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)