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Investments - Gross Unrealized Gains and (Losses) Aggregated by Investment Category (Detail) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	$ 178.1	$ 109.7
Investments, Gross Unrealized (Losses)		(0.3)
Investments, Estimated Fair Value	178.1	109.4
Time Deposits and Certificates of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	0.3	13.1
Investments, Estimated Fair Value	0.3	13.1
Bankers' Acceptance Drafts [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	2.5	4.0
Investments, Estimated Fair Value	2.5	4.0
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	3.8	61.5
Investments, Gross Unrealized (Losses)		(0.3)
Investments, Estimated Fair Value	3.8	61.2
U.S. Treasury Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	165.2	5.0
Investments, Estimated Fair Value	165.2	5.0
U.S. Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	6.3	26.1
Investments, Estimated Fair Value	6.3	26.1
Group Insurance Contracts [Member] | Long Term Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	5.3	5.2
Investments, Gross Unrealized Gains	0.7	0.6
Investments, Estimated Fair Value	$ 6.0	$ 5.8

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- Definition

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

+ References

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

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