Apex domains cannot have CNAME records.
Question and response
Question
dig awsdns-18.com. NS
Answer
awsdns-18.com. 5 NS g-ns-1746.awsdns-18.com.
awsdns-18.com. 5 NS g-ns-19.awsdns-18.com.
awsdns-18.com. 5 NS g-ns-594.awsdns-18.com.
awsdns-18.com. 5 NS g-ns-1170.awsdns-18.com.
Authority
The response has no authority records.
Additional
g-ns-19.awsdns-18.com. 5 A 205.251.192.19
g-ns-594.awsdns-18.com. 5 A 205.251.194.82
g-ns-1170.awsdns-18.com. 5 A 205.251.196.146
g-ns-1746.awsdns-18.com. 5 A 205.251.198.210
g-ns-19.awsdns-18.com. 5 AAAA 2600:9000:5300:1300:0:0:0:1
g-ns-594.awsdns-18.com. 5 AAAA 2600:9000:5302:5200:0:0:0:1
g-ns-1170.awsdns-18.com. 5 AAAA 2600:9000:5304:9200:0:0:0:1
g-ns-1746.awsdns-18.com. 5 AAAA 2600:9000:5306:d200:0:0:0:1
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0