Consolidated Statements of Income and Comprehensive Income - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Operating Revenue:
Total Operating Revenue	$ 3,094.6	$ 4,343.0	$ 3,925.3
Costs and Expenses:
Operating costs	(2,470.7)	(2,811.5)	(2,557.6)
Income from SSAT	2.2	83.1	56.3
Selling, general and administrative	(283.3)	(261.0)	(236.5)
Total Costs and Expenses	(2,751.8)	(2,989.4)	(2,737.8)
Operating Income	342.8	1,353.6	1,187.5
Interest income	36.0	8.2
Interest expense	(12.2)	(18.0)	(22.6)
Other income (expense), net	6.4	8.5	6.4
Income before Taxes	373.0	1,352.3	1,171.3
Income taxes	(75.9)	(288.4)	(243.9)
Net Income	297.1	1,063.9	927.4
Other Comprehensive Income (Loss), Net of Income Taxes:
Net Income (Loss)	297.1	1,063.9	927.4
Other Comprehensive Income (Loss):
Net change in pension and post-retirement liabilities	(2.5)	23.8	20.4
Other adjustments	1.2	0.2	(0.5)
Total Other Comprehensive Income (Loss), Net of Income Taxes	(1.3)	24.0	19.9
Comprehensive Income	$ 295.8	$ 1,087.9	$ 947.3
Basic Earnings Per Share (in dollars per share)	$ 8.42	$ 27.28	$ 21.67
Diluted Earnings Per Share (in dollars per share)	$ 8.32	$ 27.07	$ 21.47
Weighted Average Number of Shares Outstanding:
Basic (in shares)	35.3	39.0	42.8
Diluted (in shares)	35.7	39.3	43.2
Ocean Transportation
Operating Revenue:
Total Operating Revenue	$ 2,477.0	$ 3,544.6	$ 3,132.8
Logistics
Operating Revenue:
Total Operating Revenue	$ 617.6	$ 798.4	$ 792.5