Apex domains cannot have CNAME records.
Question and response
Question
dig s3-3-w.amazonaws.com. NS
Answer
s3-3-w.amazonaws.com. 5 NS ns-1573.awsdns-04.co.uk.
s3-3-w.amazonaws.com. 5 NS ns-687.awsdns-21.net.
s3-3-w.amazonaws.com. 5 NS ns-299.awsdns-37.com.
s3-3-w.amazonaws.com. 5 NS ns-1425.awsdns-50.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0