SQL & PL/SQL :: Merge Number Of Months?

I need to calculate total number of months within a year that account existed for each SSN.

SSN CODE RECORD_DATE PAYMENT
--- ---- ----------- ----------------------
AAA 00 01-FEB-89 50
AAA 01 01-AUG-89 50
BBB 00 01-FEB-89 0
BBB 01 01-AUG-89 50
CCC 00 01-FEB-89 50
CCC 01 01-AUG-89 0

A non-zero payment indicates that the account was open on that date. A zero payment indicates that the account is closed and assumes that it was open since Jan-01.

AAA: code 00 was open in February, so it was open for 11 months (Feb-Dec)
code 01 was open in August, so it was open for 5 months (Aug-Dec)
So the result should be 11

BBB: 00 - closed in February, existed for 1 month
01 - open in August, existed for 5 months
Result should be 6.

CCC: 00 - 11 months(Feb to Dec)
01 - 7 months (Jan to Aug)
Result: 12 months

Need to get:
AAA 11
BBB 6
CCC 12

Here is the source table:

SELECT 'AAA' SSN, '00' CODE, '01-FEB-89' RECORD_DATE, 50 Payment from dual union all
SELECT 'AAA' SSN, '01' CODE, '01-AUG-89' RECORD_DATE, 50 Payment from dual union all
SELECT 'BBB' SSN, '00' CODE, '01-FEB-89' RECORD_DATE, 0 Payment from dual union all
SELECT 'BBB' SSN, '01' CODE, '01-AUG-89' RECORD_DATE, 50 Payment from dual union all
SELECT 'CCC' SSN, '00' CODE, '01-FEB-89' RECORD_DATE, 50 Payment from dual union all
SELECT 'CCC' SSN, '01' CODE, '01-AUG-89' RECORD_DATE, 0 Payment from dual union all
SELECT 'DDD' SSN, '00' CODE, '01-OCT-89' RECORD_DATE, 0 Payment from dual union all
SELECT 'DDD' SSN, '01' CODE, '01-AUG-89' RECORD_DATE, 50 Payment from dual