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Investments in Marketable Securities - Debt Securities, Available-for-Sale (Details) - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022
Investments, Debt and Equity Securities [Abstract]
Debt securities, available-for-sale, maturity, year one	$ 176.5
Debt securities, available-for-sale, maturity, year two	152.6
Available-for-Sale
Cost	330.8	$ 252.3
Unrealized losses	(1.7)	(1.3)
Fair value	329.1	251.0
Trading
Cost	20.3	19.7
Unrealized losses	(1.0)	(1.7)
Fair value	$ 19.3	$ 18.0

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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).

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