Investments (Debt Securities) (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Amortized cost basis	$ 2,858.9	$ 2,806.3
Accumulated unrealized losses	(4.3)	(5.0)
Fair value	2,854.6	2,801.3
Contractual maturity:
Due in one year or less	2,621.6
Due in one to five years	231.6
Due in five to ten years	1.4
Total	$ 2,854.6	2,801.3
Weighted Average
Contractual maturity:
Weighted average life	4 months 24 days
Commercial paper
Debt Securities, Available-for-sale [Line Items]
Amortized cost basis	$ 881.1	897.4
Accumulated unrealized losses	2.1	0.0
Fair value	883.2	897.4
Contractual maturity:
Total	883.2	897.4
Government bonds
Debt Securities, Available-for-sale [Line Items]
Amortized cost basis	697.0	655.9
Accumulated unrealized losses	(1.4)	(3.3)
Fair value	695.6	652.6
Contractual maturity:
Total	695.6	652.6
Certificates of deposit
Debt Securities, Available-for-sale [Line Items]
Amortized cost basis	520.5	355.5
Accumulated unrealized losses	(0.6)	(0.1)
Fair value	519.9	355.4
Contractual maturity:
Total	519.9	355.4
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized cost basis	405.3	705.5
Accumulated unrealized losses	(4.8)	(1.6)
Fair value	400.5	703.9
Contractual maturity:
Total	400.5	703.9
Other debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized cost basis	355.0	192.0
Accumulated unrealized losses	0.4	0.0
Fair value	355.4	192.0
Contractual maturity:
Total	$ 355.4	$ 192.0

Amortized cost 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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