SIGNIFICANT ACCOUNTING POLICIES - INCOME TAXES (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2018
SIGNIFICANT ACCOUNTING POLICIES
Tax Act, income tax expense (benefit)	$ (0.2)	$ 3.1
Sequestration rate (as a percent)		6.20%

Internal Revenue Service sequestration rate on alternative minimum tax refunds.

No definition available.

Name:	matx_IncomeTaxesSequestrationRateOnAlternativeMinimuTaxRefunds
Namespace Prefix:	matx_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration