Apex domains cannot have CNAME records.
Question and response
Question
dig dns.google. NS
Answer
dns.google. 5 NS ns1.zdns.google.
dns.google. 5 NS ns4.zdns.google.
dns.google. 5 NS ns3.zdns.google.
dns.google. 5 NS ns2.zdns.google.
Authority
The response has no authority records.
Additional
ns1.zdns.google. 5 A 216.239.32.114
ns2.zdns.google. 5 A 216.239.34.114
ns3.zdns.google. 5 A 216.239.36.114
ns4.zdns.google. 5 A 216.239.38.114
ns1.zdns.google. 5 AAAA 2001:4860:4802:32:0:0:0:72
ns2.zdns.google. 5 AAAA 2001:4860:4802:34:0:0:0:72
ns3.zdns.google. 5 AAAA 2001:4860:4802:36:0:0:0:72
ns4.zdns.google. 5 AAAA 2001:4860:4802:38:0:0:0:72
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0