from http://wiki.gnucash.org/wiki/Using_GnuCash#Displaying_Split_Account_Details_in_Transaction_Report

Displaying Split Account Details in Transaction Report

For a simple transaction like this: 
<date> <ref no> "Cheques Received"
 <income account> "multiple payers"     <credit> £157.60
 <bank account>                         <debit>  £157.60

then on a Transaction Report for the bank account the details appear pretty much as above. 

For clarity of the accounts, you might enter transactions with multiple splits referring to the same account. For example, the above transaction might well be entered like this: 
<date> <ref no> "Cheques Received"
 <income account>  <first payer name>   <credit> £100.00
 <income account>  <second payer name>  <credit> £ 57.60
 <bank account>                         <debit>  £157.60

When this transaction is printed on the bank account's Transaction Report, then under "other account" it simply prints "split" instead of the account name. 

To display the additional split detail, you need to set General -> Style = Multi-Line and then you need to turn on Display -> Account Name. Do NOT turn on Display -> Other Account Name. 

You can choose whether or not to turn off the full account name using Display -> Use Full Account Name? 

The Use Full Other Account Name? has no effect in this configuration. 

--Provided by Derek Atkins (in response to Colin Scott)