Apex domains cannot have CNAME records.
Question and response
Question
dig schwab.com. NS
Answer
schwab.com. 5 NS np2.schwab.com.
schwab.com. 5 NS np3.schwab.com.
schwab.com. 5 NS a9-65.akam.net.
schwab.com. 5 NS a8-64.akam.net.
schwab.com. 5 NS np1.schwab.com.
schwab.com. 5 NS np4.schwab.com.
Authority
The response has no authority records.
Additional
np1.schwab.com. 5 A 162.93.239.33
np2.schwab.com. 5 A 162.93.193.33
np3.schwab.com. 5 A 162.93.239.34
np4.schwab.com. 5 A 162.93.193.34
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0