service cost (credit)		0	0	94
Amortization of net loss		13,586	10,966	15,981
Net periodic benefit cost		17,751	16,939	20,958
Net gain (loss) arising during the period		(16,572)	(33,043)	5,145
Amortization of prior service cost (credit)		0	0	94
Amortization of net loss		13,586	10,966	15,981
Deferred income taxes		(960)	8,831	(8,488)
Total recognized in other comprehensive income (loss)		(3,946)	(13,246)	$ 12,732
Prior service credit (cost)		0	0
Accumulated loss		(160,921)	(157,935)
Accumulated other comprehensive loss		(160,921)	(157,935)
Deferred income taxes		62,214	63,174
Accumulated other comprehensive loss, net of tax		$ (98,707)	$ (94,761)
Discount rate (a)		3.75%	4.50%
Compensation increase rate		3.00%	3.10%
Discount Rates - Pension and Postretirement Plans		4.50%	5.25%	4.50%
U.S. large-cap equities		37.00%
Long duration bonds		30.00%
Developed foreign large-cap equities		10.00%
Alternative investments		8.00%
Mid-cap equities		6.00%
Emerging markets equities		5.00%
Small-cap equities		4.00%
Total		100.00%
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months		$ 16,796
Defined Benefit Plan, Expected Future Benefit Payment, Year Two		18,011
Defined Benefit Plan, Expected Future Benefit Payment, Year Three		18,970
Defined Benefit Plan, Expected Future Benefit Payment, Year Four		20,206
Defined Benefit Plan, Expected Future Benefit Payment, Year Five		21,157
Defined Benefit Plan, Expected Future Benefit Payment, Five Fiscal Years Thereafter		117,048
Pension Plan [Member] | Subsequent Event [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions	$ 12,300
Pension Plan [Member] | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		176,645	$ 147,023
Pension Plan [Member] | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		108,282	94,646
Pension Plan [Member] | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Pension Plan [Member] | Subtotal
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		284,927	241,669
Pension Plan [Member] | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		21,081	20,002
Pension Plan [Member] | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		306,008	261,671
Pension Plan [Member] | Equity securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		176,347	146,980
Pension Plan [Member] | Equity securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		19,199	13,606
Pension Plan [Member] | Equity securities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Pension Plan [Member] | Equity securities | Subtotal
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		195,546	160,586
Pension Plan [Member] | Equity securities | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Pension Plan [Member] | Equity securities | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		195,546	160,586
Pension Plan [Member] | Government obligations | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Pension Plan [Member] | Government obligations | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		19,481	17,979
Pension Plan [Member] | Government obligations | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Pension Plan [Member] | Government obligations | Subtotal
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		19,481	17,979
Pension Plan [Member] | Government obligations | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Pension Plan [Member] | Government obligations | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		19,481	17,979
Pension Plan [Member] | Corporate obligations | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Pension Plan [Member] | Corporate obligations | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		62,981	56,484
Pension Plan [Member] | Corporate obligations | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Pension Plan [Member] | Corporate obligations | Subtotal
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		62,981	56,484
Pension Plan [Member] | Corporate obligations | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Pension Plan [Member] | Corporate obligations | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		62,981	56,484
Pension Plan [Member] | Common/collective trusts | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Pension Plan [Member] | Common/collective trusts | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		6,621	6,577
Pension Plan [Member] | Common/collective trusts | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Pension Plan [Member] | Common/collective trusts | Subtotal
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		6,621	6,577
Pension Plan [Member] | Common/collective trusts | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Pension Plan [Member] | Common/collective trusts | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		6,621	6,577
Pension Plan [Member] | Cash | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		298	43
Pension Plan [Member] | Cash | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Pension Plan [Member] | Cash | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Pension Plan [Member] | Cash | Subtotal
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		298	43
Pension Plan [Member] | Cash | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Pension Plan [Member] | Cash | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		298	43
Pension Plan [Member] | Other Investments | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Pension Plan [Member] | Other Investments | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Pension Plan [Member] | Other Investments | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Pension Plan [Member] | Other Investments | Subtotal
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Pension Plan [Member] | Other Investments | Measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		21,081	20,002
Pension Plan [Member] | Other Investments | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		$ 21,081	$ 20,002
Pension Plan [Member] | Scenario, Forecast [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior service (credit) cost					$ 0
Net loss					17,060
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan Assumed Health Care Cost Trend Rate		7.00%	7.25%
Defined Benefit Plan Assumed Ultimate Health Care Cost Trend Rate		5.00%	5.00%
Minimum Number Of Years Of Service For Certain Employees To Be Eligible To Participate In Welfare Plans That Provide Postretirement Medical And Life Insurance Benefits		5 years
Benefit obligation		$ 57,938	$ 54,823	$ 49,496
Service cost		662	596	743
Interest cost		2,261	2,404	2,347
Plan participants’ contributions		901	894
Actuarial loss		3,456	4,905
Benefits paid		(4,165)	(3,472)
Fair value of plan assets		34,133	29,550	28,641
Actual return on plan assets		5,385	1,902
Employer contributions		2,000	1,000
Plan participants’ contributions		901	894
Benefits paid		(3,703)	(2,887)
Balance at December 31		(23,805)	(25,273)
Current liabilities		0	0
Noncurrent liabilities		(23,805)	(25,273)
Balance at December 31		(23,805)	(25,273)
Expected return on plan assets		(2,257)	(2,124)	(2,253)
Amortization of prior service cost (credit)		(1,662)	(1,662)	(1,662)
Amortization of net loss		1,679	1,046	1,743
Net periodic benefit cost		683	260	918
Net gain (loss) arising during the period		(328)	(5,128)	4,393
Amortization of prior service cost (credit)		(1,662)	(1,662)	(1,662)
Amortization of net loss		1,679	1,046	1,743
Deferred income taxes		82	2,297	(1,790)
Total recognized in other comprehensive income (loss)		(229)	(3,447)	$ 2,684
Prior service credit (cost)		1,889	3,550
Accumulated loss		(12,991)	(14,341)
Accumulated other comprehensive loss		(11,102)	(10,791)
Deferred income taxes		4,398	4,316
Accumulated other comprehensive loss, net of tax		$ (6,704)	$ (6,475)
Discount rate (a)		3.75%	4.25%
Discount Rates - Pension and Postretirement Plans		4.25%	5.00%	4.25%
Year that the rate reaches the ultimate trend rate		2,022	2,022
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year		$ 2,000
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months		3,452
Defined Benefit Plan, Expected Future Benefit Payment, Year Two		3,653
Defined Benefit Plan, Expected Future Benefit Payment, Year Three		3,859
Defined Benefit Plan, Expected Future Benefit Payment, Year Four		3,993
Defined Benefit Plan, Expected Future Benefit Payment, Year Five		4,023
Defined Benefit Plan, Expected Future Benefit Payment, Five Fiscal Years Thereafter		19,302
Other Postretirement Benefits Plan [Member] | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		1,951	$ 1,777
Other Postretirement Benefits Plan [Member] | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		32,182	27,773
Other Postretirement Benefits Plan [Member] | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Other Postretirement Benefits Plan [Member] | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		34,133	29,550
Other Postretirement Benefits Plan [Member] | Equity securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		1,951	1,777
Other Postretirement Benefits Plan [Member] | Equity securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Other Postretirement Benefits Plan [Member] | Equity securities | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Other Postretirement Benefits Plan [Member] | Equity securities | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		1,951	1,777
Other Postretirement Benefits Plan [Member] | Cash | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Other Postretirement Benefits Plan [Member] | Cash | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		1,515	1,259
Other Postretirement Benefits Plan [Member] | Cash | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Other Postretirement Benefits Plan [Member] | Cash | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		1,515	1,259
Other Postretirement Benefits Plan [Member] | Insurance and group annuity contracts | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Other Postretirement Benefits Plan [Member] | Insurance and group annuity contracts | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		30,667	26,514
Other Postretirement Benefits Plan [Member] | Insurance and group annuity contracts | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Other Postretirement Benefits Plan [Member] | Insurance and group annuity contracts | Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		$ 30,667	$ 26,514
Other Postretirement Benefits Plan [Member] | Scenario, Forecast [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior service (credit) cost					(1,662)
Net loss					$ 1,338

