With their reality TV fame has come a multitude of businesses and brands -- from Kim and Khloe's diet supplement Quick Trim, to Kim's fragrance, to Kourtney's health shakes for new mothers. They credit their drive and their work ethic to their late father, Robert Kardashian, who was well-known as a friend and lawyer to OJ Simpson.
"We grew up in this life of privilege, but we were always taught when we're 18, we're gonna be cut off. We'd better figure it out, and we'd better get a job," Kim said. "My father taught us really well, and I think really instilled a good work ethic in us. We didn't have the credit cards. We didn't have the cell phones. We didn't have that, like all of our friends did, growing up."
When asked what their dad would think of their lifestyle and success, Kim said, "I just know he would be so proud of us. He would see that the whole entrepreneur side that he instilled in me. He would be so happy."
McFadden asked Kris about reports that she had encouraged daughter Kim to pose for Playboy.
"I thought it was a good idea," said Kris. "I thought that so many iconic women have done Playboy. And I thought, you know for Marilyn Monroe."
"You were pushing her," said McFadden. "Let's be honest."
"She wanted to do it, too," said Kris. "I mean, I didn't force her to go do Playboy."
"That opportunity came about to do Playboy," said Kim, "I was on the fence about it. Do I want to be viewed this way or do I want to show women that, hey, I am curvy. I'm not like all these like stick-skinny models that I see on the cover of all of these magazines, including Playboy. And I thought that it would be empowering. And so, I did it. And at the end, I was uncomfortable. And at the end, I had a great time.
"I really love my relationship with Hef," Kim added. "I love meeting all these people. And I got a completely different fan base."
McFadden noted reports that Kim regretted appearing in Playboy.
"When I said that comment, I had said...'I'm sorry that I did Playboy then, when I was in the shape that I was in,'" said Kim. "Not the shape that I'm in now. Because I had lost 15 pounds. ... So it kind of got misconstrued a little bit."
Watch the full story on "Nightline" tonight at 11:35 p.m. ET