Summary of Fair Value of Company's Plan Assets (Detail) - Fair Value, Inputs, Level 2 - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 147.9	$ 131.0
Total	442.6	384.3
U.S. Equity | Large Cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	15.7	5.0
Non-U.S. Equity
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	8.1	13.2
Non-U.S. Bonds | Corporate
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	67.0	60.4
Non-U.S. Bonds | Aggregate
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7.3	5.9
Insurance Contracts
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	38.8	36.7
Common Collective Trusts
Defined Benefit Plan Disclosure [Line Items]
Investments measured at net asset value	294.7	253.3
Other Investment
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 11.0	$ 9.8