Statements of Consolidated Comprehensive Income (Loss) (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Statement of Comprehensive Income [Abstract]
Operating Revenue	$ 1,260.4	$ 1,198.4
Operating Expenses:
Salaries, wages and employee benefits	711.0	723.8
Fuel, operating expenses and supplies	243.6	203.5
Purchased transportation	185.4	200.0
Depreciation and amortization	35.7	33.3
Other operating expenses	81.0	64.4
(Gains) losses on property disposals, net	(5.5)	1.0
Total operating expenses	1,251.2	1,226.0
Operating Income (Loss)	9.2	(27.6)
Nonoperating Expenses:
Interest expense	37.7	35.9
Non-union pension and postretirement benefits	(0.4)	(1.3)
Other, net	0.2	0.0
Nonoperating expenses, net	37.5	34.6
Loss before income taxes	(28.3)	(62.2)
Income tax expense (benefit)	(0.8)	1.1
Net loss	(27.5)	(63.3)
Other comprehensive income, net of tax	2.3	3.6
Comprehensive Loss	$ (25.2)	$ (59.7)
Average Common Shares Outstanding - Basic	51,091	50,358
Average Common Shares Outstanding - Diluted	51,091	50,358
Loss Per Share - Basic	$ (0.54)	$ (1.26)
Loss Per Share - Diluted	$ (0.54)	$ (1.26)