My Invoices describe the tasks done - similar to the wording of a Proposal, such as:
"Labor and Materials for
X Equipment"
"Total, including Taxes =
$XXX,XXX.XX"
"Payment is due within
XX, as described in Proposal/Contract Document; failure to comply will result in a call to "Mickey The Hook" hounding your butt"
just joking about the mafia based collection agent!
For "T&M" work, it is best to just be as brief as possible.
If a breakdown is requested, due so in "Units" (like all costs related to a new Panelboard for example), and be brief with these descriptions.
If a client wants any Contractor to produce a "Laundry List" of detailed items for an invoice, this Client has way too much time on their hands!
These (in my experience) are the ones who will call you endlessly with the "I Can Get These Parts At Home Depot For 10% Less" complaints.
Nearly all the Clients we deal with - and even when I invoice the Contractor I work for when doing Electrical Systems Design Injunearring work (intentionally mis-spelled "Engineer"), the Invoice states 'Labor and Materials to do (whatever work involved)"
This may be in several description lines, especially when some items might be furnished by the client or others, or when provisions for a circuit will be "Supply Power Only", connections by others.
Submitting a highly detailed Invoice to these Clients will get them "Slightly Ticked Off", to say the least!
Scott35