The amortized cost, gross unrealized holding losses and fair value of marketable securities, excluding accrued interest receivable, consisted of the following:


	September 30, 2023
	Amortized Cost		Gross Unrealized Losses		Fair Value
Commercial paper	$	88	$	—	$	88
Certificates of deposit	41		—		41
Corporate bonds	71		—		71
U.S. government agency securities	80		—		80
Treasury securities	156		(2)		154
Asset-backed securities	82		—		82
Total	$	518	$	(2)	$	516


	December 31, 2022
	Amortized Cost		Gross Unrealized Losses		Fair Value
Commercial paper	$	140	$	—	$	140
Certificates of deposit	104		—		104
Corporate bonds	110		(1)		109
U.S. government agency securities	33		—		33
Treasury securities	61		(1)		60
Asset-backed securities	28		—		28
Total	$	476	$	(2)	$	474

The fair values of marketable securities by contractual maturities at September 30, 2023:


	September 30, 2023
Due within 1 year	$	340
Due after 1 year through 5 years	172
Due after 5 years and thereafter	4

Total marketable securities	$	516

We review marketable securities for impairment during each reporting period to determine if any of the securities have experienced an other-than-temporary decline in fair value. There were no impairment losses or expected credit losses related to our marketable securities during the three and nine months ended September 30, 2023 and 2022.