Investments in Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2023

Investments, Debt and Equity Securities [Abstract]

Marketable Securities

Marketable securities consisted of the following at December 31:

			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

			UNREALIZED		UNREALIZED		FAIR
2022	COST		GAINS		LOSSES		VALUE
Marketable debt securities
U.S. tax-exempt securities	$	452.8	$	.5	$	8.2	$	445.1
U.S. taxable municipal / non-U.S. provincial bonds		191.6				10.8		180.8
U.S. corporate securities		262.5		.1		11.6		251.0
U.S. government securities		118.0		.1		3.1		115.0
Non-U.S. corporate securities		467.9				17.9		450.0
Non-U.S. government securities		78.9		.2		2.7		76.4
Other debt securities		99.4				4.7		94.7
Marketable equity securities		10.0				8.8		1.2
Total marketable securities	$	1,681.1	$	.9	$	67.8	$	1,614.2

Marketable Debt Securities Continuous Unrealized Losses

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

At December 31,	2023				2022
	LESS THAN TWELVE MONTHS		TWELVE MONTHS OR GREATER		LESS THAN TWELVE MONTHS		TWELVE MONTHS OR GREATER
Fair value	$	289.0	$	798.5	$	889.2	$	608.4
Unrealized losses		1.6		25.2		21.5		37.5

Contractual Maturities of Debt Securities

Contractual maturities on marketable debt securities at December 31, 2023 were as follows:

	AMORTIZED		FAIR
Maturities:	COST		VALUE
Within one year	$	488.3	$	482.5
One to five years		1,336.0		1,324.5
Six to ten years		.7		.6
More than ten years		11.9		10.6
	$	1,836.9	$	1,818.2