EARNINGS PER SHARE EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, shares in Thousands, $ 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
Basic EPS
Net income available for common stock	$ 292,613	$ 312,984	$ 280,773	$ 264,233	$ 62,771	$ 165,466	$ 71,476	$ 87,361	$ 1,150,603	$ 387,074	$ 352,039
Shares									411,485	297,477	211,128
Basic	$ 0.71	$ 0.76	$ 0.68	$ 0.65	$ 0.16	$ 0.43	$ 0.34	$ 0.41	$ 2.80	$ 1.30	$ 1.67
Diluted EPS
Effect of dilutive securities									$ 0	$ 0	$ 0
Effect of dilutive securities, number of shares									2,710	2,303	1,255
Net income attributable to ONEOK available for common stock and common stock equivalents									$ 1,150,603	$ 387,074	$ 352,039
Shares									414,195	299,780	212,383
Diluted	$ 0.70	$ 0.75	$ 0.68	$ 0.64	$ 0.16	$ 0.43	$ 0.33	$ 0.41	$ 2.78	$ 1.29	$ 1.66