INCOME TAXES (Details)

INCOME TAXES (Details) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current income tax provision
Federal			$ 295,000	$ 6,086,000	$ 13,191,000
State			1,670,000	2,449,000	2,967,000
Total current income taxes from continuing operations			1,965,000	8,535,000	16,158,000
Deferred income tax provision
Federal			376,728,000	193,974,000	116,681,000
State			68,589,000	9,897,000	3,761,000
Total deferred income taxes from continuing operations			445,317,000	203,871,000	120,442,000
Total provision for income taxes from continuing operations			447,282,000	212,406,000	136,600,000
Discontinued operations			0	(1,250,000)	2,031,000
Total provision for income taxes			447,282,000	211,156,000	138,631,000
Income Tax Reconciliation [Abstract]
Income before income taxes			1,040,801,000	957,956,000	521,876,000
Less: Net income attributable to noncontrolling interests			205,678,000	391,460,000	134,218,000
Net income attributable to ONEOK before income taxes			$ 835,123,000	$ 566,496,000	$ 387,658,000
Federal statutory income tax rate		21.00%	35.00%	35.00%	35.00%
Provision for federal income taxes			$ 292,293,000	$ 198,274,000	$ 135,680,000
State income taxes, net of federal benefit			16,197,000	12,303,000	5,800,000
Deferred tax rate change, inclusive of valuation allowance			141,283,000	43,000	928,000
Other, net			(2,491,000)	1,786,000	$ (5,808,000)
Deferred tax assets
Employee benefits and other accrued liabilities			85,355,000	118,831,000
Federal net operating loss			159,162,000	26,334,000
State net operating loss and benefits			73,277,000	39,759,000
Derivative instruments			30,060,000	32,082,000
Other			13,546,000	2,425,000
Total deferred tax assets			361,400,000	219,431,000
Carryforward expected to expire prior to utilization			(66,632,000)	(9,430,000)
Net deferred tax assets			294,768,000	210,001,000
Deferred tax liabilities
Excess of tax over book depreciation			64,508,000	107,249,000
Investment in partnerships			77,035,000	1,726,541,000
Regulatory assets			15,000	33,000
Total deferred tax liabilities			141,558,000	1,833,823,000
Net deferred tax assets (liabilities) before discontinued operations			153,210,000	(1,623,822,000)
Discontinued operations			0	10,500,000
Net deferred tax assets (liabilities)			153,210,000	$ (1,613,322,000)
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount			54.1
Deferred Tax Assets, Gross, Noncurrent	$ 2,100,000,000
Deferred Tax Asset, Tax Basis	8,800,000,000
Deferred Tax Asset, Book Basis	$ 3,000,000,000
Excess Tax Benefit from Share-based Compensation, Operating Activities			$ 73,400,000
ONEOK
Income Tax Reconciliation [Abstract]
Federal statutory income tax rate	37.00%

UNCONSOLIDATED AFFILIATES (Deta

UNCONSOLIDATED AFFILIATES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Investments	$ 1,003,156	$ 958,807
Equity Method Goodwill	38,800	40,100
Equity in net earnings from investments	159,278	139,690	$ 125,300
Impairment of equity investments	(4,270)	0	(180,583)
Balance Sheet [Abstract]
Current assets	151,907	143,317
Property, plant and equipment, net	2,490,692	2,579,607
Other noncurrent assets	14,793	20,784
Current liabilities	70,434	77,388
Long-term debt	479,050	649,539
Other noncurrent liabilities	53,830	69,265
Accumulated other comprehensive loss	(9,946)	(7,450)
Owners’ equity	2,064,024	1,954,966
Income Statement [Abstract]
Operating revenues	639,102	578,542	524,496
Operating expenses	277,121	260,753	304,930
Net income	347,692	293,921	200,064
Distributions paid to us	196,114	196,717	155,918
Accounts Payable, Related Parties, Current	13,600	11,100
Payments to Acquire Other Investments	87,861	68,275	27,540
Unconsolidated Affiliates [Member]
Income Statement [Abstract]
Related Party Transaction, Expenses from Transactions with Related Party	156,100	$ 140,300	104,700
Northern Border Pipeline [Member]
Schedule of Equity Method Investments [Line Items]
Net ownership percentage		50.00%		50.00%	50.00%
Investments	396,800	$ 328,456
Equity in net earnings from investments	68,153	$ 69,990	66,941
Income Statement [Abstract]
Payments to Acquire Equity Method Investments	83,000
Overland Pass Pipeline Company [Member]
Schedule of Equity Method Investments [Line Items]
Net ownership percentage		50.00%		50.00%
Investments	436,111	$ 444,138
Equity in net earnings from investments	60,067	$ 53,984	37,783
Roadrunner Gas Transmission [Member]
Schedule of Equity Method Investments [Line Items]
Net ownership percentage		50.00%		50.00%
Investments	93,048	$ 94,548
Equity in net earnings from investments	19,150	4,445	1,800
Income Statement [Abstract]
Payments to Acquire Equity Method Investments	4,000	65,000
Other Unconsolidated Affiliates [Member]
Schedule of Equity Method Investments [Line Items]
Investments	77,197	91,665
Equity in net earnings from investments	$ 11,908	$ 11,271	$ 18,776

COMMITMENTS AND CONTINGENCIES68

COMMITMENTS AND CONTINGENCIES (Details) $ in Millions	Dec. 31, 2017USD ($)
Firm Transportation and Storage Contracts [Abstract]
2,018	$ 46.1
2,019	37.6
2,020	37.3
2,021	23
2,022	14.2
Thereafter	20.8
Total	$ 179

SEGMENTS (Details)

