Accounting Policies (Claims and Insurance) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Workers' Compensation [Member]
LIability For Unpaid Claims And Claim Adjustment Expense, Adjustment Of Opening Balance [Roll Forward]
Undiscounted amount	$ 315.5	$ 339.1
Estimated settlement cost	89.4	92.8
Claim payments, net of recoveries	(103.6)	(115.0)
Change in estimated settlement cost for older claim years	(1.9)	(1.4)
Undiscounted amount	299.4	315.5
Discounted settlement cost estimate	277.0
Property Damage and Liability Claims [Member]
LIability For Unpaid Claims And Claim Adjustment Expense, Adjustment Of Opening Balance [Roll Forward]
Undiscounted amount	84.9	75.0
Estimated settlement cost	30.0	37.0
Claim payments, net of recoveries	(51.5)	(41.0)
Change in estimated settlement cost for older claim years	9.5	13.9
Undiscounted amount	72.9	84.9
Discounted settlement cost estimate	72.1
Total [Member]
LIability For Unpaid Claims And Claim Adjustment Expense, Adjustment Of Opening Balance [Roll Forward]
Undiscounted amount	400.4	414.1
Estimated settlement cost	119.4	129.8
Claim payments, net of recoveries	(155.1)	(156.0)
Change in estimated settlement cost for older claim years	7.6	12.5
Undiscounted amount	372.3	400.4
Discounted settlement cost estimate	349.1
Cargo Claims And Other Insurance Related Amounts [Member]
LIability For Unpaid Claims And Claim Adjustment Expense, Adjustment Of Opening Balance [Roll Forward]
Undiscounted amount	17.0
Undiscounted amount	$ 15.3	$ 17.0