Cash Equivalents and Investments - Available-For-Sale (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Available-for-sale debt securities:
Amortized Cost	$ 600.8	$ 437.8
Gross Unrealized Gains	38.4	37.4
Gross Unrealized Losses	(10.2)	(9.5)
Estimated Fair Value	629.0	465.7
Cash equivalents
Available-for-sale debt securities:
Amortized Cost	328.2	70.6
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	0.0	0.0
Estimated Fair Value	328.2	70.6
Short-term investments
Available-for-sale debt securities:
Amortized Cost	135.7	205.9
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	(1.4)	(3.3)
Estimated Fair Value	134.3	202.6
Long-term investments
Available-for-sale debt securities:
Amortized Cost	116.3	145.8
Gross Unrealized Gains	1.0	0.0
Gross Unrealized Losses	(0.5)	(6.2)
Estimated Fair Value	116.8	139.6
Other long-term assets
Available-for-sale debt securities:
Amortized Cost	20.6	15.5
Gross Unrealized Gains	37.4	37.4
Gross Unrealized Losses	(8.3)	0.0
Estimated Fair Value	49.7	52.9
Total fixed income securities
Available-for-sale debt securities:
Amortized Cost	580.2	422.3
Gross Unrealized Gains	1.0	0.0
Gross Unrealized Losses	(1.9)	(9.5)
Estimated Fair Value	579.3	412.8
Asset-backed and mortgage-backed securities
Available-for-sale debt securities:
Amortized Cost	38.2	37.8
Gross Unrealized Gains	0.2	0.0
Gross Unrealized Losses	(0.4)	(1.2)
Estimated Fair Value	38.0	36.6
Certificates of deposit
Available-for-sale debt securities:
Amortized Cost	3.0	0.0
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	0.0	0.0
Estimated Fair Value	3.0	0.0
Commercial paper
Available-for-sale debt securities:
Amortized Cost	41.1	0.0
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	0.0	0.0
Estimated Fair Value	41.1	0.0
Corporate debt securities
Available-for-sale debt securities:
Amortized Cost	160.2	277.5
Gross Unrealized Gains	0.7	0.0
Gross Unrealized Losses	(1.3)	(7.1)
Estimated Fair Value	159.6	270.4
Foreign government debt securities
Available-for-sale debt securities:
Amortized Cost	5.3	8.8
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	(0.2)	(0.4)
Estimated Fair Value	5.1	8.4
Time deposits
Available-for-sale debt securities:
Amortized Cost	273.6	70.6
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	0.0	0.0
Estimated Fair Value	273.6	70.6
U.S. government agency securities
Available-for-sale debt securities:
Amortized Cost	4.0	18.6
Gross Unrealized Gains	0.0	0.0
Gross Unrealized Losses	0.0	(0.6)
Estimated Fair Value	4.0	18.0
U.S. government securities
Available-for-sale debt securities:
Amortized Cost	54.8	9.0
Gross Unrealized Gains	0.1	0.0
Gross Unrealized Losses	0.0	(0.2)
Estimated Fair Value	54.9	8.8
Privately-held debt and redeemable preferred stock securities
Available-for-sale debt securities:
Amortized Cost	20.6	15.5
Gross Unrealized Gains	37.4	37.4
Gross Unrealized Losses	(8.3)	0.0
Estimated Fair Value	$ 49.7	$ 52.9

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on 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/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on 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/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481800/320-10-50-2

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Amortized cost excluding accrued interest, after allowance for credit loss, of 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
-Topic 326
-SubTopic 30
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479130/326-30-45-1

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Amount excluding accrued interest, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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