SEGMENTS (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Segment Reporting, Disclosure of Major Customers									For the year ended December 31, 2017, we had no single customer from which we received 10 percent or more of our consolidated revenues.	For the year ended December 31, 2016, we had no single customer from which we received 10 percent or more of our consolidated revenues.	For the year ended December 31, 2015, we had no single customer from which we received 10 percent or more of our consolidated revenues.
Total revenues	$ 3,792,158,000	$ 2,906,366,000	$ 2,725,772,000	$ 2,749,611,000	$ 2,654,461,000	$ 2,357,907,000	$ 2,134,107,000	$ 1,774,459,000	$ 12,173,907,000	$ 8,920,934,000	$ 7,763,206,000
Cost of sales and fuel (exclusive of depreciation and items shown separately below)									(9,538,045,000)	(6,496,124,000)	(5,641,052,000)
Operating costs									(833,586,000)	(757,184,000)	(693,331,000)
Equity in net earnings from investments									159,278,000	139,690,000	125,300,000
Depreciation and amortization									(406,335,000)	(391,585,000)	(354,620,000)
Impairment of long-lived assets									(15,970,000)	0	(83,673,000)
Impairment of equity investments									(4,270,000)	0	(180,583,000)
Impairment charges									(20,240,000)	0	(264,256,000)
Noncash compensation expense									13,421,000	31,981,000	13,799,000
Total assets	16,845,937,000				16,138,751,000				16,845,937,000	16,138,751,000	15,446,111,000
Capital expenditures									512,393,000	624,634,000	1,188,312,000
Operating income									1,380,895,000	1,285,676,000	996,159,000
Income from continuing operations					194,761,000	$ 194,792,000	$ 180,086,000	$ 175,911,000	593,519,000	745,550,000	385,276,000
Interest expense, net of capitalized interest									485,658,000	469,651,000	416,787,000
Income taxes									447,282,000	212,406,000	136,600,000
Other corporate costs and noncash items (a)									46,774,000	(11,639,000)	(5,512,000)
Noncash Contribution Expense									12,600,000	0	0
Business Combination, Acquisition Related Costs									30,000,000
Natural Gas Gathering And Processing
Segment Reporting Information [Line Items]
Total revenues									3,026,574,000	2,051,577,000	1,837,116,000
Cost of sales and fuel (exclusive of depreciation and items shown separately below)									(2,216,355,000)	(1,331,542,000)	(1,265,617,000)
Operating costs									(309,536,000)	(285,599,000)	(272,418,000)
Equity in net earnings from investments									12,098,000	10,742,000	17,863,000
Other									5,691,000	1,600,000	1,610,000
Segment adjusted EBITDA									518,472,000	446,778,000	318,554,000
Depreciation and amortization									(184,923,000)	(178,548,000)	(150,008,000)
Impairment of long-lived assets									(15,970,000)	0	(73,681,000)
Impairment of equity investments											(180,583,000)
Impairment charges									(20,240,000)
Total assets	5,495,163,000				5,320,666,000				5,495,163,000	5,320,666,000	5,123,450,000
Capital expenditures									284,205,000	410,485,000	887,938,000
Natural Gas Liquids
Segment Reporting Information [Line Items]
Total revenues									10,626,204,000	7,675,654,000	6,579,699,000
Cost of sales and fuel (exclusive of depreciation and items shown separately below)									(9,176,494,000)	(6,321,377,000)	(5,328,256,000)
Operating costs									(359,753,000)	(327,597,000)	(314,505,000)
Equity in net earnings from investments									59,876,000	54,513,000	38,696,000
Other									5,106,000	(1,574,000)	(3,342,000)
Segment adjusted EBITDA									1,154,939,000	1,079,619,000	972,292,000
Depreciation and amortization									(167,277,000)	(163,303,000)	(158,709,000)
Impairment of long-lived assets									0	0	(9,992,000)
Impairment of equity investments											0
Impairment charges									0
Total assets	8,782,700,000				8,347,961,000				8,782,700,000	8,347,961,000	8,017,799,000
Capital expenditures									114,267,000	105,861,000	226,135,000
Natural Gas Liquids | Natural Gas Liquids Regulated [Member]
Segment Reporting Information [Line Items]
Total revenues									1,199,500,000	1,200,000,000	954,800,000
Cost of sales and fuel (exclusive of depreciation and items shown separately below)									(497,400,000)	(458,700,000)	(412,600,000)
Natural Gas Pipelines
Segment Reporting Information [Line Items]
Total revenues									419,932,000	379,361,000	332,447,000
Cost of sales and fuel (exclusive of depreciation and items shown separately below)									(43,424,000)	(30,561,000)	(34,481,000)
Operating costs									(126,241,000)	(115,628,000)	(105,720,000)
Equity in net earnings from investments									87,304,000	74,435,000	68,741,000
Other									2,247,000	5,530,000	13,993,000
Segment adjusted EBITDA									339,818,000	313,137,000	274,980,000
Depreciation and amortization									(51,025,000)	(46,718,000)	(43,479,000)
Impairment of long-lived assets											0
Impairment of equity investments											0
Impairment charges									0
Total assets	2,055,020,000				1,946,318,000				2,055,020,000	1,946,318,000	1,851,857,000
Capital expenditures									95,564,000	96,274,000	58,215,000
Natural Gas Pipelines | Natural Gas Pipelines Regulated [Member]
Segment Reporting Information [Line Items]
Total revenues									264,900,000	238,700,000	266,900,000
Cost of sales and fuel (exclusive of depreciation and items shown separately below)									(44,000,000)	(30,000,000)	(31,100,000)
Total Segments [Member]
Segment Reporting Information [Line Items]
Total revenues									14,072,710,000	10,106,592,000	8,749,262,000
Cost of sales and fuel (exclusive of depreciation and items shown separately below)									(11,436,273,000)	(7,683,480,000)	(6,628,354,000)
Operating costs									(795,530,000)	(728,824,000)	(692,643,000)
Equity in net earnings from investments									159,278,000	139,690,000	125,300,000
Other									13,044,000	5,556,000	12,261,000
Segment adjusted EBITDA									2,013,229,000	1,839,534,000	1,565,826,000
Depreciation and amortization									(403,225,000)	(388,569,000)	(352,196,000)
Impairment of long-lived assets											(83,673,000)
Impairment of equity investments											(180,583,000)
Impairment charges									(20,240,000)
Total assets	16,332,883,000				15,614,945,000				16,332,883,000	15,614,945,000	14,993,106,000
Capital expenditures									494,036,000	612,620,000	1,172,288,000
Other and Eliminations
Segment Reporting Information [Line Items]
Total revenues									(1,898,803,000)	(1,185,658,000)	(986,056,000)
Cost of sales and fuel (exclusive of depreciation and items shown separately below)									1,898,228,000	1,187,356,000	987,302,000
Operating costs									(38,056,000)	(28,360,000)	(688,000)
Equity in net earnings from investments									0	0	0
Depreciation and amortization									(3,110,000)	(3,016,000)	(2,424,000)
Impairment of long-lived assets											0
Impairment of equity investments											0
Impairment charges									0
Total assets	$ 513,054,000				$ 523,806,000				513,054,000	523,806,000	453,005,000
Capital expenditures									18,357,000	12,014,000	16,024,000
Unaffiliated entity [Member]
Segment Reporting Information [Line Items]
Total revenues									12,173,907,000	8,920,934,000	7,763,206,000
Unaffiliated entity [Member] | Natural Gas Gathering And Processing
Segment Reporting Information [Line Items]
Total revenues									1,750,655,000	1,375,738,000	1,187,390,000
Unaffiliated entity [Member] | Natural Gas Liquids
Segment Reporting Information [Line Items]
Total revenues									10,009,576,000	7,168,983,000	6,248,002,000
Unaffiliated entity [Member] | Natural Gas Pipelines
Segment Reporting Information [Line Items]
Total revenues									411,490,000	373,738,000	325,676,000
Unaffiliated entity [Member] | Total Segments [Member]
Segment Reporting Information [Line Items]
Total revenues									12,171,721,000	8,918,459,000	7,761,068,000
Unaffiliated entity [Member] | Other and Eliminations
Segment Reporting Information [Line Items]
Total revenues									2,186,000	2,475,000	2,138,000
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues									0	0	0
Operating Segments [Member] | Natural Gas Gathering And Processing
Segment Reporting Information [Line Items]
Total revenues									1,275,919,000	675,839,000	649,726,000
Operating Segments [Member] | Natural Gas Liquids
Segment Reporting Information [Line Items]
Total revenues									616,628,000	506,671,000	331,697,000
Operating Segments [Member] | Natural Gas Liquids | Natural Gas Liquids Regulated [Member]
Segment Reporting Information [Line Items]
Total revenues									1,017,100,000	992,800,000	770,100,000
Operating Segments [Member] | Natural Gas Pipelines
Segment Reporting Information [Line Items]
Total revenues									8,442,000	5,623,000	6,771,000
Operating Segments [Member] | Total Segments [Member]
Segment Reporting Information [Line Items]
Total revenues									1,900,989,000	1,188,133,000	988,194,000
Operating Segments [Member] | Other and Eliminations
Segment Reporting Information [Line Items]
Total revenues									(1,900,989,000)	$ (1,188,133,000)	$ (988,194,000)
Series E Preferred Stock [Member]
Segment Reporting Information [Line Items]
Noncash Contribution Expense									$ 20,000,000

