Apex domains cannot have CNAME records.
Question and response
Question
dig s3-w.us-west-2.amazonaws.com. NS
Answer
s3-w.us-west-2.amazonaws.com. 4 NS ns-1389.awsdns-45.org.
s3-w.us-west-2.amazonaws.com. 4 NS ns-406.awsdns-50.com.
s3-w.us-west-2.amazonaws.com. 4 NS ns-649.awsdns-17.net.
s3-w.us-west-2.amazonaws.com. 4 NS ns-1891.awsdns-44.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0