Apex domains cannot have CNAME records.
Question and response
Question
dig us-east-1.amazonaws.com. NS
Answer
us-east-1.amazonaws.com. 5 NS ns-229.awsdns-28.com.
us-east-1.amazonaws.com. 5 NS ns-1610.awsdns-09.co.uk.
us-east-1.amazonaws.com. 5 NS ns-1415.awsdns-48.org.
us-east-1.amazonaws.com. 5 NS ns-869.awsdns-44.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0