	December 31,
(in millions)	2021		2020
Marketable equity securities	$	657	$	464
Non-marketable equity securities		441		217
Equity method investments		78		69
	$	1,176	$	750

(in millions)	Cost		Unrealized gains (losses)			Estimated fair value
December 31, 2021
Preferred stocks	$	17	$	—		$	17
Common stocks		418		222			640
	$	435	$	222		$	657
December 31, 2020
Preferred stocks	$	22	$	(3	)	$	19
Common stocks		354		91			445
	$	376	$	88		$	464

Net gains of $184 million and $49 million resulting from changes in the fair values of marketable equity securities were recognized for the years ended December 31, 2021 and 2020, respectively, which included net unrealized gains of $172 million and $49 million on securities still held at December 31, 2021 and 2020, respectively. Included in unrealized gains during 2021 were gains of $121 million related to the Company’s investment in Offerpad Solutions Inc., a leading tech-enabled real estate company, which began trading publicly in September 2021. Net gains and losses resulting from changes in the fair values of marketable equity securities are recognized in net investment gains/losses on the consolidated statements of income.

(in millions)	Cost			Unrealized gains	Carrying amount
December 31, 2021	$	215	$	226	$	441
December 31, 2020	$	201	$	16	$	217

A substantial majority of the Company’s investments in non-marketable equity securities are in private venture-stage companies that operate in the real estate industry and related industries, many of which offer technology-enabled products and services. Such investments include, at December 31, 2021, the Company’s investments in Orchard Technologies, Inc. with a cost and carrying amount of $41 million and $106 million, respectively, and Side, Inc. with a cost and carrying amount of $10 million and $74 million, respectively.

Unrealized gains of $210 million and $13 million related to investments in private venture-stage companies, which resulted from transactions with observable price changes, were recognized during the years ended December 31, 2021 and 2020, respectively. All such gains recognized related to securities still held at December 31, 2021 and 2020. Net gains and losses on non-marketable equity securities are recognized in net investment gains/losses on the consolidated statements of income.

Total unrealized gains recognized by the Company on both its marketable and non-marketable equity securities still held at December 31, 2021 and 2020, totaled $382 million and $65 million for the years ended December 31, 2021 and 2020, respectively.