Apex domains cannot have CNAME records.
Question and response
Question
dig s3-us-west-2-r-w.amazonaws.com. NS
Answer
s3-us-west-2-r-w.amazonaws.com. 5 NS ns-1052.awsdns-03.org.
s3-us-west-2-r-w.amazonaws.com. 5 NS ns-1831.awsdns-36.co.uk.
s3-us-west-2-r-w.amazonaws.com. 5 NS ns-427.awsdns-53.com.
s3-us-west-2-r-w.amazonaws.com. 5 NS ns-673.awsdns-20.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0