GENERAL AND SIGNIFICANT ACCOUNTING POLICIES - INVESTMENT IN SSAT (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022
Investments in affiliates
Investment in SSAT	$ 80.1		$ 80.1		$ 81.2
Financial information for equity method investment
Company Share of Net Income (Loss)	(1.4)	$ 24.7	(3.2)	$ 58.7
SSAT
Financial information for equity method investment
Company Share of Net Income (Loss)	(1.4)	24.7
SSAT
Investments in affiliates
Investment in SSAT	80.1		80.1		$ 81.2
Financial information for equity method investment
Operating revenue	242.9	391.1	473.7	821.5
Operating costs and expenses	(248.9)	(300.5)	(484.8)	(607.4)
Operating Income (Loss)	(6.0)	90.6	(11.1)	214.1
Net Income (Loss)	$ (4.1)	$ 78.0	$ (8.9)	$ 178.1