"I thought, what I do have are these guys who've all, over a period of 35 years, helped me in one way or another," he said.
"I've slept on their couches when I was broke. They loaned me money when I was broke. They helped me when I needed help over the years."
"We're all good friends. And I thought, you know, without them I don't have any of this."
The 59-year-old actor had already left his friends a bequest in his will, but asked himself why should they have to wait until he was hit by a bus.
Finding US$14 million in cash is trickier than it might seem.
After some research, the actor discovered there was a place in downtown Los Angeles where the cash was stored in pallets.
He got hold of an old florist's van and, accompanied by his assistant and a couple of nervous "security guys", he went to fetch the cash.
Clooney bought 14 holdalls. packing US$1 million dollars in each.
He then invited his friends over to his house.
"And I just held up a map and I just pointed to all the places I got to go in the world and all the things I've gotten to see because of them," he recalled.
"And I said, 'How do you repay people like that? ... Oh, well: How about a million bucks?'"
Clooney also told the magazine how he bet Brad Pitt and Don Cheadle US$10,000 to stay in a "haunted house" opposite his home on Lake Como.
He managed to convince his Ocean's 12 co-stars that the house was haunted.
The challenge was to spend the night in the house having been given a candle, six matches and a bottle of wine.
Pitt and Cheadle took up the bet while Clooney and actor Matt Damon rowed back to the middle of the lake to see how long their co-stars would last.
The answer was not very long.
"We're sitting in the boat in the middle of the lake," he said. "And we have to see the candle go by every window. It goes by like two or three windows and then we get a call - 'get us out of this house!'"
"And we came back and pulled them out."
