Buildings and Equipment (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Property, Plant and Equipment [Line Items]
ORIGINAL COST	$ 1,331.1	$ 1,250.0
ACCUMULATED DEPRECIATION	828.9	749.5
NET BOOK VALUE	502.2	500.5
Land and Improvements
Property, Plant and Equipment [Line Items]
ORIGINAL COST	11.5	11.5
ACCUMULATED DEPRECIATION	0.3	0.3
NET BOOK VALUE	11.2	11.2
Buildings
Property, Plant and Equipment [Line Items]
ORIGINAL COST	253.1	224.7
ACCUMULATED DEPRECIATION	141.4	137.7
NET BOOK VALUE	111.7	87.0
Equipment
Property, Plant and Equipment [Line Items]
ORIGINAL COST	536.5	499.7
ACCUMULATED DEPRECIATION	337.5	281.9
NET BOOK VALUE	199.0	217.8
Leasehold Improvements
Property, Plant and Equipment [Line Items]
ORIGINAL COST	530.0	514.1
ACCUMULATED DEPRECIATION	349.7	329.6
NET BOOK VALUE	$ 180.3	$ 184.5