Statements of Consolidated Comprehensive Loss (Unaudited) - USD ($) shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Operating Revenue	$ 1,214.5	$ 1,170.6
Operating Expenses:
Salaries, wages and employee benefits	729.7	718.4
Fuel, operating expenses and supplies	230.2	216.3
Purchased transportation	155.4	134.5
Depreciation and amortization	37.7	37.1
Other operating expenses	62.6	61.3
Losses on property disposals, net	3.2	2.7
Total operating expenses	1,218.8	1,170.3
Operating Income (Loss)	(4.3)	0.3
Nonoperating Expenses:
Interest expense	25.6	25.4
Non-union pension and postretirement benefits	(0.5)	3.3
Other, net	(1.9)	1.0
Nonoperating expenses, net	23.2	29.7
Loss before income taxes	(27.5)	(29.4)
Income tax benefit	(12.9)	(4.1)
Net Loss	(14.6)	(25.3)
Other comprehensive income, net of tax	2.0	4.4
Comprehensive Loss	$ (12.6)	$ (20.9)
Average Common Shares Outstanding – Basic (in shares)	32,821	32,568
Average Common Shares Outstanding – Diluted (in shares)	32,821	32,568
Basic and Diluted Loss Per Share
Income (loss) Per Share – Basic (in dollars per share)	$ (0.44)	$ (0.78)
Income (loss) Per Share – Diluted (in dollars per share)	$ (0.44)	$ (0.78)