Investments - Gross Unrealized Gains and (Losses) Aggregated by Investment Category (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	$ 227.7	$ 109.7
Investments, Gross Unrealized (Losses)		(0.3)
Investments, Estimated Fair Value	227.7	109.4
Time Deposits and Certificates of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	0.7	13.1
Investments, Estimated Fair Value	0.7	13.1
Bankers' Acceptance Drafts [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	3.8	4.0
Investments, Estimated Fair Value	3.8	4.0
U.S. Treasury Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	223.2	5.0
Investments, Estimated Fair Value	223.2	5.0
Group Insurance Contracts [Member] \| Long Term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	5.6	5.2
Investments, Gross Unrealized Gains	0.9	0.6
Investments, Estimated Fair Value	$ 6.5	5.8
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost		61.5
Investments, Gross Unrealized (Losses)		(0.3)
Investments, Estimated Fair Value		61.2
U.S. Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost		26.1
Investments, Estimated Fair Value		$ 26.1

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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- Definition

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27161-111563

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- Definition

Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

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- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

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+ References

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