Apex domains cannot have CNAME records.
Question and response
Question
dig washdc.fios.verizon.net. NS
Answer
washdc.fios.verizon.net. 5 NS ns2.verizon.net.
washdc.fios.verizon.net. 5 NS ns3.verizon.net.
washdc.fios.verizon.net. 5 NS ns4.verizon.net.
washdc.fios.verizon.net. 5 NS ns1.verizon.net.
Authority
The response has no authority records.
Additional
ns1.verizon.net. 1 A 71.252.0.71
ns2.verizon.net. 1 A 151.203.0.86
ns3.verizon.net. 1 A 68.238.66.71
ns4.verizon.net. 1 A 68.238.96.71
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0