INVESTMENTS

Marketable Securities

The following table presents the values of our marketable securities as of the dates shown.



	December 31, 2018				December 31, 2017
(in millions)	Amortized Cost		Fair Value		Amortized Cost		Fair Value
Zero coupon bonds	$	3.9	$	3.9	$	3.8	$	3.9
U.S. treasury and government agencies	20.0		19.8		6.0		6.0
Asset-backed securities	0.1		0.1		0.3		0.3
Corporate debt securities	15.1		15.0		9.1		9.2
State and municipal bonds	12.5		12.5		22.7		22.2
Total marketable securities	$	51.6	$	51.3	$	41.9	$	41.6

Gross realized gains and losses on marketable securities were not material for the years ended December 31, 2018, 2017, and 2016, respectively. Unrealized gains and losses on marketable securities were not material for the years ended December 31, 2018, and 2017, respectively.

Ownership Interest in Platform Science, Inc.

In 2018, we received a 30% ownership interest in Platform Science, Inc. in exchange for our contribution of a non-exclusive license for telematics mobile software that was developed to enable driver productivity and ensure regulatory compliance. Our ownership interest in Platform Science, Inc. is being accounted for under ASC 321, Investments - Equity Securities and is recorded at fair value in other noncurrent assets on the consolidated balance sheets. The fair value of our ownership interest at December 31, 2018 was determined to be $3.5 million through an independent valuation and is recorded in other income in the consolidated statements of comprehensive income.