Apex domains cannot have CNAME records.
Question and response
Question
dig s3-us-west-2-w.amazonaws.com. NS
Answer
s3-us-west-2-w.amazonaws.com. 5 NS ns-1240.awsdns-27.org.
s3-us-west-2-w.amazonaws.com. 5 NS ns-526.awsdns-01.net.
s3-us-west-2-w.amazonaws.com. 5 NS ns-151.awsdns-18.com.
s3-us-west-2-w.amazonaws.com. 5 NS ns-1872.awsdns-42.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0