3. Investments

Available-for-Sale Investments

Marketable investments classified as available-for-sale consisted of the following (in millions):


			Gross		Gross
	Amortized		Unrealized		Unrealized		Fair
As of March 31, 2019	Cost		Gains		Losses		Value
U.S. government and agency securities	$	1,111.8	$	1.3	$	(2.0)	$	1,111.1
Corporate debt securities		111.2		0.5		—		111.7
Total	$	1,223.0	$	1.8	$	(2.0)	$	1,222.8
Reported under the following captions on the consolidated balance sheet:
Cash and cash equivalents							$	5.9
Current marketable investments								806.4
Non-current marketable investments								410.5
Total							$	1,222.8


			Gross		Gross
	Amortized		Unrealized		Unrealized		Fair
As of December 31, 2018	Cost		Gains		Losses		Value
U.S. government and agency securities	$	1,077.4	$	0.7	$	(3.9)	$	1,074.2
Corporate debt securities		72.3		—		(0.3)		72.0
Total	$	1,149.7	$	0.7	$	(4.2)	$	1,146.2
Reported under the following captions on the consolidated balance sheet:
Cash and cash equivalents							$	—
Current marketable investments								705.8
Non-current marketable investments								440.4
Total							$	1,146.2

The following table summarizes the contractual maturities of available-for-sale marketable investments (in millions):


	As of March 31, 2019
	Amortized		Fair
	Cost		Value
Due within one year	$	813.4	$	812.3
Due in one to three years		409.6		410.5
Total	$	1,223.0	$	1,222.8


	As of December 31, 2018
	Amortized		Fair
	Cost		Value
Due within one year	$	708.2	$	705.8
Due in one to three years		441.5		440.4
Total	$	1,149.7	$	1,146.2

Investments in Privately-Held Companies

As of March 31, 2019, we maintained non-controlling equity investments in privately-held companies of approximately $142.5 million in the aggregate. Upon adoption of ASU 2016-01 on January 1, 2018, we began to measure these investments using the measurement alternative because the fair values of these investments are not readily determinable. Under this alternative, the investments are measured at cost, less any impairment, adjusted for any observable price changes. There were no observable price changes in our investments in privately-held companies during the three months ended March 31, 2019. We include our investments in privately-held companies within other non-current assets on our consolidated balance sheets. These investments are subject to a periodic impairment review and if impaired, the investment is measured and recorded at fair value in accordance with ASC 820, Fair Value Measurements.