AWSはデフォルトでIAMユーザーがBillingを見れないようになっている

Overview of managing access permissions

AWS Billing integrates with the AWS Identity and Access Management (IAM) service so that you can control who in your organization has access to specific pages on the AWS Billing console . You can control access to invoices and detailed information about charges and account activity, budgets, payment methods, and credits.

docs.aws.amazon.com