removing TDE - modify decrypt taking long

Oracle DB:

10.2.0.4

OS:	Red Hat Linux 5.6

Table:

86 Partition - Daily on date

Table size:

450 gb (indexes 120 GB - Not on TDE column

This is a large table and I am trying to remove the TDE and it has been running for 3 hours. if I kill this, it will rollback the transaction. Any suggestions about removing TDE from a huge table?

I am running 'alter table test_tde modify  patient_name decrypt;'

if this does not work, have you used EXEC DBMS_REDEFINITION to decrypt TDE. example would be great.