Statements of Consolidated Comprehensive Loss (Unaudited) - USD ($) shares in Thousands, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Statement Of Income And Comprehensive Income [Abstract]
Operating Revenue	$ 1,015.4	$ 1,272.6	$ 2,165.8	$ 2,454.9
Operating Expenses:
Salaries, wages and employee benefits	647.9	782.3	1,368.1	1,500.5
Fuel, operating expenses and supplies	162.7	228.3	370.7	464.2
Purchased transportation	126.0	158.0	262.2	304.3
Depreciation and amortization	34.2	38.5	69.9	78.5
Other operating expenses	55.2	57.4	116.8	121.2
Gains on property disposals, net	(6.0)	(6.2)	(45.3)	(4.6)
Impairment charges	0.0	0.0	0.0	8.2
Total operating expenses	1,020.0	1,258.3	2,142.4	2,472.3
Operating Income (Loss)	(4.6)	14.3	23.4	(17.4)
Nonoperating Expenses:
Interest expense	40.2	28.2	68.5	55.2
Non-union pension and postretirement benefits	(1.6)	0.5	(3.2)	0.8
Other, net	1.4	0.1	(1.2)	(0.1)
Nonoperating expenses, net	40.0	28.8	64.1	55.9
Loss before income taxes	(44.6)	(14.5)	(40.7)	(73.3)
Income tax expense (benefit)	(7.5)	9.1	(7.9)	(0.6)
Net loss	(37.1)	(23.6)	(32.8)	(72.7)
Other comprehensive income, net of tax	3.2	2.0	4.5	5.5
Comprehensive Loss	$ (33.9)	$ (21.6)	$ (28.3)	$ (67.2)
Average Common Shares Outstanding - Basic	34,021	33,247	33,906	33,199
Average Common Shares Outstanding - Diluted	34,021	33,247	33,906	33,199
Loss Per Share - Basic	$ (1.09)	$ (0.71)	$ (0.97)	$ (2.19)
Loss Per Share - Diluted	$ (1.09)	$ (0.71)	$ (0.97)	$ (2.19)