PENSION AND POST-RETIREMENT PLANS - MULTI-EMPLOYER DEFINED BENEFIT PLANS (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Multiemployer Plans
Estimated benefit plan withdrawal obligations	$ 260.0
Multiemployer Health and Benefit Plans
Multiemployer Plans
Contributions of Matson	32.5	$ 32.8	$ 30.0
Multi-employer defined contribution pension plans
Multiemployer Plans
Contributions of Matson	$ 28.4	27.3	25.5
Multi-employer defined contribution pension plans | Orange Zone
Multiemployer Plans
Expected funding deficiency period	6 years
Multi-employer defined contribution pension plans | Minimum | Green Zone
Multiemployer Plans
Funded status of multiemployer plan (as a percent)	80.00%
Multi-employer defined contribution pension plans | Maximum | Red Zone
Multiemployer Plans
Funded status of multiemployer plan (as a percent)	65.00%
Multi-employer defined contribution pension plans | Maximum | Yellow Zone
Multiemployer Plans
Funded status of multiemployer plan (as a percent)	80.00%
Multi-employer defined contribution pension plans | Maximum | Orange Zone
Multiemployer Plans
Funded status of multiemployer plan (as a percent)	80.00%
Multi-employer defined contribution pension plans | American Radio Association Pension Fund | Green Zone
Multiemployer Plans
Contributions of Matson	$ 1.0	1.1	1.0
Multi-employer defined contribution pension plans | Hawaii Terminals Multiemployer Pension Plan | Yellow Zone
Multiemployer Plans
Contributions of Matson	5.8		5.7
Multi-employer defined contribution pension plans | Hawaii Terminals Multiemployer Pension Plan | Orange Zone
Multiemployer Plans
Contributions of Matson		5.7
Multi-employer defined contribution pension plans | Hawaii Stevedoring Multiemployer Retirement Plan | Yellow Zone
Multiemployer Plans
Contributions of Matson		4.4	4.3
Multi-employer defined contribution pension plans | Hawaii Stevedoring Multiemployer Retirement Plan | Green Zone
Multiemployer Plans
Contributions of Matson	4.6
Multi-employer defined contribution pension plans | Master Mates And Pilots Pension Plan | Green Zone
Multiemployer Plans
Contributions of Matson	3.2	3.4	3.0
Multi-employer defined contribution pension plans | Masters, Mates and Pilots Adjustable Pension Plan | Green Zone
Multiemployer Plans
Contributions of Matson	1.8	1.9	1.7
Multi-employer defined contribution pension plans | M E B A Pension Trust - Defined Benefit Plan | Green Zone
Multiemployer Plans
Contributions of Matson	4.1	4.3	4.0
Multi-employer defined contribution pension plans | OCU Pension Trust Plan | Green Zone
Multiemployer Plans
Contributions of Matson	0.2	0.2	0.2
Multi-employer defined contribution pension plans | M F O W Supplementary Pension Plan | Yellow Zone
Multiemployer Plans
Contributions of Matson	0.1
Multi-employer defined contribution pension plans | M F O W Supplementary Pension Plan | Green Zone
Multiemployer Plans
Contributions of Matson		0.1
Multi-employer defined contribution pension plans | SIU Pacific District Pension Plan | Green Zone
Multiemployer Plans
Contributions of Matson	1.3	1.5	1.2
Multi-employer defined contribution pension plans | Alaska Teamster - Employer Pension Plan | Red Zone
Multiemployer Plans
Contributions of Matson	3.3	1.9	1.9
Multi-employer defined contribution pension plans | All Alaska Longshore Pension Plan | Green Zone
Multiemployer Plans
Contributions of Matson	1.3	1.2	1.0
Multi-employer defined contribution pension plans | Western Conference of Teamsters Pension Plan | Green Zone
Multiemployer Plans
Contributions of Matson	1.6	1.5	1.4
Multi-employer defined contribution pension plans | O P E I U Local 153 Pension Plan | Red Zone
Multiemployer Plans
Contributions of Matson	$ 0.1	$ 0.1	$ 0.1