Investments - Investments Classified as Short-Term Available-for-Sale Investments (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Investments classified as short-term	$ 227.7	$ 109.4
Time Deposits and Certificates of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments classified as short-term	0.7	13.1
Bankers' Acceptance Drafts [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments classified as short-term	3.8	4.0
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments classified as short-term		61.2
U.S. Treasury Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments classified as short-term	$ 223.2	5.0
U.S. Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments classified as short-term		$ 26.1