Statements of Consolidated Operations - USD ($) shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement Of Income And Comprehensive Income [Abstract]
Operating Revenue	$ 4,871.2	$ 5,092.0	$ 4,891.0
Operating Expenses:
Salaries, wages and employee benefits	2,963.7	2,950.0	2,884.2
Fuel, operating expenses and supplies	889.0	940.2	867.5
Purchased transportation	614.2	683.2	627.5
Depreciation and amortization	152.4	147.7	147.7
Other operating expenses	241.2	248.8	245.7
Gains on property disposals, net	(13.7)	(20.8)	(0.6)
Impairment charges	8.2	0.0	0.0
Total operating expenses	4,855.0	4,949.1	4,772.0
Operating Income	16.2	142.9	119.0
Nonoperating Expenses:
Interest expense	111.2	105.8	102.8
Loss on extinguishment of debt	11.2	0.0	0.0
Non-union pension and postretirement benefits	3.1	9.4	20.6
Other, net	(1.0)	(3.6)	13.7
Nonoperating expenses, net	124.5	111.6	137.1
Income (loss) before income taxes	(108.3)	31.3	(18.1)
Income tax expense (benefit)	(4.3)	11.1	(7.3)
Net Income (Loss)	$ (104.0)	$ 20.2	$ (10.8)
Average Common Shares Outstanding - Basic	33,252	32,983	32,685
Average Common Shares Outstanding - Diluted	33,252	33,859	32,685
Earnings (Loss) Per Share - Basic	$ (3.13)	$ 0.61	$ (0.33)
Earnings (Loss) Per Share - Diluted	$ (3.13)	$ 0.60	$ (0.33)