GENERAL AND SIGNIFICANT ACCOUNTING POLICIES - INVESTMENT IN SSAT (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Investments in affiliates
Investment in SSAT	$ 81.4		$ 81.4		$ 81.2
Financial information for equity method investment
Company Share of Net Income (Loss)	1.3	$ 23.4	(1.9)	$ 82.1
SSAT
Financial information for equity method investment
Company Share of Net Income (Loss)	1.3	23.4
SSAT
Investments in affiliates
Investment in SSAT	81.4		81.4		$ 81.2
Financial information for equity method investment
Operating revenue	268.4	369.8	742.1	1,191.3
Operating costs and expenses	(269.4)	(286.9)	(754.2)	(894.3)
Operating (loss) income	(1.0)	82.9	(12.1)	297.0
Net Income (Loss)	$ 1.5	$ 68.9	$ (7.4)	$ 247.0