If you are making journal entries across different companies, you are now forced to keep each company in balance and make your entries happen with standard inter-company accounting procedures. For each company you would create matching Due To/From accounts on the balance sheet. There are lots of ways to set this up but here is a quick example:
Lets assume you are only using the company segment and the account number
Company 01 would need an asset account - 01-1501 Due To/From Company 02
Company 02 would need an asset account - 02-1501 Due To/From Company 01
Now instead of one journal entry you make two, one journal entry per company. Say, for example, we posted some G&A expense to company 01 and need to move it to company 02.
Credit 01-6500 $500
Debit 01-1501 $500
Credit 02-1501 $500
Debit 02-6500 $500
If our inter-company (Due to/from) account started at $0 we would now see a $500 balance in the account for company 01 and a ($500) balance for company 02.
The inter-company account(s) must remain in balance at all times, no exceptions. Any entry made to an inter-company account requires that a corresponding entry be made to the other inter-company account immediately. Any individual using inter-company account must know that they are not allowed to leave their desk if the inter-company accounts are out of balance, no exceptions. Inter-company accounts can really get out of control if people are not careful.