QUARTERLY FINANCIAL DATA (UNA70

QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Total revenues	$ 3,792,158	$ 2,906,366	$ 2,725,772	$ 2,749,611	$ 2,654,461	$ 2,357,907	$ 2,134,107	$ 1,774,459	$ 12,173,907	$ 8,920,934	$ 7,763,206
Income from continuing operations					194,761	194,792	180,086	175,911	593,519	745,550	385,276
Income (loss) from discontinued operations, net of tax					(296)	(576)	(227)	(952)	0	(2,051)	(6,081)
Net income	64,812	166,531	175,991	186,185	194,465	194,216	179,859	174,959	593,519	743,499	379,195
Net income attributable to ONEOK	63,045	165,742	71,693	87,361	$ 90,505	$ 92,144	$ 85,944	$ 83,446	387,841	352,039	244,977
Net Income Available to Common Stockholders	$ 62,771	$ 165,466	$ 71,476	$ 87,361					$ 387,074	$ 352,039	$ 244,977
Earnings Per Share [Abstract]
Basic	$ 0.16	$ 0.43	$ 0.34	$ 0.41	$ 0.43	$ 0.44	$ 0.41	$ 0.40	$ 1.30	$ 1.68	$ 1.19
Diluted	$ 0.16	$ 0.43	$ 0.33	$ 0.41	$ 0.43	$ 0.43	$ 0.40	$ 0.40	$ 1.29	$ 1.67	$ 1.19
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount									$ 141,283	$ 43	$ 928
Asset Impairment Charges									20,240	0	264,256
Noncash Contribution Expense									12,600	$ 0	$ 0
Business Combination, Acquisition Related Costs									30,000
Series E Preferred Stock [Member]
Earnings Per Share [Abstract]
Noncash Contribution Expense									$ 20,000

SUPPLEMENTAL CONDENSED CONSOL71

SUPPLEMENTAL CONDENSED CONSOLIDATING FINANCIAL INFORMATION CONDENSED CONSOLIDATING FINANCIAL STATEMENTS, Income Statement (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017
Condensed Financial Statements, Captions [Line Items]
Commodity sales									$ 9,862,652	$ 6,858,456	$ 6,098,343
Services									2,311,255	2,062,478	1,664,863
Total revenues	$ 3,792,158	$ 2,906,366	$ 2,725,772	$ 2,749,611	$ 2,654,461	$ 2,357,907	$ 2,134,107	$ 1,774,459	12,173,907	8,920,934	7,763,206
Cost of sales and fuel (exclusive of items shown separately below)									9,538,045	6,496,124	5,641,052
Impairment of long-lived assets									15,970	0	83,673
Gain on sale of assets									(924)	(9,635)	(5,629)
Operating income									1,380,895	1,285,676	996,159
Equity in net earnings from investments									159,278	139,690	125,300
Impairment of equity investments									(4,270)	0	(180,583)
Interest expense, net									(485,658)	(469,651)	(416,787)
Income before income taxes									1,040,801	957,956	521,876
Income taxes									(447,282)	(212,406)	(136,600)
Income from continuing operations					194,761	194,792	180,086	175,911	593,519	745,550	385,276
Income (loss) from discontinued operations, net of tax					(296)	(576)	(227)	(952)	0	(2,051)	(6,081)
Net income	64,812	166,531	175,991	186,185	194,465	194,216	179,859	174,959	593,519	743,499	379,195
Less: Net income attributable to noncontrolling interests									205,678	391,460	134,218
Net income attributable to ONEOK	63,045	165,742	71,693	87,361	$ 90,505	$ 92,144	$ 85,944	$ 83,446	387,841	352,039	244,977
Less: Preferred stock dividends									767	0	0
Net income available to common shareholders	$ 62,771	$ 165,466	$ 71,476	$ 87,361					387,074	352,039	244,977
Northern Border Pipeline [Member]
Condensed Financial Statements, Captions [Line Items]
Equity in net earnings from investments									$ 68,153	$ 69,990	66,941
Equity Method Investment, Ownership Percentage	50.00%				50.00%				50.00%	50.00%		50.00%
Reportable Legal Entities | Parent Issuer & Guarantor
Condensed Financial Statements, Captions [Line Items]
Commodity sales									$ 0	$ 0	0
Services									0	0	0
Total revenues									0	0	0
Cost of sales and fuel (exclusive of items shown separately below)									0	0	0
Operating expenses									28,700	28,800	1,200
Impairment of long-lived assets									0		0
Gain on sale of assets									0	300	0
Operating income									(28,700)	(29,100)	(1,200)
Equity in net earnings from investments									1,236,600	1,063,900	583,800
Impairment of equity investments									0		0
Other income (expense), net									(1,400)	5,100	4,000
Interest expense, net									(137,100)	(102,900)	(85,100)
Income before income taxes									1,069,400	937,000	501,500
Income taxes									(480,200)	(199,000)	(130,700)
Income from continuing operations										738,000	370,800
Income (loss) from discontinued operations, net of tax										0	0
Net income									589,200	738,000	370,800
Less: Net income attributable to noncontrolling interests									201,400	386,000	125,800
Net income attributable to ONEOK									387,800	352,000	245,000
Less: Preferred stock dividends									800
Net income available to common shareholders									387,000
Reportable Legal Entities | Subsidiary Issuer & Guarantor
Condensed Financial Statements, Captions [Line Items]
Commodity sales									0	0	0
Services									0	0	0
Total revenues									0	0	0
Cost of sales and fuel (exclusive of items shown separately below)									0	0	0
Operating expenses									0	0	0
Impairment of long-lived assets									0		0
Gain on sale of assets									0	0	0
Operating income									0	0	0
Equity in net earnings from investments									1,215,700	1,066,800	589,500
Impairment of equity investments									0		0
Other income (expense), net									353,100	373,500	371,000
Interest expense, net									(353,100)	(373,500)	(371,000)
Income before income taxes									1,215,700	1,066,800	589,500
Income taxes									0	0	0
Income from continuing operations										1,066,800	589,500
Income (loss) from discontinued operations, net of tax										0	0
