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Equity Securities - (Summary of Changes in Carrying Amounts of Non Marketable Equity Securities) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Equity Securities Without Readily Determinable Fair Value [Line Items]
Carrying amount, beginning of period			$ 202.4
Carrying amount, end of period	$ 231.4		231.4
Non Marketable Equity Securities
Equity Securities Without Readily Determinable Fair Value [Line Items]
Carrying amount, beginning of period	218.3	$ 225.8	202.4	$ 224.1
Net additions	16.0	2.4	31.2	5.5
Gross unrealized gains	1.0	0.1	2.5	1.5
Gross unrealized losses and impairments	(3.9)	(9.2)	(4.7)	(12.0)
Carrying amount, end of period	$ 231.4	$ 219.1	$ 231.4	$ 219.1

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Equity securities net additions.

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Equity securities without readily determinable fair value amount unrealized gain.

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Equity securities without readily determinable fair value amount unrealized loss.

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- Definition

Amount of investment in equity security without readily determinable fair value.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 321
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479536/321-10-50-3

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 321
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479536/321-10-50-3

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 321
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479536/321-10-50-3

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 321
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479536/321-10-50-3

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