EARNINGS PER SHARE - Earnings Per Share Computation (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Earnings Per Share [Abstract]
Income (loss) from continuing operations	$ 1,373	$ 3,030	$ (82)
Income from continuing operations attributable to noncontrolling interest	41	45	41
Net income (loss) from continuing operations attributable to Cliffs shareholders	1,332	2,985	(123)
Income from discontinued operations, net of tax	3	3	1
Net income (loss) attributable to Cliffs shareholders	$ 1,335	$ 2,988	$ (122)
Weighted average number of shares:
Basic (in shares)	519	498	379
Redeemable preferred shares (in shares)	0	33	0
Convertible senior notes (in shares)	2	22	0
Employee stock plans (in shares)	3	5	0
Diluted (in shares)	524	558	379
Earnings (loss) per common share attributable to Cliffs common shareholders - basic2:
Continuing operations (in dollars per share)	$ 2.57	$ 5.62	$ (0.32)
Discontinued operations (in dollars per share)	0	0.01	0
Earnings (loss) per common share attributable to Cliffs common shareholders - basic (in dollars per share)	2.57	5.63	(0.32)
Earnings (loss) per common share attributable to Cliffs common shareholders - diluted:
Continuing operations (in dollars per share)	2.55	5.35	(0.32)
Discontinued operations (in dollars per share)	0	0.01	0
Earnings (loss) per common share attributable to Cliffs common shareholders - diluted (in dollars per share)	$ 2.55	$ 5.36	$ (0.32)
Earnings attributed to Series B Participating Redeemable Preferred Stock	$ 187