Net income									1,215,700	1,066,800	589,500
Less: Net income attributable to noncontrolling interests									0	0	0
Net income attributable to ONEOK									1,215,700	1,066,800	589,500
Less: Preferred stock dividends									0
Net income available to common shareholders									1,215,700
Reportable Legal Entities | Guarantor Subsidiary
Condensed Financial Statements, Captions [Line Items]
Commodity sales									0	0	0
Services									0	0	0
Total revenues									0	0	0
Cost of sales and fuel (exclusive of items shown separately below)									0	0	0
Operating expenses									9,200	0	0
Impairment of long-lived assets									0		0
Gain on sale of assets									0	0	0
Operating income									(9,200)	0	0
Equity in net earnings from investments									1,224,900	1,066,800	589,500
Impairment of equity investments									0		0
Other income (expense), net									353,100	373,500	371,000
Interest expense, net									(353,100)	(373,500)	(371,000)
Income before income taxes									1,215,700	1,066,800	589,500
Income taxes									0	0	0
Income from continuing operations										1,066,800	589,500
Income (loss) from discontinued operations, net of tax										0	0
Net income									1,215,700	1,066,800	589,500
Less: Net income attributable to noncontrolling interests									0	0	0
Net income attributable to ONEOK									1,215,700	1,066,800	589,500
Less: Preferred stock dividends									0
Net income available to common shareholders									1,215,700
Reportable Legal Entities | Combined Non-Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Commodity sales									9,862,700	6,858,500	6,098,300
Services									2,313,200	2,064,300	1,669,800
Total revenues									12,175,900	8,922,800	7,768,100
Cost of sales and fuel (exclusive of items shown separately below)									9,538,000	6,496,100	5,641,100
Operating expenses									1,204,000	1,121,800	1,051,500
Impairment of long-lived assets									16,000		83,700
Gain on sale of assets									(900)	(9,900)	(5,600)
Operating income									1,418,800	1,314,800	997,400
Equity in net earnings from investments									100,700	69,700	58,400
Impairment of equity investments									(4,300)		(180,600)
Other income (expense), net									(8,000)	(2,800)	(6,200)
Interest expense, net									(348,600)	(366,800)	(331,700)
Income before income taxes									1,158,600	1,014,900	537,300
Income taxes									32,900	(13,400)	(5,900)
Income from continuing operations										1,001,500	531,400
Income (loss) from discontinued operations, net of tax										(2,100)	(6,100)
Net income									1,191,500	999,400	525,300
Less: Net income attributable to noncontrolling interests									4,300	5,500	8,400
Net income attributable to ONEOK									1,187,200	993,900	516,900
Less: Preferred stock dividends									0
Net income available to common shareholders									1,187,200
Reportable Legal Entities | Total
Condensed Financial Statements, Captions [Line Items]
Commodity sales									9,862,700	6,858,500	6,098,300
Services									2,311,200	2,062,500	1,664,900
Total revenues									12,173,900	8,921,000	7,763,200
Cost of sales and fuel (exclusive of items shown separately below)									9,538,000	6,496,100	5,641,100
Operating expenses									1,239,900	1,148,800	1,047,800
Impairment of long-lived assets									16,000		83,700
Gain on sale of assets									(900)	(9,600)	(5,600)
Operating income									1,380,900	1,285,700	996,200
Equity in net earnings from investments									159,300	139,700	125,300
Impairment of equity investments									(4,300)		(180,600)
Other income (expense), net									(9,400)	2,300	(2,200)
Interest expense, net									(485,700)	(469,700)	(416,800)
Income before income taxes									1,040,800	958,000	521,900
Income taxes									(447,300)	(212,400)	(136,600)
Income from continuing operations										745,600	385,300
Income (loss) from discontinued operations, net of tax										(2,100)	(6,100)
Net income									593,500	743,500	379,200
Less: Net income attributable to noncontrolling interests									205,700	391,500	134,200
Net income attributable to ONEOK									387,800	352,000	245,000
Less: Preferred stock dividends									800
Net income available to common shareholders									387,000
Consolidating Entries
Condensed Financial Statements, Captions [Line Items]
Commodity sales									0	0	0
Services									(2,000)	(1,800)	(4,900)
Total revenues									(2,000)	(1,800)	(4,900)
Cost of sales and fuel (exclusive of items shown separately below)									0	0	0
Operating expenses									(2,000)	(1,800)	(4,900)
Impairment of long-lived assets									0		0
Gain on sale of assets									0	0	0
Operating income									0	0	0
Equity in net earnings from investments									(3,618,600)	(3,127,500)	(1,695,900)
Impairment of equity investments									0		0
Other income (expense), net									(706,200)	(747,000)	(742,000)
Interest expense, net									706,200	747,000	742,000
Income before income taxes									(3,618,600)	(3,127,500)	(1,695,900)
Income taxes									0	0	0
Income from continuing operations										(3,127,500)	(1,695,900)
Income (loss) from discontinued operations, net of tax										0	0
Net income									(3,618,600)	(3,127,500)	(1,695,900)
Less: Net income attributable to noncontrolling interests									0	0	0
Net income attributable to ONEOK									(3,618,600)	$ (3,127,500)	$ (1,695,900)
Less: Preferred stock dividends									0
Net income available to common shareholders									$ (3,618,600)

