ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) (Details) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2025	Jun. 30, 2025	Mar. 31, 2025	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Sep. 30, 2025	Sep. 30, 2024
Changes in accumulated other comprehensive income (loss) by component, net of taxes
Balance at the beginning of the period	$ 2,618.0	$ 2,633.2	$ 2,652.0	$ 2,398.5	$ 2,373.8	$ 2,400.7	$ 2,652.0	$ 2,400.7
Other adjustments	(1.6)			1.0			0.3	0.5
Balance at the end of the period	2,689.3	2,618.0	2,633.2	2,556.7	2,398.5	2,373.8	2,689.3	2,556.7
Pensions
Changes in accumulated other comprehensive income (loss) by component, net of taxes
Balance at the beginning of the period	(14.0)	(14.0)	(14.0)	(20.1)	(20.2)	(20.3)	(14.0)	(20.3)
Amortization of net actuarial gain (loss)					0.1	0.1
Balance at the end of the period	(14.0)	(14.0)	(14.0)	(20.1)	(20.1)	(20.2)	(14.0)	(20.1)
Post Retirement
Changes in accumulated other comprehensive income (loss) by component, net of taxes
Balance at the beginning of the period	6.4	7.3	8.1	9.3	10.1	11.0	8.1	11.0
Amortization of prior service credit	(0.6)	(0.7)	(0.7)	(0.7)	(0.7)	(0.7)
Amortization of net actuarial gain (loss)	(0.1)	(0.2)	(0.1)	(0.1)	(0.1)	(0.2)
Balance at the end of the period	5.7	6.4	7.3	8.5	9.3	10.1	5.7	8.5
Non-Qualified Plans
Changes in accumulated other comprehensive income (loss) by component, net of taxes
Balance at the beginning of the period	(0.4)	(0.4)	(0.4)	(0.2)	(0.2)	(0.2)	(0.4)	(0.2)
Balance at the end of the period	(0.4)	(0.4)	(0.4)	(0.2)	(0.2)	(0.2)	(0.4)	(0.2)
Other
Changes in accumulated other comprehensive income (loss) by component, net of taxes
Balance at the beginning of the period	1.7	0.3	(0.2)	0.8	0.5	1.3	(0.2)	1.3
Foreign currency exchange	(1.3)	1.4	0.3	1.0	0.3	(0.9)
Other adjustments	(0.3)		0.2			0.1
Balance at the end of the period	0.1	1.7	0.3	1.8	0.8	0.5	0.1	1.8
Accumulated Other Comprehensive Income (Loss)
Changes in accumulated other comprehensive income (loss) by component, net of taxes
Balance at the beginning of the period	(6.3)	(6.8)	(6.5)	(10.2)	(9.8)	(8.2)	(6.5)	(8.2)
Amortization of prior service credit	(0.6)	(0.7)	(0.7)	(0.7)	(0.7)	(0.7)
Amortization of net actuarial gain (loss)	(0.1)	(0.2)	(0.1)	(0.1)		(0.1)
Foreign currency exchange	(1.3)	1.4	0.3	1.0	0.3	(0.9)
Other adjustments	(0.3)		0.2			0.1
Balance at the end of the period	$ (8.6)	$ (6.3)	$ (6.8)	$ (10.0)	$ (10.2)	$ (9.8)	$ (8.6)	$ (10.0)

Matson, Inc. 10-Q