Investments in Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2024

Investments, Debt and Equity Securities [Abstract]

Marketable Securities

Marketable securities consisted of the following at December 31:

			UNREALIZED		UNREALIZED		FAIR
2024	COST		GAINS		LOSSES		VALUE
Marketable debt securities
U.S. tax-exempt securities	$	304.5	$	.6	$	1.4	$	303.7
U.S. taxable municipal / non-U.S. provincial bonds		381.1		1.2		2.2		380.1
U.S. corporate securities		864.3		3.1		3.2		864.2
U.S. government securities		287.1		.1		1.5		285.7
Non-U.S. corporate securities		606.6		3.5		2.0		608.1
Non-U.S. government securities		163.5		1.4		.6		164.3
Other debt securities		166.4		.8		.8		166.4
Marketable equity securities		10.0				3.7		6.3
Total marketable securities	$	2,783.5	$	10.7	$	15.4	$	2,778.8

			UNREALIZED		UNREALIZED		FAIR
2023	COST		GAINS		LOSSES		VALUE
Marketable debt securities
U.S. tax-exempt securities	$	312.5	$	1.2	$	3.0	$	310.7
U.S. taxable municipal / non-U.S. provincial bonds		244.9		.8		5.6		240.1
U.S. corporate securities		357.1		1.4		5.2		353.3
U.S. government securities		159.2		.6		1.7		158.1
Non-U.S. corporate securities		529.4		2.3		7.5		524.2
Non-U.S. government securities		141.0		1.5		1.3		141.2
Other debt securities		92.8		.3		2.5		90.6
Marketable equity securities		10.0				5.6		4.4
Total marketable securities	$	1,846.9	$	8.1	$	32.4	$	1,822.6

Marketable Debt Securities Continuous Unrealized Losses

Marketable debt securities with continuous unrealized losses and their related fair values were as follows:

At December 31,	2024				2023
	LESS THAN TWELVE MONTHS		TWELVE MONTHS OR GREATER		LESS THAN TWELVE MONTHS		TWELVE MONTHS OR GREATER
Fair value	$	932.9	$	365.5	$	289.0	$	798.5
Unrealized losses		5.5		6.2		1.6		25.2

Contractual Maturities of Debt Securities

Contractual maturities on marketable debt securities at December 31, 2024 were as follows:

	AMORTIZED		FAIR
Maturities:	COST		VALUE
Within one year	$	529.4	$	528.7
One to five years		2,237.1		2,237.5
Six to ten years		1.3		1.3
More than ten years		5.7		5.0
	$	2,773.5	$	2,772.5