The Company’s investments on the consolidated balance sheet include both available-for-sale and held-to-maturity debt securities (see Investments section below). The Company classifies its investments in equity securities of publicly traded and privately held companies within other assets on the consolidated balance sheet (see Equity Investments section below).

The major classes of the Company’s available-for-sale investment securities and their respective amortized cost basis and fair values at December 31 were as follows:


	2022								2021
	Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss		Fair Value		Amortized Cost		Gross Unrealized Gain		Gross Unrealized Loss		Fair Value
	(in millions)
Municipal securities	$	—	$	—	$	—	$	—	$	2	$	—	$	—	$	2
Government and agency securities	91		—		(2)		89		98		—		—		98
Corporate securities	187		—		(4)		183		214		—		—		214

Total	$	278	$	—	$	(6)	$	272	$	314	$	—	$	—	$	314

The Company’s corporate and municipal available-for-sale investment securities held at December 31, 2022 and 2021, primarily carried a credit rating of A- or better. Corporate securities are comprised of commercial paper and corporate bonds. Municipal securities are comprised of state tax-exempt bonds and are diversified across states and sectors. Government and agency securities include U.S. government bonds, U.S. government sponsored agency bonds and foreign government bonds which are denominated in the national currency of the issuing country. Unrealized gains and losses are recorded as a separate component of other comprehensive income (loss) on the consolidated statement of comprehensive income.

The maturity distribution based on the contractual terms of the Company’s available-for-sale investment securities at December 31, 2022 was as follows:

Investment income on the consolidated statement of operations primarily consists of interest income generated from cash, cash equivalents, time deposits and available-for-sale investment securities, as well as realized gains and losses on the Company’s investment securities. The realized gains and losses from the sales of available-for-sale securities for 2022, 2021 and 2020 were not material.

Included in other assets on the consolidated balance sheet are equity investments with readily determinable fair values (“Marketable securities”) and equity investments without readily determinable fair values (“Nonmarketable securities”). Marketable securities are equity interests in publicly traded companies and are measured using unadjusted quoted prices in their respective active markets. Nonmarketable securities that do not qualify for equity method accounting are measured at cost, less any impairment and adjusted for changes resulting from observable price changes in orderly transactions for the identical or similar investments of the same issuer (“Measurement alternative”).


	Balance at December 31, 2021		Purchases		Sales		Changes in Fair Value 1		Other 2		Balance at December 31, 2022
	(in millions)
Marketable securities	$	627	$	—	$	—	$	(213)	$	(15)	$	399
Nonmarketable securities	1,207		88		(7)		68		(25)		1,331
Total equity investments	$	1,834	$	88	$	(7)	$	(145)	$	(40)	$	1,730

The following table summarizes the total carrying value of the Company’s Measurement alternative investments, including cumulative unrealized gains and losses through December 31:


	2022
	(in millions)
Initial cost basis	$	503
Cumulative adjustments 1:
Upward adjustments	620
Downward adjustments (including impairment)	(36)
Carrying amount, end of period	$	1,087

The following table summarizes the unrealized gains and losses included in the carrying value of the Company’s Measurement alternative investments and Marketable securities for the years ended December 31:


	2022		2021		2020
	(in millions)
Measurement alternative investments:
Upward adjustments	$	114	$	468	$	21
Downward adjustments (including impairment)	$	(23)	$	(2)	$	(3)
Marketable securities:
Unrealized gains (losses), net	$	(213)	$	8	$	(5)