Apex domains cannot have CNAME records.
Question and response
Question
dig awsdns-20.com. NS
Answer
awsdns-20.com. 5 NS g-ns-596.awsdns-20.com.
awsdns-20.com. 5 NS g-ns-21.awsdns-20.com.
awsdns-20.com. 5 NS g-ns-1748.awsdns-20.com.
awsdns-20.com. 5 NS g-ns-1172.awsdns-20.com.
Authority
The response has no authority records.
Additional
g-ns-21.awsdns-20.com. 5 A 205.251.192.21
g-ns-596.awsdns-20.com. 5 A 205.251.194.84
g-ns-1172.awsdns-20.com. 5 A 205.251.196.148
g-ns-1748.awsdns-20.com. 5 A 205.251.198.212
g-ns-21.awsdns-20.com. 5 AAAA 2600:9000:5300:1500:0:0:0:1
g-ns-596.awsdns-20.com. 5 AAAA 2600:9000:5302:5400:0:0:0:1
g-ns-1172.awsdns-20.com. 5 AAAA 2600:9000:5304:9400:0:0:0:1
g-ns-1748.awsdns-20.com. 5 AAAA 2600:9000:5306:d400:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0