Investments in Marketable Securities (Tables)

3 Months Ended

Mar. 31, 2024

Investments, Debt and Equity Securities [Abstract]

Marketable Securities

Marketable securities at March 31, 2024 and December 31, 2023 consisted of the following:

			UNREALIZED		UNREALIZED		FAIR
At March 31, 2024	COST		GAINS		LOSSES		VALUE
Marketable debt securities
U.S. tax-exempt securities	$	259.0	$	.4	$	3.2	$	256.2
U.S. taxable municipal / non-U.S. provincial bonds		280.5		.3		5.8		275.0
U.S. corporate securities		410.4		.6		4.9		406.1
U.S. government securities		146.3				2.1		144.2
Non-U.S. corporate securities		532.8		1.3		6.1		528.0
Non-U.S. government securities		154.6		1.0		1.1		154.5
Other debt securities		66.0		.1		1.5		64.6
Marketable equity securities		10.0				7.2		2.8
Total marketable securities	$	1,859.6	$	3.7	$	31.9	$	1,831.4

			UNREALIZED		UNREALIZED		FAIR
At December 31, 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:

	March 31, 2024				December 31, 2023
	LESS THAN		TWELVE MONTHS		LESS THAN		TWELVE MONTHS
	TWELVE MONTHS		OR GREATER		TWELVE MONTHS		OR GREATER
Fair value	$	564.3	$	672.1	$	289.0	$	798.5
Unrealized losses		3.7		21.0		1.6		25.2

Contractual Maturities of Debt Securities

Contractual maturities of marketable debt securities at March 31, 2024 were as follows:

	AMORTIZED		FAIR
	COST		VALUE
Within one year	$	490.1	$	484.9
One to five years		1,347.6		1,332.9
Six to ten years		.4		.4
More than ten years		11.5		10.4
	$	1,849.6	$	1,828.6