Statements of Consolidated Comprehensive Loss (Unaudited) - USD ($) shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Statement of Comprehensive Income [Abstract]
Operating Revenue	$ 1,170.6	$ 1,120.3
Operating Expenses:
Salaries, wages and employee benefits	721.7	698.1
Operating expenses and supplies	216.3	190.2
Purchased transportation	134.5	115.5
Depreciation and amortization	37.1	40.7
Other operating expenses	61.3	62.7
(Gains) losses on property disposals, net	2.7	(0.3)
Total operating expenses	1,173.6	1,106.9
Operating Income (Loss)	(3.0)	13.4
Nonoperating Expenses:
Interest expense	25.4	26.1
Other, net	1.0	1.1
Nonoperating expenses, net	26.4	27.2
Loss before income taxes	(29.4)	(13.8)
Income tax benefit	(4.1)	(1.8)
Net loss	(25.3)	(12.0)
Other comprehensive income (loss), net of tax	4.4	(2.6)
Comprehensive Loss	$ (20.9)	$ (14.6)
Average Common Shares Outstanding – Basic (in shares)	32,568	32,264
Average Common Shares Outstanding – Diluted (in shares)	32,568	32,264
Basic and Diluted Loss Per Share
Earnings (Loss) Per Share – Basic (in dollars per share)	$ (0.78)	$ (0.37)
Loss Per Share – Diluted (in dollars per share)	$ (0.78)	$ (0.37)