Equity Securities (Tables)

6 Months Ended

Jun. 30, 2024

Investments, Debt and Equity Securities [Abstract]

Summary of Investments in Equity Securities, by Accounting Classification

Investments in equity securities, by accounting classification, are summarized as follows:

(in millions)	June 30, 2024		December 31, 2023
Marketable equity securities	$	389.9	$	436.9
Non-marketable equity securities		225.8		224.1
Equity method investments		94.4		74.6
	$	710.1	$	735.6

Summary of Investments in Marketable Equity Securities

Investments in marketable equity securities are summarized as follows:

(in millions)	Cost		Unrealized losses			Estimated fair value
June 30, 2024
Common stocks	$	402.4	$	(25.7	)	$	376.7
Preferred stocks		13.8		(0.6	)		13.2
	$	416.2	$	(26.3	)	$	389.9
December 31, 2023
Common stocks	$	429.4	$	(4.9	)	$	424.5
Preferred stocks		15.7		(3.3	)		12.4
	$	445.1	$	(8.2	)	$	436.9

Summary of Changes in Carrying Amounts of Non-Marketable Equity Securities

A summary of the changes in the carrying amounts of non-marketable equity securities, which primarily relate to the Company's venture investment portfolio, for the three and six months ended June 30, 2024 and 2023, is as follows:

	Three Months Ended June 30,						Six Months Ended June 30,
(in millions)	2024			2023			2024			2023
Carrying amount, beginning of period	$	226.1		$	384.7		$	224.1		$	395.8
Net additions		1.3			0.8			3.1			6.8
Gross unrealized gains		1.2			—			1.4			—
Gross unrealized losses and impairments		(2.8	)		(22.6	)		(2.8	)		(39.7	)
Carrying amount, end of period	$	225.8		$	362.9		$	225.8		$	362.9

Summary of Cumulative Gross Unrealized Gains and Cumulative Gross Unrealized Losses and Impairments

Cumulative gross unrealized gains and cumulative gross unrealized losses and impairments related to non-marketable equity securities at June 30, 2024 and December 31, 2023, are summarized as follows:

(in millions)	June 30, 2024		December 31, 2023
Cumulative gross unrealized gains	$	244.8	$	243.3
Cumulative gross unrealized losses and impairments	$	325.2	$	322.4