Apex domains cannot have CNAME records.
Question and response
Question
dig d157etnx36ji15.cloudfront.net. NS
Answer
d157etnx36ji15.cloudfront.net. 5 NS ns-128.awsdns-16.com.
d157etnx36ji15.cloudfront.net. 5 NS ns-1004.awsdns-61.net.
d157etnx36ji15.cloudfront.net. 5 NS ns-1523.awsdns-62.org.
d157etnx36ji15.cloudfront.net. 5 NS ns-1592.awsdns-07.co.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0