Statements of Consolidated Comprehensive Loss (Unaudited) - USD ($) shares in Thousands, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement of Comprehensive Income [Abstract]
Operating Revenue	$ 1,272.6	$ 1,326.5	$ 2,454.9	$ 2,541.0
Operating Expenses:
Salaries, wages and employee benefits	782.3	756.0	1,500.5	1,485.7
Fuel, operating expenses and supplies	228.3	242.0	464.2	472.2
Purchased transportation	158.0	177.2	304.3	332.6
Depreciation and amortization	38.5	37.6	78.5	75.3
Other operating expenses	57.4	60.6	121.2	123.2
(Gains) losses on property disposals, net	(6.2)	2.2	(4.6)	5.4
Impairment charges	0.0	0.0	8.2	0.0
Total operating expenses	1,258.3	1,275.6	2,472.3	2,494.4
Operating Income (Loss)	14.3	50.9	(17.4)	46.6
Nonoperating Expenses:
Interest expense	28.2	25.5	55.2	51.1
Non-union pension and postretirement benefits	0.5	(0.4)	0.8	(0.9)
Other, net	0.1	1.0	(0.1)	(0.9)
Nonoperating expenses, net	28.8	26.1	55.9	49.3
Income (loss) before income taxes	(14.5)	24.8	(73.3)	(2.7)
Income tax expense (benefit)	9.1	10.4	(0.6)	(2.5)
Net income (loss)	(23.6)	14.4	(72.7)	(0.2)
Other comprehensive income, net of tax	2.0	4.3	5.5	6.3
Comprehensive Income (Loss)	$ (21.6)	$ 18.7	$ (67.2)	$ 6.1
Average Common Shares Outstanding – Basic (in shares)	33,247	32,966	33,199	32,894
Average Common Shares Outstanding – Diluted (in shares)	33,247	33,794	33,199	32,894
Basic and Diluted Loss Per Share
Income (loss) Per Share – Basic (in dollars per share)	$ (0.71)	$ 0.44	$ (2.19)	$ 0.00
Income (loss) Per Share – Diluted (in dollars per share)	$ (0.71)	$ 0.43	$ (2.19)	$ 0.00