Cash Equivalents and Investments - Investments in Equity Securities (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Debt Securities, Trading, and Equity Securities, FV-NI [Line Items]
Equity investments without readily determinable fair value:	$ 145.1	$ 146.2
Total equity securities	571.3	718.7
Cash equivalents
Debt Securities, Trading, and Equity Securities, FV-NI [Line Items]
Total equity securities	370.3	519.8
Short-term investments
Debt Securities, Trading, and Equity Securities, FV-NI [Line Items]
Total equity securities	7.2	6.6
Prepaid expenses and other current assets
Debt Securities, Trading, and Equity Securities, FV-NI [Line Items]
Total equity securities	10.4	9.9
Other long-term assets
Debt Securities, Trading, and Equity Securities, FV-NI [Line Items]
Total equity securities	183.4	182.4
Money market funds
Debt Securities, Trading, and Equity Securities, FV-NI [Line Items]
Equity investments with readily determinable fair value:	387.1	536.6
Mutual funds
Debt Securities, Trading, and Equity Securities, FV-NI [Line Items]
Equity investments with readily determinable fair value:	31.9	29.3
Publicly-traded equity securities
Debt Securities, Trading, and Equity Securities, FV-NI [Line Items]
Equity investments with readily determinable fair value:	$ 7.2	$ 6.6

[Line Items] for Debt Securities, Trading, and Equity Securities, FV-NI [Table]

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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI), classified as current.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=123594786&loc=SL75136599-209740

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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI) and investment in equity security without readily determinable fair value.

+ References

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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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123583765&loc=SL75117539-209714

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