B767 First Officer reported receiving advisory messages related to the left generator during cruise. After landing; the left engine Integrated Drive Generator was found to have disintegrated.

Narrative

We were at cruise on our way to ZZZZ. The Captain was on break. I was the pilot flying (PF) and the relief pilot was the pilot monitoring (PM). We almost simultaneously observed four advisory messages. They were L GEN DRIVE; L GEN OFF; L UTIL BUS OFF; and R UTIL BUS OFF. Upon reviewing the four messages; we quickly discussed and agreed that the L GEN DRIVE advisory was the most critical and required prompt action as it indicated a possible impending failure. At this point; I started the APU and retrieved my EFB off the window mount. As I was loading the non-normal checklist; we both felt two distinct light thuds through our feet on the floor. I asked the PM to check with the FWD galley to see if they had dropped something or stowed a cart quickly. They said no they didn't" and that they also "felt that as well." We then completed the non-normal checklist for L GEN DRIVE. The PM then spoke with the purser to notify the Captain of the situation. We then cross-referenced the engine gauges; noting that everything was almost matched up and stable. I called dispatch on SATCOM to advise Maintenance Control of the situation and ask for their opinion. They agreed with our assessment of continuing on to ZZZZ was a safe plan. We did realize later on the ground that we forgot to mention the two thuds to Maintenance Control. We believe that due to confirmation bias; we discounted them since everything was running smoothly after the checklist was completed. We continued on to ZZZZ and landed safely. Shortly after reaching the gate; maintenance personnel met with us and asked us to "come see the engine." Upon walking up to the left engine; there was a small access panel on the bottom of the engine that they stated was hanging open upon our arrival. Then they showed us the destroyed Integrated Drive Generator (IDG). After seeing how violent it was with melted parts and cracked metal; we realized that those light thuds we felt were the moment it came apart.Additionally; please reference my last report concerning a R GEN failure and subsequent diversion to ZZZ. This current event occurred on the same aircraft. A notable pattern observed in both incidents involves the APU. In both cases; the APU exhibited an identical anomaly: immediately upon weight-on-wheels activation at touchdown; the APU automatically shut down and displayed an 'APU FAULT' EICAS message. I don't understand what would cause this to happen but wanted to point out this recurring pattern for further research by Maintenance Control for a root cause and to prevent future occurrences."