Investments in Marketable Debt Securities (Tables)

12 Months Ended

Dec. 31, 2020

Available For Sale Securities [Abstract]

Marketable Debt Securities

Marketable debt securities consisted of the following at December 31:

	AMORTIZED		UNREALIZED		UNREALIZED		FAIR
2020	COST		GAINS		LOSSES		VALUE
U.S. tax-exempt securities	$	388.1	$	4.4	$	.1	$	392.4
U.S. corporate securities		229.6		3.3				232.9
U.S. government and agency securities		92.1		2.3				94.4
Non-U.S. corporate securities		406.0		5.5				411.5
Non-U.S. government securities		77.0		.5				77.5
Other debt securities		216.9		3.4				220.3
	$	1,409.7	$	19.4	$	.1	$	1,429.0

	AMORTIZED		UNREALIZED		UNREALIZED		FAIR
2019	COST		GAINS		LOSSES		VALUE
U.S. tax-exempt securities	$	318.1	$	2.2	$	.1	$	320.2
U.S. corporate securities		163.8		1.9				165.7
U.S. government and agency securities		128.4		.9				129.3
Non-U.S. corporate securities		347.7		2.3		.2		349.8
Non-U.S. government securities		72.3		.2		.1		72.4
Other debt securities		123.7		1.1		.1		124.7
	$	1,154.0	$	8.6	$	.5	$	1,162.1

Marketable Debt Securities Continuous Unrealized Losses

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

At December 31,	2020				2019
	LESS THAN TWELVE MONTHS		TWELVE MONTHS OR GREATER		LESS THAN TWELVE MONTHS		TWELVE MONTHS OR GREATER
Fair value	$	81.1	$	1.3	$	177.0	$	31.4
Unrealized losses		.1				.4		.1

Contractual Maturities of Debt Securities

Contractual maturities on marketable debt securities at December 31, 2020 were as follows:

	AMORTIZED		FAIR
Maturities:	COST		VALUE
Within one year	$	313.9	$	315.7
One to five years		1,088.6		1,106.1
Six to ten years		5.2		5.2
More than ten years		2.0		2.0
	$	1,409.7	$	1,429.0