Cash Equivalents and Investments

Investments in Available-for-Sale Securities

The following table summarizes the Company's unrealized gains and losses and fair value of investments designated as available-for-sale as of December 31, 2017 and December 31, 2016 (in millions):



	As of December 31, 2017									As of December 31, 2016
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Fixed income securities:
Asset-backed securities	$	287.1	$	—	$	(0.6	)	$	286.5	$	303.0	$	0.2	$	(0.2	)	$	303.0
Certificates of deposit	83.8		—		—			83.8		66.1		—		—			66.1
Commercial paper	217.1		—		—			217.1		147.7		—		—			147.7
Corporate debt securities	929.6		0.4		(3.0		)	927.0		846.5		0.4		(2.0		)	844.9
Foreign government debt securities	62.9		—		(0.2		)	62.7		34.0		—		(0.1		)	33.9
Time deposits	239.2		—		—			239.2		264.6		—		—			264.6
U.S. government agency securities	143.9		—		(0.7		)	143.2		127.0		—		(0.3		)	126.7
U.S. government securities	406.8		0.1		(0.9		)	406.0		390.7		0.1		(0.4		)	390.4
Total fixed income securities	2,370.4		0.5		(5.4		)	2,365.5		2,179.6		0.7		(3.0		)	2,177.3
Money market funds	969.8		—		—			969.8		592.2		—		—			592.2
Privately-held debt and redeemable preferred stock securities	15.9		37.4		—			53.3		15.9		26.4		—			42.3
Publicly-traded equity securities	—		—		—			—		5.3		—		(0.7		)	4.6
Total available-for-sale securities	$	3,356.1	$	37.9	$	(5.4	)	$	3,388.6	$	2,793.0	$	27.1	$	(3.7	)	$	2,816.4

Reported as:
Cash equivalents	$	1,279.0	$	—	$	—		$	1,279.0	$	907.1	$	—	$	—		$	907.1
Restricted investments^(*)	41.8		—		—			41.8		42.9		—		—			42.9
Short-term investments	1,027.2		0.1		(1.2		)	1,026.1		753.4		0.1		(1.2		)	752.3
Long-term investments	992.2		0.4		(4.2		)	988.4		1,073.7		0.6		(2.5		)	1,071.8
Other long-term assets	15.9		37.4		—			53.3		15.9		26.4		—			42.3
Total	$	3,356.1	$	37.9	$	(5.4	)	$	3,388.6	$	2,793.0	$	27.1	$	(3.7	)	$	2,816.4

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^(*)	Balance includes $31.4 million and $4.0 million of short-term restricted investments classified as prepaid expenses and other current assets.

The following table presents the contractual maturities of the Company's total fixed income securities as of December 31, 2017 (in millions):



	Amortized Cost		Estimated Fair Value
Due in less than one year	$	1,378.2	$	1,377.1
Due between one and five years	992.2		988.4
Total	$	2,370.4	$	2,365.5

The following tables present the Company's available-for-sale securities that were in an unrealized loss position as of December 31, 2017 and December 31, 2016 (in millions):



	As of December 31, 2017
	Less than 12 Months					12 Months or Greater					Total
	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
Fixed income securities:
Asset-backed securities	$	215.2	$	(0.4	)	$	38.4	$	(0.2	)	$	253.6	$	(0.6	)
Corporate debt securities	646.7		(2.1		)	108.6		(0.9		)	755.3		(3.0		)
Foreign government debt securities	47.3		(0.2		)	6.6		—			53.9		(0.2		)
U.S. government agency securities	68.3		(0.2		)	67.9		(0.5		)	136.2		(0.7		)
U.S. government securities	260.8		(0.7		)	51.8		(0.2		)	312.6		(0.9		)
Total available-for sale securities	$	1,238.3	$	(3.6	)	$	273.3	$	(1.8	)	$	1,511.6	$	(5.4	)



	As of December 31, 2016
	Less than 12 Months					12 Months or Greater					Total
	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
Fixed income securities:
Asset-backed securities	$	122.2	$	(0.2	)	$	—	$	—		$	122.2	$	(0.2	)
Corporate debt securities	470.8		(1.9		)	76.7		(0.1		)	547.5		(2.0		)
Foreign government debt securities	20.3		(0.1		)	—		—			20.3		(0.1		)
U.S. government agency securities	106.7		(0.3		)	—		—			106.7		(0.3		)
U.S. government securities	254.1		(0.4		)	—		—			254.1		(0.4		)
Total fixed income securities	974.1		(2.9		)	76.7		(0.1		)	1,050.8		(3.0		)
Publicly-traded equity securities	4.6		(0.7		)	—		—			4.6		(0.7		)
Total available-for sale securities	$	978.7	$	(3.6	)	$	76.7	$	(0.1	)	$	1,055.4	$	(3.7	)

For available-for-sale debt securities that have unrealized losses, the Company evaluates whether (i) it has the intention to sell any of these investments and (ii) whether it is more likely than not that it will be required to sell any of these investments before recovery of the entire amortized cost basis. As of December 31, 2017, the Company had 956 investments in unrealized loss position. The gross unrealized losses related to these investments were primarily due to changes in market interest rates. The Company anticipates that it will recover the entire amortized cost basis of such available-for-sale debt securities and has determined that no other-than-temporary impairments associated with credit losses were required to be recognized during the years ended December 31, 2017, 2016, and 2015.

During the years ended December 31, 2017, 2016 and 2015, there were no material gross realized gains or losses from available-for-sale securities.

Investments in Trading Securities

As of December 31, 2017 and December 31, 2016, the total investments under the Company's NQDC plan were $27.6 million and $21.0 million, respectively, and are invested in mutual funds and classified as trading securities. During the years ended December 31, 2017, 2016 and 2015, trading gains and losses related to these trading securities were not material.

Restricted Cash and Investments

The Company has restricted cash and investments for: (i) amounts held in escrow accounts, as required in connection with certain acquisitions completed primarily between 2014 and 2017; (ii) the Directors and Officers indemnification trust ("D&O Trust"); (iii) amounts held under the Company's short-term disability plan in California; and (iv) amounts under the NQDC plan for officers and other senior-level employees. The restricted investments are designated as available-for-sale securities except relating to the NQDC plan which are designated as trading securities. As of December 31, 2017, total restricted cash and investments was $122.0 million, of which $85.9 million was included in prepaid expenses and other current assets, $36.1 million was included in restricted cash and investments on the Consolidated Balance Sheets.

Investments in Privately-Held Companies

As of December 31, 2017 and December 31, 2016, the carrying values of the Company's privately-held investments of $83.0 million and $61.3 million, respectively, were included in other long-term assets in the Consolidated Balance Sheets, of which $29.7 million and $19.0 million were accounted for under the cost method as of December 31, 2017 and December 31, 2016, respectively. See Note 5, Fair Value Measurements, for the Company's investments in privately-held companies that are carried at fair value and cost method investments measured at fair value on a nonrecurring basis.