REPORTABLE SEGMENTS (Details) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2023 USD ($)	Mar. 31, 2023 USD ($)	Jun. 30, 2022 USD ($)	Mar. 31, 2022 USD ($)	Jun. 30, 2023 USD ($) segment	Jun. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)
Segment results
Number of segments | segment					2
Total Operating Revenue	$ 773.4		$ 1,261.1		$ 1,478.2	$ 2,426.6
Total Operating Income	96.7		493.1		135.4	925.7
Interest income	8.7				16.9
Interest expense	(2.9)		(4.5)		(7.4)	(9.3)
Other income (expense), net	1.8		1.8		3.6	3.8
Income before Taxes	104.3		490.4		148.5	920.2
Income taxes	(23.5)		(109.7)		(33.7)	(200.3)
Net Income	80.8	$ 34.0	380.7	$ 339.2	114.8	719.9
Deferred dry-docking amortization					12.4	12.9
Total Assets	4,218.1				4,218.1		$ 4,330.0
(Loss) Income from SSAT	(1.4)		24.7		(3.2)	58.7
SSAT
Segment results
(Loss) Income from SSAT	(1.4)		24.7
Intersegment Eliminations
Segment results
Total Operating Revenue	54.4		69.2		94.5	142.4
Ocean Transportation
Segment results
(Loss) Income from SSAT	(1.4)		24.7		(3.2)	58.7
Ocean Transportation | Operating segments
Segment results
Total Operating Revenue	616.9		1,049.2		1,167.9	1,993.1
Total Operating Income	82.4		470.0		110.2	886.2
Ocean Transportation | Intersegment Eliminations
Segment results
Total Operating Revenue	19.0		24.0		35.1	45.8
Logistics | Operating segments
Segment results
Total Operating Revenue	156.5		211.9		310.3	433.5
Total Operating Income	14.3		23.1		25.2	39.5
Logistics | Intersegment Eliminations
Segment results
Total Operating Revenue	$ 35.4		$ 45.2		$ 59.4	$ 96.6