Explanation:
S3 is used to store the Configuration History files and any Configuration Snapshots of your data within a single bucket, which is defined within the Configuration Recorder. You can get AWS Config to create a new bucket for you and select an existing bucket. If you have multiple AWS accounts you may want to aggregate your Configuration History and Snapshot files into the same S3 Bucket for your primary account, just be aware that this can be achieved. However, you will need to grant write access for the service principal (config.amazonaws.com) in your other accounts write access to the S3 bucket.
Reference: http://docs.aws.amazon.com/config/latest/developerguide/config-concepts.html#config-items