Decomissioning Organization

To decommission your AWS Organization and close all associated accounts, you should follow these best practices:

1. First, ensure you've removed or closed all member accounts except the management account (formerly known as the master account). You mentioned you've already done this, which is a good start.

2. For any suspended member accounts, you may need to wait up to 90 days for them to be fully removed from the organization. If you can't wait, try reopening these accounts, removing them from the organization, and then closing them again.

3. Once all member accounts are removed, you can delete the organization itself. This action should be performed from the management account.

4. Regarding your concern about accessing the final bills: Before closing the management account, make sure to download and save all billing information and reports you might need for future reference. AWS typically keeps this information available for a period after account closure, but it's best to have your own copies.

5. After saving all necessary billing information, you can proceed to close the management account. This should be done using the root user credentials of the account.

6. Be aware that if you have any Reserved Instances, you may still be billed for these even after account closure until their term expires.

7. If you're having trouble deleting certain resources or closing accounts, you may need to contact AWS Support for assistance.

Remember, once you close the management account, you won't be able to reopen it or access any resources or data within it. Make absolutely sure you've backed up all necessary information and are prepared for the account to be permanently closed before proceeding with this final step.
Sources
Trying to delete Organization | AWS re:Post
Cannot remove the management account | AWS re:Post
about organization | AWS re:Post

To decommission your AWS Organization and close all associated accounts, you should follow these best practices:

1. First, ensure you've removed or closed all member accounts except the management account (formerly known as the master account). You mentioned you've already done this, which is a good start.

2. For any suspended member accounts, you may need to wait up to 90 days for them to be fully removed from the organization. If you can't wait, try reopening these accounts, removing them from the organization, and then closing them again.

3. Once all member accounts are removed, you can delete the organization itself. This action should be performed from the management account.

4. Regarding your concern about accessing the final bills: Before closing the management account, make sure to download and save all billing information and reports you might need for future reference. AWS typically keeps this information available for a period after account closure, but it's best to have your own copies.

5. After saving all necessary billing information, you can proceed to close the management account. This should be done using the root user credentials of the account.

6.Be aware that if you have any Reserved Instances, you may still be billed for these even after account closure until their term expires.

If you're having trouble deleting certain resources or closing accounts, you may need to contact AWS Support for assistance.

Remember, once you close the management account, you won't be able to reopen it or access any resources or data within it. Make absolutely sure you've backed up all necessary information and are prepared for the account to be permanently closed before proceeding with this final step.