Equity Securities (Tables)

12 Months Ended

Dec. 31, 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:

	December 31,
(in millions)	2024		2023
Marketable equity securities	$	386.8	$	436.9
Non-marketable equity securities		202.4		224.1
Equity method investments		102.1		74.6
	$	691.3	$	735.6

Summary of Investments in Marketable Equity Securities

Investments in marketable equity securities are summarized as follows:

(in millions)	Cost		Unrealized gains (losses)			Estimated fair value
December 31, 2024
Common stocks	$	397.3	$	(22.6	)	$	374.7
Preferred stocks		12.0		0.1			12.1
	$	409.3	$	(22.5	)	$	386.8
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 years ended December 31, 2024 and 2023, is as follows:

	Year ended December 31,
(in millions)	2024			2023
Carrying amount, beginning of period	$	224.1		$	395.8
Net additions (disposals)		6.0			(4.0	)
Gross unrealized gains		1.5			1.5
Gross unrealized losses and impairments		(29.2	)		(169.2	)
Carrying amount, end of period	$	202.4		$	224.1

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 December 31, 2024 and 2023, are summarized as follows:

	December 31,
(in millions)	2024		2023
Cumulative gross unrealized gains	$	244.8	$	243.3
Cumulative gross unrealized losses and impairments	$	351.6	$	322.4