Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2017

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 as of December 31 are presented below:

(in millions)	Workers’ Compensation			Property Damage and Liability Claims			Total
Undiscounted amount at December 31, 2015	$	315.5		$	84.9		$	400.4
Estimated settlement cost for 2016 claims	89.4			30.0			119.4
Claim payments, net of recoveries	(103.6		)	(51.5		)	(155.1		)
Change in estimated settlement cost for older claim years	(1.9		)	9.5			7.6
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 older claim years	(5.5		)	(6.1		)	(11.6		)
Undiscounted settlement cost estimate at December 31, 2017	$	299.3		$	70.5		$	369.8
Discounted settlement cost estimate at December 31, 2017	$	276.4		$	69.3		$	345.7

Estimated Cash Payments To Settle Claims [Table Text Block]

Estimated cash payments to settle claims which were incurred on or before December 31, 2017, for the next five years and thereafter are as follows:

(in millions)	Workers’ Compensation		Property Damage and Liability Claims		Total
2018	$	78.3	$	26.9	$	105.2
2019	50.4		19.3		69.7
2020	34.7		12.0		46.7
2021	23.7		6.5		30.2
2022	18.2		3.5		21.7
Thereafter	94.0		2.3		96.3
Total	$	299.3	$	70.5	$	369.8

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)	2017		2016
Land	$	246.0	$	248.9
Structures	783.3		769.5
Revenue equipment	1,303.5		1,375.2
Technology equipment and software	230.6		186.8
Other	206.8		206.6
Total property and equipment, at cost	$	2,770.2	$	2,787.0

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	$	—	$	—

			Fair Value Measurement at December 31, 2016
(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	$	126.7	$	126.7	$	—	$	—
Restricted amounts held in escrow-long term	12.3		12.3		—		—
Total assets at fair value	$	139.0	$	139.0	$	—	$	—