Investments (Tables)

12 Months Ended

Dec. 31, 2019

Investments [Abstract]

Fair value of short and long-term investments classified as available for sale

The following tables summarize the unrealized gains and losses and estimated fair value of our investments classified as available-for-sale as of December 31, 2019 and 2018 (in millions):

	December 31, 2019
	Gross Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Estimated Fair Value
Short-term investments:
Restricted cash	$	21	$	—	$	—	$	21
Corporate debt securities	1,653		1		—		1,654
Government and agency securities	175		—		—		175
	$	1,849	$	1	$	—	$	1,850
Long-term investments:
Corporate debt securities	957		4		—		961
	$	957	$	4	$	—	$	961

	December 31, 2018
	Gross Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Estimated Fair Value
Short-term investments:
Restricted cash	$	17	$	—	$	—		$	17
Corporate debt securities	2,615		—		(9		)	2,606
Government and agency securities	90		—		—			90
	$	2,722	$	—	$	(9	)	$	2,713
Long-term investments:
Corporate debt securities	3,682		1		(48		)	3,635
	$	3,682	$	1	$	(48	)	$	3,635

Estimated fair values of short and long-term investments classified as available for sale by date of contractual maturity

The estimated fair values of our short-term and long-term investments classified as available-for-sale by date of contractual maturity as of December 31, 2019 are as follows (in millions):  

	December 31, 2019
One year or less (including restricted cash of $21)	$	1,850
One year through two years	676
Two years through three years	198
Three years through four years	87
Total	$	2,811

Schedule of equity investments

The following table provides a summary of our equity investments as of December 31, 2019 and December 31, 2018 (in millions):

	December 31, 2019		December 31, 2018
Equity investments without readily determinable fair values	$	337	$	137
Equity investments under the equity method of accounting	18		6
Total equity investments	$	355	$	143

Schedule of investments without readily determinable fair value

The following table summarizes the total carrying value of equity investments without readily determinable fair values during the twelve months ended December 31, 2019 and December 31, 2018 (in millions):

	Year Ended December 31, 2019		Year Ended December 31, 2018
Carrying value, beginning of period	$	137	$	872
Additions	200		23
Sales	—		(718		)
Downward adjustments for observable price changes and impairment	—		(20		)
Foreign currency translation and other	—		(20		)
Carrying value, end of period	$	337	$	137