Statements Of Consolidated Operations - USD ($) shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Operating Revenue	$ 4,891.0	$ 4,697.5	$ 4,832.4
Operating Expenses:
Salaries, wages and employee benefits	2,904.8	2,823.1	2,868.2
Fuel, operating expenses and supplies	867.5	799.1	878.4
Purchased transportation	627.5	553.6	561.1
Depreciation and amortization	147.7	159.8	163.7
Other operating expenses	245.7	252.2	266.1
(Gains) losses on property disposals, net	(0.6)	(14.6)	1.9
Total operating expenses	4,792.6	4,573.2	4,739.4
Operating Income	98.4	124.3	93.0
Nonoperating Expenses:
Interest expense	102.8	103.4	107.6
Other, net	13.7	(3.7)	(10.2)
Nonoperating expenses, net	116.5	99.7	97.4
Income (Loss) before income taxes	(18.1)	24.6	(4.4)
Income tax expense (benefit)	(7.3)	3.1	(5.1)
Net Income (Loss)	(10.8)	21.5	0.7
Net Income (Loss) Attributable to Common Shareholders	$ (10.8)	$ 21.5	$ 0.7
Average Common Shares Outstanding - Basic	32,685	32,416	31,736
Average Common Shares Outstanding - Diluted	32,685	33,040	32,592
Earnings (Loss) Per Share - Basic (in dollars per share)	$ (0.33)	$ 0.66	$ 0.02
Earnings (Loss) Per Share - Diluted (in dollars per share)	$ (0.33)	$ 0.65	$ 0.02