OPERATING SEGMENTS - Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022
OPERATING SEGMENT
Net Income (Loss)	$ 12.3	$ 8.6	$ (235.5)	$ (226.9)	$ (121.6)	$ (337.4)	$ (214.6)	$ (685.9)
Income tax provision	2.3			1.8			4.6	2.5
Interest expense	103.7			95.7			307.4	278.4
Depreciation and amortization	88.7			96.9			279.1	293.0
Certain operating expense	3.8			4.3			4.0	10.5
Equity in (earnings) loss of non-consolidated entities	(3.1)			(2.8)			(5.3)	3.3
Cash distributions from non-consolidated entities	2.2			3.4			3.9	5.0
Attributable EBITDA	1.4			0.1			1.6	0.1
Investment expense (income)	(3.0)			18.3			(11.4)	12.2
Other expense (income)	(14.1)			6.2			(1.4)	110.9
Other non-cash rent benefit	(8.4)			(6.6)			(27.0)	(20.6)
General and administrative - unallocated:
Merger, acquisition and other costs	0.7			0.3			1.5	0.4
Stock-based compensation expense	7.2			(3.6)			40.9	22.3
Adjusted EBITDA	193.7			(12.9)			383.3	32.1
(Gain) loss on extinguishment of debt							(97.5)	96.4
Interest income	3.7						8.5
Shareholder litigation	(16.1)						99.3
Hycroft
OPERATING SEGMENT
Decrease (increase) in fair value of investments	(0.1)			11.8			5.4	10.8
Increase (decrease) in fair value of investment in warrants	(0.8)			(7.7)				7.4
General and administrative - unallocated:
Interest income				2.8				3.3
Investment in Hycroft Mining Holding Corporation Warrants
OPERATING SEGMENT
Increase (decrease) in fair value of investment in warrants							(5.4)
NCM
OPERATING SEGMENT
Decrease (increase) in fair value of investments				1.6
Decline in estimated fair value of investment							1.8	11.1
Attributable EBITDA
OPERATING SEGMENT
Income tax provision	0.1			0.1			(0.1)	0.1
Interest expense	0.1						0.2
Depreciation and amortization	0.4			0.7			1.0	2.0
Equity in (earnings) loss of non-consolidated entities	(3.1)			(2.8)			(5.3)	3.3
Equity in (earnings) of non-consolidated entities excluding International theatre joint ventures	(2.1)			(3.5)			(4.7)	(3.1)
Equity in earnings (loss) of International theatre joint ventures	1.0			(0.7)			0.6	(6.4)
Impairment of long-lived assets								4.2
Attributable EBITDA	1.4			0.1			1.6	0.1
Investment expense (income)	0.2						0.1	(0.2)
Other expense (income)
General and administrative - unallocated:
(Gain) loss on extinguishment of debt	(10.8)						(97.5)	96.4
Foreign currency transaction (gains) losses	$ 12.8			$ 6.3			(3.2)	$ 14.7
SCC
General and administrative - unallocated:
Gain on divestment of equity method investment							$ (15.5)