Investments in Marketable Debt Securities (Tables)

9 Months Ended

Sep. 30, 2018

Investments Debt And Equity Securities [Abstract]

Marketable Debt Securities

Marketable debt securities at September 30, 2018 and December 31, 2017 consisted of the following:

	AMORTIZED		UNREALIZED		UNREALIZED		FAIR
At September 30, 2018	COST		GAINS		LOSSES		VALUE
U.S. tax-exempt securities	$	345.2			$	2.4	$	342.8
U.S. corporate securities		132.8	$	.1		.5		132.4
U.S. government and agency securities		92.8				.6		92.2
Non-U.S. corporate securities		266.1		.3		2.1		264.3
Non-U.S. government securities		56.7		.1		.1		56.7
Other debt securities		113.4				1.5		111.9
	$	1,007.0	$	.5	$	7.2	$	1,000.3

	AMORTIZED		UNREALIZED		UNREALIZED		FAIR
At December 31, 2017	COST		GAINS		LOSSES		VALUE
U.S. tax-exempt securities	$	537.9			$	2.4	$	535.5
U.S. corporate securities		89.7	$	.2		.2		89.7
U.S. government and agency securities		48.9				.2		48.7
Non-U.S. corporate securities		459.4		1.3		1.4		459.3
Non-U.S. government securities		91.5		.3		.1		91.7
Other debt securities		142.8		.1		.7		142.2
	$	1,370.2	$	1.9	$	5.0	$	1,367.1

Marketable Debt Securities Continuous Unrealized Losses

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

	September 30, 2018				December 31, 2017
	LESS THAN		TWELVE MONTHS		LESS THAN		TWELVE MONTHS
	TWELVE MONTHS		OR GREATER		TWELVE MONTHS		OR GREATER
Fair value	$	680.5	$	143.4	$	908.5	$	18.4
Unrealized losses		5.0		2.2		4.8		.2

Contractual Maturities of Debt Securities

Contractual maturities on marketable debt securities at September 30, 2018were as follows:

	AMORTIZED		FAIR
Maturities:	COST		VALUE
Within one year	$	279.3	$	278.6
One to five years		718.0		712.0
More than ten years		9.7		9.7
	$	1,007.0	$	1,000.3