For an unindexed table, you should be getting around (or more) than 1,000,000 rows per second for each session doing work, eg this from my laptop

SQL> create table t 
  2  as select * from dba_objects where 1=0;

Table created.

SQL>
SQL> create table t1 
  2  as select d.* from dba_objects d,
  3    ( select 1 from dual connect by level <= 50 );

Table created.

SQL>
SQL> set timing on
SQL> insert /*+ APPEND */ into t
  2  select * from t1;

4048450 rows created.

Elapsed: 00:00:03.02
SQL> set timing off

My laptop runs in noarchivelog mode, so that's equivalent to setting nologging.

If you're not getting that throughput, then look at whats holding it back - indexes/constraints/triggers? or hardware?

Anyway parallel insert is your friend here. Assuming your *hardware* can cope with it, "n" parallel threads should yield approx. "n" millions of rows per second.

And obviously, a billion row table is a candidate for partitioning here.