To download invoice detail from the Customer page, use the download icon>Download Excel with all invoice lines. 
This shows reported deferred revenue or MRR values by month with detail by invoice line item and allows you to sort in Excel by:
- customer name
- invoice number
- invoice date
- invoice line item description
- line item amount
- account name and number
- Xero Tracking Code or QuickBooks Class
- start date
- end date
- amount by date