Statements of Consolidated Operations - USD ($) shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement Of Income And Comprehensive Income [Abstract]
Operating Revenue	$ 4,513.7	$ 4,871.2	$ 5,092.0
Operating Expenses:
Salaries, wages and employee benefits	2,770.1	2,963.7	2,950.0
Fuel, operating expenses and supplies	719.1	889.0	940.2
Purchased transportation	638.8	614.2	683.2
Depreciation and amortization	134.9	152.4	147.7
Other operating expenses	239.6	241.2	248.8
Gains on property disposals, net	(45.3)	(13.7)	(20.8)
Impairment charges	0.0	8.2	0.0
Total operating expenses	4,457.2	4,855.0	4,949.1
Operating Income	56.5	16.2	142.9
Nonoperating Expenses:
Interest expense	135.9	111.2	105.8
Loss on extinguishment of debt	0.0	11.2	0.0
Non-union pension and postretirement benefits	(6.3)	3.1	9.4
Other, net	0.0	(1.0)	(3.6)
Nonoperating expenses, net	129.6	124.5	111.6
Income (Loss) before income taxes	(73.1)	(108.3)	31.3
Income tax expense (benefit)	(19.6)	(4.3)	11.1
Net Income (Loss)	$ (53.5)	$ (104.0)	$ 20.2
Average Common Shares Outstanding - Basic	41,694	33,252	32,983
Average Common Shares Outstanding - Diluted	41,694	33,252	33,859
Earnings (Loss) Per Share - Basic	$ (1.28)	$ (3.13)	$ 0.61
Earnings (Loss) Per Share - Diluted	$ (1.28)	$ (3.13)	$ 0.60