Investments in Marketable Debt Securities

12 Months Ended

Dec. 31, 2017

Investments Debt And Equity Securities [Abstract]

Investments in Marketable Debt Securities

B. INVESTMENTS IN MARKETABLE DEBT SECURITIES

Marketable debt securities consisted of the following at December 31:

	AMORTIZED		UNREALIZED		UNREALIZED		FAIR
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

	AMORTIZED		UNREALIZED		UNREALIZED		FAIR
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

The cost of marketable debt securities is adjusted for amortization of premiums and accretion of discounts to maturity. Amortization, accretion, interest and dividend income and realized gains and losses are included in investment income. The cost of securities sold is based on the specific identification method. Gross realized gains were $1.4, $4.4 and $2.6, and gross realized losses were $.5, $.1 and $.8 for the years ended December 31, 2017, 2016 and 2015, respectively.

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

At December 31,	2017				2016
	LESS THAN TWELVE MONTHS		TWELVE MONTHS OR GREATER		LESS THAN TWELVE MONTHS		TWELVE MONTHS OR GREATER
Fair value	$	908.5	$	18.4	$	615.5
Unrealized losses		4.8		.2		3.7

For the investment securities in gross unrealized loss positions identified above, the Company does not intend to sell the investment securities. It is more likely than not that the Company will not be required to sell the investment securities before recovery of the unrealized losses, and the Company expects that the contractual principal and interest will be received on the investment securities. As a result, the Company recognized no other-than-temporary impairments during the periods presented.

Contractual maturities on marketable debt securities at December 31, 2017were as follows:

	AMORTIZED		FAIR
Maturities:	COST		VALUE
Within one year	$	413.7	$	413.3
One to five years		939.6		936.9
More than ten years		16.9		16.9
	$	1,370.2	$	1,367.1