Apex domains cannot have CNAME records.
Question and response
Question
dig spf3.amazon.com. NS
Answer
spf3.amazon.com. 5 NS ns-860.awsdns-43.net.
spf3.amazon.com. 5 NS ns-1626.awsdns-11.co.uk.
spf3.amazon.com. 5 NS ns-285.awsdns-35.com.
spf3.amazon.com. 5 NS ns-1036.awsdns-01.org.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0