Investments in Marketable Debt Securities (Tables)

3 Months Ended

Mar. 31, 2018

Investments Debt And Equity Securities [Abstract]

Marketable Debt Securities

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

	AMORTIZED		UNREALIZED		UNREALIZED		FAIR
At March 31, 2018	COST		GAINS		LOSSES		VALUE
U.S. tax-exempt securities	$	523.6			$	2.5	$	521.1
U.S. corporate securities		50.5	$	.1		.4		50.2
U.S. government and agency securities		59.1				.4		58.7
Non-U.S. corporate securities		246.9		.5		1.9		245.5
Non-U.S. government securities		53.4		.1		.1		53.4
Other debt securities		118.7				1.1		117.6
	$	1,052.2	$	.7	$	6.4	$	1,046.5

	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:

	March 31, 2018				December 31, 2017
	LESS THAN		TWELVE MONTHS		LESS THAN		TWELVE MONTHS
	TWELVE MONTHS		OR GREATER		TWELVE MONTHS		OR GREATER
Fair value	$	841.6	$	22.7	$	908.5	$	18.4
Unrealized losses		6.1		.3		4.8		.2

Contractual Maturities of Debt Securities

Contractual maturities on marketable debt securities at March 31, 2018were as follows:

	AMORTIZED		FAIR
Maturities:	COST		VALUE
Within one year	$	333.7	$	333.2
One to five years		694.1		688.9
More than ten years		24.4		24.4
	$	1,052.2	$	1,046.5