Accounting Policies (Estimated Cash Payments) (Details) $ in Millions	Dec. 31, 2017 USD ($)
Workers' Compensation [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
2018	$ 78.3
2019	50.4
2020	34.7
2021	23.7
2022	18.2
Thereafter	94.0
Total	299.3
Property Damage and Liability Claims [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
2018	26.9
2019	19.3
2020	12.0
2021	6.5
2022	3.5
Thereafter	2.3
Total	70.5
Total [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
2018	105.2
2019	69.7
2020	46.7
2021	30.2
2022	21.7
Thereafter	96.3
Total	$ 369.8