The 40-year-old actor was a guest on Dax Shepard's new podcast, Armchair Expert, where the two longtime friends discussed their careers, kids and relationships, as well as Kutcher's former marriage with Moore.
"Right after I got divorced, I went to the mountains for a week by myself," Kutcher revealed, adding that he spent the week in Montana.
"I did no food, no drink, just water and tea," he explained. "I took all my computers away, my phone, my everything. I was there by myself, so there was no talking. I just had a notepad, a pen and water and tea for a week."
The former That '70s Show star said he really relished his time alone, stating, "I was just doing what came to me."
"I wrote down every single relationship that I had where I felt like there was some grudge or some anything, regret, anything," Kutcher explained. "And I wrote letters to every single person. And on day seven, I typed them all out and then sent them. I handwrote them all and then typed them out and sent them."
"It was like an exercise," he continued. "I was like, 'I've probably done some damage.' So I just cleared palette."
Kutcher also opened up about his relationship with wife Mila Kunis and their two kids, 3-year-old daughter Wyatt and 1-year-old son Dimitri.
"My kids are living in a very privileged life …and they don’t know it," Kutcher expressed "They will never know it because this is the only [life] that they will know."
ET caught up with Kunis on the set of A Bad Moms Christmas last year, where she opened up about how their life has changed since baby number two.