Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2018

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Undiscounted Amounts And Material Changes In Insurance Claims [Table Text Block]

Expected aggregate undiscounted amounts and material changes to these amounts related to workers’ compensation and property damage and liability claims as of December 31 are presented below:

(in millions)	Workers’ Compensation			Property Damage and Liability Claims			Total
Undiscounted amount at December 31, 2016	$	299.4		$	72.9		$	372.3
Estimated settlement cost for 2017 claims	95.7			37.2			132.9
Claim payments, net of recoveries	(90.3		)	(33.5		)	(123.8		)
Change in estimated settlement cost for prior claim years	(5.5		)	(6.1		)	(11.6		)
Undiscounted amount at December 31, 2017	$	299.3		$	70.5		$	369.8
Estimated settlement cost for 2018 claims	95.9			40.0			135.9
Claim payments, net of recoveries	(92.4		)	(36.2		)	(128.6		)
Change in estimated settlement cost for prior claim years	(15.0		)	(0.7		)	(15.7		)
Undiscounted settlement cost estimate at December 31, 2018	$	287.8		$	73.6		$	361.4
Discounted settlement cost estimate at December 31, 2018	$	264.4		$	72.0		$	336.4

Estimated Cash Payments To Settle Claims [Table Text Block]

Estimated cash payments to settle claims which were incurred on or before December 31, 2018, for the next five years and thereafter are as follows:

(in millions)	Workers’ Compensation		Property Damage and Liability Claims		Total
2019	$	76.4	$	27.6	$	104.0
2020	48.8		20.4		69.2
2021	33.0		13.2		46.2
2022	22.4		7.0		29.4
2023	17.5		3.1		20.6
Thereafter	89.7		2.3		92.0
Total	$	287.8	$	73.6	$	361.4

Property, Plant and Equipment [Table Text Block]

The following is a summary of the components of our property and equipment at cost as of December 31:

(in millions)	2018		2017
Land	$	243.7	$	246.0
Structures	791.3		783.3
Revenue equipment	1,257.4		1,303.5
Technology equipment and software	259.7		230.6
Other	213.8		206.8
Total property and equipment, at cost	$	2,765.9	$	2,770.2

Schedule of Service Lives for Property, Plant and Equipment [Table Text Block]

We carry property and equipment at cost less accumulated depreciation. We compute depreciation using the straight-line method based on the following service lives:

	Years
Structures	10 - 30
Revenue equipment	10 - 20
Technology equipment and software	3 - 7
Other	3 - 10

Fair Value, Assets Measured on Recurring Basis [Table Text Block]

The following tables summarize the fair value hierarchy of our financial assets held at fair value on a recurring basis, which consists of our restricted cash held in escrow:

			Fair Value Measurement at December 31, 2017
(in millions)	Total Carrying Value		Quoted prices in active market (Level 1)		Significant other observable inputs (Level 2)		Significant unobservable inputs (Level 3)
Restricted amounts held in escrow-current	$	54.1	$	54.1	$	—	$	—
Total assets at fair value	$	54.1	$	54.1	$	—	$	—