Accounting Policies (Property and Equipment) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
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 cost	2,770.2	2,787.0
Depreciation	$ 147.7	$ 146.3	$ 145.5
Structures [Member] | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, service life	10 years
Structures [Member] | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, service life	30 years
Revenue equipment [Member] | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, service life	10 years
Revenue equipment [Member] | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, service life	20 years
Technology equipment and software [Member] | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, service life	3 years
Technology equipment and software [Member] | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, service life	7 years
Other [Member] | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, service life	3 years
Other [Member] | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, service life	10 years