A ledger that contains a separate account for each customer is called an accounts receivable:

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A ledger that contains a separate account for each customer is called a subsidiary ledger. This is because the subsidiary ledger is a supporting ledger to the general ledger and contains specific details about accounts such as accounts receivable for each customer. The accounts receivable subsidiary ledger can be used to manage individual customer details such as outstanding invoices and balances owed.

A Ledger That Contains a Separate Account for Each Customer