Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Millions		12 Months Ended
		Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Statement of Comprehensive Income [Abstract]
Operating Revenue		$ 5,244.7	$ 5,121.8	$ 4,513.7
Operating Expenses:
Salaries, wages and employee benefits		2,808.3	2,921.7	2,770.1
Fuel, operating expenses and supplies		1,076.6	858.1	719.1
Purchased transportation		748.5	800.2	638.8
Depreciation and amortization		143.4	143.6	134.9
Other operating expenses		308.1	293.9	239.6
(Gains) losses on property disposals, net		(38.0)	0.7	(45.3)
Total operating expenses		5,046.9	5,018.2	4,457.2
Operating Income		197.8	103.6	56.5
Nonoperating Expenses:
Interest expense		162.9	150.7	135.9
Non-union pension and postretirement benefits		10.5	59.3	(6.3)
Other, net		(2.1)	(0.4)	0.0
Nonoperating expenses, net		171.3	209.6	129.6
Income (Loss) before income taxes		26.5	(106.0)	(73.1)
Income tax expense (benefit)		4.7	3.1	(19.6)
Net Income (Loss)		$ 21.8	$ (109.1)	$ (53.5)
Average Common Shares Outstanding - Basic		51,346	50,720	41,694
Average Common Shares Outstanding - Diluted		52,233	50,720	41,694
Income (Loss) Per Share - Basic	[1]	$ 0.42	$ (2.15)	$ (1.28)
Income (Loss) Per Share - Diluted	[1]	$ 0.42	$ (2.15)	$ (1.28)

[1] Earnings (loss) per share is based on unrounded figures and not the rounded figures presented.