Investments in Marketable Debt Securities (Tables)

12 Months Ended

Dec. 31, 2016

Investments, Debt and Equity Securities [Abstract]

Marketable Debt Securities

Marketable debt securities consisted of the following at December 31:

2016	AMORTIZED COST		UNREALIZED GAINS		UNREALIZED LOSSES		FAIR 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
2015	AMORTIZED COST		UNREALIZED GAINS		UNREALIZED LOSSES		FAIR VALUE
U.S. tax-exempt securities	$	505.0	$	.7	$	.3	$	505.4
U.S. corporate securities		76.7		.1		.1		76.7
U.S. government and agency securities		15.7		.1		.1		15.7
Non-U.S. corporate securities		585.6		1.8		.4		587.0
Non-U.S. government securities		192.7		1.1		.1		193.7
Other debt securities		69.6		.1		.1		69.6
	$	1,445.3	$	3.9	$	1.1	$	1,448.1

Marketable Debt Securities Continuous Unrealized Losses

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

At December 31,	2016			2015
	LESS THAN TWELVE MONTHS		TWELVE MONTHS OR GREATER	LESS THAN TWELVE MONTHS		TWELVE MONTHS OR GREATER
Fair value	$	615.5		$	579.0
Unrealized losses		3.7			1.1

Contractual Maturities of Debt Securities

Contractual maturities on marketable debt securities at December 31, 2016 were as follows:

Maturities:	AMORTIZED COST		FAIR             VALUE
Within one year	$	274.5	$	274.7
One to five years		858.2		857.0
Six to ten years		.1		.1
More than ten years		9.1		9.1
	$	1,141.9	$	1,140.9