Statements of Consolidated Comprehensive Income (Loss) (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Statement of Comprehensive Income [Abstract]
Operating Revenue	$ 1,423.7	$ 1,313.1	$ 2,684.1	$ 2,511.5
Operating Expenses:
Salaries, wages and employee benefits	736.7	751.3	1,447.7	1,475.1
Fuel, operating expenses and supplies	287.3	217.0	530.9	420.5
Purchased transportation	206.1	210.3	391.5	410.3
Depreciation and amortization	35.5	35.0	71.2	68.3
Other operating expenses	62.1	72.2	143.1	136.6
(Gains) losses on property disposals, net	(3.2)	0.3	(8.7)	1.3
Total operating expenses	1,324.5	1,286.1	2,575.7	2,512.1
Operating Income (Loss)	99.2	27.0	108.4	(0.6)
Nonoperating Expenses:
Interest expense	38.0	37.7	75.7	73.6
Non-union pension and postretirement benefits	(0.5)	(1.1)	(0.9)	(2.4)
Other, net	(0.1)	(0.3)	0.1	(0.3)
Nonoperating expenses, net	37.4	36.3	74.9	70.9
Income (loss) before income taxes	61.8	(9.3)	33.5	(71.5)
Income tax expense	1.8	0.1	1.0	1.2
Net income (loss)	60.0	(9.4)	32.5	(72.7)
Other comprehensive income, net of tax	1.5	3.3	3.8	6.9
Comprehensive Income (Loss)	$ 61.5	$ (6.1)	$ 36.3	$ (65.8)
Average Common Shares Outstanding - Basic	51,342	50,751	51,217	50,555
Average Common Shares Outstanding - Diluted	52,135	50,751	52,183	50,555
Income (loss) per share- Basic	$ 1.17	$ (0.18)	$ 0.64	$ (1.44)
Income (Loss) per share- Diluted	$ 1.15	$ (0.18)	$ 0.62	$ (1.44)