Condensed Consolidated Statements of Income and Comprehensive Income - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Operating Revenue:
Total Operating Revenue	$ 1,071.6	$ 645.2	$ 2,658.3	$ 1,683.2
Costs and Expenses:
Operating costs	(649.3)	(495.8)	(1,809.6)	(1,370.4)
Income from SSAT	13.0	7.7	35.0	15.4
Selling, general and administrative	(57.4)	(58.7)	(171.7)	(165.6)
Total Costs and Expenses	(693.7)	(546.8)	(1,946.3)	(1,520.6)
Operating Income	377.9	98.4	712.0	162.6
Interest expense	(5.1)	(5.7)	(17.9)	(22.5)
Other income (expense), net	1.8	2.4	4.7	4.5
Income before Income Taxes	374.6	95.1	698.8	144.6
Income taxes	(91.4)	(24.2)	(165.9)	(37.1)
Net Income	283.2	70.9	532.9	107.5
Other Comprehensive Income (Loss), Net of Income Taxes:
Net Income	283.2	70.9	532.9	107.5
Other Comprehensive Income (Loss):
Amortization of prior service cost	(1.1)	(1.2)	(3.4)	(3.5)
Amortization of net loss (gain)	1.0	0.5	3.5	3.1
Other adjustments	(0.1)	0.2	(0.2)	(0.6)
Total Other Comprehensive Income (Loss)	(0.2)	(0.5)	(0.1)	(1.0)
Comprehensive Income	$ 283.0	$ 70.4	$ 532.8	$ 106.5
Basic Earnings Per Share (in dollars per share)	$ 6.60	$ 1.65	$ 12.31	$ 2.50
Diluted Earnings Per Share (in dollars per share)	$ 6.53	$ 1.63	$ 12.19	$ 2.48
Weighted Average Number of Shares Outstanding:
Basic	42.9	43.1	43.3	43.0
Diluted	43.4	43.5	43.7	43.4
Ocean Transportation Services
Operating Revenue:
Total Operating Revenue	$ 863.5	$ 498.3	$ 2,106.9	$ 1,310.0
Logistics Services
Operating Revenue:
Total Operating Revenue	$ 208.1	$ 146.9	$ 551.4	$ 373.2