Accounting Policies - Schedule of Undiscounted Amounts and Material Changes in Insurance Claims (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Liability For Claims And Claims Adjustment Expense [Line Items]
Undiscounted amount	$ 345.2	$ 359.4
Estimated settlement cost	130.5	131.4
Claim payments, net of recoveries	(135.8)	(141.7)
Change in estimated settlement cost for prior claim years	33.1	(3.9)
Undiscounted amount	373.0	345.2
Discounted settlement cost estimate	354.5
Workers’ Compensation
Liability For Claims And Claims Adjustment Expense [Line Items]
Undiscounted amount	275.2	285.6
Estimated settlement cost	92.4	95.0
Claim payments, net of recoveries	(94.8)	(88.1)
Change in estimated settlement cost for prior claim years	(5.5)	(17.3)
Undiscounted amount	267.3	275.2
Discounted settlement cost estimate	250.2
Third-Party Liability Claims
Liability For Claims And Claims Adjustment Expense [Line Items]
Undiscounted amount	70.0	73.8
Estimated settlement cost	38.1	36.4
Claim payments, net of recoveries	(41.0)	(53.6)
Change in estimated settlement cost for prior claim years	38.6	13.4
Undiscounted amount	105.7	$ 70.0
Discounted settlement cost estimate	$ 104.3