SUPPLEMENTAL CONDENSED CONSOL72

SUPPLEMENTAL CONDENSED CONSOLIDATING FINANCIAL INFORMATION CONDENSED CONSOLIDATING FINANCIAL INFORMATION, Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Financial Statements, Captions [Line Items]
Net income	$ 64,812	$ 166,531	$ 175,991	$ 186,185	$ 194,465	$ 194,216	$ 179,859	$ 174,959	$ 593,519	$ 743,499	$ 379,195
Other comprehensive income (loss), net of tax
Unrealized gains (losses) on derivatives, net of tax									(21,408)	(30,300)	41,362
Realized (gains) losses on derivatives in net income, net of tax									(63,687)	6,977	54,709
Unrealized holding gains (losses) on available-for-sale securities, net of tax									0	0	(955)
Change in pension and postretirement benefit plan liability, net of tax									4,175	16,693	(15,416)
Other comprehensive income (loss) on investments in unconsolidated affiliates, net of tax									(970)	(1,505)	(1,632)
Total other comprehensive income (loss), net of tax									37,134	(55,475)	(518)
Comprehensive income									630,653	688,024	378,677
Less: Comprehensive income attributable to noncontrolling interests									236,704	363,093	124,589
Comprehensive income attributable to ONEOK									393,949	324,931	254,088
Reportable Legal Entities | Parent Issuer & Guarantor
Condensed Financial Statements, Captions [Line Items]
Net income									589,200	738,000	370,800
Other comprehensive income (loss), net of tax
Unrealized gains (losses) on derivatives, net of tax									19,100	0	0
Realized (gains) losses on derivatives in net income, net of tax									2,500	2,100	2,100
Unrealized holding gains (losses) on available-for-sale securities, net of tax											0
Change in pension and postretirement benefit plan liability, net of tax									(4,200)	(16,700)	15,400
Other comprehensive income (loss) on investments in unconsolidated affiliates, net of tax									0	0	0
Total other comprehensive income (loss), net of tax									17,400	(14,600)	17,500
Comprehensive income									606,600	723,400	388,300
Less: Comprehensive income attributable to noncontrolling interests									232,400	357,600	116,200
Comprehensive income attributable to ONEOK									374,200	365,800	272,100
Reportable Legal Entities | Subsidiary Issuer & Guarantor
Condensed Financial Statements, Captions [Line Items]
Net income									1,215,700	1,066,800	589,500
Other comprehensive income (loss), net of tax
Unrealized gains (losses) on derivatives, net of tax									(72,200)	(35,800)	47,500
Realized (gains) losses on derivatives in net income, net of tax									86,500	(10,700)	(67,000)
Unrealized holding gains (losses) on available-for-sale securities, net of tax											0
Change in pension and postretirement benefit plan liability, net of tax									0	0	0
Other comprehensive income (loss) on investments in unconsolidated affiliates, net of tax									(1,100)	(1,800)	(1,900)
Total other comprehensive income (loss), net of tax									13,200	(48,300)	(21,400)
Comprehensive income									1,228,900	1,018,500	568,100
Less: Comprehensive income attributable to noncontrolling interests									0	0	0
Comprehensive income attributable to ONEOK									1,228,900	1,018,500	568,100
Reportable Legal Entities | Guarantor Subsidiary
Condensed Financial Statements, Captions [Line Items]
Net income									1,215,700	1,066,800	589,500
Other comprehensive income (loss), net of tax
Unrealized gains (losses) on derivatives, net of tax									(40,600)	(78,500)	70,100
Realized (gains) losses on derivatives in net income, net of tax									69,600	(26,400)	(81,100)
Unrealized holding gains (losses) on available-for-sale securities, net of tax											0
Change in pension and postretirement benefit plan liability, net of tax									0	0	0
Other comprehensive income (loss) on investments in unconsolidated affiliates, net of tax									(1,100)	(1,800)	(1,900)
Total other comprehensive income (loss), net of tax									27,900	(106,700)	(12,900)
Comprehensive income									1,243,600	960,100	576,600
Less: Comprehensive income attributable to noncontrolling interests									0	0	0
Comprehensive income attributable to ONEOK									1,243,600	960,100	576,600
Reportable Legal Entities | Combined Non-Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Net income									1,191,500	999,400	525,300
Other comprehensive income (loss), net of tax
Unrealized gains (losses) on derivatives, net of tax									(8,800)	(108,800)	111,500
Realized (gains) losses on derivatives in net income, net of tax									44,300	(33,400)	(137,900)
Unrealized holding gains (losses) on available-for-sale securities, net of tax											(1,000)
Change in pension and postretirement benefit plan liability, net of tax									0	0	0
Other comprehensive income (loss) on investments in unconsolidated affiliates, net of tax									(1,000)	(3,300)	(3,500)
Total other comprehensive income (loss), net of tax									34,500	(145,500)	(30,900)
Comprehensive income									1,226,000	853,900	494,400
Less: Comprehensive income attributable to noncontrolling interests									4,300	5,500	8,400
Comprehensive income attributable to ONEOK									1,221,700	848,400	486,000
Reportable Legal Entities | Total
Condensed Financial Statements, Captions [Line Items]
Net income									593,500	743,500	379,200
Other comprehensive income (loss), net of tax
Unrealized gains (losses) on derivatives, net of tax									(21,400)	(30,300)	41,400
Realized (gains) losses on derivatives in net income, net of tax									63,700	(7,000)	(54,700)
Unrealized holding gains (losses) on available-for-sale securities, net of tax											(1,000)
Change in pension and postretirement benefit plan liability, net of tax									(4,200)	(16,700)	15,400
Other comprehensive income (loss) on investments in unconsolidated affiliates, net of tax									(1,000)	(1,500)	(1,600)
Total other comprehensive income (loss), net of tax									37,100	(55,500)	(500)
Comprehensive income									630,600	688,000	378,700
Less: Comprehensive income attributable to noncontrolling interests									236,700	363,100	124,600
Comprehensive income attributable to ONEOK									393,900	324,900	254,100
Consolidating Entries
Condensed Financial Statements, Captions [Line Items]
Net income									(3,618,600)	(3,127,500)	(1,695,900)
Other comprehensive income (loss), net of tax
Unrealized gains (losses) on derivatives, net of tax									81,100	192,800	(187,700)
Realized (gains) losses on derivatives in net income, net of tax									(139,200)	61,400	229,200
Unrealized holding gains (losses) on available-for-sale securities, net of tax											0
Change in pension and postretirement benefit plan liability, net of tax									0	0	0
Other comprehensive income (loss) on investments in unconsolidated affiliates, net of tax									2,200	5,400	5,700
Total other comprehensive income (loss), net of tax									(55,900)	259,600	47,200
Comprehensive income									(3,674,500)	(2,867,900)	(1,648,700)
Less: Comprehensive income attributable to noncontrolling interests									0	0	0
Comprehensive income attributable to ONEOK									$ (3,674,500)	$ (2,867,900)	$ (1,648,700)

