Goodwill and Other Identifiable Intangible Assets - Estimated Future Amortization Expense for Identifiable Intangible Assets (Detail) $ in Millions	Dec. 31, 2017 USD ($)
Expected Amortization Expense
Estimated amortization expense 2017	$ 96.3
Estimated amortization expense 2018	89.2
Estimated amortization expense 2019	84.0
Estimated amortization expense 2020	77.5
Estimated amortization expense 2021	$ 70.0