Apex domains cannot have CNAME records.
Question and response
Question
dig awsdns-51.com. NS
Answer
awsdns-51.com. 5 NS g-ns-52.awsdns-51.com.
awsdns-51.com. 5 NS g-ns-1203.awsdns-51.com.
awsdns-51.com. 5 NS g-ns-627.awsdns-51.com.
awsdns-51.com. 5 NS g-ns-1779.awsdns-51.com.
Authority
The response has no authority records.
Additional
g-ns-52.awsdns-51.com. 5 A 205.251.192.52
g-ns-627.awsdns-51.com. 5 A 205.251.194.115
g-ns-1203.awsdns-51.com. 5 A 205.251.196.179
g-ns-1779.awsdns-51.com. 5 A 205.251.198.243
g-ns-52.awsdns-51.com. 5 AAAA 2600:9000:5300:3400:0:0:0:1
g-ns-627.awsdns-51.com. 5 AAAA 2600:9000:5302:7300:0:0:0:1
g-ns-1203.awsdns-51.com. 5 AAAA 2600:9000:5304:b300:0:0:0:1
g-ns-1779.awsdns-51.com. 5 AAAA 2600:9000:5306:f300:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0