Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2020

Fair Value Measurements [Abstract]

Schedule of fair value measurement on a recurring basis

December 31, 2020

	Carrying amount in				Fair Value Measurement Using
	balance sheet		Fair Value		Level 1		Level 2		Level 3
Assets:
Cash and cash equivalents:
Commercial paper	$	718	$	718	$	718	$	0	$	0
Treasury bills		7,999		7,999		7,999		0		0
Equity securities		42		42		0		0		42

December 31, 2019

	Carrying amount in				Fair Value Measurement Using
	balance sheet		Fair Value		Level 1		Level 2		Level 3
Assets:
Cash and cash equivalents:
Commercial paper	$	797	$	797	$	797	$	0	$	0
Treasury bills		7,734		7,734		7,734		0		0
Equity securities		45		45		0		0		45

Summary of changes in level 3 assets at fair value on a recurring basis

	Years Ended December 31,
	2020			2019
Beginning Balance	$	45		$	45
Change in value		(3	)		0
Ending Balance	$	42		$	45