Investments in Marketable Debt Securities (Tables)

9 Months Ended

Sep. 30, 2017

Investments Debt And Equity Securities [Abstract]

Marketable Debt Securities

Marketable debt securities at September 30, 2017 and December 31, 2016 consisted of the following:

	AMORTIZED		UNREALIZED		UNREALIZED		FAIR
At September 30, 2017	COST		GAINS		LOSSES		VALUE
U.S. tax-exempt securities	$	520.8	$	1.3	$	.1	$	522.0
U.S. corporate securities		58.6		.3				58.9
U.S. government and agency securities		12.2						12.2
Non-U.S. corporate securities		397.7		1.4		1.2		397.9
Non-U.S. government securities		97.0		.3		.1		97.2
Other debt securities		128.1		.1		.4		127.8
	$	1,214.4	$	3.4	$	1.8	$	1,216.0

	AMORTIZED		UNREALIZED		UNREALIZED		FAIR
At December 31, 2016	COST		GAINS		LOSSES		VALUE
U.S. tax-exempt securities	$	597.9	$	.2	$	3.1	$	595.0
U.S. corporate securities		47.6		.2				47.8
U.S. government and agency securities		16.0						16.0
Non-U.S. corporate securities		306.9		1.5		.4		308.0
Non-U.S. government securities		97.6		.6				98.2
Other debt securities		75.9		.2		.2		75.9
	$	1,141.9	$	2.7	$	3.7	$	1,140.9

Marketable Debt Securities Continuous Unrealized Losses

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

	September 30, 2017				December 31, 2016
	LESS THAN		TWELVE MONTHS		LESS THAN		TWELVE MONTHS
	TWELVE MONTHS		OR GREATER		TWELVE MONTHS		OR GREATER
Fair value	$	409.8	$	11.3	$	615.5
Unrealized losses		1.7		.1		3.7

Contractual Maturities of Debt Securities

Contractual maturities on marketable debt securities at September 30, 2017were as follows:

	AMORTIZED		FAIR
Maturities:	COST		VALUE
Within one year	$	404.4	$	404.6
One to five years		800.9		802.3
More than ten years		9.1		9.1
	$	1,214.4	$	1,216.0