QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Total revenues	$ 3,136,700	$ 3,393,890	$ 2,960,529	$ 3,102,077	$ 3,792,158	$ 2,906,366	$ 2,725,772	$ 2,749,611	$ 12,593,196	$ 12,173,907	$ 8,920,934
Net income	292,888	313,916	282,179	266,049	64,812	166,531	175,991	186,185	1,155,032	593,519	743,499
Net income attributable to ONEOK	292,888	313,259	281,048	264,508	63,045	165,742	71,693	87,361	1,151,703	387,841	352,039
Net income available to common shareholders	$ 292,613	$ 312,984	$ 280,773	$ 264,233	$ 62,771	$ 165,466	$ 71,476	$ 87,361	$ 1,150,603	$ 387,074	$ 352,039
Basic	$ 0.71	$ 0.76	$ 0.68	$ 0.65	$ 0.16	$ 0.43	$ 0.34	$ 0.41	$ 2.80	$ 1.30	$ 1.67
Diluted	$ 0.70	$ 0.75	$ 0.68	$ 0.64	$ 0.16	$ 0.43	$ 0.33	$ 0.41	2.78	1.29	1.66
Earnings Per Share [Abstract]
Basic									2.80	1.30	1.68
Diluted									$ 2.78	$ 1.29	$ 1.67
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount									$ 5,552	$ 141,283	$ 43
Asset Impairment Charges									0	20,240	0
Noncash Contribution Expense									0	12,600	$ 0
Business Combination, Consideration Transferred		$ 195,000							$ 195,000
Business Combination, Acquisition Related Costs										30,000
Series E Preferred Stock [Member]
Earnings Per Share [Abstract]
Noncash Contribution Expense										$ 20,000