Statements of Consolidated Comprehensive Income (Loss) (Unaudited) - USD ($) shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement Of Income And Comprehensive Income [Abstract]
Operating Revenue	$ 1,198.4	$ 1,150.4
Operating Expenses:
Salaries, wages and employee benefits	723.8	720.2
Fuel, operating expenses and supplies	203.5	208.0
Purchased transportation	200.0	136.2
Depreciation and amortization	33.3	35.7
Other operating expenses	64.4	61.6
(Gains) losses on property disposals, net	1.0	(39.3)
Total operating expenses	1,226.0	1,122.4
Operating Income (Loss)	(27.6)	28.0
Nonoperating Expenses:
Interest expense	35.9	28.3
Non-union pension and postretirement benefits	(1.3)	(1.6)
Other, net	0.0	(2.6)
Nonoperating expenses, net	34.6	24.1
Income (loss) before income taxes	(62.2)	3.9
Income tax expense (benefit)	1.1	(0.4)
Net income (loss)	(63.3)	4.3
Other comprehensive income, net of tax	3.6	1.3
Comprehensive Income (Loss)	$ (59.7)	$ 5.6
Average Common Shares Outstanding - Basic	50,358	33,791
Average Common Shares Outstanding - Diluted	50,358	35,630
Earnings (Loss) Per Share - Basic	$ (1.26)	$ 0.13
Earnings (Loss) Per Share - Diluted	$ (1.26)	$ 0.12