As of September 30, 2016, and December 31, 2015, our cash, cash equivalents, and marketable securities primarily consisted of cash, U.S. and foreign government and agency securities, AAA-rated money market funds, and other investment grade securities. Cash equivalents and marketable securities are recorded at fair value. Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. To increase the comparability of fair value measures, the following hierarchy prioritizes the inputs to valuation methodologies used to measure fair value:

Level 1—Valuations based on quoted prices for identical assets and liabilities in active markets.

Level 2—Valuations based on observable inputs other than quoted prices included in Level 1, such as quoted prices for similar assets and liabilities in active markets, quoted prices for identical or similar assets and liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data.

Level 3—Valuations based on unobservable inputs reflecting our own assumptions, consistent with reasonably available assumptions made by other market participants. These valuations require significant judgment.

We measure the fair value of money market funds and equity securities based on quoted prices in active markets for identical assets or liabilities. All other financial instruments were valued either based on recent trades of securities in inactive markets or based on quoted market prices of similar instruments and other significant inputs derived from or corroborated by observable market data. We did not hold any cash, cash equivalents, or marketable securities categorized as Level 3 assets as of September 30, 2016, or December 31, 2015.

The following tables summarize, by major security type, our cash, cash equivalents, and marketable securities that are measured at fair value on a recurring basis and are categorized using the fair value hierarchy (in millions):



	September 30, 2016										December 31, 2015
	Cost or Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Total Estimated Fair Value			Total Estimated Fair Value
Cash	$	5,730	$	—	$	—		$	5,730		$	6,201
Level 1 securities:
Money market funds	8,386		—		—			8,386			8,025
Equity securities	23		106		—			129			15
Level 2 securities:
Foreign government and agency securities	45		1		—			46			49
U.S. government and agency securities	3,695		3		(4		)	3,694			5,167
Corporate debt securities	587		2		—			589			477
Asset-backed securities	152		—		(1		)	151			117
Other fixed income securities	90		—		—			90			42
	$	18,708	$	112	$	(5	)	$	18,815		$	20,093
Less: Restricted cash, cash equivalents, and marketable securities (1)								(468		)	(285		)
Total cash, cash equivalents, and marketable securities								$	18,347		$	19,808

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(1)

We are required to pledge or otherwise restrict a portion of our cash, cash equivalents, and marketable securities as collateral for standby and trade letters of credit, guarantees, debt, real estate leases, and amounts due to third-party sellers in certain jurisdictions. We classify cash, cash equivalents, and marketable securities with use restrictions of less than twelve months as “Accounts receivable, net and other” and of twelve months or longer as non-current “Other assets” on our consolidated balance sheets. See “Note 3 — Commitments and Contingencies.”

The following table summarizes the contractual maturities of our cash equivalents and marketable fixed-income securities as of September 30, 2016 (in millions):



	Amortized Cost		Estimated Fair Value
Due within one year	$	10,647	$	10,648
Due after one year through five years	1,933		1,934
Due after five years through ten years	193		193
Due after ten years	182		181
Total	$	12,955	$	12,956

Actual maturities may differ from the contractual maturities because borrowers may have certain prepayment conditions.

We also hold equity warrant assets giving us the right to acquire stock of other companies. As of September 30, 2016, and December 31, 2015, these warrants had a fair value of $142 million and $16 million, and are recorded within “Other assets” on our consolidated balance sheets. The related gain (loss) recorded in “Other income (expense), net” was $9 million and $(1) million in Q3 2016 and Q3 2015, and $(11) million and $1 million in the nine months ended September 30, 2016 and 2015. These assets are primarily classified as Level 2 assets.