SUPPLEMENTAL CONDENSED CONSOL73

SUPPLEMENTAL CONDENSED CONSOLIDATING FINANCIAL INFORMATION CONDENSED CONSOLIDATING FINANCIAL STATEMENTS, Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current assets
Cash and cash equivalents	$ 37,193	$ 248,875	$ 97,619	$ 172,812
Accounts receivable, net	1,202,951	872,430
Materials and supplies	90,301	60,912
Natural gas and natural gas liquids in storage	342,293	140,034
Other current assets	53,008	45,986
Assets of discontinued operations	0	551
Total current assets	1,764,458	1,429,684
Property, plant and equipment
Property, plant and equipment	15,559,667	15,078,497
Accumulated depreciation and amortization	2,861,541	2,507,094
Net property, plant and equipment	12,698,126	12,571,403
Investments and other assets
Investments	1,003,156	958,807
Goodwill and intangible assets	993,460	1,005,359
Other assets	180,830	162,998
Assets of discontinued operations	0	10,500
Total investments and other assets	2,383,353	2,137,664
Total assets	16,845,937	16,138,751	15,446,111
Current liabilities
Current maturities of long-term debt	432,650	410,650
Short-term borrowings	614,673	1,110,277
Accounts payable	1,140,571	874,731
Commodity imbalances	164,161	142,646
Accrued interest	135,309	112,514
Other current liabilities	179,971	166,042
Liabilities of discontinued operations	0	19,841
Total current liabilities	2,667,335	2,836,701
Long-term debt, excluding current maturities	8,091,629	7,919,996
Deferred credits and other liabilities	401,621	1,953,139
Commitments and contingencies
Equity
Equity excluding noncontrolling interests in consolidated subsidiaries	5,527,867	188,745
Noncontrolling interests in consolidated subsidiaries	157,485	3,240,170
Total equity	5,685,352	3,428,915	3,766,336	4,005,883
Total liabilities and equity	16,845,937	16,138,751
Reportable Legal Entities | Parent Issuer & Guarantor
Current assets
Cash and cash equivalents	37,200	248,500	92,500	130,300
Accounts receivable, net	0	0
Materials and supplies	0	0
Natural gas and natural gas liquids in storage	0	0
Other current assets	9,800	7,200
Assets of discontinued operations		0
Total current assets	47,000	255,700
Property, plant and equipment
Property, plant and equipment	128,300	139,800
Accumulated depreciation and amortization	86,400	90,400
Net property, plant and equipment	41,900	49,400
Investments and other assets
Investments	5,752,100	2,931,900
Intercompany notes receivable	2,926,900	205,200
Goodwill and intangible assets		0
Other assets	416,900	103,400
Assets of discontinued operations		0
Total investments and other assets	9,095,900	3,240,500
Total assets	9,184,800	3,545,600
Current liabilities
Current maturities of long-term debt	0	3,000
Short-term borrowings	614,700	0
Accounts payable	12,000	13,000
Commodity imbalances		0
Accrued interest		25,400
Other current liabilities	65,900	19,300
Liabilities of discontinued operations		0
Total current liabilities	692,600	60,700
Intercompany debt	0	0
Long-term debt, excluding current maturities	2,726,400	1,628,700
Deferred credits and other liabilities	237,900	1,667,500
Commitments and contingencies
Equity
Equity excluding noncontrolling interests in consolidated subsidiaries	5,527,900	188,700
Noncontrolling interests in consolidated subsidiaries	0	0
Total equity	5,527,900	188,700
Total liabilities and equity	9,184,800	3,545,600
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	0
Natural gas and natural gas liquids in storage	0	0
Other current assets	1,300	0
Assets of discontinued operations		0
Total current assets	1,300	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	3,133,700	3,222,100
Intercompany notes receivable	8,627,800	10,615,000
Goodwill and intangible assets		0
Other assets	200	47,500
Assets of discontinued operations		0
Total investments and other assets	11,761,700	13,884,600
Total assets	11,763,000	13,884,600
Current liabilities
Current maturities of long-term debt	425,000	400,000
Short-term borrowings	0	1,110,300
Accounts payable	0	0
Commodity imbalances		0
Accrued interest		87,100
Other current liabilities	85,000	12,800
Liabilities of discontinued operations		0
Total current liabilities	510,000	1,610,200
Intercompany debt	0	0
Long-term debt, excluding current maturities	5,336,400	6,254,700
Deferred credits and other liabilities	0	0
Commitments and contingencies
Equity
Equity excluding noncontrolling interests in consolidated subsidiaries	5,916,600	6,019,700
Noncontrolling interests in consolidated subsidiaries	0	0
Total equity	5,916,600	6,019,700
Total liabilities and equity	11,763,000	13,884,600
Reportable Legal Entities | Guarantor Subsidiary
Current assets
Cash and cash equivalents	0	400	5,100	42,500
Accounts receivable, net	0	0
Materials and supplies	0	0
Natural gas and natural gas liquids in storage	0	0
Other current assets	0	0
Assets of discontinued operations		0
Total current assets	0	400
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	8,058,400	6,805,400
Intercompany notes receivable	3,703,100	7,031,300
Goodwill and intangible assets		0
Other assets	0	0
Assets of discontinued operations		0
Total investments and other assets	11,761,500	13,836,700
Total assets	11,761,500	13,837,100
Current liabilities
Current maturities of long-term debt	0	0
Short-term borrowings	0	0
Accounts payable	0	0
Commodity imbalances		0
Accrued interest		0
Other current liabilities	0	0
Liabilities of discontinued operations		0
Total current liabilities	0	0
Intercompany debt	8,627,800	10,615,000
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	3,133,700	3,222,100
Noncontrolling interests in consolidated subsidiaries	0	0
Total equity	3,133,700	3,222,100
Total liabilities and equity	11,761,500	13,837,100
Reportable Legal Entities | Combined Non-Guarantor Subsidiaries
Current assets
Cash and cash equivalents	0	0	0	0
Accounts receivable, net	1,203,000	872,400
Materials and supplies	90,300	60,900
Natural gas and natural gas liquids in storage	342,300	140,000
Other current assets	80,600	99,700
Assets of discontinued operations		600
Total current assets	1,716,200	1,173,600
Property, plant and equipment
Property, plant and equipment	15,431,300	14,938,700
Accumulated depreciation and amortization	2,775,100	2,416,700
Net property, plant and equipment	12,656,200	12,522,000
Investments and other assets
Investments	803,000	631,100
Intercompany notes receivable	0	0
Goodwill and intangible assets		1,005,400
Other assets	1,007,400	12,100
Assets of discontinued operations		10,500
Total investments and other assets	1,810,400	1,659,100
Total assets	16,182,800	15,354,700
Current liabilities
Current maturities of long-term debt	7,700	7,700
Short-term borrowings	0	0
Accounts payable	1,128,600	861,700
Commodity imbalances		142,600
Accrued interest		0
Other current liabilities	328,400	134,100
Liabilities of discontinued operations		19,800
Total current liabilities	1,464,700	1,165,900
Intercompany debt	6,630,000	7,236,500
Long-term debt, excluding current maturities	28,800	36,600
Deferred credits and other liabilities	208,100	285,600
Commitments and contingencies
Equity
Equity excluding noncontrolling interests in consolidated subsidiaries	7,693,700	6,472,000
Noncontrolling interests in consolidated subsidiaries	157,500	158,100
Total equity	7,851,200	6,630,100
Total liabilities and equity	16,182,800	15,354,700
Reportable Legal Entities | Total
Current assets
Cash and cash equivalents	37,200	248,900	97,600	172,800
Accounts receivable, net	1,203,000	872,400
Materials and supplies	90,300	60,900
Natural gas and natural gas liquids in storage	342,300	140,000
Other current assets	91,700	106,900
Assets of discontinued operations		600
Total current assets	1,764,500	1,429,700
Property, plant and equipment
Property, plant and equipment	15,559,600	15,078,500
Accumulated depreciation and amortization	2,861,500	2,507,100
Net property, plant and equipment	12,698,100	12,571,400
Investments and other assets
Investments	1,003,200	958,800
Intercompany notes receivable	0	0
Goodwill and intangible assets		1,005,400
Other assets	1,380,100	163,000
Assets of discontinued operations		10,500
Total investments and other assets	2,383,300	2,137,700
Total assets	16,845,900	16,138,800
Current liabilities
Current maturities of long-term debt	432,700	410,700
Short-term borrowings	614,700	1,110,300
Accounts payable	1,140,600	874,700
Commodity imbalances		142,600
Accrued interest		112,500
Other current liabilities	479,300	166,200
Liabilities of discontinued operations		19,800
Total current liabilities	2,667,300	2,836,800
Intercompany debt	0	0
Long-term debt, excluding current maturities	8,091,600	7,920,000
Deferred credits and other liabilities	401,600	1,953,100
Commitments and contingencies
Equity
Equity excluding noncontrolling interests in consolidated subsidiaries	5,527,900	188,700
Noncontrolling interests in consolidated subsidiaries	157,500	3,240,200
Total equity	5,685,400	3,428,900
Total liabilities and equity	16,845,900	16,138,800
Consolidating Entries
Current assets
Cash and cash equivalents	0	0	$ 0	$ 0
Accounts receivable, net	0	0
Materials and supplies	0	0
Natural gas and natural gas liquids in storage	0	0
Other current assets	0	0
Assets of discontinued operations		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	(16,744,000)	(12,631,700)
Intercompany notes receivable	(15,257,800)	(17,851,500)
Goodwill and intangible assets		0
Other assets	(44,400)	0
Assets of discontinued operations		0
Total investments and other assets	(32,046,200)	(30,483,200)
Total assets	(32,046,200)	(30,483,200)
Current liabilities
Current maturities of long-term debt	0	0
Short-term borrowings	0	0
Accounts payable	0	0
Commodity imbalances		0
Accrued interest		0
Other current liabilities	0	0
Liabilities of discontinued operations		0
Total current liabilities	0	0
Intercompany debt	(15,257,800)	(17,851,500)
Long-term debt, excluding current maturities	0	0
Deferred credits and other liabilities	(44,400)	0
Commitments and contingencies
Equity
Equity excluding noncontrolling interests in consolidated subsidiaries	(16,744,000)	(15,713,800)
Noncontrolling interests in consolidated subsidiaries	0	3,082,100
Total equity	(16,744,000)	(12,631,700)
Total liabilities and equity	$ (32,046,200)	$ (30,483,200)

