Investments - Gross Unrealized Gains and (Losses) Aggregated by Investment Category (Detail) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	$ 76.4	$ 227.7
Investments, Estimated Fair Value	76.4	227.7
Time Deposits and Certificates of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	22.0	0.7
Investments, Estimated Fair Value	22.0	0.7
Bankers' Acceptance Drafts [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	0.5	3.8
Investments, Estimated Fair Value	0.5	3.8
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	41.8
Investments, Estimated Fair Value	41.8
U.S. Treasury Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	11.5	223.2
Investments, Estimated Fair Value	11.5	223.2
U.S. Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	0.6
Investments, Estimated Fair Value	0.6
Group Insurance Contracts [Member] \| Long Term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	5.3	5.6
Investments, Gross Unrealized Gains	0.9	0.9
Investments, Estimated Fair Value	$ 6.2	$ 6.5

Amortized cost, after allowance for credit loss, of investment in debt security measured at amortized cost (held-to-maturity) and investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27232-111563

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27161-111563

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- Definition

Amount of cumulative unrecognized gain on investment in debt security measured at amortized cost (held-to-maturity) and investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123581744&loc=SL120269820-111563

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27161-111563

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- Definition

Fair value of investment in debt security measured at amortized cost (held-to-maturity) and investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5A
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123581744&loc=SL120269820-111563

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27161-111563

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