Fair Value of Financial Assets and Liabilities - Fair Value Hierarchy of Financial Assets and Liabilities under U.S. GAAP Guidance (Parenthetical) (Detail) $ in Millions	Mar. 31, 2018 USD ($)
Other Assets [Member] | Level 3 [Member] | Non-recurring Basis [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity securities, Assets	$ 30.9