Trade Accounts Receivable (Tables)

9 Months Ended

Sep. 30, 2021

Receivables [Abstract]

Summary of Trade Accounts Receivable

Trade accounts receivable are recorded at the contractual or invoiced amount.

	September 30,			December 31,
	2021			2020
Trade accounts receivable, current	$	4,135		$	3,932
Trade accounts receivable, long-term		224			—
Allowance for doubtful accounts		(25	)		(25	)
Trade accounts receivable, net	$	4,334		$	3,907
Unpaid deferred revenue included in trade    accounts receivable	$	590		$	1,711

Customers Accounted for 10% or More of Trade Accounts Receivable, Net

The following customers accounted for 10% or more of trade accounts receivable, net:

	September 30,			December 31,
	2021			2020
Central Banks		51	%		69	%
Practical Methods		11	%		0	%