SUPPLEMENTAL CONDENSED CONSOL74

SUPPLEMENTAL CONDENSED CONSOLIDATING FINANCIAL INFORMATION CONDENSED CONSOLIDATING FINANCIAL STATEMENTS, Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities
Cash provided by operating activities	$ 1,315,412	$ 1,353,341	$ 1,022,828
Investing activities
Capital expenditures	(512,393)	(624,634)	(1,188,312)
Contributions to unconsolidated affiliates	(87,861)	(68,275)	(27,540)
Other investing activities	0	0	(12,607)
Cash provided by (used in) investing activities	(567,633)	(615,445)	(1,190,719)
Financing activities
Dividends paid	(829,414)	(517,601)	(509,197)
Distributions to noncontrolling interests	(276,260)	(549,419)	(535,825)
Borrowing (repayment) of short-term borrowings, net	(495,604)	563,937	(508,956)
Issuance of long-term debt, net of discounts	1,190,496	1,000,000	1,291,506
Debt financing costs	(11,425)	(2,770)	(17,515)
Repayment of long-term debt	(994,776)	(1,108,040)	(7,753)
Issuance of common stock	471,358	21,971	20,669
Issuance of common units, net of issuance costs	0	0	375,660
Other	(13,836)	5,403	(15,848)
Cash provided by (used in) financing activities	(959,461)	(586,519)	92,741
Change in cash and cash equivalents	(211,682)	151,377	(75,150)
Change in cash and cash equivalents included in discontinued operations	0	(121)	(43)
Change in cash and cash equivalents included in continuing operations	(211,682)	151,256	(75,193)
Cash and cash equivalents at beginning of period	248,875	97,619	172,812
Cash and cash equivalents at end of period	37,193	248,875	97,619
Reportable Legal Entities | Parent Issuer & Guarantor
Operating activities
Cash provided by operating activities	947,400	717,000	650,300
Investing activities
Capital expenditures	0	(200)	(100)
Contributions to unconsolidated affiliates	0		(671,000)
Other investing activities	0	0	0
Cash provided by (used in) investing activities	0	(200)	(671,100)
Financing activities
Dividends paid	(829,400)	(517,600)	(509,200)
Distributions to noncontrolling interests	0	0	0
Intercompany borrowings (advances), net	(2,500,700)	(63,100)	4,600
Borrowing (repayment) of short-term borrowings, net	614,700	0	0
Issuance of long-term debt, net of discounts	1,190,500	0	492,600
Debt financing costs		0	(9,800)
Repayment of long-term debt	(87,100)	(300)	(100)
Issuance of common stock	471,400	22,000	20,700
Issuance of common units, net of issuance costs			0
Contribution from general partner			0
Other	(18,100)	(1,700)	(15,800)
Cash provided by (used in) financing activities	(1,158,700)	(560,700)	(17,000)
Change in cash and cash equivalents	(211,300)	156,100	(37,800)
Change in cash and cash equivalents included in discontinued operations		(100)
Change in cash and cash equivalents included in continuing operations		156,000
Cash and cash equivalents at beginning of period	248,500	92,500	130,300
Cash and cash equivalents at end of period	37,200	248,500	92,500
Reportable Legal Entities | Subsidiary Issuer & Guarantor
Operating activities
Cash provided by operating activities	1,348,300	1,334,500	1,196,700
Investing activities
Capital expenditures	0	0	0
Contributions to unconsolidated affiliates	0		0
Other investing activities	0	0	0
Cash provided by (used in) investing activities	0	0	0
Financing activities
Dividends paid	(1,332,000)	(1,332,000)	(1,230,500)
Distributions to noncontrolling interests	0	0	0
Intercompany borrowings (advances), net	2,001,200	(470,800)	(1,295,100)
Borrowing (repayment) of short-term borrowings, net	(1,110,300)	563,900	(509,000)
Issuance of long-term debt, net of discounts	0	1,000,000	798,900
Debt financing costs		(2,800)	(7,700)
Repayment of long-term debt	(900,000)	(1,100,000)	0
Issuance of common stock	0	0	0
Issuance of common units, net of issuance costs			1,025,700
Contribution from general partner			21,000
Other	(7,200)	7,200	0
Cash provided by (used in) financing activities	(1,348,300)	(1,334,500)	(1,196,700)
Change in cash and cash equivalents	0	0	0
Change in cash and cash equivalents included in discontinued operations		0
Change in cash and cash equivalents included in continuing operations		0
Cash and cash equivalents at beginning of period	0	0	0
Cash and cash equivalents at end of period	0	0	0
Reportable Legal Entities | Guarantor Subsidiary
Operating activities
Cash provided by operating activities	59,000	70,000	66,900
Investing activities
Capital expenditures	0	0	0
Contributions to unconsolidated affiliates	(83,000)		0
Other investing activities	(14,800)	(34,900)	(24,100)
Cash provided by (used in) investing activities	(68,200)	34,900	24,100
Financing activities
Dividends paid	(1,332,000)	(1,332,000)	(1,230,500)
Distributions to noncontrolling interests	0	0	0
Intercompany borrowings (advances), net	1,340,800	1,222,400	1,102,100
Borrowing (repayment) of short-term borrowings, net	0	0	0
Issuance of long-term debt, net of discounts	0	0	0
Debt financing costs		0	0
Repayment of long-term debt	0	0	0
Issuance of common stock	0	0	0
Issuance of common units, net of issuance costs			0
Contribution from general partner			0
Other	0	0	0
Cash provided by (used in) financing activities	8,800	(109,600)	(128,400)
Change in cash and cash equivalents	(400)	(4,700)	(37,400)
Change in cash and cash equivalents included in discontinued operations		0
Change in cash and cash equivalents included in continuing operations		(4,700)
Cash and cash equivalents at beginning of period	400	5,100	42,500
Cash and cash equivalents at end of period	0	400	5,100
Reportable Legal Entities | Combined Non-Guarantor Subsidiaries
Operating activities
Cash provided by operating activities	1,353,700	1,353,900	1,045,700
Investing activities
Capital expenditures	(512,400)	(624,400)	(1,188,200)
Contributions to unconsolidated affiliates	(4,900)		(27,500)
Other investing activities	(17,900)	25,700	(1,000)
Cash provided by (used in) investing activities	(499,400)	(650,100)	(1,214,700)
Financing activities
Dividends paid	0	0	0
Distributions to noncontrolling interests	(5,300)	(7,500)	(11,700)
Intercompany borrowings (advances), net	(841,300)	(688,500)	188,400
Borrowing (repayment) of short-term borrowings, net	0	0	0
Issuance of long-term debt, net of discounts	0	0	0
Debt financing costs		0	0
Repayment of long-term debt	(7,700)	(7,700)	(7,700)
Issuance of common stock	0	0	0
Issuance of common units, net of issuance costs			0
Contribution from general partner			0
Other	0	(100)	0
Cash provided by (used in) financing activities	(854,300)	(703,800)	169,000
Change in cash and cash equivalents	0	0	0
Change in cash and cash equivalents included in discontinued operations		0
Change in cash and cash equivalents included in continuing operations		0
Cash and cash equivalents at beginning of period	0	0	0
Cash and cash equivalents at end of period	0	0	0
Reportable Legal Entities | Total
Operating activities
Cash provided by operating activities	1,315,400	1,353,300	1,022,800
Investing activities
Capital expenditures	(512,400)	(624,600)	(1,188,300)
Contributions to unconsolidated affiliates	(87,900)		(27,500)
Other investing activities	(32,700)	(9,200)	(25,100)
Cash provided by (used in) investing activities	(567,600)	(615,400)	(1,190,700)
Financing activities
Dividends paid	(829,400)	(517,600)	(509,200)
Distributions to noncontrolling interests	(276,300)	(549,400)	(535,900)
Intercompany borrowings (advances), net	0	0	0
Borrowing (repayment) of short-term borrowings, net	(495,600)	563,900	(509,000)
Issuance of long-term debt, net of discounts	1,190,500	1,000,000	1,291,500
Debt financing costs		(2,800)	(17,500)
Repayment of long-term debt	(994,800)	(1,108,000)	(7,800)
Issuance of common stock	471,400	22,000	20,700
Issuance of common units, net of issuance costs			375,700
Contribution from general partner			0
Other	(25,300)	5,400	(15,800)
Cash provided by (used in) financing activities	(959,500)	(586,500)	92,700
Change in cash and cash equivalents	(211,700)	151,400	(75,200)
Change in cash and cash equivalents included in discontinued operations		(100)
Change in cash and cash equivalents included in continuing operations		151,300
Cash and cash equivalents at beginning of period	248,900	97,600	172,800
Cash and cash equivalents at end of period	37,200	248,900	97,600
Consolidating Entries
Operating activities
Cash provided by operating activities	(2,393,000)	(2,122,100)	(1,936,800)
Investing activities
Capital expenditures	0	0	0
Contributions to unconsolidated affiliates	0		671,000
Other investing activities	0	0	0
Cash provided by (used in) investing activities	0	0	671,000
Financing activities
Dividends paid	2,664,000	2,664,000	2,461,000
Distributions to noncontrolling interests	(271,000)	(541,900)	(524,200)
Intercompany borrowings (advances), net	0	0	0
Borrowing (repayment) of short-term borrowings, net	0	0	0
Issuance of long-term debt, net of discounts	0	0	0
Debt financing costs		0	0
Repayment of long-term debt	0	0	0
Issuance of common stock	0	0	0
Issuance of common units, net of issuance costs			(650,000)
Contribution from general partner			(21,000)
Other	0	0	0
Cash provided by (used in) financing activities	2,393,000	2,122,100	1,265,800
Change in cash and cash equivalents	0	0	0
Change in cash and cash equivalents included in discontinued operations		0
Change in cash and cash equivalents included in continuing operations		0
Cash and cash equivalents at beginning of period	0	0	0
Cash and cash equivalents at end of period	$ 0	$ 0	$ 0