For our trade receivables, we assess each counterparty’s ability to pay for service by conducting a credit review. The credit review considers the counterparty’s established credit rating or our assessment of the counterparty’s creditworthiness based on our analysis of their financial statements when a credit rating is not available.

We monitor our ongoing credit exposure through active review of counterparty balances against contract terms and due dates. Our activities include timely account reconciliation, dispute resolution, payment confirmation and monitoring current economic conditions and future forecast of economic conditions, to the extent that they impact the credit loss determination and can be reasonably estimated.

Changes in the allowance for credit losses of our trade receivables for the six months ended June 30, 2021 were as follows (in millions):


Balance as of December 31, 2020	$	8

Write-offs charged against the allowance	(1)

Balance as of June 30, 2021	$	7

We held the following receivables in connection with our equity method investments (in millions):


	June 30, 2021		December 31, 2020
Included in prepaid expenses and other assets	$	17	$	27
Included in other assets - long term	34		29
	$	51	$	56

We assess the collectability of the receivables from our equity method investments each reporting period through the impairment analysis procedures of our equity method investments which considers the loss history of the investments and the viability of the associated development projects. As of June 30, 2021 there were no expected credit losses associated with our equity method investment receivables.