Apex domains cannot have CNAME records.
Question and response
Question
dig centurylink.com. NS
Answer
centurylink.com. 5 NS authns1.qwest.net.
centurylink.com. 5 NS authns2.qwest.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0