Investments in Marketable Debt Securities (Tables)

6 Months Ended

Jun. 30, 2017

Investments, Debt and Equity Securities [Abstract]

Marketable Debt Securities

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

At June 30, 2017	AMORTIZED COST		UNREALIZED GAINS		UNREALIZED LOSSES		FAIR VALUE
U.S. tax-exempt securities	$	563.1	$	1.3	$	.4	$	564.0
U.S. corporate securities		58.8		.1		.1		58.8
U.S. government and agency securities		15.6						15.6
Non-U.S. corporate securities		377.9		1.2		.6		378.5
Non-U.S. government securities		92.9		.3		.1		93.1
Other debt securities		134.6		.2		.2		134.6
	$	1,242.9	$	3.1	$	1.4	$	1,244.6
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

Marketable Debt Securities Continuous Unrealized Losses

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

	June 30, 2017			December 31, 2016
	LESS THAN TWELVE MONTHS		TWELVE MONTHS OR GREATER	LESS THAN TWELVE MONTHS		TWELVE MONTHS OR GREATER
Fair value	$	450.3		$	615.5
Unrealized losses		1.4			3.7

Contractual Maturities of Debt Securities

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

Maturities:	AMORTIZED COST		FAIR VALUE
Within one year	$	341.9	$	342.1
One to five years		891.9		893.4
More than ten years		9.1		9.1
	$	1,242.9	$	1,244.6