Buildings and Equipment (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
ORIGINAL COST	$ 1,612.6	$ 1,467.4
ACCUMULATED DEPRECIATION	1,097.7	984.1
NET BOOK VALUE	514.9	483.3
Land and Improvements
Property, Plant and Equipment [Line Items]
ORIGINAL COST	14.5	14.5
ACCUMULATED DEPRECIATION	0.5	0.5
NET BOOK VALUE	14.0	14.0
Buildings
Property, Plant and Equipment [Line Items]
ORIGINAL COST	257.8	305.8
ACCUMULATED DEPRECIATION	163.0	156.0
NET BOOK VALUE	94.8	149.8
Equipment
Property, Plant and Equipment [Line Items]
ORIGINAL COST	816.4	731.0
ACCUMULATED DEPRECIATION	596.8	521.5
NET BOOK VALUE	219.6	209.5
Leasehold Improvements
Property, Plant and Equipment [Line Items]
ORIGINAL COST	523.9	416.1
ACCUMULATED DEPRECIATION	337.4	306.1
NET BOOK VALUE	$ 186.5	$ 110.0