deleting the master but not the detail

hi
I have one of those master-detail relationships here and I need to be able
to delete the master but leave the details untouched

But the delete command doesn't let me delete the master as long as
there are details referencing it.

ON DELETE RESTRICT | NO ACTION won't let me delete the master
CASCADE | SET NULL | SET DEFAULT will modify the details

Any idea ow to do it without the use of triggers?

SQL Server is got the option "ON DELETE DO NOTHING" or something
like that, that just oversees the deletion, but I didn't find it for postgres.
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