The following script lists logins that are members of the sysadmin server rôlerole and those having the CONTROL SERVER permission:
SELECT
spr.name as loginName
,spr.type_desc
,spr.is_disabled
,(IS_SRVROLEMEMBER ('sysadmin',spr.name)) AS IS_SYSADMIN
,spm.permission_name
,spm.state_desc
FROM
sys.server_principals spr
inner join
sys.server_permissions spm ON spm.grantee_principal_id = spr.principal_id
WHERE
spm.permission_name = 'CONTROL SERVER'
OR
IS_SRVROLEMEMBER ('sysadmin',spr.name) = 1
SELECT
spr.name as loginName
,spr.type_desc
,spr.is_disabled
,(IS_SRVROLEMEMBER ('sysadmin',spr.name)) AS IS_SYSADMIN
,spm.permission_name
,spm.state_desc
FROM
sys.server_principals spr
inner join
sys.server_permissions spm ON spm.grantee_principal_id = spr.principal_id
WHERE
spm.permission_name = 'CONTROL SERVER'
OR
IS_SRVROLEMEMBER ('sysadmin',spr.name) = 1