Statements of Consolidated Comprehensive Income (Loss) (Unaudited) - USD ($) shares in Thousands, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Statement of Comprehensive Income [Abstract]
Operating Revenue	$ 1,126.8	$ 1,423.7	$ 2,285.4	$ 2,684.1
Operating Expenses:
Salaries, wages and employee benefits	686.3	736.7	1,358.8	1,447.7
Fuel, operating expenses and supplies	227.0	287.3	467.6	530.9
Purchased transportation	150.7	206.1	302.7	391.5
Depreciation and amortization	35.8	35.5	71.1	71.2
Other operating expenses	64.0	62.1	132.0	143.1
Gains on property disposals, net	(75.9)	(3.2)	(76.4)	(8.7)
Total operating expenses	1,087.9	1,324.5	2,255.8	2,575.7
Operating Income	38.9	99.2	29.6	108.4
Nonoperating Expenses:
Interest expense	48.3	38.0	94.8	75.7
Non-union pension and postretirement benefits	1.1	(0.5)	2.3	(0.9)
Other, net	0.1	(0.1)	(0.1)	0.1
Nonoperating expenses, net	49.5	37.4	97.0	74.9
Income (loss) before income taxes	(10.6)	61.8	(67.4)	33.5
Income tax expense	4.1	1.8	1.9	1.0
Net income (loss)	(14.7)	60.0	(69.3)	32.5
Other comprehensive income (loss), net of tax	2.4	1.5	(0.2)	3.8
Comprehensive Income (Loss)	$ (12.3)	$ 61.5	$ (69.5)	$ 36.3
Average Common Shares Outstanding - Basic	52,010	51,342	51,871	51,217
Average Common Shares Outstanding - Diluted	52,010	52,135	51,871	52,183
Income (Loss) Per Share - Basic	$ (0.28)	$ 1.17	$ (1.34)	$ 0.64
Income (Loss) Per Share - Diluted	$ (0.28)	$ 1.15	$ (1.34)	$ 0.62