Former U.S. President Bill Clinton says he's gotten pretty good at doing what his wife, Hillary, used to do as a "non-governmental person."

The former president was a guest Tuesday on CBS' "Late Show with David Letterman." Letterman asked Clinton if he is able to help his wife in her duties as U.S. Secretary of State.

"Well, first of all, I'm immensely proud of her," Clinton said -- recalling the former first lady's campaign for the 2008 presidential nomination -- "and I'm proud of how she did that."

"She worked her heart out for President Obama -- she did 70 appearances for him. I was proud of her for doing that for him," Bill Clinton said. "And then he asked her to be secretary of state, and she gave up a job she truly loved (as senator of New York) ... But she knew that everybody had a responsibility to help him at a difficult time, and I'm proud of the job she's doing.

"And, frankly, I think this is a good division of labor. For most of our married life, I was in politics and she was a non-governmental person, like what I'm doing now," he said. "So, we've now reversed roles, and I've gotten pretty good at what she used to do, and she's gotten real good at what I used to do."

"I so enjoy your visits here," Letterman said. "I wish I was, geez, I don't know, smarter."

"You keep saying that, but you know ... you haven't been term-limited and you're a lot richer than I am," the ex-president said. "Why are you griping?"