with DAT (F1, F2) as ( 
select 1, 'A' from dual union all
select 1, 'A' from dual union all 
select 1, 'C' from dual union all 
select 2, 'B' from dual union all 
select 2, 'B' from dual union all 
select 2, 'D' from dual union all
select 3, 'A' from dual union all 
select 3, 'A' from dual union all 
select 3, 'E' from dual union all 
select 4, 'B' from dual union all 
select 4, 'B' from dual union all 
select 4, 'F' from dual
)
select distinct f1
      ,count(distinct f2) over(partition by f1) cnt
      ,count(distinct f2) over() cnt2
from dat
order by f1
;

COUNT(DISTINCT f2) 가 아닌 COUNT(*) 였다면 가능합니다.
SUM(COUNT(*)) OVER()
그러나 DISTINCT 부분 때문에 불가합니다.
SUM(COUNT(DISTINCT f2)) OVER() ===> (8) 원하는 결과가 아님(중복카운트발생)

그룹바이하지 않고, 바로 분석함수 사용하여 Distinct 하면 될 듯. ===> swlee710 님 답변 참조
합계를 컬럼이 아닌 행으로 빼는것은 어떨런지요?

SELECT f1
     , COUNT(DISTINCT f2) cnt
  FROM dat
 GROUP BY ROLLUP(f1)
;