Apex domains cannot have CNAME records.
Question and response
Question
dig awsdns-40.com. NS
Answer
awsdns-40.com. 5 NS g-ns-1192.awsdns-40.com.
awsdns-40.com. 5 NS g-ns-616.awsdns-40.com.
awsdns-40.com. 5 NS g-ns-41.awsdns-40.com.
awsdns-40.com. 5 NS g-ns-1768.awsdns-40.com.
Authority
The response has no authority records.
Additional
g-ns-41.awsdns-40.com. 5 A 205.251.192.41
g-ns-616.awsdns-40.com. 5 A 205.251.194.104
g-ns-1192.awsdns-40.com. 5 A 205.251.196.168
g-ns-1768.awsdns-40.com. 5 A 205.251.198.232
g-ns-41.awsdns-40.com. 5 AAAA 2600:9000:5300:2900:0:0:0:1
g-ns-616.awsdns-40.com. 5 AAAA 2600:9000:5302:6800:0:0:0:1
g-ns-1192.awsdns-40.com. 5 AAAA 2600:9000:5304:a800:0:0:0:1
g-ns-1768.awsdns-40.com. 5 AAAA 2600:9000:5306:e800:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0